Exploiting Spatial and Channel Diversity in Ad Hoc Networks

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Mobile ad hoc networks are multi-hop wireless networks, with dynamically changing networktopology. Evaluating network capacity is a hard problem in such networks because of the sharednature of the radio medium and possibility of spatial reuse. The latter is again influenced by routesused and node mobility. On the other hand, understanding the network capacity in terms of available bandwidth is crucial to design effective routing protocols. The resarchers propose empirical techniques to evaluate the network capacity. The techniques work in conjunction with a simulator and use mobility and session-level traces to compute capacity that can be compared against the network utilization reported by the simulator. Preliminary experiments indicate interesting results that more capacity is available with higher mobility; however common routing protocols fail to utilize the additional capacity for better routing performance. Preliminary analysis indicates that spatial diversity is not exploited enough by conventional protocols, indicating that multipath routing protocols and distributing traffic over multiple paths would be quite effective. While investigating better techniques to evaluate capacity will be one component of the researchers work, they will also expend substantial effort in developing multipath protocols and techniques to achieve better load balance. For efficiency they will focus on protocols with an on-demand nature. The researchers indicate in this proposal how multiple, link- or node-disjoint, loop-free routes can be computed on demand without the use of source routing, with minimal additional overhead. The researchers will further development and analysis of such protocols. The emphasis will be on obtaining as many multipathroutes as possible. Our preliminary results already indicate that such routing mechanismsreduce route discovery attempts, thus improving both delay and throughput. We will also focus onevaluating techniques to distribute load on multiple routes effectively for a fuller utilization of theavailable capacity. However, we point out that the dense nature of most ad hoc networks will form multiple routesin radio vicinity. In that case, topologically disjoint routes may still share radio medium. Toachieve diversity further, we propose using multiple channels in the underlying medium accesscontrol (MAC) layer so that independent channels can be assigned to neighboring routes. Whileindividual channels may now have less capacity, some preliminary results indicate that significantperformance gains are possible if the transmitter is capable of transmitting on multiple channelsconcurrently. The researchers wish to explore, among other things, channel selection issues for individual links and paths when multipath routes are available. To summarize, the overall goal in this project is to better our understanding of the capacity ofa mobile ad hoc network operating with real network protocols; and to exploit spatial and channeldiversity significantly with a synergistic use of multipath routing and multichannelMAC protocols.