Abstract: An imbalance estimator for quadrature modulators comprising two mixers to which are applied two carrier signals and to each of which is applied a modulating signal, output signals of said mixers being applied to a combiner to constitute a modulated signal, detects the instantaneous power of the modulated signal. The detected instantaneous power is multiplied by the modulating signals, and the resulting signals are rectified. The rectified signals are rectified to supply signals indicative of the imbalance of the modulator.

Abstract: The invention relates to apparatus for synchronizing the phase of a digital signal constituted by two digital components to be corrected defining two samples of a received signal at each symbol time, said apparatus serving to feed a regenerator for regenerating the signal in baseband by sampling and threshold decision-taking, said apparatus including: a first phase-locked loop (31) driven by a first broadband phase-error integrator (37), said first loop (31) being fed with the input signal (30) of the apparatus, and supplying a first phase error estimate (36); and an auxiliary second phase-locked structure (32) driven by re-processing means (38) for re-processing said first phase error estimate (36) established by said first phase-locked loop (31), and outputting a phase synchronized signal fed to an output regenerator (34) for regenerating the signal in baseband; said auxiliary second phase-locked structure (32) being fed with said input signal (30) of the apparatus via delay means (35).

Abstract: A method of modeling the AM--AM and AM-PM characteristics of an amplifier includes the step of transmitting a reference signal to the amplifier. The response of the amplifier to the reference signal is digitized to produce two sets of AM--AM and AM-PM reference samples, respectively. Two series of polynomials respectively representative of the AM--AM and the AM-PM characteristics are determined from the samples. The determination of each polynomial allows for the second derivative of the polynomial and for the distances between the samples and points on the curve defined by the polynomial.

Abstract: A quadrature modulator including two mixers to which two carrier signals are applied and to each of which a modulating signal is applied, output signals of the mixers being applied to a combiner to constitute a modulated signal. A defect estimator for the modulator detects a first signal representative of the instantaneous power of the modulated signal, generates a second signal representative of a reference envelope obtained from the modulating signals, and corrects the amplitude of one of the first and second signals in accordance with the mean amplitude difference observed between this amplitude corrected signal and the other signal. A processor supplies from the observed amplitude difference between the amplitude corrected signal and the other signal, at least one signal relating to the defect.

Abstract: The invention relates in particular to a method of compensating differences in group propagation times between first and second analog filters of a transmitter of signals in phase quadrature, and between third and fourth analog filters of a receiver of signals in phase quadrature. The method consists in: applying the output signals from the first and second filters respectively to the third and fourth analog filters so as to measure a time difference .DELTA.1 equal to: ?Tx+Rx!-?Ty+Ry! where Tx, Rx, Ty, and Ry are respective propagation times for the signals through the first, second, third, and fourth filters; applying the output signals from the first and second filters respectively to the fourth and third analog filters so as to measure a time difference .DELTA.2 equal to: ?Ty+Rx!-?Tx+Ry! and determining weighting coefficients from the differences .DELTA.1 and .DELTA.

Abstract: A method and apparatus for shaping the impulse response of a non-minimum phase communications channel, by reversing the CIR without enhancing the noise level using non-causal allpass filters is disclosed. Unstable allpass filters are implemented as stable non-causal filters operating in reversed time to obtain a minimum phase response from a non-minimum phase CIR. The original CIR is estimated using adaptive algorithms, and the coefficients of the allpass filters are taken directly from the estimated CIR. The cascade of the channel and allpass filter has an impulse response that is the approximate time reversed version of the original CIR. A "block" allpass equalizer and an "optimal" allpass equalizer are used in a two-stage filter to increase system performance. Other multiple stage filter configurations are disclosed, which can include use of decision feedback equalizer (DFE) decoders as well as Viterbi decoders.