Evaluating and improving TCP with adaptive transmission and routing protocols in frequency-hop wireless ad hoc networks

Wireless ad hoc networks facilitate packet switched communication among untethered devices (nodes). The untethered devices are capable of forwarding packets, and are typically constrained in energy resources and transmit power. A set of adaptive protocols was previously proposed to achieve energy efficient and reliable communication in frequency-hop spread spectrum ad hoc networks. The protocols were shown to provide superb performance for a constant rate transport protocol in such a network. However, it is unclear how a transport protocol with reactive rate control, such as the Transmission Control Protocol (TCP), will perform with the adaptive protocols. Our research is to complete the picture by evaluating TCP with adaptive protocols, and propose enhancements to improve throughput. First, a series of simulation studies is done to assess TCP performance and the dominant factors. Results show that adaptive protocols remain energy efficient, but the TCP throughput is mostly degraded. Based on the findings and analysis, we propose using a histogram of successful transmissions in each power level to reduce failure-prone transmit power reductions, such that a power level with a lower success probability is less likely to be adopted in the next transmission. The results demonstrate that the histogram control can reduce packet failures caused by adoption of low transmit power. The throughput is thus improved without sacrificing much throughput efficiency.