A Suboptimal LQ Power Control Algorithm for a CDMA Wireless System

In today´s wireless systems, power control is an important problem which is related to the quality-of-service (QoS) and battery utilization at the mobile units. This problem is studied in this work for the uplink of a direct-sequence code- division multiple-access communication (DS-CDMA) system. By a proper selection of the error function, the resulting linear decoupled feedback loops can be controlled efficiently following a distributed power control approach, and these closed-loops are independent of the user´s channel variations. A suboptimal LQ strategy is suggested and derived for power update. This control law has a variable structure that depends on the transmission roundtrip delay in the feedback system, which is a key parameter to establish closed-loop stability. It is demonstrated that in the limit of some synthesis parameters, the LQ-controller tends to a Dead-Beat response, improving the time response but sacrificing robustness. Meanwhile, the LQ-controller can be adjusted to increase its robustness. Simulation results are presented to compare the control algorithms using a standard single-step power correction approach.