Layered image/video softcast with hybrid digital-analog transmission for robust wireless visual communication
Due to the mobility of transceivers and the interference from other signals, the condition of a wireless channel may vary drastically and unpredictably. In such scenario, conventional communication systems usually suffer from cliff effect due to the nature of entropy coding and channel coding. The recently proposed SoftCast scheme, on the contrary, achieves smooth quality degradation by employing analog-like transmission, together with efficient decorrelation and power allocation. However, the analog-like transmission in SoftCast is not always efficient in terms of power usage, when compared with digital approaches. In this paper, we propose a layered image/video SoftCast scheme, in which a coarse approximation of the image is coded in a base layer and transmitted in digital way while the remained image details are represented in an enhancement layer and sent out using the SoftCast way. Since a major part of the signal energy is transmitted in the base layer using digital approach, the efficiency of power usage in the enhancement layer is improved remarkably. Experimental results show that the proposed scheme can outperform the original SoftCast scheme remarkably, while still preserving the smooth quality degradation characteristic of SoftCast.