One of the most important components of any mobile system is the antenna; antenna design can overcome or cause a number of problems that then must be addressed at other technology layers. Modern mobile platforms are beginning to include novel antenna technology such as MIMO and beam steering; these technologies increase the complexity of evaluating the effectiveness of topology formation algorithms, routing and overall performance due to the large number of configuration states the system can contain. Directional antennas allow for significant improvements in link quality and spatial reuse in wireless communication. Traditional antennas with fixed direction are effective but unable to respond to station mobility or a dynamic environment including such factors as wind and foliage growth. There is a growing body of work on using steerable and sectored antenna systems to harness the efficiency of directional antennas while retaining the flexibility of ad-hoc networks; however, there has been very little work on implementation and measurement of such networks.We examined the physical-layer properties of directional links in two real RF environments, and have evaluated higher-layer strategies for utilizing these antennas. Our results indicate the topology formation process must be a network operation, and that simple link-by-link topology optimization is likely to lead to poor overall performance. These observations drive the formation of the testing and evaluation tools we have developed. This paper describes the tools, methodology and metrics we are using in the evaluation of topology formation algorithms using a dynamically steerable phase array system.
Phased array antennas enable the use of real-time beam-forming and null-steering to further increase control of signal and interference in wireless networks. Understanding the potential of this platform for both wireless mesh networks and single-hop networks is becoming more important as smart antennas begin to emerge in networking standards such as IEEE 802.11n and 802.16. Prior attempts to test non-standard antenna platforms have typically focused around simulations, fixed directional antenna testbeds that are unable to perform null-steering, and small scale temporary setups utilizing 1 or 2 phased array antenna nodes over the span of a few hundred meters. This paper presents the challenges encountered -and solutions developed -in building WART, a permanent, campus-wide testbed for wireless networking with beam-forming antennas. We use affordable commercial off-the-shelf (COTS) hardware as both a measurement apparatus and the system under test. This approach makes it possible to develop and test networking protocols using equipment similar to what may be available operationally, but also presents difficulties beyond those typically encountered with specialized measurement hardware. We show that system-level techniques can adequately overcome those component limitations.
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