Analysis of performance degradation with generalized orthogonal codes due to channel estimation errors in Pre-Rake TDD/DS-CDMA downlink

The Pre-Rake diversity combining technique decreases the complexity, size and cost of the mobile unit while achieving the same inter symbol interference mitigation effects of conventional Rake receiver for direct sequence code division multiple access (DS-CDMA) systems. The technique is based on preprocessing of signal at the transmitter relying on knowledge of the channel state information. This a priori information is available in time division duplex (TDD) mode due to channel reciprocity. In practice, errors in channel estimation occur due to time varying nature of mobile radio channels and also due to method adopted for channel estimation. Most of the previous works on Pre-Rake for TDD/DS-CDMA systems have not taken into consideration the effect of errors in channel estimation. In this paper, we analyze Pre-Rake performance under imperfect channel estimation with generalized orthogonal (GO) codes. We also present a pilot-based correlation method for channel estimation and evaluate the Pre-Rake system through analytical and computer simulations for TDD/DS-CDMA downlink.