Technique for adaptive equalization in band-limited high data rate communication over fading dispersive channels

• US 7,590,204 B2
• Filed: 02/06/2006
• Issued: 09/15/2009
• Est. Priority Date: 02/14/2005
• Status: Expired due to Fees

• Current Assignee: Peter Monsen
• Original Assignee: Peter Monsen
• Inventors: Monsen, Peter
• Primary Examiner(s): Tran; Khanh C
• Application Number:
  US11/348,816
• Publication Number:
  US 20060182193A1
• Time in Patent Office: 1,317 Days
• Field of Search: 375/229, 375/233, 375/260, 375/267, 375/285, 375/340, 375346-350
• US Class Current: 375/350
• CPC Class Codes: H04L 1/0047 Decoding adapted to other signal detection operation in conjunction with sequence estimation or equalization H04L25/03286
• CPC Class Codes: H04L 1/0631 Receiver arrangements
• CPC Class Codes: H04L 2025/03426 transmission using multiple-input and multiple-output channels
• CPC Class Codes: H04L 25/0224 using sounding signals
• CPC Class Codes: H04L 25/03057 with a recursive structure H04L25/03031 takes precedence

Abstract

In high data rate communication applications where digital data information is error-corrected coded and interleaved and transmitted with spectral limitations over fading dispersive channels, a method and receiver is described that incorporates channel estimation and decision-feedback equalization. Channel estimation is accomplished within a receiver time block with locally generated reference symbol sequences. The parameters of the decision-feedback equalizer (DFE) are computed directly from the channel estimates. The DFE is an optimum finite length realization that includes effects from spectrum control filtering, a space-time block coder (STBC) on multiple transmit antennas, multiple receiver diversity signals, and the fading dispersive channel. The DFE includes a matched filter, forward filter, backward filter, and detector. A symbol combiner within the matched filter produces a P+1 dimensional signal that provides ideal cancellation of P intersymbol interferers in the forward filter. When P is selected to meet an intersymbol interference (ISI) criterion, all desired signal energy is collected and all ISI can be ideally cancelled. The DFE processes received signals within the receiver time block to produce information symbol estimates that are subsequently deinterleaved and error-correction decoded to recover the transmitted digital data information. Deinterleaving over multiple receiver time blocks further compensates for channel estimation variations from block to block. Additionally the STBC and DFE are used in a quadruple angle diversity technique requiring only a single antenna at each terminal of a troposcatter link to provide performance approaching that of a nonfading satellite link.

Claims

1. In a high data rate communication receiver, wherein received signals contain digital data information that is error-corrected coded and interleaved to provide information symbols that are subsequently combined with reference symbols to provide a frame of data symbols that are filtered with a finite duration spectrum control impulse response for transmission at the data symbol rate by one or more transmit antennas over a fading dispersive channel with an associated set of multipath delays, a method of operating said receiver to enable said receiver to provide receive signals from one or more receive antennas and to produce within a data frame successive information symbol estimates that are subsequently used to reconstruct the digital data information, comprising the steps of:

time-sampling received signals at an integer multiple, greater than one, of the data symbol rate within a receiver time block that has a time duration that is no more than one-half of the interleaving delay;

correlating the time-sampled received signals and the spectrum control impulse response to provide fixed filter correlated signals;

symbol combining the fixed filter correlated signals to provide nonstationary fixed filter matched signals, that depend on an estimation interval, corresponding to one or more information symbols and with duration equal to an integer multiple of the data symbol rate reciprocal, and that further depend on data symbol intervals within and later than the estimation interval;

estimating channel parameters associated with the receiver time block that depend on products of the reference symbols and the nonstationary fixed filter matched signals;

channel processing the nonstationary fixed filter matched signals and the channel parameters to provide channel matched signals;

computing forward and backward filter weights that functionally depend on the channel parameters;

creating past interference signals that depend on the estimation interval;

multiplying the channel matched signals and the forward filter weights and further subtracting the past interference signals to provide the information symbol estimates;

deinterleaving and decoding the information symbol estimates;

selecting, from each estimation interval containing one or more information symbol estimates, associated information symbol decisions corresponding to possible transmitted information symbols; and

wherein the creating step further includes;

multiplying the backward filter weights and the information symbol decisions from previous estimation intervals.

2. The method of claim 1 wherein the estimating step further includes the steps of:

multiplying the nonstationary fixed filter matched signals by the reference symbols to provide coarse channel parameters;

reference processing the reference symbols to provide a correction matrix;

multiplying the correction matrix and coarse channel parameters.

3. The method of claim 2 wherein the forward and backward filter weights minimize the mean square error between the information symbol estimate and the associated information symbol.

4. The method of claim 1 wherein a block of K information symbols are coded according to a space-time codebook to provide K_T≧

K code blocks of L≧

K_T coded symbols for transmission from each of K_T associated transmit antenna ports and where in the symbol combining step the number of information symbols in the estimation interval is K and the integer multiple is equal to L and the fixed matched filter signals depend on data symbol intervals associated with coded symbols transmitted at the same time or later than the first coded symbol in the code block and wherein the channel processing step further includes;

channel combining the nonstationary fixed filter matched signals and channel parameters to provide coded matched signals;

multiplying the coded matched signals and a decoder matrix that depends on the space-time codebook to provide the channel matched signals.

5. The method of claim 4 wherein the duration of the spectrum control impulse response spans I data symbols and the set of multipath delays spans a duration of C data symbols and the symbol combining step further includes fixed filter matched signals that correspond to the coded symbol with delay of P symbols relative to the first coded symbol and wherein P+1 is the smallest integer multiple of L that satisfies the constraint P+1≧

I+C+L−

1.

6. The method of claim 5 wherein the number of receive signals is D>

1 and the estimating step further includes;

calculating a channel vector for each of the K_TD transmission paths; and

wherein the symbol combining step further includes;

generating for each of the D receive signals a diversity fixed filter matched signal vector; and

wherein the channel processing step further includes;

computing a dot product between a channel vector and the respective diversity fixed filter matched signal vector.

7. The method of claim 6 wherein the data symbols are selected from the MPSK set and the computing step further includes:

storing precalculated spectrum control correlation matrices that depend on a continuous set of multipath delays;

matrix multiplying the spectrum control correlation matrices by channel parameters to provide forward and backward transfer matrices;

parameter processing the forward and backward transfer matrices to provide the respective forward and backward weights;

and wherein the estimating step further includes;

statistically calculating diversity correlation for use in antenna alignment.

8. For use in a high data rate communication system, wherein digital data information is error-corrected coded and interleaved to provide information symbols that are subsequently time-division multiplexed with reference symbols to provide a frame of data symbols that are filtered with a finite duration spectrum control impulse response for transmission at the data symbol rate by one or more transmit antennas over a fading dispersive channel with an associated set of multipath delays, a receiving apparatus(12), connected to one or more receive antennas that produce one or more received signals, comprising:

down-converter(30) for time-sampling the received signals at an integer multiple, greater than one, of the data symbol rate to provide received vectors within a receiver time block that has a time duration that is no more than one-half of the interleaving delay;

fixed filter correlator(50) for correlating the received vectors and the spectrum control impulse response to provide fixed filter correlated signals;

symbol combiner(51) for combining the fixed filter correlated signals to provide nonstationary fixed filter matched signals, that depend on an estimation interval, of duration equal to the data symbol rate reciprocal, associated with the estimation of a respective information symbol and the nonstationary fixed matched filter signals correspond to information symbols transmitted at the same time and later than the respective information symbol;

channel estimator(32) for combining the reference symbols and the nonstationary fixed filter matched signals to provide channel parameters associated with the receiver time block;

channel matched filter(52) for combining the nonstationary fixed filter matched signals and channel parameters to provide channel matched signals;

equalizer calculator(33) for computing forward and backward transfer matrices that are functions of the spectrum control impulse response and the channel parameters and for processing the forward and backward transfer matrices to provide respective forward and backward filter weights;

backward filter(42) for creating past interference signals that depend on the estimation interval;

forward filter(41) for multiplying the channel matched signals and the forward filter weights to provide multiplication products and for combining the multiplication products with the past interference signals to provide information symbol estimates for successive estimation intervals within the data frame;

detector(43) for selecting, at the data symbol rate, from the information symbol estimate an information symbol decision corresponding to the closest possibly transmitted information symbol;

deinterleaver and decoder(34) for reconstructing the digital data information from information symbol estimates;

and wherein the backward filter(42) further includes;

backward filter branch(62) for multiplying the backward filter weights and the information symbol decisions from previous estimation intervals to provide the past interference signals.

9. A receiver apparatus(12) according to claim 8 wherein the channel estimator further includes:

coarse channel selector(71) for multiplying the nonstationary fixed filter matched signals by the reference symbols to provide coarse channel parameters;

correction matrix calculator(72) for processing the reference symbols to provide a correction matrix;

channel vector calculator(73) for multiplying the correction matrix and coarse channel parameters to provide the channel parameters.

10. For use in a high data rate communication system, wherein digital data information is error-corrected coded and interleaved to provide groups of K information symbols that are block coded according to a space-time codebook to produce successive groups of K_T≧

K code blocks containing L≧

K_T coded symbols that are subsequently time-division multiplexed with K_T respective reference symbol sequences to provide K_T frames of data symbols that are each filtered with a finite duration spectrum control impulse response for transmission at the data symbol rate from respective K_T transmit antenna ports over a fading dispersive channel with an associated set of multipath delays, a receiving apparatus(12), connected to one or more receive antennas that produce one or more received signals, comprising;

down-converter(30) for time-sampling the received signals at an integer multiple, greater than one, of the data symbol rate to provide received vectors within a receiver time block that has a time duration that is no more than one-half of the interleaving delay;

fixed filter correlator(50) for correlating the received vectors and the spectrum control impulse response to provide fixed filter correlated signals;

symbol combiner(51) for combining the fixed filter correlated signals to provide nonstationary fixed filter matched signals, that depend on an estimation interval, of duration equal to L times the data symbol rate reciprocal, associated with the estimation of K information symbols and the nonstationary fixed matched filter signals correspond to coded symbols transmitted at the same time or later than the first coded symbol in the associated code block;

channel estimator(32) for combining reference symbols and nonstationary fixed filter matched signals to provide channel parameters associated with the receiver time block;

channel matched filter(52) for combining the fixed filter matched signals and channel parameters to provide coded matched signals and for decoding the coded matched signals to provide the channel matched signals;

equalizer calculator(33) for matrix multiplying spectrum control correlation matrices that depend on the set of multipath delays and channel parameter matrices to provide forward and backward transfer matrices and for processing the forward and backward transfer matrices to provide respective forward and backward filter weights;

backward filter(42) for creating past interference signals that depend on the estimation interval;

forward filter(41) for multiplying the channel matched signals and the forward filter weights to provide multiplication products and for combining the multiplication products with the past interference signals to provide information symbol estimates for successive estimation intervals within the data frame;

detector(43) for quantizing each information symbol estimate to provide an information symbol decision that corresponds to the closest possibly transmitted information symbol.

deinterleaver and decoder(34) for reconstructing the digital data information from information symbol estimates;

and wherein the backward filter(42) further includes;

K backward filter branches(62) for multiplying the backward filter weights and the information symbol decisions from previous estimation intervals to provide the past interference signals.

11. A receiver apparatus(12) according to claim 10 wherein the equalizer calculator(33) further includes:

means for computing forward and backward filter weights that minimize the mean square error between the information symbol estimate and the associated information symbol.

12. A receiver apparatus(12) according to claim 11 wherein the number of receive signals is D≧

1 and the channel estimator(32) further includes;

means for estimating a channel vector for each of the K_T D transmission paths; and

wherein the symbol combiner(51) further includes;

means for generating for each of the D receive signals a diversity fixed filter matched signal vector; and

wherein the channel matched filter(52) further includes;

means for computing a dot product between a channel vector and the respective diversity fixed filter matched signal vector.

13. A receiver apparatus(12) according to claim 12 wherein the symbol combiner(51) further includes fixed filter matched signals that correspond to the coded symbol with delay of P symbols relative to the first coded symbol and wherein P+1 is the smallest integer multiple of L that satisfies the constraint P+1≧

I+C+L−

1 where the duration of the spectrum control impulse spans I data symbols and the set of multipath delays spans a duration of C data symbols.

14. A receiver apparatus(12) according to claim 13 wherein the equalizer calculator(51) further includes:

means for storing constant spectrum control matrices that are functions of a continuous set of multipath delays.

15. In a high data rate communication receiver, wherein received signals contain digital data information that is error-corrected coded and interleaved to provide information symbols that are subsequently combined with reference symbols to provide a frame of data symbols that are filtered with a finite duration spectrum control impulse response for transmission at the data symbol rate by one or more transmit antennas over a fading dispersive channel with an associated set of multipath delays, a method of operating said receiver to enable said receiver to provide receive signals from one or more receive antennas and to produce within a data frame successive information symbol estimates that are subsequently used to reconstruct the digital data information, comprising the steps of:

time-sampling the received signals at an integer multiple, greater than one, of the data symbol rate to provide received vectors within a receiver time block that has a time duration that is no more than one-half of the interleaving delay;

correlating the received vectors and the spectrum control impulse response to provide fixed filter correlated signals;

symbol combining the fixed filter correlated signals to provide nonstationary fixed filter matched signals, that depend on an estimation interval, corresponding to one or more information symbols and with duration equal to an integer multiple of the data symbol rate reciprocal, and that further depend on data symbol intervals within and later than the estimation interval;

estimating channel parameters associated with the receiver time block that depend on products of the reference symbols and the nonstationary fixed filter matched signals;

creating past interference signals that depend on the estimation interval;

channel processing the nonstationary fixed filter matched signals and the channel parameters to provide channel matched signals;

computing forward and backward filter weights that functionally depend on the channel parameters;

multiplying the channel matched signals and the forward filter weights to provide the information symbol estimates;

deinterleaving and decoding the information symbol estimates;

selecting, from each estimation interval containing one or more information symbol estimates, associated information symbol decisions corresponding to possible transmitted information symbols; and

wherein the creating step further includes;

multiplying the backward filter weights and the information symbol decisions from previous estimation intervals.

wherein the channel processing step further includes;

channel combining the nonstationary fixed filter matched signals and channel parameters to provide combined matched signals;

intersymbol-interference combining the combined matched signals and the past interference signals to provide the channel matched signals.

16. A method for operating a high data rate communication system wherein at a transmitting terminal digital data information is error-correction coded and interleaved over an interleaver duration to provide information symbols within a periodic data frame for transmission over a fading dispersive channel and wherein at a receiving terminal information symbol estimates are produced from received signals, comprising:

at the transmitting terminal the steps of;

coding two information symbols according to a space-time codebook to provide two code blocks containing coded symbols;

transmitting at the same polarization the two code blocks at a coded symbol rate on respective antenna ports associated with two vertically splayed transmit beams; and

at the receiving terminal the steps of;

receiving at the same polarization two diversity signals from respective antenna ports associated with two vertically splayed receive beams;

time-sampling the diversity signals at an integer multiple, greater than one, of the coded symbol rate;

estimating angle diversity channel parameters associated with each of the four transmit and receive beam combinations;

processing the time-sampled diversity signals with angle diversity channel parameters to provide four respective diversity nonstationary matched signals;

summing diversity nonstationary matched signals associated with the same transmit beam to provide coded matched signal vectors;

multiplying the coded matched signals and a decoder matrix that depends on the space-time codebook to provide channel matched signals;

equalizing the channel matched signals to provide successive groups each containing two information symbol estimates that depend on quantized information estimates from previous groups.

17. The method of claim 16 wherein the transmitting and receiving terminals are collocated and operate with simultaneous-in-time transmitting and receiving signals that have respectively different frequency bands.

18. The method of claim 17 wherein the transmitting and receiving frequency bands are periodically changed with a frequency hop period that is equal to the data frame period and is no more than one-half the interleaver duration.

19. The method of claim 17 wherein the transmitting frequency band has a bandwidth that is greater than the coded symbol rate.

20. A method for operating a high data rate communication system wherein at a transmitting terminal digital data information is error-correction coded and interleaved over an interleaver duration into information symbols within a periodic data frame for transmission over a fading dispersive channel and wherein at a receiving terminal information symbol estimates are produced from received signals, comprising:

at the transmitting terminal the steps of;

coding two information symbols according to a space-time codebook to provide two code blocks containing coded symbols;

transmitting at the same polarization the two code blocks at a coded symbol rate on the lower of two vertically splayed transmit beams associated with respective horizontally separated antennas; and

at the receiving terminal the steps of;

receiving at the same polarization four diversity signals from respective antenna ports associated with two vertically splayed receive beams on each of two horizontally separated antennas;

time-sampling the diversity signals at an integer multiple, greater than one, of the coded symbol rate;

estimating angle diversity channel parameters associated with each of the eight transmit and receive beam combinations;

processing the time-sampled diversity signals by angle diversity channel parameters to provide eight respective diversity nonstationary matched signals;

summing diversity nonstationary matched signals associated with the same transmit antenna to provide coded matched signal vectors;

multiplying the coded matched signals and a decoder matrix that depends on the space-time codebook to provide channel matched signals;

equalizing the channel matched signals to provide successive groups each containing two information symbol estimates that depend on quantized information estimates from previous groups.

21. The method of claim 20 wherein the transmitting and receiving terminals are collocated and operate with simultaneous-in-time transmitting and receiving signals that have respectively different frequency bands.

22. The method of claim 21 wherein the transmitting and receiving frequency bands are periodically changed with a frequency hop period that is equal to the data frame period and is no more than one-half the interleaver duration.

23. The method of claim 21 wherein the transmitting frequency band has a bandwidth that is greater than the coded symbol rate.

24. For use in a high data rate communication system, wherein digital data information is error-corrected coded and interleaved over an interleaver duration to provide information symbols within a periodic data frame, a radio terminal apparatus(80) comprising:

dual-beam antenna (81) with two antenna ports that contain transmitting and receiving signals that have the same polarization for a particular transmission direction and each port is associated one of two vertically splayed beams;

modulator (22) for coding successive groups of two information symbols into successive groups of two space-time code blocks and each of the two space-time code blocks is associated with a respective vertically splayed beam;

spectrum control filter (24) for filtering data symbols associated with respective space-time code blocks to provide respective data signals that are contained within a prescribed bandwidth;

up-converter(25) for translating to a bandpass frequency band respective data signals for transmission as a transmitting signal on a respective vertically splayed beam;

down-converter(30) for translating a receiving signal associated with a respective vertically splayed beam to provide respective beam diversity signals;

duplexer (82) for separating the transmitting signals from the receiving signals;

channel estimator (32) for estimating angle diversity channel parameters of each of four paths corresponding to combinations of the two receive vertically splayed beams and two transmit vertically splayed beams associated with a distant radio terminal (30);

decision-feedback equalizer (31) for combining the angle diversity channel parameters and beam diversity signals to provide successive groups each containing two information symbol estimates that depend on quantized information estimates from previous groups.

25. A radio terminal apparatus according to claim 24 wherein up-converter (25) further includes:

means for periodically changing the center frequency of the bandpass frequency band with a frequency hop period that is equal to the data frame period and is no more than one-half the interleaver duration.

26. A radio terminal apparatus according to claim 24 wherein the interleaver duration is at least two data frame periods and the spectrum control filter (24) further includes;

means for multiplying the data symbols by a direct sequence waveform before filtering to the prescribed bandwidth.