SEP-Optimal Transmit Power Policy for Peak Power and Interference Outage Probability Constrained Underlay Cognitive Radios

• Published in: IEEE transactions on wireless communications Vol. 12; no. 12; pp. 6371 - 6381
• Main Authors: Kashyap, Salil, Mehta, Neelesh B.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.12.2013; Institute of Electrical and Electronics Engineers
• Subjects: Applied sciences; Channel estimation; Cognitive radio; Exact sciences and technology; Fading channels; imperfect channel estimates; Information, signal and communications theory; Interference; interference outage probability; Modulation, demodulation; peak power; Power outages; Radiocommunication specific techniques; Radiocommunications; Signal and communications theory; symbol error probability; Systems, networks and services of telecommunications; Telecommunications; Telecommunications and information theory; Transmission and modulation (techniques and equipments); Transmitters. Receivers; underlay; Fading channels; Parameter estimation; Quadrature amplitude modulation; Outage; Wireless telecommunication; Transmitter; Cognitive radio; underlay; Phase shift keying; Upper bound; M ary modulation; Nakagami fading; symbol error probability; Simulation; interference outage probability; Channel estimation; Peak power; Symbol error rate; imperfect channel estimates; Software radio
• ISSN: 1536-1276
• DOI: 10.1109/TWC.2013.111013.130615

In underlay cognitive radio (CR), a secondary user (SU) can transmit concurrently with a primary user (PU) provided that it does not cause excessive interference at the primary receiver (PRx). The interference constraint fundamentally changes how the SU transmits, and makes link adaptation in underlay CR systems different from that in conventional wireless systems. In this paper, we develop a novel, symbol error probability (SEP)-optimal transmit power adaptation policy for an underlay CR system that is subject to two practically motivated constraints, namely, a peak transmit power constraint and an interference outage probability constraint. For the optimal policy, we derive its SEP and a tight upper bound for MPSK and MQAM constellations when the links from the secondary transmitter (STx) to its receiver and to the PRx follow the versatile Nakagami-m fading model. We also characterize the impact of imperfectly estimating the STx-PRx link on the SEP and the interference. Extensive simulation results are presented to validate the analysis and evaluate the impact of the constraints, fading parameters, and imperfect estimates.