Fujitsu Corporation

Mitsuru Seta

Tomoyuki Ueno

Atsushi Yamashita

Hiroyuki Sogo

Yutaka Hamada

Masahiko Shirota

Tsudoi Kubo

Yasuo Tanishima

Hitoshi Ishikawa

Rikihiko Mashima

Jun Kojima

A time synchronization method in a CDMA system for synchronizing the time of a plurality of base stations and the time of a base station controller that controls each of these base stations includes providing the base station controller with a GPS receiver for receiving a signal from GPS satellites and generating a reference time based upon the received signal, adopting the reference time generated by the GPS receiver as the time of the base station controller, creating time reference information based upon this time and sending the time reference information to each base station. Each base station synchronizes its own time to the that of the base station controller based upon the time reference information it has received.

Time synchronization method in CDMA system

A base transceiver station in a wireless local loop system using a personal handy-phone system constituted by a plurality of cell stations, each accommodating a plurality of subscriber units, a hybrid section integrally handling signals transmitted and received by the plurality of cell stations via a single antenna, and a multiplexing/demultiplexing unit integrally handling the signals transferred between the plurality of cell stations and an existing network, thereby enabling construction of a wireless local loop system which is small in size, can expand the service area without an increase of interference with other base transceiver stations, has a good affinity with existing networks, is provided with ISDN functions, and, at the same time, provides backup against faults and improves the transmission quality and reliability.

Base transceiver station and subscriber unit in wireless local loop system using personal handy-phone system and method for operating same

A demultiplexer separates the data obtained by the demodulation into the data for each information medium, and a synchronous word detection state monitor detects the synchronous word contained in a received signal of a predetermined information medium and compares the state in which said synchronous word is detected with the preset standard, and outputs an output stop signal when the synchronous word detection state is worse then the preset standard. An error-correction decoder subjects the data obtained by the demodulation to an error-correction decoding processing, and an error-correction encoder subjects the decoded data to an error-correction encoding processing. A line quality estimating portion estimates the quality of the line by comparing the data obtained by the error-correction encoding processing with the demodulated data before decoding and an output controller stops outputting the received signal to the external terminal when the line quality is worse than the reference quality.

Receiving apparatus and method of outputting received signal in

An enciphered communication system is provided which has a plurality of cipher keys selectively used for enciphering data, wherein even when a cipher key number used at a transmitting side is not correctly transmitted to a receiving side, the receiving side can change the cipher key to a correct one. A transmitter has appendant data affixing means for affixing appendant data to information to be enciphered, and a receiver has appendant data detecting means for detecting the appendant data from deciphered data, and cipher key determining means for successively changing the cipher key of the receiver when the appendant data is not accurately detected. Consequently, when the cipher key is changed, for example, the receiving side itself can restore data even if the cipher key number is not correctly transmitted thereto.

Enciphered communication system

A frequency-controlled circuit for automatically detecting a center frequency of a received signal whose frequency is shifted includes a frequency control unit for receiving the input signal and changing the frequency of the received signal into another frequency, a demodulating unit for demodulating a signal outputted from the frequency control unit, an incoming detecting unit for detecting whether a demodulated signal outputted from the demodulating unit is proper or improper and a level detecting unit for dividing a frequency band of the signal, obtained in the frequency control unit by adding a receive frequency band of the received signal to the center frequency of the received signal or subtracting the center frequency thereof from the receive frequency band thereof, into a plurality of narrower frequency bands and detecting respective power values of the divided frequency bands. A center-frequency determining unit detects the maximum value from the power values detected by the level detecting unit and outputs information about the divided frequency band having the detected maximum power value. A sweep/de-sweep control unit is provided, which allows the frequency control unit to sweep the received signal at a frequency bandwidth corresponding to the information about the divided frequency bands.

Frequency-controlled circuit

The present invention provides a packet re-transmitting system for a slotted-ALOHA type satellite communication system wherein communications are effected between a central office and a large number of local offices by way of a communications satellite and which decreases a packet re-transmitting time remarkably. The central office transmits a frame synchronizing signal, manages a reception slot number in a predetermined phase relationship with the frame synchronizing signal, detects a condition of a reception signal from any of the local offices and sends back a receiving condition signal including a reception slot number and detection information of a receiving condition at the point of time. Each of the local offices manages a transmission slot number in a predetermined phase relationship with a received frame synchronizing signal, compares a transmission slot number at a point of time when a packet was transmitted with a reception slot number in the receiving condition signal and re-transmits, when the transmission slot number corresponds to the reception slot number in the receiving condition signal and detection information of a received condition indicates irregularity, the transmission packet.

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Kawasaki, Japan

Mitsuru Seta