  In Machine to Machine (M2M) networks, a robust Medium Access Control (MAC)
protocol is crucial to enable numerous machine-type devices to concurrently
access the channel. Most literatures focus on developing simplex (reservation
or contention based)MAC protocols which cannot provide a scalable solution for
M2M networks with large number of devices. In this paper, a frame-based Hybrid
MAC scheme, which consists of a contention period and a transmission period, is
proposed for M2M networks. In the proposed scheme, the devices firstly contend
the transmission opportunities during the contention period, only the
successful devices will be assigned a time slot for transmission during the
transmission period. To balance the tradeoff between the contention and
transmission period in each frame, an optimization problem is formulated to
maximize the system throughput by finding the optimal contending probability
during contention period and optimal number of devices that can transmit during
transmission period. A practical hybrid MAC protocol is designed to implement
the proposed scheme. The analytical and simulation results demonstrate the
effectiveness of the proposed Hybrid MAC protocol.
