ISSN : 1796-2021
Volume : 2    Issue : 2    Date : March 2007

Opportunistic Spectrum Access in Fading Channels Through Collaborative Sensing
Amir Ghasemi and Elvino S. Sousa
Page(s): 71-82
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Spectrum scarcity is becoming a major issue for service providers interested in either deploying
new services or enhancing the capacity for existing applications. On the other hand, recent
measurements suggest that many portions of the licensed (primary) spectrum remain unused for
significant periods of time. This has led the regulatory bodies to consider opening up under-utilized
licensed frequency bands for opportunistic access by unlicensed (secondary) users. Among
different options, sensing-based access incurs a very low infrastructure cost and is backward
compatible with the legacy primary systems. In this paper, we investigate the effect of user
collaboration on the performance of sensing-based secondary access in fading channels. In
particular, we demonstrate that under independent fading or shadowing, a low-overhead
collaboration scheme with a very simple detector as its building block, 1) improves the spectrum
utilization significantly, 2) enables the individual users to employ less sensitive detectors, thereby
allowing a wider range of devices to access the primary bands, 3) increases the robustness toward
noise uncertainty, 4) reduces the time and bandwidth resources required for satisfactory sensing
which translates into higher agility and efficiency of the secondary access.

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