TDMA satellite communications system with guard band obviating ongoing propagation delay calculation

• US 3,922,496 A
• Filed: 02/11/1974
• Issued: 11/25/1975
• Est. Priority Date: 02/11/1974
• Status: Expired due to Term

• Current Assignee: Hughes Network Systems Incorporated (Echostar Corporation)
• Original Assignee: Andrew M. Walker, Andrew M. Werth, John M. Husted, Ova Gene Gabbard, Pradman P. Kaul
• Inventors: Gabbard, Ova Gene, Kaul, Pradman P., Werth, Andrew M., Walker, Andrew M., Husted, John M.
• Primary Examiner(s): Stewart, David L.
• Application Number:
  US05/441,710
• Time in Patent Office: 652 Days
• Field of Search: 325/4,58 179/15AL,15BS,15BA 178/69.5R
• US Class Current: 370/324
• CPC Class Codes: H04B 7/2126 using a reference station

Abstract

A satellite communications system in which messages from a plurality of stations are received at a synchronous satellite in time multiplex without overlapping. The system is so arranged that the apparatus to insure absence of time overlap in received messages at the satellite is relatively simple compared with the prior art closed-loop synchronizing systems. In particular the guard time is controlled to be at least equal to the double hop propagation delay variation eliminating the need for accurate measurement of propagation delay. Furthermore, as a result of the absence of critical propagation delay measurement, the acquisition process does not require special purpose apparatus.

Claims

1. In a time multiplex communication system wherein a plurality of stations with a propagation delay variation Epsilon transmit in a TDMA mode to a satellite, a method ensuring non-overlapping reception at said satellite without measuring actual propagation delay comprising the steps of:

a. transmitting to each of said stations a reference b. transmitting from each station that has information to transmit in a time slot beginning a predetermined time subsequent to receipt of said marker, said predetermined time different for each of said stations, c. controlling said transmissions to last for a predetermined time less than the duration of said time slot so that a guard time G is provided which is at least equal to twice said propagation delay variation Epsilon .

2. The method of claim 1, wherein said transmissions are controlled to have a duration equal to or greater than said guard time G.

3. The method of claim 1 wherein at each said station said guard time G precedes said transmission.

4. The method of claim 1 wherein at each said station said guard time G succeeds said transmission.

5. The method of claim 1 wherein said time slot has a duration T, said transmission has a duration tB and said guard time G >

or = 2 epsilon such that T (tB+G) and to tB >

or = G.

6. A TDMA communication system for transmitting a plurality of burst mode messages from a plurality of stations for non-overlapping reception at a satellite transponder which eliminates the necessity for measuring propagation delays at each of said stations comprising:

marker reception means at each said station for detecting receipt of a time reference markeR, the time of receipt of said marker varying as the distance from each said station to said satellite, first and second delay means at each station, said first delay means settable at each station to a preassigned time slot of predetermined duration for each said station'"'"''"'"'s transmission, transmitter means at each said station initiated at the expiration of said first delay, said second delay means at each station for controlling the termination of said transmitter means, said second delay means terminating said transmitter means 2 epsilon prior to termination of said time slot duration at said station where epsilon is the maximum propagation delay variation among all said stations.

7. The system of claim 6 in which said predetermined duration is equal for all stations.

8. The system of claim 7 in which said predetermined duration is equal for all stations and the difference between said predetermined duration and the quantity 2 epsilon is at least equal to 2 epsilon .

9. The system in claim 6 in which said first delay means comprises a counting means operated at a predetermined rate and decoding means, responsive to the condition of said counting means for producing a signal after said counting means has counted a time interval corresponding to a first delay, said transmitter means responsive to said signal produced by decoding means.

10. The apparatus of claim 6 in which said second delay means comprises a counting means operated at a predetermined rate and decoding means, responsive to the condition of said counting means for producing a signal after said counting means has counted a time interval corresponding to a second delay, said transmitter means responsive to said signal produced by said decoding means.

11. In the system of claim 6 in which said first delay means comprises a first counting means operated at a predetermined rate and a first decoding means, responsive to the condition of said counting means for producing a first signal after said counting means has counted a time interval corresponding to a first delay, said second delay means comprising a second counting means operated at a predetermined rate and second decoding means, responsive to the condition of said second counting means for producing a second signal after said second counting means has counted a time interval corresponding to a second delay, said transmitter means responsive to signals produced by said first and second decoding means.

12. In a time multiplex communication system in which a plurality of stations may transmit information messages for reception at a satellite, said information message from each station being transmitted in a TDMA burst mode and wherein transmissions to and from said satellite are subject to propagations delays equal to a minimum propagation delay plus a variable propagation delay d in the range o <

or = d <

or = epsilon , each of said stations transmitting in a preassigned time slot of duration T in a cyclical time frame, each said time slot beginning a predetermined time after receipt of a marker, apparatus for ensuring non-overlapping reception at said satellite of said message without requiring actual measurement of progagation delay comprising, a. means for detecting receipt of said marker, b. first delay means responsive to said means for detecting for producing a first signal, c. second delay means responsive to said first signal for producing a second signal, a predetermined time after receipt of first signal, said predetermined time being less than or equal to T-2 epsilon , d. transmission means for information transmissions, e. control means responsive to said first and second signals for initiating said transmission means in response to said first signal and for inhibiting said transmission means in response to said second signal.

13. The apparatus of claim 12 wherein said both first and second delay means includes a counter, each of whiCh operates at a predetermined rate.

14. The apparatus of claim 13 in which said control means includes bi-stable circuit means for initiating said transmission.

15. In a time multiplex communication system in which a plurality of stations may transmit information messages for reception at a satellite, said information messages from each station being transmitted in a TDMA burst mode and wherein transmissions to and from said satellite are subject to propagation delays equal to a minimum propagation delay plus a variable propagation delay d in the range o <

or = d23 epsilon , each of said stations transmitting in a preassigned time slot of duration T in a cylical time frame, apparatus for ensuring non-overlapping reception at said satellite of messages from the plurality of stations without requiring measurement of actual propagation delay comprising, a. first means at each of a plurality of said stations for determining the initiation of a time slot at each of said plurality of stations, and producing a first signal simultaneous therewith, b. second means at each of a plurality of said stations operated in response to said first signal for producing a second signal at a time no greater than T-2 epsilon after production of said first signal, and control means for initiating transmission from each said station of said plurality of stations in response to said first signal and for terminating transmissions from each of said plurality of stations in response to said second signal.