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

• US 20040120299A1
• Filed: 12/18/2002
• Published: 06/24/2004
• Est. Priority Date: 12/18/2002
• Status: Active Grant

• 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
• Granted Patent: US 7,440,490 B2
• Time in Patent Office: Days
• US Class Current: 370/342
• 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 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 an output vector from the matched filter bank.

feeding the output vector into a superconducting rapid single flux quantum (RSFQ) vector processing unit;

applying a successive interference cancellation (SIC) iterative technique to solve a cross-correlation matrix to decorrelate the user binary code sequences;

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

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

2. A method according to claim 1 wherein the implemented multi-user detector of the direct sequence CDMA 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 and SIC represents a vector processing unit operating 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 the effective support of the chip waveform determined by Q=3.

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

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 the Gauss-Seidel algorithm is modified to be a block-wise iteration on sub-blocks of the matrix.

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

14. 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_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 the Gauss-Seidel algorithm is modified to be a block-wise iteration on sub-blocks of the matrix.

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 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 a matched filter output vector;

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

receiving the Rake combiner output vector into a superconducting rapid single flux quantum (RSFQ) vector processing unit;

applying a successive interference cancellation (SIC) iterative technique to solve a cross-correlation matrix to decorrelate the user binary code sequences; and

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

10. A method according to claim 9 wherein the multi-user detector method of the direct sequence CDMA 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 and SIC represents a vector processing unit operating 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 the effective support of the chip waveform determined by Q=3.

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

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

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

18. A method according to claim 9 wherein in the signal processing required for multi-user detection is performed on the 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 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 a in a first stage in 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 rapid single flux quantum (RSFQ) vector processing unit linked to the PCU and to the bank of matched filters, wherein the output from the bank of matched filters is fed into the RSFQ 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 the original user code sequences.

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

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 time T.

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

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

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

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 24 wherein an iterative linear system solver (ILSS) for processing a Gauss-Seidel algorithm in said SIC.

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