Opportunistic spectrum sharing with multiple cochannel primary transmitters

We present a distributed, collaborative algorithm to enable opportunistic spectrum access for cognitive radios in the presence of multiple cochannel transmitters. A spectrum hole detection and estimation technique based on received signal strength observations is developed, which allows the coexistence of both licensed and unlicensed transmitters. We address the issues of how to perform collaborative spectrum sensing in the presence of multiple cochannel transmitters and how to determine the maximum transmit power that can be used for a given frequency channel by a cognitive radio while avoiding harmful interference to the licensed network. Simulation results are provided to validate the feasibility and performance of the proposed scheme.

I. Introduction

Recently there has been much interest in cognitive radios (CRs) and their application to opportunistic spectrum access (OSA) to maximize the utilization of licensed spectrum [2], [3]. CRs equipped with features like frequency agility, high receiver sensitivity and location-awareness, are seen as a promising technology to allow the non-disruptive co-existence of unlicensed (secondary) users alongside the licensed (primary) users. Most of the proposed OSA schemes in the literature can be categorized into coordinated (the so-called property-rights model) and uncoordinated (the socalled commons model) frameworks [3]. In the coordinated approach, the primary and secondary nodes can exchange information and cooperatively increase spectrum utilization [4]. In uncoordinated OSA, which is the model of interest for this paper, the primary is oblivious to the existence of secondary nodes, and the secondary system senses the activity of the primary system to opportunistically use the same spectrum, provided that no harmful interference is caused to the primary. In other words, the secondary system tries to fill the “spectrum holes,” which may represent opportunities in time or space or both.