Cselt-Centro Studi E Laboratori Telecomunicazioni S.p.a.

S.i.p. Societa' Italiana Per L'esercizio Telefonico P.a.

Giancarlo Pirani

Angelo Luvison

Valerio Zingarelli

Renato Dogliotti

Giorgio Taricco

A method is described for decoding messages coded as blocks consisting of a fixed number of symbols and affected by symbol substitutions, deletions and insertions, wherein for each received message having a length comprised within predetermined limits, a sequence of words (error frames) is generated which comprise all possible error combinations which can be corrected in the message. By using such error frames, a decoded word is generated for each frame, the probability that a decoded word actually is the transmitted word is calculated and the decoded word, whose probability value satisfies predetermined criteria, is emitted as a decoded message. A device for carrying out the method is also provided.

Method of and circuit for decoding block-coded messages affected by

An adaptive equalizer for high-speed binary signals, operating in baseband, comprises a transversal filter receiving digitized samples of incoming symbols and feeding them to a decision stage. An error signal derived from the difference between the filtered and the decided samples, for each coefficient of the transversal filter and for each iteration of the processing by that coefficient, is fed to an updating unit, where its sign is compared with the sign of the corresponding filtered sample to determine their identity or disparity. The result is a binary discriminating signal sent to a coefficient calculator and to a threshold generator which receives from that calculator the current coefficient and, dependent on the polarity of that coefficient and on the logical value of the discriminating signal, produces a threshold value to be compared with the absolute magnitude of the error signal. Whenever that absolute magnitude exceeds the existing threshold, it causes the count of an up/down counter to be incremented or decremented, depending on whether the two compared signs are different or equal. Whenever the up count of the down count reaches a predetermined limit in any cycle, the counter resets itself to zero and triggers the calculator to update the existing coefficient, again on the basis of the discriminating signal, by either halving or doubling that coefficient.

Adaptive equalizer for binary signals and method of operating same

An adaptive equalizer for high-speed binary signals, operating in baseband, comprises a transversal filter receiving digitized samples of incoming symbols and feeding them to a decision stage. The samples also go to a coefficient computer, in parallel with that filter, which includes a filter simulator, an error calculator and a processor delivering corrective coefficients to the filter. A register in the filter simulator accumulates a predetermined multiplicity of received samples (e.g. 150) which are jointly convoluted with an initial set of coefficients to yield a mean square error supplied by the error calculator to the processor; the latter, for each coefficient of the initial set, selects two collateral values which are successively substituted for that coefficient to yield two further mean square errors. Using an algorithm based upon a parabolic function, the processor computes an optimized coefficient which is rounded to the nearest power of 2 constituting a new coefficient replacing the corresponding coefficient of the initial set. After all coefficients of the initial set have been thus replaced to produce an updated set, the processor determines whether the resulting mean square error is less than that obtained with the initial set and, if so, substitutes the updated set for the initial set in the transversal filter.

An analog signal sent from one telephone subscriber to another is periodically sampled at a transmitting terminal and each sample is held for a storage period equal to a sampling interval as well as to a basic pulse period of a random or pseudorandom sequence of bipolar binary pulses. A stepped wave formed from these samples is mixed with that pulse sequence before being conveyed, e.g. by frequency modulation, to a receiving terminal where the wave so distorted is mixed with a like pulse sequence to re-establish the undistorted wave which may be contaminated by interferences from other users of the same signal link. The steps of the re-established wave are integrated over periods equal to the sampling interval and the integration products are stored for like periods to produce a purged stepped wave from which high-frequency components are subsequently filtered out to restore the original analog signal. The signal link utilized may be an emergency channel made available, e.g. for communication with a mobile station, when regular channels are busy.

Method of and means for spread-spectrum transmission

An analog signal sent from one telephone subscriber to another is differentiated at a transmitting terminal and the resulting derivative is distorted by mixing with a random or pseudorandom sequence of bipolar binary pulses before being conveyed, e.g. by frequency modulation, to a receiving terminal where it is mixed with a like pulse sequence to re-establish the undistorted derivative signal with substantial suppression of interferences from other users of the same signal link. The re-established signal is integrated over intervals equal to a basic pulse period of the binary sequence and each signal sample thus obtained is additively combined with the sample from the immediately preceding period to restore the original analog signal. The signal link utilized may be an emergency channel made available, e.g. for communication with a mobile station, when regular channels are busy.

For the transmission of data by way of a fiber-optical path, three-bit code words representing eight different signal levels are generated in respective signal periods 2T and are converted into pairs of ternary luminous waveforms of duration T having two possible amplitude levels L (low) and H (high). Each waveform pair includes at least one but not more than two light pulses H, of a width not exceeding T/2, occurring in either of two time positions within a cycle T. At the receiving end, the incoming light pulses are modulated--either before or after conversion into electrical signals--with a ramp signal of recurrence period T which transposes the pulses H to either of two elevated amplitude levels depending upon their time position within a cycle, with the pulses L remaining at a low level. The resulting electrical pulses are integrated over successive periods equal to T and sampled in each of these periods for comparison with predetermined thresholds.

Data-transmission system and method using fiber-optical transmission

An incoming data stream in the output of a demodulator and its derivative in the output of a differentiator are passed by respective sampling gates to a pair of equalizers operating by recursive filtration. The optimized data pulses issuing from the first equalizer are quantized and, after storage in a shift register, are algebraically combined in a first adder with a reference signal x from that equalizer representing the vector sum of weighted data pulses from a succession of N preceding clock cycles; a resulting error signal e.sub.n is delivered to three cumulative multipliers forming part of three feedback loops which supply an optimized phase signal .zeta. to the demodulator, an optimized timing signal .tau. to the sampling gates and an optimized gain coefficient K to the equalizers. These three multipliers respectively receive the reference signal x from the first equalizer, an optimized differential signal dx/d.tau. from the second equalizer and an updating signal z from the first equalizer. A further cumulative multiplier forms part of a fourth feedback loop delivering an optimized channel coefficient G to the equalizers, this latter loop including a second adder which synthesizes another error signal e' from the incoming data pulses z and from the complex product G.multidot.x produced by the last-mentioned multiplier. Each feedback loop includes a selective delay circuit effective only during an operating phase, in contrast to an acquisition phase during which the first adder receives a locally generated test signal in lieu of the quantized data pulses.

Adaptive method of and means for recovering digital signals

Incoming data pulses from a transmission channel are differentially combined with feedback pulses from the downstream end of a cascade of (N-1) delay networks to form an updating signal fed in parallel to a first set of multipliers for weighting with respective coefficients b.sub.1 - b.sub.N.sub.-1. These multipliers deliver optimized signal components to the inputs of respective delay networks of the cascade, through the intermediary of adders in each instance except for the first delay network at the upstream end; a further adder downstream of the last delay network may superimpose the updating signal, weighted with a coefficient b.sub.N by an N.sup.th multiplier of the first set, upon the feedback pulse issuing from the last delay network to generate an additional signal component. At least the more significant signal components, from the inputs of the delay networks located further upstream in the cascade, are weighted in a second set of multipliers with respective coefficients a.sub.1, a.sub.2 etc. before being additively combined, in a summing circuit, into a composite output signal.

Digital equalizer for data-transmission system

Incoming data pulses from a transmission channel are differentially combined with weighted data pulses from preceding cycles to form an updating signal fed in parallel to a multiplicity of weighting circuits for digital multiplication with respective coefficients K.sub.1 - K.sub.N, the output signals from these weighting circuits being synthesized in staggered relationship to form a composite signal fed to a quantizing decoder. The weighting coefficients K.sub.1 - K.sub.N are continuously modified under the control of an error signal derived from a locally generated reference code during an acquisition phase and from the decoder output during an operating phase.

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Turin, Italy

Giancarlo Pirani