Hybrid Digital-Analog Video Transmission Based On Softcast And H.264/AVC

Wireless video multicast has become one of the key applications in wire-less local area network. But the main challenge of conventional wireless video multicast, i.e."cliff effect", blocks the development of wireless video multi-cast and it remains to be unsolved. Then to overcome the "cliff effect", some schemes have been proposed to surmount the "cliff effect". The typical ap-proaches are the scalable video coding schemes with hierarchical digital mod-ulation schemes. However, all these schemes are still digital video transmission schemes and they can just degrade the "cliff effect" problem rather than solving it. Recently, SoftCast which allocates-power to different chunks of transformed coefficients and transmits analog signal without quantization and entropy cod-ing is proposed in video multicast. SoftCast can solve the "cliff effect" com-pletely. However, the performance of SoftCast is unsatisfactory when the SNR is low, and it even performs worse than many classical digital video multicast schemes.To further improve the video performance meanwhile overcome the "cliff effect", the hybrid digital-analog (HDA) video transmission framework which transmits the digital bitstream with the quantization residuals is proposed in this paper. In the proposed HDA video multicast scheme, the video is coded by H.264/AVC firstly and then the quantization residuals are coded by Soft-Cast. Next, the coded digital signals and the coded analog signals are mapped to the same constellation diagram and then broadcasted to the receiver group. Besides, with effective power allocation algorithm and appropriate parameter setting, the residuals gains can be maximized meanwhile the digital bitstream can assure a basic video to the multicast receiver group.Since the MIMO channel can be divided into a set of spatial subchannels with different gains, video transmission over the MIMO channel can be re-garded as multicast to multiple antennas. Besides, the non-uniform subchannel gains on different antennas can also be regard as the "cliff effect" problem, so ParCast which is a variation of SoftCast is also applied to video transmission in MIMO to solve the "cliff effect" problem. ParCast is also an analog coding and transmission scheme with joint consideration of the source and the channel. And the HDA scheme based on ParCast with corresponding power allocation algorithms is also proposed to improve the video performance in MIMO.Simulations show that the proposed HDA schemes can overcome the "clif-f effect" completely in multicast with the transmission of residuals. What’s more, the proposed HDA multicast scheme outperforms the compared WSVC scheme by more than4dB when transmitting under the same bandwidth and the proposed HDA scheme in MIMO can further improve the performance by nearly7dB when compared with the ParCast scheme in MIMO.