Cross-layer routing and resource allocation in cognitive radio networks
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The need to wirelessly share high-quality multimedia content is driving the need for ever-increasing wireless transport capacity, which is however limited by the scarcity of the available spectrum. Cognitive radio networks have recently emerged as a promising technology to improve the utilization efficiency of the existing radio spectrum. Based on the reported evidence that static licensed spectrum allocation results in highly inefficient and unbalanced resource utilization, the cognitive radio paradigm prescribes the coexistence of licensed (or primary) and unlicensed (secondary or cognitive) radio users on the same portion of the spectrum. A key challenge in the design of cognitive radio networks is then dynamic spectrum allocation, which enables wireless devices to opportunistically access portions of the spectrum as they become available. Consequently, techniques for dynamic spectrum allocation have received significant attention in the last few years. However, mainstream cognitive radio research has mostly been focused on infrastructure-based networks, while the underlying root challenge of devising decentralized spectrum management mechanisms for infrastructure-less cognitive ad hoc networks is still substantially unaddressed. In cognitive networks with multi-hop communication requirements the dynamic nature of the radio spectrum calls for a new approach to spectrum management, where the key networking functionalities such as routing and medium access control, closely interact and are jointly optimized with the spectrum management functionality. Since in a spatially distributed ad hoc network spectrum occupancy is location-dependent the available spectrum bands may be different at each hop. Hence, controlling the interaction between the routing, medium access, and the spectrum management functionalities is of fundamental importance. The dissertation proposes distributed solutions that jointly address routing and resource allocation for cognitive radio networks in a cross-layer fashion. We explore three directions by adopting the proposed cross-layer routing and resource allocation framework. First, we propose a cross-layer opportunistic spectrum access and dynamic routing algorithm for cognitive radio networks, called ROSA (Routing and Spectrum Allocation algorithm). Through local control actions, ROSA aims at maximizing the network throughput by performing joint routing, dynamic spectrum allocation, scheduling and transmit power control. Second, we enhance the framework by additionally consider techniques to leverage the spatial diversity that characterizes the wireless channel. We propose the combined use of cooperative relaying and dynamic-spectrum-access/cognitive techniques in multi-hop network with decentralized control. Third, we explore a new framework that captures the interdependencies between spread-spectrum channelization and routing. We propose a spread-spectrum management paradigm, in which, unlike mainstream dynamic spectrum access research, digital waveforms are designed to occupy the entire available spectrum, and to adaptively track the interference profile at the receiver to maximize the link capacity while avoiding interference to primary users. A jointly-designed routing and code-division channelization algorithm, ROCH (Routing and cOdedivision CHannelization), is proposed to maximize the pre-detection secondary SINR while guaranteeing the SINR-QoS requirements for on-going transmissions from primary and secondary users. As a conclusion, we believe that our proposed framework of cross-layer routing and resource allocation lays down a solid foundation for building distributed solutions for cognitive radio networks.