Satellite communications system with random multiple access and time slot reservation

• US 4,736,371 A
• Filed: 12/29/1986
• Issued: 04/05/1988
• Est. Priority Date: 12/30/1985
• Status: Expired due to Term

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Fujii, Akira, Tejima, Shunichiro
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): Chin, Wellington
• Application Number:
  US06/947,097
• Time in Patent Office: 463 Days
• Field of Search: 370/94, 370/95, 370/104, 370/82, 370/83, 370/84, 370/89
• US Class Current: 370/236
• CPC Class Codes: H04B 7/2123 Variable assignment, e.g. demand assignment
• CPC Class Codes: H04W 28/06 Optimizing the usage of the radio link, e.g. header compression, information sizing , discarding information system modifying transmission characteristic according to link quality by modifying frame length H04L1/0007; dynamic adaptation of the packet size for flow control or congestion control H04L47/365
• CPC Class Codes: H04W 28/26 Resource reservation
• CPC Class Codes: H04W 72/20 Control channels or signalling for resource management
• CPC Class Codes: H04W 74/02 Hybrid access
• CPC Class Codes: H04W 74/04 Scheduled access hybrid access H04W74/02
• CPC Class Codes: H04W 74/08 Non-scheduled access, e.g. ALOHA hybrid access H04W74/02
• CPC Class Codes: H04W 84/06 Airborne or Satellite Networks space-based or airborne stations H04B7/185

Abstract

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.

Claims

1. A multiple access data communication system having a communication channel for interconnecting a central station and a plurality of remote stations, wherein each of said remote stations transmits a message signal on said channel to said central station which broadcasts a return message signal to said remote stations, said communication channel being divided into frames each having a predetermined number of time slots of equal length,

wherein said central station comprises:

first means for broadcasting a reservation status signal indicating reserved status of said time slots at frame intervals and a time-slot assignment signal indicating a certain of said time slots to be assigned to one of said remote stations in response to a reservation request signal transmitted therefrom;

wherein each of said remote stations comprises;

second means for discriminating a message signal having a length shorter than a time slot length as a single packet having the same length as each time slot and dividing a message signal having a length longer than the time slot length into a series of packets of the time slot length; and

third means for detecting an idle time slot from said time slots in response to said reservation status signal when said message signal is shorter than the time slot length and inserting said single packet to said detected idle time slot and for transmitting said reservation request signal indicating the number of time slots to be reserved for the packets in said series when said message signal is longer than the time slot length and inserting the packets of said series to the time slots indicated by said time-slot assignment signal.

2. A multiple access data communication system as claimed in claim 1, wherein said third means comprises means for inserting a foremost one of said series of packets and said reservation request signal to said detected idle time slot and inserting the remainder of said series of packets to the time slots indicated by said time-slot assignment singal.

3. A multiple access data communication system as claimed in claim 1, wherein said first means further comprises means for broadcasting a negative acknowledgement signal when there is an error in a received single packet, and said third means further comprises means for randomly selecting an idle time slot from said time slots in response to said reservation status signal when said negative acknowledgement is broadcast and inserting a replica of a previously transmitted packet to the randomly selected time slot.

4. A multiple access data communication system as claimed in claim 1, wherein said first means further comprises:

means for detecting a traffic volume of packets received by the central station exceeding a predetermined level and broadcasting a traffic overflow signal in response to the detection of said exceeding traffic volume,

wherein said second means further comprises;

means for causing the length of each time slot to be decreased in response to said traffic overflow signal.

5. A multiple access data communication system as claimed in claim 1, wherein each of said remote stations further comprises:

means for detecting a traffic volume of said single packets exceeding a predetermined level, causing said reservation request signal to be transmitted in response to the detection of said exceeding traffic volume and inserting said single packet and said series of packets to the time slots indicated by said time-slot assignment signal which is broadcast in response to the last-mentioned reservation request signal.

6. A multiple access data communication system as claimed in claim 1, wherein said first means further comprises means for broadcasting a negative acknowledgement signal when there is an error in a received single packet, and wherein said third means comprises means for inserting said single packet and said series of packets to the time slots indicated by said time-slot assignment signal in response to said negative acknowledgement signal.

7. A multiple access data communication system as claimed in claim 1, further comprising a satellite transponder through which said communication channel is established between said central station and said plurality of remote stations.

8. A multiple access data communication system having a communication channel for interconnecting a plurality of stations, said channel being divided into frames each having a predetermined number of time slots of equal length, comprising:

first means for broadcasting a reservation status signal indicating reserved status of said time slots at frame intervals and a time-slot assignment signal indicating a certain of said time slots to be assigned to one of said stations in response to a reservation request signal transmitted therefrom;

second means for discriminating a message signal shorter than the time slot length as a single packet having a time slot length and dividing a message signal longer than the time slot length into a series of packets of the time slot length; and

third means for detecting an idle time slot from said channel in response to said reservation status signal when said message signal is shorter than the time slot length and inserting said single packet to said detected idle time slot and for transmitting said reservation request signal indicating the number of time slots to be reserved for the packets in said series when said message signal is longer than the time slot length and inserting the packets of said series to the time slots indicated by said time-slot assignment signal.

9. A multiple access data communication system as claimed in claim 8, wherein said third means comprises means for inserting a foremost one of said series of packets and said reservation request signal to said detected idle time slot and inserting the remainder of said series of packets to the time slots indicated by said time-slot assignment singal.

10. A multiple access data communication system as claimed in claim 8, wherein said first means further comprises means for broadcasting a negative acknowledgement signal when there is an error in a received single packet, and said third means further comprises means for randomly selecting an idle time slot from said channel in response to said reservation status signal when said negative acknowledgement is broadcast and inserting a replica of a previously transmitted packet to the randomly selected time slot.

11. A multiple access data communication system as claimed in claim 8, wherein said first means further comprises:

means for detecting a total traffic volume of packets in said system exceeding a predetermined level and broadcasting a traffic overflow signal in response to the detection of said exceeding traffic volume,

wherein said second means further comprises;

means for causing the length of each time slot to be decreased in response to said traffic overflow signal.

12. A multiple access data communication system as claimed in claim 8, further comprising:

means for detecting a traffic volume of said single packets exceeding a predetermined level, causing said reservation request signal to be transmitted in response to the detection of said exceeding traffic volume and inserting said single packet and said series of packets to the time slots indicated by said time-slot assignment signal which is broadcast in response to the last-mentioned reservation request signal.

13. A multiple access data communication system as claimed in claim 8, wherein said first means further comprises means for broadcasting a negative acknowledgement signal when there is an error in a received single packet, and wherein said third means comprises means for inserting said single packet and said series of packets to the time slots indicated by said time-slot assignment signal in response to said negative acknowledgement signal.

14. A multiple access data communication system as claimed in claim 8, further comprising a satellite transponder through which said communication channel is established between said stations.

15. A method for assigning time slots in a multiple access data communication system having a communication channel for transmitting a message signal from each of a plurality of remote stations to a central station which in turn broadcasts a return message signal to said remote stations, said communication channel being divided into frames each having a predetermined number of time slots of equal length, the method comprising the steps of:

(a) broadcasting from said central station to said remote stations a reservation status signal indicating reserved status of said time slots at frame intervals and a time-slot assignment signal indicating a certain of said time slots to be assigned to a remote station in response to a reservation request signal transmitted therefrom;

(b) discriminating a message signal as a single packet having the same length as each of said time slots when the message signal is smaller than the time slot length;

(c) dividing the message signal into a series of packets of the time slot length when the message signal has a length greater than the time slot length;

(d) detecting an idle time slot from said time slots in response to said reservation status signal when said message signal is smaller than the time slot length and inserting said single packet to said idle time slot; and

(e) transmitting said reservation request signal indicating the number of time slots required for said series of packets when said message signal is longer than the time slot length and inserting said plurality of packets to the time slots indicated by said time-slot assignment signal.

16. A method for assigning time slots as claimed in claim 15, wherein the step (e) comprises inserting a foremost one of said series of packets and said reservation request signal to said detected idle time slot and inserting the remainder of said series of packets to the time slots indicated by the time-slot assignment signal which is received after the transmission of the last-mentioned reservation request signal.

17. A method for assigning time slots as claimed in claim 15, further comprising the steps of detecting a traffic volume of packets received by the central station exceeding a predetermined level, broadcasting a traffic overflow signal from the central station in response to the detection of said exceeding traffic volume, and causing the length of each time slot in said remote stations to be decreased in response to said traffic overflow signal.

18. A method for assigning time slots as claimed in claim 15, further comprising the steps of detecting a traffic volume of said single packets in each remote station exceeding a predetermined level, causing said reservation request signal to be transmitted in response to the detection of said exceeding traffic volume, and inserting said single packet and said series of packets to the time slots indicated by said time-slot assignment signal which is broadcast in response to the last-mentioned reservation request signal.

19. A method for assigning time slots as claimed in claim 15, further comprising the steps of broadcasting a negative acknowledgement signal from the central station when there is an error in a received single packet and inserting said single packet and said series of packets to the time slots indicated by said time-slot assignment signal in response to said negative acknowledgement signal.