This dissertation proposes both coding schemes and system design strategies for video wireless communications. Video coding can benefit greatly from the development of algorithms for optimal intra/inter mode switching within a rate-distortion framework. We propose an algorithm to optimally switch between intra-coding and inter-coding modes for a video coder that operates on a packet-switched network with fixed-length packets. This optimal mode selection algorithm is integrated with an efficient channel encoder. And the framework is further extended to operate on a time-varying tandem wiredline-wireless channel with feedback information from the receiver. We then discuss a cross-layer optimization scheme for the system design of a wireless video communications system. We present a video transmission scheme with adaptive bandwidth allocation over wired and wireless CDMA networks. We derive the statistics of the received signal, as well as a theoretical bound on the packet drop rate at the receiver. Based on these results, an algorithm for efficient bandwidth allocation among source coding, channel coding and spreading is derived at the packet level, which incorporates the effects of both the changing channel characteristics and the source content. Another fundamental tradeoff in the cross-layer design of a communications system that we study is how to optimize the system when there is a delay constraint imposed by the application. The key elements in this tradeoff are the queuing delay in the source encoder output buffer, the delay caused by the interleaver, and the delay caused by channel decoding
