PhD Thesis Defense - Archive
Improving Reliability and Performance of Real-time Communications in Mobile Ad Hoc Networks
Associate Professor Wendi Heinzelman
Friday, April 10, 2009
Mobile ad-hoc networks (MANETs) are expected to provide certain levels of Quality of Service (QoS) under varying wireless channel capacity and noise constraints. These noisy and varying channel conditions make it difficult to provide reliable and efficient real-time communication in MANETs. In this thesis, we explore three techniques to enable better utilization of mobile ad hoc networks under varying channel conditions: (1) employing a sufficient level of coordination among the nodes, (2) using a superposed coding scheme to provide multiple data rates for users with different channel capacities through a single transmission, and (3) utilizing a mesh networking inspired multicasting approach to vary the amount of redundancy in the routing process to overcome the performance loss due to channel errors. Specifically, we explore the effects of channel noise on different types of mobile ad-hoc networking protocols when channel capacities vary dynamically due to the unpredictable nature of the wireless channel. Our work shows that utilizing coordination among the nodes in MANETs leads to better throughput and energy efficiency for the network while maintaining acceptable packet delay as imposed by the application, even in the presence of relatively high channel error rates. Furthermore, we propose a method of utilizing different channel capacities simultaneously in order to provide individual network users the ability to select the appropriate delay-throughput trade-off for multi-hop routing in MANETs. This is done by exploiting the abilities of superposed coding to provide multiple data rates to receivers simultaneously while using much less energy and bandwidth compared to traditional methods that provide multiple data rates. In addition to the multi-rate multicasting, we propose a mesh networking inspired approach that adapts the amount of redundancy according to the current link conditions. We show that this approach can achieve good QoS levels for real-time traffic scenarios while simultaneously reducing unnecessary energy dissipation. We further explore techniques for combating the problem of lossy links in mobile ad hoc networks, and we propose a qualitative model that can provide guidance as to how different approaches should be utilized together for a given scenario.