A feasible method to implement optimum CIR-balanced power control in CDMA cellular mobile systems

Abstract

Power control is essential in the design of direct-sequence code-division multiple-access (DS-CDMA) techniques. Optimum power-control (OPC) methods with carrier-to-interference ratio (CIR) balancing have been formulated as eigenvalue problems for frequency-division/time-division multiple-access (FDMA/TDMA) cellular systems. For the CDMA cellular system, its OPC was also formulated as an eigenvalue problem based on a large link-gain matrix. The OPCs with CIR-balancing were realized by solving eigenvalue problems of link-gain matrices. We reformulate the CIR-balanced OPC in CDMA cellular systems by benefiting from the power constraints as an eigenvalue problem based on a novel link-gain matrix. For a feasible implementation, a two-level hierarchical power-control structure is proposed to carry out the eigendecomposition which is required for the CIR-balanced OPC. Shortages of unbalanced CIR and global outage are two common issues in CIR-balanced power control. To tackle these two problems, a simple linear prediction method and an adaptive on-off strategy are proposed. Furthermore, because of the capacity limitation of wireless communications, a differential pulse code modulation scheme is presented to reduce the number of bits required for the transmission of command words in the two-level hierarchical power-control structure.