Method and apparatus for adaptive channel equalization using decision feedback

• US 7,469,003 B2
• Filed: 11/22/2002
• Issued: 12/23/2008
• Est. Priority Date: 06/11/2002
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Papasakellariou, Aris
• Primary Examiner(s): Ghayour; Mohammad H
• Assistant Examiner(s): Malek; Leila
• Application Number:
  US10/302,257
• Publication Number:
  US 20030227960A1
• Time in Patent Office: 2,223 Days
• Field of Search: 375/147, 375/316, 375/229, 375/130, 375/136, 375/232, 375/348, 375/350, 381/103
• 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 a plurality of dedicated physical data channel (DPDCH) signals, a method for performing channel equalization at a receiver, comprising:

demodulating said plurality of DPDCH signals included in said spread spectrum signal;

obtaining decisions for information symbols of said DPDCH signals included in said spread spectrum signal;

re-spreading with a spreading code said decisions for information symbols of said DPDCH signals to regenerate said plurality of DPDCH signals;

adding said regenerated plurality of DPDCH signals to the CPICH signal to produce a summed signal;

re-scrambling said summed signal with a PN code to obtain an estimate signal of the transmitted spread spectrum signal received at the communication device;

using said estimate signal to perform adaptive equalization;

demodulating a voice signal included in said spread spectrum signal;

obtaining decisions for information symbols of said voice signal included in said spread spectrum signal;

re-spreading with a spreading code said decisions for information symbols of said voice signal to regenerate said voice signal;

scaling said regenerated voice signal by a smaller value than a value used to scale a regenerated DPDCH signal; and

adding said scaled voice signal, said regenerated plurality of DPDCH signals and said CPICH signal to produce said summed signal.

2. A method as defined in claim 1, wherein said demodulating includes performing descrambling, despreading, and Rake processing said plurality of DPDCH signals included in said spread spectrum signal.

3. A method as defined in claim 1, wherein said demodulating includes performing adaptive equalization, descrambling, and despreading said plurality of DPDCH signals included in said spread spectrum signal.

4. A method as defined in claim 3, wherein adaptive equalization includes performing CPICH-based normalized least-mean-squares (NLMS).

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

6. A method as defined in claim 3, wherein adaptive equalization includes performing normalized least-mean-squares (NLMS) adaptive equalization using an estimate of the transmitted spread spectrum signal.

7. A method as defined in claim 1, wherein obtaining decisions for information symbols includes soft, hard, or soft-clipped decisions.

8. A method as defined in claim 1, wherein each of said regenerated plurality of DPDCH signals is scaled by a value between 0.0 and 1.0.

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

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

11. A method as defined in claim 1, further comprising repeating the method at least once.

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

an input port for receiving the spread spectrum signal;

a demodulation section coupled to the input port for demodulating the plurality of DPDCH signals, wherein said demodulation section demodulates a voice signal included in said received spread spectrum signal;

a decision section coupled to the demodulation section for obtaining decisions for information symbols of the plurality of DPDCH signals, wherein said decision section obtains decisions for information symbols of said voice signal;

a regeneration section that re-spreads with a spreading code the decisions for information symbols of the plurality of DPDCH signals made by the decision section to regenerate the plurality of DPDCH signals and adds the regenerated plurality of DPDCH signals to the CPICH signal to produce a summed signal, wherein said regeneration section re-spreads with a spreading code the decisions for information symbols of said voice signal made by said decision section to regenerate said voice signal, scales said voice signal by a smaller value than a value used to scale a regenerated DPDCH signal, and adds said scaled voice signal, said regenerated plurality of DPDCH signals, and said CPICH signal to form said summed signal;

a scrambler that re-scrambles with a PN code said summed signal to obtain an estimate signal of the spread spectrum signal that was transmitted to the communication device; and

a normalized least-mean-squares (NLMS) equalizer coupled to the scrambler for performing adaptive equalization.

13. A communication device as defined in claim 12, wherein the demodulation section includes a normalized least-mean-squares (NLMS) equalizer.

14. A communication device as defined in claim 12, wherein the demodulation section performs descrambling, despreading and Rake processing of the DPDCH signals.

15. A communication device as defined in claim 12, wherein the demodulation section performs adaptive equalization, descrambling and despreading of the regenerated plurality of DPDCH signals.

16. A communication device as defined in claim 12, wherein the regeneration section scales each of the regenerated plurality of DPDCH signals by a value between 0.0 and 1.0.

17. A communication device as defined in claim 12, wherein the regeneration section scales each of the regenerated DPDCH signals by the power ratio of the DPDCH signals over the CPICH signal.

18. A communication device as defined in claim 12, wherein said plurality of DPDCH signals are spread with codes of at least one spreading factor.