Routing and channel assignment in multihop wireless networks: Protocols and performance issues.

摘要

In a multihop wireless network, wireless devices (nodes) with radio communication capability communicate with each other using multi-hop wireless links. The self-organizing and untethered aspects of multihop wireless networking together make it ideally suited for communication in emergency and battlefield scenarios where network infrastructure is destroyed/absent, and for enabling large-scale broadband Internet access. However, the capacity of multihop wireless networks is fundamentally limited by multiple access interference and the available wireless spectrum. So, the extent to which available network capacity is efficiently utilized largely determines end-user application performance. In this dissertation, we develop protocols to effectively exploit diversity available in the form of multiple paths and channels for enhancing performance in multi-hop wireless networks by improving routing efficiency and facilitating effective spectrum utilization.;We investigate the use of multiple paths for efficient, fault-tolerant routing in mobile ad hoc networks by focusing primarily on on-demand routing protocols that discover routes on an "as needed" basis. First, we consider a well-known on-demand multipath protocol called Dynamic Source Routing (DSR) that aggressively caches all overheard routes to reduce frequency and overhead of route discovery, but lacks effective mechanisms to promptly purge invalid (stale) routes. The use of such stale routes not only limits the benefit of caching multiple routes, but also leads to wastage of precious network capacity. We propose three mechanisms to alleviate the DSR stale cache problem when used together substantially improve cache performance, routing efficiency and application performance. Second, we develop an efficient, on-demand multipath distance vector protocol (termed AOMDV) as an extension to another prominent on-demand protocol called Ad hoc On-demand Distance Vector (AODV). The novelty of AOMDV stems from its ability to find multiple loop-free paths without having to incur high inter-nodal coordination overheads and simultaneously ensure disjointness of alternate paths without the use of source routing. Third, we consider heterogeneous ad hoc network scenarios (with diverse node transmission ranges) containing unidirectional links in addition to node mobility. The use of unidirectional links for routing can prevent network partitions as well as provide shorter paths, but it is also complex and associated with high overheads. (Abstract shortened by UMI.)