Generalized CSMA/CA Protocol for OFDMA Systems

In this paper, we present a multi-channel carrier sense multiple access with collision avoidance (CSMA/CA) protocol for orthogonal frequency division multiple access (OFDMA) systems. The protocol exploits the OFDMA system features that multiple stations can transmit simultaneously on different subchannels and the stations can obtain the channel information of all the sub-channels at each time instant. It is designed to enable the stations to contend with each other for channel access both in time and frequency domains through a two-dimensional backoff scheme. By adopting this two-dimensional backoff, the protocol takes a generalized form of the conventional single-channel CSMA/CA protocol: It allows to segment the channel bandwidth into multiple narrow-band random access channels and adjust the transmission probability according to the multichannel activity in a flexible manner. The simulation and analysis results reveal that the proposed system performs far better than the single-channel CSMA/CA system while using the same total bandwidth.