On Optimal Sensing and Capacity Trade-off in Cognitive Radio Systems with Directional Antennas

TL;DR

This paper investigates the optimal sensing duration, antenna orientations, and power control in cognitive radio systems with directional antennas to maximize secondary network capacity while managing interference and sensing errors.

Contribution

It introduces a joint optimization framework for sensing time, antenna directions, and transmit power in directional antenna cognitive radios, enhancing secondary network capacity.

Findings

Optimized sensing time and antenna directions improve capacity.

Joint optimization outperforms fixed configurations.

Simulation confirms capacity gains from the proposed method.

Abstract

We consider a cognitive radio system, in which the secondary users (SUs) and primary users (PUs) coexist. The SUs are equipped with steerable directional antennas. In our system, the secondary transmitter (SUtx) first senses the spectrum (with errors) for a duration of {\tau}, and, then transmits data to the secondary receiver (SUrx) if spectrum is sensed idle. The sensing time as well as the orientation of SUtx's antenna affect the accuracy of spectrum sensing and yield a trade-off between spectrum sensing and capacity of the secondary network. We formulate the ergodic capacity of secondary network which uses energy detection for spectrum sensing. We obtain optimal SUtx transmit power, the optimal sensing time {\tau} and the optimal directions of SUtx transmit antenna and SUrx receive antenna by maximizing the ergodic capacity, subject to peak transmit power and outage interference probability constraints. Our simulation results show the effectiveness of these optimizations to increase the ergodic capacity of the secondary network.