Codeless GPS sonde

• US 4,754,283 A
• Filed: 06/17/1986
• Issued: 06/28/1988
• Est. Priority Date: 06/17/1986
• Status: Expired due to Term

• Current Assignee: TR Navigation Corp. (Trimble Inc.)
• Original Assignee: Tracor Aerospace Austin Incorporated (BAE Systems Plc)
• Inventors: Fowler, Clarence W.
• Primary Examiner(s): Blum, Theodore M.
• Assistant Examiner(s): Issing, Gregory C.
• Application Number:
  US06/875,102
• Time in Patent Office: 742 Days
• Field of Search: 342/461, 342/418, 342/26, 342/104, 342/192, 342/352, 342/356, 375/1, 380/34
• US Class Current: 342/461
• CPC Class Codes: G01S 11/10 using Doppler effect
• CPC Class Codes: G01S 19/04 providing carrier phase data
• CPC Class Codes: G01S 19/10 providing dedicated supplementary positioning signals
• CPC Class Codes: G01S 19/43 using carrier phase measurements, e.g. kinematic positioning; using long or short baseline interferometry
• CPC Class Codes: G01S 19/52 Determining velocity

Abstract

Windfinding apparatus is described in which receiver processing of the Global Positioning System (GPS) signals is without knowledge of the spread spectrum codes. The apparatus receiver ignores the bi-phase code and recovers the carrier frequency of all satellites in view of the receiving antenna. Two of these receivers are used in a windfinding system. One of the receivers is located on the ground at a known latitude and longitude. The other receiver is placed on a weather balloon sonde and launched into the atmosphere. A telemetry transmitter aboard the sonde transmits a signal that contains the GPS carrier frequency information to the ground-based telemetry receiver. The telemetry receiver output and the local codeless GPS receiver feed a set of tracking filters. The filtered signals are evaluated to obtain a measurement of the difference between the local GPS receiver carrier frequency and the sonde GPS receiver carrier frequency caused by the velocity of the sonde relative to the ground-based receiver (i.e., doppler effect). The wind velocity is computed based on knowledge of the doppler of the sonde GPS receiver and known GPS satellite positions. The sonde velocity is computed as a three dimensional vector. This vector can then be integrated to obtain the x distance, y distance and z altitude from the sonde launch point.

Claims

1. A spread spectrum codeless receiver for reception of direct sequence spread spectrum signals without knowledge of the spreading code therein, comprising:

a quadrature mixer for accepting an input direct seguence spread spectrum signal and a local oscillator signal, for conversion of the baseband signals of the input signal to first and second quadrature signals;

first and second video amplifier channels coupled to the quadrature mixer and providing first and second amplified signals, said amplifiers having a bandwidth that passes the spreading code of the input signal; and

a multiplier circuit for multiplying the amplified signals to remove the spreading code therefrom and produce a signal representing the doppler offset of the carrier of the input signal.

2. The receiver of claim 1 wherein the multiplier circuit is a four quadrant multiplier circuit.

3. The receiver of claim 1 wherein the multiplier circuit produces an output signal that is two times the frequency of the doppler offset.

4. The receiver of claim 1 further comprising:

an oscillator circuit providing a local oscillator signal for the mixer;

a divider circuit coupled to the oscillator circuit for providing a reference signal divided-down in frequency from the frequency of the local oscillator signal; and

a summing circuit coupled to the divider circuit and the multiplier circuit, for combining the doppler offset signal and the reference signal.

5. The receiver of claim 1 wherein the quadrature mixer comprises a splitter for providing separation of the input signal into two signals of the same phase;

a 90°

coupler for providing separation of the local oscillator signal into two signals having 90°

phase difference;

a first multiplier circuit for multiplying one of the input signals and one of the local oscillator signals; and

a second multiplier circuit for multiplying the other input signal and the other local oscillator signal.

6. A windfinding sonde for airborne deployment, comprising:

an antenna for receiving direct sequence spread spectrum carrier transmissions;

an amplifier coupled to the antenna for providing a direct sequence spread spectrum signal for processing as an information signal;

a quadrature mixer for accepting the information signal produced by the amplifier and accepting a local oscillator signal, for conversion of the baseband signals of the information signal to first and second quadrature signals;

first and second video amplifier channels coupled to the mixer and having sufficient bandwidth to pass the spreading code of the information signal;

a multiplier circuit for multiplying the signals passed by the first and second video amplifier channels to remove the spreading code and produce an output signal representing the doppler offset of the carrier transmissions; and

a transmitter for transmission of the doppler offset output signal to a remote location from the sonde.

7. A windfinding system, comprising:

a first codeless receiver adapted to be carried by a balloon sonde having a telemetry link transmitter,

said receiver accepting a direct sequence spread spectrum input signal transmission and producing a signal for transmission over the telemetry link representing the doppler offset of the carrier of the input signal by removing the spreading code and recovering the carrier of the input signal;

a ground-based unit including a telemetry link receiver for acquiring the sonde transmission and providing a first doppler offset signal, and a second codeless receiver accepting the direct sequence spread spectrum input signal transmission and producing a signal representative of the doppler offset of the carrier of the input signal by removing the spreading code and recovering the carrier of the input signal; and

a computer for determining the difference in doppler offset frequency of the first and second doppler offset signals and calculating wind data including a velocity vector of the sonde.

8. The system of claim 7, further comprising:

a first tracking filter for the first doppler offset signal;

a second tracking filter for the second doppler offset signal; and

each tracking filter providing a measure of the doppler offset frequency of its respective doppler offset signal.

9. The system of claim 7 wherein the first and second codeless receivers are adapted to process GPS satellite signals.

10. A windfinding system operable based upon direct sequence spread spectrum transmissions from GPS satellites, comprising:

a first codeless receiver adapted to be carried by a balloon sonde having a telemetry link transmitter;

said receiver accepting the GPS satellite transmission and producing a signal for transmission over the telemetry link representing the doppler offset of the carrier of the GPS transmission by removing the spreading code and recovering the carrier;

a ground-based unit including a telemetry link receiver for acquiring the sonde transmission and providing a first doppler offset signal;

a second, ground-based codeless receiver accepting the GPS satellite transmission and producing a signal representing the doppler offset of the carrier of the GPS transmission as a second doppler offset signal by removing the spreading code and recovering the carrier;

a standard GPS receiver receiving the GPS satellite transmission and providing information concerning satellite transmission offset doppler; and

a computer for calculating wind data including a sonde velocity vector based upon the first and second doppler offset signals and the satellite transmission offset doppler information.

11. A system operable based upon GPS satellite transmissions to determine the velocity vector of a remote unit, comprising:

a first codeless receiver adapted to be carried by a remote unit having a telemetry link transmitter;

said receiver accepting the GPS satellite transmission and producing a signal for transmission over the telemetry link representing the doppler offset of the carrier of the GPS transmission by removing the spreading code and recovering the carrier;

a second codeless receiver adapted to be stationed with a local unit having a telemetry link receiver for acquiring the remote unit transmission and providing the remote GPS doppler offset signal;

said second codeless receiver accepting the GPS satellite transmission and producing a signal representing the doppler offset of the carrier of the GPS transmission as a local GPS doppler offset signal by removing the spreading code and recovering the carrier; and

a computer for calculating a remote unit velocity vector based upon the remote and local GPS doppler offset signals.