Channel selection strategies for multi-channel MAC protocols in wireless ad-hoc networks.

摘要

Wireless devices using the IEEE 802.11 protocol can create on demand multi-hop ad-hoc networks for information collection or dissemination. Due to the ubiquity of the Internet, the Transmission Control Protocol (TCP) and Internet Protocol (IP) often provide transport and network layer services in these networks. New Medium Access Control (MAC) protocols, such as multi-channel MAC protocols (MCMAC), have been proposed to alleviate the inefficient interactions that can occur between IEEE 802.11 and TCP.;This thesis uses ns-2 network simulations to explore the impact of channel selection techniques in the Bi-Directional Multi-Channel MAC protocol (Bi-MCMAC). Four major channel selection techniques are evaluated: Soft Channel Reservation, Soft Channel Reservation with Randomization, Lowest Channel First, and Random Channel Selection. In general, the Soft Channel Reservation techniques provide higher TCP throughput due to fewer link layer losses. In particular, the Soft Channel Reservation techniques reduce link-layer data frame losses by alleviating the Missed Reservation Problem.;The IEEE 802.11 protocol suffers from several problems when used in conjunction with TCP. The hidden and exposed terminal problems result in significant TCP throughput degradation. Furthermore, contention at the link layer results in retransmissions that increase overhead and degrade performance. MCMAC protocols diminish the effect of the hidden terminal problem and eliminate the exposed terminal problem. Bi-directional MCMAC has been proposed to further reduce contention at the link layer. MCMAC protocols, however, suffer from the multi-channel hidden terminal problem.