Distributed spectrum leasing via cooperation

“Cognitive radio” networks enable the coexistence of primary (licensed) and secondary (unlicensed) terminals. Conventional frameworks, namely commons and property-rights models, while being promising in certain aspects, appear to have significant drawbacks for implementation of large-scale distributed cognitive radio networks, due to the technological and theoretical limits on the ability of secondary activity to perform effective spectrum sensing and on the stringent constraints on protocols and architectures. To address the problems highlighted above, the framework of distributed spectrum leasing via cross-layer cooperation (DiSC) has been recently proposed as a basic mechanism to guide the design of decentralized cognitive radio networks. According to this framework, each primary terminal can ”lease” a transmission opportunity to a local secondary terminal in exchange for cooperation (relaying) as long as secondary quality-of-service (QoS) requirements are satisfied. The dissertation starts by investigating the performance bounds from an information-theoretical standpoint by focusing on the scenario of a single primary user and multiple secondary users with private messages. Achievable rate regions are derived for discrete memoryless and Gaussian models by considering Decode-and-Forward (DF), with both standard and parity-forwarding techniques, and Compress-and-Forward (CF), along with superposition coding at the secondary nodes. Then a framework is proposed that extends the analysis to multiple primary users and multiple secondary users by leveraging the concept of Generalized Nash Equilibrium. Accordingly, multiple primary users, each owning its own spectral resource, compete for the cooperation of the available secondary users under a shared constraint on all spectrum leasing decisions set by the secondary QoS requirements. A general formulation of the problem is given and solutions are proposed with different signaling requirements among the primary users. The novel idea of interference forwarding as a mechanism to enable DiSC is proposed, whereby primary users lease part of their spectrum to the secondary users if the latter assist by forwarding information about the interference to enable interference mitigation at the primary receivers. Finally, an application of DiSC in multi-tier wireless networks such as femtocells overlaid by macrocells whereby the femtocell base station acts as a relay for the macrocell users is presented. The performance advantages of the proposed application are evaluated by studying the transmission reliability of macro and femto users for a quasi-static fading channel in terms of outage probability and diversity-multiplexing trade-off for uplink and, more briefly, for downlink

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Abstract-Within the paradigm of spectrum leasing via cooperation, primary (licensed) nodes can lease some of the owned spectral resources to secondary (unlicensed) users in exchange for cooperation. Secondary users, in turn, set a minimal quality-of-service (QoS) requirement on the spectrum leased as a precondition for cooperation. Previous work assumed that a single primary user makes spectrum-leasing decisions in the presence of possibly multiple secondary users. In this paper, the analysis is extended to accommodate multiple primary users by adopting the framework of generalized Nash equilibrium (GNE) problems. Accordingly, multiple primary users, each owning its own spectral resource, compete for the cooperation of the available secondary users under a shared constraint on all spectrum-leasing decisions set by the secondary QoS requirements. A general formulation of the problem is given, and solutions are proposed with different signaling requirements among the primary users. Then, application of the framework is discussed for a practical example that includes communication over fading channels with retransmissions. Numerical results bring insight into the advantages of spectrum leasing and of the effectiveness of the proposed solutions. Index Terms-Cognitive radio, cooperative systems, generalized Nash equilibrium (GNE), spectrum leasing, variational inequality (VI)