Turbo Coding with 180 degree transparency

摘要

In a turbo coding scheme, the output of the turbo encoder is often serialized ofr subsequent BPSK moudlated transmission, and 180 degree phase ambiguity may be present at the demodulator output. One way fo solving this phase ambiguity si to devise a code that is 180 degree transparent to the turbo encoder. Sufficient ocnditions to have 180 degree rotational transparency for the ocnstituent convolutional encoder are derived in both NSFF and RSC encoder cases. implications for turbo codes to have 180 degree tansparency are then investigated.