Satellite communication system

• US 5,430,732 A
• Filed: 03/14/1994
• Issued: 07/04/1995
• Est. Priority Date: 03/18/1992
• Status: Expired due to Term

• Current Assignee: NEC Corporation
• Original Assignee: NEC USA (NEC Corporation)
• Inventors: Sengupta, Bhaskar, Lee, Duan-Shin
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): Nguyen, Chau T.
• Application Number:
  US08/213,379
• Time in Patent Office: 477 Days
• Field of Search: 370/85.2, 370/85.8, 370/95.1-95.3, 370/104.1, 370/110.1, 370/94.1, 370/94.2, 340/825.6-825.07, 340/825.08, 340/825.54
• US Class Current: 370/319
• CPC Class Codes: H04B 7/18528 Satellite systems for providing two-way communications service to a network of fixed stations, i.e. fixed satellite service or very small aperture terminal [VSAT] system

Abstract

A satellite communication system increases its efficiency by using adaptive pipeline polling as the control protocol. In this protocol, the earth stations are separated into active and inactive sets and a first number of slots (salary) is assigned to each active station. Additionally, periodically active stations are queried as to the length of their queues and assigned salary slots not needed by any active station are reallofted to stations with queues that exceed their assigned salary in proportion to the size of such excess. A contention period is included outside of the normal salary and bonus periods during which stations in the inactive are allowed to contend to be included in the active set.

Claims

1. In a satellite communication system that includes a plurality of earth stations that includes an active set with a queue of information to transmit and an inactive set with no queue of information to transmit and a satellite a control system for controlling cyclically the access of individual earth stations to the satellite for permitting the earth stations with information to transmit to transmit such information in turn, comprising

means for cyclically querying each individual station in the active set for answers as to the length of its queue of packets awaiting transmission to the satellite,

means based on the answers to the queries for calculating both a salary to be allotted in the cycle to each station in the active set and the total number of slots not needed in such cycle by the active stations because some of such stations have a salary that exceeds their queue, where the salary is the number of slots available for transmission in the cycle divided by the number of stations in the active set, and for apportioning among stations in the active set with queues in excess of their salary said total number of slots as bonuses,

means for allowing in each cycle each station in the active set in turn first to transmit for the number of time slots that comprises its salary to the extent needed and thereafter for allowing each station in the active set in turn to transmit any bonus, and

means operative periodically for allowing each station in the inactive set, after it has acquired a queue, to participate in a contention process by transmitting to the satellite a request for transfer to the active set and to transfer successful stations into the active set in the succeeding cycle.

2. A satellite communication system that includes a plurality of earth stations, a satellite and a control system for controlling access to the satellite by the earth stations for communication between one another, the control system comprising

means for querying each earth station for answers as to the length of its queue of packets awaiting transmission, whereafter each earth station is initially assigned either to an active set of stations having a queue of packets awaiting transmission or to an inactive set of stations not having such a queue, and only the stations in the active set are queried in subsequent cycles,

means using said answers for determining both the number of slots to be allotted in the next cycle to each station in the active set as salary, wherein the salary is the number of slots available for the transmission in the cycle divided by the number of stations in the active set, and also the total number of slots allotted as salary that will not be needed by the stations of the active set whose queues are less than their salaries,

means for apportioning such unneeded slots as bonuses between stations in the active set that have queues longer than their salary in proportion to the excess,

means for allowing each station in the active set to transmit in turn its queue up to length of its salary,

means for thereafter allowing each station awarded a bonus to transmit in turn its bonus, and

means for permitting periodically each station in the inactive set that has acquired a queue of packets to contend with other such stations for transfer to the active set and for transferring successful stations to the active set.

3. The satellite communication system of claim 2 in which the control system further comprises means for reclassifying into the inactive set a station in the active set that no longer has a queue to transmit.

4. For use in a satellite transmission system including a plurality of earth stations and a satellite, a process for controlling cyclic access by the earth stations to the satellite for transmission that includes the steps of

querying initially each earth station in turn as to the length of its queue of packets and classifying each earth station either as active if it has a queue to transmit or inactive if it has no queue to transmit,

determining for the next cycle a basic allotment of slots in the satellite for each active station by dividing the slots available for transmission in the cycle by the number of stations in the active set,

determining for the cycle an extra allotment of slots in the satellite for each active station whose basic allotment is less than its queue by dividing among the stations with queues longer than their basic allotment the number of slots that had been allotted as basic allotment to active stations but that are not needed because some stations had queues less than their basic allotment.

allowing each active station access in turn to the satellite for transmission for as many slots of its basic allotment as it has packets in its queue,

allowing thereafter each active station with an extra allotment access in turn to the satellite for transmission for the length of its extra allotment,

periodically allowing stations that had been inactive but had now acquired a queue to contend for classification in the active set, and reclassifying any that succeed as in the active set, and

reclassifying in the inactive set a station that had been in the active set after it no longer has a queue to transmit.

5. In a satellite communication system, a process for allocating cyclically time slots in the satellite to earth stations that have been classified as active with queues of packets to be supplied to the satellite for transmission to other earth stations that comprises the steps of

querying each active station as to the size of its queue,

dividing the number of time slots available in one cycle of transmission by the number of active stations to reach a salary number,

calculating the total number of time slots that will be unused by those active stations whose salary number is larger than its queue and dividing this total number as a bonus among the active stations with queues in excess of their salary number in proportion to such excesses,

allowing each station in the active set access in turn to the satellite for time slots equal to the lesser of its queue or its salary number, and then

allowing each station in the active set with a queue in excess of its salary number access in turn to the satellite for time slots equal to its bonus.