CN1162891A - Filter in digital timing recovery system - Google Patents

Abstract

Timing recovery system receives signals representing continuous symbol of multi-symbol rate form transmitter, and derives sampling signal from the input signal and uses an oscillator of single fixed-frequency. Sample source 10 is sampled in fixed frequency. Interpolator 12 receives sample generated by source response control signal and which is obtained in a period of time synchronous to transmitter continuous symbol. A phase error detector 16 receives phase error between sampling time detected by interpolator and continuous symbol time, and provides phase error signal to an input terminal of an adder, and standard delaying signal source 31 is connected to another input terminal. NC-delayer 34 to 36 generate interpolator control signal. And interpolator output signal is processed by a non-adaptive pulse shaping filter 14.

Description

Filter in the digital timing recovery system

The present invention relates to digital information processing system, relate in particular to a kind of timing recovery system that is suitable for being used in such as in the digital signal receiver of TV-signal receiver one class.

Generally require to realize three kinds of functions from containing the digital video and for information about the restore data that transmits on digital receiver: the timing of sign synchronization recovers, and carrier wave recovers (frequency demodulation) and balanced.Regularly recovering is a kind of receiver clock (time base) and synchronous process of transmitter clock of making.This signal that allows to receive is sampled with temporal optimum, to reduce the chance of the amplitude limit error appearance that is associated with the determination processing of received value of symbol.In some receiver, with the signal sampling of multiple to being received of transmitter symbol rate.For example, some receiver is with the signal sampling of transmitter symbol rate to receiving of twice.In any occasion, the sampling clock of receiver must with the transmitter symbol clock synchronization.

It is a kind of process that makes RF signal frequency displacement after frequency displacement is arrived than the Low Medium Frequency passband of receiving recover modulating baseband information with permission to base band that carrier wave recovers.Equilibrium is the process of compensation transmission channel to the interference of receiving signal.More particularly, equilibrium has been removed by transmission channel and has been disturbed caused intersymbol cross (talk) (ISI).ISI causes the value of given symbol to distort because of value of symbol former and subsequently.(MA has made detailed description to these functions and relevant function in USA) for Kluwer Academic Press, Boston in digital communication for Lee and Messerschnitt.

Existing receiver requires metastable sampling clock signal source to remain controlled, and it can be locked in the transmitter symbol clock like this.VCXO (VCXO) is generally used for this function.The clock signal that VCXO produces is stable, but controlled on narrower scope, so it can be locked to the transmitter symbol clock.Yet voltage controlled oscillator is a kind of analog component such as VCXO, so it is expensive, and is easy to shorten its life-span.In addition, if must be from different transmitters (such as the European satellite system) received signal with distinct symbols clock frequency, each such transmitter must have an independent VCXO, and this has further increased the cost of receiver.

Be necessary to provide a kind of symbol timing recovery system that can support more than one symbol rate.Also recognize and be necessary to provide a kind of like this timing recovery system, timing recovery system with known type, for example those systems that comprise a plurality of VCXO of corresponding each symbol rate of receiving compare, and it brings such as benefit on the performance of hardware requirement aspect and the superiority on the cost.

The purpose of this invention is to provide the filter in a kind of digital timing recovery system.According to principle of the present invention, the timing recovery system of digital signal receiver receives the signal of representing continuous symbol from transmitter.Interpolater responsive control signal that is coupled to symbolic source be used to produce with the sampling that obtains from the synchronous time of the continuous symbol of transmitter.The symbol of receiving presents multiple character rate.Corresponding to the interpolater output signal of timing recovery network output by fixing, a non-self-adapting pulse shaping filter filtering.More particularly, this system comprises the sampling source of representing received signal, and sampling obtains with fixed frequency.An interpolater is coupled to sampling source and responsive control signal.This interpolater produce with the sampling that obtains from the synchronous time of the continuous symbol of transmitter.Before offering application network, these samples are by a fixing pulse shaping filter filtering.A phase error detector is coupled to interpolater, the phase error between the sample time of the transmitter synchronous sampling that the detection interpolater produces and the time of continuous transmitter symbol, and phase error signal is provided.Phase error signal is coupled to an input of adder, and the standard delay signal source is coupled to another input.The response of numerical control delayer produces the interpolater control signal from the signal of adder.

Disclosedly begin with the signal sampling of fixed frequency receiving a little more than the twice of the required transmitter symbol rate of maximum according to timing recovery system of the present invention.Handle the signal of this initial sample to produce and the synchronous sampled sequence of transmitter symbol rate by interpolater then.These synchronous sampling offer digital phase error detector.The output of digital phase error detector offers second-order loop filter.A predetermined value representing the required standard sample time to postpone is added on the output signal of loop filter.The Combination Control of preassigned delay and loop filter output signal provides the numerical control delayer of integer and mark clock delay component signal.The integer part of clock delay component signal is used to control the generation with the synchronous receiver sampling clock signal of transmitter symbol rate.Can on frequency, further divide this sampling clock signal so that the receiver symbol clock signal to be provided.The fractional part that postpones component is applied to the control input end of interpolater, thereby the sampled signal that interpolater produces representative is in the value of receiving signal in required sample time.The sampled signal of this generation is by this fixed pulse shaping filter filtering.

Support variable symbol rate regularly to recover valuably according to timing recovery system of the present invention and need not to utilize as the symbol timing base or utilize a plurality of simulation VCXOs of Via Adaptive Pulse Shaping filter.Allow to select the required receiver sampling rate of any half less than the initial sample rate according to timing recovery system of the present invention.With the relevant problem of a plurality of particular crystal oscillators of utilizing sef-adapting filter and special symbol rate, such as increasing hardware complexity and cost, capture time depends on that crystal oscillator frequency can be transferred to how soon to wait and is avoided.Useful is that disclosed digital system allows to utilize single fixing oscillator to carry out the function of VCXO.

For with the transmitter symbol rate of twice receiver, be lower than half any transmitter symbol rate of initial fixation sampling rate according to system of the present invention support to the input signal sampling.Be easy to obtain desired frequency accuracy with the crystal that can buy, this be because the capture range of being tested greater than+/-1000ppm.This system has been carried out test and shown promptly obtaining to timely lock, even when the timing slip of 1000ppm is arranged, represented trooping after 500 samples, and locked trooping after several thousand samples in short time span.Even feature performance benefit, adding up makes the present invention also very attractive under the situation that relates to the monadic symbols rate except that VCXO.

More particularly, disclosed system supports many symbol rates valuably, and is employed in European satellite is used such as those.In example discussed below, receiver is sampled to input signal with the twice of transmitter symbol rate.For example, proved that disclosed timing recovery system utilizes 62MHz initial sample clock frequency to support the symbol rate of per second 20,000,000 symbols (20M symbol/second) to 30M symbol/second.This has provided the ratio of 62/30 and 62/20 initial sample clock frequency and symbol clock frequency.In these expression formulas, molecule is initial sample rate (MHz), denominator is-symbol rate (M symbol/second).Therefore, be used to support the recovery of 20M symbol/second and 30M symbol/second symbol rate in this case from the single fixedly 62MHz initial sample clock frequency of single fixed crystal control generator.

In the accompanying drawing:

Fig. 1 is the block diagram that comprises according to the receiver input signal of the QPSK modulation of the timing recovery network of the principle of the invention;

Fig. 2 is the block diagram according to the symbol timing recovery system of the principle of the invention;

Fig. 3 is the more detailed block diagram that is used in the interpolater in Fig. 2 system; And

Fig. 4 is the more detailed block diagram that is used in the phase error detector in Fig. 2 system.

Fig. 1 is the receiver input signal that comprises according to the QPSK modulation of the timing recovery network of the principle of the invention, for example block diagram of direct broadcasting satellite receiver.Except unit 266 is according to the symbol timing recovery network of the present invention, the block diagram shown in Fig. 1 on the function and the configuration on be conventional.

Input (" input ") is coupled to the signal source (not shown) of modulated QPSK signal, such as antenna or cable link.This input (" input ") is coupled to input processor 262, processor 262 comprises an inputting channel tuner, some RF (radio frequency) amplifier, an IF (intermediate frequency) amplifier is converted to the mixer stage that is suitable for the further lower band of handling with being used for downwards with input signal, an automatic gain Control Network and an output analog-digital converter (ADC), they do not illustrate in the drawings but all are provided with in known manner.One can be that the fixed oscillator 261 of for example crystal oscillator provides fixed sampling frequency clock signal AD to ADC and other circuit unit (for example timing recovery network 266) in following mode in greater detail.

Contiguous baseband output signal from unit 262 is provided for according to timing recovery network 266 of the present invention.Timing recovery network 266 produces the sample that transmits and other timing signal of representative and transmitter symbol clock synchronization in the following mode of more describing in detail.In shown embodiment, every emission symbol produces two samples.Sampling and other timing signal that transmitter is synchronous are provided to carrier recovery network 264, this network 264 demodulates the signals to base band, and comprise equalizer, circulator, amplitude limiter and phase error detection network, and the phase controller that is used to control equalizer and circulator operation, all as is known.Before with Reed-Solomon EDC error detection and correction unit 276 EDC error detection and correction, from the demodulated baseband signal of carrier recovery unit 264 by 272 decodings of viterbi decoder unit and by deinterleave unit 274 deinterleaves.The function of these unit is described in the article of for example above-mentioned Lee and Messerschmitt.

From Reed-Solomon EDC error detection and correction unit 276 through the signal of error correction descrambling selectively in descrambling unit 278.Signal from descrambling unit 278 is provided to output processor 280, and processor 280 provides descrambling data is connected to the needed function of other signal shaping network.These functions comprise make the suitable logic level of data fit and clock signal is provided so that with the engaging of other network.Although mpeg compatible is optional in implementing system of the present invention, with the data that mpeg compatible transmission processor 282 is handled from output processor 280, this mpeg compatible transmission processor 282 provides the synchronous and error indication information that is used in the video data decompression.Transmission processor 282 is also according to the analysis of heading message mask data by type.The contract dateout of device 284 decompression from processors 282 of mpeg decompression is suitable for video encoding unit 286 for example with the video data such as the predetermined standard coding of NTSC or PAL one class to provide.Output signal from video encoding unit 286 is applied to video and the video-stream processor 288 that comprises the image display (not shown).

Systematic microprocessor 268 provides initiation parameter and other control signal corresponding units in the receiver in a known way, comprises timing recovery network 266.The special parameter and the control signal that are offered timing recovery network 266 by systematic microprocessor 268 will be described in more detail below.

Fig. 2 is the more detailed block diagram according to the symbol timing recovery system of the principle of the invention.In Fig. 2, with fine rule simulation or simple digital signal are shown, the complex digital signal of the reality (homophase) that comprises known way under and void (quadrature) component signal is shown with thick line.In symbol timing recovery system shown in Figure 2, useful feature comprise one allow the designer select less than the input sampling rate half any required symbol rate the standard delay register and utilize the possibility of the more accurate interpolater design that higher-order troops.Deriving symbol and sampling clock in the output that numerical control postpones operation allows signal do not needing to make it possible to valuably to do realize synchronous design fully under the situation of analog component of phase place and frequency lock.

In Fig. 2, representative is carried out initial sample and is converted to plural digital form by analog-digital converter (ADC) 10 (for the part of input processor 262 Fig. 1) from the input analog signal IN of the signal that transmitter is received.The initial fixation frequency sampling clock AD timing that ADC10 produces with fixed frequency crystal oscillator 261 (Fig. 1) this locality.Plural digital data stream from ADC10 is applied to the multiple interpolater 12 (following detailed description) of 4 taps, and interpolater 12 is also by initial fixation frequency sampling clock signal AD timing.Aforementioned interpolation functions is actually regularly regulatory function, is referred to as digital phase-shifting technique and sampling rate conversion sometimes.The output of interpolater 12 is the multiple sample flow that synchronously produce with fixed frequency sampling clock signal AD, it has passed through the shaping pulse filtering of fixing (non-self-adapting) recovering pulse shaping filter 14, and filter 14 responsive stationary frequency sampling clock signal AD and sampling clock allow signal (producing as described below).The output of filter 14 provides to the multiple sample flow of the filtering of other system unit shown in Figure 1.The output of interpolater 12 also is applied to phase error detector 16 (following detailed description).

Corresponding divider 20 and 22 are coupled in the output of phase error detector 16, and divider 20 and 22 is pressed barrel shifter in the embodiment shown and implemented.Filter loop integer constant Ki is applied to shift unit 20, and loop ratio constant K p is applied to shift unit 22.The value of loop integer constant Ki and loop ratio constant K p calculates and offers respectively divider 20 and 22 in a known way by systematic microprocessor 268 (Fig. 1).The first input end of adder 24 is coupled in the output of divider 20.Delay cell 26 is coupled in the output of adder 24, and second input of adder 24 and the first input end of adder 28 are coupled in the output of delay cell 26.From the signal of divider 20 in adder 24 with delay form addition from this signal of delayer 26.The output of divider 22 is coupled to second input of adder 28.From the signal of delay cell 26 in adder 28 with the output addition of divider 22.The output of adder 28 is anti-phase with unit gain by inverter module 30.First and second dividers 20 and 22, adder 24 and 28, delay cell 26 and inverter module 30 are combined and are formed a second-order loop filter.The output of inverter module 30 forms the output of loop filter.Poor between synchronous desirable sample time of interpolation time when this output representative produces from the sample of interpolater 12 and transmitter clock.

Standard delay register 31 receives represents time delay standard or desired of transmitter between the synchronous sample time from Fig. 1 systematic microprocessor 268.This standard delay value is calculated in the mode of describing in detail below by systematic microprocessor.In the embodiment shown, the signal of receiving to be doubling the speed sampling of symbol rate, so the standard delay between the sampled signal is half of desired interval between the symbol that sends.The first input end of adder 32 is coupled in the output of standard delay register 31.The output of loop filter in adder 32 with the addition of preassigned length of delay.From the output signal of adder 32 digital signals of transient delay value between the sample of representative and transmitter symbol clock synchronization.Outfit standard delay time register 31 is in order to allow the receiver timing loop initial near being similar to the incoming symbol rate, to catch with acceleration.The capture range of this system only is subjected to the restriction of phase error detector 16 characteristics.

Signal value from adder 32 is expressed by means of the fixed frequency clock periodicity, and comprises the integer part of representative sample whole fixed frequency clock umber of pulse between the time, and represents the fractional part in two sample times between the adjacent fixed frequency samples.In the embodiment shown, the digital signal from adder 32 is to have two highest significant positions that carry integer part and 22 fixing point digital signals of carrying the remaining bit of fractional part.Systematic microprocessor (Fig. 1) insertion in the following manner is worth in the standard delay register 31.At first standard delay register 31 will possess the signal of logic ' 1 ' value and insert wherein.This signal 20 positions that move to left then.This places logic ' 1 ' signal the least significant bit of integer part.This available following Digital Logic expression formula is represented:

1＜＜RS-IS (1) wherein RS be the standard delay register size, for example be 22 in the embodiment shown, IS is the size of integer part, for example is 2 in the present embodiment.This expression formula becomes in the embodiment shown:

1＜＜(22-2)??????????(2)

Then, calculated to determine the standard delay between the synchronous sample of transmitter by systematic microprocessor, the synchronous sample of transmitter is expressed as the fixed frequency clock periodicity:

D=FR/ (2S) (3) wherein D is the standard delay that is expressed as between the transmitter synchronizing symbol of fixed frequency clock periodicity, and FR is the fixed frequency clock frequency, and S is the transmitter symbol frequency.The former content combination of this result of calculation and standard delay register 31.In order to have inserted the value ' 1 ' in the standard delay register 31 with result's compensation of expression formula (1) and/or (2), must be from standard delay value D value of deducting 1 of equation (3) calculating.Therefore, description by the expression formula that systematic microprocessor (Fig. 1) is positioned over the standard delay value in the standard delay register 31 is:

DR31=(1＜＜(22-2)) (FR/ (2S)-1) (4) wherein DR31 is that systematic microprocessor is stored in the value in the standard delay register 31.

Be applied to an input of multiplexer 34 from the output signal of adder 32.Another input of multiplexer receives the value of typical value-1.Adder 36 receives first input from multiplexer 34 outputs.The output of adder 36 is coupled to the delay cell 38 as accumulator.Accumulator 38 is by fixed frequency sampling clock signal AD timing; Same clock signal drives ADC10.The output of delay cell 38 is representative digital signal MU to the time delay of next transmitter synchronized samples.Digital signal MU comprise represent fixed frequency clock signal AD up to the integer part of the periodicity of next transmitter synchronized samples and representative from the fractional part of last this fixed frequency clock signal up to the time delay of the time of transmitter synchronized samples.

In the embodiment shown, digital signal MU has two highest significant positions that carry integer part and 22 fixed point digital signals that carry the remaining bit of fractional part.The technical staff in digital operational circuit field will be understood that and can use different sizes and form.For example, in a QAM receiver, represent this time delay with 26 position digital signals.Time-delay signal MU is provided for integer part selector 40, and it selects two highest significant positions from signal MU (MU:0-1).Integer part offers comparison circuit 41, and this circuit with this integer and signal value of zero relatively and equals to produce a signal at 0 o'clock in integer part.Time-delay signal MU also offers fractional part selector 48, and fractional part selector 48 produces the signal of eight highest significant positions of the fractional part that contains signal MU (MU:2-9), the i.e. most significant byte of time inhibit signal MU fractional part.This fractional part most significant byte is coupled to the control input end of interpolater 12.22 complete bit time inhibit signal MU are coupled to second input of adder 36.

The output of comparator 41 is applied to the control input end and the delay cell 42 of multiplexer 34.Delay cell 42 provides the required delay of delay coupling between the corresponding output (following detailed description) that time-delay signal MU and phase detectors 16 response this time-delay signal MU are produced.The output of time delay unit 42 is that sampling clock allows signal, and is applied to the input of modulo-two counter 44 and the first input end of AND gate 46.The output of modulo-two counter 44 is coupled to second input of AND gate 46.The output of AND gate 46 produces symbol clock and allows signal.Modulo-two counter 44 for example comprises a D flip-flop and is removed by 2 in this example.This computing is used in the application that two samples of every symbol are provided.In other was used, such as the occasion of four samples of the every symbol of utilization, counter 44 can be mould 4 counters, and has the function divided by 4.

During work, the frequency of fixed frequency sampling clock AD is a little more than the twice of greatest hope transmitter symbol frequency.Systematic microprocessor 268 (Fig. 1) calculates the standard of symbol rate of current positive received signal or desired cycle in sample time, and with this value loading standard delay time register 31.This is similar to the operation that begins numerical control delayer (NCD) with correct sampling period.NCD is regulated and locked to phase error detector 16 to the actual sampling rate that transmits with relevant loop filter is common.Allow signal and use from the sampling clock of delay cell 42 from other processing unit that the symbol clock of AND gate 46 allows signal to be received in the machine (shown in Fig. 1).For example, pulse shaping filter 14 (Fig. 2) receives fixed frequency sampling clock AD and sampling allows clock signal.

As mentioned above, adder 32 produces the digital signal that the instantaneous time of representative from a last transmitter synchronized samples to next transmitter synchronized samples postpones, and NCD accumulator 38 produces the digital signal of representative up to the remaining time of next transmitter synchronized samples time.In the embodiment shown, these time representation signals represent that with 22 binary words of a fixed point 22 binary words of this fixed point have two highest significant positions and carry integer part, and remaining bit carries fractional part.Time value by these signal indications was expressed with the cycle of fixed frequency sampling clock AD.This time representation signal has from 0 to 4-2-20 scope.For example, the one-period of value " 1 " expression fixed frequency sampling clock AD, and have value 0100000000000000000000 ₂, wherein subscript 2 is pointed out what this numerical value was represented with base 2 or binary format.

If the integer part that is stored in the time delay in the accumulator 38 is greater than zero, the output of comparator 41 is logic ' 0 ' signals.Under this state, must be before obtaining next transmitter synchronized samples through the more than one fixed frequency sampling clock AD cycle.Accumulator 38 integer part value countdowns.Multiplexer 34 is coupled to adder 36 by logic ' 0 ' signal adjustment with the signal with-1 value at comparator 41.Adder 36 then should-1 signal be added in (promptly subtracting 1) accumulator 38 on the signal value, and in accumulator 38 the up-to-date value of successively decreasing of storage.In addition, because the output of comparator 41 is logic ' 0 ' signals, all not to be in effective status so sampling clock allows signal and symbol clock to allow signal (having done suitable delay by delay cell 42).

The fractional part of accumulator 38 values represents the fixed frequency sampling clock AD cycle up to the part that obtains next transmitter synchronized samples.The highest effective eight delays that are used to control interpolater 12 of fractional part.This is divided into 256 parts with the time span of fixed frequency sampling clock AD between the cycle basically.Therefore, interpolater can be 256 phase multiphase filter groups.No longer surplus before obtaining next transmitter synchronized samples have complete fixed frequency sampling clock AD during the cycle, and the integer part of signal is 0 in the accumulator 38.In this case, the signal from comparator 41 outputs is logic ' a 1 ' signal.

When the output signal from comparator 41 is logic ' 1 ' signal, obtaining a sample from interpolater 12, and produce sampling clock and allow signal with circuit timing that starts the back level and the sample of handling this new generation by the time of the most significant byte control of the fractional part of accumulator 38 values.In addition, modulo-two counter 44 is by timing, if the transmitter symbol time, AND gate 46 also produces symbol clock and allows signal.Simultaneously, adjust multiplexer 34 and will be sent to adder 36 from the signal of adder 32.The transmitter synchronous sampling time that adder 36 combination is required and the fractional part of NCD accumulator 38 (as mentioned above, integer part is zero), thus the time will obtain next transmitter synchronized samples the time be placed in the accumulator 38.Through loop filter this loop of NCD value closure by the change of response phase error detector 16 output signals.

Sampling clock allows signal to offer such as the system unit of unit 14,16,26,44 and 46 1 classes and handles all other back level processing units (Fig. 1) of each transmitter synchronized samples.This unit also needs sampling to allow signal except fixed frequency sampling clock signal AD.For the transmitter synchronous sampling of obtaining with the symbol time of emission, it is effective that symbol clock allows signal.Symbol clock allows signal to offer those system units to the symbol manipulation of emission, for example, and the identifying unit that is associated with carrier recovery network such as carrier recovery unit 264 (Fig. 1) class.This cell response fixed frequency sampling clock signal AD and symbol clock allow signal and work.

For example, if illustrated embodiment is suitable for being used in the broadcasting-satellite system (for example Satlink), the frequency of fixed frequency sampling clock signal AD is 62MHz.The symbol rate of an exemplary broadcast signal was 30,000,000 symbol/seconds.Because received signal is that sampling clock allows signal by this way with the sampling of the twice of symbol rate, make that promptly the mean sample rate is that the required sampling rate of 2 samples of every symbol is forbidden fixed frequency clock signal AD.Therefore for being being under an embargo the fixed frequency sampling clock AD cycle of 60,000,000 samples/sec and per second 2,000,000 30,000,000 symbol/seconds.Interpolater 12 produces the interpolations sampling, makes in the fixed frequency sampling clock AD cycle of each startup, and sample similarly is to obtain with the required transmitter synchronous sampling time.That is having as these samples from the sample of interpolater 12 is the numerical value of obtaining from ADC10, and ADC10 is the 60MHz timing in this example by with suitable sampling frequency.Under the situation of the clock signal (per second 2,000,000) of accidental saltus step, when sampling appears at 62MHz fixed frequency clock signal AD transition.

When disclosed system is used to handle the QPSK input signal, observes the error rate and be no more than 0.1dB in the decline of the 4dB signal to noise ratio (snr) threshold value place of the invalid part that usually becomes near error correcting code.The timing controlled loop is restrained fully in 3000 samples.This loop shows and is converged in 0dB SNR, has the decay of about 0.5dB simultaneously.These performance characteristics show that disclosed timing recovery system also is applicable to residual sideband (VSB) modulating input signal of the type that is proposed to be used in Grand Alliance HDTV system.Following form has been concluded the systematic function of some SR ratio, and wherein the SR ratio is a fixed frequency sampling rate (A/D conversion rate) and the ratio of symbol rate, adopts two samples of every symbol.

The SR ratio	??SNR	Decay
			??62/30	??9dB	????0.2dB
??62/30	??6dB	????0.05dB
			??62/30	??4dB	????0.1dB
??62/20	??9dB	????0.1dB
			??62/20	??6dB	????0.00dB
??62/20	??4dB	????0.04dB

In resembling the system such to the QAM system of input signal sampling with homophase (I) and quadrature (Q) component, can be with native system with the speed of the twice of in-less-than symbol rate to input I and the sampling of Q orthogonal signalling, and produce the Serial No. of transmitter synchronized samples with the twice of transmitter synchronizing symbol rate, as long as fixed frequency sampling clock signal AD speed is greater than the value by following equation definition:

FR=S * BW _E+ M (5) wherein FR is a fixed frequency clock signal AD speed; S is-symbol rate; BW _EIt is the extra bandwidth part; And M is the smooth amplitude of interpolater and the boundary of group delay bandwidth.In having the system of little extra bandwidth, this can reduce the A/D sampling rate 10%-30% (under the perfect condition 49.9%).Digital processing system per unit clock after interpolater need be handled a plurality of samples, so it need or utilize the parallel method deal with data with higher clock rate work.

Fig. 3 shows the structural segmented parabolic interpolation device of implementing with the fixed-point algorithm of hardware designs 12 of a kind of Farrow (Fig. 2).Interpolater 12 utilizes the sectional parabola filter, because it forms the low-complexity interpolater with enough performances in this enforcement.Troop for resembling the such high-order of 64QAM or 256QAM, may need more complicated interpolation filter.As shown in adder 32 (Fig. 2), the standard delay signal is added to allows the systematic microprocessor (not shown) control standard delay between the required transmitter synchronous sampling on the output signal of loop filter valuably, and this loop only needs to keep this speed constant.

Especially, the interpolater 12 of Fig. 3 is a kind of 4 tap segment parabola filters, and its type is people such as Lars at ieee communication collected works " interpolation method in the digital modems " second portion: advised in " realizing and performance ".In Fig. 3, input IN is coupled to the output of ADC10 (Fig. 2).This input IN receives one 6 bit-pattern, carries from-32 to+31 number range, and is coupled to: the delay cell 50 that is connected in series, adder 60, delay cell 51, adder 61, delay cell 52, adder 62 and delay cell 53; And inverting input, delay cell 55, adder 64, delay cell 56, adder 65 and the delay cell 57 of the delay cell 54 that is connected in series, adder 63.Input IN also is coupled to the inverting input separately of adder 60,61 and 65 and the normal phase input end of adder 62.Input IN also is coupled to the input of one * 2 multipliers 68, and its output is coupled to the input of adder 67 and the inverting input of adder 66.Adder 66 is coupled to an input of adder 63, and adder 67 is coupled to the input of adder 64.Input IN also is coupled to each second input of adder 66 and 67.Input IN also is coupled to delay cell 92 and one * 2 multipliers 94 of six time cycles that are connected in series in addition.

Control input end MU is coupled to the most significant byte of numerical control delayer (Fig. 2) accumulator 38 fractional parts.Control input end MU is coupled to multiplier 70, delay cell 72, multiplier 74, limiter 76, delay cell 78, multiplier 80, delay cell 84 and the adder 90 that is connected in series.The output of delay cell 53 is coupled to second input of multiplier 70; The output of delay cell 57 is coupled to second input of multiplier 74; The output of * 2 multipliers 94 is coupled to second input of adder 90.A two cycles delay cell 82 is coupling between control input end MU and multiplier 80 second inputs.The output of adder 90 produces the synchronous sampling of transmitter, and is coupled to output OUTPUT.Output OUTPUT is coupled to pulse shaping filter 14 (Fig. 2).

Interpolater 12 shown in Figure 3 is worked in the mode described in people's articles such as above-mentioned Lars.Control signal MU represents the timesharing of adjacent fixed frequency sampling clock AD between the cycle, and the synchronous sampling of transmitter will obtain constantly from this.Interpolater 12 shown in Figure 3 carries out interpolation with the represented time of control signal MU in adjacent ADC10 sample, to produce the sampling of interpolation at output OUTPUT.In the embodiment shown, there is the delay in one three fixed frequency clock signal AD cycle in the sampling output from control signal MU is input to interpolation.This delay must be compensated in the generation of sampling that is produced by numerical control delayer (Fig. 2) and symbol clock permission signal.Delay cell 42 (Fig. 2) provide this time bias, is one three clock cycle delay unit in the embodiment shown.

Fig. 4 is the more more detailed block diagram of Fig. 2 phase error detector 16.In Fig. 4, the corresponding output end of interpolater 12 (Fig. 2) is coupled in mutually orthogonal homophase (I) and quadrature (Q) signal input part " I input " and " Q input ".In-phase input end " I input " is coupled to the inverting input of the delay cell 102, delay cell 103 and the adder 108 that are connected in series.In-phase input end " I input " also is coupled to second input of adder 108.The output of adder 108 is coupled to the first input end of multiplier 110, and the output of delay cell 102 is coupled to second input of multiplier 110.The output of multiplier 110 is coupled to the first input end of adder 114.

Orthogonal input " Q input " is coupled to the inverting input of the delay cell 104, delay cell 105 and the adder 106 that are connected in series.Orthogonal input " Q input " also is coupled to second input of adder 106.The output of adder 106 is coupled to the first input end of multiplier 112, and the output of delay cell 104 is coupled to second input of multiplier 112.The output of multiplier 112 is coupled to second input of adder 114.The output of adder 114 produces the signal of representing the phase error between transmitter synchronous sampling signal that is produced by numerical control delay cell in the receiver and the actual sample time that transmits, and all operations carries out in a known way.

Be that timing recovery system described here can be handled and the relevant many symbol rates input signal of single clock that is produced by fixed oscillator valuably.In addition, sampling clock allows signal and symbol clock to allow signal all to derive from input signal itself.As other places herein explaining, it is with the speed sampling of symbol rate multiple that sampling clock allows the output of signal indicating interpolater.

Disclosed system utilizes a fixed pulse shaping filter 14 and a fixed frequency clock oscillator 261 to support a plurality of input sampling rates valuably.The structure of filter 14 does not need to be revised as a plurality of incoming symbol rates that are adapted to.Be positioned at timing recovery network 14 pairs of signal filterings of pulse shaping filter afterwards, thereby strengthen its signal-to-noise performance with identical pulse integral form character.

Can be applicable to for example BPSK, QPSK, CAP and QAM according to symbol timing recovery of the present invention system, and Grand Alliance high definition TV (HDTV) the VSB modulating system that system adopted that is applied to for example be proposed to be used in the U.S..One of ordinary skill in the art will recognize that in order to make disclosed symbol timing recovery system adapt to required modulation needs to make which design and change, and can understand how to design shown in parts under desired modulation, work.Noticed that said system reaches locking with the quite short time cycle.Known that the QPSK symbol is clustered in locking after several thousand samples, and this is visual after being clustered in 500 samples, even if having the timing slip of 1000ppm.Because voltage controlled oscillator function is carried out on digitlization ground, these performance characteristics are attended by the hsrdware requirements of reduction, even this system of making also is very attractive when operating with respect to the monadic symbols rate.

In the disclosed embodiment, sampling clock allows the clock of signal on corresponding units to allow/forbid end to start and forbids clock signal AD, rather than starts and forbid fixed oscillator 261 itself.Gated clock also is that a kind of the selection also can be considered according to the requirement of concrete system.

Claims (5)

1, a kind of signal receiver system that is used to handle the input signal of representing continuous symbol is characterized in that:

Be used to receive the input processor (10 of the data flow that contains the symbol that presents multiple symbol rate; 262);

Be used to handle from described input processor, comprise that the output signal of the symbol that presents multiple symbol rate is to produce the digital symbol timing recovery network (12 of synchronizing symbol; 266); And

Before being applied to application network, be used for the non-self-adapting digital filter (14) of filtering from the output signal of described timing recovery network.

2, according to the system of claim 1, its feature also is: a fixed oscillator that is associated with described timing recovery network.

3, according to the system of claim 1, it is characterized in that: described filter is a kind of pulse shaping filter.

4, according to the system of claim 1, it is characterized in that: described timing recovery network comprises and is used for the interpolater that interpolation is coupled to described filter from the output signal and the output of described input processor.

5, according to any one signal receiver system in the aforementioned claim, its feature also is:

Be used to receive the A-D converter of the data flow that contains the symbol that presents multiple symbol rate;

Processing from the output signal of described A-D converter to produce the described digital symbol timing recovery network of described synchronizing symbol; And

Be associated with described timing recovery network and provide fixed frequency clock to arrive the fixed oscillator of described A-D converter.

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