Description

Energy efficiency and Spectral efficiency are plays an important role in wireless communication systems. The increase in demand for frequency bands with high data rate requirements, we are in a need to efficiently utilize the available spectrum with better energy efficiency. So cognitive radio (CR) networks are plays vital role in utilizing the available unused spectrum efficiently with better energy efficiency. Existing work investigated power allocation schemes for a single CR user based MIMO–OFDM system. In this project the system MIMO–OFDMA, which is a promising candidate for 3GPP-LTE, is proposed. The sum capacity of a multiuser synchronous CDMA system is completely characterized in the general case of asymmetric user power constraints. The sum capacity computation relies on a duality between the Gaussian vector broadcast channel and the sum-power constrained Gaussian multiple-access channel. The numerical algorithm is based on a Lagrangian dual decomposition technique and it uses a modified iterative water-filling approach for the Gaussian multiple-access channel. The algorithm converges to the sum capacity globally and efficiently.