Altruistic networks: where every node matters

Abstract

Traditionally, wireless ad hoc networks have been used for emergency situations due to the feasibility of fast deployment and connectivity. However, multimedia services are much demanded nowadays and bandwidth and delay requirements of this kind of services are very restrictive. Offering real-time video services in wireless ad hoc networks is not an easy task because of the difficulty of guaranteeing certain quality in a shared medium. In this kind of network, nodes should be ready to route and forward data packets coming from other nodes. The cooperation of every node is essential for the proper operation of the network because there are many factors that may cause video quality degradation, from radio interferences to node mobility, which causes link breakages until a new route is calculated, producing annoying video interruptions to the receiver. The variability in network capacity and link quality, together with the dynamic network topology, has clearly influenced emerging wireless mesh networks, which tend to maintain a static backbone in order to provide sufficient Quality of Service. Moreover, since wireless propagation nature allows any node to overhear any neighbor transmission, the way opportunistic and cooperative routing protocols take advantage of the broadcast nature of wireless medium can be adopted for new routing proposals. In this sense, this chapter proposes and describes a new cross-layer mechanism for recovering lost packets by means of caching overheard packets in neighbor nodes and retransmit them to destination. Additionally, a video-aware cache is implemented in order to recover full frames and prioritize more significant frames. On the other hand, energy consumption is critical in mobile nodes because they may rely on battery power, and the whole network connectivity may be affected if some of the routing nodes run out of battery eventually. Thus, energy consumption is also taken into account in the recovering algorithm design to ensure longer network connectivity life. Finally, results show the improvement in reception, increasing the throughput as well as video quality, and reduce large video interruptions considerably. Moreover, by being aware of nodes energy consumption, the proposed algorithm is able to maintain network lifetime longer.