Optimal and Suboptimal Power Allocation Schemes for OFDM-based Cognitive Radio Systems

• Published in: IEEE transactions on wireless communications Vol. 7; no. 11; pp. 4710 - 4718
• Main Authors: Bansal, G., Hossain, M.J., Bhargava, V.K.
• Format: Journal Article
• Language: English
• Published: Piscataway, NJ IEEE 01.11.2008; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Algorithms; Allocations; Applied sciences; Base stations; Channels; Chromium; Cognitive radio; Degradation; Downlink; Exact sciences and technology; FCC; Information, signal and communications theory; Interference; interference reduction; Multiplexing; Nulling; OFDM; opportunistic spectrum access; Optimization; Orthogonal Frequency Division Multiplexing; power adaptation; Radio; Radio transmitters; Radiocommunication specific techniques; Radiocommunications; Signal and communications theory; Stations; Studies; Systems, networks and services of telecommunications; Telecommunications; Telecommunications and information theory; Transmission and modulation (techniques and equipments); Transmitters. Receivers; Wireless communication; Performance evaluation; OFDM; power adaptation; Noise reduction; Base station; Transmitter; Downlink; Subcarrier; Power allocation; Varying speed; opportunistic spectrum access; Degradation; interference reduction; Optimal planning; Channel capacity; Optimal algorithm; Cognitive radio; Cognitive system; Interference suppression; Orthogonal frequency division multiplexing; Signal processing; Numerical simulation; Transmission rate; Dynamic load; Software radio
• ISSN: 1536-1276; 1558-2248
• DOI: 10.1109/T-WC.2008.07091

In this paper, we investigate an optimal power loading algorithm for an OFDM-based cognitive radio (CR) system. The downlink transmission capacity of the CR user is thereby maximized, while the interference introduced to the primary user (PU) remains within a tolerable range. We also propose two suboptimal loading algorithms that are less complex. We also study the effect of a subcarrier nulling mechanism on the performance of the different algorithms under consideration. The performance of the optimal and suboptimal schemes is compared with the performance of the classical power loading algorithms, e.g., water-filling and uniform power but variable rate loading schemes that are used for conventional OFDM-based systems. Presented numerical results show that for a given interference threshold, the proposed optimal scheme allows CR base station (BS) to transmit more power in order to achieve a higher transmission rate than the classical loading algorithms. These results also show that although the proposed suboptimal schemes have certain degradation in performance compared to the optimal scheme, they outperform the classical loading algorithms. We also present numerical results for nulling mechanism. Finally, we investigate the effect of imperfect channel gain information at the transmitter.