With advances in wireless networking technologies, wireless multimedia transmission has grown dramatically in recent years. The simplicity, flexibility, and low up-front costs of such systems have not only enabled mobility support for existing multimedia applications but also stimulated the development of new wireless multimedia services. Despite having many advantages, wireless multimedia services, particularly video services, also pose a number of challenges that have prevented them from reaching their full potential. In this thesis, we propose a novel framework that (1) efficiently uses available wireless resources by means of cross-layer design in intermediate nodes, wireless relays, and end systems and (2) opportunistically optimizes wireless resource use by leveraging path diversity with agile path selection to support wireless video transmission.;The proposed solution consists of two building blocks: PRO and TAR. PRO (Protocol for Retransmitting Opportunistically) is an efficient opportunistic retransmission protocol residing in the MAC layer. Opportunistic retransmission employs overhearing nodes, if any, distributed in physical space to function as relays that opportunistically retransmit failed packets on behalf of the source. Relays with better connectivity to the destination have a higher chance of delivering packets successfully than the source does, thereby resulting in a more efficient use of the channel. TAR. (Time-based Adaptive Retransmission) is a MAC-centric cross-layer strategy that leverages application-level information to improve MAC (re)transmission. As the name suggests, TAR dynamically determines whether to (re)transmit or discard a packet based on the retransmission deadline of the packet assigned by the video server regardless of how many trials have been issued for the packet. TAR significantly reduces the number of late packets and avoids using scarce wireless bandwidth to retransmit useless packets. The ultimate solution, PROTAR is a seamless combination of PRO and TAR that further pushes the performance envelope.;To illustrate the efficacy of the proposed solutions, analytical results, testbed experimental results, real-world experimental results, and user studies of subjective video quality for a wide range of wireless scenarios are conducted. The evaluation results consistently show that PRO and TAR can contribute individually. Moreover, PROTAR provides further performance gain in network throughput and visual quality, especially in contended channels, udder fading, or with user mobility.
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