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Typical MAC protocols for IEEE 802.11-based ad hoc networks employ a direct transmission strategy whenever the transmitter can directly reach the receiver (one-hop transmission). While such a design enjoys simplicity, it limits the number of admitted transmissions in a given neighborhood. Due to the performance anomaly of 802.11-based wireless networks, transmission with low data rates occupy the shared medium for longer periods of time. Occupying the transmission medium for a longer period of time results in less available transmission time for other nodes, which consequently reduces the number of transmitted packets during the same period of time, leading to a reduction in network throughput. To improve the overall network throughput, we present a cooperative multi-channel MAC protocol for single-hop wireless mobile ad hoc networks that attempts at computing the path with the minimum required transmission time for a given source–destination pair (including the channel assignment along that path). The proposed protocol attempts at improving network performance by means of cooperative communications. According to our approach, if the one-hop (direct) path between communicating nodes supports low data rate (requires longer transmission time), the source selects a multi-hop path to the destination such that the total amount of required transmission time is minimized. Through simulations, we show that our proposed protocol achieves significant throughput and fairness improvement compared to the standard IEEE 802.11-based protocol. [ABSTRACT FROM AUTHOR]

Abstract: Cognitive radio (CR) is a revolutionary technology in wireless communications that enhances spectrum utilization by allowing opportunistic and dynamic spectrum access. One of the key challenges in this domain is how CR users cooperate to dynamically access the available spectrum opportunities in order to maximize the overall perceived throughput. In this paper, we consider the coordinated spectrum access problem in a multi-user single-transceiver CR network (CRN), where each CR user is equipped with only one half-duplex transceiver. We first formulate the dynamic spectrum access as a rate/power control and channel assignment optimization problem. Our objective is to maximize the sum-rate achieved by all contending CR users over all available spectrum opportunities under interference and hardware constraints. We first show that this problem can be formulated as a mixed integer nonlinear programming (MINLP) problem that is NP-hard, in general. By exploiting the fact that actual communication systems have a finite number of available channels, each with a given maximum transmission power, we transfer this MINLP into a binary linear programming problem (BLP). Due to its integrality nature, this BLP is expected to be NP-hard. However, we show that its constraint matrix satisfies the total unimodularity property, and hence our problem can be optimally solved in polynomial time using linear programming (LP). To execute the optimal assignment in a distributed manner, we then present a distributed CSMA/CA-based random access mechanism for CRNs. We compare the performance of our proposed mechanism with reference CSMA/CA channel access mechanisms designed for CRNs. Simulation results show that our proposed mechanism significantly improves the overall network throughput and preserves fairness. [Copyright &y& Elsevier]