Achieving Higher Throughput and Better Fairness in Multihop Wireless Networks Using Modified MAC 802.11 Protocol

Multihop Wireless Networks (MWNs) provide a fast and easy way for communication between multiple nodes. But they are susceptible to fading, noise, path loss and interference causing a grave degradation in their performance. The IEEE 802.11 MAC (Medium Access Control) protocol used in these networks plays an important role in their performance. The IEEE 802.11 MAC works well on single-hop networks but not on mutlihop networks. In overloaded MWNs, nodes far away from the destination experience further throughput decline, caused by increased collisions, along the way to the destination, thus resulting in more data loss. The Transmission Control Protocol (TCP) ACK (Acknowledgment) packets are also prone to collisions just like data packets, causing unnecessary re-transmissions. Previous studies show that fragmentation threshold and buffer size at the MAC layer play an important role in enhancing aggregate throughput. However, not too much research considered the fairness problem. To mitigate the fairness problem, we suggest changing, besides the fragmentation and buffer thresholds, the nodes' transmission rate threshold. In this work, we introduce a new MAC algorithm; we named Adaptive Transmission Rate, Fragmentation and Buffer thresholds (ATFB). ATFB considers the location of nodes relative to their destination to compute the collision probability of both packets and ACKs. It then uses these values to estimate new transmission, fragmentation, and buffer thresholds for all nodes in the network. We show that ATFB significantly over-performs the default 802.11g MAC protocol in terms of individual nodes' throughput, end-to-end throughput, fairness, delay and response time.