WO2003075482A1 - Egaliseur automatique et procede d'apprentissage des coefficients - Google Patents

Egaliseur automatique et procede d'apprentissage des coefficients Download PDF

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Publication number
WO2003075482A1
WO2003075482A1 PCT/JP2002/001085 JP0201085W WO03075482A1 WO 2003075482 A1 WO2003075482 A1 WO 2003075482A1 JP 0201085 W JP0201085 W JP 0201085W WO 03075482 A1 WO03075482 A1 WO 03075482A1
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WIPO (PCT)
Prior art keywords
equalizer
coefficient
target
output
transfer function
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PCT/JP2002/001085
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English (en)
Japanese (ja)
Inventor
Mitsuo Kakuishi
Nobukazu Koizumi
Hideyuki Araki
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Fujitsu Limited
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Application filed by Fujitsu Limited filed Critical Fujitsu Limited
Priority to PCT/JP2002/001085 priority Critical patent/WO2003075482A1/fr
Publication of WO2003075482A1 publication Critical patent/WO2003075482A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03006—Arrangements for removing intersymbol interference
    • H04L25/03012—Arrangements for removing intersymbol interference operating in the time domain
    • H04L25/03019—Arrangements for removing intersymbol interference operating in the time domain adaptive, i.e. capable of adjustment during data reception
    • H04L25/03057—Arrangements for removing intersymbol interference operating in the time domain adaptive, i.e. capable of adjustment during data reception with a recursive structure
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B3/00—Line transmission systems
    • H04B3/02—Details
    • H04B3/04—Control of transmission; Equalising
    • H04B3/14—Control of transmission; Equalising characterised by the equalising network used
    • H04B3/142—Control of transmission; Equalising characterised by the equalising network used using echo-equalisers, e.g. transversal
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03006—Arrangements for removing intersymbol interference
    • H04L2025/03433—Arrangements for removing intersymbol interference characterised by equaliser structure
    • H04L2025/03439—Fixed structures
    • H04L2025/03445—Time domain
    • H04L2025/03471—Tapped delay lines
    • H04L2025/03484—Tapped delay lines time-recursive
    • H04L2025/0349—Tapped delay lines time-recursive as a feedback filter

Definitions

  • the present invention relates to an automatic equalizer and a coefficient training method thereof, and is suitable for use, for example, in an apparatus for receiving a signal transmitted by a discrete multi-tone (Discrete Multi-Tone) modulation method using a subscriber line pair cable as a transmission path.
  • the present invention relates to an automatic equalizer and its coefficient training method.
  • XDSL Digital Subscriber Line
  • This xDSL is a transmission method using the existing subscriber line (pair cable) and is one of the modulation and demodulation technologies.
  • x DSL is broadly divided into the upstream transmission speed from the subscriber's home (hereafter, the subscriber side) to the accommodation station (hereafter, the office side) and the downstream transmission speed from the office side to the subscriber side.
  • the subscriber side home
  • accommodation station hereafter, the office side
  • the downstream transmission speed from the office side to the subscriber side are categorized as symmetric and asymmetric.
  • a symmetric type has a high-bit-rate DSL (HD SL) with an uplink and downlink transmission speed of about 1.5 to 2.0 Mbps (megabit-noise), and a 160 k to 2
  • HD SL high-bit-rate DSL
  • SDSL Single-line DSL
  • AD SL Asymmetric DSL
  • the AD SL further includes "G.dmt” having a downlink transmission speed of about 8 Mbps and "G.lite” (also called a simplified AD SL) having a downlink transmission rate of about 1.5 Mbps.
  • G.dmt having a downlink transmission speed of about 8 Mbps
  • G.lite also called a simplified AD SL
  • DMT Discrete Multi-Tone
  • This DMT modulation method is, in a nutshell, a subcarrier whose transmission frequency band is about every 4 kHz (in the case of “G.lite”, depending on the conditions, up to 128 carriers in the downlink direction). And modulates each carrier.
  • This DMT modulation method has a feature that it is resistant to noise of a specific frequency because communication with another subcarrier is possible even if a certain subcarrier becomes unusable due to the influence of noise having a specific frequency.
  • DMT modulation method The details of the principle of the DMT modulation method are described in, for example, the document "JACBingham, Multicarrier Modulation For Data Transmission An Idea Whose Time has Come", IEEE Co. n. Mag., Pp5-14, May, 1990J. I have.
  • DSL digital subscriber line
  • the ADSL transmission system focuses on its main components.
  • a device (AD SL modem) 210 is connected to each other via a transmission line (metallic line) 300 such as a subscriber line pair cable.
  • the subscriber-side modem 110 includes a DMT modulator 101, a digital transmission filter 102, a digital Z-analog (D / A) converter 103, an analog band-pass filter as a transmission system. (BPF: Band Pass Filter) 104, etc., and the station-side modem 210 has a transformer 201, analog low-pass filter (LPF) 202, AZD converter 203, digital B PF 204, Time-domain Equalizer (TEQ) 205, Fast Fourier Transformer (FFT) 206, Frequency-domain Equalizer (FEQ) 207, Classifier 208 Etc. are provided.
  • LPF analog low-pass filter
  • FFT Fast Fourier Transformer
  • FEQ Frequency-domain Equalizer
  • the ADSL modem 110 of the subscriber 100 receives the signal from the ADSL modem 210 of the office 200 (hereinafter referred to as the office modem 210).
  • a receiving system having the same function as the system is provided, and the station-side modem 210 is provided with a transmitting system having the same function as the transmitting system in the subscriber-side modem 110.
  • the communication of (2) is performed in the same manner as the uplink communication described below.
  • the DMT modulation section 101 is for performing DMT modulation on transmission data transmitted from a subscriber terminal such as a personal computer (PC).
  • a subscriber terminal such as a personal computer (PC).
  • PC personal computer
  • a serial-to-parallel buffer Serial to Parallel Buffer
  • Encoder encoder
  • IFFT inverse fast Fourier transformer
  • the serial-to-parallel buffer 111 stores transmission data, which is serial data, for one symbol time (approximately l / 4 kHz), converts the stored data into parallel data, and outputs the parallel data. According to a predetermined transmission bitmap (not shown), the number of transmission bits is assigned to each carrier (subcarrier) (frequency band division).
  • the entire M-bit data is simultaneously transmitted on Nc carrier waves as a whole, and the receiving side (station side 200) transforms Ns time data (symbols) into a fast Fourier transform (FFT: Fast).
  • FFT fast Fourier transform
  • M bits of information are extracted from the amplitude and phase of the Nc carrier waves.
  • each carrier is placed at a distance of Afc (about 4 kHz) in the used frequency band.
  • Afc about 4 kHz
  • the number of symbols Ns is a power of 2 It is common to use "64" or "256".
  • the encoder 112 performs quadrature amplitude modulation (for example, QAM (Quadrature Amplitude Modulation)) on the bit string output from the serial-parallel buffer 111 by changing the amplitude and phase for each carrier.
  • the IFFT 113 performs inverse fast Fourier transform on the signal point data (data in the frequency domain) output from the encoder 112 to obtain the signal point. It converts the data into Ns time-domain signal sequences. As a result, the M-bit data is converted into a time-domain signal (symbol) consisting of Ns sample values and transmitted.
  • the digital transmission filter 102 is for removing unnecessary components of the symbol sequence (digital data) obtained by the DMT modulator 101, and the 0/8 converter 103
  • the output of the digital transmission filter 102 is converted to analog data, and the analog BPF 104 is for removing unnecessary components of the output of the DZA converter 103.
  • the transformer 201 is for cutting off the direct current (dc) component of the signal received from the transmission line 300
  • the analog LPF 202 is for cutting off the high frequency component signal and the noise component.
  • the AZD converter 203 converts the received signal (analog signal) passed through the analog LPF 202 into a digital signal.
  • the digital BPF 204 removes noise components and the like outside the desired band from the output of the AZD converter 203, and the TEQ 205 generates inter-symbol interference (ISI: Inter Symbol Interference) with the input signal on the transmission side ( This is to perform predetermined processing so that it falls within the cyclic prefix added on the subscriber side 100).
  • ISI Inter Symbol Interference
  • one point of the DMT modulation method is that by providing a period called a guard time between symbol sequences, demodulation on the receiving side can be made less susceptible to transmission line distortion.
  • a part (L sample) corresponding to the guard time at the end of the symbol sent after that is sent in advance is a cycle
  • the TEQ 205 adaptively updates its own coefficient (tap coefficient), and determines the length of the impulse response from the output of the transmitting IFFT 113 to the receiving FFT 206 via the transmission path 300 by the guard time. It works as follows. However, in practice, it is difficult to completely reduce the portion exceeding the guard time to zero, and the size is reduced as much as possible.
  • the purpose of the TEQ205 applied to the ADSL transmission system is quite different from that of the equalizer used in systems other than the DMT modulation system.
  • the frequency characteristics of the amplitude and group delay time are flattened. Is the main purpose.
  • the TEQ 205 itself is a FIR (Finite Impulse Response) type transversal equalizer, and has the same configuration as the equalizer used in the QAM system and the like.
  • the coefficient is updated based on the difference between the equalized output of the TEQ 205 and the output of the channel target equalizer 205a, which is obtained by the adder 205b (the details will be described later).
  • the guard time is lengthened, the TEQ 205 is unnecessary or the required order can be reduced.However, if the guard time is lengthened, the transmission efficiency deteriorates, so the guard time is selected to be about 1Z16 of the symbol time. Is common.
  • the FFT 206 is for converting the output after equalization by the TEQ 205 into frequency-domain data by the fast Fourier transform
  • the discriminator 208 includes a real part and an imaginary part of the output of the FEQ 207. Each of them is converted to digital data (digital I and Q values) (hereinafter referred to as identification processing).
  • the obtained digital data is output to a subsequent DMT demodulation section (not shown) as received data, and the DMT demodulation section modulates the data at a DMT modulation section 101 on the transmission side (subscriber side 100).
  • the reverse processing decoding, parallel-to-serial conversion, etc.
  • the signal is orthogonally demodulated.
  • the reception level greatly varies depending on the length of the transmission path 300, and therefore, an AGC converter for making the input level to the A / D converter 203 almost constant before the AZD converter 203 is used. (Automatic Gain Controlled)
  • a digital AGC is inserted after the AZD converter 203 in order to reduce the operation word length in digital signal processing. Illustration is omitted.
  • the operation of the ADSL transmission system configured as described above will be described.
  • the transmission data is held in the serial-parallel buffer 111 for one symbol time (1/4 kHz).
  • the stored data is divided for each predetermined number of transmission bits per carrier and output to the encoder 112.
  • the encoder 112 converts each of the input bit strings into signal points for quadrature amplitude modulation, and outputs the signal points to the IFFT 113.
  • IFFT 113 quadrature amplitude modulation is performed on each signal point by performing an inverse fast Fourier transform on the output of encoder 112.
  • a predetermined sample of the output of IFFT 113 is added to the head of the symbol as a cyclic prefix.
  • the IF FT output to which the cyclic prefix has been added as described above is input to a DZA converter 103 after unnecessary components have been removed by a digital transmission filter 102, where a predetermined sampling frequency (for example, 1.104 MHz ), Is converted into an analog signal, and is output to the transmission path 300.
  • a predetermined sampling frequency for example, 1.104 MHz
  • the analog signal received through the transmission path 300 is input to the analog LPF 202 via the transformer 201, and after the unnecessary components are removed by the analog LPF 202, the AZD converter 203 At digital Converted to a signal.
  • the obtained digital signal is input to a TEQ 205 after further removing unnecessary components by a digital BPF 204, and the length of the impulse response of the reception path is determined by the TEQ 205 to the guard time (size). (The click prefix).
  • the equalized signal is input to the FFT 206, where it is subjected to a fast Fourier transform to be converted into frequency-domain signal point data.
  • the obtained signal point data is subjected to the FEQ 207 to compensate for the influence on the amplitude and phase caused by passing through the transmission path 300 for each carrier having a different frequency.
  • the data is converted to digital data (digital I and Q values) and output to the subsequent processing unit (DMT demodulation unit) as received data.
  • a method of obtaining the tap coefficient of TEQ 205 described above (coefficient update) will be described below.
  • the method of obtaining such a coefficient is described in, for example, US Patent 5,285,474, 'Method for Equalizing A Multi-carrier Communication System'.
  • a circuit block (equalizer) called “channel target”.
  • channel target is a circuit with a transversal filter configuration having transfer characteristics equivalent to the transmission system from the IFFT output of the transmitting side (subscriber side 100) to the FFT input of the receiving side (station side 200).
  • the block length is set to L or less, which is the number of taps equivalent to the guard time.
  • the same signal (training signal) is sent to this “channel target” and the transmission system (hereinafter referred to as “real route”) from the transmitting IFFT output to the receiving FFT input, and the difference between their outputs Adaptively change the coefficients of the TEQ 205 included in the transversal filter of the channel target 205a (hereafter referred to as the target equalizer 205a) and the actual route so that is always zero.
  • the target equalizer 205a Adaptively change the coefficients of the TEQ 205 included in the transversal filter of the channel target 205a
  • the actual route so that is always zero.
  • a training time is provided, during which the same data sequence as the input data sequence of the transmission side (subscriber side 100) generated by the transmission side random bit sequencer 121 is sent to the pseudo random bit sequencer 205.
  • Target equalization by c The output of the TEQ 205 and the output of the evening get equalizer 205a are compared (added) by the adder 205b, and the evening get equalizer is set so that the difference becomes small.
  • the tap coefficients of 205a and TEQ205 are changed adaptively.
  • the impulse response between the transmitting-side IFFT output and the receiving-side FFT input is almost the same as that of the target equalizer 205a.
  • the impulse response of the evening gate is the tap coefficient itself of the target equalizer 205a, and its time width is shorter than the guard time, so that the impulse response between the transmitter I FFT output and the receiver FFT input is The length is also equal to or less than the guard time, and the effect of transmission line distortion on DMT modulation can be suppressed.
  • the method of obtaining the values on the time axis uses a conventionally well-known transversal filter coefficient updating method. That is, the tap coefficient is updated using the difference between the two outputs and the output value of the delay element in the transversal filter. It should be noted that when a solution is obtained in this time range, an extremely long transmission path 300 involves an extremely large time delay in an actual route. Therefore, such a delay is dealt with by correcting a delay of an integral multiple of the sampling period using a delay unit 205d shown in FIG.
  • the characteristics of both the TEQ 205 and the target equalizer 205a are matched as much as possible regardless of the time axis and the frequency axis.
  • the target characteristic simulates the characteristic from the transmitter IFFT output to the receiver FFT input, so that the gain is sufficient in the frequency band where the transmission signal passes, compared to the other bands. High, that is, in a band through which the transmission signal passes, the difference in signal delay due to frequency in the pass band is small, and it may be incomplete, but it is desirable that delay equalization be performed.
  • a range from about 26 kHz corresponding to sub-channel “6” to about 138 kHz corresponding to sub-channel “32” is assigned as a frequency band from the subscriber to the central office, and the maximum passband frequency is 138 kHz.
  • the target equalizer 205a of the DMT modulation method processing at 552 kHz, which is four times the frequency of the bandpass filter, should have the initial value of the transfer function of the band-pass filter with a pass band of approximately 26 to 138 kHz. is there.
  • the coefficient of the channel target 205 is fixed, the coefficient of the TEQ 205 is made variable, and when the TEQ coefficient stops moving, the coefficient of the target equalizer is made variable to further reduce the difference. By adopting it, the characteristics of TEQ205 can be obtained efficiently.
  • the TEQ205 makes the amplitude of the part of the impulse response of the actual route that is longer than the guard time width extremely small, and each subchannel obtained as the output of the FFT206 The received data is not interfered with by other subchannel signals of the current symbol, nor by the signal of the previous symbol (that is, ISI is as small as possible).
  • the S / N deteriorates, and the amount of information (number of bits) transmitted through the sub-channels decreases.
  • the number of bits that can be arranged for each sub-channel is reduced by the noise of the transmission path 300 in addition to the above-mentioned intra-channel interference and inter-channel interference.
  • the total number of bits that can be arranged for each subchannel is the total number of arranged bits per symbol, and the total number of arranged bits multiplied by the symbol repetition frequency is the throughput.
  • the in-band characteristics of the TEQ205 are gently high-pass filter characteristics that equalize the line characteristics of the line, and when the line length is zero, The in-band characteristics of the TEQ 205 are flat loss characteristics.
  • a “bridge tap” is an open-ended branch line of an unspecified length for a branch in the middle of a track.
  • the transfer characteristic often has a large loss in a specific frequency band of the passband, and cannot be handled by the conventional TEQ 205, and there is a large loss between the actual route and the target route. The difference remains, and as a result, the length of the impulse response of the actual route cannot be shortened, and the total number of arranged bits often decreases.
  • TEQ 205 is an FIR-type adaptive equalizer, and therefore is not suitable for equalizing a peak of a loss centered on a specific frequency. That is, in general, in an FIR type adaptive equalizer such as a transpersal type equalizer, the transfer function is only a numerator function and no denominator function is present, so a steep loss peak can be realized, but a steep gain It is not suitable for realizing the characteristics of the peak (that is, compensating for the steep valley of the gain).
  • IIR type equalizers cannot be used as TEQ 205.Therefore, when a “bridge tap” is present, there is a problem that sufficient good throughput may not be obtained. Was.
  • the method of adaptively finding the coefficient is not clear, for example, one having a simple F (frequency) characteristic such as an emphasis circuit that changes the coefficient stepwise in association with the AGC gain At present, it was not used for any other purpose.
  • the present invention has been made in view of such a problem, and has found a method for stably and adaptively obtaining coefficients of an IIR type equalizer, thereby sufficiently compensating for a steep gain valley of a received signal.
  • the purpose is to be able to use IIR type equalizers in addition to FIR type equalizers.
  • an automatic equalizer of the present invention adaptively performs equalization processing on a signal received from a predetermined transmission path, and has the following units. It is characterized by.
  • An equalizer that shortens the length of the impulse response characteristics of the reception transmission line (from the transmission IFFT output to the FFT input) (hereinafter referred to as a real route equalizer)
  • the target equalizer that simulates the impulse response characteristics of the route up to the output of the real route equalizer including the transmission path
  • the tap coefficients of the target equalizer are updated based on the output of the real root equalizer and the output of the evening get equalizer, and a part of the updated tap coefficients ( ) Is used to set some tap coefficients of the real root equalizer.
  • the tap coefficient of the evening equalizer is calculated based on the output of the real root equalizer and the output of the target equalizer during the coefficient training period. Is updated and the transfer function of the target equalizer.
  • the tap coefficients of the IIR type equalizer can be set so that some reciprocals of the factorized factor are used as transfer functions.
  • an IIR type equalizer having a denominator function part as a transfer function and suitable for compensating for a steep valley in the gain of a received signal, and thereby, regardless of the conditions of the transmission path, It is possible to always obtain a good transmission amount, that is, a throughput.
  • FIG. 1 and 2 are block diagrams illustrating the principle of the present invention.
  • FIG. 3 is a block diagram showing a configuration of the automatic equalizer according to the first embodiment of the present invention.
  • 4 to 7 are block diagrams for explaining the function of the coefficient update block shown in FIG.
  • FIG. 8 is a block diagram showing a configuration example of the first-channel first-get equalizer shown in FIGS.
  • FIG. 9 is a block diagram showing a configuration example of the second channel sunset-equalizer shown in FIGS.
  • FIG. 10 is a block diagram showing a configuration example of the transversal equalizer (T EQ) shown in FIG.
  • FIG. 11 is a block diagram showing a configuration example of the recursive equalizer shown in FIG.
  • FIG. 12 is a diagram for explaining pole determination during coefficient training according to the present embodiment.
  • FIG. 13 is a block diagram showing a configuration in a case where the recursive equalizer shown in FIGS. 4 to 7 is arranged after TEQU.
  • FIG. 14 is a block diagram for explaining a function of a coefficient update block of the automatic equalizer according to the second embodiment of the present invention.
  • FIG. 15 is a diagram for explaining the operation of the coefficient update block according to the second embodiment.
  • FIG. 16 is a block diagram for explaining the function of the coefficient update block according to the second embodiment after the completion of coefficient training.
  • Figure 17 is a block diagram showing the configuration of a conventional digital subscriber line (AD SL) transmission system. It is a lock figure.
  • AD SL digital subscriber line
  • FIG. 18 is a block diagram showing a configuration of the DMT modulator shown in FIG.
  • FIG. 19 is a block diagram for explaining the method of updating the TEQ coefficient shown in FIG. BEST MODE FOR CARRYING OUT THE INVENTION
  • the point of the present invention is to adaptively obtain the coefficients of the IIR type equalizer on the receiving system (real route) side input to the FFT using the target equalizer.
  • a pseudo transmission path (target route) is provided. Therefore, a system as shown in Fig. 1 can be considered because it can be compared with the signal from the actual transmission path (real route).
  • the transfer function of the transmission path is HI (z) (z—, the transfer function of TEQ is H
  • Figure 3 shows an automatic equalizer configuration that achieves this.
  • the configuration shown in FIG. 3 is also applied to, for example, the office-side modem 210 shown in FIG. 17, where 1 is a recursive equalizer, 2 is a TEQ equivalent to the TEQ 205 shown in FIG. 17, 3 is a window block, and 4 is a diagram.
  • FFT equivalent to FFT 206 shown in 17 and 5 show a coefficient update block, respectively.
  • the recoverable equalizer 1 converts the input signal (the output of the digital BP F 204 in the case of FIG.
  • H teq d This is an IIR (Infinite Impulse Response) type equalizer using z as the denominator of the transfer function.
  • IIR Infinite Impulse Response
  • z the denominator of the transfer function.
  • it is configured as a 3-tap IIR type equalizer as shown in FIG. 11.
  • predetermined coefficients are respectively multiplied by the multipliers 15 and 16.
  • the sum is obtained by the adder 12, and the result is added to the current input signal by the adder 11, so that an equalized output for the input signal can be obtained. ing.
  • FIR type equalizer transversal type equalizer
  • the sum by the adder 23 is obtained as an equalized output with respect to the input signal (the output of the reciprocating equalizer 1).
  • the number of taps in TEQ2 is based on the number of samples L corresponding to the guard time length, but there is no problem if it is larger than that. Also, their initial values may all be "0.0".
  • the window block 4 is for delaying the output of TEQ2 by a predetermined time and inputting it to the FFT 4
  • the coefficient update block 5 is for recursive equalizer 1
  • the coefficient of TEQ 2 are adaptively updated based on the output of TEQ 2.
  • the recursive switching signal and the TEQ switching signal pass the recursive equalizer 1 through the input signal (through). )
  • the state can be changed, and the updated coefficient value can be reflected (set) in the reactive equalizer 1.
  • the functional units shown in FIGS. 4 and 6 are realized by software processing. That is, as shown in FIGS.
  • the coefficient update block 5 includes a pseudo-random bit sequencer 51, a delay block 52, a first channel target equalizer 53, and a second channel target equalizer. It has an adder 54, an adder 55 and an inverse second channel evening get function block 56.
  • the pseudo-random bit sequencer 51 generates the same pseudo-random signal (training signal) as the pseudo-random bit sequencer 12 1 on the transmitting side described above with reference to FIG. 19, and the delay block 52
  • the delay time of the pseudo-random signal on the target route side input from the pseudo-random pit sequencer 51 is adjusted, and the pseudo-random bit sequencer 121 on the transmitting side is input to the TEQ 2 via the transmission path 300 by the pseudo-random bit sequencer 121. This is to match the delay time of the pseudo-random signal on the real route side with the delay time of the pseudo-random signal on the target route side.
  • the delay block 52 may be provided on the real route side (the output side of TEQ 2) (the delay time of the pseudo random signal on the real route side may be adjusted).
  • the first channel evening get equalizer (hereinafter referred to as the first target equalizer) 53 acts on the output (pseudo-random signal) of the delay block 52, for example, as shown in FIG.
  • the first target equalizer acts on the output (pseudo-random signal) of the delay block 52, for example, as shown in FIG.
  • FIR type transversal type
  • the first target equalizer 53 the number of registers (delay elements) 531 corresponding to the number of taps, the time axis obtained by holding the input signals one by one in time series, is obtained.
  • the sample data at the above plural points are multiplied by a multiplier coefficient in a multiplier 532, respectively, and the sum of those multipliers is added to the input signal (output of the delay block 52). It can be obtained as output.
  • the number of taps in the first evening get equalizer 53 is equal to the number of taps corresponding to the guard time length described above. A value close to the number L of pulls, and the initial value uses a value preset by the above-described method.
  • the second channel target equalizer (subordinate equalizer) 54 acts on the post-equalization output of the first evening equalizer 53.
  • the first target equalizer 54 is used. It is configured as an FIR type equalizer in the same way as 53.
  • the second channel target equalizer (hereinafter, referred to as the second target equalizer) 54 has a lower order (2 to 4 order; 3 to 4) than the first target equalizer 53 described above.
  • the tap coefficients of the recursive equalizer 1 that will be the denominator function part on the real route side are finally set using the tap coefficients, the tap coefficient of the first tap is considered.
  • the numerical value is fixed to "1.0", and the other tap coefficients are initially set to "0.0".
  • FIG. 9 shows the configuration of the second target equalizer 54 in the case of three taps.
  • the time axis obtained by holding the input signals one by one in time series in the two resistors (delay elements) 54 1 is obtained.
  • Multipliers 542, 543, and 544 multiply the sample data of the above three points by tap coefficients, and the sum of those multipliers is added to the input signal (first target equalizer). (The output of the device 53).
  • the adder 55 obtains a difference between the output of the TEQ 2 and the output of the second target equalizer 54 (an equalization error signal e; hereinafter, simply abbreviated as “error e”).
  • error e an equalization error signal
  • the coefficients of the TEQ 2, the first target equalizer 53, and the second target equalizer 54 are updated so that the error e is minimized.
  • the error e 'taking into account the deformation in the second target equalizer must be used instead of the error e obtained by the adder 55. No. This is because the error used for updating the coefficients of the transversal equalizer must be the error of the (immediate) output terminal.
  • an inverting amplifier gain is “1.0”, but the phase is rotated by 180 degrees
  • the error e ′ is obtained by the inverse second channel target function block (Yuichi get output point error calculation block) 5 6, and the inverse of the transfer function of the equalizer of the second target equalizer 54 is It has a transfer function, and the error obtained by the adder 55 is equalized in the time domain by the equalizer function to obtain an error e 'at the output point of the first target equalizer 53. It is used for updating the coefficient of the first target equalizer 53.
  • the coefficient update block 5 of the present embodiment includes the adder 55, the inverse second channel target function block 56, the first evening get equalizer 53, and the second evening get equalizer 5. It is composed of a first difference calculation updating unit that updates each coefficient of 4 and TEQ 2.
  • the pseudo-random bit sequencers 12 1 and 51 add the same pattern of pseudo-random signals to the real route (TEQ 2) and the target route (delay block 52). .
  • the recursive equalizer 1 is set to the through setting by the recursive switching signal, the coefficient of the first target equalizer 53 is fixed, and the TEQ 2 and the second evening are set.
  • the coefficients of the one-get equalizer 54 are made variable, and the coefficients are updated adaptively (first acquisition process).
  • the coefficient updating method (automatic equalization algorithm) is that the target route output (the output of the second target equalizer 54) is subtracted from the actual route output (the output of TEQ 2) by the adder 55.
  • the error e obtained by the above, a well-known method of adaptively approaching the coefficient value in the multiplier in the transversal type equalizers 2, 54 to the best value is used. is there.
  • the second correction algorithm for the coefficient C (j) is expressed by the following equation (3).
  • Xj M represents the input signal sequence of TEQ2
  • e (v) represents the error.
  • the details of the automatic equalization algorithm are described in, for example, the document “Adaptive Signal Processing” (edited by Shokodo Shigeo Tsujii, first published on May 15, 1995, p. 24), and described in other documents other than the above. It is also possible to apply various algorithms.
  • the coefficient update block 5 next performs a second pull-in process in which the coefficient of the first target equalizer 53 is also made variable and the error e is further reduced. .
  • the recursive equalizer 1 and TEQ 2 are maintained in the through setting by the recursive switching signal.
  • the coefficient update block 5 performs the recursive equalizer 1 so that the transfer function of the recursive equalizer 1 becomes the reciprocal of the transfer function of the second target equalizer 54.
  • Set the tap coefficient of That is, the tap coefficients to be multiplied by multipliers 543 and 544 in FIG. 9 are set to the tap coefficients to be multiplied by multipliers 15 and 16 in FIG. 11, respectively.
  • the second target equalizer 54 on the target route side performs a process of setting to through, and the recursive equalizer 1 is set to non-through by a recursive switching signal.
  • the coefficient update block 5 makes the coefficient of the TEQ 2 and the coefficient of the first target equalizer 53 variable, and updates the coefficient so that the error e is further reduced.
  • the coefficient of the Jamaica equalizer 1 is fixed.
  • the tap coefficient is later set as the tap coefficient of the recursive equalizer 1, and the pole of the transfer function of the recursive equalizer 1 is set on the complex plane. It is necessary to check the updated value so that it is not placed outside the unit circle (hereinafter simply referred to as “unit circle”).
  • b O. 9, b ⁇ a—0.9, b ⁇ —a—0.9 is derived (actually, it is 1.0 instead of 0.9, In the case of actual operation, the margin is set to 0.9 in consideration of the effects of coefficient rounding, etc.). This indicates that it suffices that a and b exist within the triangular area shown in FIG.
  • the coefficient update block 5 controls the coefficient update by software so as to satisfy this condition. That is, the coefficient update block 5 sets the tap coefficients in the multipliers 542 and 543 to the multipliers 15 and 16 as they are when the pole exists outside the triangular area shown in FIG. If they exist outside the triangle area shown in Fig. 12, the vertices of the triangle shown in Fig. 12 are (-1.8,0.9), (1.8,0.9), and (0.0, -0.9), respectively. Depending on which side 6 to 8 of the triangle the pole (a, b) is near, the following three processes (1) to (3) are performed, and then a 'and b' are multiplied by multipliers 15, 16 Set to each.
  • the introduction of the IIR type recursive equalizer 1 having the denominator function as the transfer function (equalizer function) reduces the number of orders, With a small amount of hardware, it is possible to effectively compensate for a steep gain valley that TEQ 2 is not good at. Therefore, a good transmission amount, that is, a throughput can always be obtained regardless of the condition of the transmission path 300.
  • the coefficient of the recursive equalizer 1 the tap coefficient of the equalizer on the evening gate side is used at the time of training, so that the parameter can be obtained quickly and stably.
  • the F (frequency) characteristic of the first target equalizer 53 mainly depends on the characteristics of an analog filter (for example, filters 104 and 202 shown in FIG. 17) applied to the transmission side and the reception side.
  • an analog filter for example, filters 104 and 202 shown in FIG. 17
  • the second pull-in process may be omitted in some cases because an evening get equalizer with a fixed coefficient can be used substantially.
  • the arrangement position of the above-described recursive equalizer 1 can be considered to be after the TEQ 2 as shown in FIG. 13, for example.
  • the error e ⁇ for updating the tap coefficient of the TEQ 2 can be considered.
  • the same theory as the configuration shown in Fig. 4 (Fig. 6) ("The error used for updating the coefficients of the trans-persal equalizer is the output immediately after it)
  • the inverse recovery equalizer 1 ' is required.
  • the target equalizer is not separated from the first target equalizer 53 and the second target equalizer 54 as in the first embodiment, and the recursive equalization is performed as shown in FIG.
  • One (L + L '— first-order) channel target equalizer 57 whose order is increased by the order L', which is the denominator function of unit 1, performs the pull-in process, and at the stage when the coefficient training progresses, this target Factor the transfer function of equalizer 57 (Step S 1 in Figure 15), convert it to the product of a first-order or second-order z- 1 function, and select an appropriate one (L '— Extraction of linear function: As shown in step S 2) of FIG. 15 and FIG.
  • the coefficient updating block 5 performs processing to make the denominator function of the transfer function of the recursive equalizer 1 with the fixed coefficients on the real root side. For the remaining terms that are not set for relocation, function expansion is performed (step S4 in Fig. 15), and the tap coefficients are set so as to be the transfer function of the evening-equalizer 57 'with a predetermined order L or less. Try again.
  • the coefficient update block 5 in the second embodiment updates the tap coefficients of the evening equalizer 57 so that the difference between the output of the TEQ 2 and the output of the target equalizer 57 is minimized. It has a function as a second difference calculation update unit, and after the training period ends, the transfer function of the target equalizer 57 is factorized and the zero point is desirably present in the unit circle.
  • the tap coefficient of the recursive equalizer 1 is set so that the inverse function of the z function becomes the transfer function of the recursive equalizer 1 with fixed coefficients.
  • the transfer function has no denominator function and is only a numerator function, so its zero is allowed inside and outside the unit circle.
  • the denominator function of the transfer function of recursive equalizer 1 Since is not allowed outside the unit circle, we must check the zeros of the factorized function and select from the terms whose zeros are inside the unit circle. The check of the zero point is as described above in the first embodiment.
  • the frequency characteristics of the gain of the final target route should be as flat as possible in the transmission frequency band or as close to single-line characteristics as possible, and the gain should decrease monotonically with the frequency gap. Choose so that no large gain dips or peaks remain, or small gain dips or peaks.
  • the initial target equalizer 57 also includes a term corresponding to the recursive equalizer 1 as in this example, it is difficult to specify the initial value of the target equalizer 57. Therefore, in this case, it is desirable to provide an initial value to TEQ 2 and to initially fix the coefficient of TEQ 2 and make the coefficient of the target equalizer 57 variable.
  • the coefficient update block 5 updates the coefficient of the TEQ 2 and the target equalizer 5 7 ′ while fixing the coefficient of the recursive equalizer 1, and further compresses the error e. .
  • a fixed-coefficient recursive equalizer 1 updated at the evening-get-point side during training is introduced, thereby reducing the amount of hardware. Therefore, it is possible to sufficiently compensate for the steep gain valley of the received signal that TEQ 2 is not good at. Therefore, irrespective of the conditions of the transmission path 300, a good transmission amount, that is, a throughput can always be obtained, and all parameters of the equalizer system can be obtained at high speed and in a stable manner.
  • either the time domain or the frequency domain calculation method can be applied to update the coefficients of the equalizer system.
  • the FIR type is realized by introducing a fixed coefficient IIR type equalizer that uses the tap coefficients of the Eich device that is updated stably on the target route side during training.
  • a fixed coefficient IIR type equalizer that uses the tap coefficients of the Eich device that is updated stably on the target route side during training.
  • High throughput can be secured. Therefore, high-speed, high-quality services can be provided to subscribers in ADSL services and the like, and their usefulness is considered to be extremely high.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Power Engineering (AREA)
  • Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)

Abstract

Pour calculer la mise à jour de coefficients, on utilise un dénominateur fourni par un égaliseur de type IIR (infinite impulse response) utilisé pour la fonction de transfert, et un numérateur fourni par un égaliseur de type FIR (finite impulse response) (53, 54). Cette association permet un calcul stable et adaptatif du coefficient pour l'égaliseur de type IIR. Afin de compenser suffisamment une forte pente de gain, en plus de ce que fait l'égaliseur de type FIR (2), il est ainsi possible d'utiliser l'égaliseur de type IIR alors qu'on ne pouvait pas le faire conventionnellement.
PCT/JP2002/001085 2002-02-08 2002-02-08 Egaliseur automatique et procede d'apprentissage des coefficients WO2003075482A1 (fr)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS583414A (ja) * 1981-06-30 1983-01-10 Fujitsu Ltd インパルス応答自動等化器
JPH0548391A (ja) * 1991-01-23 1993-02-26 Fujitsu Ltd 適応等化器
JPH05152893A (ja) * 1991-07-29 1993-06-18 Oki Electric Ind Co Ltd 適応等化器
JPH05152894A (ja) * 1991-07-29 1993-06-18 Oki Electric Ind Co Ltd 適応等化器
JP2000244777A (ja) * 1999-02-23 2000-09-08 Matsushita Electric Ind Co Ltd 波形等化装置

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS583414A (ja) * 1981-06-30 1983-01-10 Fujitsu Ltd インパルス応答自動等化器
JPH0548391A (ja) * 1991-01-23 1993-02-26 Fujitsu Ltd 適応等化器
JPH05152893A (ja) * 1991-07-29 1993-06-18 Oki Electric Ind Co Ltd 適応等化器
JPH05152894A (ja) * 1991-07-29 1993-06-18 Oki Electric Ind Co Ltd 適応等化器
JP2000244777A (ja) * 1999-02-23 2000-09-08 Matsushita Electric Ind Co Ltd 波形等化装置

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