Nec Corporation

Shunichiro Tejima

Akira Fujii

Takahiro Aoki

A communication system, which includes a central station and a plurality of peripheral stations and as a packet data signal and a speech signal, assigns a speech communication channel by using the packet data communication channel. The speech communication is done over the assigned carrier between one peripheral station and the central station or another peripheral station.

Communication system and devices thereof

In a satellite communication system for carrying out communication between a central station and local stations, each local station includes a receiving apparatus (41) which comprises a converting unit (43) for converting a received radio signal of a received carrier frequency into a converted signal by using a reception carrier signal of a reception carrier frequency and a demodulating unit (44) for demodulating the converted signal into a demodulated signal. Connected to the demodulating unit, a deciding unit (45) decides whether the demodulated signal is normal or abnormal. The deciding unit produces an abnormal signal when the demodulated signal is abnormal. After reception of the abnormal signal, a timer circuit (47) measures a lapsed time to produce a time up signal when the lapsed time is equal to an integral multiple of a predetermined time interval. Responsive to the time up signal, a supplying section (49) alternately supplies first and second carrier signals indicative of first and second memorized frequency signal preliminarily memorized in a memorizing section (48), respectively, one at a time as the reception carrier signal to the converting unit.

Receiving arrangement with a reception carrier frequency alternately

A random access multipoint data communication system comprises a central station and a plurality of remote stations. A multiple access channel is established from the remote stations to the central station and a broadcast channel is established from the central station to the remote stations. The central station generates a timing signal for causing each of the remote stations to define commonly shared time slots on the multiple access channel. Each remote station transmits data on a randomly determined time slot of the multiple access channel. The central station periodically and sequentially interrogates the remote stations to return an acknowledgment and processes the returned acknowledgements to determine the presence of a malfunctioning remote station. To avoid data collision, the central station specifies an idle time slot on which the interrogated remote station is requested to send the acknowledgment.

Multipoint data communication with a supervisory system for detecting a

In a TDMA satellite communication network comprising control and local earth stations communicable with one another through a satellite, a time difference between transmission and reception of a reference burst is measured at the control earth station to detect a time deviation (Tb) from a standard offset time (SO) predetermined for the control earth station. In the control earth station, the time deviation is doubled and added to the standard offset time to provide a reception time instant (t.sub.4) for the local earth station. Thus, the reception time instant is varied and predicted in the control earth station with reference to the time deviation detected in the control earth station. The local earth station determines a transmission time instant (t.sub.2 or t.sub.2 ') by delaying a reception timing signal by a predetermined time interval (Ta).

Synchronization control capable of establishing synchronization without

A multiple access data communication system is disclosed wherein a communication channel is shared by a plurality of stations. The channel is divided into frames each being partitioned into time slots smaller in number than the number of stations of the system. A reservation status signal is constantly broadcast at frame intervals from a central station to all remote stations to indicate reserved status of the time slots. When a transmission request is made in a remote station, it discriminates a message signal shorter than the time slot length as a single packet having a time slot length and detects an idle time slot from the channel using the reservation status signal. If the message signal is longer than the time slot length, the station divides it into a series of packets of the time slot length and transmits a reservation request to the central station to receive from it a time-slot assignment signal and inserts the long-message packets to time slots specified by the time-slot assignment signal.

Satellite communications system with random multiple access and time

In order to detect bursts transmitted in a manner that each burst is located within an allocated time slot within each consecutive frame, the bursts are labelled in accordance with a burst time plan signal to produce a burst discriminating signal. Thereafter, information of window position and burst condition and window mode, is stored, with respect to each burst, in respective memories using the burst discriminating signal. The stored data are renewed and read out from the memories also using the burst discriminating signal. Further, the burst discriminating signal is further used to change the window mode each predetermined frames.

Arrangement for detecting bursts

A high-speed burst monitoring device for large capacity burst signal processing which constantly monitors receipt conditions of received burst signals in a time division multiplex access (TDMA) communications system, in which each frame comprises several individual burst signals; and, depending upon the result of examining each of the receipt conditions, transmits a control message to a remote station which has transmitted a particular burst signal. Bursts are each allocated to a particular address of high-speed store means with a burst identification number used as address data. Every time a burst signal is received, record data associated with that burst is read out of the high-speed store means, burst condition data is updated by a burst condition signal generated this time, it is determined whether a condition for the generation of a control message is satisfied, and the updated data is stored anew in the high-speed store means as the latest burst condition data. Such a procedure is repeated at a high speed whereby all the receipt condition data are integrated burst by burst to decide whether generation of a control message is needed. In the case of large capacity burst signal processing, a control message transmission request signal may be temporarily stored in a memory buffer if a massage cannot immediately be sent so as to convert the data rate between high-speed data processing sections such as burst condition decision means and low-speed data processing sections such as a message processing section.

Growing community of inventors

Tokyo, Japan

Shunichiro Tejima