Channel estimation for the downlink of the UMTS-TDD component

The time division duplex (TDD) component of the Universal Mobile Telecommunications System (UMTS) employs synchronous CDMA techniques with orthogonal spreading codes to provide protection against cochannel interference. In the presence of multipath propagation, however, the code orthogonality is lost and multiaccess interference is generated at the receiver. In such conditions an estimate of the channel impulse response is required for reliable detection. In this paper we propose a method for channel estimation in the downlink of the UMTS-TDD system. In addition to the channel impulse response, the algorithm provides estimates of the users´ powers, which may be needed to perform multiuser detection. Theoretical analysis and computer simulations are used to assess the performance in terms of mean squared estimation error. It is shown that the accuracy of the proposed estimator attains the Cramer-Rao bound (CRB) at signal-to-noise ratios of practical interest