Research on TCP Fairness Improvement over Wireless Ad Hoc Networks

Nodes in wireless Ad Hoc networks often encounter spatially-correlated contention, where multiple nodes in the same neighborhood all sense an event they need to transmit information about. The IEEE 802.11 DCF protocol can lead to severe unfairness, i.e., some nodes seize the whole channel capacity while others are starved. It is found that the main reason lies in the unfairness of MAC (media access and control) protocol, while the TCP timeout mechanism makes the unfairness more severe. This paper proposes a non-uniform backoff algorithm with packet related initial contention window. Each node dynamically adjusts the initial contention window according to the TCP packet length. But unlike DCF scheme, the proposed algorithm does not use a time-varying contention window from which a node randomly picks a transmission slot. The proposed algorithm uses a fixed-size contention window once it was chosen and a non-uniform probability distribution of transmitting in each slot within the window.