Robust wireless video streaming using hybrid spatial/temporal retransmission
Bandwidth demands and timing constraints are two major challenges for wireless video streaming applications. In this paper, we present a hybrid spatial/temporal retransmission protocol that tackles both of these challenges. To increase individual throughput as well as overall network capacity, the system uses an opportunistic retransmission protocol (PRO, Protocol for Retransmitting Opportunistically) that relies on overhearing nodes distributed in physical space to function as relays that retransmit failed packets on behalf of the source. Specifically, the best relay out of the set of nodes that currently have the copy of the packet is responsible for retransmitting (relaying) the packet. Relays with stronger connectivity to the destination have a higher chance of delivering packets successfully than the source, thereby resulting in a more efficient use of the channel. To meet timing constraints, a Time-based Adaptive Retransmission strategy (TAR) is applied by both the source and the relays. With TAR, the MAC dynamically determines whether to (re)transmit or discard a packet based on the retransmission deadline of the packet assigned by the video server. This significantly reduces the number of late packet arrivals at the receiver. Our extensive evaluation results both on a testbed and in the real world demonstrate that hybrid temporal/spatial retransmission can boost streaming performance in diverse wireless environments. The benefits are most pronounced for busy networks, under fading conditions, or for mobile users.