Energy efficiency and throughput for TCP traffic in multi-hop wireless networks

We study the performance metrics associated with TCP-regulated traffic in multi-hop wireless networks that use a common physical channel (e.g., IEEE 802.11). In contrast to earlier analyses, we focus simultaneously on two key operating metrics - the energy efficiency and the session throughput. Using analysis and simulations, we show how these metrics are strongly influenced by the radio transmission range of individual nodes. Due to tradeoffs between the individual packet transmission energy and the likelihood of retransmissions, the total energy consumption is a convex function of the number of hops (and hence, of the transmission range). On the other hand, the TCP session throughput decreases supra-linearly with a decrease in the transmission range. In certain scenarios, the overall network capacity can then be a concave function of the transmission range. Based on our analysis of the performance of an individual TCP session, we finally study how parameters such as the node density and the radio transmission range affect the overall network capacity under different operating conditions. Our analysis shows that capacity metrics at the TCP layer behave quite differently than corresponding idealized link-layer metrics.