Optimized subcarrier power allocation in OFDM underlay cognitive radio system

Abstract

This paper develops an optimized subcarrier power allocation mechanism for orthogonal frequency division multiplexing (OFDM) based cognitive radio (CR) system. It is reported in the literature that both classical i.e. uniform power loading scheme and water filling method that allocates power based on the channel gain developed for OFDM system, are not effective for cognitive radio network (CRN) as the schemes introduce large interference to primary user (PU). To this aim, the present work proposes a simple, computationally efficient yet effective power loading scheme that maximizes the transmission capacity of CR while keeping the interference introduced to the PU and the total power below acceptable limits. To meet the objective, proposed power allocation to subcarriers not only consider channel gains but also the relative distances between CR subcarriers and PU band. Numerical results show that the relative gain on CR capacity is ∼1.7 times compared to the existing hybrid and suboptimal OFDM power allocation schemes when interference introduced to PU is set at 3×10-6 (in watt). © 2011 Springer-Verlag.