Fuzzy power control with weighting function in DS-CDMA cellular mobile communication system

Power control based on signal-to-interference ratio (SIR) is more preferable than signal strength-based power control since the former´s quality of service (QoS) is guaranteed. However, power control based on SIR alone usually causes the vicious circle problem, due to which every mobile station (MS) continuously increases its transmitted power (Tx_power) to achieve the desired SIR (SIRd). The vicious circle problem leads to an infeasible power control problem, due to which the MS transmits with maximum power but fails to achieve the desired SIR. In this paper, power transmitted by each MS is used to individually weight its SIR-based power control adjusting factors, outputted from a fuzzy proportional-plus-integral controller (FPIC) in order to prevent each MS from the infeasible power control problem. In direct sequence code division multiple access (DS-CDMA) cellular systems, QoS enhancement basically reduces the system capacity. By solving the infeasible power control problem by the proposed algorithm, the average outage probability, the average infeasible outage probability, and the average transmitted power of each mobile station, as shown in simulation results, are reduced. These show that the proposed power control algorithm can simultaneously enhance QoS and the capacity of the system.