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: 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 plurality of elongate rectangular tissues (10) of cigarette paper, of a width equal to, and of a length greater than a desired cigarette paper sheet, are respectively folded over along transverse folds (12) coinciding with their minor axes, are stacked and stapled together near their respective, opposite shorter sides (14, 16), and are perforated along transverse lines (18, 20) near each shorter side, at a distance from the transverse fold equal to half the desired length of the cigarette paper sheet.

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 coding scheme of order n for digital communications, in particular optical communication, for obtaining a coded signal x(t) which represents binary data which are constituted by sequences of information bits {uk} with rate T, the scheme having N=2n states, named ?i, for i=1, 2, . . . , N, and comprising predetermined elementary signals si(t) which are combined in the signal x(t). According to the scheme, if, at the time t=kT, the coding is in a state ?m of the N states, the arrival of the information bit uk of the sequence {uk} forces a transition to the state ?q of the N states and the selection of the elementary signal si(t) as x(t), where q and i are given by the following equations: di=m?1 mod 2; d0=d1+ukmod 2; y=2(m?1)+d0; q=(r mod N)+1; and i=r+1 if r<N, or i=r?2N otherwise.

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 coding scheme of order n for digital communications, in particular optical communication, for obtaining a coded signal x(t) which represents binary data which are constituted by sequences of information bits {uk} with rate T, the scheme having N=2n states, named &Sgr;i, for i=1, 2, . . . , N, and comprising predetermined elementary signals si(t) which are combined in the signal x(t). According to the scheme, if, at the time t=kT, the coding is in a state &Sgr;m of the N states, the arrival of the information bit uk of the sequence {uk} forces a transition to the state &Sgr;q of the N states and the selection of the elementary signal si(t) as x(t), where q and i are given by the following equations: di=m−1mod2; do=d1+ukmod2;y=2(m−1)+d;q=(rmodN)+1; and i=r+1 if r<N, or i=r−2N otherwise.

Abstract: An adaptive blind equalization method and device uses self-decisions both in the convergence phase and the steady-state phase, making it possible to obtain a good and smooth adaptation in the convergence phase and a low error probability for the decided symbols in the steady state phase. By using the self-decided error and a reference error, a binary consent function is constructed which tells when it is allowed to proceed with the adaptation and when the adaptation should not be used. The binary consent function compares the self-decided error sign with the reference error sign and is based on the discovery that in certain areas of the symbol constellation plane, when the signs of the previous errors are equal, there is a high probability that the self-decided error signs and true error signs (unknown) will also be equal.

Abstract: The adaptive auto-orthogonalizing equalizer in the discrete frequency domain comprises a filter with N cells operating by the overlap-save method, a decision element which assigns one of the possible levels to the filtered samples, and a control circuit which at each iteration varies the cell gains on the basis of the input samples, the output samples and the decided symbols, and which comprises an estimator (S.sub.A) for estimating the gradient of the mean square error, an estimator (S.sub.B) for estimating a matrix which modifies said gradient such that its direction always passes as close as possible to the minimum to be sought, a projector (P.sub.S) for projecting said corrected gradient into a constraint region, and a circuit for adjusting the filter cell gain vector at each iteration.