Optimizing 802.11 Wireless Mesh Network Performance Using Physical Carrier Sensing

Multi-hop ad-hoc networks suffer from the presence of hidden and exposed nodes that diminish aggregate network throughput. While there are various approaches to mitigating these problems, in this work we focus exclusively on the role of physical carrier sensing (PCS). Specifically, tuning the PCS threshold leads to a trade-off between the ‘exposed’ and ‘hidden’ areas. The contributions of this work are (at-least) two-fold: i. we develop an analytical formulation (assuming constant rate nodes) to determine the optimal PCS threshold. It is shown that choosing the carrier sensing range equal to the interference range is the appropriate optimality principle for PCS based network optimization. An important component of this analysis is an improved link layer model in contrast to much of the existing literature, that leads to significantly new and different insights into enhancing 802.11 network performance. Further, ii. in attempting to support the analysis via simulations with OPNET, several problems with various aspects of OPNET’s implementations of the 802.11 link and MAC layers were exposed. Our description of these issues as well as fixes are likely to be of interest to the broader research community interested in using OPNET for their own investigations in 802.11 network performance. Physical Carrier Sensing, Throughput Optimization, Hidden and Exposed Terminals, 802.11 WLAN, OPNET Simulations