An optimum downlink power control method for CDMA cellular mobile systems

Power Control is essential in the design of DS-CDMA techniques. The optimum power control (OPC) methods with carrier-to-interference ratio (CIR) balancing have been identified as eigenvalue problems. For the CDMA cellular system, Wu (see IEEE Trans. Veh. Technol., vol.48, p.571-5, 1999) formulated the CIR-balanced power control problem to an eigenvalue problem based on a newly proposed link-gain matrix. However, the size of the matrix is proportional to the number of active mobiles in a CDMA cellular system. Therefore the implementation will be infeasible due to the exceedingly large size. We present a novel link-gain matrix, whose size is only proportional to the number of cells of a whole CDMA system. Based on the proposed link-gain matrix, the CIR-balanced power control in a CDMA cellular system is formulated as an eigenvalue problem and the corresponding implementation algorithm is presented as well that is optimum in the sense that the interference probability is minimized. As a result of the small size of link-gain matrix, the proposed OPC algorithm has better convergence performance than Wu's. The numerical results indicate that our proposed OPC method achieves the same performance as Wu's regardless of the pretty small size of the proposed link-gain matrix.