A distributed prioritized multiple access scheme for Ad Hoc networks using time-frequency hopping communications

In the time-frequency hopping (TFH) communications, a terminal transmits data at pseudo-random time slots and carrier frequencies, leading to high security against eavesdropping and anti-interference capability. However, in an ad hoc network using the TFH communications, it is challenging to coordinate stations in a distributed manner to share the time/frequency resources, avoid collision, and provide service differentiation. In this paper, we propose a distributed, prioritized multiple access control (MAC) protocol for TFH-based ad hoc networks, named TFH-MAC. In this scheme, the channel occupancy ratio (COR) is introduced to indicate the transmission of stations in a matrix of time-frequency resource blocks. By assigning different predetermined COR thresholds and contention window sizes to traffic classes, the priorities in channel access can be provided. Furthermore, the low-complexity random linear coding (RLC) is employed to repair frames from time-frequency spread segments with partial collision. In particular, the segments correctly received in previous transmissions can be combined with newly successfully received segments for decoding. Thus, the transmission efficiency is increased. An analytical model using mean value analysis is proposed to study the performance of saturated TFH-MAC theoretically, and the transmission probability, collision probability, throughout, and frame service time are derived. Extensive simulation results have verified the analytical model and demonstrated the optimal traffic load and resource matrix dimension to maximize the network throughput.