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Abstract - Cognitive Radios (CRs) can mitigate the impending spectrum scarcity problem by utilizing their capability of accessing licensed spectrum bands opportunistically. While most existing work focuses on enabling such opportunistic spectrum access for stationary CRs, mobility is an important concern to Secondary Users (SUs) because future mobile devices are expected to incorporate CR functionality. In this paper, the authors identify and address three fundamental challenges encountered specifically by mobile SUs. First, they model channel availability experienced by a mobile SU as a two-state Continuous-Time Markov chain (CTMC) and verify its accuracy via in-depth simulation. Then, to protect primary/incumbent communications from SU interference, the authors introduce guard distance in the space domain and derive the optimal guard distance that maximizes the spatio-temporal spectrum opportunities available to mobile CRs.
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