Power Control in Cognitive Radio Networks: How to Cross a Multi-Lane Highway

TL;DR

This paper analyzes how secondary users in cognitive radio networks can optimize their transmission power to maximize spectrum opportunities and throughput while minimizing interference to primary users, using analytical models and physical-MAC layer interactions.

Contribution

It provides a quantitative analysis of power control effects on spectrum opportunity detection and throughput, highlighting the exponential decay of opportunities with increased power and the PHY-MAC layer relationship.

Findings

Spectrum opportunity probability decreases exponentially with secondary user power.

Reliable detection occurs in extreme power ratio regimes.

PHY-MAC interaction depends on application and handshake signaling.

Abstract

We consider power control in cognitive radio networks where secondary users identify and exploit instantaneous and local spectrum opportunities without causing unacceptable interference to primary users. We qualitatively characterize the impact of the transmission power of secondary users on the occurrence of spectrum opportunities and the reliability of opportunity detection. Based on a Poisson model of the primary network, we quantify these impacts by showing that (i) the probability of spectrum opportunity decreases exponentially with respect to the transmission power of secondary users, where the exponential decay constant is given by the traffic load of primary users; (ii) reliable opportunity detection is achieved in the two extreme regimes in terms of the ratio between the transmission power of secondary users and that of primary users. Such analytical characterizations allow us to study power control for optimal transport throughput under constraints on the interference to primary users. Furthermore, we reveal the difference between detecting primary signals and detecting spectrum opportunities, and demonstrate the complex relationship between physical layer spectrum sensing and MAC layer throughput. The dependency of this PHY-MAC interaction on the application type and the use of handshake signaling such as RTS/CTS is illustrated.