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

摘要

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.