Three-Degree of Freedom Adaptive Power Control for CDMA Cellular Systems
The successful operation of CDMA systems depend on the use of power control. This is needed to address the "near far" effect and to mitigate the effects of fading. Other factors also impact on the achievable performance of the power control loop including the fact that only the sign of the power increments are transmitted. The paper presents new methods and results to improve control with respect to the latter strongly non-linear effect. An adaptive control architecture, having three degrees of freedom, is therefore proposed for inner loop power control. The three degrees of freedom are used to address errors resulting from (i) channel and interference variations, (ii) quantization of the power increments and (iii) saturation of the power increments. Simulations show that the proposed controller outperforms other related schemes. A major reason for this is the ability of the three degree of freedom controller to reduce the variation of the control signal to be quantized.