To solve the problems of control channel bottleneck and communication delay in multi-radio wireless sensor networks, this paper designs an asynchronous MAC protocol named UMD2-MAC in which a union mechanism of prime channel hopping(PCH for short) and control-channel reservation is used. The channel hopping makes sure that the average delay of selecting the same channel is small while the reservation at control channel is employed when the time of channel hopping is long. In addition, to reduce ACK overheads, a conflict-notification mechanism is introduced. Through theoretical analysis, this paper observes that the PCH mechanism of UMD2-MAC consumes less time compared to the random channel hopping mechanism. In order to evaluate the performance of UMD2-MAC, extensive simulations are conducted. The simulation results show that UMD2-MAC not only can adapt to the traffic variation, but also outperforms protocols only with random channel hopping and protocols only with control channel reserving in aspects of throughput, energy and latency respectively.
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