Equalisation apparatus and methods

• US 7,333,540 B2
• Filed: 10/09/2003
• Issued: 02/19/2008
• Est. Priority Date: 10/15/2002
• Status: Expired due to Fees

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Yee, Mong Suan
• Primary Examiner(s): Ghayour; Mohammed
• Assistant Examiner(s): PANWALKAR, VINEETA S
• Application Number:
  US10/681,300
• Publication Number:
  US 20040132416A1
• Time in Patent Office: 1,594 Days
• Field of Search: 375229-232, 375/345, 375/130, 375/316
• US Class Current: 375/232
• CPC Class Codes: H04L 1/0618 Space-time coding
• CPC Class Codes: H04L 2025/03414 Multicarrier
• CPC Class Codes: H04L 25/03171 Arrangements involving maximum a posteriori probability [MAP] detection

Abstract

The invention relates to apparatus, methods and computer program code for equalisation. A soft-in-soft-out (SISO) equaliser for use in a receiver for receiving data from a transmitter configured to transmit data from a plurality of transmit antennas simultaneously is described. The equaliser comprises at least one received signal input for inputting a received signal; a plurality of likelihood value inputs, one for each transmit antenna, for inputting a plurality of decoded signal likelihood values from a SISO decoder; a processor configured to determine from said plurality of signal likelihood values an estimated mean and covariance value for a signal from each of said transmit antennas; an expected signal determiner coupled to said processor to determine an expected received signal value using said mean values; a subtractor coupled to said received signal input to subtract said expected received signal value from said received signal to provide a compensated signal; a filter coupled to said subtractor to filter said compensated signal to provide a plurality of estimated transmitted signal values, one for each said transmit antenna; a filter coefficient determiner coupled to said processor to determine coefficients of said filter using said covariance values; and an output stage coupled to said filter to output a plurality of transmitted signal likelihood values, one for each said transmit antenna, for input to said SISO decoder.

Claims

1. A soft-in-soft-out (SISO) equaliser for use in a receiver of a communications system employing a plurality of transmit antennas, the equaliser comprising:

at least one received signal input for inputting a received signal;

a plurality of likelihood value inputs, one for each transmit antenna, for inputting a plurality of decoded signal likelihood values from a SISO decoder;

a processor configured to determine from said plurality of signal likelihood values an estimated mean and covariance value for a signal from each of said transmit antennas;

an expected signal determiner coupled to said processor to determine an expected received signal value using said mean values;

a subtractor coupled to said received signal input to subtract said expected received signal value from said received signal to provide a compensated signal;

a filter coupled to said subtractor to filter said compensated signal to provide a plurality of estimated transmitted signal values, one for each said transmit antenna;

a filter coefficient determiner coupled to said processor to determine coefficients of said filter using said covariance values; and

an output stage coupled to said filter to output a plurality of transmitted signal likelihood values, one for each said transmit antenna, for input to said SISO decoder.

2. A SISO equaliser as claimed in claim 1 further comprising an adjuster to adjust said expected received signal value by an amount dependent upon said estimated mean values.

3. A SISO equaliser as claimed in claim 2 further comprising a filter gain controller configured to control the gain of said filter dependent upon said estimated covariance values.

4. A SISO equaliser as claimed in claim 1 wherein said filter comprises a linear or transversal filter.

5. A SISO equaliser as claimed in claim 1 wherein said filter coefficient determiner is configured to determine said filter coefficients according to a mean square error cost function.

6. A SISO equaliser as claimed in claim 1 wherein said filter coefficient determiner is configured to determine said filter coefficients responsive to covariance values of estimated transmitted signal values derived from said signal likelihood values from said SISO decoder.

7. A SISO equaliser as claimed in claim 1 configured to utilise substantially constant filter coefficients for equalising a block or packet of received data symbols.

8. A SISO equaliser as claimed in claim 7 wherein said filter coefficient determiner is configured to operate in the frequency domain, said equaliser further comprising Fourier transform means prior to said filter and inverse Fourier transform means following said filter.

9. A SISO equaliser as claimed in claim 1 for use in a receiver for receiving data from a transmitter configured to transmit data from a plurality of transmit antennas simultaneously, the equaliser comprising a plurality of received signal inputs each coupled to said subtractor for inputting a plurality of received signals one from each of a plurality of receive antennas, and wherein said subtractor is configured to subtract a plurality of expected signal values relating to said plurality of receive antennas from said plurality of received signals to provide compensated signals to said filter.

10. A receiver incorporating a soft-in-soft-out (SISO) equaliser for use in a receiver of a communications system employing a plurality of transmit antennas, the equaliser comprising:

at least one received signal input for inputting a received signal;

a plurality of likelihood value inputs, one for each transmit antenna, for inputting a plurality of decoded signal likelihood values from a SISO decoder;

a processor configured to determine from said plurality of signal likelihood values an estimated mean and covariance value for a signal from each of said transmit antennas;

an expected signal determiner coupled to said processor to determine an expected received signal value using said mean values;

a subtractor coupled to said received signal input to subtract said expected received signal value from said received signal to provide a compensated signal;

a filter coupled to said subtractor to filter said compensated signal to provide a plurality of estimated transmitted signal values, one for each said transmit antenna;

a filter coefficient determiner coupled to said processor to determine coefficients of said filter using said covariance values; and

an output stage coupled to said filter to output a plurality of transmitted signal likelihood values, one for each said transmit antenna, for input to said SISO decoder.

11. A method of equalising received data in a communications system employing a receiver with at least one receive antenna and a transmitter with a plurality of transmit antennas, the method comprising:

inputting at least one received signal from said at least one receive antenna;

inputting a plurality of decoded signal likelihood values, one for each transmit antenna, from a SISO decoder;

determining from said plurality of signal likelihood values an estimated mean and covariance value for a signal from each of said transmit antennas;

determining an expected received signal value using said mean values;

subtracting said expected received signal value from said received signal to provide a compensated signal;

determining coefficients for a filter using said covariance values;

filtering said compensated signal in accordance with said coefficients to provide a plurality of estimated transmitted signal values, one for each said transmit antenna; and

outputting a plurality of transmitted signal likelihood values, one for each said transmit antenna, derived from said estimated transmitted signal values, for input to said SISO decoder.

12. A method as claimed in claim 11 further comprising adjusting said expected received signal value by an amount dependent upon said estimated mean values.

13. A method as claimed in claim 12 further comprising controlling the gain of said filter dependent upon said estimated covariance values.

14. A method as claimed in claim 11 wherein said filtering comprises linear or transversal filtering.

15. A method as claimed in claim 11 wherein said determining substantially minimises a mean square estimated transmitted signal error cost function.

16. A method as claimed in claim 11 wherein said determining is responsive to covariance values of estimated transmitted signal values derived from said signal likelihood values from said SISO decoder.

17. A method as claimed in claim 11 further comprising maintaining said filter coefficients substantially constant over a block or packet of received data symbols.

18. A method as claimed in claim 11 wherein said filtering is performed in the frequency domain.

19. A method as claimed in claim 18 further comprising transforming said received signal into the frequency domain prior to said filtering and transforming the result of said filtering into the time domain following said filtering.

20. A method as claimed in claim 11 for use in a receiver receiving data from a transmitter configured to transmit data from a plurality of transmit antennas simultaneously, the method comprising inputting a plurality of received signals from a plurality of receive antennas, and wherein said subtracting comprises subtracting a plurality of expected signal values relating to said plurality of receive antennas from said plurality of received signals to provide compensated signals for said filtering.

21. A method of turbo equalisation comprising iteratively equalising data by the method comprising:

inputting at least one received signal from said at least one receive antenna;

inputting a plurality of decoded signal likelihood values, one for each transmit antenna, from a SISO decoder;

determining from said plurality of signal likelihood values an estimated mean and covariance value for a signal from each of said transmit antennas;

determining an expected received signal value using said mean values;

subtracting said expected received signal value from said received signal to provide a compensated signal;

determining coefficients for a filter using said covariance values;

filtering said compensated signal in accordance with said coefficients to provide a plurality of estimated transmitted signal values, one for each said transmit antenna;

outputting a plurality of transmitted signal likelihood values, one for each said transmit antenna, derived from said estimated transmitted signal values, for input to said SISO decoder; and

decoding said transmitted signal likelihood values from said equalising to provide decoded signal likelihood values for said equalising.

22. A method of equalising data in a receiver of a communications system with a plurality n_I of transmit antennas the method comprising:

inputting a received signal vector Z_n comprising a block of received signal data at an index n;

inputting from a SISO decoder a set of bit likelihood values L(c_n,jⁱ), i=1 to n_I, j=1 to m where c_n,jⁱ, denotes a portion of an m-bit codeword symbol at an index n;

determining expectation E(x_nⁱ) and covariance cov(x_nⁱ,x_nⁱ) values for estimated transmitted signal values x_nⁱ using the values L(c_n,jⁱ) where x_nⁱ denotes an estimated value of a signal transmitted from a transmit antenna i at an index n;

determining an updated estimated transmitted signal value {circumflex over (x)}_nⁱ at index n for each transmit antenna i using {circumflex over (x)}_nⁱ=K_nⁱf_n^iH[Z_n−

(E(Z_n)−

eⁱE(x_nⁱ))] where E(Z_n)=HE(X_n) and H is a channel impulse response matrix and E(X_n) is an expectation value of an estimated transmitted signal vector X_n at index n derived from values E(x_nⁱ), where eⁱ is the ith column of a matrix S and S=H[0<sub>nI×

(N2+L−

1)nI</sub> I<sub>nI×

nI</sub> 0<sub>nI×

N1nI</sub>]^H where matrix I<sub>i×

i</sub> is an i×

i identity matrix and 0<sub>i×

j</sub> is a matrix in which each element is substantially zero, f_nⁱ is the ith column of a filter matrix F_n and F_n is derived from cov(x_n,x_n), and where K_nⁱ is a scalar filter gain; and

outputting equalised likelihood values L_e(c_n,jⁱ) derived from values {circumflex over (x)}_nⁱ.

23. A method of equalising data as claimed in claim 22 further comprising decoding said values L_e(c_n,jⁱ) to provide said values L(c_n,jⁱ).

24. A method as claimed in claim 23 comprising iteratively equalising and decoding to determine values for L_e(c_n,jⁱ) and L(c_n,jⁱ) until a termination criterion is reached.

25. A method as claimed in claim 24 further comprising deinterleaving said L_e(c_n,jⁱ) values and interleaving said L(c_n,jⁱ) values.

26. A method as claimed in claim 22 wherein F_n is derived from [R_WW+HR_XXH^H]⁻

1S where R_XX=cov(x_n,x_n) and R_WW is a noise covariance matrix.

27. A method as claimed in claim 22 wherein n indexes time.

28. A method as claimed in claim 22 wherein n indexes frequency.

29. Processor control code to, when running, implement a method of equalising received data in a communications system employing a receiver with at least one receive antenna and a transmitter with a plurality of transmit antennas, the method comprising:

inputting at least one received signal from said at least one receive antenna;

inputting a plurality of decoded signal likelihood values, one for each transmit antenna, from a SISO decoder;

determining from said plurality of signal likelihood values an estimated mean and covariance value for a signal from each of said transmit antennas;

determining an expected received signal value using said mean values;

subtracting said expected received signal value from said received signal to provide a compensated signal;

determining coefficients for a filter using said covariance values;

filtering said compensated signal in accordance with said coefficients to provide a plurality of estimated transmitted signal values, one for each said transmit antenna; and

outputting a plurality of transmitted signal likelihood values, one for each said transmit antenna, derived from said estimated transmitted signal values, for input to said SISO decoder.

30. A carrier carrying the processor control code of claim 29.

31. An equaliser configured to operate in accordance with a method of equalising received data in a communications system employing a receiver with at least one receive antenna and a transmitter with a plurality of transmit antennas, the method comprising:

inputting at least one received signal from said at least one receive antenna;

inputting a plurality of decoded signal likelihood values, one for each transmit antenna, from a SISO decoder;

determining from said plurality of signal likelihood values an estimated mean and covariance value for a signal from each of said transmit antennas;

determining an expected received signal value using said mean values;

subtracting said expected received signal value from said received signal to provide a compensated signal;

determining coefficients for a filter using said covariance values;

filtering said compensated signal in accordance with said coefficients to provide a plurality of estimated transmitted signal values, one for each said transmit antenna; and

outputting a plurality of transmitted signal likelihood values, one for each said transmit antenna, derived from said estimated transmitted signal values, for input to said SISO decoder.

32. A data communications receiver including an equaliser configured to operate in accordance with a method of equalising received data in a communications system employing a receiver with at least one receive antenna and a transmitter with a plurality of transmit antennas, the method comprising:

inputting at least one received signal from said at least one receive antenna;

inputting a plurality of decoded signal likelihood values, one for each transmit antenna, from a SISO decoder;

determining from said plurality of signal likelihood values an estimated mean and covariance value for a signal from each of said transmit antennas;

determining an expected received signal value using said mean values;

subtracting said expected received signal value from said received signal to provide a compensated signal;

determining coefficients for a filter using said covariance values;

filtering said compensated signal in accordance with said coefficients to provide a plurality of estimated transmitted signal values, one for each said transmit antenna; and

outputting a plurality of transmitted signal likelihood values, one for each said transmit antenna, derived from said estimated transmitted signal values, for input to said SISO decoder.

33. Processor control code to, when running, implement a method of equalising data in a receiver of a communications system with a plurality n, of transmit antennas the method comprising:

inputting a received signal vector Z_n comprising a block of received signal data at an index n;

inputting from a SISO decoder a set of bit likelihood values L(c_n,jⁱ), i=1 to n_I, j=1 to m where c_n,jⁱ, denotes a portion of an m-bit codeword symbol at an index n;

determining expectation E(x_nⁱ) and covariance cov(x_nⁱ,x_nⁱ) values for estimated transmitted signal values x_nⁱ using the values L(c_n,jⁱ) where x_nⁱ denotes an estimated value of a signal transmitted from a transmit antenna i at an index n;

determining an updated estimated transmitted signal value {circumflex over (x)}_nⁱ at index n for each transmit antenna i using {circumflex over (x)}_nⁱ=K_nⁱf_n^iH[Z_n−

(E(Z_n)−

eⁱE(x_n ⁱ))] where E(Z_n)=HE(X_n) and H is a channel impulse response matrix and E(X_n) is an expectation value of an estimated transmitted signal vector X_n at index n derived from values E(x_nⁱ), where eⁱ is the ith column of a matrix S and S=H[0<sub>nI×

(N2+L−

1</sub>)n_I I<sub>nI×

mI</sub> 0<sub>nI×

N1nI</sub>]^H where matrix I<sub>i×

i</sub> is an i×

i identity matrix and 0<sub>i×

j</sub> is a matrix in which each element is substantially zero, f_nⁱ is the ith column of a filter matrix F_n and F_n is derived from cov(x_n,x_n), and where K_nⁱ is a scalar filter gain; and

outputting equalised likelihood values L_e(C_n,jⁱ) derived from values {circumflex over (x)}_nⁱ.

34. A carrier carrying the processor control code of claim 33.

35. An equaliser configured to operate in accordance with a method of equalising data in a receiver of a communications system with a plurality n_I of transmit antennas the method comprising:

inputting a received signal vector Z_n comprising a block of received signal data at an index n;

inputting from a SISO decoder a set of bit likelihood values L(c_n,jⁱ), i=1 to n_I, j=1 to m where c_n,jⁱ, denotes a portion of an m-bit codeword symbol at an index n;

determining expectation E(x_nⁱ) and covariance cov(x_nⁱ,x_nⁱ) values for estimated transmitted signal values x_nⁱ using the values L(c_n,jⁱ) where x_nⁱ denotes an estimated value of a signal transmitted from a transmit antenna i at an index n;

determining an updated estimated transmitted signal value {circumflex over (x)}_nⁱ at index n for each transmit antenna i using {circumflex over (x)}_nⁱ=K_nⁱf_n^iH[Z_n−

(E(Z_n)−

eⁱE(x_nⁱ ))] where E(Z_n)=HE(X_n) and H is a channel impulse response matrix and E(X_n) is an expectation value of an estimated transmitted signal vector X_n at index n derived from values E(x_nⁱ) where eⁱ is the ith column of a matrix S and S=H[0<sub>nI×

(N2+L−

1)nI</sub> I<sub>nI×

nI</sub> 0<sub>nI×

N1nI</sub>]^H where matrix I<sub>i×

i</sub> is an i×

i identity matrix and 0<sub>i×

j</sub> is a matrix in which each element is substantially zero, f_nⁱ is the ith column of a filter matrix F_n and F_n is derived from cov(x_n, x_n), and where K_nⁱ is a scalar filter gain; and

outputting equalised likelihood values L_e(c_n,jⁱ ) derived from values {circumflex over (x)}_nⁱ.

36. A data communications receiver including an equaliser configured to operate in accordance with a method of equalising data in a receiver of a communications system with a plurality n_I of transmit antennas the method comprising:

inputting a received signal vector Z_n comprising a block of received signal data at an index n;

inputting from a SISO decoder a set of bit likelihood values L(c_n,jⁱ), i=1 to n_I, j=1 to m where c_n,jⁱ denotes a portion of an m-bit codeword symbol at an index n;

determining expectation E(x_nⁱ) and covariance cov(x_nⁱ,x_nⁱ) values for estimated transmitted signal values x_nⁱ using the values L(c_n,jⁱ), where x_nⁱ denotes an estimated value of a signal transmitted from a transmit antenna i at an index n;

determining an updated estimated transmitted signal value {circumflex over (x)}_nⁱ at index n for each transmit antenna i using {circumflex over (x)}_nⁱ=K_nⁱf_n^iH[Z_n−

(E(Z_n)−

eⁱE(x_nⁱ ))] where E(Z_n)=HE(X_n) and H is a channel impulse response matrix and E(X_n) is an expectation value of an estimated transmitted signal vector X_n at index n derived from values E(x_nⁱ), where eⁱ is the ith column of a matrix S and S=H[0<sub>nI×

(N2+L−

1)nI</sub> I<sub>nI×

nI</sub> 0<sub>nI×

N1nI</sub>]^H where matrix I<sub>i×

i</sub> is an i×

i identity matrix and 0<sub>i×

j</sub> is a matrix in which each element is substantially zero, f_nⁱ is the ith column of a filter matrix F_n and F_n is derived from cov(x_n,x_n), and where K_nⁱ is a scalar filter gain; and

outputting equalised likelihood values L_e(c_n,jⁱ) derived from values {circumflex over (x)}_nⁱ.