An intelligent hybrid spread spectrum MAC for interference management in mobile ad hoc networks

This paper presents and analyses a fully distributive intelligent hybrid spread spectrum MAC for ad hoc networks. The IHSS MAC scheme has been developed with the aim to mitigate far field interference with the use of a robust DSSS physical layer, while managing near field interference with the use of intelligent slow frequency hopping. The IHSS design ensures a minimum required SINR threshold at active receivers, under low outage probability constraints. IHSS does not inhibit any nodes in space neither thins them out in time. A lower bound on transmission capacity for the case where the size of the frequency hopping zone is variable is derived in this paper. The mathematical model is validated through simulation. The simulation is based on a hopping sequence selection methodology that randomizes the available hopping sequences within a frequency hopping zone around each active receiver. The implementation utilises the RTS/CTS concept of the CSMA MAC, with a slight modification. The performance criterion used for analysis is transmission capacity normalized by the required bandwidth. It is observed that implementation of a suitable sized frequency hopping zone using the proposed IHSS MAC, shows superior performance over ALOHA and guard zone based MACs.