Channel equalization for block transmission systems

For communication over channels subject to fast time variation, for example, the HF channel, the information symbols are arranged in the form of blocks separated by known symbols. Such a system is called a block transmission system. Its known convenient receiver is the Nonlinear Data Directed Estimator (NDDE). Appropriate equalization methods for this system are derived, using a nonstationary innovations representation based on Cholesky factorization in order to define a noise whitener and a maximum likelihood block detector. Zero forcing and minimum mean squared error block linear and block decision feedback equalizers are also derived. Their performances are evaluated and compared. They are shown to perform better than the conventional equalizers. As compared with the NDDE, the deduced block decision feedback equalizers have better performance and are much less complex. Whereas the NDDE uses the Levinson algorithm to solve M/2 Toeplitz systems of decreasing order (where M is the number of symbols per block), the deduced equalizers need to process only one Toeplitz system. The Schur algorithm, proposed for Cholesky factorization, allows the complexity to be further reduced.