Sender- and Receiver-Initiated Multiple Access Protocols for Ad-Hoc Networks

摘要

This thesis focuses on the medium access control (MAC) layer. Many MAC protocols for wireless networks proposed or implemented to date are based on collision-avoidance handshakes between sender and receiver. The key objective of collision-avoidance handshakes is reducing or eliminating the collision of data packets from a source at any given receiver due to interference from packets from other sources. In the vast majority of these protocols, including the IEEE 802.11 standard, the handshake is sender- initiated, in that the sender asks the receiver for permission to transmit using a short control packet, and transmits only after the receiver sends a short clear-to-send notification. There are two main objectives in this work: analyze the effect of reversing the collision-avoidance handshake as a way to improve the performance of MAC protocols under any conditions in the network, and design MAC protocols that provide correct floor acquisition without carrier sensing or code pre-assignment. We show that receiver-initiated collision- avoidance MAC protocols not only outperform any sender-initiated ones, but also guarantee collision-free data transmission and seamless support for mobility by using simple, low-cost wireless radios. We study the effect of persistent carrier sensing in receiver- as well as sender-initiated MAC protocols. We extend our work to multi-channel radios and introduce novel collision-avoidance MAC protocols that eliminate the need for carrier sensing and code pre- assignment, and improve the utilization of the medium in the presence of unicast, multicast and broadcast traffic.