Channel access mechanisms and protocols for opportunistic cognitive radio networks

High traffic load over the unlicensed portion of the radio spectrum (a.k.a., ISM bands) along with inefficient usage of the licensed spectrum gave impetus for a new paradigm in spectrum allocation, whose main purpose is to improve spectrum efficiency through opportunistic access. Cognitive radios (CRs) have been proposed as a key enabling technology for such paradigm. Operating a CR network (CRN) without impacting the performance of licensed (primary) users requires new protocols for information exchange as well as mathematical tools to optimize the controllable parameters of the CRN. In this dissertation, we target the design of such protocols. First, we develop a distributed CRN MAC (COMAC) protocol that enables unlicensed users to dynamically utilize the spectrum while limiting the interference they inflict on primary (PR) users. The main novelty in COMAC lies in not assuming a predefined CR-to-PR power mask and not requiring coordination with PR users. Second, we propose a novel distance-dependent MAC protocol for CRNs in which each CR is equipped with multiple transceivers. Our protocol (called DDMAC) attempts to maximize the CRN throughput by following a novel probabilistic channel assignment mechanism. This mechanism exploits the dependence between the signal's attenuation model and the transmission distance while considering the traffic profile. We show that through its distance- and traffic-aware, DDMAC significantly improves network throughput. Finally, we address the problem of assigning channels to CR transmissions, assuming one transceiver per CR. The main goal of our design is to maximize the CRN throughput with respect to both spectrum assignment and transmission power. Specifically, we present centralized and distributed solutions that leverage the unique capabilities of CRs. Compared with previously proposed protocols, our schemes are shown to significantly improve network throughput.