Use of error control coding and antenna diversity to improve performance of subband coding

The use of error control coding and diversity to improve the error performance of a portable radio system was investigated, along with their effect on the performance of a subband code operating at 16 kb/s. Use was made of the probability of dropping a speech frame and the perceptual quality of speech as the performance criteria. Use of two-branch diversity by means of predetection power selection is seen to result in about a 10-dB improvement over the no-diversity case. The channel encounters random errors caused by the additive white Gaussian noise. Time-varying multipath (Rayleigh) fading of the signal envelope below the Gaussian noise tends to cause long bursts. A 30-dB variation in the sensitivity of the segmental SNR to bit errors is seen, from the most significant to least significant bits. The slow fading nature of the portable channel and the structure of the radio system tend to make the errors highly bursty, and this results in error correction coding performing about 2.5-dB better than error detection coding. When the synchronization advantages of the error detection scheme are taken into account, this gain may be somewhat smaller