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Opportunistic Spectrum Access in Fading Channels Through Collaborative Sensing

Amir Ghasemi and Elvino S. Sousa
Electrical and Computer Engineering Department University of Toronto

Abstract-Spectrum scarcity is becoming a major issuefor service providers interested in either deploying newservices or enhancing the capacity for existing applications.On the other hand, recent measurements suggest that manyportions of the licensed (primary) spectrum remain unusedfor signi_cant periods of time. This has led the regulatorybodies to consider opening up under-utilized licensedfrequency bands for opportunistic access by unlicensed(secondary) users. Among different options, sensing-basedaccess incurs a very low infrastructure cost and is backwardcompatiblewith the legacy primary systems. In this paper,we investigate the effect of user collaboration on the performanceof sensing-based secondary access in fading channels.In particular, we demonstrate that under independent fadingor shadowing, a low-overhead collaboration scheme with avery simple detector as its building block, 1) improves thespectrum utilization signi_cantly, 2) enables the individualusers to employ less sensitive detectors, thereby allowinga wider range of devices to access the primary bands, 3)increases the robustness toward noise uncertainty, 4) reducesthe time and bandwidth resources required for satisfactorysensing which translates into higher agility and ef_ciency ofthe secondary access.

Index Terms-spectrum sensing, opportunistic access,cognitive radio, collaborative sensing

Cite: Amir Ghasemi and Elvino S. Sousa, "Opportunistic Spectrum Access in Fading Channels Through Collaborative Sensing," Journal of Communications, vol. 2, no. 2, pp. 71-82, 2007.