Nec Corporation

Nec Solution Innovators, Ltd.

Yukari Kou

Hirofumi Tanaka

Natsuko Tamura

Display screen or portion thereof with graphical user interface

In a channel access system wherein a common communication channel is divided into frames on each having a predetermined number of time slots which are classified into random access time slots and reservation time slots, a central station including a data selector section (31) carrying out a reservation request for time slots for a destined remote station. A central reservation slot control section (32) generates a central slot assignment table including reservation time slots exclusively for each of the remote stations. A reservation information generating section (33) generates reservation assignment information indicative of the reservation time slots. Each remote station comprises a reservation control section (50) for setting the number of necessary reservation time slots in accordance with conditions of occurrence and storing of remote transmission data thereof. A remote reservation slot control section (53) generates a remote slot assignment table on the basis of the reservation assignment information. A transmission control section (51) transmits, on the basis of the number of the reservation time slots, the remote transmission data with reservation request information suitably added to the remote transmission data on a selected one of the reservation time slots exclusive therefor or the random access time slots.

Satellite communications system carrying out reservation of necessary

In a satellite communications system comprising a central station and remote stations, each remote station sends a packet containing user data on a randomly determined slot of a forward satellite channel. If the packet is received by the central station, it sends traffic data and an acknowledgment signal. If the absence of acknowledgment signal is detected by the remote station, it generates a random number in a range determined by the traffic data and increments a count value indicating a number of instances where the acknowledgment signal is not returned. The packet containing the count value is retransmitted on a time slot determined by the random number. If an acknowledgment signal is received, the count value is reset to zero. The central station, on receiving a packet, generates an acknowledgment signal, and derives a sum of the total of packets received during a predetermined interval and the total of count values contained in such packets. The traffic data is derived from the sum and transmitted with the acknowledgment signal and host data on a backward satellite channel.

Random access satellite communication system using random numbers

In a satellite communication network, a reference station simultaneously announces a reference time of a reference clock once in a predetermined duration of time to all terrestrial stations of the network. In each terrestrial station which comprises a local clock, a packet forming arrangement, a data extracting arrangement for extracting a local time datum from a packet received from a different terrestrial station, and a calculation unit for calculating a propagation delay time between the different terrestrial station and the terrestrial station under consideration by subtracting from the local time datum a current time indicated by the local clock when the local time datum is extracted, a time setting arrangement sets the current time at a sum of the local time datum and a constant preassigned to the terrestrial station in question. The constant is preliminarily decided by calculating a distance on the earth between the terrestrial station and the reference station based on their longitudes and latitudes, calculating a physical length of a communication link by using the distance, and calculating a time necessary for electromagnetic waves to travel the physical length.

Synchronization of clocks in a satellite communication network by

In a random access communication system comprising a central station and user stations, each user station transmits a packet to the central station on a randomly selected timeslot of a time-division multiple access channel and defines a plurality of 'minislots' within the selected timeslot and transmits a burst on one of the minislots. The central station monitors the defined monislots to detect the burst transmission, and assigns as many timeslots as required if more than one burst transmission is detected within a timeslot interval. A slot assignment signal is sent from the central station to the user stations containing a negative acknowledgment of the transmitted packet. The user station from which the packet was transmitted is responsive to the negative acknowledgment to select one of the assigned timeslots and retransmit to the central station a copy of the packet on the selected assigned timeslot.

Random access data communication system with slot assignment capability

A multiple access satellite communication system in which a plurality of mini-earth stations each transmit data packets to hub earth station via a satellite over an inbound channel, while the hub station transmits to the mini-earth stations in a broadcast mode over outbound channels. Each mini-earth station selectively uses a fixed assignement access method, random access method, and demand assignment access method, depending on the frequency of the transmission from a terminal connected thereto, the amount of transmitted data, and whether or not the transmission from the terminal is periodic. The hub station outputs a reception response signal to the outbound channels by determining whether or not a conflict of data packets or a transmission error has occurred on the inbound channels. Packets for re-transmission are sent out to the inbound channels by the demand assignment access method at all times, with no regard to the access method used at the time of transmission.

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Tokyo, Japan

Yukari Kou