Abstract: A method for demodulating a received signal relating to a sequence of transmitted symbols that have been modulated by continuous phase modulation includes normalizing samples of a sequence of samples generated from the received signal, to obtain a normalized sequence of samples, wherein an amplitude of each sample of the normalized sequence of samples has an absolute value equal to unity; estimating, on the basis of the normalized sequence of samples, a time offset and a frequency offset of the received signal, and using the estimated time offset and the estimated frequency offset for compensating the normalized sequence of samples for the time and frequency offsets, to obtain a compensated sequence of samples; and determining a sequence of symbols corresponding to the transmitted sequence of symbols on the basis of the compensated sequence of samples.

Abstract: A data detection method, having the steps of: a. receiving a signal transmitted over a communication channel, the signal being representative of at least a stream of interfering symbols xk, each representing one or more bits of a transmitted message; b. filtering the received signal through at least a filter bank having at least a first filter representative of a linear response of the channel and a second filter representative of a non-linear response of the channel, and sampling the filtered signals at the symbol rate, thus obtaining respective sequences of filtered samples rk(1) rk(3); and c. jointly computing the a posteriori probabilities of N>1 consecutive symbols xk. A data detector for carrying out such a method, and a method of transmitting data over a nonlinear channel, optimizing spectral efficiency when data detection is performed using such a method is also provided.

Abstract: A method for demodulating a received signal relating to a sequence of transmitted symbols that have been modulated by continuous phase modulation includes normalizing samples of a sequence of samples generated from the received signal, to obtain a normalized sequence of samples, wherein an amplitude of each sample of the normalized sequence of samples has an absolute value equal to unity; estimating, on the basis of the normalized sequence of samples, a time offset and a frequency offset of the received signal, and using the estimated time offset and the estimated frequency offset for compensating the normalized sequence of samples for the time and frequency offsets, to obtain a compensated sequence of samples; and determining a sequence of symbols corresponding to the transmitted sequence of symbols on the basis of the compensated sequence of samples.

Abstract: A data detection method, having the steps of: a. receiving a signal transmitted over a communication channel, the signal being representative of at least a stream of interfering symbols xk, each representing one or more bits of a transmitted message; b. filtering the received signal through at least a filter bank having at least a first filter representative of a linear response of the channel and a second filter representative of a non-linear response of the channel, and sampling the filtered signals at the symbol rate, thus obtaining respective sequences of filtered samples rk(1) rk(3); and c. jointly computing the a posteriori probabilities of N>1 consecutive symbols xk. A data detector for carrying out such a method, and a method of transmitting data over a nonlinear channel, optimizing spectral efficiency when data detection is performed using such a method is also provided.

Abstract: Generating updated coefficients for an adaptive equalizer involves generating phase tracking information using asynchronous detection strategy (ADS) based on resolved data, and equalized signals, and estimating a phase corrected error based on the equalized signals, the phase tracking information and the resolved data. An inhibit signal is generated to inhibit updating of the equalization coefficients, the inhibit signal representing a likelihood of the phase corrected error being accurate, determined according to the phase corrected error, and the equalized signals. The equalization coefficients for the equalizer are adapted based on the received signals, and on the phase corrected error, and the adapting is inhibited according to the inhibit signal. Compared to conventional ADS, the new combination with the inhibit signal can enable improved convergence of coefficient adaptation. This is particularly useful for coherent receivers for optical systems.

Abstract: An FDM-CPM multi-user detector (30) jointly detects the received symbols for all users by determining from the received multi-user signal an a-posteriori probability mass function (pmf) of a time-sequence of states and transmitted symbols of all users, by iterative message passing corresponding to a specific factorisation of the pmf. The factorisation involves a combined variable representing possible transmitted symbols and CPM states of each user for each symbol time interval, so as to make the iterative process convergent. Non exponential complexity is enabled by disregarding multiple access interference (MAI) from at least some of the other users. Applications can include hubs for satellite communication ground stations.

Abstract: Generating updated coefficients for an adaptive equaliser involves generating phase tracking information using asynchronous detection strategy (ADS) based on resolved data, and equalised signals, and estimating a phase corrected error based on the equalised signals, the phase tracking information and the resolved data. An inhibit signal is generated to inhibit updating of the equalisation coefficients, the inhibit signal representing a likelihood of the phase corrected error being accurate, determined according to the phase corrected error, and the equalised signals. The equalisation coefficients for the equaliser are adapted based on the received signals, and on the phase corrected error, and the adapting is inhibited according to the inhibit signal. Compared to conventional ADS, the new combination with the inhibit signal can enable improved convergence of coefficient adaptation. This is particularly useful for coherent receivers for optical systems.

Abstract: A method (10) of compensating phase noise in a coherent optical communications network. The method comprises: receiving a traffic sample (12); receiving an optical carrier and determining a phase noise estimate for the optical carrier (14); and removing the phase noise estimate from the traffic sample to form a phase noise compensated traffic sample (16).

Abstract: A method of and a receiver(20) for detection of a received signal in an optical fiber communication system using Viterbi algorithm methodology in which branch metrics are obtained using approximated expressions to calculate the branch metrics. Use of the expressions results in practically the same performance as a receiver based on exact metrics.

Abstract: An FDM-CPM multi-user detector (30) jointly detects the received symbols for all users by determining from the received multi-user signal an a-posteriori probability mass function (pmf) of a time-sequence of states and transmitted symbols of all users, by iterative message passing corresponding to a specific factorisation of the pmf. The factorisation involves a combined variable representing possible transmitted symbols and CPM states of each user for each symbol time interval, so as to make the iterative process convergent. Non exponential complexity is enabled by disregarding multiple access interference (MAI) from at least some of the other users. Applications can include hubs for satellite communication ground stations.

Abstract: A method (10) of compensating phase noise in a coherent optical communications network. The method comprises: receiving a traffic sample (12); receiving an optical carrier and determining a phase noise estimate for the optical carrier (14); and removing the phase noise estimate from the traffic sample to form a phase noise compensated traffic sample (16).

Abstract: A polarization multiplex transmission system (10) comprises two optical signals (z1, z2) transmitted over the same optical fiber (15) at the same wavelength but with orthogonal polarizations. The system is characterized by receiving apparatus (10) which is operable to filter the two components with orthogonal polarization of the signal received in accordance with an appropriate transfer matrix which is dynamically controlled on the basis of the output signals in such a manner as to approximate the reverse transfer matrix of the fiber in the region of the spectrum occupied by the signal so as to compensate for Polarization Mode Dispersion (PMD) and polarization rotation introduced by the fiber and eliminating distortion and mutual interference effects for both the signals and thereby obtain a demultiplexed output corresponding to the two transmitted signals.

Abstract: A method of and a receiver(20) for detection of a received signal in an optical fibre communication system using Viterbi algorithm methodology in which branch metrics are obtained using approximated expressions to calculate the branch metrics. Use of the expressions results in practically the same performance as a receiver based on exact metrics.

Abstract: A method for the adaptive adjustment of a PMD compensator in optical fiber communication systems comprises the steps of taking the signal at the compensator output and extracting the components y1(t) and y2(t) on the two orthogonal polarizations, computing the signal y(t)=[y1(t)]2+[y2(t)]2, sampling the signal y(t) at instants tk=kT with T=symbol interval to obtain samples y(tk), computing the mean square error e(k)=y(tk)?u(k) with u(k) equal to the symbol transmitted, and adjusting the parameters of the compensator to seek to minimize e(k).

Abstract: A polarization multiplex transmission system (10) comprises two optical signals (z1, z2) transmitted over the same optical fibre (15) at the same wavelength but with orthogonal polarizations. The system is characterised by receiving apparatus (10) which is operable to filter the two components with orthogonal polarization of the signal received in accordance with an appropriate transfer matrix which is dynamically controlled on the basis of the output signals in such a manner as to approximate the reverse transfer matrix of the fibre in the region of the spectrum occupied by the signal so as to compensate for Polarization Mode Dispersion (PMD) and polarization rotation introduced by the fibre and eliminating distortion and mutual interference effects for both the signals and thereby obtain a demultiplexed output corresponding to the two transmitted signals.

Abstract: A method for the adaptive adjustment of a PMD compensator in optical fiber communication systems with the compensator comprising a cascade of adjustable optical devices through which passes an optical signal to be compensated and comprising the steps of computing the Stokes parameters S0, S1, S2, S3 in a number Q of different frequencies of the signal output from the compensator, producing control signals for parameters of at least some of said adjustable optical devices so as to make virtually constant said Stokes parameters computed at different frequencies.

Abstract: A method for the adaptive adjustment of a PMD compensator in optical fiber communication systems with the compensator comprising a cascade of adjustable optical devices through which passes an optical signal to be compensated and comprising the steps of computing the Stokes parameters S0, S1, S2, S3 in a number Q of different frequencies of the signal output from the compensator, producing control signals for parameters of at least some of said adjustable optical devices so as to make virtually constant said Stokes parameters computed at different frequencies.

Abstract: A method for the adaptive adjustment of a PMD compensator in optical fiber communication systems comprises the steps of taking the signal at the compensator output and extracting the components y1(t) and y2(t) on the two orthogonal polarizations, computing the signal y(t)=[y1(t)]2+[y2(t)]2, sampling the signal y(t) at instants t1=kT with T=symbol interval to obtian samples y(tk), computing the mean square error e(k)=y(tk)?u(k) with u(k) equal to the symbol transmitted, and adjusting the parameters of the compensator to seek to minimize e(k).

Abstract: A non-coherent receiver for digitally modulated signals, linearly or not, possibly combined with channel coding, is described. In the case of M-PSK, or M-QAM modulations, the received signal is demodulated and filtered by a filter matched to the transmitted pulse. In the case of linear modulations in presence of intersymbol interference, and non-linear M-CPM modulations, the reception filter is of the whitened matched type. The signal is filtered and sampled and the samples are accumulated in a relevant memory containing N-1 samples preceding the current one. These samples are processed by a Viterbi processor estimating the sequence of transmitted symbols according to a maximum likelihood criteria. A first embodiment calculates suitable trellis branch metrics using an implicit estimation of the carrier phase in PSP mode (Per- Survivor-Processing).

Abstract: It is described a non-coherent receiver for digital modulated radio signals, linear or not, possibly affected by channel coding. In the case of M-PSK, or M-QAM modulations, possibly combined with a channel coding, the signal received is demodulated and filtered by a filter matched to the pulse transmitted. In the case of linear modulations in presence of ISI, and of non-linear M-CPM modulations, the reception filter is a matched and whitened one. The signal is filtered and sampled and the samples are accumulated in a relevant phase reconstruction memory containing N−1 samples preceding the actual one. Samples are processed making use of a Viterbi processor estimating the sequence of symbols transmitted according to maximum likelihood. The first embodiment calculates the branch metrics using an estimation of the carrier phase in PSP mode (Per-Survivor-Processing). This improves the performance of the receiver.