Wireless Ad Hoc and Sensor Networks

304 Wireless Ad Hoc and Sensor Networksad hoc wireless network or WSN must consider the following designcriteria:Centralized vs. distributed approaches: Distributed fair scheduling algorithmfor WSN is preferred over a centralized scheme.Fairness metric: Selection of an appropriate fairness metric is importantfrom a design aspect. It should address the fair allocationof service proportional to weights selected by user-defined QoSmetrics.Scalability: The scheduling scheme should deploy well in WSNs withdynamic topology and link failures.Efficiency of the protocol: Because a trade-off exists between throughputand fairness, fair scheduling should render reasonable throughputto all flows.Persistency of quality of service: Fair scheduling should meet QoS of allflows during topology changes and dynamic channel states.A number of fair scheduling schemes for efficient bandwidth managementexist in the literature; in which some are centralized (Golestani 1994,Luo et al. 2001, Demers et al. 2000), and others are distributed (Lee 1995,Jain et al. 1996, Luo et al. 2001, Vaidya et al. 2000). There has been workon achieving fairness using the distributed MAC protocol for wirelessnetworks (Golestani 1994, Bennett and Zhang 1996, Jain et al. 1996). A recentwork (Vaidya et al. 2000) proposes a distributed fair scheduling protocolfor wireless local area networks (LANs). Distributed fair scheduling (DFS)allocates bandwidth proportional to the weights of the flows. This protocol(Vaidya et al. 2000) performs a fair allocation of bandwidth using aself-clocked fair queuing algorithm (Golestani 1994). However, this protocolmay not be suitable for multihop networks with dynamic channelconditions and changing topologies. With node mobility, the network statecan change demanding weight updates. Additionally, DFS results in largedelay variations, or jitter, in the reception of packets at the destinations.Finally, selection of initial weights is not addressed in DFS. Unless weightsare selected appropriately, fairness cannot be guaranteed even for wirelessnetworks with stationary nodes.In general, these fair scheduling schemes determine appropriateweights to meet QoS criteria. In most schemes, weights are assigned andnot updated when dynamic network conditions apply, and thus do notprovide the advantage seen in an adaptive and distributed fair scheduling(ADFS) -enabled network (Regatte and Jagannathan 2004). The relevantchapter from Regatte and Jagannathan (2004) presents an ADFS protocolfor wireless ad hoc networks (which operates in the CSMA/CA paradigm).The proposed algorithm is fully distributed in nature, and it followsthe fairness criterion defined in Goyal et al. (1997) and in Vaidya et al. (2000).