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We consider an opportunistic cognitive radio (CR) system in which secondarytransmitter (SUtx) is equipped with a reconfigurable antenna (RA). Utilizingthe beam steering capability of the RA, we regard a design framework forintegrated sector-based spectrum sensing and data communication. In thisframework, SUtx senses the spectrum and detects the beam corresponding toactive primary user's (PU) location. SUtx also sends training symbols (prior todata symbols), to enable channel estimation at secondary receiver (SUrx) andselection of the strongest beam between SUtx-SUrx for data transmission. Weestablish a lower bound on the achievable rates of SUtx-SUrx link, in thepresence of spectrum sensing and channel estimation errors, and errors due toincorrect detection of the beam corresponding to PU's location and incorrectselection of the strongest beam for data transmission. We formulate a novelconstrained optimization problem, aiming at maximizing the derived achievablerate lower bound subject to average transmit and interference powerconstraints. We optimize the durations of spatial spectrum sensing and channeltraining as well as data symbol transmission power. Our numerical resultsdemonstrate that between optimizing spectrum sensing and channel trainingdurations, the latter is more important for providing higher achievable rates.

Achievable Rates of Opportunistic Cognitive Radio Systems Using Reconfigurable Antennas with Imperfect Sensing and Channel Estimation