Reducing signal distortion due to transmission error via multiresolution digital modulations

Although the different bits in a pulse code modulation (PCM) word that represent the level of quantized analog samples require different degrees of error protection, this factor is rarely taken into account in traditional digital wireless communication system designs. Multiresolution modulation schemes that consist of nonuniformly spaced symbols allow for unequal error protection (UEP) of transmitted bits within a symbol according to their importance. In this article, we investigate the problem of matching asymmetrical phase shift keying (PSK) modulations with the multiresolution temporal waveform coding scheme to minimize the effect of transmission errors in 1-D and 2-D analog signals. We show that both the mean and the variance of signal distortion can be reduced considerably, especially when the channel condition deteriorates, by mapping the PCM bits to a suitable asymmetric PSK signal constellation such that the most significant bits have a lower probability of being in error than the least significant bits. This embedding gain can be translated into energy and/or spectral efficiency improvement over the baseline uniform PSK case for a specified distortion level.