Method and apparatus for incoherent adaptive mean-square equalization of

Abstract

An incoherent adaptive transversal equalizer for the receiver of a differentially phase-modulated data transmission system wherein a pair of tapped delay lines are located in memory of a digital computer or central processor which performs equalization of a sampled data signal according to the mean-square error algorithm defined by equations (1) - (4). In-phase and quadrature-phase tap gains c.sub.-.sub.n and d.sub.-.sub.n are each selectively combined with both the in-phase and quadrature-phase sampled signal component words A.sub.k.sub.+n and B.sub.k.sub.+n, respectively, at associated tap lines of the delay lines (except the principal or center tap line, where n = 0 here) to produce a plurality of weighted tap signals c.sub.-.sub.n A.sub.k.sub.+n ; -d.sub.-.sub.n B.sub.k.sub.+n ; c.sub.-.sub.n B.sub.k.sub.+n, and d.sub.-.sub.n A.sub.k.sub.+n. These weighted tap signals and the center tap line signals A.sub.k.sub.+0 and B.sub.k.sub.+0 are selectively combined to produce equalized in-phase and equalized quadrature-phase sampled signal component words A.sub.k ' and B.sub.k ' that are defined by equations (5) and (6). These equalized component words A.sub.k ' and B.sub.k ' of a current signal sample are operated on to obtain an indication .DELTA..theta. of the actual difference between phases of the current (k.sup.th) and prior (k-1.sup.th) signal samples. Common error signals AE.sub.k ' and BE.sub.k ' are produced during a current symbol interval by subtracting the in-phase and quadrature phase components of the k-1.sup.th equalized signal sample vector (A.sub.k.sub.-1 ', B.sub.k.sub.-1 '), after this vector is rotated by the phase angle .DELTA..theta., from the equalized in-phase and quadrature-phase components A.sub.k ' and B.sub.k ', respectively, of the current (k.sup.th) signal sample (see equations (3) and (4)). The products of the in-phase and quadrature-phase sampled signal component words A.sub.k.sub.+n and B.sub.k.sub.+n at associated tap lines of the delay lines, except the principal tap lines, where n = 0 here, and associated common in-phase and quadrature-phase error signals AE.sub.k ' and BE.sub.k ', respectively, are combined during a current symbol interval to produce values of the in-phase incremental tap gains .DELTA.c.sub. .sub.-n in equation (1). Tap gains c.sub.-.sub.n (where n .noteq. 0) that are obtained during a prior signal sample are combined during a current symbol interval with the new incremental tap gains .DELTA.c.sub.-.sub.n to obtain updated values of tap gains c.sub.-.sub.n for use during the next symbol interval, a principal tap gain here being the constant c.sub.o = 1. Also, the products of these component words A.sub.k.sub.+n and B.sub.k.sub.+n at each tap line of the delay lines, except the principal tap, where n = 0 here, and associated quadrature-phase and in-phase error signals BE.sub.k ' and AE.sub.k ', respectively, are combined during a current symbol interval to produce new values of the quadrature-phase incremental tap gains .DELTA.d.sub.-.sub.n in equation (2). Tap gains d.sub.-.sub.n (where n .noteq. 0) that are obtained during a prior signal sample are combined during the current symbol interval with the new incremental tap gains .DELTA.d.sub.-.sub.n to obtain updated values of tap gains d.sub.-.sub.n for use during the next symbol interval, the other principal tap gain here being the constant d.sub.o = 0.