Method of determining the tap weights of a decision feedback equaliser

摘要

A decision feedback equaliser DFE comprises a feedforward filter section 10 and a feedback filter section 12 including a decision stage 14. Each of the filter sections includes a transversal filter, the tap weights of which are calculated to overcome the dispersive effects of a communications channel on the received signal. A known method of calculating the tap weights recursively comprises w=R-1p where R is the autocorrelation matrix describing the DFE, p is the cross correlation vector of the desired and received samples and w is the vector of the equaliser tap weights. In order to avoid the problem of matrix inversion and to permit the calculations to be done directly in a single operation with a reduced amount of computation and storage requirements the above equation is restated as Rw = p and the autocorrelation matrix R is factorised using Gaussian elimination techniques into upper (U) and lower (L) triangular matrices. Thus ULw = p (or LUw = p). This equation is solved in two stages; (1) Solve Uc = p (or LC = p) where c is the unknown and (2) solve Lw = c (or Uw = c). As the triangular matrices are expressed in terms of the channel impulse response samples, then many of the terms can be entered, without computation, on the basis of an estimate of the channel impulse response. IMAGE