IEEE 802.11 Contention-Based Medium Access for Multiple Channels

The IEEE 802.11(TM) medium access protocol is based on carrier sensing, and contention, i.e., collision avoidance of frame transmissions from different radio stations. This contention-based protocol is discussed in this paper and extended for the usage in multiple parallel frequency channels, in which a multi-channel station groups channels for increasing its own achievable throughput. We discuss a capture effect that occurs if single-channel and multi-channel stations operate in parallel. Methods to enable multi-channel stations and single-channel stations to coexist by sending out redundant preambles, frame headers, and control frames on each individual frequency channel before the channels are grouped, are studied. Single-channel "legacy" stations operating in one of the grouped channels can then detect that the data frame that follows is not intended for them. We provide a first analytical evaluation for the expected efficiency of the proposed modifications.