The performance of multichannel transmission in spectrum sharing system is studied in this paper. Both QoS constraints and interference limitations are considered. The activities of the primary users (PU)s are initially detected by secondary users (SU)s who perform sensing process over multiple channels. They transmit in a single channel at variable power and rates depending on the channel sensing decisions and the fading environment. The cognitive operation is modeled as a state transition model in which all possible scenarios are studied. The QoS constraint of the secondary users is investigated through statistical analysis. Analytical form for the effective capacity of the cognitive radio channel is found. Optimal power allocation and optimal channel selection criterion are obtained. Impact of several parameters on the transmission performance, as channel sensing parameters, number of available channels, fading and others, are identified through numerical example.
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