Outer loop power control using channel-adaptive processing for 3G WCDMA

Abstract

In power control systems for wide-band code division multiple-access (WCDMA), the outer loop power control (OLPC) algorithm initially sets a target signal-to-interference ratio (SIR) based on the required target block error rate (BLER), assuming a particular channel condition. A mismatch between the BLER and the target SIR usually results since the actual and assumed channel conditions are rarely the same. This mismatch tends to be especially large at very low BLERs. The OLPC depends on cyclic redundancy checks (CRCs) and often takes a long time to converge to the required target SIR for low target BLERs. In this paper, a channel-adaptive algorithm is presented that controls the target SIR for downlink transmission in WCDMA TDD. The proposed algorithm characterizes the multipath channel profile using predefined multipath channel patterns and compensates for the channel/mapping errors. Link level simulations are conducted in various channel conditions defined by 3GPP and the ITU. The comparison in performance between the channel-adaptive algorithm and the generic "jump algorithm" is illustrated and conclusions are drawn.