ABSTRACT
A review of various approaches to channel modeling and estimation for wireless mobile systems is presented. We begin with channel models suitable for channel estimation and equalization. Emphasis is on linear baseband equivalent models with a tapped delay line structure, and both time-invariant and time-variant models are discussed. Basis expansion modeling for time-variant channels is also presented where the basis functions are related to the physical parameters of the channel (such as Doppler and delay spreads). Channel modeling is followed by a discussion of various approaches to channel estimation, including training-based approaches, blind approaches, semiblind approaches, and hidden pilot-based approaches. In the training-based approach a sequence known to the receiver is transmitted in the acquisition mode. In blind approaches no such sequence is available (or used) and the channel is estimated based solely on the noisy received signal exploiting the statistical and other properties of the information sequence. Semiblind approaches utilize a combination of training-based and blind approaches. In the hidden pilot-based approaches a periodic (nonrandom) training sequence is arithmetically added (superimposed) at a low power to the information sequence at the transmitter before modulation and transmission.
