Joint Power Allocation for Hybrid Digital-Analog Transmission in Relay Networks

Due to the quantization errors introduced by source coding, the transmission performance in digital communication systems might remain constant when the channel quality gets better, which is referred to as the quality saturation effect. To combat this effect, hybrid digital-analog (HDA) transmission is proposed, where the quantization errors are transmitted in an analog mode to achieve graceful improvement for better channels. In this paper, we focus on HDA transmission in wireless relay networks (WRNs). We propose a power allocation scheme for HDA transmission in a three-node WRN (3-WRN) to eliminate the quality saturation effect and improve the distortion performance. It should be emphasized that HDA transmission involves not only digital-analog power allocation but also source-relay power allocation. Therefore, the joint power allocation is considered. We formulate the joint power allocation problem as a nonlinear fractional programming problem. Then, we propose an effective algorithm to search the solution and obtain the optimal distortion performance. Finally, we conduct simulations to validate our work. The results show that the proposed joint power allocation scheme outperforms existing schemes in terms of end-to-end distortion under various channel conditions.