Cooperative diversity architecture for wireless networks

Official URL: http://192.168.1.20/record=b1378203 (Table of Contents)

The burgeoning demand for wireless networks necessitates reliable and energy-efficient communication architectures that are robust to the impairments of the wireless medium. Cooperative communication emerges as an appropriate technique that mitigates the severe effects of channel impairments through the use of cooperative diversity. Notwithstanding the fact that cooperative diversity is a very suitable technique to provide robust and reliable communication, the realization of cooperation idea precipitates many technical challenges that are associated with the overhaul of the wireless network design. This dissertation proposes a cooperative diversity architecture for wireless networks, that spans the physical, medium access and routing layers with parameters (jointly) optimized for overall system performance, taking into account the cost of cooperation in each layer. First, we present a new cooperative MAC protocol, COMAC, that enables cooperation of multiple relays in a distributed fashion. Through the proposed protocol, we investigate and demonstrate at what rate and for which scenarios cooperation brings benefits in terms of throughput and energy-efficiency. Our results demonstrate that cooperation initiation has a significant cost on both the throughput and energy-efficiency, which have been often disregarded in the literature. We next study the energy minimal joint cooperator selection and power assignment problem under transmit power constraints such that the cooperative transmissions satisfy an average bit error rate (BER) target. We derive the average BER of the cooperative system and we propose a simple yet close approximation to facilitate cooperator selection methods with closed form power assignment solutions. We formulate the joint cooperator selection and power assignment problem, we present the optimal solution (O-CSPA) and we also propose a distributed implementation (D-CSPA). Our results demonstrate that smart cooperator selection is essential, as it provides efficient resource allocation with reduced overhead leading to improved system performance. Our implementation and simulations of D-CSPA algorithm in COMAC protocol demonstrate that our distributed algorithm causes minimal overhead, yields improved throughput and reduced delay, while reducing the energy consumption. Finally, we propose a cooperative routing framework and a cross-layer architecture, RECOMAC, for wireless ad hoc networks. The RECOMAC architecture facilitates formation of cooperative sets on the fly in a decentralized and distributed fashion, requiring no overhead for relay selection and actuation, and resulting in opportunistically formed cooperative links that provide robust and reliable end-to-end communication, without the need for establishing a prior non-cooperative route, unlike existing schemes. The results demonstrate that under wireless channel impairments, such as fading and path loss, our cooperative forwarding framework and cross-layer architecture, RECOMAC significantly improve the system performance, in terms of throughput and delay, as compared to non-cooperative conventional layered network architecture with AODV routing over IEEE 802.11 MAC.