Wireless Ad Hoc and Sensor Networks

Predictive Congestion Control for Wireless Sensor Networks 455Throughput/weight (Kbps)700600500400300200100Proposed schemew/o weight adap-Proposed schemeDPCIEEE 802.11CODA01 2 3 4 5Flow IDFIGURE 9.10Performance for unbalanced tree topology.DPC because, by alleviating congestions, it does not waste bandwidth forcollisions and retransmissions. However, it is not able to provide fairservice for all flows as it cannot identify flows hampered by congestionon preceding hops. In contrast, when the weighted fairness part is addedto the proposed congestion control scheme, it identifies that flows 2through 5 are hindered because of congestion and network topology; thus,their weights are adjusted at the next hops to meet fairness criteria. As aresult, at the destination, all the flows achieve the same weighted throughputand end-to-end delay.The 802.11 protocol performs unsatisfactorily for all flows as it stallsbecause of severe congestion. In comparison, the CODA scheme improvesthe performance of the network over the 802.11 protocol as it restrictsnetwork traffic during the congestion by using the backpressure mechanism.However, CODA is not able to achieve throughput comparable tothe proposed protocol because the proposed scheme can mitigate onsetof congestion by precisely controlling queue utilization. In contrast,CODA uses a binary bit to identify the onset of congestion and has noprecise control over the incoming flows; thus, it cannot completely preventbuffer overflows. Additionally, the CODA scheme does not considerweighted fairness, thus unfairly handling different flows. Overall, theproposed protocol improves the performance of the network by 93 to 98%when compared with the CODA scheme, thus justifying increased processingrequirements of the proposed scheme.