Multiple access satellite communication system for mini-earth station networks

• US 5,172,375 A
• Filed: 06/25/1990
• Issued: 12/15/1992
• Est. Priority Date: 06/22/1989
• Status: Expired due to Term

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Kou, Yukari
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): SAMUEL, TEMESGHEN
• Application Number:
  US07/543,677
• Time in Patent Office: 904 Days
• Field of Search: 370/95.3, 370/94.1, 370/104.1, 370/95.1, 370/94.2
• US Class Current: 370/322
• CPC Class Codes: H04B 7/212 Time-division multiple access [TDMA]
• CPC Class Codes: H04B 7/2123 Variable assignment, e.g. demand assignment
• CPC Class Codes: H04L 1/16 in which the return channel carries supervisory signals, e.g. repetition request signals
• CPC Class Codes: H04L 1/18 Automatic repetition systems, e.g. Van Duuren systems
• CPC Class Codes: H04L 2001/0093 Point-to-multipoint

Abstract

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.

Claims

1. A multiple access satellite communication system for data transmission by a method which is a combination of a fixed assignment access method and a combined random and demand access method, comprising:

a single hub earth station;

a plurality of mini-earth stations connected to said hub earth station by satellite channels;

said plurality of mini-earth stations each transmitting a data packet to said hub earth station over an inbound channel by time division multiple access;

said hub earth station transmitting identical data to said mini-earth stations over outbound channels;

said plurality of mini-earth stations each accommodating a terminal which generates data to be transmitted in a slot of the inbound channel by a fixed assignment access method, and a terminal generating data to be transmitted in a slot of the inbound channel by a combined demand assignment access and random access method;

said hub earth station comprising;

receiving means for producing packet data by demodulating a signal on the inbound channel, generating an error detection signal packet data by packet data by detecting errors in the packet data, and extracting from the packet data free from errors received data and reservation slot request information which any of said plurality of mini-earth stations may transmit;

means for generating a frame timing signal for the outbound channel;

control means for producing reservation assignment information in response to said reservation slot request information and producing a reception response in response to said error detection signal;

means for multiplexing said reservation assignment information and said reception response with data fed from a host terminal which is connected to said hub earth station; and

means for transmitting said multiplexed data over the outbound channels after modulating said multiplexed data;

said plurality of mini-earth stations each comprising;

receiving means for demodulating a signal on the outbound channel to separate said frame timing signal for the outbound channel, said reservation assignment information, said reception response signal, and the data from the host terminal;

means for generating an in-station frame timing signal exclusive for said mini-earth station in response to said frame timing signal;

slot supervising means for outputting slot assignment information on the basis of said in-station frame timing signal and said reservation assignment information;

a first buffer for temporarily storing data to be transmitted by the demand assignment access method;

a second buffer for temporarily storing data to be transmitted by the random access method;

a third buffer for temporarily storing data to be transmitted by the fixed assignment access method;

access method detecting means for transferring, when data inputted from any of said terminals connected to said mini-earth station is data to be transmitted by the fixed assignment access method, said data to said third buffer and transferring other data to a message length detecting section;

said message length detecting section being for detecting, when a re-transmission mode signal is OFF, a data length of the input data, transferring to said second buffer short data which can be transmitted in one time slot, dividing long data which cannot be transmitted in one slot into a plurality of data portions, transferring a first one of said plurality of data portions to said second buffer, transferring the other data portions to said first buffer, and outputting a first request signal representative of a request for reservation of a necessary number of slots, and transferring, when said re-transmission mode signal is ON, all of said input data to said first buffer and outputting said first request signal with no regard to the data length;

data selecting means for reading, when said re-transmission mode signal is OFF, data out of said first buffer when said slot assignment information is indicative of a demand assignment access slot, data out of said second buffer when said slot assignment information is indicative of a random access slot, and data out of said third buffer when said slot assignment information is indicative of a fixed assignment access slot, and, when said re-transmission mode signal is ON, reading data out of said first and second buffers when said slot assignment information is indicative of a demand assignment access slot and data out of said third buffer when said slot assignment information is indicative of a fixed assignment access slot;

re-transmission control means for storing the data read by said data selecting means, discarding, when said reception response is positive (ACK), the data associated with said ACK response and transferring, when said reception response is negative (NAK), the data associated with said NAK response to said first buffer while outputting a second request signal representative of a request for reservation of a necessary number of slots, turning said re-transmission mode signal ON when a reception response in reply to a packet transmitted in the random access slot is negative, and turning said re-transmission signal OFF when a reception response to re-transmitted data is positive;

reservation request adding means for producing said reservation slot request information in response to said first and second reservation requests and adding said reservation slot request information to an output of said data selecting means; and

means for sending an output of said reservation request adding means to the inbound channel.

2. A system as claimed in claim 1, wherein said re-transmission control means transfers re-transmission data to said third buffer when a reception response to a packet transmitted in the fixed assignment access slot is negative.

3. A multiple access satellite communication system for data transmission by a method which is a combination of a fixed assignment access method and a combined random and demand access method, comprising:

a single hub earth station;

a plurality of mini-earth stations connected to said hub earth station by satellite channels;

said plurality of mini-earth stations each transmitting a data packet to said hub earth station over an inbound channel by time division multiple access;

said hub earth station transmitting data to said mini-earth stations over outbound channels;

said plurality of mini-earth stations each accommodating a terminal which generates data to be transmitted in a slot of the inbound channel by a fixed assignment access method, and a terminal which generates data to be transmitted in a slot of the inbound channel by a combined demand assignment access and random access method;

said hub earth station comprising;

receiving means for receiving packet data on the inbound channel, generating an error detection signal packet data by packet data by detecting errors in the packet data, and extracting from the packet data free from errors received data and reservation slot request information which any of said plurality of mini-earth stations may transmit;

control means for producing reservation assignment information in response to said reservation slot request information and producing a reception response in response to said error detection signal; and

means for transmitting over the outbound channels said reservation assignment information and said reception response, and data fed from a host terminal which is connected to said hub earth station;

said plurality of mini-earth stations each comprising;

receiving means for receiving said reservation assignment information, said reception response, and the data from the host terminal;

slot supervising means for outputting slot assignment information on the basis of said reservation assignment information;

transmitting means for transmitting data by using a slot assigned to said fixed assignment access method to said hub station when the data is to be transmitted by said fixed assignment access method, for transmitting data by using a slot assigned to said random access method to said hub station when the data is to be transmitted by said random access method, and for transmitting data by using a slot assigned to said demand assignment access method and said reservation slot request when the data is to be transmitted by said demand assignment access method; and

re-transmission control means for storing the data which is transmitted to the hub station by said transmitting means, discarding, when said reception response is positive (ACK), the data associated with said ACK response and transferring, when said reception response is negative (NAK), the data associated with said NAK response to said transmitting means as said data to be transmitted by said demand assignment access method.