Wireless mesh networks (WMNs) have been proposed as an effective solution for ubiquitous lastmile broadband access. Three key factors that affect the usability of WMNs are high throughput, costeffectiveness and ease of deployability. Recent research has focused on increasing WMN throughput assuming the use of multiple radios equipped with omnidirectional antennas accompanied with channel assignment to enable frequency separation between contending transmissions. Compared to omni antennas, directional antennas offer spatial separation between contending transmissions and have the potential to further enhance the throughput of WMNs. In this paper, we propose DMesh, a WMN architecture that combines spatial separation from directional antennas with frequency separation from orthogonal channels to improve the throughput of WMNs. An important requirement in DMesh is to accomplish this throughput improvement without inhibiting the other two key WMN requirements: cost-effectiveness and ease of deployability. The high cost of smart beamforming directional antennas and their form factor make it difficult to achieve these two requirements. Thus, in DMesh, we focus our effort on incorporating practical directional antennas that are widely and cheaply available (e.g. patch and yagi). The key challenge in DMesh is to exploit spatial separation from such practical directional antennas despite their lack of electronic steerability and interference nulling as well as the presence of significant sidelobes and backlobes. In this paper, we study how such practical directional antennas can improve the throughput of a WMN. Central to our architecture is a distributed, directional channel assignment algorithm for mesh routers that effectively exploits the spatial and frequency separation opportunities in a DMesh network. Simulation results show that DMesh improves the throughput of WMNs by up to 231% and reduces packet delay drastically compared to a multi-radio multi-channel omni network. A DMesh implementation in our 802.11b WMN testbed using commercially available practical directional antennas provides TCP throughput gains ranging from 31% to 57%.


Mesh networks, directional antennas, testbed, multi-channel, system design

Date of this Version

August 2005