Method and apparatus for multi-user detection using RSFQ successive interference cancellation in CDMA wireless systems

• US 7,440,490 B2
• Filed: 12/18/2002
• Issued: 10/21/2008
• Est. Priority Date: 12/18/2002
• Status: Expired due to Fees

• Current Assignee: Anna Kidiyarova-Shevchenko, Erik Strom, Tony Ottosson
• Original Assignee: Anna Kidiyarova-Shevchenko, Erik Strom, Tony Ottosson
• Inventors: Kidiyarova-Shevchenko, Anna, Strom, Erik, Ottosson, Tony
• Primary Examiner(s): TSE, YOUNG TOI
• Application Number:
  US10/321,609
• Publication Number:
  US 20040120299A1
• Time in Patent Office: 2,134 Days
• Field of Search: 375142-144, 375/147, 375/148, 375/150, 375/152, 375/260, 375/343, 370/320, 370/335, 370/342
• US Class Current: 375/148
• CPC Class Codes: H04B 1/7103 the interference being multiple access interference
• CPC Class Codes: H04B 1/7105 Joint detection techniques, e.g. linear detectors
• CPC Class Codes: H04B 1/71072 Successive interference cancellation

Abstract

A method and apparatus for using a multi-user detector for reducing multiple access interference (MAI) in a direct sequence CDMA wireless system such as W-CDMA. A superconducting rapid single flux quantum (RSFQ) RF digital receiver operating in combination with an RSFQ successive interference canceller (SIC) is located in the base stations of the wireless system. In the present invention, the RSFQ SIC is a vector machine capable of processing the cross-correlation matrices using an iterative method to decorrelate the user binary code sequences from the input signal in which the interference components are removed. According, the reduction in interference results in a significant increase in system capacity while improving cellular coverage area.

Claims

1. A method of reducing multi-user interference (MAI) in a wireless direct sequence CDMA wireless system comprising at least one base station transmitting to and receiving signals from a plurality of mobile station users, wherein the method includes reducing interference with a multi-user detector located within said at least one base station comprising the steps of:

receiving at the at least one base station a digital input signal comprised of a plurality of binary code sequences from the mobile station users;

processing the digital input signal with a bank of matched filters and producing matched filter output vectors from the bank of matched filters;

feeding the matched filter output vectors into a superconducting digital rapid single flux quantum (RSFQ) vector processing unit applying a successive interference cancellation (SIC) iterative technique (RSFQ SIC) to solve a cross-correlation matrix to decorrelate the plurality of binary code sequences;

reducing the interference by removing interference components between the binary code sequences; and

feeding an output from the RSFQ SIC into a bank of Rake combiners to recover original data transmitted by the mobile station users.

2. A method according to claim 1 wherein the implemented multi-user detector of the direct sequence CDMA wireless system operates in accordance with the Wideband Code Division Multiple Access (W-CDMA) standard.

3. A method according to claim 1 wherein in the receiving step, the binary code sequences from the mobile station users are W-CDMA Gold long spreading codes having a sequence length of 2⁴¹, or VL-Kasami short spreading codes with a sequence length of 256.

4. A method according to claim 1 wherein the RSFQ SIC operates at a frequency of at least 54 GHz and is capable of removing interference in a W-CDMA system operating with at least 100 simultaneous voice user per sector with at least 10 resolvable multipath components per user, and an effective support Q of a chip waveform determined by Q=3.

5. A method according to claim 1 wherein in the applying step, the SIC iterative technique employs a Gauss-Seidel iteration algorithm to solve the cross-correlation matrix R_MF of the binary code sequences given by,

${\left[R_{\mathrm{MF}}\right]}_{q,r}=\sum _{}^{}$

m = - ( N - 1 ) N - 1 ⁢

⁢

v ( [ mN s + ( n - n ′

) ⁢

NN S + ( p k , l - P k ′

, l ′

) +  

QN s ] ⁢

T c / N s ) ⁢

⁢

∑

i = 0 N - 1 ⁢

⁢

c n , k ′

⁡

[ i ] ⁢

⁢

c n ′

, k ′

′

⁡

[ i - m ]

where k, l, n and k′

, l′

, n′

depend on q and r, c_n,k^′

[i] is the binary code sequence for the nth user'"'"'s kth symbol, v(t) is a causal pulse with a raised-cosine spectrum, T_c=l/f_chip, and τ

_k,l=p_k,lT_c/N_s is a delay of the kth user'"'"'s lth propagation path, wherein q and r are the qth and rth element of R_MF;

T_c is a sampling time with N_s being an oversampling factor.

6. A method according to claim 1 wherein a partial cross-correlation unit (PCU) is used to calculate the elements in the cross-correlation matrix R_MF.

7. A method according to claim 6 wherein the output from the PCU is used by an iterative linear system solver (ILSS) to estimate a block diagonal matrix Hd whereby a Gauss-Seidel algorithm is modified to be a block-wise iteration on sub-blocks of the block diagonal matrix.

8. A method according to claim 1 wherein the RSFQ vector processing unit receives inputs that includes a vector of channels gains and a vector of relative channels delays from a channel estimation unit (CEU).

9. A method of reducing multi-user interference (MAI) in a wireless direct sequence CDMA wireless system comprising at least one base station transmitting to and receiving signals from a plurality of mobile station users, wherein the method includes reducing interference with a multi-user detector located within said at least one base station comprising the steps of:

receiving at the at least one base station a digital input signal comprised of a plurality of binary code sequences from the mobile station users;

processing the digital input signal with a bank of matched filters to produce matched filter output vectors;

receiving the matched filter output vectors into a bank of Rake combiners to produce Rake combiner output vectors;

receiving the Rake combiner output vectors into a superconducting digital rapid single flux quantum (RSFQ) vector processing unit applying a successive interference cancellation (SIC) iterative technique (RSFQ SIC) to solve a cross-correlation matrix to decorrelate the plurality of binary code sequences; and

reducing the interference by removing interference components between the plurality of binary code sequences.

10. A method according to claim 9 wherein the direct sequence CDMA wireless system operates in accordance with the Wideband Code Division Multiple Access (W-CDMA) standard.

11. A method according to claim 9 wherein, in the receiving step of the digital input signal, the binary code sequences from the mobile station users are W-CDMA Gold long spreading codes having a sequence length of 2⁴¹, or VL-Kasami short spreading codes with a sequence length of 256.

12. A method according to claim 9 wherein the RSFQ SIC operates at a frequency of at least 54 GHz and is capable of removing interference in a W-CDMA system operating with at least 100 simultaneous voice user per sector with at least 10 resolvable multipath components per user, and an effective support of a chip waveform.

13. A method according to claim 9 wherein in the applying step, the SIC iterative technique employs a Gauss-Seidel iteration algorithm to solve the cross-correlation matrix R_rake of the binary code sequences given by,

${\left[R_{\mathrm{rake}}\right]}_{q,r}=\sum _{}^{}$

i = 1 L ⁢

⁢

∑

i ′

= 1 L ⁢

⁢

h k , l * ⁢

h k ′

, l ′

* ⁡

[ A ] l , l ′

where A is a certain L×

L submatrix of R_MF, and h_k,l is a complex channel gain of a kth user'"'"'s lth propagation path, wherein q and r are the qth and rth element of R_MF;

T_c is a sampling time with N_s being an oversampling factor.

14. A method according to claim 9 wherein a partial cross-correlation unit (PCU) is used to calculate the elements in the cross-correlation matrix R_rake.

15. A method according to claim 14 wherein the output from the PCU is used by an iterative linear system solver (ILSS) to estimate a block diagonal matrix d whereby a Gauss-Seidel algorithm is modified to be a block-wise iteration on sub-blocks of the block diagonal matrix.

16. A method according to claim 9 wherein the RSFQ vector processing unit receives inputs that includes a vector of channels gains and a vector of relative channels delays from a channel estimation unit (CEU).

17. A method according to claim 9 wherein in the RSFQ SIC, inner iterations, performed inside of main iterations dealing with signals arrived at different time intervals, are performed in a parallel way.

18. A method according to claim 9 wherein signal processing required for said multi-user detector is performed on a chip level.

19. A multi-user detector apparatus for use with interference cancellation in a radio base station receiver operating within a direct sequence CDMA wireless system, wherein said base station receiver includes a channel estimation unit (CEU) for estimating characteristics of a channel, a pseudo-number generator for use with despreading user code sequences, a bank of matched filters for rejecting interference in an input signal, a bank of Rake combiners for processing signal multipaths, said multi-user detector apparatus comprising:

a partial cross-correlation unit (PCU) linked to the CEU for calculating the elements of a cross-correlation matrix related to the user code sequences; and

a superconducting digital rapid single flux quantum (RSFQ) vector processing unit linked to the PCU and to the bank of matched filters, wherein the output vectors from the bank of matched filters are fed into the RSFQ vector processing unit for iterative processing, and wherein the output of the RSFQ processing unit is fed into the bank of Rake combiners for removing interference components from original user code sequences.

20. An apparatus according to claim 19 wherein the RSFQ vector processing unit is a vector machine that comprises superconducting logic circuits capable of performing a successive interference cancellation (SIC) iterative technique for decorrelating the cross-correlation matrix associated with the user code sequences and is designated as an RSFQ SIC.

21. An apparatus according to claim 20 wherein the RSFQ SIC comprises a plurality of Multiply-accumulate units (MAC) such that all processors in one chain are performed in parallel in such a way that each block is computing one dedicated element of vector of transmitted symbols at rime T.

22. An apparatus according to claim 20 wherein an iterative linear system solver (ILSS) for processing a Gauss-Seidel algorithm in said SIC iterative technique.

23. An apparatus according to claim 20 wherein the RSFQ SIC further comprises an iterative linear system solver (ILSS) unit for running a Gauss-Seidel algorithm.

24. A multi-user detector apparatus for use with interference cancellation in a radio base station receiver operating within a direct sequence CDMA wireless system, wherein said radio base station receiver includes a channel estimation unit (CEU) for estimating characteristics of a channel, a pseudo-number generator for use with despreading user code sequences, a bank of matched filters for rejecting interference in an input signal, a bank of Rake combiners for processing signal multipaths, said multi-user detector apparatus comprising:

a partial cross-correlation unit (PCU) linked to the CEU for calculating elements of a cross-correlation matrix related to the user code sequences; and

a superconducting digital rapid single flux quantum (RSFQ) vector processing unit linked to the PCU and to the bank of matched filters, wherein the output vectors from the bank of matched filters are fed into the bank of Rake combiners, and the output vectors of the bank of Rake combiners are fed into the RSFQ vector processing unit for iterative processing for removing interference components from original user code sequences.

25. An apparatus according to claim 24 wherein the RSFQ vector processing unit is a vector machine that comprises superconducting logic circuits capable of performing a successive interference cancellation (SIC) iterative technique for decorrelating the cross-correlation matrix associated with the user code sequences and is designated as an RSFQ SIC.

26. An apparatus according to claim 25 wherein the RSFQ SIC comprises a plurality of Multiply-accumulate units (MAC) such that all processors in one chain are performed in parallel in such a way that each block is computing one dedicated element of vector of transmitted symbols at time T.

27. An apparatus according to claim 25 wherein an iterative linear system solver (ILSS) for processing a Gauss-Seidel algorithm in said SIC iterative technique.

28. An apparatus according to claim 25 wherein the RSFQ SIC further comprises an iterative linear system solver (ILSS) unit for running a Gauss-Seidel algorithm.

29. An apparatus according to claim 24 wherein signal processing required for multi-user detection is located before the bank of matched filters and a memory for storing signal processing data is included such that a size of the memory is in proportion to a total number of transmitted signals per packet multiplied by an oversampling factor.

30. A method of reducing multi-user interference (MAI) in a wireless direct sequence CDMA wireless system comprising at least one base station transmitting to and receiving signals from a plurality of mobile station users, wherein the method includes reducing interference with a multi-user detector located within said at least one base station comprising the steps of:

receiving at the at least one base station a digital input signal comprised of a plurality of binary code sequences from the mobile station users;

processing the digital input signal with a bank of matched filters and producing matched filter output vectors from the bank of matched filters;

feeding the matched filter output vectors into one of a superconducting digital rapid single flux quantum (RSFQ) vector processing unit and a bank of Rake combiners applying a successive interference cancellation (SIC) iterative technique (RSFQ SIC) to solve a cross-correlation matrix to decorrelate the binary code sequences;

reducing the interference by removing interference components between the binary code sequences; and

feeding an output from the RSFQ vector processing unit into the bank of Rake combiners to recover original data transmitted by the mobile station users, or feeding the output of the bank of Rake combiners into the RSFQ vector processing unit.