Exploiting Spatial and Channel Diversity in Ad Hoc Networks

移动自组网是一种多跳无线网络，网络拓扑结构动态变化。由于无线介质的共享性和空间重用的可能性，评估网络容量是这类网络中的一个难题。后者再次受到使用的路由和节点移动性的影响。另一方面，了解可用带宽方面的网络容量对于设计有效的路由协议至关重要。研究人员提出了评估网络容量的经验方法。这些技术与模拟器一起工作，并使用移动性和会话级别跟踪来计算容量，这些容量可以与模拟器报告的网络利用率进行比较。初步的实验结果表明，移动性越高，可用容量越大；然而，常见的路由协议不能利用额外的容量来提高路由性能。初步分析表明，传统协议对空间分集的利用还不够充分，这表明多路径路由协议和在多条路径上分配流量将是非常有效的。虽然研究更好的技术来评估容量将是研究人员工作的一个组成部分，但他们也将花费大量精力开发多路径协议和技术，以实现更好的负载平衡。为了提高效率，他们将重点放在按需协议上。研究人员在该方案中指出了如何在不使用源路由的情况下，以最小的额外开销按需计算多条链路或节点不相交的无环路由。研究人员将进一步开发和分析此类协议。重点将是获得尽可能多的多通道。我们的初步结果已经表明，这种路由机制减少了路由发现尝试，从而提高了时延和吞吐量。我们还将重点评估在多个路由上有效地分配负载以更充分地利用可用容量的技术。然而，我们指出，大多数自组织网络的密集特性将在无线电附近形成多条路由。在这种情况下，拓扑不相交的路由可能仍然共享无线电介质。为了进一步实现分集，我们建议在底层的媒体接入控制(MAC)层使用多个信道，以便将独立的信道分配给相邻的路由。虽然现在单个信道的容量可能较小，但一些初步结果表明，如果发射机能够同时在多个信道上传输，则可能获得显著的性能提升。研究人员希望探索当多径路由可用时，单个链路和路径的频道选择问题。总而言之，本项目的总体目标是更好地理解使用真实网络协议的移动自组织网络的容量，并通过协同使用多路径路由和多信道MAC协议来显著地利用空间和信道分集。

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.