EP0411538A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Satellite communications system operating in asynchronous mode for central-to-terminal station transmission
Assignee: NEC Corp
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Filing: 1990-07-30
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Granted: —
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Expires: 2010-07-30
Abstract
Abstract In a satellite communications system, a unique word is transmitted from a central station at frame intervals to the satellite and broadcast to terminal stations. Blocks of data from the central station are composed into packets which are exclusively encrypted, and asynchronously transmitted to the satellite by giving priority to the unique word by interrupting the transmission of packets. A copy of data signals from the central-station data terminals is stored and retransmitted to a terminal station in response to a repeat request signal received therefrom. In each terminal station, the unique word is detected to generate a timing signal in response to which the encrypted packet is deciphered. The deciphered packets are decomposed into blocks of data, and sent to a destination data terminal. If there is an error in the decomposed packets, a repeat request signal is transmitted from the terminal station through a terrestrial link to the central station to cause retransmission of a copy of the stored version of the disrupted packet.
Inventors
- 👤 Mikio C/O Nec Engineering Ltd. Ujiie
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-05 21:13
CPC Classifications
H; H04; H04L; H04L1/00; H04L1/12; H04L1/16; H04L1/18; H04B; H04B7/00; H04B7/14; H04B7/15; H04B7/185; H04B7/18528; H04B7/204; H04B7/212; H04B7/2125; H04L2001/0092; H04L2001/0093
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
239 words
A satellite communications system having a central station serving central-station data terminals for transmitting signals through a one-way satellite channel to a satellite transponder which broadcasts received signals to a plurality of terminal stations each serving terminal-station data terminals, said central station comprising: unique word generator means for generating a unique word at periodic intervals; packet assembler means including means for composing blocks of data from the central-station data terminals into packets each containing address of a terminal-station data terminal and asynchronously supplying the packets to an output terminal, said packet assembler means further including means responsive to the presence of said unique word for interrupting said packet composing means and allowing said unique word to be supplied to said output terminal while said composing means is interrupted; encrypting means connected to said output terminal of the packet assembler means for exclusively encrypting said packets and generating a series of encrypted packets and nonencrypted unique words for transmission to said satellite transponder; and each of said terminal stations comprising: unique word detector means for detecting a unique word from a signal received from said satellite transponder to generate a timing signal; decrypting means for decrypting the encrypted packets in said received signal in response to said timing signal; and packet deassembler means for decomposing the deciphered packets into blocks of data, applying the data blocks to the terminal-station data terminals according to the address contained in the decomposed packets.
Claim 2
Dependent Claim
239 words
A satellite communications system having a central station serving central-station data terminals for transmitting signals through a one-way satellite channel to a satellite transponder which broadcasts received signals to a plurality of terminal stations each serving terminal-station data terminals, said central station comprising: unique word generator means for generating a unique word at periodic intervals; packet assembler means including means for composing blocks of data from the central-station data terminals into packets each containing address of a terminal-station data terminal and asynchronously supplying the packets to an output terminal, said packet assembler means further including means responsive to the presence of said unique word for interrupting said packet composing means and allowing said unique word to be supplied to said output terminal while said composing means is interrupted; encrypting means connected to said output terminal of the packet assembler means for exclusively encrypting said packets and generating a series of encrypted packets and nonencrypted unique words for transmission to said satellite transponder; and each of said terminal stations comprising: unique word detector means for detecting a unique word from a signal received from said satellite transponder to generate a timing signal; decrypting means for decrypting the encrypted packets in said received signal in response to said timing signal; and packet deassembler means for decomposing the deciphered packets into blocks of data, applying the data blocks to the terminal-station data terminals according to the address contained in the decomposed packets.
Claim 3
Dependent Claim
118 words
A satellite communications system as claimed in claim 1, said central station further comprises retransmit means for storing a copy of data blocks from said central-station data terminals and supplying the stored copy to said packet assembler means in response to a repeat request signal, and wherein the packet deassembler means further comprises means for detecting an error in a received packet, each of said terminal stations further including repeat request transmit means for transmitting a said repeat request signal to said central station in response to the detection of said error by said packet deassembler means, wherein said repeat request signal contains a dialing signal and is transmitted via a switched communications network to said central station.
Claim 4
Dependent Claim
82 words
A satellite communications system as claimed in claim 1 or 2, wherein the unique word generator means further generates a second unique word at periodic intervals for disabling said encrypting means during a period of time in which packets not requiring encryption are transmitted to said transponder, and wherein said unique word detector means further detects said second unique word for disabling said decrypting means during a period of time in which said packets not requiring encryption are received from said transponder.
Claim 5
Dependent Claim
46 words
A satellite communications system as claimed in claim 1, 2 or 3, wherein said central station further comprises a forward error correction encoder for exclusively encoding said packets, and wherein each of said terminal stations includes a forward error correction decoder for exclusively decoding said packets.
Claim 6
Dependent Claim
189 words
A communication method for a satellite communications system having a central station serving central-station data terminals for transmitting signals through a one-way satellite channel to a satellite transponder which broadcasts received signals to a plurality of terminal stations each serving terminal-station data terminals, comprising: a) transmitting a unique word at periodic intervals to said satellite transponder, composing blocks of data from the central-station data terminals into packets each containing address of a terminal-station data terminal and asynchronously transmitting the packets to said satellite transponder such that transmission of a packet that coincides with a unique word is interrupted for a period of said unique word; b) exclusively encrypting said packets and transmitting the encrypted packets to said satellite transponder; c) receiving a signal from said satellite transponder by each of said terminal stations and detecting said unique word from the receive signal to generate a timing signal; d) decrypting the packets in said received signal in response to said timing signal; and e) decomposing the deciphered packets into blocks of data, transmitting the data blocks to the terminal-station data terminals according to the address contained in the decomposed packets.
Claim 7
Dependent Claim
189 words
A communication method for a satellite communications system having a central station serving central-station data terminals for transmitting signals through a one-way satellite channel to a satellite transponder which broadcasts received signals to a plurality of terminal stations each serving terminal-station data terminals, comprising: a) transmitting a unique word at periodic intervals to said satellite transponder, composing blocks of data from the central-station data terminals into packets each containing address of a terminal-station data terminal and asynchronously transmitting the packets to said satellite transponder such that transmission of a packet that coincides with a unique word is interrupted for a period of said unique word; b) exclusively encrypting said packets and transmitting the encrypted packets to said satellite transponder; c) receiving a signal from said satellite transponder by each of said terminal stations and detecting said unique word from the receive signal to generate a timing signal; d) decrypting the packets in said received signal in response to said timing signal; and e) decomposing the deciphered packets into blocks of data, transmitting the data blocks to the terminal-station data terminals according to the address contained in the decomposed packets.
Claim 8
Dependent Claim
86 words
A method as claimed in claim 5, further comprising the steps of: storing a copy of data blocks from said central-station data terminals and transmitting the stored copy to said satellite transponder in response to a repeat request signal from said terminal stations; detecting an error in said decomposed packets; generating a dialing signal in response to the detection of said error; and transmitting a said repeat request signal containing said dialing signal to said central station from a terminal station via a switched communications network.
Claim 9
Dependent Claim
91 words
A method as claimed in claim 5 or 6, further comprising: transmitting a second unique word at periodic intervals to said satellite transponder from said central station, and disabling the step (b) for a period of time in which packets not requiring encryption are transmitted to said transponder, detecting said second unique word at each of said terminal stations, and disabling the step (d) in response to the detection of said second unique word for a period of time in which said packets not requiring encryption are received from said transponder.
References Cited (Backward Citations)
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