Abstract: In a network wherein all the receive stations connected to a radio link or a bus type wire link are capable of observing information which is being transmitted over the link, a method of allowing each receive station to send back a repeat request signal in multi-station packet communication in which a single transmit station transmits the same message to a plurality of receive stations. The same number of frequencies as packets are used so that a sinusoidal wave having a particular one of the frequencies which is associated with a packet with an error is sent. Alternatively, the same number of time slots as packets are set up so that a burst signal is sent as a repeat request signal in a particular one of the time sots which is associated with information on a packet with an error.

Abstract: In a multipoint communication system, first polling signals are sequentially and respectively transmitted to terminal stations on a broadcast channel from a central station, asking a request for reservation without waiting for a reply from the terminal stations. A reservation signal is transmitted on a multiple access channel from a terminal station requesting the reservation to the central station in response to the first polling signal addressed to it. A second polling signal is then transmitted on the broadcast channel in response to the reservation signal and the multiple access channel is reserved for a period of time variable in accordance with the reservation signal. A data signal is transmitted from the terminal station requesting the reservation on the reserved multiple access channel in response to the second polling signal.

Abstract: A data communication device for use either as an interface between a data processing device and a transmission medium of a CSMA/CD network or as a repeater between a CSMA/CD network and an additional data communication network which shares a transmission medium with the CSMA/CD network, sends an obstruction signal towards the CSMA/CD network when an input buffer tends to overflow on storing an input data packet for delivery to the data processing device or for transmission towards the additional data communication network. The obstruction signal is for causing a collision in the CSMA/CD network. The additional data communication network may be plural in number. When the additional data communication networks are CSMA/CD networks, the transmission of data packets thereto is suspended when a collision is detected at the repeater. The transmission is restarted a variable interval after disappearance of the collision. The variable interval corresponds to a weighted random number known in the art.

Abstract: A signal detector for use in the digital signal communication, comprising a tentative decision means for assigning certain symbols to receiving signals based on a predetermined value; a first memory means for storing the output of said tentative decision means in sequence; a second memory means for storing a plurality of reference values prepared in association with all the signals to be received, said signals corresponding to the symbol sequence assigned by said first memory means; a selection means for selecting at least one of said reference values based on at least a part of the contents of said first memory; and a processing means wherein there is proceeded by using said selected reference value the process to relate said receiving signals with signals to be received that are most likely receiving signals among all the signals to be received, thereby producing output.

Abstract: A demodulator responsive to baseband signals from a coherent detector having an automatic equalizer part for supplying equalized signals to derive transmitted datum and a phase control part responsive to equalized signals. The automatic equalizer part includes a delay member with a plurality of taps and variable attenuators connected to the respective taps of the delay member. The phase control part is provided with a phase shift circuit such as a coherent detector and a control circuit for detecting phase variation components of equalized signals. Further, the control circuit feeds phase variation components detected to the phase shift circuit and simultaneously supplies error signals which are dependent on phase variation components to the respective variable attenuators of the automatic equalizer.