CDMA Cellular Mobile Systems Research Articles

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

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.

Distributed Power Balancing with Linear Prediction and Adaptive On-OffStrategies for CDMA Cellular Mobile Systems

Several distributed balance (DB) power control algorithms that can achieve SIR balance have already been proposed for cellular mobile systems [1–3]. In the present paper, two simple strategies, namely linear prediction and adaptive on-off strategies, are further applied to forward link distributed balance (DB) power control in DS/CDMA cellular mobile systems. The linear prediction is used to track the variance of the short-term fading and compensate it in advance, and the adaptive on-off strategy is applied to solve the problem that the received SIR of all the communication links less than the minimum required SIR. Simulation results indicate that DB power control with these two strategies can achieve much better performance than the original DB power control.

Intercell interference cancellation for TD-CDMA mobile systems

ETSI UTRA time division duplex (TDD) signalling (TD-CDMA) uses a combination of frequency, time and code division multiple access techniques (FDMA, TDMA and CDMA). In CDMA cellular mobile systems both intersymbol interference (ISI) and multiple access interference (MAI) degrade the system performance. In TD-CDMA a joint detection (JD-CDMA) processor performs signal estimation to eliminate this interference within the reference cell. An extension of these JD-CDMA receiver processors is proposed to achieve intercell interference cancellation.

Centralised power control in CDMA cellular mobile systems

Efficient power control is of great importance in the design of high capacity cellular radio systems. Optimum power control scheme, in the sense that it minimises the outage probability, has been fully investigated for FDMA/TDMA cellular systems. The authors propose optimum power control and several centralised power control algorithms for CDMA cellular systems. Simulation results indicate that the optimum power control scheme outperforms the perfect average power control algorithm by ~1.9 dB under the IS-95 defined radio condition.