Hybrid Digital-Analog transmission taking into account D/A and A/D conversion
Efficient digital transmission of continuous-amplitude signals requires source coding which comes at the price of unavoidable quantization errors. Thus, even in clear channel conditions, the quality of the decoded signal is limited due to these source coding errors (quantization). Hybrid Digital-Analog (HDA) codes circumvent this limitation by additionally transmitting the source coding error with quasi-analog methods (discrete-time, quasi-continuous-amplitude) with neither increasing the total transmission power, nor the occupied frequency bandwidth on the radio channel. So far, for HDA transmission, the potential distortion additionally introduced by D/A and A/D conversion of the analog signal has not been considered. In this paper, the effect of clipping and limited resolution of this conversion on the performance of HDA transmission is evaluated. For random variables and speech signals, simulations verify that even with poor A/D and D/A conversion (3 bit resolution) the HDA concept outperforms conventional purely digital transmission systems at all channel qualities while additionally eliminating the quality limitation effect.