A Cooperative Diversity-based Virtual MISO Framework for Multi-hop Wireless Networks

This dissertation work focuses on improving wireless link reliability and end-to-end delay in multi-hop wireless networks. It is well known that wireless channel effects (e.g., multipath fading and attenuation) result in time-varying and packet high-error rates. In single-hop wireless networks, link-layer retransmission mechanisms are typically used to reduce the effects of these high-error rate channels. However, the cumulative effect of multiple link-layer transmission at every hop along a multi-hop path results in significant performance problems (e.g., high end-to-end delay, high jitter, and low throughput).;This dissertation presents A Cooperative Diversity-based Virtual MISO Framework for Multi-hop Wireless Networks. The framework operates at the medium access control and physical layers and is designed to overcome the performance-reducing effects of multi-hop wireless paths. Two key concepts, cooperative diversity and virtual MISO with space time coding, are combined to form an integrated opportunistic cooperative relaying framework that is able to improve network performance in the presences of both high-quality and low-quality wireless channels. Specifically, the developed CDRM protocol is able to improve end-to-end delay and reliability when link quality is poor by utilizing the available resources and taking advantage of the spatial diversity via helper nodes, eliminating the need for packet retransmissions. Although the helper nodes remain idle, they do not participate in the packet transmission when link quality is high. The proposed OVM protocol extends the CDMR protocol so that idle helper nodes are used even when link quality is high. This is accomplished by employing space-time coding, allowing the primary relay node and helper nodes to transmit simultaneously. This has the effect of increasing the effective transmission range (without increasing transmit power and energy consumption), thereby reducing path length and end-to-end delay. We have conducted extensive simulation experiments and compared the CDMR and the OVM framework to traditional multi-hop routing strategies (i.e., AODV and DSR) and the related Virtual MISO protocol. The simulation results showed that the framework is able to improve end-to-end network performance by up to eighty-six percent.