Apparatus and methods employing distribution preserving tomlinson

Abstract

A transmitter is provided with a distribution preserving Tomlinson coder which predistorts shaped data signals such that the power of each data signal exiting the coder is substantially similar to the power of the data signal entering the coder and such that upon transmission of the predistorted data signal over a channel, the effect of ISI of the channel is substantially removed. The transmitter is primarily intended for coded modulation systems utilizing a 'coset' code, and the predistortion is preferably accomplished according to a linear function ##EQU1## where r.sub.k is a data signal entering the coder, a.sub.l and b.sub.l are the coefficients of polynomials relating to the channel impulse response, x.sub.k is the predistorted data signal exiting the coder, and s.sub.k is a multiple of a given value (N) which is chosen to cause x.sub.k and r.sub.k to occupy identical defined regions in space, where the total length of each defined region is the given value N. One and two dimensional regions are disclosed which are chosen in several ways. Receivers which cooperate with the provided transmitters are also provided. The receivers receive a sequence of signals, and process the sequence to provide a sequence of signals whose k'th term is an estimate of r.sub.k -s.sub.k. From the estimate of r.sub.k -s.sub.k, the receiver generates an estimate of x.sub.k by multiplying the received estimate by the channel ISI. From the estimate of x.sub.k and the estimate of r.sub.k -s.sub.k, the receiver determines the particular value of s.sub.k, and hence the value of an estimate of r.sub.k.