KR20070017511A - Apparatus for and method of developing equalized values from samples of a signal received from a channel - Google Patents

Abstract

Equalizer 200A includes a feedforward filter 210, the feedforward filter comprising a plurality of feedforward filter taps, the coefficients being associated with a plurality of feedforward filter taps and associated with a plurality of feedforward filter taps. The values of all the coefficients are determined dynamically. In some embodiments, the equalizer also includes a decision feedback equalizer 216.

Description

Apparatus and method for developing equalized values from samples of a signal received from a channel.

Reference to Related Applications

This application claims the priority of US Provisional Application No. 60 / 561,085, filed April 9, 2004 entitled "Advanced Digital Receiver," and also filed on August 12, 2004, entitled "Advanced Digital Receiver." United States claims priority to application 60 / 601,026. The present application is also filed on April 4, 2003, entitled "Carrier Recovery for DTV Receivers," US Patent Application No. 10 / 408,053, on June 6, 2001, "Adaptive Equalizer Having a Variable Step Size Influenced by Output." US application Ser. No. 09 / 875,720 (current US patent 6,829,297) filed under the heading "from a Trellis Decoder", US application filed on April 4, 2003 entitled "System and Method for Symbol Clock Recovery" 10 / 407,634, U.S. Patent No. 09 / 884,256, filed "Juvened Trellis Decoder and Decision Feedback Equalizer," issued June 19, 2001, and "Transposed Structure for a Decision Feedback Equalizer Combined, April 4, 2003." See, US application Ser. No. 10 / 407,610, filed with " with a Trellis Decoder. "

TECHNICAL FIELD The present invention relates generally to digital communication techniques, and more particularly, to an apparatus and method for developing equalized values from samples of a signal received from a channel.

Discrete data transmission is the transmission of messages from a transmitter to a receiver over a communication channel. A message sender or sending device disposed at the transmitter communicates with the message receiver by selecting a message and transmitting a corresponding signal or waveform representing the message over a communication channel. The receiver determines the message sent by observing the channel output. Continuous transmission of discrete data messages is known as digital communication. Often, channel noise interferes with the transmission and degrades the transmitted message, causing some uncertainty at the receiver regarding the content of the original message. The receiver uses a procedure known as detection to determine which message or sequence of messages the sender has sent. Optimal detection is to minimize the likelihood of false receiver determination that a message was sent.

Messages consist of bits of a digital sequence that are converted into electrical signals transmitted over a channel. Typically, these bits are encoded prior to modulation. Encoding is the process of converting a message from its innate form, typically bits to values representing the message. Modulation is the procedure of converting these values into analog signals for transmission over a channel. The channel distorts the transmitted signals deterministically and with random noise. Such conditions that interfere with proper reception include additive white Gaussian noise (AWGN) and coherent noise, frequency dependent channel distortion, time dependent channel distortion, and fading. It includes fading multipath. Because of these effects, there is some possibility that the transmitted message could collapse when it reaches the receiver.

Upon reception, the receiver demodulates an incoming waveform. In general, demodulation is to recover the originally transmitted signals as accurately as possible and convert the recovered signals into estimates of values. The process includes downmixing radio frequency (RF) and near-baseband intermediate frequency (IF) signals to downmixing, channel equalization, and decoding to baseband representation, There are several steps to this process. Symbol and carrier recovery is performed so that the discrete time samples are at the correct symbol rate and the signal moves accurately down to the baseband. The receiver employs a detector to probabilistically determine the value estimates. Methods for demodulating and detecting a received signal as employed by a receiver are important to consider both potential transmission values and potential for channel-induced errors. The value estimates are then decoded by converting the value estimates back to the native form of the message.

Digital communication systems receive the transmitted information by periodically sampling the output of the demodulator once per symbol interval. This relates to symbol-timing and carrier recovery under non-ideal transport channel conditions and requires the design of a receiver to overcome the problems associated with system synchronization. In general, the optimal times for a receiver to sample a received signal are not known due to the effects of channel conditions such as multipath and propagation delay from the transmitter to the receiver. In addition, the propagation delay of the transmitted signal results in a carrier phase offset. For the transmission system requiring a receiver to employ a phase-coherent detector, the receiver develops an estimate of the propagation delay and derives an estimate of the transmitted symbol timing and a phase signal from the directly received signal. . An exception to this is when pilot or control signals are embedded in the transmitted signal. In this case, the receiver uses embedded pilot or control signals to synchronize the receiver to the transmitter. In either case, the receiver overcomes system synchronization obstacles by performing three basic functions: carrier recovery, timing recovery and channel equalization.

As mentioned above, the carrier recovery process includes a number of steps, such that the received radio frequency (RF) signal is demodulated. In part, the near-baseband signal is demodulated to recover the information-bearing baseband signal and remove any residual carrier phase offset. This final step is often referred to as phase-locking.

The timing recovery process is used to recover the transmitter time base and synchronize the receiver and transmitter clocks. Once achieved, this synchronization allows the receiver to sample the received signal in a timely and optimal position and to reduce slicing errors.

The channel equalization process is to compensate for imperfections in the transmission channel that change the amplitude and phase of the received signal as the received signal passes through the channel. In general, these defects are frequency dependent, time dependent and dynamic. For this reason, it is advantageous to employ an adaptive equalizer filter system to remove distortions in amplitude and phase from the channel.

Many existing phase-locked loop (PLL) techniques exist. A limited list of example approaches that can be understood by those skilled in the art include Costas loops, squaring loops, and more generally decision directed and non-decision directed loops. decision directed loops).

Typically, phase-locking mechanisms are associated with three common elements. They are phase error detection / generation, phase error processing and local phase reconstruction. The phase error detection task implemented by the phase detector derives a phase difference measure between the transmitted signal phase detected at the receiver and the phase estimate of the incoming signal being enveloped by the receiver. The phase error measure is the difference between the phase of the received signal and the actual transmitted signal.

Typically, phase error processing operations implemented by an integrator or low-pass loop filter intrinsic phase difference by averaging the magnitude of the phase error over a period of time or within a time window. Infer the tendencies of Properly designed phase error processing operations avoid any noise and other undesirable components of the phase error signal. To ensure stability, the loop filter absorbs the gain in the phase detector. Analog, digital and hybrid analog-digital phase error detection methods exist that are utilized within phase-locked loops. These methods are modulo-2π phase detectors, binary phase detectors, phase-splitting filters, and maximum-near-carrier phase estimators -likelihood carrier phase estimators), but is not limited to these.

The local phase recovery task is to control the phase and generation of the local oscillator. The local oscillator is used to demodulate the near-baseband signal with a locally generated oscillator frequency having the same frequency and phase as the near-baseband signal. When locked, the generated local oscillator signal has the same frequency and phase characteristics as the signal demodulated to baseband. The local oscillator can be implemented using either analog or digital means. Various types of voltage controlled liquid crystal oscillators and numerically controlled oscillators, VCXO's and NCO's can be used to regenerate local carriers.

In the case of analog circuits, local phase recovery operations are implemented using voltage-controlled oscillators. The VCXO uses the processed phase error information to regenerate the local phase of the incoming signal by bringing the phase error to zero.

The phase-locking mechanism has some finite delay in practice so that the mechanism can predict the incoming phase and then measure the accuracy of that prediction in the form of a new phase error. The faster the phase-lock mechanism tracks the deviation of the phase, the better the mechanism is sensitive to the instrument or any noise and other defects. This is even more so if the received signal is in a powerful multipath environment. Thus, when designing a synchronization system, an appropriate trade-off is made between these two opposing effects.

Timing recovery or synchronization is the process by which the receiver synchronizes the local time base to the transmitter symbol rate. This allows precise sampling of the time instants during the symbol period in order to maximize the possibility of accurately determining the value of the transmitted symbol. As mentioned above, the PPL subsystem is sufficient to recover the symbol rate. Instead, a separate symbol-timing recovery function is added in combination with the PLL to provide timing recovery. Proper symbol-timing recovery is one source of intersymbol interference (ISI) and significantly degrades the performance of the receiver.

Those skilled in the art will appreciate that proper sampling of the demodulator output directly depends on proper timing recovery. There are a number of methods utilized by the systems to perform local clock recovery. In the first system, various types of clock signals are encoded in the bit stream. In the second system, no predefined synchronization symbols are transmitted, only data is transmitted and the locked local clock is derived from the received data stream. It should be noted that the latter system is more extensive due to the demand for bandwidth efficiency.

In addition, timing recovery methods are distinguishable with respect to their use of the decision device output of the receiver. Non-decision aided methodology does not depend on the output of the decision device. An example of this methodology is the square-law timing recovery method. In addition, envelope-timing recovery is an equivalent square-low timing recovery method utilized in a quadrature amplitude modulation (QAM) receiver.

Decision directed (also known as decision-assisted) timing recovery uses decision device output. One example of a decision directed timing recovery method minimizes the mean-squared difference across the sampling time phase between the output of either a linear equalizer (LE) or a decision feedback equalizer (DFE) and the output of the decision device.

The determining device serves to assign a symbol value to each sample obtained from the demodulator. There are both hard and soft decision devices. One example of a hard decision device is a decision slicer or a Viterbi decoder. In the case of decision-oriented timing recovery methods, care must be taken to ensure that there is no excessive delay between the decision device output and the input sampling function. Excessive delays degrade the overall performance of the receiver or, in the worst case, cause the phase locking loop to become unstable. As will be appreciated by those skilled in the art, the quality of the symbol-timing estimates depends on the overall signal-to-noise ratio (SNR) and is a function of channel characteristics and signal pulse normal.

As measured by either the overall data transmission rate or the bit error rate (BER) of the receiver design, there are various sources of channel distortion and interference that may result in poor receiver performance. Among the factors are noise, AWGN, intersymbol interference (ISI) and multipath conditions.

Receivers also compensate for channels with significant multipath features. Depending on channel frequency response and time varying multipath effects, there are various means of classifying and describing multipath phenomena. Four common categories familiar to those skilled in the art include slow changing frequency non-selective fading, fast changing frequency non-selective fading, slow change frequency non-selective fading, slow changing frequency selective fading and fast changing frequency selective fading.

Multipath is typically the result of a transmission signal arriving at a receiver through different transmission paths, each with a unique composite propagation time for the receiver. Multipath induced ISI generates a non-linear phase response and a non-constant amplitude and contending receiver of the channel. The second effect is referred to as fading. Fading is due to the propagation delay associated with each propagation path that creates constructive and destructive interference at the receiver. Fading causes degradation of SNR.

As summarized by the actual implications, this simple description is further subdivided into four categories that are familiar to those skilled in the art. In practice, a channel exhibiting slowly changing frequency non-selective fading means that all propagation paths are accommodated within one symbol period and the channel affects all signal frequency components evenly. do. This is the most easily compensated fading channel phenomenon. Fast changing frequency non-selective fading occurs when the channel changes over a symbol period. Fast fading is very difficult to compensate effectively.

The channel may be characterized as having a slow frequency-selective multipath if the channel distorts the received symbols in the frequency domain and not all frequency components are equally affected. As a result, the baseband pulse shape is distorted and inter-symbol interference (ISI) occurs. Finally, fast varying frequency-selective fading is the type considered to be the worst case of the channel, and occurs when the accepted symbol is spread over many symbol periods and the channel characteristics also change during the symbol period.

In addition, fading is roughly divided into large-scale and small-scale fading categories, as shown in FIG. Large movements of the receiver, such as those occurring in mobile applications, cause large-scale fading, while small-scale fading is due to the movement of the receiver. Since the amplitude has a log-normal probability density function, large-scale fading may also be referred to as logarithmic fading. Typically, small-scale fading is described as Rayleigh- or Ricean-fading, depending on whether the probability distribution function (pdf) best describes it. In addition, a Nakagami-m distribution has been used to characterize some multipath channel conditions.

Many modern digital communication systems employ suitable equalization to compensate for the effects of changing conditions and disturbances in the signal transmission channel. Equalization is used to eliminate baseband ISI caused by distortion of the transmission channel and may be performed in conjunction with baseband or passband signals. Often, equalization is performed with respect to the near-baseband signal prior to carrier recovery and down mixing to produce a baseband signal. In particular, this is a decision directed carrier recovery process that requires one or more partially open eyes as is well known to those skilled in the art.

2, a diagram of the vestigial sideband (eye diagram) of the 8-VSB is shown. The eye diagram is an overlay of the RF signal amplitude received at the sampling instant. The convergence of many signal traces forms seven "eyes" that coincide with the generation of clock pulses at the receiver. At each sampling time, the demodulated RF amplitude takes one of eight possible levels. If the 8-VSB signal corrupts during transmission, these "children" close up or disappear because the RF signal no longer immediately has the correct amplitude.

In essence, an adaptive equalizer filter system is an adaptive digital filter with a modifiable frequency and phase response that compensates for channel distortions. As will be appreciated by those skilled in the art, there are several configurations, methods, and algorithms available for performing this function. In one embodiment, a feed-forward equalizer (FFE) develops a partially equalized signal provided to a decision feedback equalizer (DFE). In conventional systems of this type, the FFE serves to minimize or eliminate ghosts generated from the precursor ISI, while the DFE serves to minimize or eliminate ghosts generated from the postcursor ISI. In another system, FFE reduces or eliminates ghosts due to precursor and some postcursor ISI, while DFE reduces or eliminates ghosts generated from postcursor ISI.

The impact associated with receiver performance of multipath induced ISI is reduced by the application of channel estimation and equalization. The validity of channel estimation has a direct relationship to the elimination of ISI. Ideally, channel estimation in theory allows for complete elimination of ISI. However, it is uncertain to obtain an ideal channel estimate, especially when there are bad channel features.

Another approach to improve performance in the presence of multipath interference is based on diversity principles. Different propagation paths are used in combination to mitigate multipath fading. This is typically possible because the propagation paths are not related to each other, which means that it is not easy for them all to fade simultaneously. The diversity concept models the channel fading mechanism as channel burst error. Thus, providing temporally or frequency-based redundant copies of the transmitted information enhances the likelihood of successful data transmission.

Diversity techniques include temporary diversity and frequency diversity. Frequency diversity has the requirement that the same information be transmitted across multiple carriers if the spacing of consecutive carriers is equal to or exceeds the coherent bandwidth of the information channel. Temporary diversity consists of a large number of identical information-bearing signals transmitted into L different time slots when the interval between successive time slots is equal to or exceeds the coherence time of the channel. Use independent fading versions of L). Thus, L copies of the information transmitted at varying times based on the transmission path are provided to the receiver.

One implementation of this concept is a Rake Receiver. The Rake Receiver utilizes a multipath phenomenon to improve system performance. Multipath baseband correlators are used to individually process multiple multipath components. The correlator outputs are then added to increase the overall signal strength.

The above characteristics are intended only as a partial, non-limiting list of example techniques that may be employed, and are not intended to impose any limitation on the disclosed invention in any way.

Although there are a number of technologies available in the current technical field, receivers exhibit significant degradation in performance in a strong multipath environment. This is especially true for terrestrial digital broadcasting systems. In particular, the current state of the art receiver using an equalizer typically uses a subtractive method to eliminate coherent multipath signals. This is an obvious disadvantage in changing the multipath fading environment. In particular, these receiver systems attempt to identify and lock on a single strongest received signal coming over a given transmission path or channel. This is accomplished by constructing a unity sized tap at the center of the FFE at start up of the equalizer. Upon reception, signals corresponding to other transmission paths are subtracted from the entire incoming signal. This effectively removes all diversity from the receiving process (if diversity is used in the system). In addition, the receiver may lose lock if the strength of the primary multipath signal fades or a new stronger signal appears. This introduces a significant carrier phase offset at the receiver. Thus, changing the multipath conditions may cause the receiver to reacquire the carrier lock, resulting in a noticeable disruption in the flow of information from the receiver to the user.

According to one embodiment of the invention, an equalizer comprises a feedforward filter, the feedforward filter comprising a plurality of feedforward filter taps, coefficients associated with the plurality of feedforward filter taps, and the plurality of feeds The values of all the coefficients associated with the forward filter are determined dynamically.

According to a further embodiment of the invention, an equalizer comprises a feedforward filter, wherein the feedforward filter comprises a plurality of feedforward filter taps, and coefficients are associated with the plurality of feedforward filter taps. The equalizer further includes a decision feedback equalizer. In addition, the values of all the coefficients associated with the plurality of feedforward filter taps are dynamically determined.

According to another embodiment of the present invention, a method for developing equalized values from samples of a signal received from a channel comprises: associating coefficients with a plurality of taps of a feedforward filter, the samples according to the coefficients. Developing a series of feedforward filter values from the modules and dynamically determining the value of all coefficients.

According to another embodiment of the present invention, a method of developing equalized values from samples of a signal received from a channel comprises: associating coefficients with a plurality of taps of a feedforward filter, the samples according to the coefficients. Developing a stream of feedforward filter values from the data, generating a stream of equalized decision feedback from the stream of feedforward filter values, and dynamically determining the value of all coefficients.

According to yet another embodiment of the present invention, a computer readable medium for developing equalized values from samples of a signal received from a channel is provided for implementing a first routine for implementing a feedforward filter. Programming, wherein the coefficients are associated with a plurality of taps of the feedforward filter. The first routine develops a series of feedforward filter values from samples in accordance with the coefficients. The programming also includes a second routine that dynamically determines the values of all the coefficients.

According to yet another embodiment of the present invention, a computer readable medium for developing equalized values from samples of a signal received from a channel includes programming to implement a first routine for implementing a feedforward filter. , Coefficients are associated with a plurality of taps of the feedforward filter. The first routine also develops a stream of feedforward filter values from samples according to the coefficients. The programming also includes a second routine to implement a decision feedback equalizer to develop a stream of decision feedback equalizing values. Furthermore, the programming further includes a third routine for dynamically determining the values of all coefficients.

1 is a graph showing the relationship between small-scale and large-scale fading over time;

FIG. 2 is a graph showing an 8-VSB modulated open eye pattern; FIG.

3 is a schematic block diagram of an advanced digital receiver in accordance with the present invention;

4 is a diagram of an ATSC baseband framing coder segment showing a data segment and a frame sync structure;

5 is a schematic diagram of one embodiment of an equalizer for use in the advanced digital receiver of FIG. 3;

6 is a block diagram of one embodiment of a segment sync based channel delay estimation unit (CDEU);

7 is a diagram showing the relative position of a virtual center with respect to ghosts detected in the transport channel;

8 is a diagram showing relative positions of ghosts detected in a transport channel;

9 is a block diagram of one embodiment of an ATSC segment sync correlator;

10 is a block diagram of one embodiment of a "leaky" integrator;

11 is a block diagram of one embodiment of a centroid estimator;

12 is a flowchart illustrating the operation of the CDEU;

13 is a block diagram of another embodiment of a segment sync based CDEU;

14 is a block diagram of one embodiment of a frame sync based CDEU;

15 illustrates the location of ghost signals in a transport channel with respect to windowing functions;

16 is a flowchart illustrating operation of a further embodiment of the CDEU;

17 illustrates the location of ghost signals in a transport channel with respect to windowing functions;

18 is a block diagram of another embodiment of a frame sync based CDEU;

19A-19D illustrate the relationship between the virtual channel, FFE output (Zout), and the virtual center and coefficients of the FFE and DFE taps;

20A and 20B illustrate the relationship between virtual channel, FFE output (Zout) and FFE and DFE taps;

FIG. 21 is a flow diagram illustrating operation of the system 20 of FIG. 3 to develop an equalizer or an overlapped equalizer structure without a fixed center tap;

22 is a block diagram of one embodiment of an overlapped equalizer with a phase tracker;

23 is a block diagram of one embodiment of an overlapped equalizer with a phase tracker;

24 is a block diagram of one embodiment of an overlapped equalizer with a phase tracker;

25 is a block diagram of one embodiment of an overlapped equalizer with a phase tracker;

26 is a block diagram of one embodiment of an overlapped equalizer with a phase tracker;

27 is a block diagram of one embodiment of an overlapped equalizer with a phase tracker;

28 is a block diagram of one embodiment of an overlapped equalizer with a phase tracker;

29 is a block diagram of one embodiment of a tuning and demodulation feedback system employing an overlapped equalizer;

30 is a flow diagram illustrating the operation of another embodiment of the system 900 of FIG. 29 for controlling the overlapping equalizer's optimization process and tuning and demodulation control feedback loops.

31 is a block diagram of a further embodiment of a tuning and demodulation feedback system employing an overlapped equalizer;

32 is a block diagram of one embodiment of an overlapped equalizer in a combined demodulation and tuning feedback loop;

33 is a block diagram of one embodiment of an overlapped equalizer in a combined demodulation and tuning feedback loop;

34 is a block diagram of one embodiment of an overlapped equalizer in a combined demodulation and tuning feedback loop;

35 is a block diagram of one embodiment of an overlapped equalizer in a combined demodulation and tuning feedback loop;

36A and 36B show qualitative characteristics of respective timing offset post filter and carrier offset post filter;

FIG. 37 is a block diagram of one embodiment of a field / frame sync correlation directed control system for controlling VCXOs in a digital receiver system; FIG.

38A-38C illustrate the relationship of correlation weighting function to the location of ghost signals in a channel;

39 is a block diagram of one embodiment of a correlation directed tuning feedback system;

40 is a flow diagram illustrating operation of one embodiment of a correlation oriented tuned feedback loop system.

41 is a block diagram of one embodiment of a system for generating a segment sync based correlation directed control signal;

42 is a flow diagram illustrating operation of one embodiment of a system for generating a segment sink based correlation directed control signal.

43 is a block diagram of one embodiment of a segment sync based correlation oriented carrier tracking feedback loop.

44 is a block diagram of one embodiment of a channel delay oriented tuned feedback loop.

For the purpose of introducing and understanding the principles of the invention, reference is made to the embodiments illustrated in the drawings, and specific expressions will be used to describe the embodiments. Nevertheless, it should be understood that no limitation is intended to the scope of the invention. As will typically occur in the art, modifications and additional modifications to the described embodiments and any additional applications of the principles of the invention described herein may be considered.

One embodiment of the present system illustrated in FIG. 3 is a digital receiver system with significantly improved stability and performance when receiving demodulated signals in a poor multipath environment. The techniques, devices and systems employed in this new digital receiver can be optimized for a variety of demodulation formats, including but not limited to QAM, Offset-QAM and VSB. By way of example, one such non-limiting example transmission standard is the ATSC standard, which is adopted for HDTV broadcasting in the United States. The ATSC transmission standard utilizes a suppressed carrier 8-VSB signal with a pilot signal at a suppressed carrier frequency for use in achieving a carrier lock of a VSB receiver. As shown in FIG. 4, the ATSC data transmission format includes two fields per frame. Each field has 313 segments of 832 multilevel symbols. Each segment has four symbol segment sync characters followed by a payload of 828 symbols. The first segment of each field comprises a field sink segment, while the remaining segments are used to carry data packets. The field sink features a preset 511 symbol pseudorandom number (PN) sequence and three preset 63-symbol long (PN) sequences. The middle 63-symbol long (PN) sequence is inverted in each successive field. The VSB mode control signal (formed to be VSB constellation magnitude) follows the last 63 PN sequence followed by 92 reserved symbols and 12 symbols copied from the previous field. Those skilled in the art will appreciate that the present invention is applicable to other transmission standards without undue experimentation.

One embodiment of the present invention is the system 20 shown in FIG. The system 20 receives and processes ATSC broadcast signals, and includes an analog front end receiver 30, a tuner 40, a digital demodulator 42, a Nyquist Root Filter (NRF) 44, an equalizer. (46), forward error correction (FEC) 48, non-coherent control (NCC) 50, decision directed control (DDC) 52, and control system 54. Further embodiments of system 20 also detect the presence of segment sync, field / frame sync and signal-to-noise ratio (SNR) at various points in system 20. By way of example, some embodiments of system 20 determine an SNR of received data. Other embodiments determine the SNR of the received signal based on the received tuned signals. Other particular embodiments quantify the performance of the equalizer based on the data error rate. Similarly, other elements of system 20 use the data error rate to quantify its performance. Still other embodiments use performance metrics developed by a trellis decoder of an equalizer as described in US Pat. No. 6,828,297.

Some embodiments of system 20 also detect a frame or field sync signal at one of the outputs of equalizer 46. Other embodiments of system 20 determine whether tuner 40 or digital demodulator 42 is locked to the received signal.

Control system 54 is connected to various elements of system 20 (not shown) and generally indicates a function of system 20. By way of example, in some embodiments, control system 54 oversees system startup, work mode selection, and adaptation of equalizer coefficients. As described below, control system 54 receives channel delay estimate 84, equalizer output 88, and adaptation symbol decision 94. The control system 54 also receives a signal segment sink 96, a field / frame sink 98, an SNR 100, a VCXO lock 102 and an NCO lock 104. Segment sink 96 is a signal that indicates whether a valid segment sink has been detected at the desired output of equalizer 46 or other elements of system 20. Field / frame sync 98 is a signal that indicates whether a valid field / frame sync has been detected at the desired output of equalizer 46 or other elements of system 20. Similarly, SNR 100 is an estimated SNR of the signal received at the desired output of equalizer 46. The VCXO lock 102 is a signal that indicates whether the tuner 40 is locked to the time base of the incoming signal. Finally, NCO lock 104 is a signal indicating whether digital demodulator 42 is locked to an incoming carrier.

The input of the analog front end receiver 30 is connected to an antenna or other signal source that receives a broadcast signal. The analog front end receiver 30 is tuned to the desired RF broadcast signal, provides automatic gain control (AGC) and signal amplification, and converts the received signal to an intermediate frequency (IF) to be used in the demodulation process. The analog front end receiver 30 may include an RF tuning circuit, an IF circuit and an AGC circuit to optimize the received signal in the presence of noise. The analog front end receiver 30 also down-converts the received signal to a near-baseband signal. By way of example, the received IF passband of the near-baseband carrier suppressed 8-VSB signal employed in ATSC may be centered at approximately 5.38 MHz.

According to the present invention, the tuner 40 is part of an overall timing recovery function that serves to sample the incoming signal and the tuning system 20 on a time base of the incoming signal. The tuner 40 receives the analog near-baseband signal 60 from the analog front end receiver 30 and generates a digitized near-baseband signal 62. The tuner 40 also receives a decision directed tuning feedback signal 66 from the decision directed control 52 and a non-coherent tuning feedback signal 64 from the non-coherent controlling 54.

In some embodiments of the present invention, tuner 40 includes incoming analog near-baseband signal 60 to generate a digital near-baseband signal 60 based on a sample clock generated by a feedback-controlled VCXO. ), An A / D converter (not shown). The control system 54 selects the decision directed tuning feedback signal 66 or the non-coherent tuning feedback signal 64 to control the tuner 40 to control the phase and frequency of the A / D sample clock. In another embodiment, tuner 40 also receives a redirection directed control feedback signal (not shown). The selected feedback signal is filtered to produce a control signal that governs the VCXO output frequency and phase.

Illustratively, in certain embodiments the control system 54 initially configures the tuner 40 to use the non-coherent tuning feedback signal 64 to dominate the VCXO operation. The analog near-baseband signal 60 is sampled based on the VCXO sample clock that is feedback-controlled by the tuner 40. After the system 20 has at least partially converged, the control system 54 optionally configures the tuner 40 to govern the VCXO operation using the decision directed tuning feedback signal 66. By way of example, some embodiments of tuner 40 optimized for an ATSC system include a VCXO that drives A / D sampling at a rate of approximately 21.52 MHz, which is twice the symbol rate of the signal received in the ATSC system. do. After the VCXO is locked to the time base of the received signal, control system 54 receives a positive indication from VCXO Lock 102. It will be appreciated that there are several techniques available in the art for determining whether a VCXO is locked to an incoming signal.

In other embodiments, tuner 40 resamples the output of a fixed sampling rate A / D. By way of example, A / D samples the incoming signal 60 at a fixed rate. The sample rate converter re-samples the digitized near-baseband signal to develop a desired output sample rate that is tuned to the incoming symbol rate. Similar to the above, the control system 54 uses the non-coherent tuning feedback signal 64 or the decision directed tuning feedback signal 66 to select the re-sampling process based on the working state of the system 20. To control.

Digital demodulator 42 is part of the overall carrier tracking and recovery function of system 20 and demodulates the near-baseband output of tuner 40 to the baseband. As shown in FIG. 3, the digital demodulator 42 includes a digitized near-baseband signal 62 from the tuner 40, a decision directed carrier tracking feedback signal 74 from the decision directed control 52, and Receive a non-coherent carrier tracking feedback signal 72 from coherent control 50. Although not shown, other embodiments of the digital demodulator 42 also receive a correlation directed control feedback signal. According to one embodiment, the digital demodulator 42 is near to a double over-sampled complex baseband output with an in-phase component signal 68 and a quadrature component signal 70. Digitally demodulate the baseband signal 62. Prior to the filtering steps described below, the in-phase component signal 68 and the quarter period component signal 70 have both negative and positive frequency components. The output of the digital demodulator 42 is lowpass-filtered to remove out-of-band signals by the Nyquist Root Filter 44.

As described below, the control system 54 selectively controls the feedback signal that governs the operation of the digital demodulator 42. At startup of the initial system, digital demodulator 42 operation is governed by a non-coherent carrier tracking feedback signal from NCC 50. The NCC 50 tracks the received carrier frequency and dominates the down mix frequency generated by the NCO portion of the digital demodulator. After the system 20 has at least partially converged, the control system 54 configures the digital demodulator 42 and governs the down conversion process to utilize the decision directed control feedback loop signal to provide improved carrier tracking. At some desired point in the digital demodulation operation, NCO Lock 104 instructs control system 54 to lock the NCO to the carrier of the signal being received.

In some embodiments of the invention, only the in-phase component signal 68 is used by the equalizer 46 to reduce the complexity of the system. Alternatively, other embodiments of the present invention utilize an over-sampled baseband signal associated with frictionally spaced FFEs included in equalizer 46 of system 20.

Demodulator 42 provides in-phase component signal 68 and quadrature component signal 70 as inputs to both NRF 44 and NCC 50. NRF 44 is a high frequency from the demodulated signal to generate filtered in-phase baseband signal I _F 76 and filtered quarter period baseband signal Q _F as inputs to equalizer 46. Filter out the components. In some embodiments, NRF 44 is a low-pass filter having a double-sided bandwidth of 5.38 MHz and a rolloff of 11%.

Applicant's pending applications, ie US Patent Application No. 10 / 408,053 and "System and Method for Symbol Clock Recovery," filed under the title "Carrier Recovery for DTV Receivers", which is hereby incorporated by reference. As described in US patent application Ser. No. 10 / 407,634, the NCC 50 is configured for upper and lower Nyquist slopes to develop a non-coherent carrier tracking feedback signal and a non-coherent symbol timing tuning signal. Utilize pilot signals and redundant information. As described above, the NCC 50 outputs a non-coherent carrier tracking feedback signal 72 as an input to the digital demodulator 42 and a non-coherent tuning feedback signal 64 as an input to the tuner 40. to provide.

As illustrated in FIG. 3, equalizer 46 receives baseband component signals I _F 76 and Q _F 78 from NRF 44. In some embodiments, equalizer 46 utilizes I _F 76 and QF 78. In other embodiments, only equalizer 46 utilizes I _F 76, also referred to as the real component of the demodulated signal.

Some embodiments of equalizer 46 establish and update coefficients using feed forward techniques, while other embodiments use feedback techniques such as LMS fitting. Certain embodiments estimate channel delay as part of this process. Equalizer 46 provides CDE 84 to control system 54. The control system 54 then utilizes an equalizer coefficient adaptation process via an LMS algorithm to advantageously combine the diversity of the received ghost signals to develop a virtual channel response that generates a stable received signal. guides you through the process.

In other embodiments, equalizer 46 includes a grating decoder that is integrated within the equalizer structure. In some embodiments, the output of the grating decoder is used to update the data samples of the equalizer DFE or to guide the equalizer coefficient adaptation process in relation to the ongoing basis. In other embodiments, the intermediate grid decoder stage outputs are used to guide the equalizer. Still other embodiments include a combined DFE-lattice decoder structure, as shown in US patent application Ser. No. 10 / 407,610, filed "Transported Structure for Decision Feedback Equalizer Combined with Trellis Decoder." In another embodiment, as shown in US patent application Ser. No. 09 / 884,256, the outputs from the intermediate stages of the grating encoder are coupled with the inputs of a particular stage of the DFE through a mapper.

As described herein, equalizer 46 includes techniques for estimating the channel delay of the transmission channel through which the information-supported signal is transmitted. Equalizer 46 provides control system 54 with CDE 84, which is used to derive tap coefficients of equalizer 46 in conjunction with other equalizer less techniques. Control system 54 uses CDE 84 to align the equalizer with respect to the channel. CDE 84 is developed from estimation of channel impulse response (CIR). Some embodiments estimate the CIR by correlating sync signal arrivals. Certain embodiments use field / frame sync signals. Other embodiments use a segment sync signal. Still other embodiments utilize both segment sync and frame sync to train the coefficients of equalizer 46. Further embodiments further estimate the CIR by correlating other signals in the received signal.

Some embodiments of equalizer 46 do not have a center tap or a reference tap. This allows the equalizer to remain stable even if multipath ghost significantly reduces the received main signal. Other embodiments include an overlapped equalizer with a virtual center output. In the overlapped equalizer, some samples included in the FFE and DFE portions of equalizer 46 are temporarily related. The overlapped equalizer structure allows the virtual center to be strategically placed within the equalizer to minimize the effects of noise and improve overall performance. In addition, some embodiments of the equalizer 46 include a decision directed phase tracker to remove residual phase noise that is not removed by the digital demodulator 42. Some of these embodiments also include techniques for associating the operation of the decision oriented carrier tracking feedback signal with the operation of the decision oriented phase tracker.

As illustrated in FIG. 3, in some embodiments of system 20, equalizer 46 provides tuned symbol decision 86 and correspondingly equalized data signal 88 to decision-directed control 52. do. As described herein, the equalized data signal 88 is a data signal provided to a determining device (not shown) of the equalizer. Tuning symbol determination 86 is a value generated by the determination device in the equalizer. In some embodiments, tuned symbol decision 86 is the output of a decision slicer. In other embodiments, tuning symbol determination 86 is the output from the selected stage of the grating decoder. In certain embodiments of the present invention, equalizer 46 provides decision directing controller 52 with an intermediate equalized signal 90 corresponding to tuning symbol decision 86. As described below, in some embodiments an intermediate equalized signal 90 comes from the output of the FFE. In other embodiments, the intermediate equalized signal 90 is a phase-corrected FFE output.

In some embodiments, adaptive symbol determination 94 is a known training signal, such as a generated tuning signal. In other embodiments, adaptive symbol determination 94 is the output of the decision slicer of equalizer 46. In certain embodiments, adaptive symbol determination 94 is the output of equalizer 46 lattice decoder or an intermediate stage or other stage of the lattice decoder. In still other embodiments, adaptive symbol determination 94 is dependent upon the operating state of system 20 or equalizer 46.

The decision directed control 52 generates a decision directed carrier tracking feedback signal 74 and a decision directed tuning feedback signal 66. The decision directed carrier tracking feedback signal 74 is a decision weighted carrier tracking error estimate for a specially received symbol. Similarly, decision directed tuning feedback signal 66 is a decision weighted timing error estimate for the received symbol.

The input of the FEC 48 receives the FEC symbol decision 80 of the equalizer 46. The FEC performs a number of post signal processing steps to correct for errors included in the received data. By way of example, FEC 48 performs frame tuning, data de-interleaving, and Reed-Solomon forward error correction.

Equalizer 46 illustrated as equalizer 200 of FIG. 5 is, as input, a filtered in-phase baseband signal (IF) 76 and a filtered quarter period baseband signal (QF) 78. And provide, as output, an FEC symbol decision 80, a tuning symbol decision 86, an equalized data signal 88, an intermediate equalized signal 90 and an adaptive symbol decision 94. As described herein, some embodiments of equalizer 200 do not handle Q _F.

The equalizer 200 further includes a feedforward equalizer 210, an adder 212, a determination device 214, a DFE 216, and a control system. As illustrated in FIG. 5, in some embodiments of equalizer 500, FFE 210 receives a filtered in-phase baseband signal 76 as input. Although not shown in FIG. 5 for convenience of description, some embodiments of the FFE 210 also receive Q _F. The output of the FFE 216 provides a second input of the adder 212. The output of adder 212 is an equalized signal 88 that serves as an input to decision device 214. Although not shown, the control system 54 is connected to the various elements of the equalizer 200, governs the operation of the equalizer 200, and allows the coefficients of the FFE 210 and the DFE 216 to fit. FFE is one of a range of filters known in the art, including FFF's (feedforward filters) and finite impulse response (FIR) filters, and those skilled in the art can use FFF or FIR as a suitable substitute for the FFE used herein. I will definitely understand.

As illustrated in FIG. 5, the determination device 214 provides various outputs including an FEC symbol determination 80, a tuning symbol determination 86, an equalizer feedback symbol output 92, and an adaptive symbol determination 94. . Equalizer feedback symbol output 92 is a decision device output provided to DFE 216. FEC symbol decision 80 is the final output of equalizer 200 provided to FEC 48, while tuned symbol decision 86 is provided to decision directing control 52 (see FIG. 3). In some embodiments, tuned symbol decision 86 is the output of a decision slicer circuit. In other embodiments, tuned symbol determination 86 is obtained from the output of a grating or Viterbi decoder or selected stage. In still other embodiments, the tuning symbol decision 86 is selectively obtained from the output or state of the grating decoder or the decision slicer circuit depending on the operating state of the equalizer 200. In the embodiment described herein, tuning symbol determination 86 may provide different outputs to each of the carrier tracking and tuning feedback loops.

In some embodiments, equalizer feedback symbol output 92 is obtained from the output of the decision slicer circuit. In other embodiments, the equalizer feedback symbol output 92 is obtained from the output of the grating or Viterbi decoder or from the selected stage. In another embodiment, equalizer feedback symbol output 92 updates the values of DFE 216 so that they can be corrected. Alternatively, control system 54 optionally takes a data source for equalizer feedback symbol output 92 in accordance with system operating conditions.

Control system 54 uses adaptive symbol determination 94 to ensure that the coefficients of equalizer 200 are fitted. Similar to tuned symbol determination 86, in some embodiments, adaptive symbol determination 94 is the output of a decision slicer circuit. In other embodiments, adaptive symbol determination 94 is obtained from the output of the grating decoder or the selected stage. In yet another embodiment, adaptive symbol determination 94 is a training symbol. In another embodiment, adaptive symbol determination 94 is optionally obtained from a decision device decision slice circuit, an intermediate lattice decoder stage, or a lattice decoder output, depending on the operating state of equalizer 200.

In certain embodiments, FEC symbol determination 80, tuning symbol determination 86, equalizer feedback symbol output 92, and adaptive symbol determination 94 are the same signal from the decision slicer output of decision device 214. In some other embodiments, the FEC symbol determination 80, the tuning symbol determination 86, the equalizer feedback symbol output 92, and the adaptive symbol determination 94 are functionally different, as described above, of the determination device 216. It is obtained from different stages.

As a non-limiting example, in some embodiments of the present invention, the determining device 214 is a grating decoder and selectively controls the source of the respective outputs. By way of example, tuned symbol determination 86 may optionally be obtained from a desired portion of the grating decoder. In a first example, control system 54 selectively controls tuning symbol determination 86 to be the decision slicer output of decision device 216. In a second example, control system 54 selectively controls tuning symbol determination 86 to be a partially or completely error-corrected symbol from the lattice decoder of determination device 216.

As shown in FIG. 5, the DFE 216 receives as an input equalizer feedback symbol output 92. In some embodiments, for example, if the determining device 214 includes a grating decoder, the feedback symbol output 92 is optionally controlled. By way of example, in a particular embodiment of the invention, the equalizer feedback symbol output 92 may be the output of the decision slicer portion of the grating decoder. If the equalizer coefficients are optimized to remove a portion of the transmission channel distortion, control system 54 may optionally update the values of DFE 216 from the corrected symbols of the grating decoder. In some other embodiments, as described in US Patent Application No. 10 / 407,610, filed with the title “Transposed Structure for a Decision Feedback Equalizer Combined with a Trellis Decoder,” the determination device ( 214 provides an error-corrected symbol output to DFE 216 from one of the trace memories of the grating decoder. In another embodiment, the outputs of the stages of the lattice decoder of the DFE are described as described in US patent application Ser. No. 09 / 884,256, filed with the applicant, pending "Combined Trellis Decoder and Decision Feedback Equalizer." It is used to develop inputs for at least a portion of the stages.

In the system shown in FIG. 5, not all connections are shown for ease of explanation, but control system 54 is connected to FFE 210, decision device 214, DFE 216, and CDEU 230. . In addition, control system 54 includes CDE 84, equalized data signal 88, adaptive symbol determination 94, segment sync signal 96 from segment sync detector (not shown), field / frame sync detector ( Receive field / frame sync signal 98 and SNR signal 100 from 218.

First of all, control system 54 initializes and controls various stages and parts of equalizer 200, clock generation, and initialization and operation of system 20. As described below, control system 54 also develops or optimizes filter coefficients of equalizer 200 to remove the effects of pre-ghost and post-ghost signals.

The equalizer 200 further includes a CDEU 230 that includes techniques for estimating the CIR of the transport channel that are used sequentially to estimate the channel delay of the transport channel. In some embodiments, CDEU 230 receives in-phase baseband signal I _F 76 filtered as inputs, and CDE 84, which is developed from an estimate of CIR as an output to control system 54. ). In some other embodiments, the CDEU 230 does not utilize the filtered quarter period baseband signal 78. In still other embodiments, FFE 210 receives both I _F and Q _F. As will be appreciated by those skilled in the art, the representation of the equalizer 200 operating in conjunction with I _F is for convenience of description and is not meant to be limiting.

As will be discussed below, CDEU 230 provides CDE 84 that represents a composite delay at the input of FFE 210 to control system 54. As will be described below, the composite delay reflects the delay associated with the ghost signals present in the channel. Based on the CDE 84, the control system 54 uses any of the techniques described herein to determine the desired temporary location of segment sync and frame sync signals at the output of the equalizer 200. Control system 54 adapts the coefficients of FFE 210 and DFE 216 based on the difference between equalized data signal 88 and adaptive symbol determination 94. Some embodiments may include a field / frame sync signal 98 and an optional segment sync signal instructing the control system 54 whether the field / frame sync signal 98 has been detected (by the field / frame sync detector 218). 96). Finally, the SNR signal instructs the control system 54 of the relative signal-to-noise ratio and / or data error rate of the equalized signal at the output of the equalizer 46.

One implementation of CDEU 230, such as CDEU 230A, which estimates the channel delay of the channel by detecting the relative delay and correlation strength of the segment sync sequences of the various ghost signals received at the input of FFE 210 within the segment period. An example is shown in FIG. 6. As will be described in more detail below, the CDEU 230A correlates the received signal for a given symbol time in a segment period having a known segment sync sequence. The correlation strengths represent an estimate of the CIR of the transmission channel. Then, the correlation strengths for each symbol time are temporarily filtered over the sequence of segment periods. As described in connection with FIG. 7, the CDEU 230A then develops the CDE 84 by calculating the centroid of the correlation strengths that are temporarily filtered within the data segment period for the local time base. . Although specific embodiments of the CDEU 230 have been described as having specific hardware and software partitions, this is merely illustrative and not limiting. It is to be understood that other partitioning and configurations can be implemented as commonly practiced in the art.

As a first non-limiting example illustrated in FIG. 7, system 20 receives an ATSC signal transmitted over a channel. The received signal includes a first ghost G1 and a second ghost G2. The relative delay between the landings of G1 and G2 is the estimated delay in the landing of each ghost's segment sync sequence at the receiver within the segment period. The strength or magnitude of each ghost is estimated from the correlation strength of the segment sync sequence landing at a particular symbol time slot in the segment period. By way of example, G ₁ and G ₂ are located at symbol times 128 and 512 in the symbol clock segment period, respectively. As shown, the correlation of the segment sync sequence of G1 is 60% of the correlation size of the segment sync sequence associated with G2. Applying a weighted average or centroid calculation, the CDE of the channel is estimated to correspond to the symbol time 368.

In the further example illustrated in FIG. 8, the channel of FIG. 7 includes ghost signals G ₃ , G ₄ and G ₅ at data symbol times 64, 256 and 768, respectively. In some embodiments of the invention, G ₃ , G ₄ and G ₅ are also taken into account when calculating the CDE. In another embodiment, a threshold function is applied that filters out considerations of these smaller-size ghost signals.

Referring back to FIG. 6, the CDEU 230A is adapted to operate in the presence of ghost signals in the transport channel of an onshore ATSC broadcast system. CDEU 230A receives the filtered in-phase baseband signal I _F as input to correlator 310. Integrator 312 receives the output of correlator 310 and provides its output to correlation buffer 314.

Similarly, centroid estimator 340 receives the output of correlation buffer 314 via interface 342. In the illustrated embodiment, the interface 342 is unidirectional, and the centroid estimator 340 only reads the contents of the correlation buffer 314. In other embodiments, interface 342 is bi-directional, and centroid estimator 340 may read and write the contents of correlation buffer 314.

In some embodiments, the symbol counter 316 receives an input from a symbol clock (not shown) and modulates a symbol count output (SC) corresponding to the number of symbols received during a data segment period. ) It is a counter. The symbol clock provides a clock edge every Morris symbol time. As an example, the ATSC system segment period consists of 832 symbol times. Thus, one embodiment of a symbol counter suitable for an ATSC system is the remaining 832 counter with output values from 0 to 831. The symbol counter output is each symbol time incremented; It does not have to be aligned with the segment sink. In addition, some embodiments of the symbol counter 316 all include a segment indicator output to which 832 symbol times are allocated. The segment indicator output is timed for the first symbol counted by the symbol counter 316.

One embodiment of segment counter 318 receives a segment indicator output SI of symbol counter 316. The segment counter 318 counts the number of segment indications generated by the symbol counter and provides a segment count SEGCNT corresponding to the number of segment indications received within the frame time. In still other embodiments, the segment counter 318 is the remaining 313 counter corresponding to 313 segments per data field in the ATSC transmission. In an alternate embodiment, segment counter 318 receives input from the symbol clock and increments all 832 symbol times.

Controller 320 includes a first control interface operably connected to control system 54 for communicating with other elements of equalizer 200, including correlator 310, integrator 312, correlation. A second interface for communicating with other elements of the CDEU 230A including the buffer 314, the symbol counter 316, the segment counter 318, the memory 330, and the centroid estimator 340. It may be. A second control interface, as is acceptable in the art, includes resetting memory and buffers to zero, reading and writing configuration registers, controlling reset signals, and controlling access to memory and register locations. Control various elements of the CDEU 230A, buffer management of various devices, and various controls and techniques, including but not limited to these. Controller 320 also receives SEGCNTs and signals SC from segment counter 318 and symbol counter 316, respectively.

As illustrated in FIG. 6, some embodiments of the CDEU 230A couple the controller 320 and the correlation buffer 314. Correlation buffer 314 has memory locations corresponding to the number of symbol times in the data segment period, referred to herein as array M (i) (i is the index of the array). The maximum value of i corresponds to the number of symbol times included in the data segment. Although not shown, the index variable i is provided to the correlation buffer 314 by the controller 320. As described herein, in some examples the index variable i has the same value as the SC provided by the symbol counter 316. However, in another example, index variable i is provided by controller 320 to calculate CDE 84.

By way of example, one embodiment of the present invention adopted for the ATSC standard includes a correlation buffer 314 having 832 memory locations corresponding to 832 symbols per data segment. As will be appreciated by those skilled in the art, in certain embodiments controller 320 dominates the operation of correlation buffer 314 exclusively. Other embodiments allow the integrator 312, controller 320, and centroid estimator 340 to access the correlation buffer 314. Various techniques, interfaces, buffer management techniques, memory organizations, and types are used in various embodiments that can be realized in the art, and all descriptions herein are illustrative only and not intended to be limiting.

The controller 320 is also coupled to the memory 330 and the centroid estimator 340. Other embodiments of the CDEU 230A allow the control system 54 to access the memory 330. As shown in FIG. 6, one embodiment of memory 330 includes a CDE register 332, a centroid estimate (CENT) register 334, a coring threshold register 336 and a segment count register ( 338). As described in more detail below, the CDE register 332 maintains a current estimation delay associated with the channel delay measured at the input of the FFE 210. The CENT register 334 includes the centroid estimates generated by the centroid estimator 340 corresponding to the values stored in the CDE register 332. As described below, the coring threshold register 336 includes a coring threshold variable that is used to filter out or minimize false segment sync detection. Finally, the contents of the segment count register 338 are correlated to the CDEU 230A generated by the correlator 310 to produce a set of segment sync correlation values that are temporarily filtered for each symbol time in the segment period. The number N of segments integrating the values. In some alternative embodiments, the coring threshold and the values of N are static.

Functionally, the correlator 310 receives and correlates the four most recently received values of I ^F 76 with a known segment sync sequence to produce a symbol correlation value SCV (i). By way of example, in some embodiments, SCV (i) is a symbol correlation value for the i ^th symbol time of the data segment and at the output of the i ^th array location M (i) and symbol count 316 of the correlation buffer 314. Corresponding. As shown in FIG. 9, one embodiment of the correlator 310 is designed for an ATSC system and includes a summer 350 and a delay line 360. Delay line 360 has first, second, third and fourth delay elements (not shown), which receive I _F 76 as input and receive first delay output 362. to provide. The second delay element receives a first delay output 362 and provides a second delay output 364. The third delay element receives a second delay output 364 and provides a third delay output 366 to the fourth delay element, which further provides a fourth delay output 368. The outputs of the first, second, third and fourth delay elements correspond to the four most recently received values of I _F , designated I _F3 , I _F2 , I _F1 and I _F0 , respectively. Summer 350 generates an output SCV (i) from inputs I _F3 , I _F2 , I _F1 and I _F0 . At symbol time i the output of summer 350 is SCV (i) = I _F3 -I _F2 -I _F1 + I _F0 . As will be appreciated by those skilled in the art, a segment sync sequence, that is, a relatively short length of four symbol times, will often result in noisy correlation SCV (i). By way of example, data passing through correlator 310 (see FIG. 6) is self-aligned in a predetermined manner resulting in a maximum correlation output. Integrating the values of SCV (i) over multiple segments averages these noisy correlation values.

In one embodiment, integrator 312 is a complete integrator. In yet another embodiment of integrator 312, integrator 312A shown in FIG. 10 is a " Like " integrator and data input buffer 370, memory input buffer 374, scalar 374, adder 376. ) And an output buffer 378. Integrator 312A receives SCV (i) in data input buffer 370 from correlator 310 (see FIG. 9) corresponding to SC of symbol counter 316. INT (i) is a temporarily averaged value of SCV (i) obtained by integrating the value of SCV (i) over time and is stored in array M (i) of correlation buffer 314. Integrator 312A is simply denoted INT _OLD (i) and accepts a pre-calculated integral value corresponding to the symbol count of symbol counter 316 in memory input buffer 372. It should be understood that SCV (i) and INT _OLD (i) correspond to the same symbol time in the data segment period. Memory input buffer 372 provides INT _OLD (i) to scalar 374. Scalar 374 multiplies INT _OLD (i) by the desired scalar S and provides the product to adder 376. Further, the adder 376 receives the output of the data input buffer 370 and provides the sum _NEW INT (i) = SCV (i) + (S · INT _OLD (i)), the output buffer 378. Output buffer 378 provides a _NEW INT (i) in the correlation buffer 314 to store _NEW INT (i) of the M (i).

In some embodiments where integrator 312A is a complete integrator, the scalar value is 1 ( S = 1). In embodiments with a leaky integrator, the scalar value is less than one. By way of example, one embodiment of the present invention uses S = 255/256. Integrating the values of SCV (i) over multiple segment periods filters out noise of data received in the correlator 310.

As illustrated in FIG. 11, one or more embodiments of the centroid estimator 340 include a filter 380, a threshold register 382, a subtractor 386, a PCDE register 388 and an integrator 390. do. Controller 320 (see FIG. 6) reads and writes parameters for threshold register 382 and PCDE register 388. As described below, the integrator 390 provides a centroid error estimate 344 value to the controller 320. In some embodiments, the controller 320 writes the variable threshold (variable threshold) to the coring threshold register 336, a threshold register 382 from (see Fig. 6). In another embodiment, threshold register 382 is equivalent to coring threshold register 336. PCDE register 388 includes a proposed channel delay estimate (PCDE) under evaluation. In some embodiments of the invention, the PCDE register 388 is equivalent to the CDE register 332 (see FIG. 6).

Controller 320 (FIG. 6) provides index variable i to centroid estimator 340 of FIG. 11, which centroid estimator 340 also provides a correlation buffer 314 at the first input 342 of filter 380. Accept INT (i) from The filter 380 also includes a second input for accepting a variable threshold from the threshold register 382 and provides an output to the first input of a multiplier 384. PCDE register 388 provides a variable PCDE to the positive input of subtractor 386. A negating input of subtractor 388 receives the index variable i from controller 320. The output of subtractor 386 is the distance from PCDE used to calculate the "moment" (in mathematical sense) corresponding to INT (i). The output of the subtractor 386 is provided as a second input to the multiplier 384, which provides an enemy to the input of the integrator 390.

As discussed below, the controller 320 searches for PCDE values that minimize the absolute size of the metric referred to herein as CCE (PCDE). Other embodiments of the present invention search for the sign change of CCE (PCDE) to select a CDE regardless of the absolute size of the CDE. Filter 380 performs a filter function F (INT (i), threshold) with respect to the absolute value of INT (i) values stored in correlation buffer 314. By way of example, in some embodiments, filter 380 takes the absolute value of INT (i) and compares it with a threshold. The output of filter 380 is F (INT (i), threshold) = 0 for values of | INT (i) | <threshold; The filter 380 has an output F (INT (i), threshold) = | INT (i) | with respect to | INT (i).

In other embodiments, filter 380 compares the squared value of INT (i) with a threshold such that if INT (i) ² ≥ threshold, the output of filter 380 is equal to INT (i) ² , and so on. Otherwise, these outputs equal zero. In another embodiment, filter 380 has an output F (INT (i), threshold) for an | INT (i) | ² > threshold. Otherwise, filter 380 has an output F (INT (i), threshold) for | INT (i) ² ≤ threshold.

The subtractor 386 develops a sample distance difference (PCDE-i) that represents the delay or number of samples between the proposed CDE location and the i ^th sample corresponding to INT (i). The multiplier 384 multiplies the sample distance difference signal by the output of the filter 380. The multiplier provides an input to an integrator 390 that performs less addition.

Here, CCE (PCDE) is a CIR centroid error estimate and reflects the distance of PCDE from the location of the centroid of CIR (ie CDE). The function Dist (x ₀ , x ₁ ) calculates the number of samples from the first symbol time x ₀ to the second symbol time x ₁ . By way of example, in some embodiments of ATSC, Dist (PCDE, i) is a negative sign for [(PCDE +416) mod 832] ≤i <PCDE and for PCDE≤i (PCDE + 416) mod 832. It is defined to have a positive sign.

As a non-limiting example, one or more embodiments of a system suitable for ATSC standard broadcasting includes a correlation buffer 314 (see FIG. 6) with 832 memory locations. Assuming a current value of PCDE = 26,

Where d (PCDE, i) is a non-negative distance metric d (x ₀ , x ₁ ) = │x ₀ -x ₁ │ and ₀ ≦ i ≦ 831. It should be understood that different boundary conditions and techniques for calculating weighted mean or centroid estimates may be implemented by those skilled in the art without undue experimentation. Some alternative embodiments of the system are a non-linear distance metric function. In some embodiments, the distance metric function d _K (x ₀ , x ₁ ) = | x ₀ -x ₁ | ^K. By way of example, K = 2 in some embodiments. In another embodiment, K is a fraction.

Hereinafter, one embodiment of the CDEU 230A will continue to refer to the elements of FIG. 6 and refer to the flow chart of FIG. 12 illustrating the operation of a suitable system 400 for an ATSC broadcast system to estimate channel delay. Will be discussed. At 402, “initialization” controller 320 includes, but is not limited to, the contents of correlation buffer 314, symbol counter 316, segment counter 318, and integrator 382; Initialize 230A. In various embodiments, this also includes proper initialization of the various control registers. In some embodiments, accepting the first three symbol times of the filtered in-phase baseband signal I _F 76 initializes the correlator 310. After initialization of the CDEU 230A, control passes to 404.

At 404, correlator 310 accepts a new symbol from baseband signal I _F 76 and calculates the value of SCV (i) corresponding to the symbol count generated by symbol counter 316. By way of example, initial launch correlator 310 generates SCV (0), where SC = 0. System 400 changes to 406 after SCV (i) calculation.

At 406, the “integral” integrator 312 receives SCV (i) from correlator 310 and INT _OLD (i) from array M (i) of correlation buffer 314. Each INT (i) = 0 at the initial start. Otherwise, INT (i) is an already stored integral value. Integrator 312 adds SCV (i) to the scaled value of INT _OLD (i) to produce INT _NEW (i) in output buffer 378. The system 400 then proceeds to 410.

At 410, i.e., "SC = 831", the controller 320 determines whether the SC, such as index variable i, is equal to the maximum output of the symbol counter output 816. In the condition SC = 831 (YES) where the SC ranges from 0 to 831, the system 400 proceeds to 141. Otherwise, the system 400 proceeds to 412 with a negative determination (NO). The CDEU 230A then increments the segment counter 316. Upon accepting the new value of SC, controller 320 increments index variable i and advances system 400 back to 404.

At 414, ie “SEGCNT <N,” controller 320 compares the output of segment counter 318 SEGCNT with the value N stored in segment count register 338. Positive Decision At SEGCNT &lt; N (YES), controller 320 branches CDEU 230A task to 416 where segment counter 318 is incremented by one. In addition, the output of the symbol counter 315 is set to zero (ie SC = 0). However, at negative decision SEGCNT <N (NO), it was determined that SEGCNT = N, and control proceeds to 420.

At 420, "Find Initial CDE", controller 320 searches correlation buffer 314 for the location of array M (i) containing the maximum value of INT (i). The index number variable i corresponding to the maximum size of INT (i) is selected as the initial value of the channel delay estimate CDE and is located in the CDE register 332 and / or the PCDE register 388.

At 422, or " CDEU, " the centroid estimator 340 calculates CCE (PCDE) for the CDE value that has been proposed. At 424, or "Found Initial CDE", controller 320 evaluates whether CCE (PCDE) = 0 or SGN (CCE) ≠ SGN (CENT), where SGN () restores the sign of the number in parentheses. The return function is the signum () function. If either condition is found to be true, the operation of system 400 branches to 432. Otherwise, operation of system 400 branches to 426.

At 426, ie "CCE (PCDE)> 0", the controller 320 determines whether CCE (PCDE)> 0. In a positive decision (YES), the work of CDEU 230A branches to 430. Otherwise, in the negative decision NO, the CDEU 230A branches to 428. At 428, i.e., "Increment PCDE", controller 320A writes the current values of PCDE and CCD (PCDE) to CDE register 332 and CENT register 334, respectively, and the value of PCDE stored in PCDE register 388. Increment The operation of system 400 then proceeds to 422 and CDEU 230A continues to retrieve the CDE.

At 430, or "Decrement PCDE", controller 320A writes the current values of PCDE and CCE (PCDE) to CDE register 332 and CENT register 334, respectively, and the value of PCDE stored in PCDE register 388. Increment The operation of system 400 then returns to 422, and CDEU 230A continues to search for CDE.

At 432, ie, "CCE (PCDE) = 0", controller 320 evaluates whether CCE (PCDE) = 0. In a positive decision (YES), the PCDE value is the desired value and CDEU 230A proceeds to 434, where controller 320 writes the value of PCDE to CDE register 332 and proceeds to Exit. Otherwise, at negative decision NO, system 400 proceeds to 436.

At 436, i.e., " Select Nearest ", the controller 320 determines whether CENT &lt; CCE (PCDE). In a positive decision, the value stored in CDE register 332 is the desired value of CDE and CDEU 230A proceeds to Exit. Otherwise, the PCDE value is the desired value of the CDE (see 434), so the controller 320 writes the value of the PCDE register 388 to the CDE register 332. The system 400 then proceeds to Exit. Other search algorithms for selecting PCDE values are those that will be or will be apparent to those skilled in the art for use in use in this system, and are not intended to be limiting above.

Another embodiment of the CDEU 230 as illustrated in FIG. 13 is a CDEU 230B suitable for operation in the presence of ghost signals such as those present in terrestrial ATSC broadcasting. CDEU 230B uses both baseband component signals I _F 76 and Q _F 78 from Nyquist Root Filter 44 to develop the estimated CDE. The function and operation of the CDEU 230B is similar to the function and function of the CDEU 230A except that it uses both I _F and Q _F to calculate the correlation of the received signal and the segment sync sequence. In addition, the CDEU 230B adds correlation results of the corresponding I _F and Q _F signals for each symbol time.

Thus, similar to the CDEU 230A, the CDEU 230B includes a first correlator 310, a first integrator 312, a first correlation buffer 314, a symbol counter 316, a segment counter 318. ), Controller 320A, memory 330, and centroid estimator 340. The CDEU 230B also includes a second correlator 310A, a second integrator 312A and a second correlation buffer 314A. The CDEU 230B receives the filtered baseband signals I _F 76 and Q _F 78 as inputs to the first correlator 310 and the second correlator 310A, respectively. Similar to integrator 312, integrator 312A receives the output of correlator 310A and SCV _Q (i) and INT _QOLD (i) from correlation buffer 314A. Integrator 312A provides INT _QNEW (i) as output to correlation buffer 314. SCV _Q (i) is the symbol correlation value for i ^th symbol time in the data segment with Q _F and corresponds to the output of the symbol counter 316 and the i ^th array location M _Q (i) of the correlation buffer 314A. .

Correlator 310, integrator 312 and correlation buffer 314 have similar functions and operations as described above with respect to CDEU 230A. Similarly, correlator 310A, integrator 312A and correlation buffer 314A are functionally identical to correlator 310, integrator 312 and correlation buffer 314 of CDEU 230A. Have similar operations and functions; They are intended to work in conjunction with the quarter period baseband signal Q _F 78. Exemplarily, correlation buffer 314 holds correlation value INT _I (i) corresponding to I _F 76, and correlation buffer 314A corresponds to correlation value INT _Q (i) corresponding to Q _F 78. Hold.

The outputs of correlation buffers 314 and 314A provide INT _I (i) and INT _Q (i) to the inputs of magnitude calculator 392, respectively. The output of magnitude calculator 392 provides the composite size of MAG (i), INT _I (i) and INT _Q (i) to centroid estimator 340 and controller 320A. Otherwise, controller 320A is functionally and operatively similar to controller 320 described above. Other embodiments calculate MAG (i) = INT _I (i) 2 + INT _Q (i) ² . As can be appreciated, in other embodiments different metrics for composite size are used.

Otherwise, the CDEU 230B works well in the same way as the CDEU 230A, except that the CDEU 230B uses the output MAG (i) of the size calculator 392 to calculate the centroid, while the CDEU 230A Only use the size of INT (i). By way of example, after going through a sufficient number of segment periods, the controller 320A determines the initial position of the PCDE by determining the value of the index variable i corresponding to the maximum size of the MAG (i).

Another embodiment of the CDEU 230 illustrated in FIG. 14 is a CDEU 230C that is also suitable for an ATSC broadcast system. The CDEU 230C estimates the position of the channel delay by detecting the correlation strength of the various received ghost signals with the known frame sync sequence PN511 in the desired sample window. It should be understood that ATSC frame sync includes a pseudo random sequence having a cyclic convolution property. Some embodiments of the present invention are advantageous for calculating the correlation strength of a particular ghost by using a matched filter to take advantage of the relatively long length of the field / frame sync sequence. Other embodiments develop a correlation strength estimate by correlating the received signal with the predicted PN511 sequence.

As illustrated in FIG. 15, another non-limiting example transport channel includes ghosts G ₁ , G ₂ , G ₃ and G ₄ , each having correlation intensities above the detection threshold level. The channel also includes ghosts G ₅ , G ₆ and G ₇ , each of which has a correlation strength that is below the detection threshold or above the coring threshold level. Finally, the example channel has ghosts G ₈ and G ₉ below the coring threshold level. The relative multipath delay of each ghost is reflected at their relative position along the horizontal axis.

Some embodiments of the CDEU 230C apply a windowing function to the received ghost signals. Ghost signals in the window are used to calculate the channel delay estimate. In some embodiments, the span of the window is based on the detected first ghost signal having a frame sync correlation strength above the detection threshold. As illustrated in FIG. 15, CDEU 230C first detects G ₁ having a correlation strength above the detection threshold. CDEU 230C then selects a centered window span W ₁ for G ₁ . Ghosts outside the window are not taken into account when estimating the location of the channel delay. It should be understood that G ₄ is not within W ₁ and is not taken into account when estimating the location of the channel delay.

Other embodiments of the CDEU 230C select a centered window for ghost with maximum or local maximum correlation strength. As illustrated in Figure 15, CDEU (230C) detects the early G ₁ to W _1, and select a current window centered on G _1. In turn, the CDEU 230C detects G ₂ having a correlation strength greater than that of G ₁ . CDEU 230C then selects a new window W ₂ centered for G ₂ . As a result, G ₇ and G ₉ are not taken into account in the channel delay estimation; G ₄ is considered because it belongs to W ₂ .

Referring back to FIG. 14, CDEU 230C includes symbol counter 316, segment counter 318, centroid estimator 340A, size calculator 392, correlators 510 and 512, correlation buffer 514. ), A threshold detector 516, a controller 520, and a memory 530. The CDEU 230C receives the filtered baseband signals I _F 76 and Q _F 78 as inputs to the first correlator 510 and the second correlator 512, respectively.

Correlators 510 and 512 provide SCV _I (i) and SCV _Q (i) to size calculator 392. The correlators 310 of FIG. 13 except that the correlators 510 and 512 are arranged to provide correlation between the received I _F 76 and Q _F 78 signals and the frame or field sync sequence. And 312). SCV _I (i) and SCV _Q (i) are the correlation strength of the received I _F 76 and Q _F 78 with the frame or field sync sequence. The magnitude calculator 392 provides the MAG _FS (i) as output to the threshold detector 516 and the correlation buffer 514. MAG _FS (i) is similar in form and function to MAG (i) in FIG. 13 but operates directly on SCV _I (i) and SCV _Q (i) instead of integrated values. Correlation buffer 514 is operably coupled to centroid estimator 340A. Controller 520 interacts with memory 530 and accepts values of SC and SEGCNT from symbol counter 316 and segment counter 318 respectively. Similar to the controller 320 of FIG. 13, the controller 520 provides a channel delay estimate 84 and has a first control interface coupled to the control system 54 (see FIG. 3). In addition, the controller 520 may include a second interface (not shown for convenience of description), a correlator 512, a correlation buffer 514, and a threshold detector 516 to the control interface of the correlator 510. , A memory 530, a symbol counter 316, a segment counter 318, and a centroid estimator 340A.

The second control interface of controller 520 reads and writes configuration registers, issues reset signals, controls access to memory and registers, manages buffers of various devices, and occurs in the art. It governs the operation of various elements of the CDEU 230C, including but not limited to other functions that may be possible. In various alternative embodiments, the first and second control interfaces of the controller 520 may include separate data buses or utilize a single data bus as is possible in the art, or a plurality of individual between components. Each consists of data channels.

Finally, memory 530 includes a CDE register 332, a CENT register 334, a coring threshold register 336, a detection threshold register 532 comprising a variable detection threshold T _DET , and a window center comprising a variable WINCENT. Register 534, FSYM register 536 including variable frame sync symbol position (FRYM) and FSEG register 538 including variable frame sync segment position (FSEG). Some embodiments include a window end register 540 that includes a variable WINEND and a window start register 542 that includes a variable WINSTART. The detection threshold T _DET is the minimum output value of the magnitude calculator 392 that is believed to correspond to the detection of the frame sync sequence in the incoming data stream. WINCENT corresponds to a memory location in the correlation buffer 514 that is the center of the windowing function. FSYM and FSEG are the values of symbol counter 315 and segment counter 318 respectively corresponding to the symbol time located at the center of the windowing function. Finally, WINSTART and WINEND correspond to the first and last memory locations of the desired window in correlation buffer 514.

In some embodiments, correlation buffer 514 is configured as a circular buffer with 2n memory locations addressed by indexer variable i having a value between 0 and 2n-1. In other embodiments, correlation buffer 514 holds 2n + 1 correlation values. As a non-limiting example, for a transport channel with a centroid at WINCENT, WEND = (WINCENT + n) modulo (2n) and WSTART = (WINCENT + n + 1) modulo (2n).

Another embodiment of the CDEU 230C illustrated as the system 600 operating according to the flow chart of FIG. 16 is also adapted for ATSC broadcasting. At 602, "Initialization", as those skilled in the art will appreciate, elements of CDEU 230C are initialized. By way of example, with the additional reference of FIG. 14, controller 520 may register registers in memory 530, symbol counter 316, segment counter 318, size calculator 392, correlator 510, and the like. Initialize the correlation buffer 514. Further, index variable i is initialized to zero.

At 604, or “Correlation,” correlators 510 and 512 receive the most recently filtered in-phase and quarter period baseband signals I _F 76 and Q _F 78, respectively, and most recently. Perform correlation with respect to the sequence of received bits. As in the embodiment described above with reference to FIG. 14, magnitude calculator 392 receives SCV _I (i) and SCV _Q (i) from correlators 510 and 512, respectively, and the magnitude of correlation MAG _FS ( calculate i) MAG _FS (i) is provided as an output to correlation buffer 514 and threshold detector 516. Correlation buffer 514 stores MAG _FS (i) in array M (i). System 600 then proceeds to 606.

At 606, i.e., "Detect Frame Sync", if MAG _FS (i) &gt; T _DET (YES), a positive indication is sent to controller 520. The system 600 then branches to 610. Otherwise, threshold detector 516 sends a negative indication NO (no frame sync detected) to controller 520. The system 600 then branches to 612. In some embodiments, controller 520 branches CDEU 230C task to 610 only upon detection of the first frame sync. Similar to window W ₁ of FIG. 15, this creates a window function centered for the first ghost signal with frame sync correlation above T _DET .

In other embodiments, the CDEU 230C task branches to 610 if a frame sync is detected at 606 or if MAG (i)> CENT. By way of example, the CENT register is initialized with CENT = T _DET . The first positive indication YES is sent to the controller 520 when MAG _FS (i) ≥T _DET . On each positive indication, controller 520 sets CENT = MAG _FS (i). Additional positive indications are generated when MAG _FS (i) ≧ CENT. This creates a window function centered on a ghost signal with maximum frame sync correlation, similar to window W2 in FIG. Otherwise, controller 520 branches the CDEU 230C job and system 600 proceeds to 612.

At 610, or "Store Center", controller 520 sets FSYM = SC and FSEG = SEGCNT, where FSYM and FSEG represent the location of the detected frame sink within the data packet field / frame structure. Controller 520 sets CDE = i as the initial estimate of channel delay. In some embodiments, controller 520 also sets CENT = MAG (i) as the magnitude of the correlation corresponding to the initial channel delay estimate. Controller 520 also calculates the location WINEND. The system 600 then proceeds to 612.

At 612, ie, “Continue,” controller 520 branches the CDEU 230C's work depending on whether WINEND has been reached. In the negative indication NO, the CDEU 230E did not detect the frame sync in advance, or the CDEU 230E detected the frame sync in advance, but i ≠ WINEND. In this case, system 600 branches the job to 614. Otherwise, controller 520 determines if WINEND has been reached and branches the job to 615 FIND CDE. As described below, system 600 determines the CDE of a channel in FIND CDE.

At 614, the values of symbol counter 316 and segment counter 318 are updated. Index variable i is also incremented. System 600 returns to 604.

Some embodiments of the CDEU 230C include a centroid estimator 340A that estimates the delay of the channel by calculating the centroid or weighted average of the correlation values in the windowing function. As will be appreciated by those skilled in the art, the centroid estimator 340A is operatively operated with the centroid estimator 340 except that it is intended to operate in relation to the value of the MAG _FS (i) stored in the correlation buffer 514. And structurally similar. The controller 520 and the correlation buffer 514 of the centroid estimator 340A interact and operate in an equivalent or more like manner with the controller 320 and the correlation buffer 314 of the centroid estimator 340. Thus, similar to centroid estimator 340, centroid estimator 340A performs the following summation over the values included in the desired WINDOW of the memory locations of correlation buffer 514:

 Similar to the controllers 320 and 320A of the above-described embodiments of the CDEU 230, the controller 520 may use the correlation buffer 514 and the centroid estimator 340A to determine the location of the correlation value corresponding to the delay of the channel. ) (Not shown).

Other embodiments of the CDEU 230C determine the delay of the channel by calculating the centroid or weighted average of the correlation values of the subset of correlation values within the windowing function. As illustrated in FIG. 17, in some embodiments, the controller 520 divides the window into regions centered around a ghost signal having a maximum correlation value G _MAX , corresponding to sample i = I _MAX , thereby in-windowing. Let M (I _MAX ) = G _MAX at. In other embodiments, region R ₀ has some width for I _MAX . Region R ₁ is the window portion from WINSTART to region R ₀ and contains pre-ghost signals for I _MAX . Region R ₂ is the window portion from region R ₀ to WINEND and includes pre-ghost signals for I _MAX .

By way of example, controller 520 initially searches correlation buffer 514 to locate G _MAX . The ghost signal G _POST and (M (I _PRE) = G _PRE - Then, the controller 520 is closest to the I _MAX (M (I _POST) = G corresponding to the i = I _POST to the _POST) post that corresponding to the i = I _pRE) pre-search regions R ₁ to position the ghost signal G _pRE. In some embodiments, controller 520 only considers ghost signals with MAG _FS (i)> T _DET . As shown in FIG. 15, G ₂ is G _PRE and G ₃ is G _POST .

In analogy to the controller 320 in CDEU (230A), controller 520 is _{equation: CCE (PCDE) = G MAX} · Dist (PCDE, I MAX) + G PRE · Dist (PCDE, I PRE) + G POST · Determine the location of PCDE by evaluating Dist (PCDE, I _POST ), where Dist (PCDE, i) is negative for values of i placed between WINSTART and CDE, and for values of i placed between CDE and WINEND. It is defined as a quantity. In still other embodiments, controller 520 first considers ghost signals with MAG _FS &gt; T _DET ; However, ghost signals above the threshold are also considered. By way of non-limiting example, one embodiment of a system 20 suitable for ATSC standard broadcasting has a correlation buffer 514 comprising 1024 samples with a window width of 1024 samples. Under one possible channel condition, FSYM = 128, WINSTART = 640 and WINEND = 639. Given PCDE = 26:

Here, d (PCDE, i) is a non-negative distance metric d (x ₀ , x ₁ ) = | x ₀ -x ₁ | and ₀ ≦ i ≦ 1023.

Different boundary conditions and techniques for calculating weighted mean or centroid estimates can be applied to this system without undue experimentation. In some embodiments, controller 520 selects a value of CDE that minimizes the absolute size of CCE (PCDE). In other embodiments, controller 520 selects the value of CDE for which the sign of CCE (PCDE) changes.

Another embodiment of the CDEU 230 illustrated in FIG. 18, which is also suitable for an ATSC broadcast system, detects the delay of the channel by detecting the correlation strength of various received ghost signals with the frame sync sequence PN511 within the desired sample window. Is the CDEU 230D. The CDEU 230D is similar in form and function to the CDEU 230C, except that it only works in conjunction with the filtered in-phase baseband signal I _F 76, while the CDEU 230C has an I _F (76). ) And Q _F (78). Thus, correlator 510 provides SCV (i) to correlation buffer 514 and threshold detector 516. Since CDEU 230D does not include SCVQ (i), it is not necessary to calculate MAG _FS (i). As will be appreciated by those skilled in the art, the CDEU 230D is intended to estimate the delay of the channel based on the size of the frame sync with I _F while the CDEU 230C uses both I _F and Q _F. Thus, correlation buffer 514 stores M (i) = SCV _I (i). CDEU 230D functions similarly to CDEU 230C except that it uses SCV _I (i) instead of MAGFS (i). therefore:

Similarly, the filter 380 is compared to one of the square or the absolute value of the SCV _I (i) to the value of the threshold and │SCV _I (i) │> output to the threshold value F (SCV _I (i), threshold) before = Gives SCV _I (i). Otherwise, filter 380 has an output F (SCV _I (i), threshold) = 0 for │SCV _I (i) │≤ threshold.

Alternatively, other embodiments SCV _I ² (i)> based on the threshold value by filtering the SCV _I (i) and outputted to the │SCV _I (i) │ ^2> threshold value F (SCV _I of the filter 380 ( i), threshold) = │SCV _i (i) │ provides ^2. Otherwise, filter 380 has a │SCV _I (i) │ ² output for ≤ threshold F (SCV _I (i), threshold) = 0.

After the delay of the channel is estimated, the values of FSEG and FSYM are adjusted to reflect the location of the correlation value corresponding to the delay of the channel. FSYM and FSEG are values of symbol counter 315 (SC) and segment counter 318 (SEGCNT) respectively corresponding to the symbol time located at the center of the windowing function. In some embodiments, controller 520 estimates the channel's delay by searching for a PCDE value that minimizes the absolute size of the CCE. In other embodiments, the controller 520 estimates the channel delay by searching for a PCDE value that causes a sign change of the CCE (PCDE). Controller 520 increments PCDE until the sign of CCE (PCDE) changes. Controller 520 then selects the current PCDE value as the CDE value regardless of the absolute size of CCE (PCDE).

Returning to FIG. 5, in normal operation, the equalizer system 200 compensates for interference distortion between channel symbols by performing filtering on the received signal. FFE 210 receives the filtered in-phase baseband signal I _F 76 as an input. Adder 212 sums the outputs of DFE 216 and FFE 210 to produce an equalized data signal 88. The determining device 214 samples the equalized data signal 88 and estimates the received symbol.

Initially, control system 54 optimizes the coefficients of the FFE to remove portions of the associated channel distortion and DFE 216 is disabled. After a certain period of time, the coefficients of the FFE 210 are sufficient to remove portions of channel related distortion and noise, allowing the DFE to operate effectively. Following the initial initiation, the DFE 216 is enabled and the coefficients of the FFE 210 and the DFE 216 use various techniques available in the art to remove the remainder of the channel distortion, such as LMS adaptation. Is optimized. Decision device 214 samples the equalized data signal 88 to obtain a symbol-level representation of the signal received at the output of the decision slicer.

Determination device 214 provides an equalizer feedback symbol output 92 to DFE 216 as input. In some embodiments, for example, decision device 214 is a decision slicer and equalizer feedback symbol output 92 is an output of the decision slicer. In other embodiments of the equalizer 200 where the determining device 214 includes a grating decoder, the equalizer feedback symbol output 92 can be selectively controlled. The equalizer feedback symbol output 92 at initial system startup is an uncorrected symbol output from the determining device 214. In some embodiments that include a decision device having a lattice decoder, equalizer control system 54 may selectively control control equalizer feedback symbol output 92 to provide an output of a lattice decoder or stage of the lattice decoder trace memory. have. In still other embodiments, US patent application Ser. No. 09 / 884,256 and "Transposed Structure for a Decision Feedback Equalizer Combined with a Trellis Decoder", filed with the subject of "Combined Trellis Decoder and Decision Feedback Equalizer" As indicated in the column heading 10 / 407,256, the determining device 214 continuously updates the recovered symbol values used by the DFE so that they are corrected by the grating decoder. In addition, in some embodiments, the equalizer 200 is optimized, such as a real filter or a complex filter, to be compatible with various modulation techniques.

Certain embodiments develop equalizer coefficients in some manner such that there is a predefined or fixed center tap. Instead, the FFE output has a virtual center that does not correspond to a particular filter tap or combination of taps, all of which are dynamically determined. The virtual center position is based on an estimate of the transmission channel delay.

As illustrated in FIG. 19A, with reference to certain items in FIG. 5, one non-limiting example of a possible channel condition (represented by channel impulse response 711) is two ghost signals 710 of the same intensity. And a virtual center 712 of the virtual channel. Equalizer 200 provides control system 54 with a channel delay estimate that is an estimate of the delay of the channel present at the input of FFE 210 over the local time of system 20. The control system 54 uses the channel delay estimate to calculate the offset position for the training symbol sequence (eg segment or frame sync sequence) generated by adding the channel delay measured at the FFE to the desired delay of the equalizer output. . As described herein, the control system 54 compares the received signal with the generated training signal. In some embodiments, the training signal is a segment sync sequence. In other embodiments, the generated training signal is a combination of a field / frame sync sequence or other tuning signals predicted in the received signal. In another embodiment, control system 54 initially generates a segment sync sequence. After the equalizer has at least partially converged, the control system 54 generates a frame / field sequence. The control system 54 optimizes the equalizer coefficients to align the tuned signals of the received signals with the desired temporary location with reference to the generated tuned signals. By way of example, in some embodiments, system 20 aligns the output of equalizer 200 with a particular FFE tap, thereby optimizing the equalizer for a particular channel condition.

As illustrated in FIG. 20A, as a non-limiting example described with continued reference to FIG. 5, one embodiment of the equalizer 200 is an FFE 210 with 1024 FFE taps and a DFE 216 with 512 DFE taps. It includes. Individual taps in the DFE refer to the tap index. The control system 54 aligns the equalizer such that the output of the equalizer 200 is temporarily aligned with the 768 ^th tap of the FFE 210. Moving the virtual center 712 to a later point in time improves the performance of the equalizer for pre-ghost signals. As another non-limiting example shown in FIG. 20B, one embodiment of the same system is an FFE 210 with a 512 ^th tap and equalizer (FFE) so that it works equally well with respect to the pre-coast and post-ghost components of the channel. Control system 54 to align 200.

With continued reference to FIG. 5 and with reference again to FIG. 19B, the FFE 210 is centered relative to the desired virtual center position 712 corresponding to the FFE tap Z _OUT based on the location of the various sync signals in the received signal. Initially optimized for developing the output. Some embodiments of the system 20 are adapted to operate in conjunction with an ATSC system and to train an equalizer based on the expected arrival time SEGMENT_SYNC_OUT of the segment sync signal. Control system 54 generates a segment sync signal as a training sequence when SC = SEGMENT_SYNC_OUT. The received signal is compared with the generated training sequence to develop an error signal used to optimize the coefficients of the equalizer 200. Still other embodiments train the coefficients of the equalizer 200 based on the predicted arrival time FRAME_SYNC_OUT of an ATSC frame or field sink. Thus, as before, control system 54 generates a frame sync signal as a training sequence when SEGCNT = FRAME_SYNC_OUT. The received signal is compared with the generated frame sync training sequence to develop an error signal used to optimize the coefficients of the equalizer 200. Still other embodiments of system 20 use both frame sync and segment sync to optimize the coefficients of the equalizer.

By way of example, given the desired equalizer output location, Z _OUT , control system 54 may determine the relatively predicted timing of the training signal derived from the ATSC segment sink at symbol counter time SEGMENT_SYNC_OUT = (Z _OUT + CDE) mod 832. Position. Similarly, control system 54 calculates the values of symbol counter 316 and segment counter 318 to position the relative timing of training signals derived from ATSC frame / field sync. The control system 54 generates a frame / field sink based training signal when the symbol counter 316 output SC is equal to SEGMENT_SYNC_OUT = (Z _OUT + CDE) mod 832 and the segment counter 318 output SEGCNT is equal to FRAME_SYNC_OUT = FSEG. Be sure to By way of example, one embodiment of a system 20 suitable for ATSC standard broadcasting has a 1024-sample-long correlation buffer 514 and uses field / frame sync and segment sync to optimize the coefficients of the equalizer 200. . Assuming the desired output delay at FFE 210 is Z _OUT = 768 with CDE = 800 and FSEG = 312, control system 54 calculates SEGMENT_SYNC_OUT = 736 and FRAME_SYNC_OUT = 312.

Additionally, in some embodiments of system 20, control system 54 may be configured to adjust the equalizer 200's time over time to create a virtual center that moves in response to changing channel conditions (indicative of the delay of FPE 210). Optimize the filter coefficients. The equalizer constitutes signals or ghost signals that include a virtual channel or several signal transmission paths and is not necessarily aligned with one ghost signal. Thus, the stability of the equalizer 200 is not dependent on a single main ghost signal. This provides an additional advantage in that the addition or deletion of any one multipath contributory does not cause the equalizer to become unstable or otherwise requires re-initialization or re-acquisition of the signal.

As illustrated in FIG. 19B, in some embodiments of equalizer 200, FFE 210 and DFE 216 are overlapped regions where parts of samples in FFE 210 and DFE 216 are temporarily associated. Works on Some alternative embodiments of equalizer 200 include partially spaced FFEs. In any case, samples of FFE 210 and DFE 216 are temporarily related but not necessarily aligned for the same sample interval. In another embodiment of the equalizer 200 as shown in FIG. 19C, some embodiments of the equalizer 200 include an overlapped region where all samples of the DFE 216 are temporarily associated with samples of the FFE 210. do.

As shown in FIG. 19B, some embodiments control the equalizer operation such that the coefficients of the equalizer 200 are initially set to a predetermined value, and the coefficients of the FFE 210 are adapted to remove some portion of the channel distortion. Once the equalizer reaches the desired state of performance, the coefficients of the DFE 216 are freely optimized. As illustrated in FIG. 19C, the coefficients of the DFE 216 begin to grow, which typically results in a reduction in the magnitude of one or more of the coefficients of the FFE 210. In some embodiments, as shown in FIG. 19D, the coefficients of the FFE 210 in overlapped zeros tend to point to a magnitude of zero, so the coefficients of the DFE 216 become large. However, in other embodiments, the coefficients of FFE 210 have some remaining magnitude in the overlapped region. As will be appreciated by those skilled in the art, this operation occurs automatically as a result of the design of the equalizer 200 and allows the control system 54 to balance the noise and ghost performance of the equalizer 200.

Control system 54 further eliminates channel distortion by using various error estimation techniques to optimize the equalizer coefficients, as will be appreciated by those skilled in the art. Illustratively, certain embodiments use Reduced Constellation Algorithm (RCA) error calculation in combination with the LMS algorithm to optimize the equalizer coefficients. The RCA-LMS algorithm detects channel equalization errors and leads to an improved equalizer response over time. Other embodiments use data detection techniques in combination with the LMS algorithm to optimize the equalizer coefficients. Still other embodiments use other blind equalization techniques to optimize the coefficients of the equalizer 200. By way of example, some embodiments use a constant modulus algorithm (CMA) to blindly optimize the equalizer coefficients.

As will be discussed in more detail below, control system 54 initially optimizes (ie, determines) the FFE coefficients. If the FFE 210 of the equalizer 200 is operating, the system enables the DFE 216 and further optimizes the equalizer coefficients, responding to changes in channel conditions and removing all residual channel distortion. All of the DFE coefficients are initially set to zero, and at least a portion of the coefficients of the DFE 216 evolve to non-zero values.

In other embodiments, the FFE 210 uses partially spaced samples, and the system sub-samples or samples the FFE output to provide appropriate temporary aligned data to the determination device 216. Sample rate converting techniques. In some embodiments, a sample rate conversion process occurs at the FFE output. In certain embodiments, the FFE is partially spaced apart and produces "n" output samples for all decision device outputs. The FFE output is randomized to n: 1 to maintain proper sample data alignment. Alternatively, in other embodiments the equalizer down-samples data at the input of the determining device. This allows other elements of system 20 to take advantage of the increased bandwidth associated with partially spaced samples.

In another particular embodiment, the FFE output rate is not related to the determining device symbol rate by a simple integer multiple relationship. As a non-limiting example, the FFE output may provide a number of samples of 3/4 of the determination device symbol ratio. In certain embodiments, selecting the sample closest to the determination device sample time randomly determines the FFE output. In another embodiment, a sample rate converter is used to down-sample the FFE output. As a non-limiting example, the sample rate conversion process may occur at the FFE output, adder input or adder output. Thus, although not shown in FIG. 5, some embodiments of equalizer 200 include partially spaced FFEs, where samples of FFE 210 and DFE 216 are temporarily related but necessarily for the same sample interval. It should be understood that they do not have to be sorted temporarily.

Still other embodiments of an equalizer with temporally related samples at FFE 210 and DFE 216 transfer coefficient values from FFE 210 to DFE 216 to improve initial DFE initiation and convergence. As one example, some systems first enable FFE 210 and optimize the FFE coefficients to reduce channel distortion. After the FFE coefficients are relatively stable or the bit error rate is reduced to the desired threshold level, the system activates the DFE 216 and then optimizes the coefficients of the FFE 210 and the DFE 216 to be combined. do. The system then determines which of the temporarily related samples the FFE 210 and the DFE 216 should use based on the channel delay. The samples to be used by the FFE 210 and the DFE 216 are adjusted as the delay of the channel moves.

Some embodiments of the present invention appropriately change the techniques used to derive equalizer tap coefficients to eliminate channel interference and ghosts. By way of example, certain embodiments optimize the equalizer tap coefficients of FFE 210 and DFE 216 to minimize the least mean square (LMS) between the equalizer output and the determination device output. This technique derives equalizer tap coefficients over time in response to changing channel or system conditions. By way of example, some optimization algorithms initially use RCA techniques to drive the LMS optimization algorithm, and then switch to decision-oriented techniques or a combination of different optimization strategies depending on channel conditions prior to applying the decision-oriented equalizer coefficient optimization process. do.

Some embodiments of the equalizer 200 improve the stability of the equalizer by limiting the magnitude of certain DFE coefficients. With continued reference to FIG. 19C, control system 54 (FIG. 5) limits the sizes of the DFE coefficients as a function of the tap index of the tap with which the coefficient is associated. In some embodiments, the range of values of DFE coefficients is divided into regions. Taps with smaller tap indices (ie, closest to Z _OUT ) have a first pre-set range of size constraints. The second group of DFE taps has a second pre-set range of acceptable sizes. Finally, the DFE taps with the largest tap indices (ie, the stop from Z _OUT ) have a third pre-set range of size constraints. As a first non-limiting example, assuming that the coefficients have a maximum size of 1, the taps closest to Z _OUT have a maximum coefficient size of .85. The second group of DFE taps located farther from Z _OUT has a maximum coefficient magnitude of .95. Finally, the DFE taps farthest from Z _OUT have a maximum coefficient magnitude of one.

In some embodiments, the maximum coefficient magnitude of the taps closest to Z _OUT can range from .75 to .85. In other embodiments, the maximum coefficient magnitude of the second group taps disposed between the furthest and closest taps with respect to Z _OUT has a range between .925 and .95. Still other embodiments, the DFE taps farthest from Z _OUT have a maximum coefficient magnitude in the range of .95-1.

It should be understood that the DFE taps can be split into fewer or more groups and the relative maximum coefficient sizes depend on the number of DFE taps and the indexes of those taps (place to Z _OUT ). By way of example, in some embodiments only a portion of the DFE taps is limited. In the above embodiments, limiting the size of the DFE coefficients with smaller tap indices reduces the effect of decision errors made by the grating decoder.

Other embodiments of equalizer 200 apply a drain function to the FFE and DFE coefficients. In some embodiments, the drain function is a constant drain and reduces the magnitude of the coefficient by a controlled amount with respect to the regular basis. In other embodiments, the drain function is non-linear and tends to remove smaller coefficient values faster than large coefficient values. In another embodiment, the drain function reduces the coefficient magnitudes in part with respect to the proportional and regular regular basis.

Some embodiments of equalizer 200 apply a drain function, for example, where the magnitude of the coefficients of DFE taps with a higher tap index is at a faster rate (or alternatively) than the magnitude of the coefficients of taps with smaller tap indices. The amount controlled according to the tap index is changed so as to be reduced by a larger amount). The controlled amount change may be a function of the tab index or the tabs may be grouped by ranges of tab indices and a separate controlled amount may be applied to each group. In some other embodiments of the equalizer, the operation of the equalizer such that the equalizer is reduced by a smaller controlled amount if it is starting and then by a larger controlled amount if the equalizer is operating in steady state mode. The amount controlled may vary depending on the state. Similarly, the amount controlled may vary depending on the performance of the equalizer. In this case, a smaller controlled amount can be used to reduce the magnitudes of the coefficients, for example when the SNR is relatively small, and a larger controlled amount can be used when the SNR becomes high. In still other embodiments, taps farther from the virtual center of the FFE are drained at a faster rate than FFE taps closer to the virtual center.

As a non-limiting example, and referring to FIGS. 5, 6 and 21, some embodiments of system 20 are techniques employed by system 740, where the operation is an overlapped equalizer structure without reference or center taps. Or a technique such as that shown in FIG. 21 for developing the equalizer. At 742, ie “Initialization,” the control system 54 initializes the various parts of the system 20 as will be appreciated by those skilled in the art. Control system 54 then transitions the system from 740 to 744.

At 744, "CDE Estimate," system 20 estimates the delay associated with the transport channel and determines the values of SEGMENT_SYNC_OUT and FRAME_SYNC_OUT. System 20 fixes the delay offset of the training sequence for its system clock, symbol counter 316 and sequence counter 318. As a non-limiting example, in some embodiments system 20 uses a segment sync technique to determine CDE. In other embodiments, system 20 uses a frame sync technique to determine the CDE. In another embodiment, system 20 uses a combination of segment sync and frame sync techniques to determine the CDE. Control system 54 then transitions the system from 740 to 746.

At 746, ie “FFE Enable,” control system 54 enables the FFE portion of the equalizer of system 20. The DFE portion of the system 20 equalizer is disabled. Control system 54 dynamically develops FFE coefficients using an optimal error signal generated based on the desired or predicted arrival of a tuning signal embedded in the transmission. By way of example, in some embodiments of system 20 including equalizer 200A, control system 54 generates tuning signals at a desired or predicted temporary location based on CDEU 230 estimate of CDE. (Or cause it to be created). By way of example, control system 54 generates a segment sync training signal to optimize equalizer 20 when SC = SEGMENT_SYNC_OUT.

The control system 54 then generates an optimal error signal by subtracting the equalized data signal 88 from the generated tuning signals generated by the control system 54. Control system 54 selects the portion of the optimum error based on the windowing technique to optimize the coefficients of the equalizer. The selected window depends on the operating state of the system 20. For example, in some embodiments control system 54 uses a segment sync signal to optimize FFE coefficients at initial system initiation. In other embodiments, control system 54 uses the field / frame sync signal to optimize FFE coefficients at initial system initiation. In another embodiment, control system 54 first uses the segment sync signal to optimize the FFE coefficients and then transitions to use the field / frame sync signal in combination with the segment sync signal.

As discussed below, once reliable tuning is obtained, control system 54 optimizes FFE coefficients based on desired or predicted temporary locations of tuning signals as determined by the CDEU estimate of the CDE. The control system 54 generates tuning signals in a temporary location that is desired or predicted based on the CDEU of the CDE. The control system 54 then generates an optimum error signal by subtracting the signal received from the generated tuning signal. Control system 54 then uses the optimal error signal to optimize the coefficients of the FFE based on the optimal error signal.

In some embodiments, control system 54 generates an optimal difference signal by subtracting the signal received from the receiver generated segment sync signal. Some embodiments generate an optimal difference signal by subtracting the signal received from the receiver generated frame sync signal. Still other embodiments optimize the FFE coefficients based on the expected arrival of the segment sync signal. After reaching a certain level of performance, such as detecting the presence of a reliable frame sync signal, the control system 54 generates a difference signal that is generated using both the segment sync signal and the field / frame sync signal.

In some embodiments, control system 54 transitions system 740 operation to 742 if reliable tuning signals are not detected after some time period. Similarly, in some embodiments control system 54 transitions the system from 740 to 742 if it detects a loss of the field / frame sync signal. Otherwise, control system 54 transitions the system from 740 to 748 when the equalizer output SNR performance (based on the SNR of the received tuned signals) is greater than the predetermined DFE_ENB threshold. Hysteresis may be provided by selecting a DFE_ENB threshold> RETURN_FFE threshold.

At 748, ie, "DFE Enabled," control system 54 enables DFE portion 216 of equalizer 200 to act as an infinite impulse response (IIR) filter. Control system 54 uses the optimal error signal generated based on the segment sync signal and the field / frame sync signal to optimize the FFE and DFE coefficients of the equalizer. Optimal error signal generation is similar to that used in " FFE Enabled " Data input to the DFE is quantized to a level according to the precision possible through the DFE delay path.

Control system 54 transitions the system from 740 to 742 if it detects a loss of the field / frame sync signal. Otherwise, control system 54 transitions the system from 740 to 750 when the equalizer output SNR performance is greater than the predetermined RCA_ENB threshold if the signal to noise performance is based on the SNR of the received tuned signals. However, in some embodiments control system 54 transitions the system from 740 to 746 when the equalizer output SNR performance falls below the RETURN_FFE threshold. The hysteresis can be specified by selecting RCA_ENB threshold> RETURN_DFE threshold> DFE_ENB threshold. Some embodiments use other techniques known in the art such as averaging filter and continuity counters to improve the performance of the system.

At 750, or "RCA", the FFE and DFE coefficients are updated using an optimal error signal based on the reduced constellation algorithm (RCA). The RCA assumes that the input data is 2-leveled, so the locally generated reference signal is a binary slice of incoming data. By way of example, in some embodiments including equalizer 200A, control system 54 generates an optimal error signal by subtracting the equalized data signal 88 from the optimal symbol decision 94 of decision device 214. Let's do it. Control system 54 configures an optimal symbol decision 94 to provide a binary slice of the equalized data signal 88. The binary slice maps an 8-VSB signal with levels normalized at -7, -5, -3, -1, +1, +3, +5, +7 to -5.25 and +5.25. In some embodiments, slicing is performed with a two level basis. In another embodiment, slicing is performed with a four level basis. Still other embodiments, such as CMA, use kurtosis of signal constellations. Finally, other embodiments use other reduced constellation techniques known in the art. The optimum error signal is used to update both FFE and DFE coefficients. As before, the data to the DFE is quantized slice data (8- or 16-level decision slicer) and the DFE acts as an IIR filter.

In some embodiments, control system 54 optimizes FFE and DFE coefficients using only the RCA algorithm of the received data. In another embodiment, the control system 54 compares the received tuning signals with the signals generated by the control system 54. In another embodiment, the control system 54 weights the effects of the RCA and tuning signal-based optimal techniques depending on the performance or operational state of the system.

If control system 54 detects a loss of the field / frame sync signal, control system 54 transitions the system from 740 to 742. Otherwise, control system 54 transitions the system from 740 to 752 when the equalizer output SNR performance is greater than the DATA_DIRECTED threshold. In some embodiments, the technique of calculating the SNR includes examining both the received tuned signal and the data signals. If system SNR performance falls below the RETURN_DFE threshold instead of improving, control system 54 transitions the system from 740 to 748. The hysteresis may be specified by selecting DATA_DIRECTED threshold> RCA_ENB threshold> RETURN_RCA threshold.

At 752, ie “Trellis Decoder Enabled,” the FFE and DFE taps are updated using an optimized error signal generated based on the grid decoder output. Similar to the foregoing, control system 54 constructs an optimal symbol decision 94 to provide an output from the grating decoder. Control system 54 uses a decision oriented LMS technique to optimize the equalizer coefficients. In some embodiments, the optimal error signal is determined by looking at the output of the lattice decoding of the 8-VSB signal. In another embodiment, the optimal error signal is determined by examining the output of one of the grating decoder stages. Similar to the above, the data input to the DFE is slice data quantized to a predetermined number of levels, and the DFE acts as an IIR filter.

As described above, control system 54 transitions the system from 740 to 742 if it detects a loss of the field / frame sync signal. Otherwise, control system 54 transitions the system from 740 to 754 when the equalizer output SNR performance is greater than the DFE_UPDATE threshold. If the system falls below the RETURN_RCA threshold instead of improving the SNR performance of the system, the control system transitions the system from 740 to 752. The hysteresis may be specified by selecting DFE_UPDATE threshold> RETURN_RCA threshold> RCA_ENB threshold.

At 754, "DFE Decision Update", system controller 54 updates the FFE and DFE coefficients using an optimal error signal based on the grid decoder output. The controller 54 also configures the determining device of the equalizer to provide grid-decoded data into the DFE 216. By way of example, in some embodiments of system 20 including equalizer 200A, control system 54 selectively selects equalizer feedback signal 92 to provide grid decoder correction data to DFE 216. To control. In other embodiments, control system 54 selectively controls equalizer feedback signal 92 to update DFE 216 with corrected data from various stages of the grating decoder. Thus, DFE 216 initially receives the decision slicer output of decision device 214. The grating decoder portion of decision device 214 then updates the DFE reception decisions with the correction enabled. Another embodiment is entitled to U.S. Patent Application No. 10 / 407,610 filed with the title "Transposed Structure for a Decision Feedback Equalizer Combined with a Trellis Decoder" and "Combined Trellis Decoder and Decision Feedback Equalizer". It is operated by providing grid decoder update values from the intermediate stages of the grid decoder to the stages of the DFE as described in the filed US patent application Ser. No. 09 / 884,256.

As described above, control system 54 transitions the system from 740 to 742 if it detects a loss of the field / frame sync signal. Otherwise, control system 54 transitions from 740 to 752 if the equalizer output SNR performance falls below the RETURN_TRELLIS_ENABLE threshold.

Some embodiments of system 20 use the average magnitude of the optimal error signal instead of SNR. Other embodiments of the system 20 use the bit error rate detected by the grating decoder. Still other embodiments of system 20 use the bit error rate of FEC symbol determination 80. Another embodiment, similar to US Pat. No. 6,829,297, modifies the optimal process according to performance metrics developed by the grating decoder. It should be understood that system 740 may be optimized for systems without grid decoding by omitting certain steps. Likewise, the transition point can be adjusted for optimal performance depending on the operating conditions and the application. In addition to the hysteresis provided by the transition threshold levels, some embodiments of the system 20 include a confidence counter, average filter, or similar transition smoothing technique to improve stability and provide instantaneous performance in system performance. Cancel the shifts.

It should be understood that in some embodiments system 740 may be simplified by eliminating intermediate stages between 746 and 754. By way of example, embodiments that do not have a grating decoder or do not include the grating decoder's ability to update a sample in a DFE as one feature do not require stage 752 or 754.

Another embodiment of equalizer 46 illustrated as equalizer 200A in FIG. 22 is equalizer 200 except the addition of phase tracker 240 between the output of FFE 210 and the first input of adder 212. ) Is similar in form and function. As shown in FIG. 22, phase tracker 240 receives input and feedback signals 246 from FFE 210 and provides an output to adder 212. As will be described in detail below, the phase tracker 240 receives various feedback signals 246. Feedback signals 246 may include one or more corresponding signals generated by or within system 20. By way of example, in some embodiments of system 20, feedback signals 246 comprise an equalized data signal 88. In another embodiment, the feedback signal 246 includes an equalized data signal 88 and tuned symbol determination 86. In yet another embodiment, the feedback signals 246 include the intermediate equalizer signal 90, the equalized data 88 and the equalizer feedback signal 92. As discussed below, phase tracker 240 uses feedback signals to develop a phase correction vector that is used to correct the output of FFE 210.

One embodiment of phase tracker 240 of equalizer 200A receives phase tracker 800A as illustrated in FIG. 23, receiving signal 242 and feedback signals 246A and 246B from FFE 210. to be. The feedback signal 246A is the sine (ie sinθ) of the estimated phase error present in the received signal. Similarly, feedback signal 246B is the cosine (ie cos θ) of the estimated phase error present in the received signal. The output of phase tracker 800A is the input of adder 212 of equalizer 200A.

Phase tracker 800A includes delay line 810, phase-shift filter 812, rotator 814, integrator 816, subtractor 818, and multipliers 822, 824, 826. The phase tracker 800A generates the phase tracker determination error signal E _PTD 248 by taking the difference between the output of the determination device 214 and the corresponding equalized data signal 88. As illustrated in FIG. 23, one or more embodiments include a subtractor 830 and a delay element 832. The input of delay element 832 receives an equalized data signal 88 that is the output of adder 212. Each of the negative and positive input of subtractor 830 receives a delayed equalized data signal 88 from delay element 832 and an output of decision device 214. The output of the subtractor 830 is a phase tracker determination error signal E _PTD 248. Thus, phase tracker decision error signal (E _PTD ) 248 is developed by taking the difference between the output of decision device 214 and the appropriately delayed equalized data signal 88. As such, phase tracker determination error signal E _PTD 248 is the error between the determination output and the input that generated the output. Delay element 832 provides a sufficient signal propagation delay to enable accurate temporal alignment of inputs into subtractor 830 and varies with the nature of the output of decision device 214.

By way of example, some embodiments develop a phase tracker decision error signal (E _PTD ) 248 by subtracting an appropriately delayed equalization data signal 88 from the decision slicer output of decision device 214. Still other embodiments develop phase tracker decision error signal (E _PTD ) 248 by subtracting the appropriately delayed equalized data signal 88 from the lattice decoder output of decision device 214. Still other embodiments develop phase tracker decision error signal (E _PTD ) 248 by subtracting the appropriately delayed equalized data signal 88 from the intermediate output stage of the grating decoder of decision device 214. Certain embodiments develop the phase tracker decision error signal (E _PTD ) 248 by subtracting the appropriately equalized data signal 88 from the optimal symbol decision 94 of the decision device 214. In still other specific embodiments, control system 52 selects the output of decision device 214 used to generate phase tracker decision error signal 248 in accordance with the state of the system, equalizer and / or channel conditions.

Phase tracker 800A develops a phase error feedback signal, as will be appreciated by those skilled in the art. Delay line 810 and phase-shift filter 812 receive input signal 242, which is the output of FFE 210. Delay line 810 provides an output to the in-phase signal input of rotator 814 and multiplier 826. Multiplier 826 also receives feedback signal 246A, i. Phase-shift filter 812 provides an output to both the quarter-cycle signal input of rotator 814 and multiplier 824. Multiplier 824 also receives feedback signal 246B, that is, cosθ.

In some embodiments, phase-shift filter 812 includes a 90 degree phase-shift filter or a quarter period filter. In another embodiment, phase-shift filter 812 includes a Hilbert filter or truncated Hilbert filter. In another embodiment, phase-shift filter 812 has several filter tap coefficients optimized to minimize the mean square error (MMSE) of the filter output for a 90 degree phase-shifted channel and a particular receiver acquisition threshold. FIR filter of desired length. By way of example, some embodiments of phase-shift filter 812 are a FIR filter having MMSE-optimized filter tap coefficients and a length of 31 samples for a VSB or offset-QAM receiver acquisition SNR threshold of 15.1 dB. Other embodiments of the phase-shift filter 812 include filter tap values optimized for a receiver acquisition SNR threshold of 15.1 dB. One or more embodiments of the present invention include phase-shift filter 812 coefficients optimized for an acquisition SNR threshold of 15 dB.

Negative and positive inputs of subtractor 818 receive the outputs of multiplier 826 and multiplier 824, respectively. Subtractor 818 provides a phase error estimate to multiplier 822 that receives phase tracker determination error signal E _PTD 248 from subtractor 830. Integrator 816 receives the output of multiplier 822 and provides a phase correction signal θ at the input of rotator 814. Finally, rotator 814 provides a phase-corrected output to adder 212 of equalizer 200A.

In some embodiments, phase tracker 800A receives the output of FFE 210 as a real or in-phase signal I _FFE . The output of the FFE 210 passes through a phase-shift filter 812 to produce a corresponding imaginary or quarter period signal Q _FFE .

The output of FFE 210 also passes through delay line 810 such that I _FFE and Q _FFE can be temporarily aligned and correspond to the same FFE 210 output. I _FFE and Q _FFE may be considered to be a vector pair having a predetermined size and phase. However, some embodiments of FFE 210 receiving I _F and G _F will output both real and phase-quadrant components without the need for delay line 810 and phase-shift filter 812. You have to understand. Phase tracker 800A rotates I _FFE and Q _FFE to minimize the phase error present at the output of equalizer 200A. Rotator 814 is the input to integrator 816 is E _PTD. (Q _FFE cosθ-I _FFE sinθ) and E _PTD is a phase tracker determination error signal temporarily associated with feedback signals 246A and 246B. The phase correction vector e ^{j θ} based on the phase correction signal θ provided by the integrator 816 is multiplied by I _FEE and Q _FFE . Thus, the input to the integrator is a decision directed phase error signal associated with the particular output of the FFE 210. As such, the output of the integrator 816 is the phase correction signal θ, where at sample index i, θ _i = θ _i-1 + μ · E _PTD · (Q _FFE cosθ _i-1 -I _FFE sinθ _i-1 And μ are some update step size parameters. In some embodiments, it should be understood that the range of values for θ is limited.

The rotator 814 rotates the vector pairs I _FFE and Q _FFE using the phase correction signal θ. In some embodiments, rotator 814 includes a complex multiplier, a sine look-up table, and a cosine look-up table. Rotator 814 converts the received phase correction signal θ into a phase-correction vector e ^{j θ} , which is used to rotate I _FFE and Q _FFE . Rotator 814 generates a phase corrected in-phase or real signal I _PT . In some embodiments, rotator 814 also generates a quadrant or imaginary signal Q _PT (not shown). As will be appreciated by those skilled in the art, these descriptions are illustrative only, and in some embodiments other delay elements not shown in FIG. 23 will be included to maintain accurate temporary relationships between the various signals.

The phase error feedback signal is generated by estimating the phase error present in the stage of equalizer 200A (see FIG. 22). Some embodiments of phase tracker 800A estimate the phase error present in one of the equalizer output signals depending on the mode of operation of the equalizer. In some embodiments, a phase error estimate is derived from the output of the FFE 210. In other embodiments, a phase error estimate is derived from the output of adder 212 of equalizer 200A. In another embodiment, a phase error estimate is derived from the output of phase tracker 800A. In another embodiment, the signal used to derive the phase error estimate by the control system 54 according to the performance of the equalizer is selected.

Another embodiment of phase tracker 240 as 800B is shown in FIG. Phase tracker 800B is operatively similar to phase tracker 800A except that signals I _FFE and Q _FFE are first multiplied by phase tracker determination error signal 248. As such, phase tracker 800B includes a multiplier 822 at different locations and further includes an additional multipler 828.

Multiplier 826 receives as input an IFFE and phase tracker error signal (E _PTD ) 248. Multiplier 822 receives as input the feedback signal 246A (sin [theta]) and the output of multiplier 826. Multiplier 828 receives QFFE and phase tracker error signal (E _PTD ) 248 as input. Multiplier 824 receives feedback signal 246B (cosθ) and the output of multiplier 828 as input. Negative and positive inputs of subtractor 818 receive the outputs of multipliers 822 and 824, respectively, the difference being provided to integrator 816 as output. As in phase tracker 800A, integrator 816 receives the output of subtractor 818 and provides a phase correction signal θ at the input of rotator 814. Finally, rotator 814 provides a phase-corrected output to adder 212 of equalizer 200A.

The phase correction signal θ of the phase tracker 800B with respect to the sample index i is θ _i = θ _i-1 + μE _PTD (Q _FFE cosθ _i-1 -I _FFE sinθ _i-1 ), where the feedback signal ( 246A, ie sinθ and feedback signal 246B, cosθ, is related to the phase tracker determination error signal E _PTD 248. As before, the rotator 814 multiplies the incoming data vectors I _FFE and Q _FFE by the phase correction vector e ^{j θ} , thereby correcting the phase of the output of the FFE 210. As will be appreciated by those skilled in the art, these descriptions are illustrative only, and other delay elements not shown in FIG. 24 are used in various embodiments to maintain accurate temporal relationships between the various signals.

Another embodiment of phase tracker 240 in equalizer 200A is a phase tracker 800C and offset QAM modulation system suitable for VSB. As illustrated in FIG. 25, phase tracker 800C receives input signal 242 and phase tracker determination error signal E _PTD 248 from FFE 210. The output of phase tracker 800C is connected to the input of adder 212 of equalizer 200A. As shown in FIG. 25, phase tracker 800C employs techniques similar to those used in phase tracker 800A to generate phase tracker determination error signal E _PTD 248.

Similar to the phase tracker 800A, the phase tracker 800C also includes a delay line 810, a phase-shift filter 812, a rotator 814, an integrator 816, and a multiplier 822. Inputs of delay line 810 and phase-shift filter 812 receive an input signal 242 from FFE 210 and have IFFE and QFFE as outputs, respectively. The output of delay line 810 provides an I _FFE , a delayed version of input signal 242, to the in-phase signal input of rotator 814. The output of phase-shift filter 812 provides a Q _FFE to the quadrature signal input of multiplier 828 and rotator 814. As a result, QFFE is used as the phase error signal. Multiplier 822 also receives phase tracker determination error signal (E _PTD ) 248 and provides an enemy to integrator 816 as input. Integrator 816 provides a phase correction signal θ to the input of rotator 814.

Similar to the phase tracker described above, passing through the output of the FFE 210 through the delay line 810 and the phase-shift filter 812 produces signals I _FFE and Q _FFE . Multiplier 822 multiplies QFFE with phase tracker decision error signal 248 to produce a decision directed phase error estimate, which is integrated by integrator 816 and at phase index i, the phase correction signal, θ _i = θ _ij + μ · (Q _FFE ) · (E _PTD ) is formed. Rotator 814 receives ^θ and develops phase correction vector e ^{j θ} . Rotator 814 multiplies the vector pairs I _FFE and Q _FFE by the phase correction vector e ^{j θ} to produce a phase correction real or in-phase output. As will be appreciated by those skilled in the art, these examples are merely examples. In some other embodiments, other delay elements (not shown in FIG. 25) are used to maintain correction temporal relationships between the various signals depending on the latency in phase tracker determination error signal development. By way of example, the phase error estimate and phase tracker determination error signal 248 correspond to the output of the FFE 210. However, since the output of the multiplier 822 is integrated to obtain an average phase correction signal, in some embodiments the phase correction signal e ^{j θ} applied to I _FFE (n) and Q _FFE (n) is equal to I _FFE (n ) And may not include contributions from Q _FFE (n); It should be understood that I _FFE (n) and Q _FFE (n) are n ^th I _FFE and Q _FFE samples.

Another embodiment of phase tracker 240 in equalizer 200A is phase tracker 800D, which is also suitable for VSB and offset QAM modulation systems. As illustrated in FIG. 26, phase tracker 800D receives an input signal 242 and a phase tracker determination error signal (E _PTD ) 248 from FFE 210 and adder 212 of equalizer 200A. To provide output. As shown in FIG. 26, the phase tracker 800D generates a phase tracker determination error signal (E _PTD ) 248 using techniques similar to those described above with respect to the phase tracker 800A. The phase tracker determination error signal E _PTD 248 shown as part of the phase tracker 800D is similar in form and function to that used in the phase tracker 800A.

Similar to the phase tracker 800C, the phase tracker 800D includes a delay line 810, a phase-shift filter 812, a rotator 814, and a multiplier 822. Like the phasetracker described above, the inputs of delay line 810 and phase-shift filter 812 receive input signals 242 from FFE 210 and generate I _FFE and Q _FFE at their respective outputs. . Rotator 814 receives I _FFE and Q _FFE at its in-phase and quarter period inputs, respectively. Rotator 814 generates phase-corrected in-phase or real signal I _PT and quadrature or imaginary signal Q _PT . The adder 212 of equalizer 200A receives the real signal I _PT as input. Multiplier 822 receives quadrant Q _PT and phase tracker determination error signal (EPTD) 248 of rotator 814. Multiplier 822 provides the integrator 816 with the product of Q _PT and E _PTD . The output of the multiplier 822 is integrated to generate a phase correction signal θ as an output for the correction vector input of the rotator 814.

Phase tracker 800D is an F _PTD as a phase error estimate at the output of rotator 814. And the enemy of Q _PT . Multiplier 822 multiplies QPT and phase tracker decision error signal 248 to produce a decision directed phase error estimate, which is a phase correction signal θ _i = θ _ij + μ · (Q _PT ) · (E _PTD ) Is integrated by the integrator 816 to form a. Rotator 814 receives ^θ and develops phase correction vector e ^{j θ} . In some embodiments, the maximum phase correction is limited to the desired range. As a non-limiting example, in some embodiments the maximum phase correction signal limits the phase correction provided by rotator 814 to ± 45 degrees. The rotator 814 then multiplies the vector pairs I _FFE and Q _FFE by the phase correction vector e ^{j θ} to produce a phase-corrected real or in-phase output I _PT . As will be appreciated by those skilled in the art, these descriptions are merely examples. The interrelationship between the phase error estimate Q _PT and the phase tracker determination error signal E _PTD is such that the output of the multiplier 822 becomes a crystal directed phase error estimate corresponding to the output from the FFE 210 (the input signal 242). In some embodiments, other delay elements not shown in FIG. 26 are used.

Still other embodiments of phase tracker 240 of equalizer 200A are phase trackers 800E suitable for VSB and offset QAM modulation systems. As illustrated in FIG. 27, phase tracker 800E receives input signal 242 from FFE 210 and outputs phase-corrected real or in-phase output I _PT to adder 212 of equalizer 200A. to provide. Similar to the embodiments described above, as shown in FIG. 27, the phase tracker 800E uses phase tracker determination error signal E _PTD using techniques and devices similar to those described above with respect to phase tracker 800A. Produces (248). The phase tracker determination error signal (E _PTD ) 248 shown as part of the phase tracker 800E is similar in form and function to that used in the phase tracker 800A.

Like the phase tracker 800D, the phase tracker 800E also includes a delay line 810, a phase-shift filter 812, a rotator 814 and a multiplier 822. Inputs of delay line 810 and phase-shift filter 812 receive input signal 242 from FFE 210. Delay line 810 and phase-shift filter 812 then provide I _FFE and Q _FFE to the in-phase and quarter period inputs of the rotator, respectively. Rotator 814 receives the phase correction signal θ from integrator 816 and provides phase-corrected in-phase or real signal I _PT to adder 212 of equalizer 200A.

In addition, the phase tracker 800E further includes a phase-shift filter 840 having similar functions and characteristics with respect to the phase-shift filter 812. In certain embodiments as shown in FIG. 27, phase-shift filter 840 receives an equalized data signal 88. In certain other embodiments not shown, the input of phase-shift filter 840 receives the output of decision device 214. By way of example, in some embodiments, phase-shift filter 840 receives the output of a decision slicer in decision device 214. In other embodiments, phase-shift filter 840 receives the output of the lattice decoder of decision device 214. In still other embodiments, phase-shift filter 840 receives an output from one of the stages of the grating decoder of decision device 214. Alternatively, in some embodiments of 800E (not shown), phase shift filter 840 receives I _PT instead of equalized data signal 88.

Inputs of the multiplier 822 receive the outputs of the phase-shift filter 840 and the phase tracker determination error signal E _PTD 248. As shown in FIG. 27, phase-shift filter 840 receives an equalized data signal 88 and provides an imaginary or quadrature signal Q _EQ as an output to multiplier 822. Q _EQ is a phase error estimate for the equalizer output provided to phase-shift filter 840. Multiplier 822 generates a decision directed phase error estimate by multiplying the Q _EQ and phase tracker decision error signal (E _PTD ) 248. The integrator 816 integrates the output of the multiplier 822 to form the phase correction signal θ _i = θ _ij + μ · (Q _EQ ) · (E _PTD ). Rotator 814 receives the phase correction signal θ and develops the phase correction vector e ^{j θ} . Rotator 814 then multiplies the vector pair I _FFE and Q _FFE by the phase correction vector e ^{j θ} to produce a phase-corrected real or in-phase output I _FFE . As will be appreciated by those skilled in the art, these descriptions are merely examples. In order to maintain a temporary relationship between the phase error estimate Q _EQ and the E _PTD such that the output of the multiplier 822 is a decision directed phase error estimate corresponding to the recovered symbol, other delay elements not shown in FIG. 27 are used. .

Additional embodiments of phase tracker 240 of equalizer 200A include a first delay line 810, phase-shift filter 812, rotator 814 and integrator 816, illustrated in FIG. 28. Phase tracker 800F as shown. Phase tracker 800F receives input signal 242 from FFE 210 at delay line 810 and phase-shift filter 812. Delay line 810 and phase-shift filter 812 provide I _FFE and Q _FFE to the in-phase and quarter period inputs of rotator 814, respectively.

Phase tracker 800F is configured to reduce subtractor 818, multiplier 822, multiplier 824, delay line 836, delay line 838, phase-shift filter 840, and delay line 842. It includes more. Delay lines 836 and 838 receive I _FFE and Q _FFE , respectively. Delay line 836 provides a delayed version of the Q _FFE at one input of multiplier 822. As shown in FIG. 28, in some embodiments delay line 842 and phase-shift filter 840 receive output from decision device 214. In some embodiments, the crystal slicer of the crystal device 214 provides an output to the delay line 842 and the phase-shift filter 840. In other embodiments, the grating decoder of decision device 214 provides an output to delay line 842 and phase-shift filter 840. In another embodiment, one of the stages of the grating decoder of decision device 214 provides an output to delay line 842 and phase-shift filter 840. Still other embodiments alternatively provide an equalized data signal 88 at the input of decision device 214 as input to delay line 842 and phase-shift filter 840. In addition, other specific embodiments of phase tracker 800F select inputs for phase-shift filter 840 and delay line 842 according to the operating state of equalizer 200a or system 20.

Phase-shift filter 840 produces a quarter-cycle output Q _DD . Delay line 842 provides a delayed version of the in-phase input as output I _DD . It should be understood that delay line 842 compensates for the delay introduced by phase-shift filter 840 and temporarily aligns Q _DD and I _DD .

It should also be understood that delay lines 836 and 838 compensate for the delay introduced by signal processing in equalizer 200A and temporarily align I _DD and Q _DD with delayed versions of I _FFE and Q _FFE . Accordingly, multiplier 822 receives a delayed version of I _FFE and Q _DD from phase-shift filter 840 and delay line 836, respectively. Accordingly, multiplier 822 receives the delayed version of I _FFE and Q _DD from phase-shift filter 840 and delay line 836, respectively. Similarly, multiplier 824 receives delayed versions of Q _FFE and I _DD from delay lines 842 and 838, respectively. The delay provided by delay lines 836 and 838 aligns the inputs with multipliers 822 and 824 so that they correspond to the same received symbol.

Negative and positive inputs of subtractor 818 receive the outputs of multiplier 822 and multiplier 824, respectively, and subtractor 818 provides a crystal directed phase error output to integrator 816. do. Similar to previous phase tracker embodiments, integrator 816 provides rotator 814 with phase correction signal θ, where θ _i = θ _ij + μ · [(Q _EFE ) · (I _DD ) − (I _FFE · Q _DD )].

Rotator 814 receives ^θ and develops phase correction vector e ^{j θ} . Rotator 814 multiplies the vector pairs I _FFE and Q _FFE by the phase correction vector e ^{j θ} to produce a phase-corrected real or in-phase output I _PT . As will be appreciated by those skilled in the art, these descriptions are merely examples. In order to maintain a temporary relationship between I _FFE , Q _FFE , I _DD and Q _DD in multipliers 822 and 824 such that the output of subtractor 818 is a decision directed phase error estimate corresponding to the recovered symbol. In some embodiments other delay elements not used in FIG. 28 are used.

Phase tracker 800 and specific embodiments 800A- 800F represent FFE 210 receiving only I _F , but some embodiments of phase tracker 800 receive I _F and Q _F and FFE ( It is to be appreciated that the embodiments are optimized for embodiments of FFE 210 that provide I _FFE and Q _FFE as direct output from 210 to rotator 814. Likewise, in some embodiments, the maximum phase correction range is limited. As a non-limiting example, some embodiments limit the maximum phase correction provided by rotator 814 to ± 45 degrees. In still other embodiments, the value of θ is limited to control the range of the phase correction signal. In addition, although described with respect to ATSC, it should be understood that the techniques and devices included in embodiments of phase tracker 800 may be optimized for other modulation techniques and data constellations.

Similarly, it should be understood that some embodiments of phase tracker 800 are intended to operate with embodiments of FFE 210 having partially spaced samples. Finally, some embodiments of phase tracker 800 are adapted to receive both real and quarter period input signals as input from FFE 210; Thus, it should be understood that the _FFE 210 provides the I _FFE and Q _FFE directly without requiring the delay line 810 and the phase shifter 812.

Another embodiment of the system 20 of FIG. 3 is the system 900 shown in FIG. 29. According to one embodiment, the system 900 employs a technique for developing a carrier tracking feedback loop and a timing tuned feedback loop. System 900 includes tuner 910, digital demodulator 920, equalizer 930, decision directed control (DDC) 940, non-coherent control (950) and control system (954). Each of which is similar in form and function to elements 40, 42, 46, 52, 50, and 54 of system 20 (FIG. 3). Similar to system 20, system 900 develops the signal segment sink 96, field / frame sink 98, SNR 100, VCXO lock 102, and NCO lock 104 described above. do. Like the control system 54 of the system 20, the control system 954 is responsible for the segment sink 96, the field / frame sink 98, the SNR 100, the VCXO lock 102 and the NCO lock 104. Receive. In addition, it should be understood that various embodiments of equalizer 930 include the above described embodiments of equalizers 48, 200, and 200A. Similarly, some embodiments of equalizer 930 include the above described embodiments of phase trackers 800, 800A, 800B, 800C, 800D, 800E, and 800F.

Also, signals 64A, 66A, 72A, and 74A are similar in form and function to signals 64, 66, 72, and 74 of FIG. For simplicity, Nyquist filtering of the digital modulator output is not illustrated in the system 900; It is to be understood that this is for convenience only and is not intended to be limiting. Those skilled in the art will appreciate that Nyquist filtering may appear in any of various forms of various embodiments of the present system.

As shown in FIG. 29, system 900 receives near-baseband signal 60A from a front end receiver (eg, receiver 30 of FIG. 3) and digitizes near-base to digital modulator 920. Provides a band signal 62A. The output of the digital modulator 920 provides the baseband signal 920A as an input to the equalizer 930. Equalizer 930 provides outputs 930A, 930B, 930C, and 930D to decision-oriented control unit 940. DDC 940 includes a subtractor 942, a carrier access post filter 944, a timing offset post filter 946, a multiplier 948, and a multiplier 950. DDC 940 provides a decision directed tuning feedback signal 66A to tuner 910 and further provides a decision directed carrier tracking feedback signal 74A to digital demodulator 920.

In some embodiments, equalizer 930 is an overlapped equalizer. In other embodiments, equalizer 930 does not have a predefined or fixed center tap. Certain embodiments of equalizer 930 also include a phase tracker. Thus, as described in more detail below, in some embodiments outputs 930A and 930B are partially equalized signals. By way of example, in some embodiments equalizer outputs 930A and 930B are outputs of the FFE portion of equalizer 930. In another embodiment, equalizer outputs 930A and 930B are outputs of the equalizer phase tracker unit. In yet another embodiment, equalizer outputs 930A and 930B are input signals to the equalizer determination device. In yet another embodiment, equalizer outputs 930A and 930B are provided by different sources. As a non-limiting example, in some embodiments the equalizer output 930A is also the input signal to the equalizer's determining device while the equalizer output 930B is the output of the equalizer phase tracker.

Another embodiment of the system is the development of a decision error signal similar to the phase tracker decision error signal (E _PTD ) 248. Thus, in some embodiments, equalizer outputs 930C and 930D are input device and input device 930C corresponding to decision device of equalizer 930, respectively. In certain embodiments, the equalizer output 930D is the output of the grating decoder. In still other embodiments, the equalizer output 930D is the output of the intermediate stage of the grating decoder.

Using one or more delay elements (not shown), the system 900 temporarily sorts the data provided to the subtractor 942 by applying techniques available in the art. Accordingly, the subtractor 942 generates an error feedback signal 942A which is the difference between the decision device output of the equalizer 930 and the input to the corresponding decision device. Similarly, system 900 also temporarily aligns the inputs provided to multipliers 948 and 950. Thus, inputs to multiplier 948 correspond to the same baseband signal 920A. Similarly, inputs to the multiplier 950 correspond to the same baseband signal 920A. Finally, while FIG. 29 shows multipliers 948 and 950 receiving the same error feedback signal 942A, it should be understood that this is only an example and is not intended to be limiting. Thus, in some embodiments the error signal used for carrier tracking is calculated differently than the error signal used for tuning. By way of example, in some embodiments the error feedback signal 942A for carrier tracking is formatted with the slicer output of the equalizer 930 while the error feedback signal 942A for tuning is the lattice decoder of the equalizer 930. Is formed with the output.

Carrier offset post filter 944 and timing offset post filter 946 receive equalizer outputs 930A and 930B, respectively. Negative and positive inputs of subtractor 942 receive equalizer outputs 930C and 930D, respectively, and produce error feedback signal 942A. Multiplier 948 receives the outputs of carrier offset post filter 944 and error feedback signal 942A. Multiplier 948 provides a decision directed carrier tracking feedback signal 74A to loop filter 926. Similarly, multiplier 950 receives the outputs of timing offset post filter 946 and error feedback signal 942A. Multiplier 950 provides a decision directed tuning feedback signal 66A to loop filter 916.

The carrier offset post filter 944 detects the carrier frequency and phase offset present at the equalizer output 930A. In some embodiments, the carrier offset post filter 944 is a phase error detector and provides a phase error estimate. In other embodiments, the carrier offset post filter 944 is a phase-shift filter or quadrature filter similar in form and function to the phase-shift filter 812. Thus, some embodiments of carrier offset post filter 944 include a Hilbert filter or truncated Hilbert filter. In another embodiment, the carrier offset post filter 944 is optimized filter tap coefficients to minimize the mean squared error (MMSE) of the filter output for a receiver having a 90 degree phase-shifted channel and a predetermined acquisition threshold. Is the FFE of the desired length.

By way of example, some embodiments of the carrier offset post filter 944 as described above with respect to the phase-shift filter 812 have a length of 31 samples and are optimized for a 15.1 dB VSB or offset-QAM receiver acquisition SNR threshold. FIR filter with filter tap coefficients MMSE. The resulting filter is quantitatively illustrated in FIG. 36B. Other embodiments of the carrier offset post filter 944 include filter tap values optimized for receiver acquisition SNR thresholds less than 15.1 dB. One or more embodiments of the carrier tracking feedback loop include a carrier offset post filter 944 with coefficients optimized for an acquisition SNR threshold of 15 dB. In other embodiments, the carrier offset post filter 944 develops the phase error estimate with an output similar to the phase error estimate developed in the embodiments 800A, 800C, 800D, and 800E of the phase tracker. do.

The multiplier 948 forms the decision directed carrier tracking feedback signal 74A by multiplying the output of the carrier offset post filter 944 by the error feedback signal 942A. It should be understood that one or more delay elements are used in various embodiments to temporarily align the inputs with respect to multiplier 948.

Timing offset post filter 946 filters equalizer output 930B to detect timing or tuning offsets. In some embodiments, timing offset post filter 946 is a correlation filter optimized for detecting any small fractional timing offset. In other embodiments, the timing offset post filter 946 combines the outputs of the timing lead filter and the timing lag filter, where the timing read filter detects positive timing offsets and the timing lag filter negative. Detect timing offsets. Other embodiments of timing offset post filter 946 combine the timing read and timing lag filters to produce a symmetric timing offset error signal at the output of timing offset post filter 946. Still other embodiments of timing offset post filter 946 MMSE-optimize the coefficients for the FIR filter to generate an impulse response in the presence of white noise for a given receiver acquisition threshold. By way of example, in some embodiments filter coefficients are developed by a technique that includes summing the coefficients of the first filter and the second filter, wherein the first and second filter coefficients are read timing offset and lag. Optimized for detecting timing offsets respectively. In other embodiments, developing the coefficients of the timing offset post filter 946 further includes averaging the coefficients of the first and second filters.

In certain embodiments, developing the coefficients of the timing offset post filter 946 includes adding or averaging the coefficients of the two filters. Each filter is MMSE-optimized to generate an impulse response to detect any small partial timing offsets in the presence of white noise, where the SNR is less than or equal to the receiver acquisition threshold. The coefficients of both filters are optimized to detect timing offsets in the opposite direction. By way of example, in some embodiments the first filter is optimized to detect a 1/10 ^th symbol timing offset (lead) and the second filter is optimized to detect a −1/10 ^th symbol timing offset (lag). The first and second filter coefficients are asymmetrical. The coefficients of the filter 946 are then obtained by averaging or adding the coefficients of the first and second filters.

The resulting filter is a symmetric filter as quantitatively shown in FIG. 36A, which detects any small fractional timing offsets in the presence of white noise, where the SNR is less than or equal to the receiver acquisition threshold.

Adding or averaging the coefficients of the first and second filters produces coefficients of filter 946 that are symmetrical and correlate reading and lagging timing offsets. By way of example, some embodiments of filter 946 are MMSE-optimized to generate an impulse response in the presence of white notes in a channel with 15.1 dB. Still other embodiments of the filter 946 generate the maximum correlation for the 1/10 ^th symbol timing offset.

Still other embodiments of timing offset post filter 946 include an FFE having a length of 31 samples with MMSE-optimized filter tap coefficients for a VSB or offset-QAM receiver acquisition SNR threshold of 15.1 dB. Other embodiments of timing offset post filter 946 include filter tap values optimized for receiver acquisition SNR thresholds less than 15.1 dB. One or more embodiments of the present invention include timing offset post filter 946 coefficients that are optimized for an acquisition SNR threshold of 15 dB.

Referring back to FIG. 29, the multiplier 950 multiplies the output of the timing offset post filter 946 by the error feedback signal 942A to produce a decision directed tuning feedback signal 66A corresponding to the received particular symbol. . It should be understood that in some embodiments delay elements are used to temporarily align the inputs with respect to the multiplier 950.

Data received by system 900 is provided to A / D 912 that samples near-baseband signal 60A received at a clock rate governed by feedback-controlled VCXO 914. Digital mixer 922 down modulates digitized near-baseband signal 62A from A / D 912 based on the local carrier frequency generated by feedback-controlled NCO 924. The output of digital mixer 922 is filtered (not shown for brevity) to produce digitized baseband signal 920A. In some embodiments, as shown in FIG. 3, a Nyquist filter filters the output of the digital mixer. Those skilled in the art will appreciate that other filters may be used to filter the output of the digital mixer 922. Referring back to FIG. 29, equalizer 930 receives digitized baseband signal 920A and removes residual channel distortion and multipath interference therefrom. In addition, some embodiments of equalizer 930 include a phase tracker to eliminate residual carrier phase error.

As described below, the operation of the tuner 910 is selectively governed by a non-coherent tuned feedback signal 64A or a decision directed tuned feedback signal 66A based on the operating state of the system 900. Similarly, the operation of the digital modulator 920 is selectively governed by the non-coherent carrier tracking feedback signal 72A or the decision directed carrier tracking feedback signal 74A based on the operating state of the system 900.

The NCC 950 receives the output of the digital mixer 922 which develops both the non-coherent tuned feedback signal 64A and the carrier tracking feedback signal 72A. NCC 950 is a non-coherent carrier tracking feedback signal 72A and a non-coherent method in the manner described in co-pending US patent application Ser. No. 10 / 408,053 and US patent application Ser. No. 10 / 407,634, which are incorporated herein by reference. Use a combination of pilot signal and redundant information on the upper and lower Nyquist slopes to develop the coherent tuned feedback signal 64A. The development of these signals by the NCC 950 is preferably not dependent on the output of the equalizer 930.

As described above, equalizer 930 provides equalizer outputs 930C and 930D to subtractor 932, which forms error feedback signal 942A. The equalizer 930 also provides an equalizer output 930A to the carrier offset post filter 944. Carrier offset post filter 944 filters equalizer output 930A to detect carrier frequency or phase errors. The multiplier 948 forms the decision directed carrier tracking feedback signal 74A by multiplying the output of the carrier tracking filter 944 by the error feedback signal 942A. Similarly, the timing offset post filter 946 filters the equalizer output 930B to detect timing and tuning errors, and the multiplier 950 then outputs the output of the timing offset post filter 946 and the error feedback signal ( Multiplying 942A forms a decision directed feedback tuned feedback signal 66A. As described above, the delay feedback not shown in FIG. 29 lies within the various signal paths to temporarily align the various signals so that the error feedback signal 942A outputs the carrier offset post filter 944 and the timing offset post filter 946. It should be understood that each of

The feedback loop controlling the digital demodulator 920 is formed by feeding the non-coherent carrier tracking feedback signal 72A and the decision directed carrier tracking feedback signal 74A back to the loop filter 926. As described below, depending on the operating state of the system 900, the control system 954 loops to use either the non-coherent carrier tracking feedback signal 72A or the decision directed carrier tracking feedback signal 74A. Optionally control filter 926. Loop filter 926 filters the selected feedback signal and provides a control signal to NCO 924. NCO 924 provides a digital representation of the local carrier to digital mixer 922 to down modulate digitized near-baseband signal 62A. In some embodiments, loop filter 926 low-pass filters the selected feedback signal. In other embodiments, loop filter 926 integrates the selected feedback signal and then low-pass filters the integrated output. By way of example, in certain embodiments, the selected feedback signal passes through a complete integrator before being low-pass filtered and provided to the NCO 924. In other particular embodiments, the selected feedback signal is passed through a " Like " integrator before it is low-pass filtered and provided to the NCO 924.

Similarly, a feedback loop controlling the tuner 910 is formed by feeding the non-coherent tuned feedback signal 64A and the decision directed tuned feedback signal 66A back to the loop filter 916. As described below, depending on the operating state of system 900, control system 970 uses loop filter 916 to use non-coherent tuning feedback signal 64A or decision directed tuning feedback signal 66A. Optional control. Loop filter 916 filters the selected feedback signal and provides a control signal to VCXO 914. A / D 912 receives a feedback-controlled sampling clock from VCXO 914 that minimizes synchronization-introduced errors in the outputs of equalizer 930.

Still referring to the system 900 of FIG. 29 and yet another embodiment of the system 900 whose operation is illustrated in FIG. 30 illustrates a system 1000 that controls the operation of the equalizer optimization process and controls the tuning and demodulation control feedback loops. Include. At 1010, "initial acquire mode", control system 954 initializes system 900. Equalizer 930 is not yet working. The phase trackers of the CDEU and equalizer are not yet functional or remain reset. NCC 950 is operable. Control system 954 loops to place tuner 910 and digital demodulator 920 in acquisition mode and to select tuned feedback signal 64A and non-coherent carrier tracking feedback signal 72A of NCC 950. The filter 916 and the loop filter 926 are selectively controlled. After some time period, the control system 954 receives positive assertions from the VCXO lock 102 and the NCO lock 104 where the tuner 910 and the digital demodulator 920 are locked to the incoming signal. After both the VCXO lock and the NCO lock are asserted, the control system 954 transitions the system 900 operation from state 1010 to 1012.

At 1012, "calculate channel delay estimate," control system 954 turns on the CDEU portion of equalizer 930. Other parts of the equalizer 930 remain non-operational. The control system 954 keeps the tuner 910 and the digital demodulator 920 in an acquisition mode. The non-coherent feedback signals of the NCC 950 continue to dominate the tuning and demodulation operations of the system 900. After calculating the CDEU additional channel delay estimate of the equalizer 930 and determining the desired timing for segment sync and frame sync at the output of the FFE, the control system 954 transitions the system 900 operation from the 1012 state to the 1014 state. Let's do it.

At 1014, "equalizer training with segment sync", control system 954 activates the FFE portion of equalizer 930 and places the DFE portion of equalizer 930 in IIR mode. In IIR mode, the DFE receives sliced data from the determining device of equalizer 930. In embodiments with a phase tracker, the phase tracker is placed in bypass mode. Control system 954 uses segment sync as a training signal to optimize FFE coefficients. After the control system 954 receives one or more positive indications from the field / frame sink 98 from which the field / frame sync was detected, the control system 954 transitions the system 900 operation from state 1014 to 1016. . However, in some embodiments, where a sufficient number of field / frame sync indications are received to indicate progress towards proper optimization of the equalizer coefficients, the system 900 may include a time-out feature to control the system. 954 returns operation of system 900 to state 1012 from 1010.

In some embodiments, the segment sync comes from the CDEU of equalizer 930. In other embodiments, when the CDEU calculates a channel delay estimate based on the correlation of the field / frame sync sequence and the incoming signal, the frame sync signal is from the CDEU of the equalizer 930. Otherwise, a portion of equalizer 930 generates a frame sync based on the equalized signal or equalizer output in the middle of the equalizer (similar to equalized signal 90 in middle of FIG. 5 or equalizer output 88). .

At 1016, ie, "equalizer training with segment sync" and field / frame sync, control system 954 uses both field / frame sync and segment sync as training signals to develop coefficients of the FFE portion of equalizer 930. Ping. The DFE portion of equalizer 930 continues to operate in IIR mode. Similarly, the phase tracker portion of the equalizer 930 continues to operate in bypass mode. If the measured signal has an estimated SNR greater than the predetermined RCA_ENB Threshold, the control system 954 monitors the field / frame sink 98 and SNR 100 and transitions the system 900 operation from state 1016 to 1018. Let's do it. However, control system 954 transitions system 900 operation from state 1016 to 1010 if it detects a loss of the field / frame sync indication.

In 1018, ie, "equalizer training in RCA mode," control system 954 enables the DFE portion of the equalizer of system 900. Control system 954 optimizes FFE and DFE coefficients using an RCA-related LMS algorithm with respect to the data being received. In other embodiments, the control system 54 further includes a technique for comparing the received tuning signals with those generated by the control system 54. In yet other embodiments, control system 54 augments the effects of RCA and tuned signal based optimization techniques depending on system performance or operating conditions. Control system 954 transitions system 900 operation from state 1018 to 1020 when the measured signal has an estimated SNR greater than a predetermined Decision Directed Threshold, eg, 12 dB. Instead, if the estimated SNR falls below a predetermined Return_Sync_Training Threshold, for example 6 dB, the control system 954 transitions the system 900 operation from state 1018 to 1016. Similarly, control system 954 transitions system 900 operation from 1018 to 1010 if it detects a loss of the field / frame sync indication.

In 1020, or "Decision Directed Mode," control system 954 optimizes FFE and DFE coefficients using decision-oriented LMS techniques in connection with received data and tuning signals. The control system 954 also selectively controls the loop filter 916 and the loop filter 926 to select the decision directed tuning feedback signal 66A and the decision directed carrier tracking feedback signal 74A, respectively. The control system 954 keeps the system 900's work at 1020 as long as the estimated SNR remains above the predetermined RETURN_RCA_MODE Threshold, but if the estimated SNR falls below the RETURN_RCA_MODE Threshold, then the operation of the system 900 is dropped at state 1020. Transfer to 1018. The control system 954 transitions the operation of the system 900 from state 1020 to 1010 upon detecting the loss of the field / frame sync indication.

Another embodiment of a system 900, shown as system 900A of FIG. 31, includes components that correlate decision directed phase tracking and carrier tracking feedback loops. System 900A is similar in form and function to equalizer 200A in FIG. 27 that includes phase tracker 800E. It is to be understood that other embodiments of system 900A use other embodiments of phase tracker 800. However, system 900A also receives digitized near-baseband signal 62A and provides digitized baseband signal 920A as input to FFE 210. Loop filter 926 receives phase correction signal θ 74B from integrator 816, while loop filter 926 receives crystal directed carrier tracking feedback signal 74A in system 900 (FIG. 29).

System 900A couples decision directed carrier tracking feedback and decision directed phase error signals. The input to integrator 816 is a decision directed phase error signal 843, similar to the decision directed carrier tracking feedback signal 74A. In some embodiments, the decision directed phase error signal 843 and the decision directed carrier tracking feedback signal 74A are equivalent. Integrator 816 integrates the crystal directed phase error signal 843 at the output of phase detector 841 to provide phase correction signal θ 74B. Phase detector 841 may be implemented in any manner known in the art; For example, any of the approaches illustrated in FIGS. 23-28 may be used. For example, phase detector 841 may be implemented by phase shift filter 840 and multiplier 822 of FIG. 27. The loop filter 926 further low-pass filters the phase correction signal θ and provides a control signal to the NCO 924. This effectively links phase tracker feedback and carrier tracking loops. As a result, rotator 814 corrects more instantaneous phase errors resulting from carrier tracking errors, while digital demodulator 920 tracks out longer periods of carrier tracking errors. In addition, the interaction of the phase tracker and digital demodulator feedback loops ensures that the phase tracker operation is not fully operational. Those skilled in the art will also understand that similar techniques may be combined with other phase tracker embodiments described above.

In another particular embodiment of the system 900, shown as the system 900B of FIG. 32, the decision oriented carrier tracking and phase tracking feedback loops are correlated. System 900B is similar in form and function to system 900A in FIG. 31 and includes equalizer 200A in FIG. 27 with phase tracker 800E and digital demodulator 920. Digital demodulator 920 receives digitized near-baseband signal 62A and provides digitized baseband signal 920A as input to FFE 210. However, the crystallographic phase error signal 843 from the output of the phase detector 841 (input of the integrator 816) is instead of the phase correction signal? From the output of the integrator 816. 74B '). Loop filter 926 receives and low-pass filters the output of phase detector 841 to provide a control signal to NCO 924. This effectively links phase tracker feedback and carrier tracking loops. As a result, rotator 814 corrects the more instantaneous phase errors generated from carrier tracking errors, while digital demodulator 920 tracks longer periods of carrier tracking errors. The interaction of the phase tracker and digital demodulator feedback loops allows the carrier tracking feedback loop to compensate for the saturation of the potential phase tracker. One skilled in the art would be able to apply this technique to the other phase trackers described above without undue experimentation. Still other embodiments of the illustrated system 900, such as the system 900C of FIG. 33, use the outputs of the equalizer determination device to develop a carrier tracking feedback signal 74C and a tuning feedback signal 66C. System 900C is similar in form and function to system 900 except that decision directed control 940 is replaced with decision directed control 940C. Equalizer 930 provides an equalized output 930E and a grating decoder output 930F as inputs to DDC 940C.

Decision directed control 940C provides a decision directed tuning feedback signal 66C to the tuner 910 instead of a decision directed tuning feedback signal 66A. Decision directed control 940C provides a decision directed carrier tracking feedback signal 74C to the digital demodulator 920 instead of the decision directed carrier tracking feedback signal 74A (see FIG. 29).

Decision directed control 940C includes pulse shaping filters 960 and 962, conjugate 964, delay line 966, two-symbol clock delay 968. ), A subtractor 970, a single-symbol clock delay 972, a complex multiplier 974, and a complex multiplier 976. Filter 960 receives the equalized output 930E and provides a complex signal output Y (n + n ₀ ) to delay line 966, where n ₀ is the lattice decoder and conjugate 964 of equalizer 930. Is the delay of the symbol clocks introduced by Delay line 966 introduces delayed n ₀ symbol clocks and provides Y (n) as output to the two-symbol clock delay 968, the positive input of subtractor 970 and complex multiplier 976. Two-symbol clock delay 968 introduces an additional two-symbol clock of delay and provides Y (n-2) to subtractor 970. Similarly, pulse shaping filter 962 receives grid decoder output 930F and provides complex signal output A (n) to conjugate 964. In some embodiments, it should be understood that the functions of pulse shaping filter 962 and conjugate 964 are combined. Conjugate 964 conjugate 964 provides A ^* (n) to single-symbol clock delay 972, which is one symbol clock delay output A ^* (n-1) to complex multiplier 974. Provides as input. Conjugate 964 also provides A ^* (n) to complex multiplier 976.

Pulse shaping filter 960 receives an equalizer decision slicer output that does not have a corrected error. Pulse shaping filter 960 is a decision slicer output of complex-valued in-phase / quadrant pair representation Y (n + n ₀ ) = I _S (n + n ₀ ) + j Q _S (n + n ₀ ). I _S (n + n ₀ ) is 90-degree phase-shifted or quarter-cycle filtered on the real-valued input to the pulse shaping filter 960.

Similarly, pulse shaping filter 962 receives a corrected correction of the equalizer decision slicer output from the lattice decoder of equalizer 930. Pulse shaping filter 962 provides a decision slicer output A (n) = I _T (n) + j Q _T (n) of the complex-valued in-phase / quadrant pair representation. I _T (n) is a delayed version of the real-valued input to the pulse shaping filter 962. Q _T (n) is 90 degrees phase-shifted or quarter-filtered on the real-valued input to pulse shaping filter 962.

In some embodiments, pulse shaping filters 960 and 962 are similar to Hilbert transform filters, respectively, and are phase-shifted or quartered to produce quadrant portions of complex pairs Q _S (n) and Q _T (n). Delay lines for providing filter and real-value outputs I _S (n) and I _T (n), respectively. In some embodiments, the phase-shift or quadrature filter is similar in form and function to the phase-shift filter 812 described above with respect to FIGS. 23-28.

를 보상한다. 따라서, 지연 라인(966) Y(n) = I_S(n) + j Q_S(n) 및 콘쥬게이트 A^*(n) = I_T(n) - j Q_T(n)의 출력들은 동일한 결정 슬라이서 출력들과 임시적으로 관련된다. 차감기(970)의 출력은 차이 Y(n) - Y(n-2)이며 콘쥬게이트(964)의 하나의 심볼 클록 지연 출력 A^*(n-1)과 곱해진다. 이는, 앞선 그리고 다음에 디코딩된 심볼들과 관련하여 보정된 결정 슬라이서 출력의 프로젝션에 효과적이고 동조 관련 ISI를 나타낸다. 멀티플라이어(974)의 출력의 실수 부 F_66C는 루프 필터(916)에 제공되는 결정 지향 동조 피드백 신호(66C)이다: Delay line 966 shows propagation delay between equalized output 930E on the one hand and grating decoder output 930F and conjugate 964 on the other.

To compensate. Thus, the outputs of delay line 966 Y (n) = I _S (n) + j Q _S (n) and conjugate A ^* (n) = I _T (n)-j Q _T (n) are the same decision. Temporarily related to slicer outputs. The output of subtractor 970 is the difference Y (n)-Y (n-2) and is multiplied by one symbol clock delay output A ^* (n-1) of conjugate 964. This represents an effective and tuned ISI for the projection of the crystal slicer output corrected in relation to the preceding and following decoded symbols. Real part F _66C of the output of multiplier 974 is a decision directed tuning feedback signal 66C provided to loop filter 916:

F _66C = I _T (n-1) · [I _S (n)-I _S (n-2)] + Q _T (n-1) · [Q _S (n)-Q _S (n-2)]

In some embodiments, loop filter 916 integrates the decision directed tuning feedback signal 66C and then low-pass filters to generate a control signal to govern the work of NCO 924. In other embodiments, loop filter 916 only low-pass filters the decision directed tuning feedback signal 66C to generate a control signal to govern the work of NCO 924.

Similarly, multiplier 976 performs a complex multiplication operation. The imaginary part F _74C of the output of the multiplier 976 is provided to the outputs F _74C = I _T (n) Q _S (n)-I _S (n) I _S (n) to the loop filter 926. Is a decision directed carrier tracking feedback signal 74C.

In some embodiments, loop filter 926 integrates and then low-pass filters the decision directed carrier tracking feedback signal 74C to generate a control signal to govern the operation of VCXO 914. In other embodiments, loop filter 926 only low-pass filters the decision directed carrier tracking signal 74C to generate a control signal to govern the operation of VCXO 914.

Still other embodiments of the illustrated system 900, such as the system 900D of FIG. 34, use the outputs of the decision device of the equalizer to develop the decision directed tuning feedback signal 66D. Functionally, system 900D is similar in form and function to system 900 except that decision-oriented controller 940 has been replaced by decision-oriented controller 940D. As shown in FIG. 34, system 900D also generates a decision directed tuning feedback signal 74C similar to system 900C. However, in system 900D, delay line 966 provides an output for single-symbol clock delay 972, while in system 900C, delay line 966 receives the output of conjugate 964. . Similarly, the positive input of the two-symbol clock delay 968 and the subtractor 970 receives the output of the conjugate 964 while the delay line 966 in the system 900C causes the two-symbol clock delay. Provide an output to the positive input of 968 and subtractor 970.

Similar to system 900C, pulse shaping filter 960 receives equalized output 930E rather than corrected error from equalizer 930. Pulse shaping filter 960 provides an in-phase / quadrant pair representation Y (n + n ₀ ) = I _S (n + n ₀ ) + j Q _S (n + n ₀ ) of the complex value of the crystal slicer output. do. As described above, I _S (n + n ₀ ) is a delayed version of the real value input to the pulse shaping filter 960, while Q _S (n + n ₀ ) is the real value input to the pulse shaping filter 90. 90 degree phase-shifted or quarter-cycle filtered output for. Delay line 966 compensates for the delay introduced by the lattice decoders of conjugate 964 and equalizer 930 and provides a delayed complex representation of the decision device decision slicer output with a 1-symbol-clock delay 972 and a multiplier ( 976). The output of the 1-symbol-clock delay 972 provides an additional symbol clock of delay between the output of the delay line 966 and the input of the multiplier 974.

The pulse shaping filter 962 is similar in shape and function to the pulse shaping filter 960 and receives the grid decoder output 930F of the equalizer 930. Pulse shaping filter 962 provides complex representation of grating decoder output to conjugate 963. Conjugate 964 provides a conjugate of the input received to the positive input of multiplier 976, two-symbol clock delay 968 and subtractor 970. Two-symbol clock delay 968 provides the two-symbol clock delay output of conjugate 964 to the negative input of subtractor 970. Multiplier 974 performs a complex multiplication of the received inputs and generates a real component F _66D at the output as the decision directed tuning feedback signal 66D: F _66D = I _S (n-1) · I _T (n) -I _T (n-2)] + Q _S (n-1)-[Q _T (n)-Q _T (n-2)].

Although not shown, similar to system 900C, system 900D provides a decision directed tuning feedback signal F66D to loop filter 916 and generates a control signal to govern the operation of VCXO 914. Low-pass filtering after integrating the decision directed tuning feedback signal 66D. In other embodiments of the system 900D, the loop filter 916 only low-pass filters the decision directed tuning feedback signal 66D to generate a control signal to govern the operation of the VCXO 914.

Another embodiment of the illustrated system 900, such as the system 900E of FIG. 35, which continues with reference to the system 900C of FIG. 33, provides an equalizer 930 to develop a decision directed tuning feedback signal 66E. Use the output of Functionally, system 900E is similar in form and function to systems 900C and 900D except for the formation of decision directed tuning feedback signal 66E provided to loop filter 916 shown in FIG. As shown in FIG. 35, the system 900E includes an equalizer 930, a delay line 966, a two-symbol clock delay 968, a subtractor 970, a multiplier 974, and a multiplier 976. Four-symbol clock delay 978, two-symbol clock delay 980, four-symbol clock delay 982, subtractor 984 and subtractor 986.

Equalizer 930 provides an equalized output 930E, also referred to as Y (n + n _a ), to delay line 966. Delay line 966 introduces delayed n _a symbol clocks to compensate for the delay of the grating decoder of equalizer 930. Delay line 966 provides Y (n) as an output for two-symbol clock delay 968, a positive input of subtractor 970, and four-symbol clock delay 978. Four-symbol clock delay 978 introduces additional four-symbol clocks of delay and provides Y (n-4) to the negative input of subtractor 970. The subtractor 970 provides the difference signal Y (n)-Y (n-4) to the multiplier 974.

Lattice decoder output 930F (hereinafter referred to as A (n)) is provided to the positive input of two-symbol clock delay 980, four-symbol clock delay 982 and subtractor 984. Four-symbol clock delay 982 provides a four clock delay copy A (n-4) of grid decoder output 930F to the negative input of subtractor 984.

Multiplier 976 provides red Y (n-2) [A (n)-A (n-4)] to the positive input of subtractor 986. Similarly, multiplier 974 receives difference Y (n) -Y (n-4) from subtractor 970 and A (n-2) from two-symbol clock delay 980. Multiplier 974 provides the enemy A (n-2) [Y (n)-Y (n-4)] to the negative input of subtractor 986. The output of the subtractor 986 is a decision directed tuning control signal.

F _66E = Y (n-2) [A (n)-A (n-4)]-A (n-2) [Y (n)-Y (n-4)]

Developer

In some embodiments, the CDE estimate is calculated once at the start of each equalizer optimization process, and illustratively the receiver is tuned to a different signal source each time. In other embodiments, the CDE estimate is recalculated as an ongoing process to find the optimal virtual center position when channel conditions change. The virtual center is shifted according to the updated position of the virtual center by slowly changing the sampling clock frequency or by repositioning the training signals over a period of time while maintaining the integrity of the system.

As illustrated in FIG. 37, another embodiment of system 20 is correlation directed control (CDC) 1100. Similar to the CDEU 230C of FIG. 14, the CDC 1100 includes a symbol counter 316, segment counter 318, correlators 510 and 512, size calculator 392A, correlation buffer 514A, threshold Detector 516A, controller 520 and memory 530. The CDC 1100 further includes a centroid weighting function 1 CW, switches 1104, 1106 and 1108, a filter 1110 and an adder 1120.

Although not shown, controller 520 also includes configuration and control interfaces for the elements of CDC 1100. This includes, for example, provisions for transmitting or receiving indications to or from other elements, or between other elements with a reset and enabling signal. Some embodiments of the CDC 1100 further include a centroid estimator that is similar in form and function to the centroid estimator 340A as described above in FIG. 14.

The correlation directed control 1100 receives the filtered baseband signals I _F 76 and Q _F 78 as inputs to the correlators 510 and 512, respectively. In some embodiments, the CDC 1100 is adapted to receive twice (2x) over-sampled representations of I _F and Q _F. In other embodiments, the CDC 1100 is adapted to receive a symbol rate representation of I _F and Q _F. Still other embodiments of the CDC 1100 are optimized for other over-sampled representations of the input signals. Correlators 510 and 512 operate in conjunction with I _F and Q _F to generate frame sync correlation signals SCV _I (i) and SCV _Q (i) provided to magnitude calculator 392A. Similar to the size calculator 392, the size calculator 392A calculates MAG _FS (i). In some embodiments, MAG _FS (i) = | SCV _I (i) + + SCV _Q (i) | In other embodiments, MAG _FS (i) = SCV _I ² (i) + SCV _Q ² (i). The output of the size calculator 392A is the frame sync correlation size FSCM (i). In some embodiments, FSCM (i) is MAG _FS (i). In other embodiments, size calculator 392A low pass filters MAG _FS (i) to produce FSCM (i). Correlation buffer 514A and threshold detector 516A receive FSCM (i) from magnitude calculator 392A. By way of example, some embodiments of a magnitude calculator 392A that receives a 2x over-sampled representation of IF and QF include a three-tap FIR filter. This allows the FIR filter to capture the majority of the power of a single field / frame sync correlation impulse regardless of the sampling phase. The number of taps and the filter complexity are based on the over-sampled ratio and are needed for noise reduction.

Correlation buffer 514A is scaled to accommodate the samples produced by the size calculator. By way of example, in some embodiments correlation buffer 514A is scaled to accommodate 2049 values of FSCM (i). Still other embodiments include 1025 FSCM (i) samples. Some embodiments of the correlation buffer 514A are scaled to interact with partially spaced samples. Controller 520 interacts with memory 530 and receives values of SC and SEGCNT from symbol counter 316 and segment counter 318, respectively. As described above in the above embodiments, the controller 520 also provides a channel delay estimate 84 and is coupled to the control system 54 (see FIG. 3).

Similar to the CDEU 230C of FIG. 14, the system 1100 detects the location of frame / field sinks present in the received signals. As will be described in detail below, threshold detector 516A receives FSCM (i) values and compares them with the frame sync detection threshold T _DET in the incoming data stream which is the maximum FSCM (i) for detecting the sequence. If a frame sync sequence is detected, the controller 520 assigns values of WINCENT = i, FSYM = SC and FSEG = SEGCNT. Controller 520 then calculates search window variables WINSTART and WINEND corresponding to the first and last memory locations of the desired window in correlation buffer 514A.

Finally, similar to finding regions G _MAX , G _PRE, and G _POST as shown in FIG. 17, controller 520 defines regions R ₀ , R _1, and R ₂ within the window defined by WINSTART and WINEND. . As in the non-limiting example illustrated in FIG. 38A, P ₀ , P ₁ and P ₂ correspond to ghost signals having power or maximum sync correlation values in the respective regions R ₀ , R ₁ and R ₂ . In some embodiments, R ₀ , R ₁ and R ₂ span the entire window between WINSTART and WINEND. In other embodiments, R ₀ , R ₁ and R ₂ span only a portion of the window, as shown in FIG. 38A. As shown in Figure 38, the window W _FS is over 2M + 1 symbol time; There are M symbol times that precede and follow the symbol time for P ₀ . This causes the CDC 1100 to select the first maximum value of FSCM (i) as P ₀ . Still other embodiments reconfigure threshold detector 516A to locate FSCM (i) ≧ P ₀ . As a result, the CDC 1100 selects FSCM (i) of the final maximum value within the span of the entire window as P ₀ .

After locating initial PO, controller 520 reconfigures threshold detector 516A to locate FSCM (i) ≧ P ₀ . If threshold detector 516A detects FSCM (i) ≥P ₀ , controller 520 searches by setting WINCENT = i, FSYM = SC, FSEG = SEGCNT, P ₀ = FSCM (i) and I _MAX = i. Recenter the window. Controller 520 then recalculates the values of WINSTART and WINEND. This process continues until i = WINEND. Controller 520 selects regions R ₀ , R _1, and R ₂ based on the final value of WINCENT. Controller 520 then searches correlation buffer 514A to find region maximums P ₁ and P ₂ in regions R ₁ and R ₂ , respectively.

The centroid weighting function 1102 receives the FSCM (i) from the correlation buffer 514A and calculates a weighted average to drive the filter 1110. In some embodiments, CWF 1102 uses FSCM (i) associated with P0, P1, and P2, and CWF 1102 outputs:

Has

In other embodiments, CWF 1102 calculates a weighted average of all correlation values in regions R ₀ , R _1, and R ₂ :

As shown in FIG. 38B, the windowing function FCW (i) is a set of piecewise linear ramp functions. Other embodiments of FCW (i) are odd functions defined to have zero values outside of regions R ₀ , R ₁ and R ₂ . Some embodiments also have a value of 0 in the regions R ₁ and R ₂ . As illustrated in FIG. 38C, some embodiments of CDC 1100 include F _CW (i) based on a windowed sine function.

The centroid weighting function 1102 provides a CWF _OUT to the first input of the switch 1104. The second input of the switch 1104 receives digital zero. First and second inputs of switch 1106 receive digital 0 and output of switch 108 (SLEW), respectively. Controller 520 provides control signals SLEW ENABLE 1112 to switches 1104 and 1106. Assessing SLEW ENABLE 1112 selects the second inputs of switches 1104 and 1106. This allows the controller 520 to control the output of the VCXO by selecting the output of the switch 1114. Otherwise, switches 1104 and 1106 provide CWF _OUT and digital 0, respectively, to the inputs of filter 1110 and adder 1120. Switch 1108 receives offset values + F _OFFSET 1116 and -F _OFFSET 1118. In some embodiments, F _OFFSET may be dynamically increased by the integrator of controller 520 when it is determined that a larger value is required. In other embodiments, there is a limitation with the integrator to keep F _OFFSET below the maximum value. Signal SLEW CONTROL 1114 from controller 520 selects the value of SLEW provided to the second input of switch 1106. Controller 520 slews the VCXO output frequency by selecting either + F _OFFSET 1116 or -F _OFFSET 1118. The switch 1104 provides an output to the filter 1110. Filter 1110 and switch 1106 provide inputs to adder 1120, which creates VCXO _CONTROL 1140.

In some embodiments, filter 1110 is a low pass filter. By way of example, some embodiments of filter 1110 are configured as a lead-lag filter. As shown in FIG. 37, filter 1110 includes scalars 1122, 1124, 1126, adders 1128, 1130, and delay elements 1132. Both scalar 1122 and 1124 receive the output of switch 1104 as an input. Scalar 1122 multiplies the received input by a scalar value C ₁ and provides an output to adder 1130. Delay element 1132 receives the output of adder 1130 and provides (F _LOW ) to adder 130. F _LOW represents the low-frequency component of the VCXO frequency offset with respect to the received signal time base. In some embodiments, F _LOW is each field / frame sync period updated. In other embodiments described below, F _LOW is each segment sync period updated. Scalar 1124 multiplies the output of switch 1104 by a scalar value C ₂ . Adder 1128 receives the outputs of scalar 1124 and adder 1130. Scalar 1126 multiplies the output of adder 1128 with a scalar value C ₃ and provides the output to adder 1120.

As illustrated in FIG. 37, switches 1104 and 1106 form a double-pole double-throw configuration that is selectively controlled by controller 520 signal SLEW ENABLE 1112. . If the SLEW ENABLE signal 1112 is not asserted, the filter 1110 receives CWF _OUT and the filter transfer function H (z) = C ₃ [C ₁ (1 + Z ⁻¹ ) + C ₂ ]. therefore,

VCXO _CONTROL = C ₃ [(C ₁ + C ₂ ) CWF _OUT + F _LOW ]

Where F _LOW is the low frequency VCXO offset of the system stored in delay element 1132.

When the SLEW ENABLE signal 1112 becomes functional, the output of the adder 1120 is

VCXO _CONTROL = C ₃ F _LOW + SLEW

Where SLEW is + F _OFFSET or -F _OFFSET Same as either of Output F _LOW of delay element 1132 remains constant, while SLEW ENABLE signal 1112 is asserted. This preserves low frequency offset information until SLEW ENABLE 1112 is de-asserted.

As illustrated in FIG. 39, one embodiment of a system 20 that includes a correlation directed tuning control loop 1150 has a tuner 910A, a demodulator 920, and a correlation directed control (CDC) 1100. The tuner 910A is similar to the tuner 910 of the system 900 as described above in the above embodiments; However, tuner 910A includes loop filter 916A instead of loop filter 916.

As shown in FIG. 39, some embodiments of the correlation directed tuning control loop 1150 include a CDC 1100 that receives both I _F and Q _F , while the CDEU 230A of FIG. 6 or the FIG. 41 of FIG. 41. Other embodiments similar to the CDC 1250 receive only I _F. Referring again to FIG. 39, loop filter 916A has three feedback inputs. Similar to loop filter 916, loop filter 916A receives non-coherent tuned feedback signal 64 and decision directed tuned feedback signal 66. The loop filter 916A further includes an interface for receiving VCXO _CONTROL from the CDC 1100. Loop filter 916A also includes devices and techniques for switching between the various feedback control signals provided with inputs. Some embodiments of loop filter 916A also include techniques for weighting received feedback control signals. By way of example, some embodiments of loop filter 916A employ a weighted average for transition between VCXO _CONTROL and decision directed tuning feedback signal 66 based on the operating state of system 20.

As illustrated in FIG. 39, tuner 910A receives analog near baseband signal 60 and provides digitized near baseband signal 62 to demodulator and Nyquist filter block 920. Demodulator and Nyquist filter block 920 provide I _F 76 to CDC 1100. In some embodiments demodulator 920 also provides Q _F 78 to CDC 1100.

The CDC 1100 generates VCXO _CONTROL as input to the loop filter 916A. Loop filter 916A filters the received control signal and provides the control signal to VCXO 914. A / D 912 receives the clock generated by VCXO 914 and samples the received analog near baseband signal 60. Some embodiments of system 20 rely exclusively on CDC 1100 to provide a control feedback signal to tuner 910A. Similarly, other embodiments of system 20 may include some sub-combinations of non-coherent tuned feedback control signal 64, decision directed feedback signal 66, and correlation directed control signal VCXO _CONTROL . .

Another embodiment of a CDC 1100 suitable for ATSC broadcasting, in which operation is implemented by the system 1200 of FIG. 40, will be described with continued reference to the elements of FIGS. 37 and 39. At 1202 in FIG. 40, ie, “Initialization,” elements of the CDC 1100 will be initialized as will be appreciated by those skilled in the art. By way of example, controller 520 resets elements of CDC 1100; Registers in memory 530, symbol counter 316, segment counter 318, size calculator 392A, correlator 510, correlator 512, correlation buffer 514A, CWF 1102 And initializing the filter 1110; Configure various control signals, shown or not shown. For example, a register containing a value of P ₀ is set to TDET. In addition, SC, SEGCNT, and index variable i are initialized. The system 1200 then proceeds to 1204.

At 1204, or “Correlation,” correlators 510 and 512 receive the most recently filtered in-phase and quarter period baseband signals I _F 76 and Q _F 78, respectively. Similar to the CDEU 230C of FIG. 14, correlators 510 and 512 correlate I _F 76 and Q _F 78 with frame sync sequences. As in the embodiments described above, the magnitude calculator 392A receives SCV _I (i) and SCV _Q (i) from the correlators 510 and 512, respectively, and calculates the magnitude MAG _FS (i) of the correlation. do. The magnitude calculator 392A low pass filters the MAG _FS (i) to produce the FSCM (i) provided to the correlation buffer 514A and the threshold detector 516A. Correlation buffer 514A stores FSCM (i) in array M (i). As mentioned above, some embodiments of the magnitude calculator do not include a low pass filter function; FSCM (i) = MAG _FS (i). System 1200 proceeds to 1206.

At 1206, i.e., "Detect Frame Sync", if FSCM (i) <T _DET and FSCM (i) <P ₀ (negative result), the threshold detector 516A indicates that the controller has not detected a frame sync or maximum ghost signal ( A negative indication is sent to 520. Controller 520 then branches system 1200 to 1212. Otherwise, if FSCM (i) ≥ T _DET and FSCM (i) ≥ P ₀ (positive result at 1206), threshold detector 516 sends a positive indication to controller 520 where a valid maximum value ghost signal is detected. do. Given initially that P ₀ = T _DET , the first indication is the detected first field / frame sync. Subsequently setting P ₀ = FSCM (I ₀ ) causes the system 1200 to detect the maximum frame sync correlation until P ₀ ≧ T _DET . System 1200 operation then branches to 1208.

At 1208, or "Store Center", controller 520 sets FSYM = SC and FSEG = SEGCNT, which stores the temporary location of the maximum frame sync correlation detected within the data packet field / frame structure. The controller 520 also sets WINCENT = i and calculates search window variables WINSTART and WINEND corresponding to the first and last memory locations of the desired window in the correlation buffer 514A. Finally, controller 520 stores I ₀ = i and P ₀ = FSCM (I ₀ ). Controller 520 then branches the system 1200 task to 1212.

At 1212, ie, “Continue,” controller 520 determines whether to continue to 1216 “Find Regional Maximums”. If system 1200 does not pre-detect field / frame sync or i ≠ WINEND, system 1200 branches to 1214. Otherwise, if system 1200 detects a field / frame sync and i = WINEND, (YES), controller 520 branches system 1200 operations to 1216.

At 1214, ie, "Increment", the values of symbol counter 316 and segment counter 318 are updated. In addition, the index variable i is incremented. System 1200 operation continues to 1204.

At 1216, ie, "Find Regional Maximums," controller 520 defines regions R ₀ , R _1, and R ₂ . Controller 520 then searches regions R ₁ and R ₂ to locate P ₁ and P ₂ , respectively. As mentioned above, in some embodiments the CDC 1100 also estimates the channel delay based on the same field / frame sync correlation results. System 1200 continues to 1218.

If 1218, that is, "P _0> 4P _1" in the P _0> 4P _1, system 1200 continues to 1222. Otherwise, system 1200 continues to 1220.

At 1220, ie, “Select New P ₀ ”, controller 520 selects P ₁ as the new P ₀ . This produces P ₀ which does not correspond to a ghost with the largest frame sync sequence. Following the selection of the new P ₀ , the controller 520 redefines the areas R ₀ , R ₁ and R ₂ . Controller 520 then searches regions R ₁ and R ₂ to relocate P ₁ and P ₂ , respectively. Finally, system 1200 continues to 1222.

In 1222, that is, _{"P 0> P 2/9} ", from P _0> P _2/9, system 1200 continues to enter the ring VXCO slew control loop by proceeds to 1224. Otherwise, the system 1200 continues to 1230.

At 1224, ie, "-F _OFFSET ", controller 520 asserts slew enable signal 1212. This causes the output of adder 1120 to provide VCXO _CONTROL = C3F _LOW -F _OFFSET . As a result, the VCXO clock sampling the received data signal has a reduced frequency. This effectively moves the ghost P ₂ towards the R ₀ region. The VCXO long term frequency offset F _LOW from the transmitter symbol timebase is stored in delay element 1132 and represented by C ₃ · F _LOW . However, the training signals (Frame Sync and Segment Sync) used to derive the equalizer coefficients maintain the same timing based on the precomputed channel delay. As a result, the virtual center is temporarily shifted for ghosts appearing in the channel without requiring re-initialization of the equalizer structure or re-calculation of the channel delay estimate. The system 1200 then proceeds to 1226.

Then, at 1226, ie SEGCNT = FSEG in "Update Correlation", the system controller is responsible for developing CDC 1100 to develop new values of FSCM (i) in Windows and _FS defined by WINSTART, WINEND, FSYM and FSEG. ). The correlation value FSCM (i) is updated with respect to the frame or field sync rate. As illustrated in FIG. 38A, the window W _FS with 2m + 1 samples initiates m symbol times prior to SC = FSYM and SEGCNT = FSEG. Typically the window W _FS is based on the first FSCM (i) value detected by the CDC 1100 above the threshold T _DET . Thus, subsequent correlation updates may ensure that P ₀ is not centered within W _FS . In other embodiments, P ₀ averages W _FS Allow W _FS to move over time to be centered within. Still other embodiments recenter W _FS such that the relative position of P ₀ moves over time. After the values of the updated FSCM (i) have been placed in the correlation buffer 514A, the controller 520 locates new positions of P ₀ , P ₁ and P _{2 in} the predefined regions R ₀ , R ₁ and R ₂ . do. The system 1200 then proceeds to 1228.

1228, that _{"P 0> P 2/2} " if at P0 ≤ P _2/2 (negative result), system 1200 continues to 1224. This forms a control loop to gradually adjust the VCXO timing and to cause P ₂ to move toward region R ₀ . Once P _0> P _2/2 a (a positive result), system 1200 proceeds di parting loops and the control is 1230.

1230, that is in the _{"P 0> 2P 1" P} 0> 2P ₁ if the system 1200 proceeds to 1238. Otherwise, if P ₀ ≦ 2P _{1, the} system 1200 enters 1232 to enter the VCXO slew control mode.

1232, ie VCXO _CONTROL = C ₃ F _LOW + F _OFFSET at "+ F _OFFSET ". The VCXO clock frequency increases and temporarily reduces the delay of the signal generation correlation P ₁ . This causes P ₁ to move towards the R ₀ region. Similarly, delay element 1132 maintains a value of F _LOW and C ₃ · F _LOW preserves the VCXO low frequency offset from the transmitter time base. However, the timing of the timing pulses (frame sync / segment sync) used to derive the equalizer coefficients remains the same. As a result, the virtual center temporarily moves relative to ghosts appearing on the channel without requiring re-initialization of the equalizer structure or re-calculation of the channel delay.

Then at 1234, "Update Correlation", controller 520 configures CDC 1100 to develop new values of FSCM (i) similar to "Update Correlation" 1236. Controller 520 searches correlation buffer 514A to locate P ₀ , P ₁ and P ₂ at W _FS .

1236, that is, if at _{"P 0> 3P 1" P} 0 ≤ 3P 1 ( negative result), system 1200 continues to 1232. This forms a loop for gradually adjusting the VCXO timing and allowing P ₁ to move toward the region R ₀ . However, once P ₀ > 3P ₁ (positive result at 1236), system 1200 deflects from the loop and returns to 1222.

At 1238, ie "CWFOUT", controller 520 de-asserts SLEW ENABLE and VCXO _CONTROL = C ₃ [(C ₁ + C ₂ ) CWF _OUT + F _LOW ].

At 1240, ie, "Update Correlation", system 1100 develops new values of FSCM (i) corresponding to Windows and _FS . Controller 520 searches correlation buffer 514A to update P ₀ , P ₁ and P ₂ as found in R ₀ , R ₁ and R ₂ . Delay element 1132 updates F _LOW = CWF _OUT C ₁ + F _LOW . The system 1200 then returns to 1222. In some embodiments, one or more of decision blocks 1212, 1218, 1222, 1228, 1230, and 1236 may have several types of confidence counters used to condition the crystal transitions.

Another embodiment of a system 20 suitable for ATSC standard broadcasting, such as the CDC 1250 of FIG. 41, includes a CDEU 230A, a centroid weighting function 1102, a switch 1104, 1106, 1108, a filter. 1110, adder 1120, and correlation buffer 1134.

Similar to the CDEU 230A of FIG. 6, the system 1250 receives filtered baseband signals I _F 76 as input to the correlator 310. Although not shown, some embodiments of system 1250 are similar to CDEU 230B and calculate the magnitude of the correlation of the segment sync sequence with I _F 76 and Q _F 78 as described above. In some embodiments similar to the CDC 1100, the system 1250 accepts a 2X over-sampled representation of I _F and Q _F. In other embodiments, system 1250 is adapted to receive a symbol rate representation of IF and QF. Another embodiment of system 1250 includes another over-sampled representation of I _F 76 and Q _F 78.

As illustrated in FIG. 41, the correlator 310 operates in conjunction with I _F 76 to produce a symbol correlation value SCV (i). Integrator 312 receives SCV (i) and generates INT (i) that is stored in memory location M (i) of correlation buffer 314. However, as described below, the above-described embodiments of the CDEU 230A compute symbol sync correlation over N segment sync periods to develop a channel delay estimate, while the system 1250 continues to have a correlation buffer ( Update the correlation values INT (i) stored in 314. This allows for continuous updates to the correlation directed control signal 1252, which is also referred to VCXO _CONTROL signal 1252 hereinafter. The correlation filter 1134 low pass filters the values of INT (i) received from the correlation buffer 314. Some embodiments of the system 1250 similar to the CDEU 230B of FIG. 13 calculate MAG (i) prior to the low pass filtering operation. In some embodiments, MAG (I) = | INT (i) | In some embodiments of system 1250, MAG (i) = INT (i) ² . If both I _F 76 and Q _F 78 are processed, MAG (i) = │INT _I (i) │ + │INT _Q (i) │ or MAG (I) = [INTI (i) ² + INT _Q (i) ² ]. Still other embodiments of 1250, not shown, do not include correlation filter 1134 and rely on integrator 314 to provide the necessary temporary filtering.

The centroid weighting function 1102 is scaled to receive the appropriate number of samples produced by the correlation filter 1134. By way of example, in some embodiments, the centroid function 1102 is scaled to receive 1664 samples. Still other embodiments include 832 samples. Controller 320 interacts with memory 330 and receives values of SC and SEGCNT from symbol counter 316 and segment counter 318, respectively. Similar to the controller 320 of FIG. 6, the controller 320 interacts with the control system 54 (see FIG. 3). Controller 320 further includes interfaces to elements of system 1250 that are not shown but are required for configuration and control.

Similar to the CDEU 230A of FIG. 6, the system 1250 detects the location of segment sinks present in the received signals and determines a CIR estimate. The channel delay is estimated from the CIR estimate and used to position the virtual center of the overlapped equalizer. Similar to controller 520 of CDC 1100 of FIG. 37, controller 320 searches correlation buffer 314 to locate P ₀ corresponding to the maximum value of MAG (i). Controller 320 centers region R ₀ with respect to P ₀ . The controller 320 then searches the correlation buffer 314 to find the local maximum values P ₁ and P ₂ of MAG (i) in the regions R ₁ and R ₂ , respectively. As shown in FIG. 38A, P ₀ , P ₁ and P ₂ are defined as ghost signals having the maximum correlation value and power in the respective regions R ₀ , R ₁ and R ₂ . P ₀ , P ₁ and P ₂ are located at I ₀ , I ₁ and I ₂ , respectively. In some embodiments, R ₀ , R _1, and R ₂ span the entire segment sink period. In other embodiments, R ₀ , R ₁ and R ₂ span only a portion of the segment sync period.

The correlation filter 1134 low pass filters the MAG (i) values provided to the CWF 1102. In some embodiments, CWF 1102 only uses values of P ₀ , P ₁ and P ₂ ; CWF 1102 outputs:

Has

In other embodiments, CWF 1102 calculates a weighted average of all ghosts in regions R ₀ , R _1, and R ₂ :

Similar to the CDC 1100 of FIG. 37, some embodiments of the CDC 1250 have a windowing function F _CW (i) similar to the discrete linear ramp function of FIG. 38B that is appropriate for the appropriate sampling rate. Other embodiments of F _CW (i) are geometric functions defined to have zero values outside of regions R ₀ , R ₁ and R ₂ . Some embodiments of the CDC 1250 include an F _CW (i) based on a windowed sine function suitable for a sampling rate similar to that of FIG. 38C.

Otherwise, system 1250 operates substantially similar to CDC 1100 to generate the correlation directed control signal VCXO _CONTROL at the output of adder 1120. The centroid weighting function 1102 provides its output as the first input of the switch 1104. The second input of the switch 1104 is digital zero. The first input to switch 1106 is digital zero. The second input of the switch 1106 is the signal SLEW from the switch 1108. Switch 1108 accepts offset values + F _OFFSET 1116 and -F _OFFSET 1118. Similar to controller 520 of CDC 1100, controller 320 provides SLEW CONTROL signal 1114 to switch 1108, and the + F _OFFSET 1116 and -F _OFFSET 1118 as described below. By slewing the output of the correlation directed control signal 125. The switch 1104 provides an output to the filter 1110. Filter 1110 and switch 1106 provide inputs to adder 1120. The output of adder 1120 is correlation directed control signal VCXO _CONTROL 1252.

Similar to the CDC 1100 of FIG. 37, the switches 1104 and 1106 form a double-pole double-throw configuration. If controller 320 does not assert SLEW ENABLE 1112, the output of adder 1120 is VCXO _CONTROL = C ₃ [(C ₁ + C ₂ ) CWF _OUT + F _LOW ], where F _LOW is the delay. The low frequency offset of the system stored in element 1132. The transfer function of the filter 1110 is H (z) = C ₃ [C ₁ (1 + Z ^-1 ) + C ₂ ].

When the SLEW ENABLE signal 1112 is functioning, the output of the adder 1120 is VCXO _CONTROL = C ₃ F _LOW + SLEW, where SLEW is + F _OFFSET or -F _OFFSET . The output FLOW of delay element 1132 remains constant while the SLEW ENABLE signal 1112 is asserted. This preserves the low frequency offset information until the signal 1112 is asserted, allowing normal operation of the filter 1110 to resume. In some embodiments, F _OFFSET may be dynamically increased by the integrator of controller 520 if it is determined that a larger value is required. In other embodiments, there is a limitation with the integrator to keep F _OFFSET below the maximum value.

Another embodiment of the system 1250 will now be described with reference to the elements of FIG. 41, such as the system 1300 illustrated in FIG. 42 and suitable for ATSC broadcast and symbol sampling rates. At 1302, "Initialization", controller 320 initializes the elements of system 1250. For example, the controller 320 may include registers of the memory 330, a symbol counter 316, a segment counter 318, a size calculator 392, a correlator 310, a correlation buffer 314, and a CWF ( 1102, filter 1110, correlation filter 1134 and various control signals are initialized. In addition, SC, SEGCNT and index variable i are initialized. After initialization of system 1300, operation proceeds to 1304.

Similar to the system 400 of FIG. 12 at 1304, i.e., "SCV", the correlator 310 accepts a new symbol time of data from the filtered in-phase baseband signal I _F 76 and generates a symbol counter ( The value of SCV (i) corresponding to the symbol count generated by 316 is calculated. System 1304 transitions to 1306.

Similar to the CDEU 230A at 1306, ie, "Integration", the integrator 312 receives the SCV (i) from the correlator 310 and stores the INT ( Calculate the value of i). The system 1300 then proceeds to 1308.

At 1308, ie “SC = 831”, similar to 410 of the system 400 of FIG. 12, the controller 320 determines whether the SC is equal to the maximum output of the symbol counter 316. By way of example, if the SC has a range from 0 to 831, a positive result occurs when SC = 831 and the system 1300 transitions to 1312. Otherwise, if a negative result occurs at 1308, the system 1300 transitions to 1310 such that the symbol counter 316 increments the value of the SC and the controller 320 increments the index variable i. Control then returns to 1304.

At 1312, i.e., " SEGCNT &lt; N &quot;, the controller 320 compares the output SEGCNT of the segment counter 318 with the value N stored in the segment count register 338. If SEGCNT <N, controller 320 branches system 1300 operation to 1314, symbol counter 316 sets SC = 0 and segment counter 318 increments SEGCNT. However, if SEGCNT = N, system 1300 operation transitions to 1316.

At 1316, "Find Regional Maximums", similar to 1216 of system 1200 of FIG. 40, controller 320 defines regions R ₀ , R _1, and R ₂ . Controller 320 then searches regions R ₁ and R ₂ , respectively, to locate P ₁ and P ₂ . In some embodiments, controller 320 inter-operates with the centroid estimator shown as centroid estimator 340 of FIG. 41 to determine an appropriate CDE value.

1318, that is, if at _{"P 0> 4P 1" P} 0> 4P 1, system 1300 continues to 1322. Otherwise, system 1300 continues to 1320.

At 1320, ie “Select New P ₀ ” similar to 1220 of system 1200 of FIG. 40, controller 320 selects P ₁ as the new P ₀ . In some cases, this results in P ₀ which does not correspond to the maximum value of MAG (i) of correlation buffer 314. Following this selection, the controller 320 redefines the regions R ₀ , R ₁ and R ₂ based on the location of the new P ₀ . Controller 320 then searches regions R ₁ and R ₂ , respectively, to locate P ₁ and P ₂ . Finally, system 1300 continues to 1324. 1322, that is in the _{"P 0> P 2/9} " is similar to the system 1200 of FIG. _{40, P 0 ≤ P 2/} 9 of the case takes place a negative result, the system 1300 includes a VCXO slew control by continuing to 1322 Enter the loop. Otherwise, if P _0> P _2/9 occurs a positive result, the system 1300 to continue in 1330.

At 1324, ie “-F _OFFSET ” similar to 1224 of system 1200 of FIG. 40, controller 320 asserts signal SLEW ENABLE 1112. This causes the output of adder 1120 to provide VCXO _CONTROL = C ₃ F _LOW -F _OFFSET . Thus, similar to the CDC 1100, the delay element 1132 preserves the low frequency offset F _LOW of the filter 1110. At 1326, "Update Correlation", system 1300 updates the correlation values stored in correlation buffer 314. In some embodiments, system 1250 integrates SCV (i) values generated during the most recent segment sync period. In other embodiments, system 1250 re-initializes portions of 230A and develops a new set of INT (i) and MAG (i) over multiple segment sink periods. The controller 320 searches the correlation buffer 314 to locate the updated P ₀ , P ₁ and P ₂ that fall within the windows created by the existing R ₀ , R ₁ and R ₂ . Correlation filter 1134 receives the updated correlation buffer 314 output and provides updated low pass filtered MAG (i) to CWF 1102. The CWF 1102 then calculates the updated CWF _OUT . As described above, some embodiments of system 1250 use only updated P ₀ , P ₁ and P ₂ to generate an updated CWF _OUT . However, similar to the CDC 1100, some embodiments of the system 1250 move regions R ₀ , R ₁ and R ₂ in response to a change in the location of P ₀ .

In 1328, that is, _{"P 0> P 2/2} ", a negative result occurs when the P ₀ ≤ P _2/2, the system 1300 is held by going back to 1324 from the VCXO slew control loop. This forms a loop for gradually adjusting the VCXO _CONTROL . If P0> P2 / 2, a positive result occurs: the system 1300 departs from the VCXO slew control loop; Eventually system 1300 continues to 1330.

1330, that is in the "P _0> 2P _1" occurs and a positive result if P _0> 2P _1, system 1300 proceeds to 1338. Otherwise, a negative result occurs when P ₀ ≦ 2P ₁ , and the system 1300 enters the VCXO slew control loop by proceeding to 1332.

At 1332, ie, “+ F _OFFSET ” similar to system 1200, control 320 asserts signal SLEW ENABLE 1112 and selects SLEW = + F _OFFSET . Similar to system 1100, output 1252 of adder 1120 is VCXO _CONTROL = C ₃ F _LOW + F _OFFSET , where delay element 1132 sets the low frequency offset F _LOW of filter 1110. Preserve

Then at 1334, ie “Update Correlation,” system 1300 updates the correlation values stored in correlation buffer 314, similar to the operations described above in 1326. The values of INT (i) generated during the most recent segment sync period are updated. The correlator 320 searches the correlation buffer 314 to locate the updated P ₀ , P ₁ and P ₂ that fall within the search window generated by the existing R ₀ , R ₁ and R ₂ . As illustrated in FIG. 41, correlation filter 1134 receives the updated correlation buffer 314 output and provides the updated low pass filtered INT (i) to CWF 1102. The CWF 1102 then calculates the updated CWF _OUT . System 1300 proceeds to 1336.

At 1336, “P ₀ > 3P ₁ ”, a negative result occurs when P ₀ ≦ 3P ₁ , and the system 1300 continues in the VCXO slew control loop by returning to 1332. This forms a loop for gradually adjusting the VCXO _CONTROL . If P ₀ > 3P ₁ a positive result occurs, so system 1300 departs from the VCXO slew control loop and system 1300 returns to 1322.

At 1338, ie, "CWF _OUT ", after a positive result at 1330, controller 320 sets slew control signal 1112 to pass CWF _OUT through switch 1104 and zero through switch 1106. do. CWF _OUT is passed to filter 1110. Adder 1130 forms an output VCXO _CONTROL = C ₃ [(C ₁ + C ₂ ) CWF _OUT + F _LOW ], where as described above, F _LOW is a value stored in delay element 1132. Thereafter, the system 1338 proceeds to 1340. At 1340, "Update Correlation", system 1250 updates the correlation values stored in correlation buffer 314 as described above. The controller 320 searches the correlation buffer 314 for updated values of P ₀ , P ₁ and P _{2 in} the predefined regions R ₀ , R ₁ and R ₂ . Delay element 1132 updates F _LOW = CWF _OUT C ₁ + F _LOW . The system 1300 then returns to 1322. In some embodiments, one or more of decision blocks 1312, 1318, 1322, 1328, 1330, and 1336 may have some type of confidence counter used to condition the crystal transitions. As illustrated in FIG. 43, another embodiment of the system 20 includes a correlation oriented carrier tracking system 1350. The correlation oriented carrier tracking system 1350 includes a demodulator 920A and a correlation oriented control 1250A. Demodulator 920A is similar in form and function to demodulator 920 of system 900; However, loop filter 926 is replaced with loop filter 926A. As described below, loop filter 926A further includes a third feedback control input 1252A for receiving a correlation directed tracking signal. The correlation oriented control unit 1250A is similar in form and function to the correlation oriented control unit 1250; However, similar to the CDEU 230B of FIG. 13, the CDC 1250A is adapted to correlate both the segment sync sequence with the I _F 76 and the Q _F 78.

Demodulator 920A receives digitized near baseband signal 62 and provides signals I _F 76 and Q _F 78 as outputs to CDC 1250A. Demodulator 920A also receives a non-coherent carrier tracking feedback signal 72 and a decision directed carrier tracking feedback signal 74. In addition, demodulator 920A further receives correlation directed carrier tracking signal 1252A from CDC 1250A.

As illustrated in FIG. 44, another embodiment of the system 20 includes a channel delay orientation including a tuner 910, a demodulator 920, a CDEU 230E, a subtractor 1360, and a delay 1136. Control system 1360.

CIR directed control system 1360 receives analog near baseband signal 60 at tuner 910. The tuner 920 digitizes the analog near baseband signal 60 and provides the digitized near baseband signal 62 to the demodulator 920. Demodulator 390 demodulates digitized near baseband signal 62 and provides I _F 76 and Q _F 78 as inputs to CDEU 230E. CDEU 230E works in conjunction with I _F 76 and Q _F 78 to calculate the updated channel delay estimate CDE _NEW . CDEU 230E then provides CDE _NEW as input to positive input and delay unit 1362 of subtractor 1360. Delay 1136 provides as output the pre-calculated value CDE _PREVIOUS of the channel delay estimate to the negative input of subtractor 1360. The tuner 40 receives the tuning control signal 1164 from the subtractor 1360.

Similar to the embodiments described above of the CDEU 230, the CDEU 230E estimates the channel impulse response of the transport channel by detecting the correlation strength and delay of the ghost signals received at the input of the CDEU 230E. Some embodiments of the CDEU 230E are similar in form and function to the above-described embodiments of the CDEU 230. By way of example, some embodiments of the CDEU 230E are arranged to estimate the channel delay in an ATSC broadcast system by detecting the correlation strength PN511 of the received ghost signal frame sync sequence. Similarly, other embodiments of the CDEU 230E are similar to the embodiments of the CDEU 230 that estimate the channel delay based on the correlation of the segment sync. However, the CDEU 230E is adapted to provide continuously updated channel delay estimates. By way of example, some embodiments of the CDEU 230E provide a single channel delay estimate used to set up and optimize the overlapped equalizer, while embodiments of the CDEU 230E provide successive channel delay estimate updates. do. Some embodiments of the CDEU 230E provide an updated channel delay estimate for every frame or field sync period. Other embodiments of estimating channel delay based on acceptance of segment sync sequences provide an updated channel delay estimate after a desired number of segment sync periods. Still further embodiments provide an updated channel delay estimate for every segment sync period.

In some embodiments delay 1136 is a latch or register used to store a precalculated channel delay estimate provided by CDEU 230E. The subtractor 1360 generates the tuning control signal ₁₂₆₄ by subtracting the CDE _PREVIOUS from the CDE _NEW . The tuning control signal 1164 represents a change in the channel delay estimate due to the movement of the virtual center. The tuner 910 receives the control signal 1164 and controls the clock frequency used to sample the analog near baseband signal 60. This adjusts the relative delay introduced into the equalizer of the system 20 and compensates for movement in the virtual center. It should be understood that the lengths of the quadrant and strain filter instruments are optimized for the total feedback loop response. By way of example, in an embodiment where the modifying filter performing a 90 degree rotation is a Hilbert filter operating in conjunction with the received in-phase signal, the length of the Hilbert filter will be adjusted to optimize the phase tracker loop response. Similarly, analysis of Hilbert deformations can be optimized for the complexity of the hardware and the required accuracy. Similarly, the phase error integrator 812 may be optimized to balance the phase tracker bandwidth with the need for more desired and more accurate phase error information.

Alternatively, in some embodiments with partially spaced equalizers, the point at which data is downsampled prior to the equalizer determination device may be moved to provide greater control loop bandwidth. As illustrated in FIG. 29, in some embodiments of the system 900, the carrier tracking post filter 944 receives samples partially spaced from the FFE 210 prior to down sampling. Decision device 212 effectively downsamples the received data by sampling the equalizer output signal 88 in relation to the symbol timing basis. In another embodiment, if the partially spaced FFE samples are not related in an integer relationship of N: 1, the inputs to the equalizer determining device is the sample rate that is converted to the appropriate sample rate. Some embodiments employ similar techniques for decision directed phase tracker and decision directed tuning feedback loops. Additionally, certain embodiments employ sample rate converters to down sample the output of partially spaced FFEs and perform a phase tracker function.

It should be understood that the techniques and devices described herein may be applied to modulation techniques with one-dimensional constellation. Thus, the present invention includes embodiments that are modified to operate with data constellations having multiple levels. Similarly, if the simple 90 degree phase shift is sufficient to convert the Offset QAM baseband complex signal to only a real VSB baseband signal, the techniques and devices described herein may be based on VSB or Offset for Offset QAM modulation. It can be applied to modulation of QAM.

Furthermore, any of the systems and / or methods described herein are applicable to any broadcast standard. For example, the systems and methods herein are described in "ATSC Digital Television Standard", ATSC Doc. Available with signals compliant with ATSC as specified in A / 53, September 16, 1995. By way of example only and not by way of limitation, any of the systems and / or methods described herein are described in Zhang, W, et. al is available with signals that conform to the standards specified in the "An Advanced Digital Television Broadcasting System" Supplement to Proceedings 7th International Symposium on Broadcasting Technology, 2001 (hereafter referred to as the "ADTB-T standard").

In some embodiments, it should be understood that the equalizer works with respect to the in-phase and quarter period data. Similarly, embodiments and figures herein represent an FFE of an equalizer located in the baseband region of the receiver, while other embodiments of the receiver place the FFE in a passband or IF region. By way of example, in some embodiments, an FFE of an equalizer is disposed between the tuner component and the demodulator component of the system.

Variations in the implementation of the invention will occur in the art. By way of example, some or all of the generation and calculations of the signals may be performed by a specific-application and / or general purpose integrated circuit and / or by separate components and / or in software. All publications, previous applications, and other documents mentioned herein are incorporated by reference in their entirety as if each were individually cited and listed as a whole.

While the invention has been illustrated and described in detail in the drawings and above description, it should be considered that the features are illustrative only and not intended to be limiting, and only preferred embodiments are shown and described, and are within the spirit of the invention. It should be understood that all variations and modifications should be protected.

Claims (97)

An equalizer comprising a feedforward filter, The feedforward filter includes a plurality of feedforward filter tabs, coefficients are associated with the plurality of forward filter tabs, and values of all coefficients associated with the plurality of feedforward filter tabs are dynamically determined. Equalizer. The method of claim 1, And the value of the coefficients is determined dynamically in response to reception by a feedforward filter of samples developed from the received signal. The method of claim 1, And the value of at least a portion of the coefficients is determined dynamically according to a least mean squared algorithm. The method of claim 1, At least a portion of the coefficients is dynamically determined according to a blind equalization technique. The method of claim 4, wherein The blind equalization technique uses a constant modulus algorithm. The method of claim 4, wherein Said blind equalization technique employs a reduced constellation algorithm. The method of claim 2, Wherein said feedforward filter operates in a training mode in which said received signal responds according to a predetermined transmitted signal. The method of claim 7, wherein And said predetermined transmitted signal is a synchronization signal. The method of claim 8, The synchronization signal comprises a segment sync sequence. The method of claim 8, And said synchronization signal comprises at least a portion of a field sync sequence. The method of claim 8, And the synchronization signal comprises at least a portion of a frame sync sequence. The method of claim 7, wherein And the coefficients are determined dynamically in training mode. The method of claim 1, A filter delay is associated with the feedforward filter, and the filter delay is determined according to the characteristics of the channel. The method of claim 13, Wherein said characteristic is a channel impulse response. The method of claim 13, The characteristic is a channel delay. The method of claim 13, And said filter delay is varied in response to a change in said characteristic. The method of claim 16, The characteristic of the channel is a channel impulse response. The method of claim 16, The channel characteristic is a channel delay. The method of claim 16, The characteristic of the channel is intersymbol interference. The method of claim 13, The equalizer is reinitialized according to the filter delay. The method of claim 13, The feedforward filter is reinitialized according to the filter delay. The method of claim 1, At least a portion of said coefficients is complex valued and has a non-zero imaginary component. The method of claim 1, The magnitude of the coefficients is adjusted regularly by a controlled amount. The method of claim 23, wherein And said controlled amount varies upon operation of said equalizer. The method of claim 23, wherein The controlled amount is equal for all coefficients associated with the feedforward filter tap. The method of claim 23, wherein And said controlled amount varies with the magnitude of said coefficient. The method of claim 23, wherein A tap index is associated with the plurality of feedforward filter taps, and the controlled amount is varied according to a tap index associated with the feedforward filter tap with associated coefficients. The method of claim 1, Wherein said equalizer is adapted to receive an ATSC compliant signal. The method of claim 1, Wherein said equalizer is adapted to receive an ADTB-T compliant signal. In the equalizer, A feedforward filter, the feedforward filter including a plurality of feedforward filter tabs, coefficients associated with the plurality of feedforward filter tabs; A decision feedback equalizer (DFE); And the values of all the coefficients associated with the plurality of feedforward filter taps are dynamically determined. The method of claim 30, The DFE comprises a plurality of DFE taps, coefficients associated with the plurality of DFE taps, and values of the coefficients of the DFE tap and the feedforward filter tap are jointly optimized. The method of claim 30, A filter delay is associated with the feedforward filter, and the filter delay is determined according to the characteristics of the channel. The method of claim 32, Wherein said characteristic is a channel impulse response. The method of claim 32, The characteristic is a channel delay. The method of claim 32, And said filter delay is varied in response to a change in characteristics of said channel. 36. The method of claim 35 wherein The characteristic of the channel is a channel impulse response. 36. The method of claim 35 wherein The channel characteristic is a channel delay. 36. The method of claim 35 wherein And the characteristic of the channel is intersymbol interference. The method of claim 32, The equalizer is reinitialized according to the filter delay. The method of claim 32, The feedforward filter is reinitialized according to the filter delay. The method of claim 32, And a symbol estimate stream is provided to the DFE, the symbol estimate stream being temporarily aligned with the filter delay. 42. The method of claim 41 wherein And the symbol estimate stream is developed by a determining device. The method of claim 42, And the determining device comprises a slicer. The method of claim 42, The determining device comprises a trellis decoder. The method of claim 44, The trellis decoder uses a Viterbi algorithm. The method of claim 30, Wherein the value of at least a portion of the coefficients is plural and has a nonzero imaginary component. The method of claim 30, Wherein at least one magnitude of the coefficients of the DFE taps is limited to a limit. The method of claim 47, The magnitude of all coefficients of the DFE taps is limited to a certain limit. The method of claim 47, Wherein the magnitude of two or more coefficients of the DFE taps is limited to the same limit. The method of claim 47, The limit is adjusted according to the characteristics of the DFE tap with which the coefficient is associated. The method of claim 47, A tap index is associated with the plurality of DFE taps, and the limit is varied according to the tap index of the DFE tap with which the coefficient is linked. The method of claim 47, The magnitude of the coefficients associated with the group of DFE taps is limited to a range of values. The method of claim 52, wherein A tap index is associated with the plurality of DFE taps, and the membership of the DFE taps in the group is defined according to the tap index of the DFE tap. The method of claim 47, Equalizer characterized in that the magnitude of one or more coefficients associated with the DFE tap is limited to be lower than the limit. The method of claim 30, The magnitude of the coefficients is adjusted regularly by a controlled amount. The method of claim 55, And said controlled amount varies upon operation of said equalizer. The method of claim 55, And said controlled amount is equal for all coefficients associated with said feedforward filter tap. The method of claim 55, The controlled amount is equal for all coefficients associated with the DFE tap. The method of claim 55, And said controlled amount varies in accordance with a characteristic of said coefficient. The method of claim 59, The characteristic of the coefficient is the magnitude of the coefficient. The method of claim 55, A tap index is associated with the plurality of feedforward filter taps, and the controlled amount is varied according to a tap index associated with the feedforward filter tap with which the coefficient is associated. The method of claim 55, A tap index is associated with the plurality of DFE taps, and the controlled amount is varied according to a tap index associated with the DFE tap with which the coefficient is associated. The method of claim 30, Wherein said equalizer is adapted to receive an ATSC compliant signal. The method of claim 30, Wherein said equalizer is adapted to receive an ADTB-T compliant signal. A method for developing an equalized value from a sample of a signal received from a channel, the method comprising: Associating a plurality of taps and coefficients of the feedforward filter; Developing a series of feedforward filtering values from the sample according to the coefficients; And  Dynamically determining the value of all coefficients. 66. The method of claim 65, Said determining step determines values of all coefficients according to samples of a received signal. The method of claim 66, wherein Said determining step determines values of all coefficients according to samples of said received signal, said received signal responsive to transmission of a predetermined symbol sequence. The method of claim 66, wherein Calculating a filter delay associated with said feedforward filter, wherein said calculating uses characteristics of a channel. The method of claim 68, wherein And the characteristic of the channel is a channel delay. 66. The method of claim 65, And regularly adjusting the magnitude of the coefficients by a controlled amount. 66. The method of claim 65, And the signal received from the channel is an ATSC compliant signal. 66. The method of claim 65, The signal received from the channel is an ADTB-T compliant signal. A method for developing an equalized value from a sample of a signal received from a channel, the method comprising: Associating a plurality of taps and coefficients of the feedforward filter; Developing a stream of feedforward filtering values from the sample according to the coefficients; Generating a stream of decision feedback equalizing values from the stream of feedforward filtering values; And Dynamically determining the value of all coefficients. The method of claim 73, wherein Wherein said generating comprises associating coefficients with a tap of a decision feedback equalizer (DFE). The method of claim 73, wherein Calculating a filter delay associated with said field forward filter, wherein said calculating uses characteristics of a channel. 76. The method of claim 75 wherein Developing the stream of feedforward filtering values comprises developing a stream of symbol estimates. 77. The method of claim 76, Developing the stream of symbol estimates using a decision device. 76. The method of claim 75 wherein Developing the stream of symbol estimates is temporarily aligned with the filter delay to estimate. The method of claim 74, wherein Limiting the magnitude of the coefficients associated with the tap of the DFE to a limit. The method of claim 74, wherein And regularly decreasing the magnitude of the coefficients by a controlled amount. The method of claim 73, wherein And the signal received from the channel is an ATSC compliant signal. The method of claim 73, wherein The signal received from the channel is an ADTB-T compliant signal. A computer readable medium for developing an equalized value from a sample of a signal received from a channel, the method comprising: Programming to implement a first routine and a second routine, The first routine implements a feedforward filter, coefficients are associated with a plurality of taps of the feedforward filter, and a series of feedforward filtering values is developed from the sample according to the coefficients; And said second routine dynamically determines the value of all coefficients. 84. The method of claim 83 wherein And another routine for calculating a filter delay associated with the feedforward filter, wherein the filter delay is calculated using characteristics of the channel. 87. The method of claim 84, And another routine for regularly adjusting the magnitude of one or more coefficients by a controlled amount. 84. The method of claim 83 wherein And the signal received from the channel is an ATSC compliant signal. 84. The method of claim 83 wherein And the signal received from the channel is an ADTB-T compliant signal. A computer readable medium for developing an equalized value from a sample of a signal received from a channel, the method comprising: Programming to implement a first routine, a second routine, and a third routine, The first routine implements a feedforward filter, coefficients are associated with a plurality of taps of the feedforward filter, and a stream of feedforward filtering values is developed from the sample according to the coefficients; The second routine implements a decision feedback equalizer (DFE) that develops a stream of decision feedback equalizing values; And said third routine dynamically determines the value of all coefficients. 89. The method of claim 88 wherein And said second routine comprises another routine for associating coefficients with taps of said DFE. 92. The method of claim 89, And another routine for calculating a filter delay of the feedforward filter from the characteristics of the channel. 92. The method of claim 90, And another routine for developing a stream of symbol estimates from the stream of feedforward filtering values. 92. The method of claim 91 wherein And the routine for developing the stream of symbol estimates implements a determining device. 92. The method of claim 91 wherein And the output of the routine for developing the stream of symbol estimates is temporarily aligned with the filter delay. 92. The method of claim 89, And another routine for limiting the magnitude of a coefficient associated with one or more taps of the DFE to a limit. 92. The method of claim 89, And another routine for regularly adjusting the magnitude of one or more coefficients by a controlled amount. 89. The method of claim 88 wherein And the signal received from the channel is an ATSC compliant signal. 89. The method of claim 88 wherein The signal received from the channel is an ADTB-T compliant signal.

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