Method and apparatus for approximating propagation delay for use in transmission compensation to orbiting satellites
First Claim
1. A method in a synchronous communication system for approximating a transmit time advance offset for use by a subscriber unit in transmitting information to a first satellite having a plurality of beams, one of which is a current beam projected about said subscriber unit, said information arriving at said first satellite during a receive window, and said transmit time advance offset corresponding to a propagation delay in said current beam between said subscriber unit and said first satellite, said method comprising the steps of:
- when said subscriber unit does not possess a current geolocation position of said subscriber unit, receiving a first transmission from said first satellite, said first transmission in said current beam comprising a first beam identifier and a first beam center defining a first geographical coordinate of an approximated center of said current beam;
determining if said current beam servicing said subscriber unit is a centrally located beam among said plurality of beams of said first satellite;
when said current beam is centrally located among said plurality of beams defining said first beam center as an approximation of a subscriber unit location;
calculating a distance between said first satellite and said subscriber unit, said distance being derived from said subscriber unit location; and
estimating said transmit time advance offset from said distance between said first satellite and said subscriber unit.
4 Assignments
0 Petitions
Accused Products
Abstract
A subscriber unit (30) operates in a synchronous communication system having dynamic nodes such as satellites (12). Satellites (12) employ a strict transmit and receive time window and all transmissions directed to satellites (12) must fall within the receive window to be recognized. In a dynamic communication system where low earth orbit satellites (12) continuously orbit, propagation timing between a satellite (12) and a subscriber unit (30) vary rapidly over a wide range. Subscriber unit (30) must approximate a transmit timing advance for use in inaugurating a transmission to satellite (12). Subscriber unit (30) utilizes a valid geolocation position when available but when a position is unavailable or stale, relies on configuration characteristics of the constellation for generating an initial approximation of propagation delay.
70 Citations
17 Claims
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1. A method in a synchronous communication system for approximating a transmit time advance offset for use by a subscriber unit in transmitting information to a first satellite having a plurality of beams, one of which is a current beam projected about said subscriber unit, said information arriving at said first satellite during a receive window, and said transmit time advance offset corresponding to a propagation delay in said current beam between said subscriber unit and said first satellite, said method comprising the steps of:
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when said subscriber unit does not possess a current geolocation position of said subscriber unit, receiving a first transmission from said first satellite, said first transmission in said current beam comprising a first beam identifier and a first beam center defining a first geographical coordinate of an approximated center of said current beam; determining if said current beam servicing said subscriber unit is a centrally located beam among said plurality of beams of said first satellite; when said current beam is centrally located among said plurality of beams defining said first beam center as an approximation of a subscriber unit location; calculating a distance between said first satellite and said subscriber unit, said distance being derived from said subscriber unit location; and estimating said transmit time advance offset from said distance between said first satellite and said subscriber unit. - View Dependent Claims (2, 3, 4, 5, 6)
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7. In a subscriber unit, a method for approximating a transmit time advance offset for use by said subscriber unit in transmitting information to a first satellite, said first satellite having a receive time window wherein said first satellite recognizing said information transmitted by said subscriber unit and said first satellite projecting a plurality of beams upon the earth, said method comprising the steps of:
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when said subscriber unit does not possess a current geolocation position of said subscriber unit, receiving in a current beam projected about said subscriber unit a first transmission comprising a first beam identifier and a first beam center, said current beam being one of said plurality of beams projected by said first satellite and said first beam center defining a first geographical coordinate of an approximated center of said current beam; when said first beam identifier denotes said current beam as being centrally located among said plurality of beams of said first satellite, defining said first beam center as an approximation of a subscriber unit location; calculating a distance between said first satellite and said subscriber unit, said distance being derived from said subscriber unit location; and estimating said transmit time advance offset from said distance between said first satellite and said subscriber unit. - View Dependent Claims (8, 9, 10, 11, 12)
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13. A subscriber unit for approximating a transmit time advance offset for use by a subscriber unit in transmitting information to a first satellite having a plurality of beams, one of which is a current beam projected about said subscriber unit, said information arriving at said first satellite during a receive window, and said transmit time advance offset corresponding to a propagation delay in said current beam between said subscriber unit and said first satellite, said subscriber unit comprising:
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a transceiver for receiving in said current beam a first transmission comprising a first beam identifier and a first beam center, said current beam being one of a plurality of beams projected by said first satellite and said first beam center defining a first geographical coordinate of an approximated center of said current beam said transceiver further employing said transmit time advance offset for transmitting said information to said first satellite during said receive window; a processor for calculating an approximation of a subscriber unit location, and for estimating said transmit time advance offset from said approximation of said subscriber unit location; and a memory for storing data that serves as instructions to said processor. - View Dependent Claims (14, 15, 16, 17)
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Specification