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SUMMARY The medium access control protocol determines system throughput in wireless mobile ad hoc networks following the ieee 802.11 standard. Under this standard, asynchronous data transmissions have a defined distributed coordination function that allows stations to contend for channel usage in a distributed manner via the carrier sensing multiple access with collision avoidance protocol. In distributed coordination function, a slotted binary exponential backoff (BEB) algorithm resolves collisions of packets transmitted simultaneously by different stations. The BEB algorithm prevents packet collisions during simultaneous access by randomizing moments at stations attempting to access the wireless channels. However, this randomization does not eliminate packet collisions entirely, leading to reduced system throughput and increased packet delay and drop. In addition, the BEB algorithm results in unfair channel access among stations. In this paper, we propose an enhanced binary exponential backoff algorithm to improve channel access fairness by adjusting the manner of increasing or decreasing the contention window based on the number of the successfully sent frames. We propose several configurations and use the NS2 simulator to analyze network performance. The enhanced binary exponential backoff algorithm improves channel access fairness, significantly increases network throughput capacity, and reduces packet delay and drop. Copyright © 2013 John Wiley & Sons, Ltd.

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Multicasting is one of the relevant issues of communication in infrastructure or centralized administration networks. The reliable delivery of multicast data packets needs feedback from all multicast receivers to indicate whether a retransmission is necessary. A reliable multicast delivery in the wireless Ad-hoc network requires a multicast packet to be received by all multicast receiver nodes. Thus, one or all members need to buffer data packet for possible error recovery. Furthermore, different buffer strategies are essentially used in existing reliable multicast protocols towards support error recovery and reducing buffer overflow. This study proposed two algorithms to improve the performance of the source tree reliable multicast (STRM) protocol. The first algorithm was developed to avoid buffer overflow in the sender node as the forward server (FS) nodes of STRM. This reduction is achieved by managing the buffer of the FS nodes, i.e., selecting the FS nodes depending on its empty buffer size and reducing the feedback sent from the receiver nodes to their FS node. The second algorithm was developed to decrease duplicated packets in the multicast members of the local group, which may be achieved by sending the repair packets to the requesting member. The FS in the local group should create a dynamic and temporary subgroup whose members are only those that requested the repair packet retransmission. The algorithms were tested using detailed discrete event simulation models encompassing messaging systems including error, delay, and mobility models to characterize the performance benefits of the proposed algorithms compared with the existing wireless Ad-hoc network protocols. Several experiments were conducted, revealing numerous results that verify the superior performance of the proposed algorithms over the existing algorithms.

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