Performance analysis and optimization of CSMA-based wireless mesh networks [electronic resource]

Wireless Mesh Networks consist of nodes interconnected by wireless links. User data packets are transported from sources to destinations over paths comprising of multiple wireless links. The functionality underlying nodes in a wireless mesh network consists of selection of paths between sources and destinations of traffic (Routing), coordination of access to the shared wireless medium (Media Access Control (MAC)), and transmission of data packets on the wireless channel (Physical Layer functionality). In most wireless mesh networks currently deployed, these functions follow the IEEE 802.11 standard, also known as "WiFi". In this standard, the MAC protocol is Carrier Sense Multiple Access (CSMA), whereby a node is blocked from transmitting when it senses the medium busy due to transmissions from other nodes in the network. In such networks, the performance is sensitive to both physical layer parameters and routing. In this thesis, we analyze the performance of CSMA-based wireless mesh networks, and determine how to select physical layer parameters and routes, so as to achieve the best performance possible. The first part of the thesis consists of the development of an analytical model for CSMA-based wireless mesh networks. The model accurately represents all aspects of the CSMA protocol in a multihop network (the effect of blocking, the effect of interference, and the acknowledgement traffic). The model is computationally more efficient than computer simulation models. The accuracy of results obtained by using the model has been verified by comparison to results obtained by using a high-fidelity simulation model. Given the propagation characteristics of wireless links in the network, and the traffic to be carried on these links, the model allows one to determine whether the traffic load is feasible or not. For a feasible load, it also provides link-related performance measures; namely, the average packet error rate on each link, and the fraction of time that the channel is sensed busy by the transmitter of each link. The second part of the thesis addresses specifically the performance optimization of CSMA-based wireless mesh networks. Key to achieving the best performance in a wireless mesh network is to maximize the number of transmissions that can take place concurrently in the network (i.e., the degree of spatial reuse of the wireless channel). This requires an optimum setting of physical layer parameters associated with links carrying traffic. The links carrying traffic are determined by the routing function, and the selection of these links is based on the links' physical layer parameters. Thus, achieving the best performance requires joint optimization of the physical layer parameters and routes. We consider networks in which the signal attenuation between nodes follows a power law function of distance. In that case, the best performance is achieved when routing uses links on which attenuation is in the lowest possible range, as this leads to the highest degree of spatial reuse.

Keywords: Electrical Engineering
Advisor: Cox Donald C. primary advisor. Thesis advisor
Tobagi Fouad A.
Medepalli Kamesh