GB1412747A - Method and apparatus for use in a data transmission system - Google Patents

Abstract

1412747 Transversal equalizers GRETAG AG 8 Nov 1972 [8 Nov 1971] 51627/72 Heading H4R In an arrangement for adjusting the multipliers 26, Fig. 5, of a transversal equalizer 13, Figs. 4 and 5, a test signal is transmitted over the transmission system and correlated, in 22, Fig. 5, at the taps of the transversal equalizer delay device 28 with a locally generated replica of the test signal, from generator 16, Fig. 4, to provide adjustment signals for the multipliers 26, this adjustment phase equalizes the group delay characteristic of the system. During a second phase of the adjustment the output of the equalizer is fed to a threshold detector 15, to detect the nominal signal amplitude, and an error signal is derived between the input signal and output signal of the threshold detector and the error signal correlated with the signals at the delay device taps to provide the adjustment signals for the equalizer multipliers 26. As described signals are fed to the transmission system via a precoder (3), Fig. 2 (not shown), and a transmission filter (5) to provide partial response transmission and recovered therefrom via a reception filter (7) and decoder (9). During group delay equalization the characteristics of the filters does not have to be compensated and therefore an inverse filter 12, having a characteristic which is inverse the characteristics of the transmission and reception filters, is placed in circuit. In an alternative arrangement the filter 12 is omitted and a model filter of similar characteristic to that provided by the transmission and reception filters is inserted between the generator 16, supplying a replica of the transmitted test signal, and the input B of the equalizer 13. The multipliers 24 of the correlators may act on analogue signals or only on the polarity of the signals, in which case they comprise Mod-2 adders. During the first adjustment phase the difference circuit 14 is switched out of circuit then after a predetermined time, the switches 18, 19, 34, 35, are operated to cut the inverse filter 12 out of circuit, disconnnect the local generator 16, and put the error signal determining circuit 14 into operation. The detector 15 may be a zero slicer or a multilevel slicer depending on the number of possible levels of the transmitted signal. During the second phase of the adjustment the reference signal from which the error signal is derived may be taken from after the decoder 9 in which case the reference signal is applied to the subtractor 14 via a coder (33), Fig. 9 (not shown), identical to the coder used at the transmitter and a model filter (17), providing a partial response characteristic.