Linear and Nonlinear Decoupling for Inner Loop Power Control in 3G Mobile Communications

Abstract Inner loop power control is a crucial part of the operation of 3G mobile communication systems. This is necessary to deal with the, so called, ‘near-far’ problem and to combat the effects of time variations in the channel gain. In practice, power control is dealt with in a decentralized fashion, i.e., using one SISO control loop for each user. However, significant multivariable coupling occurs due to the fact that each user is a source of interference to every other user. This means that the actual performance is significantly degraded relative to the idealized SISO case. In this paper, we describe a novel nonlinear decoupling algorithm for the uplink of the WCDMA 3G cellular system which effectively compensates for the MIMO interactions. We also develop a simplified linearized form of the algorithm. We explore the relative merits of the scheme for typical mobile communication scenarios incorporating grant changes, fading and quantization. Our simulations show that, in all cases, the decoupling strategies lead to significant performance gains relative to the use of decentralized strategies in common use.