Optimum Power Allocation over Fading Channels in Cognitive Radio Mimo Networks

A cognitive radio (CR) is a transceiver which automatically detects the available unused channels in the wireless spectrum. A cognitive radio network (CRN) is formed by either allowing the secondary users (SUs) to coexist with the primary users (PUs) or enabling the SUs to use the unoccupied portion of the spectrum. In this paper, the ergodic capacity maximization problem is studied in Rayleigh, Nakagami and Rician fading channels with Multiple Input and Multiple Output (MIMO) technique and the optimum power allocation is realized to achieve the ergodic capacity. This study includes the Symbol Error Rate (SER) performance analysis with respect to various Space Time Block Codes (STBC) such as Alamouti code, VBlast code, Silver code, Golden code for all the three fading channels. The various modulation schemes used in this analysis are Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), Quadrature Amplitude Modulation (QAM) and Multiple Frequency Shift Keying (MFSK). Simulation results are presented to evaluate the power allocation scheme using Lagrangian multiplier and Water filling (WF) algorithms.