List-coloring based channel allocation for open-spectrum wireless networks

The current fixed spectrum allocation scheme leads to low spectrum utilization across the whole spectrum. It requires a more effective spectrum allocation and utilization policy, which allows unused parts of spectrum to become available temporarily for other usage so that the scarcity of the spectrum can be largely mitigated. This paper is an attempt to study such wireless networks with opportunistic spectrum availability and access. We study the dynamics in the available channels caused by the location and traffic load of the primary users and proposed several distributed algorithms to exploit the available channels for secondary users. The performance of different algorithms is evaluated in networks with static and time-varying channel availability. I. INTRODUCTION The current fixed spectrum allocation scheme leads to sig- nificant spectrum underutilization. For instance, experiments conducted by Shared Spectrum Company indicate as much as 62% of white space below 3GHz band even in the most crowed area near downtown Washington DC, where both government and commercial spectrum usage are intensive (1). Such low utilization and increasing demand for the radio spectrum suggest that a more effective spectrum allocation and utilization policy is necessary, where unused parts of spectra can be temporarily utilized by other users so that the scarcity of the spectrum can be largely mitigated. In this paper, we focus on the opportunistic exploration of the white space by users other than the primary licensed ones on a non-interfering or leasing basis. Such usage is being enabled by regulatory policy initiatives and radio technology advances. First, both the Federal Communications Commis- sion (FCC) and the federal government have made important initiatives towards more flexible and dynamic spectrum usage, e.g., (2), (3). Further, opportunistic spectrum sharing is enabled by software-defined radio or cognitive radio technologies. Such technology advances provide the capability for a radio device to sense and operate on a wide range of frequencies us- ing appropriate communication mechanisms, and thus enable dynamic and more intense spectrum reuse in space, time, and frequency dimensions. We focus on the study of the secondary users who ob- serve the channel availability dynamically and explore it opportunistically. Here, secondary users refer to spectrum users who are not owner of the spectrum and operate based on agreements/etiquettes imposed by the primary users or regulatory entities. We study the impact of the opportunistic spectrum availability on the secondary users who explore the spectrum when allowed by the primary users of the spectrum. (Note that the secondary users may have their own licensed/allocated bandwidth where they are primary users, which is not the concern of this paper.) Because of the traffic load and the distribution of the primary users, the available channels observed by the secondary users are time- varying and location-dependent. We study the impact of the characteristics of primary users on the spectrum opportunistic availability. We present a general framework to model the correlation between primary and secondary users. We also propose several distributed spectrum access schemes and study their performance under the above-mentioned time-varying and location-dependent channel availabilities.