An adaptive equalizer performs equalization at IF, demodulates the input signal and then generates the equalization coefficients at baseband from the demodulated data. Coefficient updating can be done on a non-real time basis and coefficients for individual bursts stored in a coefficient memory for retrieval when the same burst occurs in the next frame, thus obtaining a pseudo-continuous equalization for each burst. The error signal is derived from demodulated equalized data and correlated with demodulated unequalized data to generate the correlation coefficients, and individual error signals from each channel can be combined into a single composite error signal for correlation purposes.
A segmented digital transversal filter comprising a first transversal filter 4 that eliminates all frequency components from a signal sequence above half the subsampling frequency, a second transversal filter 11 that convolutes the output of the first filter with a decimated and energy compensated lower band of filter coefficients (HI.sub.1 '), a third transversal filter 22 that convolutes the output of the first filter and a decimated and energy-compensated upper band of filter coefficients (HI.sub.2 '), and a fourth transversal filter 32 that convolutes the original signal sequence and the central band of filter coefficients (HI.sub.3). Delays 21 and 31 are added so that the outputs of the second, third and fourth filters arrive concurrently at an adder 51, the sum being the output of the invention.
An adaptive equalizer arrangement for digital transmission system comprises at the output of the transmission channel a first in-phase path and in parallel with this first path, a second quadrature path, both paths being of the non-recursive transversal filter type having n branches and (n-1) delay circuits between the inputs of these branches, each of these n branches comprising, arranged in series, a mixer, a low-pass filter, a multiplier, and having their outputs connected to an adder which is followed by a sampling circuit and thereafter by a comparator circuit to decide the symbols to be transmitted from the outputs of these paths. The arrangement also comprises a third control path which comprises two subtracting circuits to determine the differences between the signals before and after decision and a control circuit of a voltage-controlled oscillator, 2n phase shifters and 2n multipliers.
In an adaptive equalizer system for equalizing, in response to a plurality of controllable tap gains, a received signal carrying a transmission data sequence digitized by a reference clock signal, a correlation detecting circuit (63') comprises a divider (111) for frequency dividing a reproduced clock signal representative of a reproduction of the reference clock signal to produce a divided clock signal. A serial-parallel converter (120) is for converting a reproduced data sequence representative of a reproduction of the transmission data sequence and a digital error signal relative to the reproduced data sequence into a plurality of converted data sequences and a plurality of converted error signals in synchronism the divided clock signal. As Exclusive logic circuit (70) is for carrying out an exclusive logic operation on the converted error signals and the converted data sequences to produce a plurality of correlation signals which are collectively used in controlling the controllable tap gains.
Optimum tap coefficients corresponding to equalization characteristics are stored in a memory circuit and when an equalization characteristics is designated, an optimum tap coefficient is read out of the memory circuit and a transversal type equalizer is controlled by the read-out optimum tap coefficient. According to a modified embodiment, where a tap coefficient for a combined characteristic based on a combination of a plurality of transmission characteristics is necessary, a convolution operation of the tap coefficients for respective transmission characteristics is effected to determine a new tap coefficient which is used to set taps of the transversal type equalizer.
Adaptive equalization system for allowing the equalization of a base-band line of a DCE, includes an adaptive filter for adjusting its coefficients in accordance with an adaptive algorithm. The equalizer includes controls to work during a preliminary period, in an adaptive or non-adaptive mode according to the convergence of the recursive algorithm process. The algorithm is triggered depending on whether the equalized signal belongs to one of several predefined intervals of convergence. After this preliminary period, when the mean square of the residual error is considered small enough to ensure the convergence of the adaptive process, the algorithm is computed on a continuous mode.
