MXPA98009020A - Method and system for recovery of synchronization and channel estimation joints for multiple discre detono modems - Google Patents

Abstract

A method and system for acquiring the synchronization of a data block in a discrete multiple tone modem system in which an acquisition block having a first predetermined number of pulse signals is generated. Each pulse signal is separated in time by 2 (P + 1) Ts, such that 1 / Ts, is a rate of transmission of the sample, and P is a time interval in the samples of a cyclic prefix that is summed to a data block. The length of the cyclic prefix P is chosen in such a way that the pulse response of the channel observed in the receiver effectively covers no more than P + 1 samples, when a received signal is sampled at a rate of 1 / Ts. The data blocks are generated after the acquisition block. Each data block includes a cyclic prefix and at least as many data samples as samples of the cyclic prefix. The acquisition block and data are converted to an analog signal for transmission. The received acquisition block is sampled and a sum window is advanced one sample at a time through the received acquisition block. The sampled acquisition block is added to each sum window, with each sum window covering P + 1 samples of the acquisition block. A value of the maximum sum is determined when the sum window advances, and a limit of the data block is determined based on the sum window corresponding to the value of the maximum sum. A response of the channel impulses is estimated based on the P + 1 samples of the received acquisition block corresponding to the maximum sum value, and the data are coherently detected based on the response and the impulse of the estimated channel

Description

METHOD AND SYSTEM FOR SYNCHRONIZATION RECOVERY AND CHANNEL ESTIMATION JOINTS FOR MULTI-TONE MODEMS DISCRETE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the field of telecommunications. More particularly, the present invention relates to a method and system for acquiring and tracking the boundaries of the block of a Discrete Multiple Tone (DMT) signal received in a DMT system. 2. Description of the Related Art In conventional Discrete Multiple Mode (DMT) modems, they use long pseudorandom (PN) sequences and correlation calculations for the acquisition of synchronization and tracking. The long sequences used result in a high complexity in the implementation, as well as a higher overall load and a delay in the processing of the signals associated with the establishment of a call and the transmission of data. The PN sequences are first encoded in discrete tones, and then transformed using an inverse discrete Fourier transform in time domain samples for transmission. The received samples are transformed by a REF: 28782 Fourier transform method to reproduce the PN sequence, and then their correlations are tested to identify the boundaries of the block. The estimation of the channel, which is used for the detection of coherent signals / is made only during the establishment of the call, which requires separate PN sequences. Consequently, the detection of subsequent signals is susceptible to clock variations. What is needed is an efficient and effective technique that can be used with DMT modems for the recovery of synchronization and joint channel estimation.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides an efficient and effective technique that can be used with DMT modems for the recovery of synchronization and joint channel estimation. The clock recovery for DMT modems is simplified using the channel's scattering properties and, as a result, the overall load and time delay in the call set-up and during data transmission is reduced, minimizing the time, the effects of a bad synchronization. For example, in an HDSL (High Speed Digital Subscriber Line) environment, where highly dispersive stranded copper wires are used for high-speed data transmission, the present invention significantly reduces the total load and complexity of computing and, consequently, the time required to establish and track the boundaries of the DMT block. Additionally, the estimation of the channel is carried out jointly, thus making the detection of the signal less sensitive to the sampling synchronization. The invention is also applicable to radio transmissions, where the modulation of the carrier is used to deflect the signal from the transmission at the desired frequency ranges. The advantages of the present invention are provided by a method and a system for acquiring the synchronization of a data block in a discrete multiple tone modem system in which an acquisition block having a first predetermined number of signals is generated. of impulses. According to the invention, the separation of the pulse signals in time is 2 (P + 1) TS, so that 1 / T3 is a speed of transmission of the sample, and P is the period of time in the samples. samples of a cyclic prefix that is added to a block of data. Preferably, the length of the cyclic prefix P is chosen such that a response of the channel pulses is observed in a receiver effectively encompassing no more than P + 1 samples, where a signal received at the receiver is sampled at a speed of 1 / TS. The data blocks are generated after the acquisition block, for example, from an inverse discrete Fourier transformation over a set of discrete tones that contain information data. Each data block includes (after the inverse discrete Fourier transformation) a cyclic prefix and at least as many data samples as samples of the cyclic prefix. The acquisition block and the data block are then converted from a digital signal to an analog signal for transmission. The receiver samples the received acquisition block and advances a sample from the sum window at the same time through the received acquisition block. The sampled acquisition block is added to each sum window, with each sum window covering P + 1 samples of the acquisition block. A value of the maximum sum is determined when the sum window advances and a limit of the data block is determined based on the sum window corresponding to the value of the maximum sum. An impulse response of the channel is estimated based on the P + 1 samples of the received acquisition block corresponding to the maximum sum value, and the data are coherently detected based on the response of the estimated channel impulses. A synchronization block is generated after each predetermined number of data blocks having a second predetermined number of pulse signals. Accordingly, each pulse signal of the synchronization block is separated in time from each other by 2 (P + 1) TS. A first pulse signal from each synchronization block is separated in time by 2 (P + l) Ta from a last data sample in a data block immediately preceding the synchronization block, and a last pulse signal from each synchronization block is separated in time by 2 (P + 1) T3 from a first prefix sample of a data block that is immediately after the synchronization block. The synchronization block is sampled in the receiver, and a sum window makes it advance through the synchronization block received, again, one sample at a time. The synchronization block sampled is added to each sum window, with each sum window covering P + 1 samples of the synchronization block. A value of the maximum sum is determined when the sum window advances and the limit of the data block is updated based on the sum window corresponding to the value of the maximum sum. The impulse response of the estimated channel is also updated based on the P + 1 samples of the received synchronization block corresponding to the value of the maximum sum, and the data are coherently detected based on the impulse response of the estimated channel updated ,- BRIEF DESCRIPTION OF THE DRAWINGS The present invention is illustrated by way of example and not limitation in the accompanying figures, in which similar numerical references indicate similar elements, and in which: Figure 1 shows a schematic block diagram of a circuit for generating a signal for acquisition of synchronization and tracking according to the present invention; Figure 2 shows a synchronization diagram for a transmitted signal used for synchronization and tracking acquisition according to the present invention; Figure 3 shows a schematic block diagram of a circuit for acquiring and tracking the boundaries of a block according to the present invention; and Figure 4 shows a timing diagram for a received signal used for synchronization and tracking acquisition according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a technique of low general load and low complexity to acquire and track block boundaries (i.e., symbols) optimally of a Discrete Multiple Tone (DMT) signal received in a DMT system. Additionally, the technique of the present invention produces an estimate of the impulse response of the channel, which is required for the detection of coherent signals. As a result, any adverse impact on the acquisition of synchronization and tracking caused by the clock variation is minimized. The present invention utilizes a predetermined number of appropriately time-separated digital pulses, i.e. discrete delta signals, which are transmitted during the establishment of a call. The effects of the channel scattering on the impulse response of the signal transmitted on the receiver is determined by advancing a sum window over a possible time slot of the received spread pulse and determining the sum window that provides a maximum sum of samples squares within the sum window compared to 'the sums obtained from the other sum windows. The acquisition of joint channel synchronization and estimation is achieved by the maximum sum sum window that identifies the limit of the data block and by the samples of pulses received within the sum window that approximates the response of the channel pulses. The technique provided by the present invention is optimal since a symbol boundary is chosen so that the average signal-to-noise ratio is maximized. According to the invention, the synchronization noise is effected in a similar manner. A short synchronization block containing a predetermined number of appropriately separated time pulses is inserted into a superblock formed from several blocks of data, each of which is larger than the synchronization block. The tracking of the synchronization is then provided by identifying the maximum sum as a sum window advancing within the boundaries of the synchronization block. Accordingly, the channel estimate is provided simultaneously and is used to coherently detect the subsequent data blocks that occur within the next superblock. Figure 1 shows a schematic block diagram of a circuit 10 for generating a signal for acquisition of synchronization and tracking according to the present invention. The circuit 10 includes a multi-tone data block generator 11 and a discrete pulse generator 12 which are coupled at their respective inputs to a multiplexer 13. The multiplexer 13 is controlled in a well-known manner to selectively produce a tone signal multiple generated by the multi-tone data block generator 11 or a discrete pulse signal output produced by the discrete pulse generator. The exit of the multiplexer 13 is applied to the input of a digital-to-analog converter (D / A) 14. The output of the D / A converter 14 is applied to a transmitter 15 for its transmitter. The transmitter 15 converts the output of the D / A converter 14 in a well-known manner to a signal having characteristics and parameters that are appropriate for the environment in which the circuit 10 is used. Figure 2 shows a synchronization diagram for a transmitted signal used for the acquisition of synchronization and tracking according to the present invention. Before the transmission of the data, a predetermined number of discrete pulses I separated in time are transmitted twice the effective length of the impulse response of the channel to a receiver within a synchronization acquisition block 20. That is, each pulse I is separated in the time by 2 (P + 1) T3, where 1 / T3 is the velocity "of the sample transmission, and P is the time interval in the samples of a cyclic prefix that is added to a block of data or symbols . the cyclic prefix length P is chosen such that the impulse response seen at the receiver effectively channel covers no more than P + 1 samples, if the received signal is ALSO -muestreada speed 1 / TS. a block data 21, having a plurality of data samples and increases the cyclic prefix, follows the timing acquisition block. Figure 3 shows a schematic block diagram of a circuit 30 to acquire and track unit boundaries acue of the present invention. The circuit 30 includes a receiver 31 that receives a transmitted signal. The output of the receiver 31 is applied to the input of an analog-to-digital (A / D) converter 32. The A / D converter 32 samples the received signal at the rate of 1 / T3. The sample outputs of the A / D convert 32 are square by the quadrature circuit 33 and are then summed by the summation circuit 34 using an advance sum window that spans P + l samples. The sum window that produces a maximum sum is determined in a manner well known to the processor 35. The processor 35 uses the maximum sum window to determine the limit of a data block and to estimate a response of ld "s pulses of the The impulse responses of the estimated channel is then derived to a coherent multiple tone signal detector 36 to coherently detect the data using the impulse response of the estimated channel.

Figure 4 shows a synchronization diagram for a received signal used for synchronization acquisition and tracking according to the present invention. In the receiver, each transmitted pulse I within an acquisition block 20 becomes a pulse response for the channel, contaminated by noise and interference. The dispersion of the channel causes the transmitted impulse to diffuse in an effective time spanning up to P + 1 samples. In this way, the signal received during the acquisition block is defined as the same number of responses of the pulses of the channel contaminated as transmitted pulses, with each of the pulses of the channel being followed by P + 1 samples of an essentially zero signal . During the data block 21 of the received signal, the total signal at any time is the superposition of P + 1 individual signals originating from P + 1 transmitted data samples. To establish a block limit (symbol) or equivalent, an effective limit of a received signal is used due to a transmitted discrete pulse, a sum window that has a time interval of P + 1 samples received to calculate a sum of the squares of the samples kept in the window. The sum window advances through the synchronization acquisition block receiving one sample at a time, so that a maximum sum can be terminated and identified. The P + 1 effective samples give rise to a maximum sum taken as the response of the impulses of the channel, and is used for the coherent detection of data. Fine synchronization steps can be performed to improve both synchronization acquisition and tracking. For example, multiple summation windows can be used to determine a maximum sum, the sampling rate can be increased during synchronization acquisition and tracking blocks, and a dedicated pilot tone can be used within each data block to correct clock variations . The synchronization accuracy estimation can be improved when the addition is made using multiple summation windows that are separated in time P + 1 samples. Additionally, a sampling rate greater than 1 / T3 may be used at the receiver during the acquisition and synchronization tracking blocks for fine synchronization of the channel impulse response estimate. The synchronization acquisition method of the present invention described above achieves the acquisition of the initial synchronization. The same technique can be applied to achieve tracking of synchronization during data transmission if, after each predetermined number of data blocks (symbols), a shortened synchronization block (represented by 20 in Figures 2 and 4) has a predetermined number of discrete pulses I is inserted into the transmission signal. As with the acquisition block, each discrete pulse I of a synchronization block is separated in time from each other by 2 (P + 1) T3. Additionally, the first discrete pulse is separated in time from the last data sample in the preceding data block by the same amount. Similarly, the last discrete pulse is separated in time by 2 (P + 1) T3, from the first sample of the prefix of the next data block. The tracking of the synchronization is carried out by identifying a maximum sum associated with a summing window that advances in time through the synchronization block received on a sample in time. As above, multiple summing windows and / or increasing sampling rates may be used during the synchronization block. The samples received in a sum window that form a maximum sum are an updated channel impulse response that can be used to detect data symbols between a synchronization block "and the next synchronization block. additionally entered for each data symbol, if the data symbol block contains a dedicated pilot tone. The number of discrete pulses used in a synchronization block may be less than the number used during the synchronization acquisition block because the initial synchronization has been established. Although the present invention has been described in connection with the illustrated embodiments, it should be appreciated and understood that modifications can be made without departing from the true spirit and scope of the invention. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the -invention as above, property is claimed as contained in the following:

Claims (16)

1. A method for generating a signal to acquire the synchronization of a data block in a discrete multiple tone modem system, the method is characterized in that it comprises the steps of: generating an acquisition block, the acquisition block has a first predetermined number of pulse signals, each pulse signal is separated in time by 2 (P + 1) TS, so that 1 / T3 is a transmission speed of the sample, and P is the time interval in the samples of a cyclic prefix that is added to a data block; and generating at least one data block subsequent to the acquisition block, each data block has its own cyclic prefix and at least as many data samples as samples of the cyclic prefix of the data block. The method according to claim 1, characterized in that it further comprises the step of transmitting the acquisition block and at least one data block. The method according to claim 1, characterized in that the length of the cyclic prefix P is chosen in such a way that the response of the pulses of the channel observed in the receiver effectively covers no more than P + 1 samples when a signal received in "the receiver is sampled at the rate of 1 / T3 4. The method according to claim 2, characterized in that it also comprises the steps of: receiving the acquisition block, sampling the acquisition block received, advancing a window of sum through the acquisition block received, add the acquisition block sampled on each addition window, each sum window covers P + 1 samples of the acquisition block, and determine a sum window corresponding to a maximum sum. The method according to claim 4, characterized in that the step of advancing the sum window advances the sum window one sample at a time. according to claim 4, characterized in that the received acquisition block is sampled at a rate of 1 / T3. The method according to claim 4, characterized in that the received acquisition block is sampled at a rate greater than 1 / T3. 8. The method of compliance with the claim 4, characterized in that the step of advancing the sum window through the received acquisition block includes the step of advancing a plurality of summation windows through the acquisition block received / where the step of adding the acquisition block Sampling on each sum window includes the step of adding the acquisition block sampled on each of the plurality of summation windows, and wherein the step of determining the sum window corresponding to the maximum sum includes the step of determining the plurality of sum windows that correspond to a maximum sum over the plurality of sum windows. The method according to claim 1, characterized in that it further comprises the steps of generating a synchronization block after each predetermined number of data blocks, the synchronization block has a second predetermined number of pulse signals, each signal of pulses of the synchronization block is separated in time from each other by 2 (P + 1) T3, a first pulse signal of each synchronization block is separated in time by 2 (P + 1) T3 / from a last sample of data in a data block that is immediately preceding the synchronization block, and a last pulse signal of each synchronization block is separated in time by 2 (P + 1) T3 of a first sample of the prefix of a block of data that - is immediately subsequent to the synchronization block; and transmit the synchronization block. 10. The method of compliance with the claim 9, characterized in that it further comprises the steps of: receiving the synchronization block; sample the received synchronization block; advancing a sum window through the received synchronization block; add the synchronization block sampled on each addition window, each sum window covers P + 1 samples of the synchronization block; and determining a sum window for the synchronization block corresponding to a maximum sum. 11. The method according to the claim 10, characterized in that the step of advancing the sum window advances the sum window one sample at a time. The method according to claim 9, characterized in that it further comprises the step of tracking a limit of a data block ~ "previously determined on the basis of the sum window for the synchronization block corresponding to the maximum sum. The method according to claim 12, characterized in that it further comprises the steps of: updating an impulse response of the estimated channel based on the received synchronization block portion corresponding to the summation window, of the maximum sum for the synchronization block, and coherently detect data based on the impulse response of the updated channel 14. A system for generating a signal to acquire block synchronization data in a discrete multiple-tone modem system, the system for generating the signal it is characterized because cc - • rende: a multi-tone data block generator that produces at least one ton data block In many cases, each data block includes a cyclic prefix having at least one sample and at least as many data samples as samples of the cyclic prefix of the data block; a discrete pulse generator that produces a discrete pulse signal having a predetermined number of pulses, each pulse is separated in time by 2 (P + 1) T3 / where 1 / T3 is a sample transmission rate, and P is a time interval in the samples of a cyclic prefix of a multi-tone data block; and a multiplexer coupled to the generator of the multi-tone data block and the discrete pulse generator, the multiplexer selectively produces an acquisition block signal and a subsequent data block signal "to the signal of the acquisition block, the signal of the The acquisition block includes the discrete pulse signal and the signal of the data block includes at least one multi-tone data block 15. The system according to claim 14, characterized in that the length of the cyclic prefix P is chosen in such a way that that a channel impulse response observed in the receiver effectively covers no more than P + 1 samples when a signal received at the receiver is sampled at the rate 1 / T3 16. The system according to claim 14, characterized in that the multiplexer further produces a synchronization block after each predetermined number of data blocks, the synchronization block have a n second predetermined number of pulses generated by the discrete pulse generator, each pulse signal of the synchronization block is separated in time by 2 (P + 1) T3, a first pulse signal of each synchronization block is found separated in time by 2 (P + 1) T3, from the last * data sample in a data block that is immediately preceding the synchronization block, and the last pulse signal from each synchronization block is separated in- the time by 2 (P + 1) T., of a first sample of the prefix of a data block that is immediately subsequent to the synchronization block. SUMMARY OF THE INVENTION A method and system for acquiring the synchronization of a data block in a discrete multiple tone modem system in which an acquisition block having a first predetermined number of pulse signals is generated. Each pulse signal is separated in time by 2 (P + 1) TS, such that 1 / T3, is a rate of transmission of the sample, and P is a time interval in the samples of a cyclic prefix that is added to a data block. The length of the cyclic prefix P is chosen such that the pulse response of the channel observed in the receiver effectively spans no more than P + 1 samples, when a received signal is sampled at a rate of 1 / T3. The data blocks are generated after the acquisition block. Each data block includes a cyclic prefix and at least as many data samples as samples of the cyclic prefix. The acquisition and data block, they are converted to an analog signal for transmission. The received acquisition block is sampled and a sum window is advanced one sample at a time through the received acquisition block. The sampled acquisition block is added to each sum window, with each sum window covering P + 1 samples of the acquisition block. A value of the maximum sum is determined when the sum window advances, and a limit of the data block is determined based on the sum window corresponding to the value of the maximum sum.An impulse response of the channel is estimated. based on the P + 1 samples of the received acquisition block that correspond to the value of the maximum sum, and the data are coherently detected based on the response and the estimated channel impulses.