  We present in this paper a new medium access control (MAC) scheme devoted to
orthogonal frequency division multiple access (OFDMA) systems which aims at
reducing collision probabilities during the channel request period. The
proposed MAC relies on the classical carrier sense multiple access/collision
avoidance (CSMA/CA) protocol with RTS / CTS ("Request To Send" / "Clear To
Send") mechanism. The proposed method focus on the collision probability of RTS
messages exploiting a multi-channel configuration for these messages while
using the whole band for data transmissions. The protocol may be interpreted as
an asynchronous frequency multiplexing of RTS messages. This method achieves
strong performance gains in terms of throughput and latency especially in
crowded networks. Index Terms-Carrier sense multiple access/collision avoidance
(CSMA/CA), multiband, throughput, MAC protocol.
