Throughput of Underwater Wireless Ad Hoc Networks With Random Access: A Physical Layer Perspective

Due to frequency selectivity, long propagation delay caused by low speed of sound, and fast channel variation, multiple-access protocols that work well in terrestrial networks may not perform as well in underwater environment. We take a physical-layer approach and investigate frequency-selective underwater channels with uncoordinated multiple bursty transmissions. We first derive the statistical distribution of the interference as seen by a typical receiver, considering burstiness of interference transmissions, packet length, and spatial distributions of the interferers. We then derive expressions for the probability density functions of the frequency-dependent signal-to-interference-and-noise ratio (SINR). Expressions for the outage probability of a typical link between two nodes are obtained in the frequency-selective scenarios and the flat-fading special cases. The outage probabilities depend on the bursty transmission probability and the number of interfering transmitters. Previous expressions in the literature on outage probability for flat fading channels and interference-limited systems can be recovered as special cases of our results. Analysis on the throughput of network is provided. Optimization over the number of nodes and bursty transmission probability is performed to maximize the network throughput. Simulation results are presented, which validate the theoretical results and illustrate typical features of the interference in an underwater network.