Kokusai Denshin Denwa Kabushiki Kaisha

Kokusai Denshin Denwa Co., Ltd.

Akira Ogawa

Yasuo Hirata

Tatsuo Watanabe

Hideki Saito

Toshio Takahashi

Yukio Nakagome

Yutaka Yasuda

Kazunori Inagaki

Hiroshi Kurihara

Masahisa Yamaguchi, Deceased

A maximum likelihood error correcting technique for a digital communication in which a transmit side provides coded data with some redundancy through a convolutional coding circuit, and a receive side corrects transmission errors automatically through a maximum likelihood error correcting circuit has been improved by deleting some symbols at a transmit side to increase a coding rate close to 1, and inserting dummy symbols at a receive side into each bit position where a symbol has been deleted at a transmit side. A likelihood value for that dummy symbol inserted at a receive side for the maximum likelihood decoding is a fixed predetermined value. Thus, both a coding circuit in a transmit side and a decoding circuit in a receiving circuit have only to handle original low rate code, while keeping a coding rate in a transmission line high. Then, the codec for high rate code obtained merely by adding the simple circuits to the simple codec for low rate code provides an excellent error correcting capability compared with other conventional error correcting techniques of the same coding rate.

Maximum likelihood error correcting technique

A satellite repeater for a digital satellite communication system for use on board of satellites. Receivers are provided with respective antennas for receiving radio-frequency signals from a plurality of ground stations. A signal processing circuit switches signals received in synchronism with stable clock timings. Transmitters receive the switched outputs of the signal processing circuit to provide radio-frequency signals for transmission through respective antennas of the transmitters. Timing detectors receive the outputs of the receivers and detect the frame timings of the output signals of the receivers. Signal storage circuits are provided between respective outputs of the receivers and the signal processing circuit for storing the respective output signals of the receivers by respective amounts. Control circuitry connected to the timing detectors, the signal storage circuits and the signal processing circuit control the storage operations of the signal storage circuits so that each of the frame timings of the received signals and the switching timing of the signal processing circuit have a desired timing relationship.

Satellite repeater

A space diversity system in a TDMA communication system employing a communication satellite, in which in order to equalize the path lengths of respective sending paths at the start of communication, a pre-burst is sent out to one of the paths making up the diversity system in a time slot of one frame assigned to an instant station. A sub-burst is sent out to the other of the paths in the assigned time slot. A relative time difference between the pre-burst and the sub-burst is detected from signals sent back to the instant station from the communication satellite or signals received by a distant terrestral station via the communication satellite. On the basis of the result of a comparison operation of relative time difference between the pre-burst and the sub-burst at the time of their sending-out from the instant station with a relative time difference between the pre-burst and the sub-burst received via the communication satellite, variable delay means inserted in one of the paths is controlled so that the two relative time differences become equal to each other.

Space diversity system in TDMA communication system

A system for compensating for cross polarization coupling in a dual-polarization satellite communication system, in which two polarized waves of the same frequency and orthogonal to each other are alternately transmitted as a pilot wave from an earth station at a predetermined period. The same polarized wave components of the two signals received by a communication satellite are sent back to the earth station, so that the sent back signal is received by the earth station. An amplitude ratio and a phase difference between the same polarized wave components of the two signals of the received pilot signal are detected. A communication signal wave to be transmitted from the earth station is formed as an elliptically polarized wave by the use of the detected information, thereby compensating for cross polarization coupling of the communication signal wave caused during propagation between the earth station and the communication satellite.

System for compensating for cross polarization coupling

A space diversity PCM-TDMA telecommunication system using a stationary communication satellite, in which fixed delay circuits are respectively inserted in the sending side and the receiving side of one route at a control equipment, while variable delay circuits are inserted in the sending side and the receiving side of the other route at the control equipment, so that electrical length of one route from the satellite to the control equipment may be the same as that of the other route from the satellite to the control equipment through the route including connection links between the two sites. Diversity switching can be performed with no duplication and lack of signals in accordance with the above construction.

Space diversity system in PCM-TDMA telecommunication system using

A system for determining burst sending timing in a time division multiple access communication system using a communication satellite, in which burst signals transmitted from a plurality of stations are arranged on the communication satellite in one frame at predetermined intervals. On the transmitting side connected to the communication satellite through a radio wave path, a first signal composed of a first signal state over one frame length defined by the sending frame timing is sent, and then second, third, fourth, . . . signals each composed of the first signal state and a second state different from the first signal state are sent. In this case, the position or length of the first signal state in one frame is altered by a certain amount. On the receiving side connected to the communication satellite through a radio wave path, the number of frames of the burst signals transmitted is counted during a duration from the detection of the first signal to the detection of the next first or second state at a predetermined time slot in a frame of the burst signals, and the sending timing of each station based on the sending frame timing is determined on the base of the counted number of frames and the certain amount.

Growing community of inventors

Machida, Japan

Akira Ogawa