Systems, methods, devices and subassemblies for rapid-acquisition access to high-precision positioning, navigation and/or timing solutions
Position, navigation and/or timing (PNT) solutions may be provided with levels of precision that have previously and conventionally been associated with carrier phase differential GPS (CDGPS) techniques that employ a fixed terrestrial reference station or with GPS PPP techniques that employ fixed terrestrial stations and corrections distribution networks of generally limited terrestrial coverage. Using techniques described herein, high-precision PNT solutions may be provided without resort to a generally proximate, terrestrial ground station having a fixed and precisely known position. Instead, techniques described herein utilize a carrier phase model and measurements from plural satellites (typically 4 or more) wherein at least one is a low earth orbiting (LEO) satellite. For an Iridium LEO solution, particular techniques are described that allow extraction of an Iridium carrier phase observables, notwithstanding TDMA gaps and random phase rotations and biases inherent in the transmitted signals.
1. A method comprising:
receiving at a navigation radio, signals transmitted from a first low earth orbit (LEO) satellite and computing therefrom first carrier phase measurements spanning first and second time epochs during a single overhead pass of the first LEO satellite;
receiving at the navigation radio, signals transmitted from at least three additional satellites and computing therefrom respective carrier phase measurements including at least respective second, third and fourth carrier phase measurements; and
computationally estimating parameters, including at least receiver position and time parameters, of a system of equations that model carrier phase for signals transmitted from the first LEO satellite at the first and second successive time epochs and for the at least three additional satellites,
wherein the computing of carrier phase measurements spanning first and second time epochs during a single overhead pass of the first LEO satellite includes:
using motion constraints to patch temporal gaps in the received signals transmitted from the first LEO satellite; and
statistically estimating to substantially eliminate from the computed carrier phase measurements otherwise random phase rotations in the received signals transmitted from the first LEO satellite.
2. The method of claim 1 ,
wherein none of the first, second, third or fourth carrier phase measurements used in the estimation or receiver position and time parameters is differenced from carrier phase measured at a fixed terrestrial reference station.
3. The method of claim 1 ,
wherein time elapsed between the first and second time epochs provides, from perspective of the receiver, at least about 20 degrees of angular travel by the first LEO satellite along the single overhead pass.
4. The method of claim 1 ,
wherein the at least three additional satellites are part of a medium earth orbit (MEO) constellation.