Pulse or digital communications – Repeaters – Testing
Patent
1997-07-28
2000-01-11
Chin, Stephen
Pulse or digital communications
Repeaters
Testing
375206, 375208, 342120, 342357, H04B 1500
Patent
active
060144041
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Field of the Invention
The present invention relates to a procedure for the independent reduction of acquisition thresholds and tracking of spread spectrum codes received in orbit.
2. State of the Prior Art
The invention combines three basic elements:
Each of these elements will be considered below.
The receiver may be any type of satellite-mounted equipment capable of receiving spread spectrum signals (see references [1], [2], [5]). Said signals may be transmitted by other orbiting satellites or from terrestrial transmitters. The receivers may, for example, be of any of the following types:
The GPS and GLONASS satellite constellations are described in references [3] and [4] respectively.
GNSS1 designates the geostationary equipment complementing GPS and/or GLONASS using the navigation packages of the INMARSAT 3 satellites. GNSS2 designates the future civil constellation of navigation satellites.
DORIS NG designates a planned global radionavigation and spatial radiolocalization system, based particularly on the use of spread spectrum signals transmitted by terrestrial beacons and received by orbiting satellites.
The orbitography filter is a digital processing system located in the receiver, for example. It uses raw measurements taken by receivers, i.e. pseudodistance and pseudovelocity measurements relative to ground-based or orbiting spread spectrum signal transmitters. These measurements are processed to give independently determined parameters for the orbit and/or the position and velocity of the carrier satellite. Definitions of these measurements are given in reference [5]. The filter may be one of the following types that are given as examples:
This filter is also capable of determining the following parameters: transmitter No. i. receiver clock, where a "dot"above a variable signifies the driviative of the variable with respect to time.
The clock can therefore estimate pseudodistances PD.sub.i and pseudovelocities PV.sub.i.
The given magnitudes can be estimated even if the signals transmitted by transmitter No. i are not processed by the receiver and its associated navigation filter provided the position, velocity and clock coefficients of said transmitter can be estimated or established.
The orbital navigator estimates these pseudodistances and pseudovelocities to accuracies of .delta.PD and .delta.PV.
The orbital navigator can receive remote commands describing maneuvers of the carrier satellite. These maneuvers can be described using the parameters .DELTA.Vx(t0), .DELTA.Vy(t0) and .DELTA.Vz(t0) where .DELTA.V.sub.i represents the components of the velocity pulse at date t0.
Maneuvers are described with an accuracy noted as .delta.Vx, .delta.Vy, .delta.Vz for the three axes. The overall accuracy of the description of the maneuver is .delta.v where ##EQU1##
The technique of reducing the threshold using a fine radial velocity (or radial pseudovelocity) aid applies where receivers are fitted with one or more phase loops coupled to one or more code loops. It is assumed that said loops use digital technology.
When a signal is received with a signal-to-noise (C/NO) ratio lower than the usual reception threshold in assisted acquisition mode the carrier signal loop is open and the digitally-controlled oscillator (OCN) is driven by an external radial velocity (or pseudovelocity) prediction.
Typical reception in assisted acquisition mode is illustrated in reference [1].
This velocity prediction must be fine and must be provided by a sensor other than the receiver. Typically said sensor may be an inertial unit, for example.
This type of technology is normally used for tracking low equivalent C/NO ratio GPS signals received by military GPS receivers (C/A and P code) embarked on fighter aircraft fitted with inertial units. This technique is described as being "code only" since only the pseudo-random code is tracked down to very low thresholds.
SUMMARY OF THE INVENTION
The present invention relates to a procedure for independently reducing acquisition thresholds and tracking spread spectrum c
REFERENCES:
patent: 4806935 (1989-02-01), Fosket et al.
patent: 5101416 (1992-03-01), Fenton et al.
patent: 5760738 (1998-06-01), Kawano
Centre National d'Etudes Spatiales
Chin Stephen
Liu Shuwang
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