Training sequence-based multiuser channel estimation for block-synchronous CDMA

Uplink channel estimation for a block-synchronous chip-asynchronous CDMA system as proposed for the time-division duplex (TDD) option of 3rd generation cellular systems is considered. Training midambles are employed for joint channel estimation of all users. An unstructured approach based on modeling the effective user channels as unknown FIR filters is compared with two structured methods that exploit a priori knowledge about the user channels such as the maximum delay spread, the transmit chip-shaping pulse and the path delays. A low-complexity, high-performance delay estimator based on maximum-likelihood is proposed which explicitly estimates the delays of the individual multipath components of each user.