Hardware and software for performing computations in a short-code spread-spectrum communications system

• US 20030076875A1
• Filed: 03/14/2002
• Published: 04/24/2003
• Est. Priority Date: 03/14/2001
• Status: Active Grant

• Current Assignee: Mercury Systems, Incorporated
• Original Assignee: Mercury Computer Systems Incorporated
• Inventors: Oates, John H.
• Granted Patent: US 7,110,431 B2
• Time in Patent Office: Days
• US Class Current: 375/147
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 1/7093 Matched filter type
• CPC Class Codes: H04B 1/7105 Joint detection techniques, e.g. linear detectors
• CPC Class Codes: H04B 1/71052 using decorrelation matrix
• CPC Class Codes: H04B 1/71075 Parallel interference cancellation
• CPC Class Codes: H04B 1/7115 Constructive combining of multi-path signals, i.e. RAKE receivers
• CPC Class Codes: H04B 2201/70707 Efficiency-related aspects
• CPC Class Codes: H04B 2201/70711 with modular structure

Abstract

The invention provides methods and apparatus for multiple user detection (MUD) processing that have application, for example, in improving the capacity CDMA and other wireless base stations. One aspect of the invention provides a multiprocessor, multiuser detection system for detecting user transmitted symbols in CDMA short-code spectrum waveforms. A first processing element generates a matrix (hereinafter, “gamma matrix”) that represents a correlation between a short-code associated with one user and those associated with one or more other users. A set of second processing elements generates, e.g., from the gamma matrix, a matrix (hereinafter, “R-matrix”) that represents cross-correlations among user waveforms based on their amplitudes and time lags. A third procesing element produces estimates of the user transmitted symbols as a function of the R-matrix.

Claims

1. In a spread spectrum system of the type that processes a plurality of waveforms transmitted by respective users, the improvement comprising:

two registers associated with l^th and k^th users each for storing elements of a code sequence associated with one of the l^th and k^th users, an alignment of the code sequence loaded in one register being shifted relative to that of the other register by m elements,

two further registers, each for storing mask sequences associated with the code sequences of a respective one of the l^th and k^th users, such that a mask element is zero or non-zero if a corresponding element of the associated code sequence is zero or non-zero, respectively, an alignment of the mask sequence in one of the further registers being shifted relative to those in the other of the further registers by m elements,

a logic unit coupled to said registers for performing an arithmetical operation on said code sequences and mask sequences to generate, for mth transmitted symbol, (l, k) element of a matrix that represents correlations among the code sequences associated with the respective users.

2. The system of claim 1, wherein the arithmetical operation comprises obtaining a sum of multipliers of non-zero aligned elements of the code sequences.

3. The system of claim 2, wherein the logic unit performs the arithmetical operation by, for any two aligned elements of the code sequences of the lth and kth user and the corresponding elements of the mask sequences, performing the following steps:

(i) performing an XOR operation between the code elements,

(ii) performing an AND operation between the mask elements,

(iii) performing an AND operation between results of the step (i) and step (ii) to generate a multiplier corresponding the aligned elements, and

(iv) summing the multipliers to generate the (l, k) element of the matrix.

4. The system of claim 3, wherein the logic unit comprises two AND gates each for performing one of said logic AND operations.

5. The system of claim 4, wherein the logic unit comprises an XOR gate coupled to said AND gates for performing said logic XOR operation.

6. The system of claim 5, further comprising storage for storing the computed matrix representing correlations among the code sequences associated with the users.

7. In a method of processing code spread spectrum waveforms transmitted by a plurality of users of a spread spectrum system, the improvement comprising:

generating a matrix for a shift of m chips indicative of correlations among code sequences associated with the users by performing the following steps;

(i) for each user, loading elements of a code sequence associated with that user in a register, and loading a mask sequence associated with that sequence in another register such that a mask element is zero or non-zero if a corresponding element of the associated code sequence is zero or non-zero, respectively, and

(ii) for any two users l and k, shifting an alignment of the code and mask sequences of the lth user relative to those of the kth user by m elements, and performing an arithmetical operation on the aligned elements to obtain (l, k) element of the matrix.

8. The method of claim 7, wherein the step of performing said arithmetical operation comprises obtaining a sum of multipliers of non-zero aligned elements of the code sequences.

9. The method of claim 8, wherein the step of obtaining the sum comprises performing following logic operations:

for any two aligned elements of the code sequences of the lth and kth user and the corresponding elements of the mask sequences performing the following steps;

(i) performing an XOR operation between the code elements,

(ii) performing an AND operation between the mask elements,

(iii) performing an AND operation between results of the step (i) and step (ii) to generate a multiplier corresponding the aligned elements, and

(iv) summing the multipliers to generate the (l, k) element of the matrix.

10. The method of claim 9, further comprising the step of storing the matrix in persistent memory.

11. The method of claim 9, wherein the (l, k) matrix for a shift of m chips is defined in accord with the relation:

12. The method of claim II, further comprising the step of computing a matrix (herein referred as C-matrix) that represents correlations among time lags and code sequences associated with the respective users in accord with the relation:

13. The method of claim 12, further comprising the step of computing a matrix (herein referred to as r matrix) representing cross-correlations among the waveforms transmitted by the users as a function of the C matrix in accord with the relation:

14. The method of claim 13, further comprising the step of generating detection statistics corresponding to symbols transmitted by the users and encoded in the waveforms as a function of said cross-correlation matrix in accord with the relation:

15. The method of claim 14, further comprising the step of estimating the transmitted symbols as a function of the detection statistics in accord with the relation:

16. In a spread spectrum system of the type that processes a plurality of waveforms transmitted by respective users, the improvement comprising:

a first logic module for computing a matrix indicative of correlations among codes associated with the users, and

a second logic module in communication with said first logic module for computing a matrix indicative of cross correlations among the waveforms transmitted by the users as a function of the matrix representing correlations among the code sequences,

wherein the first logic module generates an (l, k) element of the matrix representing correlations among the waveforms transmitted by l^th and k^th users by performing the following operations;

(i) for each user, loading elements of a code sequence associated with that user in a register, and loading a mask sequence associated with that sequence in another register such that a mask element is zero or non-zero if a corresponding element of the associated code sequence is zero or non-zero, respectively, and

(ii) shifting an alignment of the code and mask sequences of the lth user relative to those of the kth user by m elements, and performing an arithmetical operation on the aligned elements to obtain (l, k) element of the matrix.

17. The system of claim 16, wherein the second logic module computes the cross-correlation matrix by computing a matrix component (herein referred to as C matrix) representing correlations among time lags and code sequences associated with the waveforms transmitted by the users in accord with the relation:

18. The system of claim 17, wherein the second module computes the cross-correlation matrix as a function of the C matrix in accord with the relation:

19. The system of claim 18, further comprising a third logic module in communication with said second logic module for computing detection statistics corresponding to symbols transmitted by the users.

20. The system of claim 19, wherein the third logic module computes estimates of the symbols transmitted by the users as a function of the detection statistics.