Method and apparatus for performing rate determination using orthogonal rate-dependent walsh covering codes

• US 6,147,964 A
• Filed: 05/07/1998
• Issued: 11/14/2000
• Est. Priority Date: 05/07/1998
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Stein, Jeremy M., Black, Peter J.
• Primary Examiner(s): MARCELO, MELVIN C
• Application Number:
  US09/075,406
• Time in Patent Office: 922 Days
• Field of Search: 370/208, 370/209, 370/252, 370/342, 375/142, 375/145, 375/149
• US Class Current: 370/209
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04J 13/0048 Walsh
• CPC Class Codes: H04L 1/08 by repeating transmission, e.g. Verdan system H04L1/1858 and H04L1/189 take precedence
• CPC Class Codes: H04L 25/0262 Arrangements for detecting the data rate of an incoming signal

Abstract

A method and apparatus for rate determination in a communication system using orthogonal rate-dependent Walsh covering codes. Orthogonal rate-dependent Walsh codes are used to cover repeated code symbols prior to transmission over a communication link. In one embodiment, the Walsh codes comprise orthogonal binary codes that increase by powers of two for each data rate used in the system. Code symbols are repeated and then covered at the symbol rate using the inventive orthogonal Walsh codes. The inventive code symbol repetition and encoding method and apparatus is particularly advantageous in encoding data that contains long sequences of logical zeros and ones. The orthogonal nature of the code symbols encoded in accordance with the present invention allows use of a more accurate and less complex data rate determination apparatus in the receiver. Rate determination is thereby improved resulting in an improvement in data service capability and a reduction in decoding errors. In one embodiment, symbol error rate (SER) blocks are used to generate rate-dependent SER metrics for each of the candidate rates. SER estimators associated with soft combiners using incorrect data rate hypotheses produce high symbol error rates with respect to the symbol error rate produced by the SER estimator associated with the soft combiner using the correct rate hypothesis. In another embodiment of the data rate determination and decoding method and apparatus of the present invention, energy metric calculators are used to generate rate-dependent re-encoded energy metrics for each candidate data rate. The energy metrics produce an estimate of the symbol energy. The symbol energy is used as another data rate indicator.

Claims

1. A method of determining data rates of code symbols transmitted over a communication link, wherein the code symbols are repeated a predetermined number of times per symbol depending upon the data rate used for transmission, and wherein the code symbols are transmitted at a selected one of a plurality of available data rates, comprising the steps of:

a) covering the code symbols with a selected one of a plurality of rate dependent orthogonal Walsh covering codes, each such Walsh covering code being associated with a unique data rate;

b) transmitting the covered code symbols over the communication link at the selected date rate;

c) deriving rate-dependent metrics based upon the transmitted covered code symbols; and

d) determining the selected data rate based upon the derived rate-dependent metrics.

2. The data rate determination method of claim 1, wherein the rate-dependent Walsh covering codes are selected from an 16-ary Walsh code space.

3. The data rate determination method of claim 1, wherein the rate-dependent Walsh covering codes are binary.

4. The data rate determination method of claim 3, wherein the rate-dependent Walsh covering codes comprise binary codes that increase by powers of two for each successive data sub-rate.

5. The data rate determination method of claim 1, wherein the communication link comprises a radio link.

6. The data rate determination method of claim 5, wherein the communication link is part of a digital cellular communication system.

7. The data rate determination method of claim 6, wherein the digital cellular communication system is a Code Division Multiple Access (CDMA) system.

8. The data rate determination method of claim 1, wherein the rate-dependent orthogonal Walsh covering codes have values of W_xⁿ, and wherein W_xⁿ represents the Walsh code "x" of an "n-ary" Walsh code space.

9. The data rate determination method of claim 8, wherein W_xⁿ represents the negative of W_xⁿ.

10. The data rate determination method of claim 8, wherein the Walsh covering codes have the following values for four pre-determined data rates comprising date rate 1,1/2,1/4, and

11. The rate determination method of claim 10, wherein "+" represents a logical zero, and wherein "-" represents a logical one.

12. The rate determination method of claim 10, wherein rate 1 comprises 9.6 kbps, rate 1/2 comprises 4.8 kbps, rate 1/4 comprises 2.4 kbps, and rate 1/8 comprises 1.2 kbps.

13. The rate determination method of claim 1, wherein one of the derived rate-dependent metrics is a symbol error rate (SER) metric.

14. The rate determination method of claim 13, wherein an SER metric is derived for each available data rate.

15. The rate determination method of claim 14, wherein the step of deriving the SER metric comprises:

a) de-interleaving the transmitted covered code symbols and providing the de-interleaved code symbols as inputs to a plurality of soft combiners, wherein each available data rate has an associated and respective soft combiner;

b) combining the de-interleaved code symbols for each available data rate;

c) decoding the combined code symbols;

d) re-encoding the decoded code symbols;

e) comparing the combined code symbols with the re-encoded code symbols on a symbol-by-symbol basis; and

f) generating an SER for each available data rate based upon the comparison made in step e).

16. The rate determination method of claim 1, wherein one of the derived rate-dependent metrics is a re-encoded energy metric.

17. The rate determination method of claim 16, wherein the re-encoded energy metric is derived for each available data rate.

18. The rate determination method of claim 17, wherein the step of deriving the re-encoded energy metric comprises:

a) de-interleaving the transmitted covered code symbols and providing the de-interleaved code symbols as inputs to a plurality of soft combiners, wherein each available data rate has an associated and respective soft combiner;

b) combining the de-interleaved code symbols for each available data rate;

c) decoding the combined code symbols;

d) re-encoding the decoded code symbols;

e) projecting the re-encoded code symbols onto the combined code symbols on a symbol-by-symbol basis; and

f) generating an energy metric for each available data rate based upon the comparison made in step e.

19. The rate determination method of claim 18, wherein the projection step e) comprises performing an inner product of the re-encoded code symbols and the combined code symbols on a symbol-by-symbol basis.

20. The rate determination method of claim 19, wherein the generating step f) comprises summing the inner products for the total number of code symbols, and dividing the sum by the total number of code symbols thereby generating an estimate of the energy per symbol E_s for each available data rate.

21. The rate determination method of claim 14, wherein the SER metrics are used to distinguish between correct and incorrect data rate hypotheses.

22. The rate determination method of claim 21, wherein the incorrect data rate hypotheses produce SER metrics that are distinguishably greater than the SER metric produced by the correct data rate hypothesis.

23. The rate determination method of claim 17, wherein the re-encoded energy metrics are used to distinguish between correct and incorrect data rate hypotheses.

24. The rate determination method of claim 23, wherein the incorrect data rate hypotheses produce re-encoded energy metrics approaching zero, and wherein the re-encoded energy metric produced by the correct data rate hypothesis is distinguishably greater than zero.

25. A rate determination apparatus adapted for use in a communication system having a communication link, comprising:

a) means for covering code symbols with a selected one of a plurality of rate-dependent orthogonal Walsh covering codes, each such Walsh covering code being associated with a unique data rate;

b) means, operatively connected to the covering means, for transmitting the covered code symbols over the communication link at a selected available data rate associated with the selected one Walsh covering code;

c) means, responsive to the transmitting means, for deriving rate dependent metrics based upon the transmitted code symbols; and

d) means, responsive to the deriving means, for determining the selected available data rate based upon the metrics derived.

26. A system for performing rate determination in a communication system having a communication link, wherein code symbols are transmitted over the communication link at a selected one of a plurality of available data rates, comprising:

a) a symbol repetition and encoding block wherein code symbols are repeated and covered with a selected one of a plurality rate-dependent orthogonal Walsh covering codes, each such Walsh covering code being associated with a unique data rate;

b) means, operatively connected to the symbol repetition and encoding block, for transmitting the covered code symbols over the communication link at the selected available data rate associated with the selected one Walsh covering code;

c) a plurality of soft combiners in wireless communication with the transmitting means, wherein each soft combiner has a respective data rate associated thereto, and wherein the soft combiners output de-interleaved combined code symbol sequences;

d) a plurality of Viterbi decoder and rate re-encoder pairs operatively connected to respective associated soft combiners, wherein the rate re-encoders output re-encoded code symbols;

e) a plurality of symbol error rate (SER) blocks having a first input that is operatively connected to a respective associated soft combiner and having a second input that is operatively connected to a respective associated re-encoder output, wherein each SER estimator generates an SER metric by comparing, on a symbol-by-symbol basis, code symbols generated by its associated soft combiner with code symbols generated its associated re-encoder; and

f) means, responsive to the SER estimators, for determining the selected available data rate based upon the SER metrics generated by the SER estimators.

27. A system for performing rate determination in a communication system having a communication link, wherein code symbols are transmitted over the communication link at a selected one of a plurality of available data rates, comprising:

a) a symbol repetition and encoding block wherein code symbols are repeated and covered with a selected one of a plurality rate-dependent orthogonal Walsh covering codes, each such Walsh covering code being associated with a unique data rate;

b) means, operatively connected to the symbol repetition and encoding block, for transmitting the covered code symbols over the communication link at the selected available data rate associated with the selected one Walsh covering code;

c) a plurality of soft combiners in wireless communication with the transmitting means, wherein each soft combiner has a respective data rate associated thereto, and wherein the soft combiners output de-interleaved combined code symbol sequences;

d) a plurality of Viterbi decoder and rate re-encoder pairs operatively connected to respective associated soft combiners, wherein the rate re-encoders output re-encoded code symbols;

e) a plurality of energy metric calculators having a first input that is operatively connected to a respective associated soft combiner and having a second input that is operatively connected to a respective associated re-encoder output, wherein each energy metric calculator generates an energy metric by multiplying, on a symbol-by-symbol basis, code symbols generated by its associated soft combiner and code symbols generated by its associated re-encoder; and

f) means, responsive to the energy metric calculators, for determining the selected available data rate based upon the energy metrics generated by the energy metric calculators.

28. A computer program executable on a general purpose computing device, wherein the program is capable of determining data rates of code symbols transmitted over a communication link, wherein the code symbols are repeated a pre-determined number of times per symbol depending upon the data rate used for transmission, and wherein the code symbols are transmitted at a selected one of a plurality of available data rates, comprising:

a) a first set of instructions for covering the code symbols with a selected one of a plurality of rate-dependent orthogonal Walsh cover codes, each such Walsh covering code being associated with a unique data rate;

b) a second set of instructions for deriving rate-dependent metrics based upon the covered code symbols; and

c) a third set of instructions for determining the selected transmission data rate based upon the derived rate-dependent metrics.

29. The computer program of claim 28, wherein the program is executed by a general purpose computing device in a mobile station.

30. The computer program of claim 28, wherein the program is executed by a general purpose computing device in a base station.

31. The computer program of claim 28, wherein the program executes in a field programmable gate array device.