PROGRAM | Electrical and Computer Engineering

By: Yao Xiao Chair: Leonard J. Cimini, Jr.

ABSTRACT

Cooperative communications has been shown to be effective in combating fading in wireless channels. In order to realize the potential benefits promised by cooperative communications in practical wireless networks, careful cross-layer design is essential. In particular, investigations of the interactions among the physical, link, and network layers are critical in developing cooperation-enabled MAC or routing protocols. Recently, cross-layer design for cooperative networks has become a very active research area; many efficient and elegant cooperative networking techniques that provide significant performance gains have been proposed. Cooperation, however, also introduces new challenges, including increased overhead and interference, that must be addressed in order to efficiently implement cooperative networks. Although cooperation is promising in improving performance, it requires much more overhead to implement compared with conventional point-to-point communications. In addition, with cooperation, the interference environment will change; this means that new interference management techniques are required. In this dissertation, we focus on the overhead-performance trade-off and interference management for wireless cooperative networks. The overhead in implementing cooperation, particularly the overhead to estimate the channels, select the relay(s), and coordinate the transmissions, is investigated. Taking into account the overhead, the spectral and energy efficiencies of several different relaying schemes are studied. Through analyses and simulations, we demonstrate the impact of the overhead on these efficiencies, and provide guidelines for determining the appropriate cooperative scheme for specific applications. In order to realize the promised benefits of cooperative communications in practical wireless networks, cooperation-enabled routing algorithms are essential. Motivated by the analysis of the performance-overhead trade-off for cooperative relaying, we propose a novel cooperative routing algorithm that reduces the amount of overhead incurred in implementations and hence provides a significant performance gain. Specifically, we describe Location-Aware Cooperative Routing (LACR), a routing protocol for multi-hop wireless networks, which incorporates cooperative transmissions into geographical routing. Simulation results show that LACR performs well, providing a high probability of discovering a route with low overhead; these advantages are particularly apparent when the network is sparse. In addition to requiring more overhead, employing cooperation in wireless networks affects the performance of existing interference management techniques. Focusing on multi-hop linear cooperative networks, we investigate the impact of cooperation on spatial reuse scheduling. The impact of enabling spatial reuse and incorporating cooperation on the network throughput is studied. Through analyses and simulations, we show that appropriate reuse is critical for efficient networks, and incorporating cooperation is effective in improving the network performance when the direct links are suffering high outages. Furthermore, the reuse factor that maximizes the network throughput is derived, the performance of which is illustrated via simulations.

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