Kokusai Denshin Denwa Kabushiki Kaisha

Kokusai Denshin Denwa Co., Ltd.

Nec Corporation

Yasuo Hirata

Akira Ogawa

Fumio Takahata

Toshio Takahashi

Yutaka Yasuda

Kazunori Inagaki

Shuji Murakami

Yukitsuna Furuya

Yukio Nakagome

Katsuhiro Nakamura

Mitsuo Nohara

Hiroshi Kurihara

In a frequency division multiple access (FDMA) communication system, a plurality of carrier frequencies relating to a predetermined frequency band for transmitting a PSK (phase shift keying) signal are provided on a frequency scale. When a service is a low bit rate signal, it is transmitted by using a single carrier frequency and its related frequency band. When a service is a high bit rate signal which can not be transmitted in a single carrier signal, the service signal is divided in to a plurality of low bit rate PSK signals, each of which is transmitted by using a single carrier frequency and the related frequency band.

Frequency assignment system in FDMA communication system

A Viterbi decoder synchronization circuit comprises a circuit that derives a word synchronization signal from a received bit stream of convolutional codes. A first detector detects a maximum of metric values derived from the Viterbi decoder at different locations in time. A memory is provided for storing therein the address codes derived at different times and the maximum metric values detected by the first detector. A second detector is connected to the memory for detecting the presence of a path between the states addressed by the address codes stored in the memory. An integrator is connected to the second detector to integrate its output signal. To the integrator is connected a third detector which detects when the integrator output reaches a value indicative of one of word-in-sync and word-out-of-sync conditions of the Viterbi decoder. A phase shift signal is generated in response to an output signal from the third detector and applied to a phase shifter to introduce a delay time to the bit stream.

Synchronization circuit for a Viterbi decoder

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 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 transmultiplexer, in which after a pulse code modulated, time division multiplex signal of the voice band signal is converted into an analog signal, the analog signal is separated by filters into signals of respective channels and then the signals of the respective channels are combined together to provide a single sideband frequency divided, multiplex signal. In a reverse signal flow type, after a single sideband frequency-divided multiplex signal is separated by filters into signals of respective channels, the signals of respective channels are converted into digital signals and thereafter combined together to provide a pulse code modulated, time division multiplex signal. In accordance with this invention, a sign bit inverter is provided for reversing sign bits of predetermined specific channels in the pulse code modulated, time division multiplex signal every other frame.

Transmultiplexer

A system for controlling teletype signals, in which a start-stop telegraph signal train may be received at the reversed polarity state. The polarity of a signal element of a received character is decided at a specified instant in a time slot at which the stop element of the received character is expected to arrive. The polarity of a signal element of the received character is again decided in a time slot at which a stop element after a predetermined number of characters from the specified instant is expected to arrive. Only when the polarities of the signal elements of the received characters are decided as the same A-polarity during both of the decision operations, the polarity of the telegraph signal train is automatically reversed.

System for controlling polarity state of start-stop telegraph signal

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

Tokyo, Japan

Yasuo Hirata