Throughput Analysis on Slotted Underwater Acoustic Sensor Networks With Guard Time

A guard time is a short time interval that is added between packet transmissions, and has been applied in time- slotted underwater acoustic sensor networks (UASNs) to balance the transmission rate and the inter-slot interference. In this article, we take a physical-layer approach and investigate the throughput performance in time-slotted UASN with guard time. Based on the geographical node distribution, we first derive the probability distribution of the arrival time of an interfering packet and further the distribution of the packet overlap duration. We then derive the expression of the probability density functions (pdfs) of the signal-to-interference-plus-noise ratio (SINR). Expressions for the outage probability and the normalized throughput of a typical link between two nodes are also obtained. We show that when the length of guard time is properly selected, time-slotted network with guard time has higher throughput than those without guard time. Simulation results validate the theoretical results and illustrate typical features of the interference in an underwater network.