Method for rapid signal acquisition in a satellite communications system
First Claim
1. A method for a radio to acquire a communication signal having a predetermined signal carrier frequency, which is received from at least one communications satellite or a constellation of satellites, the radio having a clock and an ephemeris of the at least one satellite, comprising the steps of:
- determining a first spatial position for the radio at a first point in time as indicated by the clock;
saving the first spatial position with an associated first time;
determining, at a current time, an amount of time that has passed since the first time;
estimating a second spatial position said radio could move to from said first spatial position during said amount of time that has passed since the first spatial position was determined;
searching a frequency band for the communication signal determined by .the estimated second spatial position, current time, and ephemeris data, within a frequency bandwidth based on said amount of time that has passed.
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Accused Products
Abstract
The signal acquisition process of the present invention enables a radio to rapidly acquire a pilot signal from a satellite after the radio has been out of contact with the satellite for a length of time. The radio first acquires a satellite pilot signal and determines its position in relation to the earth. If the radio is now shut off or loses track of the pilot signal for some other reason, the radio keeps track of the length of time that it has been out of contact with the satellite. This length of time enables the radio to estimate the extent of possible position changes and, therefore, which satellites might be in view and their relative positions to the radio. This allows the radio to make assumptions about variables such as the Doppler shift of the signal that reduces the uncertainty inherent in the acquisition process and the size of the window that must be searched.
42 Citations
20 Claims
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1. A method for a radio to acquire a communication signal having a predetermined signal carrier frequency, which is received from at least one communications satellite or a constellation of satellites, the radio having a clock and an ephemeris of the at least one satellite, comprising the steps of:
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determining a first spatial position for the radio at a first point in time as indicated by the clock; saving the first spatial position with an associated first time; determining, at a current time, an amount of time that has passed since the first time; estimating a second spatial position said radio could move to from said first spatial position during said amount of time that has passed since the first spatial position was determined; searching a frequency band for the communication signal determined by .the estimated second spatial position, current time, and ephemeris data, within a frequency bandwidth based on said amount of time that has passed. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A method for a radio to acquire a spread spectrum communication signal having a predetermined PN spreading code applied, which is received from at least one communications satellite of a constellation of satellites, the radio having a clock and an ephemeris of the at least one satellite, comprising the steps of:
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determining a first spatial position for the radio at a first point in time as indicated by the clock; saving the first spatial position with an associated first time; determining, at a current time, an amount of time that has passed since the first time; estimating a second spatial position said radio could move to from said first spatial position during said amount of time that has passed since the first spatial position was determined; searching a PN code phase space for the predetermined PN spreading code, said phase space being determined by the estimated second spatial position, current time, and ephemeris data, within a phase bandwidth based on said amount of time that has passed. - View Dependent Claims (14, 15, 16, 17, 18, 19)
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20. A method for a code division multiple access radiotelephone to rapidly acquire a pilot signal, having a frequency, from a first satellite of a constellation of satellites, the radiotelephone having memory, a clock, and an ephemeris of each satellite of the constellation of satellites stored in the memory, each satellite communicating with a plurality of ground base stations, each ground base station having a clock, a first ground base station transmitting a clock signal from the clock to the first satellite, the method comprising the steps of:
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synchronizing the radiotelephone clock to the clock signal; determining a spatial position for the radiotelephone, the position determined at a first time as indicated by the radiotelephone clock; storing the spatial position and the first time in memory; determining a second time from the radiotelephone clock; estimating a second spatial position in response to a difference between the first time and the second time, the second spatial position being at an increasing distance from the first spatial position as the difference between the first and second times increases up to a predetermined maximum difference; and searching a predetermined frequency band for the frequency in response to the second spatial position.
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Specification