AUTHORS: Panagiotis Varzakas
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ABSTRACT: In this paper, the problem of estimating the optimum radio capacity of a spread spectrum noncellular Cognitive Radio (CR) system, operating in a Rayleigh fading environment, is examined. In contrast to previously published works, here, the radio capacity is expressed in terms of the number of simultaneously transmitting secondary users, considering only one primary user, which receives the spread spectrum simultaneously transmitted signals, through an optimum maximal-ratio combiner (MRC) RAKE receiver. Specifically, the problem to finding the number of secondary simultaneously transmitting users, which maximizes the normalized average channel capacity (expressed in bits/sec/Hz) available to primary user, is considered. Then, the theoretical analysis, avoiding the application of a complex and lengthy simulation process, leads to a simple but novel closed-form expression for the system’s optimum radio capacity, which is related with the system’s parameters and can be useful for the practical design of a CR system and for an initial quantitative analysis. Finally, numerical results and respective graphs are presented to illustrate the presented analysis.
KEYWORDS: Cognitive Radio systems, Radio capacity, Channel capacity, Rayleigh fading
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