Method and system for time to first fix (TTFF) reduction of GPS receivers using satellite based augmentation system (SBAS) signal
A Global Positioning System (GPS) receiver, a control method of the GPS receiver, and a GPS system are provided, which are capable of reducing an initial position check time using an SBAS signal transmitted from a SBAS satellite. The control method of a GPS receiver includes receiving an SBAS signal from a SBAS satellite and calculating a satellite clock and a satellite position of the GPS receiver using the received SBAS signal. The SBAS signal may contain a difference value between the ephemeris data and the almanac data of the GPS satellite. The difference value between the ephemeris data and the almanac data may include a satellite clock difference value and a satellite position difference value for the GPS satellite. Accordingly, it is possible to acquire the current position and time information more quickly and accurately, by shortening the initial position check time using the difference value between the ephemeris data and the almanac data included in the SBAS signal.
1. A control method of a Global Positioning System (GPS) receiver, comprising:
receiving a Satellite Based Augmentation System (SBAS) signal from a SBAS satellite; and
calculating a satellite clock and a satellite position of a GPS satellite using the received SBAS signal,
wherein the SBAS signal comprises a difference value between ephemeris data and almanac data of the GPS satellite,
wherein the difference value between the ephemeris data and the almanac data comprises a satellite clock difference value and a satellite position difference value for the GPS satellite,
wherein the satellite clock difference value between the ephemeris data and almanac data for the GPS satellite is calculated by:
Δ T j ( t 0 )= T E j ( t 0 )− T A j ( t 0 ) [Equation 1]
and the satellite position difference value between the ephemeris data and almanac data for the GPS satellite is calculated by:
Δ x j ( t 0 )= x E j ( t 0 )− x A j ( t 0 ) [Equation 2]
where t 0 is the time of calculating the satellite clock difference value at a ground station, ΔT j (t 0 ) is the satellite clock difference value calculated at time t 0 at the ground station for j-th GPS satellite among a plurality of GPS satellites, T E j (t 0 ) is the satellite clock ephemeris data of the j-th GPS satellite, T A j (t 0 ) is the satellite clock almanac data of the j-th GPS satellite, Δx j (t 0 ) is the satellite position difference value calculated at time t 0 at the ground station for the j-th GPS satellite among the plurality of GPS satellites, x E j (t 0 ) is the satellite position ephemeris data of the j-th GPS satellite, and x A j (t 0 ) is the satellite position almanac data of the j-th GPS satellite.
2. The control method of claim 1 , wherein the calculating the satellite clock and satellite position of the GPS satellite using the received SBAS signal comprises calculating the satellite clock ephemeris data of the GPS satellite by:
{tilde over (T)} E j ( t )= T A j ( t )+Δ T j ( t 0 ) [Equation 3]
and calculating the satellite position ephemeris data of the GPS satellite by:
{tilde over (x)} E j ( t )= x A j ( t )+Δ x j ( t 0 ) [Equation 4]
where, t is the time of calculating the satellite clock ephemeris data at a GPS receiver, {tilde over (T)} E j (t 0 ) is the satellite clock ephemeris data calculated at time t for a j-th GPS satellite, T A j (t 0 ) is the satellite clock almanac data already maintained in the GPS receiver at time t for the j-th GPS satellite, ΔT j (t 0 ) is the satellite clock difference value between the ephemeris data and the almanac data acquired from a SBAS message for the j-th GPS satellite, {tilde over (x)} E j (t) is the satellite position ephemeris data calculated at time t for the j-th GPS satellite, x A j (t 0 ) is the satellite position almanac data already maintained in the GPS receiver at time t for the j-th GPS satellite, Δx j (t 0 ) is the satellite position difference value between the ephemeris data and almanac data acquired from the SBAS message for the j-th GPS satellite, and t 0 is the time of calculating the satellite position difference value at the ground station.
3. The control method of claim 1 , wherein the SBAS signal comprises a difference value in the position, and a difference value in a time correction value, for 4 or more GPS satellites, by 50 bits per second or less.
4. A GPS receiver, comprising:
a receiver configured to receive a SBAS signal from a SBAS satellite; and
a controller configured to calculate a satellite clock and a satellite position of a GPS satellite using the received SBAS signal,
wherein the SBAS signal comprises a difference value between ephemeris data and almanac data of the GPS satellite,
wherein the difference value between the ephemeris data and the almanac data comprises a satellite clock difference value and a satellite position difference value for the GPS satellite,
wherein the satellite clock difference value between the ephemeris data and almanac data for the GPS satellite is calculated by:
Δ T j ( t 0 )= T E j ( t 0 )− T A j ( t 0 ) [Equation 1]
and the satellite position difference value between the ephemeris data and almanac data for the GPS satellite is calculated by:
Δ x j ( t 0 )= x E j ( t 0 )− x A j ( t 0 ) [Equation 2]
where t 0 is the time of calculating the satellite clock difference value at a ground station, ΔT j (t 0 ) is the satellite clock difference value calculated at time t 0 at the ground station for j-th GPS satellite among a plurality of GPS satellites, T E j (t 0 ) is the satellite clock ephemeris data of the j-th GPS satellite, T A j (t 0 ) is the satellite clock almanac data of the j-th GPS satellite, Δx j (t 0 ) is the satellite position difference value calculated at time t 0 at the ground station for the j-th GPS satellite among the plurality of GPS satellites, x E j (t 0 ) is the satellite position ephemeris data of the j-th GPS satellite, and x A j (t 0 ) is the satellite position almanac data of the j-th GPS satellite.
5. The GPS receiver of claim 4 , wherein the controller calculates the satellite clock ephemeris data of the GPS satellite by:
{tilde over (T)} E j ( t )= T A j ( t )+Δ T j ( t 0 ) [Equation 3]
and the controller calculates the satellite position ephemeris data of the GPS satellite by:
{tilde over (x)} E j ( t )= x A j ( t )+Δ x j ( t 0 ) [Equation 4]
where t is the time of calculating the satellite clock ephemeris data at a GPS receiver, {tilde over (T)} E j (t) is the satellite clock ephemeris data calculated at time t for a j-th GPS satellite, T A j (t) is the satellite clock almanac data already maintained in the GPS receiver at time t for the j-th GPS satellite, ΔT j (t 0 ) is the satellite clock difference value between the ephemeris data and the almanac data acquired from a SBAS message for the j-th GPS satellite, {tilde over (x)} E j (t) is the satellite position ephemeris data calculated at time t for the j-th GPS satellite, x A j (t) is the satellite position almanac data already maintained in the GPS receiver at time t for the j-th GPS satellite, Δx j (t 0 ) is the satellite position difference value between the ephemeris data and almanac data acquired from the SBAS message for the j-th GPS satellite, and t 0 is the time of calculating the satellite position difference value at the ground station.
6. The GPS receiver of claim 4 , wherein the SBAS signal comprises a difference value in the position, and a difference value in a time correction value, for 4 or more GPS satellites, by 50 bits per second or less.
7. A ground station configured to calculate a difference value between ephemeris data and almanac data of a GPS satellite, and include the calculated difference value in a SBAS message and transmit the same to a SBAS satellite,
wherein the difference value between the ephemeris data and the almanac data comprises a satellite clock difference value and a satellite position difference value for the GPS satellite,
wherein the satellite clock difference value between the ephemeris data and almanac data for the GPS satellite is calculated by:
Δ T j ( t 0 )= T E j ( t 0 )− T A j ( t 0 ) [Equation 1]
and the satellite position difference value between the ephemeris data and almanac data for the GPS satellite is calculated by:
Δ x j ( t 0 )= x E j ( t 0 )− x A j ( t 0 ) [Equation 2]
where t 0 is the time of calculating the satellite clock difference value at a ground station, ΔT j (t 0 ) is the satellite clock difference value calculated at time t 0 at the ground station for j-th GPS satellite among a plurality of GPS satellites, T E j (t 0 ) is the satellite clock ephemeris data of the j-th GPS satellite, T A j (t 0 ) is the satellite clock almanac data of the j-th GPS satellite, Δx j (t 0 ) is the satellite position difference value calculated at time t 0 at the ground station for the j-th GPS satellite among the plurality of GPS satellites, x E j (t 0 ) is the satellite position ephemeris data of the j-th GPS satellite, and x A j (t 0 ) is the satellite position almanac data of the j-th GPS satellite.
8. The ground station of claim 7 , wherein the ground station calculates the satellite clock ephemeris data of the GPS satellite by:
{tilde over (T)} E j ( t )= T A j ( t )+Δ T j ( t 0 ) [Equation 3]
and calculates the satellite position ephemeris data of the GPS satellite by:
{tilde over (x)} E j ( t )= x A j ( t )+Δ x j ( t 0 ) [Equation 4]
where, t is the time of calculating the satellite clock ephemeris data at a GPS receiver, {tilde over (T)} E j (t) is the satellite clock ephemeris data calculated at time t for a j-th GPS satellite, T A j (t) is the satellite clock almanac data already maintained in the GPS receiver at time t for the j-th GPS satellite, ΔT j (t 0 ) is the satellite clock difference value between the ephemeris data and the almanac data acquired from a SBAS message for the j-th GPS satellite, {tilde over (x)} E j (t) is the satellite position ephemeris data calculated at time t for the j-th GPS satellite, x A j (t) is the satellite position almanac data already maintained in the GPS receiver at time t for the j-th GPS satellite, Δx j (t 0 ) is the satellite position difference value between the ephemeris data and almanac data acquired from the SBAS message for the j-th GPS satellite, and t 0 is the time of calculating the satellite position difference value at the ground station.
9. The ground station of claim 7 , wherein the SBAS signal comprises a difference value in the position, and a difference value in a time correction value, for 4 or more GPS satellites, by 50 bits per second or less.