On the Usefulness of Outer-Loop Power Control With Successive Interference Cancellation.

It is well known that multiuser detection can obtain significant performance advantages over the conventional matched filter receiver in code division multiple access systems. Further, since optimal multiuser detection is exponentially complex, the majority of research has focused on suboptimal approaches such as successive interference cancellation (SIC). SIC has been shown to require a geometric distribution of received powers to achieve equal performance for all received signals. In this paper we propose a power control scheme for SIC to achieve this profile (or the profile corresponding to any desired and achievable set of error rates) based on frame-error rate (FER) or bit-error rate (BER). Specifically, we derive the relationship between received power and BER for linear SIC and show that for unlimited mobile powers, a deterministic distributed BER-based outer-loop power control will drive the received powers to the optimal power profile. The convergence of the deterministic BER-based algorithm is examined in the absence of inner loop power control errors. The simulated performance of a stochastic version of this algorithm is examined using instantaneous FER measurements. The stochastic algorithm is shown to provide unbiased estimates of the true power updates and converge to the optimal power vector provided the mobiles have unlimited power. Further, we consider power limits for specific mobiles and find that individual mobile limits do not affect the performance of other signals. Further, we examine the impact of system loading, multiple FER targets, error correction, and inner loop power control error on the performance of the algorithm. [ABSTRACT FROM AUTHOR]