Throughput Of Wireless Mesh Networks : An Experimental Study
Mesh network is gaining importance as the next generation network for many high speed applications such as multimedia streaming. This is because it is easy and inexpensive to setup mesh networks with mobile and PDA devices and can be used as a private network. Hence research is active in the field of routing protocols and routing metrics to improve the mesh network performance. Though most of the protocols are evaluated based on simulation, we implemented protocols based on a few metrics like Expected Transmission Count (ETX) Per-hop Packet Pair Delay (Pkt Pair) and WCETT (Weighted Cumulative Expected Transmitted Time) to investigate the performance of the network through experiments. An advanced version of DSR protocol called LQSR (Link Quality Source Routing) protocol of Microsoft Research along with MCL (Mesh Connectivity Layer) allows multiple heterogeneous adapters to be used in mesh network. Since wireless adapters of 802.11a standard offer 12 non-interfering channels and 802.11b/g standard offer 3 non-interfering channels, using multiple adapters of different bands operating on non-interfering channels to improve capacity and robustness of mesh networks was also investigated. In this thesis we explore the possibility of increasing the coverage area of Wireless Mesh Networks (WMN) to enhance the capacity of WMN and minimize the problems due to interference. Theoretical achievable capacity to every node in a random static wireless ad-hoc network with ideal routing is known to be where n is the total number of nodes in the network. Therefore, with increasing number of nodes in a network, throughput drops significantly. Our measurements show that throughput in a single WMN for different path length is closer to the throughput with nodes across two WMNs of the same path length. We propose to interconnect the networks by using multiple wireless adapters in a gateway node configured with the SSID of the networks in operation. We exploit the DSR protocol feature of assigning locally unique interface indices to its adapters. Performance of a network depends heavily on the metrics used for routing packets. Different metrics were studied in the thesis by setting up a 10-node testbed with a combination of nodes with single and two radios. Testbed was partitioned into two networks with two gateway nodes. Performance of multi-radio performance with the above metrics was compared with baseline single radio nodes in the network with the same metric. It is found that multi-radio nodes out-perform single radio nodes in the multi-hop scenario. Also, operating multi-mesh networks using multiple interfaces configured to those networks in a gateway node increases the coverage area and robustness without loss of performance.