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Taking advantage of the independent fading channel conditions among multiple wireless users, opportunistic transmissions schedule the user with the instantaneously best condition and thus increase the spectrum utilization efficiency of wireless networks. So far, most proposed opportunistic scheduling policies for wireless ad hoc networks exploit local multiuser diversity, i.e., each transmitter selects its best receiver independently. However, due to co-channel interference, the decisions of neighboring transmitters are highly correlated. Furthermore, the neighboring links without a common sender also experience independent channel fading. Taking the contention relationship and the channel diversity among links into account, we extend the concept of multi-user diversity to a more generalized one, by which a set of senders cooperatively schedule the instantaneously and globally best out-going links. We formulate the cooperative and opportunistic scheduling problem with fairness requirements into an optimization problem and present its optimal solutions. By graph theoretically analyzing the optimal solutions, we also propose GOS, a distributed Graph theory based and Opportunistic Scheduling algorithm, which modifies IEEE 802.11 protocol to implement the optimal scheduling policy. The theoretical analysis and simulation results both verify that our implementation achieves higher network throughput and provides better fairness support than the existing algorithms.
Date of Conference: 26-30 Nov. 2007