Link-Layer Throughput of FHSS with Interference Mitigation: Analysis and Cross Layer Design

We consider ad hoc wireless networks that use frequency hopping to provide multiple access capability among radios. In such systems, the multiple-access control (MAC) protocol must be designed to provide an appropriate level of simultaneous transmissions to efficiently utilize the channel, while not causing so much multiple-access interference that data transmissions cannot be decoded correctly. The transmission rates of the radios should be adapted based on the number of radios that simultaneously have data to transmit in the network. However, for most networks employing spread spectrum, it is difficult to determine the number of radios contending in the network at any particular time. In this paper, we present a method of estimating the number of radios in a system employing frequency-hopping spread spectrum by observing the interference activity at the physical layer of each radio. Each radio uses its locally generated interference estimate to adapt its transmission probability to maximize the sum throughput of the overall network. Simulation results are presented to demonstrate that this approach offers performance close to the maximum possible sum throughput.