Impulse response correction system

TL;DR: In this article, the impulse response of the transmission channel is determined by correlating previously received data in shift register 52 Fig. 1, with the incoming signal from sampling device 51 in the cross correlators 53 a-n to produce signals hi to hn which are proportional to the amplitude of impulse response at the sampling instants of the data channel immediately following an impulse.

Abstract: 1,203,306. Determining impulse response. NORTH AMERICAN ROCKWELL CORP. June 5, 1968 [June 5, 1967], No.26849/68. Heading G1U. [Also in Division H4] In an automatically adjusting equalizer the impulse response of the transmission channel is determined by correlating previously received data in shift register 52 Fig. 1, with the incoming signal from sampling device 51 in the cross correlators 53 a-n to produce signals hi to hn which are proportional to the amplitude of the impulse response at the sampling instants of the data channel immediately following an impulse. The impulse response signals hi to hn are combined in summing device 72, with signs, provided by multipliers 71, derived from the previously received data as stored in shift register 52. The combination signal is subtracted from the received signal in 73 in order to reproduce the originally transmitted signal. The transmitted signal is made pseudo random at the transmitter either by mod 2 adding the data signal to a pseudo random sequency of pulses, or by passing the signal through a linear sequential coding network. At the receiver the inverse operation is performed using a similar pseudo random generator 75 or an inverse coding network, to retrieve the original data. The transmitted pulses may be shaped, e.g. by a cos 2 fn. to reduce distortion. In a modification, Fig. 8 (not shown) in which two data streams are transmitted by modulation of two carrier signals in quadrature, the received data in each channel is correlated not only with the received signal of its own channel but also with the received signal of the other channel in order to define an effective impulse response due to cross talk, and to derive a correction signal to eliminate cross talk.