Balanced media access methods for wireless networks

Abstract

The wireless medium is a scarce shared resource in mobile com-puting. Consequently, the media access control (MAC) layer in-fluences the fairness and robustness of the wireless network. Ac-cording to the current MAC protocols, stations are not able to gain access equally to the shared wireless medium. This problem is commonly known as the fairness problem. The fairness problem occurs mostly because of the existence of hidden stations and the presumption of a non-fully connected wireless network topology. This paper addresses solutions to the fairness problem in wireless networks, p-persistent carrier sense multiple access based algo-rithms are proposed in which a fair wireless access for each user is accomplished using a pre-calculated link access probability, ptj, that represents the link access probability from station s to j. Link access probabilities are calculated at the source station in two ways using connection-based and time-based media access methods. According to the used methods, each active user broadcasts information on either the number of logical connections or the av-erage contention time to the stations within the communication reach. This information exchange provides partial understanding of the topology of the network to the stations. Each station reserves a specific priority for itself to gain access to the shared medium. It is suggested that the information is exchanged during the link access discovery procedure for the connection-based method, and periodically for the time-based method. Link access probabilities are modified every time the exchanged information is received. The proposed algorithms are dynamic and sensitive to the changes in the network topology. The algorithms have been implemented in a specific media access control protocol [1], but they are applicable to all media access control protocols. Simulation results show that the algorithms result in an order of magnitude performance improvement in terms of throughput in a wireless network.