Improvement of fuzzy power control for DS-CDMA cellular mobile system having variable number of users

Power control based on signal-to-interference ratio (SIR) alone usually causes a vicious circle, due to which every mobile station (MS) continuously increases its transmitted power (Tx_power) to achieve the desired SIR (SIRd) in order to guarantee its quality of service (QoS). This leads to an infeasible power control problem, due to which MS transmits with the maximum power but fails to achieve the SIRd. Besides, the severity of the vicious circle problem in Direct Sequence Code Division Multiple Access (DS-CDMA) power control systems is a function of the number of users in the system (N_user); therefore, in this paper, a Fuzzy Weighting Controller (FWC) functioning to Tx_power of each MS (Tx_power⁽ⁱ⁾) and N_user in each cell site (N_user^(j)) having i^th MS inside is introduced to individually weight its SIR-based power control adjusting factors output from Fuzzy Proportional-plus-Integral Controller (FPIC) in order to prevent each MS from an infeasible power control problem. Moreover, three types of N_user^(j) are assigned in the simulated system; i.e., 1) N_user^(j) is equally fixed, 2) N_user^(j) is equally changed, and 3) N_user^(j) is randomly changed. In the DS-CDMA cellular system, QoS enhancement basically reduces the system capacity; however, by solving the infeasible power control problem with the proposed algorithm, the average outage probability, the average infeasible outage probability, and the average transmitted power of each MS in all cases of N_user^(j) assignment, 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.