Medium access control in multi-hop ad hoc networks

Abstract

In recent years, a wide range of wireless mobile devices are emerging, such as notebook computers, personal digital assistants, and handheld game consoles. IEEE 802.11 is a standard medium access control (MAC) protocol for wireless devices. It not only supports communication via access points, but also supports a network of mobile devices communicating between each other without any infrastructure, known as ad hoc networks. Unfortunately, operating IEEE 802.11 in ad hoc networks causes instability and unfairness problems, especially in a multi-hop scenario. Many solutions have been proposed in recent years, tackling these problems at different layers, including transport, network and MAC layers. The performance of these solutions is evaluated comprehensively in this thesis. After that, a new solution based on receiver initiated algorithm and adaptive voluntary pause time is introduced to solve the problem. In the proposed solution, mobile stations work in close collaboration on medium access. For that reason, stability, coexistence, and fairness of the connection are maintained, even if there are multiple traffic streams in a shared channel. Although the mobile stations cooperate in medium access, the proposed solution does not introduce any overhead due to periodic information exchange. Moreover, the proposed solution is totally compatible to current IEEE 802.11. Finally, a proposed improvement of the current error handling procedure of acknowledgement packet loss in IEEE 802.11, selective retransmission, is also presented. One of the difference between this thesis and previous works is that thorough simulations have been carried out with over twenty different scenarios and the results confirm that the proposed solution achieve a stable and fair throughput in all these different scenarios.