Abstract
This paper proposes a robust 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 is based on p-persistent CSMA mechanism, which allows M2M devices to compete 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 authors' proposed MAC scheme, the TI is basically a TDMA frame and each M2M device is 802.11 enabled. Each M2M transmitter device and its corresponding one-hop distant receiver communicate using IEEE 802.11 DCF protocol within each TDMA slot to overcome the limitations of TDMA mechanism. The simulation results demonstrate the effectiveness of the proposed hybrid-MAC protocol.