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In this paper, we present a novel contention-based medium access control (MAC) protocol, namely, the channel reservation MAC (CR-MAC) protocol. The CR-MAC protocol takes advantage of the overhearing feature of the shared wireless channel to exchange the channel reservation information with little extra overhead. Each node can reserve the channel for the next packet waiting in the transmission queue during the current transmission. We theoretically prove that the CR-MAC protocol achieves much higher throughput than the IEEE 802.11 RTS/CTS mode under saturated traffic. The protocol also reduces the packet collision, thereby saving the energy for retransmission as well. We also evaluate the protocol by simulations under both saturated traffic and unsaturated traffic. Our simulation results not only validate the theoretical analyses on saturated throughput, but also reveal some other good features of the protocol. For example, under saturated traffic, both the saturated throughput and fairness measures of the CR-MAC are very close to the theoretical upper bounds. Moreover, under unsaturated traffic, the protocol also achieves higher throughput and better fairness than IEEE 802.11 RTS/CTS.