Research On Wireless Video Transmission Based On SoftCast

With the continuous development of mobile Internet and intelligent terminals,wireless video quality requirements gradually improve.In order to meet the needs of users,wireless video broadcasting is a good choice.But traditional video broadcasting technology adopts separated source coding and channel coding design,facing with the challenge of scalability and robustness.The proposed soft broadcast technology,SoftCast,adopts joint source and channel coding,providing linear received video quality changes with channel conditions,and it has good scalability and robustness.This paper conducts a study on wireless video compression broadcast technology.The achievements and innovations are as follows:First,SoftCast is introduced from encoder and decoder and physical layer three aspects and then subjective and objective reconstructed video quality evaluation are introduced.Based on objective evaluation PSNR,we compare SoftCast and H.264 two broadcast video compression technology and conclude the following results:(1)SoftCast realizes source compression and error protection as a cross layer technology.(2)SoftCast's linear transformation makes received video quality and signal-to-noise ratio relate linearly,avoiding cliff effect.(3)SoftCast resists packet loss very well,which guarantees each packet of equal importance and there are not disproportionate video distortion because of a packet's loss.Second,we conclude that chunk dividing module has optimization space according to analysis,involving chunk size,compression ratio CR and GoP three parameters.Choosing right chunk size can make a compromise between quality and complexity.Right compression ratio can be used to balance received video quality and bandwidth resources.GoP is a secondary optimization parameters due to video 's variability.When system's complexity is dominant factor,choosing as far as possible big chunk and small compression ratio can get lower complexity and better received video quality.When limited bandwidth is dominant factor,compression ratio should be adjusted to adapt to the needs of bandwidth,and a smaller chunk is selected to guarantee better received video quality.Third,we improve SoftCast's transmission video quality from the point of relaying.Traditional AF has advantages of simpleness and low delay but it only amplifies the received signal and not uses side information from the source node and-destination node.We further discuss AF's improvement scheme,sawtooth relay,which uses modulus or triangle relay function.Sawtooth is suitable for processing real number domain signal,providing high channel capacity compared with AF.Combining SoftCast with sawtooth can make full use of the advantages of the two technology.In different channel conditions,the combination between SoftCast and Sawtooth improves more reconstructed video quality,compared with AF.