The carrier sense multiple accesses with collision avoidance (CSMA/CA) of IEEE 802.11 plays an importance role in the collision avoidance and alleviates the hidden nodes problems. In this paper, we investigate the MAC protocol of IEEE 802.11 wireless networks on the non-2.4G Unlicensed Channels. We improve the traditional MAC protocol from three aspects. First, differential services with respect to time latency are classified; Second, the control frame are rectified with back-off channels lists (BCLs) where the available channel with the channel state, availability time etc. are marked; Third, a novel back-off scheme is proposed which not only adjust the contention window (CW) dynamic but also improves the fairness of the existing systems. Numerical results verify that the proposed i-MAC protocol can make full use of the cognitive system resource, thus having more advantage in terms of the system throughput, delay and fairness.
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