Abstract: An arrangement for adjusting an adaptive digital balance filter included in a subscriber unit connected to a telephone line includes a selection unit, which can be connected to the subscriber unit either via the exchange or via a separately arranged switch. When the selection unit is connected to the subscriber unit, the balance filter is disconnected from both branches of the subscriber unit. A test signal generator is included in the selector unit for sending a signal on the lines via both branches of the subscriber unit. There is further included a plurality of digital filters wherein the transfer function of any of the filters closely coincides with the transfer function of the filter formed by the line impedance and the portion of the subscriber unit which is connected to the line and to the balance filter.

Abstract: An FIR-type balance filter for preventing, in adaptive echo cancellation in a telecommunication system in which digital information transferred in duplex over a single conductor pair, that the local data transmitter disturbs the local data reception. The filter is thereby arranged so that the total number of links (N) in the filter is divided into at least a first group (I) and a second group (II). The apparatus contains a memory (MI) addressable from the filter links and said first group, there being written into and read from said memory the correction values from and to a correction unit (KB1), sending signals for correcting the filter parameters. The memory (M1) also sends signals to a summing circuit (A2), to which are also supplied the output signals from said second group of filter links, said output signals possibly being originated by table look-up in a further memory, or by vector multiplication. A second correction unit (KB2) corrects the filter parameters in said second group.

Abstract: An apparatus is provided in a digital communication system for connecting digital terminals to a terminal junction point which in turn is in communication with a digital exchange. The terminal junction point contains directing means (9) for sending, in a first state, a flag signal both to all terminals (3) and to the exchange (1) and sending, in a second state, an information packet received from a terminal both to the exchange and to all terminals. The terminals have means (27,28) for sending an information packet in response to the flag signal having been received a given number of times, the reception of the packet at the junction point resetting the directing means to its second state. The terminal also contains comparison means for determining whether the packet information sent back from the junction point corresponds to the terminal's own sent-out packet information, and for disconnecting the terminal in the opposite case.

Abstract: A method and an apparatus, in a telecommunication system for transmission of digital information in duplex over a signal conductor pair for automatically adjusting a balance filter included in a hybrid coupler circuit with the aid of adaptive echo cancellation so that the local data transmitter does not disturb the local data reception, without utilizing any particular testing procedure in initiating the adaptive echo cancellation. A control signal (.epsilon..sub.k) is formed, with the help of which the correction unit (KB) is caused to generate signals for rapid updating of the balance filter (B) parameters, in spite of that knowledge is lacking in the initiation instant concerning the value of the signal transmitted from the remote end to the apparatus, and that no counteraction between level correction and filter adaption is obtained. The apparatus includes a quantizer (Q) in which a sampled, received signal (r.sub.k) is quantized, an estimated signal (a.sub.

Abstract: Orthogonal-diphase coded digital signals are transferred in bursts on a transmission line. In order to facilitate synchronization of the signal receiver to the incoming signal bursts an extra pulse is added at the beginning of each transmitted burst, the polarity of this pulse being opposite to that of the following signal element. At the receiver this extra pulse is detected by comparison of the received signals with a threshold voltage and the next zero transition is then used as a basis for the synchronization. The threshold voltage will be self-adaptive if it is allowed to decrease exponentially with time from a start value corresponding to a short transmission line to a final value corresponding to a long transmission line. Furthermore, in order to eliminate DC residuals an extra pulse may be added at the end of each transmitted burst, the polarity of this pulse being opposite to that of the preceding signal element.