Wireless Mesh Network Performance Evaluation

Sponsor:	CACC
Period:	July 2002 - June 2003
Student:	Jangeun Jun

Overview

Wireless mesh networks (WMNs) are a relatively new type of ad-hoc networks. One of the main applications is providing last mile broadband Internet access. In this project we tackle two fundamental problems encountered in WMNs used as broadband Internet access networks:

Provisioning: One of the first question an Internet customers asks is How much bandwidth do I get?. The answer for WMNs is: It depends. More precisely it depends on the radio technology used (e.g. 11Mbps radio bandwidth for 802.11b), on the network topology, on how many users are sharing one Internet gateway, on how many hops away is the gateway, on what version of TCP the customers run, and on how good is the routing algorithm.
Fairness and QoS: Unfortunately, in WMNs, if the simple forwarding mechanisms used for Internet forwarding are used, severe unfairness can occur. In particular, the nodes several hops away from the gateway can be completely starved by the nodes close to the gateway (without any any malicious intention from these users). The second goal of this project is to restore the fairness of of WMNs.

Accomplishments

Bottleneck
collision domain.

We tackled the problem of determining the exact capacity of a WMN. The key concept that we introduced to enable the calculation was the bottleneck collision domain[1,3] that is defined as the geographical area of the network that bounds from above the amount of data that can be transmitted in the network. We showed that for WMNs, the throughput of each node decreases as O(1/n), where n is the total number of nodes in the network. In contrast with most existing work on ad hoc network capacity, we do not limit our study to the asymptotic case. In particular, for a given topology and the set of active nodes, we provided exact upper-bounds on the throughput of any node.

In the process of calculating the nominal capacity, we assumed an ideal fairness, i.e. fair allocation of bandwidth among all active nodes. In reality, absolute fairness in a multihop wireless network is very difficult to achieve, the system being inherently unfair. We determined different strategies for restoring fairness and providing different classes of quality of service [2] for wireless mesh networks.

Related Publications

[1] Jangeun Jun and Mihail L. Sichitiu, The Nominal Capacity of Wireless Mesh Networks, in Wireless Communications Magazine, October 2003.

[2] Jangeun Jun and Mihail L. Sichitiu, Fairness and QoS in Multihop Wireless Networks, in Proc. of the IEEE Vehicular Technology Conference (VTC 2003), Orlando, FL, Oct. 6-9, 2003.

[3] Jangeun Jun "Capacity of Wireless Mesh Networks", MS Thesis Report, Dept. of Electrical and Computer Engineering, NC State University, Dec. 2002.

[4] Jangeun Jun, Pushkin Peddabachagari and Mihail Sichitiu, Theoretical Maximum Throughput of IEEE 802.11 and its Applications, Proc. of the 2nd IEEE International Symposium on Network Computing and Applications (NCA'03), Cambridge, MA, April 16-18, 2003, pp. 249-256.