Optimization Design For Wireless Video Transmission Based On Softcast

In recent years, wireless video multicast transmission gain wide attention by people. Traditional point-to-point transmission schemes require the sender to know the receiver’s channel conditions, and select the most appropriate corresponding coding modulation scheme to achieve the best reception. But in the multicast scenarios, this scheme is easy to produce the cliff effect, namely the signal-to-noise ratio is less than a certain threshold, receiving a sharp drop in quality. In2009, a new video transmission scheme called SoftCast is put forward by American scholar S.Jakubczak and D.Katabi. Unlike conventional schemes, SoftCast transform by lossless lossy transmission ways, keep the signal in the actual transmission channel has a linear relation with the original video pixel values, so the video receiving quality depends only on the current user’s own channel conditions, avoiding the cliff effect.The Research point of this thesis is SoftCast video chunk division process, Traditional SoftCast transmission scheme used to using equal chunk partition method after3DDCT, In order to obtain the ideal effect of power distribution and error protection, We need to divide each chunk small enough, as a result, we need to transport many metadata, this will produce a large number of redundancy signals, consuming channel resources, because the number metadata keep proportional relationship with the number of video blocks. However, The DCT coefficients’ amplitude distribution is not uniform, from the dc component of the transition to a low frequency and high frequency component amplitude will decrease sharply. SoftCast’s typical equal chunk division method ignores this law. To this end, this thesis proposes two kinds of video block division improvement plan. Firstly, there was a kind of two-dimensional adaptive chunk division method have been proposed, this algorithm can significantly reduce the number of chunks needed for when get the same transmission performance. In this thesis, the algorithm is extended to three dimensional space, we adopt the method of adaptive partition in a video frame, between the frames,considering the DCT coefficients’amplitude decrease sharply from the former frame to the latter frame, so we put forward to reduce the distribution chunk numbers frame by frame, and the simulation results verified the effectiveness of the proposed method; Secondly, adaptive partition algorithm’s compute complexity is very high, need for each frame scheme for dividing the repeated iteration to get the best video data, this thesis proposed a three dimensional space of video block diagonal dividing method by using DCT coefficients’ amplitude distribution law, the amplitude distribution characteristics of frame differences before and after comprehensive consideration to divide the video block. This method has improved receiving quality significantly compared with the equal video chunk division scheme, and the complexity is close; compared with adaptive partitioning scheme, diagonal division method greatly reduces the complexity, and video receiving quality is only slightly reduced.