Abstract: Telecommunication systems such as PON-FITL-Systems are known having a TDMA frame structure and comprising a main station and a number of substations. The known systems can comprise apparatus for coarse ranging and for fine ranging. A Pseudo Noise Sequence based coarse ranging technique employs coarse ranging at a fixed position within the upstream multiframe reserved for ranging, preferably for fine ranging. By applying a low power Pseudo Noise Sequence for coarse ranging and sampling the range in the main station only within a fine ranging window the position of which is known to the main station, a more accurate coarse ranging is achieved. Within the fine ranging window normally no data are present, and thus the signal-to-interference ratio is an order of magnitude better than in the other part of the frame.

Abstract: Telecommunication systems such as PON-FITL-Systems have a TDMA frame structure comprising a main station and a number of substations. In order to achieve accurate fine ranging, an A/D-converter for acquiring samples from a ranging pulse transmitted from the substation is operated at a frequency which is high with respect to the master or bit clock, i.e. real time oversampling occurs. Such high speed A/D-converters are expensive, consume much power and have limited resolution. Furthermore, for systems with even higher bit rates the known oversampling becomes cumbersome. A quasi-oversampled coarse and/or fine ranging is proposed operating at relatively low sampling rates. Thus the substations send a repetitive ranging-bit-pattern which is sampled in the main station and thereafter reconstructed in a processing apparatus to a quasi-oversampled ranging-bit-pattern.

Abstract: Telecommunications passive optical networks are known which employ a TDMA frame structure for transmission between a main station and a number of substations. Due to increased capacity demands and still further service demands, there is a need for higher bit rates over such networks. The invention provides a high bit rate passive optical network wherein the substations operate at only a fraction of the network bit rate, and so are hardly more complex than in lower bit rate networks. That is achieved by formation by the main station of sub-frames of the data intended for transmission to a number of the substations, and bit interleaving the sub-frames to form a data frame which is transmitted over the optical fiber cable. Each substation is adjusted to only listen to the sub-frame to which it is assigned.

Abstract: A device for writing, reading or erasing a record carrier has a coil with a winding arranged between an objective lens and the record carrier. Optical radiation is focused to a spot, the converging beam passing through the coil opening. A core of a transparent material, having an index of refraction which significantly decreases vergence of the focused beam, is placed in the winding opening. As a result the diameter of the coil can be reduced, and permit increase of the generated magnetic field.

Abstract: A modular coupling unit which functions as an interface between a communication unit or peripheral apparatus and the communication network includes a code word signal generator for generating a unique address code which is representative of the geographical location in which the relevant coupling unit is "permanently" included in the communication network. This signal generator is and continues to be energized as soon as and for so long as a communication unit or peripheral apparatus is and has been connected to the coupling unit. The address codes generated in bursts by such a generator are transferred via a connecting cable between the relevant communication unit and the coupling unit to this communication unit. The relevant address code is stored in the coupling unit. On request and within the time regime holding for the communication network, the address code is read and transferred to a diagnostic module via the communication network.

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: Echo canceller for use in a homochronous data transmission system, comprising two-wire and four-wire connections and arranged for suppressing echo signals occurring in the four-wire connection. This echo canceller comprises an adjustable signal processing arrangement 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. To generate a residual signal, the synthetic echo signal is subtracted from the signals in the receive path.For the adjustment of the signal processing arrangement there is added to this residual signal, outside the receive path of the four-wire connection, an auxiliary signal which is not correlated to this residual signal. The sum signal thus obtained is sampled with a suitably chosen sampling rate which is harmonically related to the symbol rate.

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: 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: 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 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.