Data transmission system comprising a decision feedback equalizer and using partial-response techniques

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG.
1 a block diagram is shown of a system for data signal transmission with a data transmitter 1, a transmission channel 2 and a data receiver 3.
The data transmitter 1 comprises a data signal source 10 for generating a data signal.
This data signal is converted by an encoder 11 into a data signal which is transmitted through transmission channel 2 at a symbol rate 1/T.
The intersymbol interference (ISI) and noise developed during this transmission are combated in the data receiver 3.
Thereto, data receiver 3 comprises an equalizer 30 of the decision feedback type which includes a feedforward filter 31 which is dimensioned for suppressing in the best way possible pre-cursive ISI and noise.
On the basis of symbol decisions which are formed in a symbol decision circuit 32 a feedback filter 33 subsequently forms a cancelling signal for post-cursive ISI which is subtracted from the output signal of feedforward filter 31 by means of a difference circuit 34 for obtaining the input signal of symbol decision circuit 32.
Finally, from the formed symbol decisions a decoder 35 forms a replica of the original data signal which is applied to a data signal sink 36.
To illustrate the problem for which the invention provides a solution, FIG.
2 shows a functional discrete-time model of the system of FIG.
1 when employing conventional measures.
In the FIGS.
1 and 2 corresponding elements are denoted by the same reference symbols.
The model of FIG.
2 is given for the case in which data signal source 10 generates a binary data signal and data transmitter 1 applies a ternary data signal to transmission channel 2.
A binary data signal d.
sub.
k generated by data signal source 10 is converted by a non-linear part 12 of the encoder 11 into a likewise binary data signal a.
sub.
k which, subsequently, by the linear part 13 of the encoder 11 is converted into a ternary data signal b.
sub.
k to be applied to discrete-time transmission channel 2.
To characterize the operation performed in this linear part 13 a partial-response polynomial g