Abstract
This chapter proposes a new hybrid MAC protocol for direct communication among M2M devices with gateway coordination. The proposed protocol combines the benefits of both contention-based and reservation-based MAC schemes. The authors assume that the contention and reservation portion of M2M devices is a frame structure, which is comprised of two sections: contention interval (CI) and transmission interval (TI). The CI duration follows p-persistent CSMA mechanism, which allows M2M devices to contend for the transmission slots with equal priorities. After contention, only those devices which have won time-slots are allowed to transmit data packets during TI. In the proposed MAC scheme, the TI duration follows TDMA mechanism. Each M2M transmitter device and its corresponding one-hop distant receiver communicate using IEEE 802.11 DCF protocol within each TDMA slot to overcome various limitations of TDMA mechanism. The authors evaluate the performance of the proposed hybrid MAC protocol in terms of aggregate throughput, average transmission delay, channel utility, and energy consumption.