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

Sip - Societa Italiana Per L-Esercizio Delle Telecomunicazioni P.a.

Sip - Societa Italiana Per L'esercizio Delle Telecommunicazioni

Telespazio S.p.a. Per Le Comunicazioni Spaziali

Roberto Montagna

Daniele Sereno

Rosario Drogo De Iacovo

Enrico Impallomeni

Giuseppe Giandonato

Luciano Nebbia

Francesco Gandini

The set of possible excitation signals is subdivided into a plurality of subsets, the first of which provides the contribution to the coded signal necessary to set up a transmission at a minimum rate guaranteed by the network, while the others supply a contribution which, when added to that of the first subset, causes a rate increase by successive steps. At the receiving side, a decoded signal is generated by using the excitation contribution of the first subset alone if the coded signals are received at the minimum rate, while for rates higher than the minimum rate the contributions of the subsets which have allowed such rate increase are also used.

Method of and device for coding speech signals with

System for embedded coding of speech signals

A low-delay audio signal coding system, using analysis-by-synthesis techniques, has circuitry for adapting the spectral parameters and the prediction order of synthesis filters, and of perceptual weighting filters in the order at each frame, starting from the reconstructed signal relevant to the previous frame. In the case of a CELP coder, gain controls are also provided to adapt, starting from the reconstructed sinal, a factor, bound to the average power of the input signal, of the gain by which the innovation vectors are weighted.

Low-delay audio signal coder, using analysis-by-synthesis techniques

The method provides the use, for the determination of the estimation echo-channel pulse response, of digital filtering techniques of the transversal adaptive type, and the subdivision of the pulse-response of the equivalent echo channel into three intervals, the second of which consists of the significant portion of the pulse response and is determined by the iterative search for the value and the position of the coefficient of maximum absolute value; the first interval corresponds to a pure delay and the third corresponds to the contribution given by the lowest frequencies of the base band. To copy the echo-signal, there are only considered the pulse-response coefficients whose indexes are comprised in the second interval, and the samples of the signals to be copied belonging to preceding sampling instants, whose indexes are also comprised in the second interval.

Method of and device for the digital cancellation of the echo generated

At a subscriber station AU communicating with a central office of a data network, a logic unit UM includes a processing subunit UE which, under the control of a microprogrammed subunit UC comprising a microinstruction memory MM and a sequencer SQ, digitally demodulates an incoming carrier and synthesizes an outgoing carrier modulated in the DPSK (differential-phase-shift keying) mode. The modulation is effected by multiplying stored bits of an outgoing signal, read out from a data memory MD, with bits representing digitized sine and cosine samples of the carrier wave obtained from a calculator AL within subunit UE, followed by conversion to analog form and filtering; demodulation is carried out in a similar manner, after conversion of analog samples of the incoming carrier to digital form, by multiplying the resulting bits with those of the calculated sine and cosine samples. The sampling instants are established by a timing signal T2 digitally synchronized with the central-office clock through a phase-locking loop including an adjustable frequency divider DP controlled by an error signal from the calculator AL, emitted when the peak-indicating derivative sample has an absolute value exceeding a predetermined threshold.

Terminal equipment for data-transmission network including digitally

A signal receiver of a QPSK data-transmission system comprises two noncoherent demodulators feeding digitized in-phase and quadrature components to a pair of transversal filters whose coefficients are read out, during successive keying intervals, from a read/write memory accessed by an arithmetic unit which generates corrective terms updating these coefficients. A comparator in the output of each filter detects estimated phase jumps between delayed and undelayed filtered samples of each signal component and delivers them to a decision circuit as well as to an error detector which also receives quantized output signals from the decision circuit to produce two error signals fed to the arithmetic unit; the latter further receives the delayed and undelayed filtered samples as well as ancillary data temporarily stored in these filters to calculate the corrective terms.

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Turin, Italy

Roberto Montagna