Abstract: A method and apparatus for use in a digital radio transmission system comprising stationary radio stations arranged in a cellular network and to which are assigned a plurality of mobile radio stations. Transmission of digital messages from a stationary radio station to the mobile radio stations assigned to it is effected by wide-band code division multiplex modulation, and transmission of digital messages from such mobile radio stations to the stationary radio station is effected by narrow-band frequency multiplex modulation. This reduces bandwidth requirements and improves the signal-to-noise ratio for each direction of transmission.

Abstract: In a data transmission system messages can be transmitted in the form of sequentially linked modified code words of a linear block code, the modified code words being produced by combining the code words formed from the data with a protection word.When such modified code words are interleaved bit-wise in order to recognize random errors, the sequence of code words of the transmitted message may be changed after de-interleaving at the receiver, by bit shift, due to faulty synchronization of the transmitter and receiver. In order to recognize this, each code word is linked to a protection word which identifies its position within the message. The modified code words thus obtained are interleaved bit-wise, transmitted and de-interleaved again at the receiver. Each word thus obtained at the receiver is combined with a check word identifying its position within the message.

Abstract: In a communication system having a plurality of mutually independent subscriber stations, these stations seize a common duplex transmission channel for establishing a connection in accordance with a multiple-access method. To prevent simultaneous access and the resultant access destruction and also in the case of frequent access destruction of the blocking of the common duplex transmission channel, each transmission station, to initiate a transmission therefrom, seizes the duplex transmission channel by means of a signalling character. The signalling character is transmitted by the subscriber station during a time slot allocated for that purpose. To distinguish between reporting subscriber stations, a pulse function from a system of orthogonal or substantially orthogonal pulse functions is used as an identification character.

Abstract: Disclosed is a full duplex communication system connecting by a two wire link a main station and a local station. Both the main station and the local station has a clock pulse generator. The local clock pulse generator is switchable between a pulse rate which corresponds to that of the main clock and another pulse rate which defers about a fixed value. A comparator compares the phase of the incoming signal with the local clock signal and switches the local clock generator when its output is out of phase with the received signals.

Abstract: A system is disclosed in which a modulated transmission is itself delta-modulated, in order to derive a transmission clock signal characteristic of the transmission, as opposed to being characteristic of an underlying data signal which is used as a modulating waveform in the transmission. The delta-modulation detects changes in state of the data transmission, which changes in state can be monitored in order to derive the transmission clock signal utilized. In a preferred embodiment, a phase-locked loop may be utilized to produce a pulse train having the same frequency as, and being in phase with, such changes of state in the transmission.

Abstract: A data waveform modulates a carrier to produce a data-waveform-modulated input signal v, which is applied to the input of a delta-modulation transmitter of controllable quantization-step size. The delta-modulated output signal d of the transmitter is fed through a shift register, to the individual stages of which the inputs of a coincidence gate are connected. The output signal of the coincidence gate is transmitted through a narrowband filter tuned to a frequency f.sub.s equal to the symbol transmission rate of the data-waveform-modulated input signal v. The narrowband-filter output signal is utilized to control quantization step size.