Abstract: A digital echo canceller has a receive path (2) and a send path (3) and comprises combining apparatus (10) for forming a send output signal [r(k)] as the difference between the signal [z(k)] applied to the send input (SI) and a replica signal [e(t)] used for cancelling an additive echo signal [e(k)] at the send input (SI) that has developed in response to a receive input signal [x(k)] applied to the receive input (RI), which echo canceller at least includes transforming apparatus (13, 15) for transforming the receive input signal [x(k)] and the send output signal [r(k)]; transforming apparatus (14) for transforming the replica signal [e(k)]; a digital adaptive filter (9) which has a number of filter coefficients for generating the replica signal [e(t)] in response to the receive input signal [x(k)] and the send output signal [r(k)], adaptation apparatus (12) for determining for each block m, adaptation components [A(p;m)] for each of the filter coefficients [W(p;m)] in response to the receive input signal [x(

Abstract: A digital echo canceller [1] with a good protection against double-talk comprises a first filter [9] for the echo cancellation proper, a second adaptive filter [11] for making continuously adapted filter coefficients available to the first filter [9] and gate means [15] which will only apply the adapted filter coefficients to the first filter [9] if certain conditions are satisfied. In the echo canceller [1] a specific filter combination is used, in which the first filter [9] is a time-domain programmable filter (TDPF) and the second filter [11] is a frequency-domain block-adaptive (FDAF), and further means [20,20(1)] are provided that are arranged in cascade with the gate means [15] for transforming the frequency-domain filter coefficients [W(p;m)] of the FDAF [11] into time-domain filter coefficients [w(i;m)] for the TDPF [9].

Abstract: A system for transmitting a data signal (a.sub.k) at a given symbol rate 1/T comprises a data transmitter (1), a channel (3(1)) of a transmission facility (3) having a plurality of channels (3(1)-3(M), and a data receiver (2) with an equalizer (7) of the decision feedback type. This equalizer comprises a feedback filter (12) with a memory span NT and a feedforward filter (8) which includes a low-pass filter section having a substantially minimum-phase character and an amplitude-frequency characteristic .vertline.W(f).vertline. which has a pronounced maximum .vertline.W(f.sub.m).vertline. for a frequency f.sub.m near to the frequency f=1/((N+1)T) and which is decreasing for frequencies exceeding f.sub.m [FIG. 5A]. Consequently, with respect to conventional dimensionings of the equalizer (7), this achieves an improved transmission quality and/or a reduced complexity of the feedback filter (12).

Abstract: The transmitter (DTR) and the receiver (DRC) of a system for transmitting data signals at a given symbol rate 1/T comprise discrete-time smearing filters (SM and DSM) for combatting the effect of additive pulse-like disturbances (p'(t)) in the transmission channel (TCH). In many cases these disturbances (p'(t)) turn out to have a pronounced bandwidth-limited nature. By utilizing this feature the implementation of the smearing filters (SM and DSM) is simplfied and/or their performance level is improved in that the non-zero values of their impulse responses s(i) and d(j) only occur at the points of grids of the indices i and j recurring with a period of L, where L is an integer greater than 1 and where L is determined substantially by the ratio L.sub.0 of the symbol rate 1/T to twice the highest significant frequency f.sub.m of these disturbances (p'(t)).

Abstract: An arrangement for full-duplex data transmission over a two-wire circuit (1) comprises a transmit channel (2) connected to a baseband data transmitter (6) and including a smearing filter (18), a receive channel (3) connected to a baseband data receiver (9) and including a complementary smearing filter (19), a hybrid junction (4), an echo canceller (14) with an adaptive filter (15) and an adjusting circuit (16), and a combining circuit (17) inserted in the receive channel (3).

Abstract: A frequency-domain block-adaptive digital filter (FDAF) having a finite impulse response of length N for filtering a time-domain input signal in accordance with the overlap-save method includes window means (11) for obtaining modifications (B(p;m)) of the 2N frequency-domain weighting factors (W(p;m)) from correlation products (A(p;m)). A known FDAF of this type contains five 2N-point FFT's, two of which are used in the window means (11). By utilizing a special time-domain window function which can be implemented very efficiently in the window means (11) with the aid of a frequency-domain convolution, a FDAF of this type containing only three 2N-point FFT's is obtained whose convergence properties are comparable to those of the known FDAF containing five 2N-point FFT's.

Abstract: In DAV (data above voice)-systems an analog speech signal is transmitted in the low-frequency portion of the spectrum of an encoded data signal. When a data signal encoded by the known WAL2 code is used, the high-pass filters, required for the separation of the two signals produce intersymbol interference extending over a large number of bit intervals, requiring complicated equalisers at the receive end for good detection. When encoding the data signal in accordance with the DAV-code, as illustrated in FIG. 2 this drawback is remedied. In addition, this DAV-code is advantageous in that the amplitude fractions, represented by a and b, can basically be chosen at will, allowing the low-frequency content of the code to be affected. When (a; b)=(11/16; 3/16) the encoded data signal can be generated very accurately and in a simple manner.

Abstract: A data transmission system comprising a transversal smearing filter at the transmitting end and a transversal desmearing filter at the receiving end. To simplify the filters, at least the sequence of coefficients of the desmearing filter is formed by elements of the set {-1, 0, +1}, which results in an optimum smearing of noise pulses in the system compared with a system without such a filter.

Abstract: A transmission system for transmitting data signals in a modulation band comprising a transversal smearing filter at the transmitter end and a transversal desmearing filter at the receiver end. In order to obtain an optimum smearing efficiency, the sequence of real individual coefficients of the multiplying factors of the transversal desmearing filter satisfy the requirement that for a given upper limit for the intersymbol interference produced by the cascade arrangement formed by the smearing filter, and the desmearing filter a substantially maximum value is derived for a merit factor indicating by what factor the maximum value of a disturbance is decreased by including a smearing filter and a desmearing filter in the transmission system.

Abstract: A data communication system for transmission of bi-phase signals modulated by data symbols and in which the signals are filtered in accordance with a frequency response which approximates zero at 0 H.sub.z and at and exceeding the frequency 3/(2T) H.sub.z and which has an approximately sinusoidal variation between those frequencies, T being the symbol interval. This filter characteristic minimizes intersymbol interference and improves the signal-to-noise ratio. The requisite filtering may be provided in the receiver or in part in the receiver and in part in the transmitter of the communication system.

Abstract: In the duplex transmission of data signals over two-wire transmission paths the phenomenon of echo-signals is encountered, while simultaneously intersymbol interference occurs between the data symbols themselves. In order to reduce the influence of both the echo signals, and the intersymbol interference, the arrangement comprises a random access memory (16) which produces a correction value (c(i)) at each sampling instant to correct the received data signal. The memory is addressed from registers (13, 14) and a counter (15), the contents of the registers being determined by the data ssymbols transmitted last and the data symbols received last, respectively. A D-A converter (19) converts the correction value into a correction signal (c(t)), which in a difference producer (20) is subtracted from the received data signal. A sampling arrangement (21) samples the corrected received data signal. After D-A conversion (22) and multiplication (17) by a predetermined factor .alpha.

Abstract: Echo canceler for use in a data transmission system, comprising two and four-wire connections and arranged to suppress echo signals occurring in the four-wire connection. This echo canceler is provided with an adjustable signal processing device to which the data signal to be transmitted is applied and which produces a synthetic echo signal. A signal formed by a received data signal and an echo signal is present in the receive path of the four-wire connection. From the signals in the receive path there is now subtracted the synthetic echo signal, in order to generate a residual signal.To adjust the signal processing device an adjusting device is connected thereto to which a digital control signal is applied, which is constituted by a digital version of the residual signal.

Abstract: Arrangement having a non-recursive filter and means for weighting a sequence of delayed versions of the input signal in accordance with a sequence of coefficients which are each adjusted iteratively by positive and negative correction steps, respectively, with variable step-sizes, the step-size parameter being selected for each iteration and for each coefficient by means of a run-length detector to which the sign of each correction step is applied and which selects a larger or a smaller step-size parameter depending on the number of correction steps having the same sign and preceding the relevant iteration.Use: echo canceller, equalizer.

Abstract: Arrangement for checking the synchronization of a data signal receiver. When frequency division is used as part of the clock signal regeneration process, a phase ambiguity may occur. To eliminate this ambiguity use is made of a monitoring device. In the present monitoring circuit the data signal is sampled twice in each symbol interval and a reliable criterion is obtained by integration of the amplitude differences of the samples.

Abstract: Arrangement for clock signal generation from a received data signal located in baseband, for use in baseband modems. In addition to signal transitions which provide clock information in a reliable manner, several types of data signals contain disturbing signal transitions. These disturbing transitions are eliminated by converting the spectrum of the received data signal into the spectrum of a bi-phase modulated signal. It is possible to obtain a reliable clock signal from the signal transitions of the converted signal with small acquisition times.

Abstract: A transmission system for the transmission of binary data symbols is described in which a so-called "crankshaft code," in combination with a receiver having a special filter characteristic, enables a more optimum signal detection, independent of the cable characteristic.The system is used for digital transmission over cables in the local telephone network.

Abstract: A digital filter and demodulation arrangement for passband signals, whose corresponding baseband signal has a bandwidth limited to a given maximum frequency. The passband signals are filtered according to two bandpass characteristics which, apart from their asymmetrical distortion relative to their central frequency, are versions from one another shifted 90.degree. in phase. The filtered passband signals are demodulated with an in-phase carrier and a quadrature carrier and the demodulated signals are combined to a baseband signal.In the digital filtering process the sampling frequency is reduced from a value higher than twice the highest frequency in the passband signals to a value which is not higher than twice said maximum frequency in the baseband signal and in the digital demodulation and combination processes the reduced sampling frequency is also used so that a considerable reduction in the internal processing speed is obtained.

Abstract: A non-recursive discrete filter for simultaneously realizing for example two band-pass filter characteristics starting from a given lowpass transfer characteristic, wherein one bandpass filter has an in-phase transfer characteristic and the other filter the quadrature transfer characteristic of this in-phase filter. The central frequency of these filters is f.sub.o and the output sampling frequency is f.sub.s = 8f.sub.o. This discrete filter comprises multiplying means in which input signal samples x(n) are modified by an associated filter coefficient a(i) for generating modified input signal samples z(n,i) = a(i)x(n-i). The coefficients a(i) are the same for both transfer characteristics and are given by: ##EQU1## WHEREIN H.sub.1 (I) REPRESENTS THE DISCRETE IMPULSE RESPONSE OF THE LOWPASS FILTER.To realize the in-phase transfer characteristic the samples z(n,i) are thereafter multiplied by a factor sgn[cos (.pi.i/4)] and the products thus obtained are accumulated.