Method and apparatus for adaptive channel equalizaton using decision feedback

• US 20030227960A1
• Filed: 11/22/2002
• Published: 12/11/2003
• Est. Priority Date: 06/11/2002
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Papasakellariou, Aris
• Granted Patent: US 7,469,003 B2
• Time in Patent Office: Days
• US Class Current: 375/147
• CPC Class Codes: H04L 2025/03617 Time recursive algorithms H04L2025/03643 takes precedence
• CPC Class Codes: H04L 25/03038 with a non-recursive structure H04L25/03031 takes precedence

Abstract

The equalizer circuit (200) equalizes the channel prior to despreading thereby restoring the orthogonality of signals that typically exists in the forward link of CDMA systems and thus suppressing interference and improving the performance. The equalization method is based on the well-established normalized least-mean-squares (NLMS) algorithm. The tracking ability and the strength of the training signal of the NLMS are enhanced in the invention by using data feedback, in addition to the common pilot, to form the training signal. Based on initial data decisions, the transmitted signal can be reconstructed and included in the training signal. In cases where the transmitted signal for the receiver employs several codes as in a multicode transmission environment, the quality of the training signal can be significantly improved. This in turn results in considerable performance improvements to the extent that the resulting performance may be superior to that of other equalization techniques of similar or larger complexity.

Claims

1. In a communication device receiving a spread spectrum signal which includes a common pilot channel (CPICH) signal and dedicated physical data channel (DPDCH) signals, a method for performing channel equalization at a receiver, comprising the steps of:

(a) demodulating said DPDCH signals;

(b) obtaining decisions for information symbols of said DPDCH signals;

(c) using decisions from step (b) to regenerate the DPDCH signals;

(d) adding the regenerated DPDCH signals to the CPICH signal to obtain an estimate signal of the transmitted spread spectrum signal received at the communication device; and

(e) using said estimate signal to perform adaptive equalization.

2. A method as defined in claim 1, wherein said demodulating in step (a) includes the steps of performing descrambling, despreading, and Rake processing of the DPDCH signals.

3. A method as defined in claim 1, wherein said demodulating in step (a) includes the steps of performing adaptive equalization, descrambling, and despreading of the DPDCH signals.

4. A method as defined in claim 3, wherein the adaptive equalization step includes performing CPICH-based NLMS.

5. A method as defined in claim 3, wherein the adaptive equalization step includes performing Prefilter-Rake equalization.

6. A method as defined in claim 3, wherein the adaptive equalization step includes performing NLMS adaptive equalization using an estimate of the transmitted spread spectrum signal.

7. A method as defined in claim 1, wherein the obtaining of decisions in step (b) includes soft, hard, or soft-clipped decisions.

8. A method as defined in claim 1, wherein each of the regenerated DPDCH signals in step (c) is scaled by a value between 0.0 and 1.0.

9. A method as defined in claim 1, wherein each of the regenerated DPDCH signals in step (c) is scaled by the power ratio of said DPDCH signal over said CPICH signal.

10. A method as defined in claim 1, wherein said adaptive equalization in step (e) uses a normalized LMS chip-based equalizer.

11. A method as defined in claim 1, wherein steps (a) to (e) are repeated at least once.

12. A method as defined in claim 1, wherein said DPDCH signals are spread with codes of at least one spreading factor.

13. A communication device for receiving a spread spectrum signal that includes a common pilot channel (CPICH) signal and dedicated physical data channel (DPDCH) signal, the communication device comprising

an input port for receiving the spread spectrum signal;

a demodulation section coupled to the input port for demodulating the DPDCH signals;

a decision section coupled to the demodulation section for obtaining decisions for information symbols of the DPDCH signals;

a regeneration section that takes the decisions made by the decision section to regenerate the DPDCH signals;

an adder section coupled to the regeneration section for adding the regenerated DPDCH signals to the CPICH signal to obtain an estimate signal of the spread spectrum signal that was transmitted to the communication device; and

a NLMS equalizer coupled to the adder for performing the adaptive equalization.

14. A communication device as defined in claim 13, wherein the demodulation section includes a normalized least-mean-squares (NLMS) equalizer.

15. A communication device as defined in claim 13, wherein the demodulation section performs descrambling, despreading and Rake processing of the DPDCH signals.

16. A communication device as defined in claim 13, wherein the demodulation section performs adaptive equalization, descrambling and despreading of the DPDCH signals.

17. A communication device as defined in claim 13, wherein the regeneration section scales each of the regenerated DPDCH signals by a value between 0.0 and 1.0.

18. A communication device as defined in claim 13, wherein the regeneration section scales each of the regenerated DPDCH signals by the power ratio of the DPDCH signal over the CPICH signal.

19. A method as defined in claim 13, wherein said DPDCH signals are spread with codes of at least one spreading factor.