Nortel Networks Corporation

Xixlan Chen

Guoqiang Xue

This invention enables determining whether a received frame is an erasure, a DTX mode frame or a CONT mode frame, using a metric m derived from the log likelihood ratio (LLR). The new metric is obtained by calculating the mean for the LLRs for a frame; a threshold T for this metric is also established. A received frame is declared a CONT frame if the CRC value indicates a successfully recovered frame, and m&#x3e;T. A received frame is a DTX frame if m&#x3c;T. Finally, a frame is declared an erasure if the CRC value indicates a failed frame, and m&#x3e;T. The mean absolute LLR may also be used for determining the transmission rate of the system. In this case, a voice frame is decoded for all rates available; the transmission rate is that which corresponds to a passed CRC and has the highest m.

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Nepean, Canada

Xixlan Chen