Global Positioning System telecommand link

• US 5,153,598 A
• Filed: 09/26/1991
• Issued: 10/06/1992
• Est. Priority Date: 09/26/1991
• Status: Expired due to Fees

• Current Assignee: Daniel F. Alves Jr
• Original Assignee: Daniel F. Alves Jr
• Inventors: Alves, Daniel F. Jr.
• Primary Examiner(s): Blum, Theodore M.
• Application Number:
  US07/765,680
• Time in Patent Office: 376 Days
• Field of Search: 342/352, 342/356, 342/357, 375/1
• US Class Current: 342/352
• CPC Class Codes: G01S 19/25 involving aiding data received from a cooperating element, e.g. assisted GPS

Abstract

An improvement to the present system of Global Positioning System of satellites and ground stations, adding the capability of transmitting and receiving telecommand information, when required, to the current Navigation information. Three alternate embodiments are proposed. The first approach utilizes a spread-spectrum transmission of the command message, requiring few added components to the transmitter, and additional despread components to the receiver to extract the telecommand message. The second approach is simpler. Here the telecommand message is transmitted on a single frequency signal which is not modulated by a spreading code. The additional hardware in the receiver is a simple detector and demodulator. The third approach is based on redefining portions of the present GPS Navigation message to include telecommand information bits. No additional transmitter components are required, and only a command demultiplexer is added to the receiver.

Advantages of the invention include a great reduction in required power, volume and weight of satellites and unmanned vehicles, as well as greater control and security of command signals.

Claims

1. An improvement to the present Global Positioning System (GPS) of transmitters and receivers, to incorporate a capability of transmitting and receiving telecommand messages;

the improvement comprising;

(a) telecommand processing components added to a GPS receiver;

said components comprising a correlator, a single code track delay-lock loop, a doppler measure and a BPSK demodulator;

said correlator and delay-lock loop being connected to the output of the wide band IF amplifier in said GPS receiver, for performing a despreading function on the received telecommand message;

said doppler measure being connected to the clock source of said GPS receiver and having its output carrier reference signal connected input to said correlator;

said correlator despreading the received spread-spectrum telecommand message and outputting a digitized, filtered telecommand message to the BPSK demodulator;

said BPSK demodulator demodulating the telecommand message for use; and

(b) telecommand processing components added to a GPS transmitter;

said components comprising a digitizer circuit means, a spreader circuit means, an RF oscillatator and a mixer;

said digitizer, digitizing an input telecommand message and presenting a digitized command signal connected to said mixer;

said RF oscillator, operating at one of three selected frequencies;

L1;

1575.42 MHz, L2;

1227.6 MHz, or L3;

1381.05 MHz;

said spreader circuit means being connected and synchronized with the clock in said GPS transmitter and also to said RF oscillator, and presenting a spread-spectrum signal at a selected oscillator frequency to said mixer;

said mixer operating on its input digitized telecommand message and spread-spectrum signal to produce a spread-spectrum telecommand message signal for connection to said GPS transmitter circuit wide band amplifier;

said amplifier, amplifying said spread spectrum telecommand signal together with its normal input spread GPS NAV information message signal, and transmitting the combined telecommand and GPS NAV signals by antenna.

2. An improvement to the present Global Positioning System (GPS) of transmitters and receivers, to incorporate a capability of transmitting and receiving telecommand messages;

the improvement comprising;

(a) telecommand processing components added to a GPS receiver;

said components comprising a detector circuit means and a demodulator circuit connected in series;

said detector circuit being connected to the output of the wide band IF amplifier in said GPS receiver, and performing a discriminating function on the received signal, presenting a digitized telecommand message signal to said demodulator circuit;

said demodulator circuit producing the telecommand message from the presented, modulated input signal; and

(b) telecommand processing components added to a GPS transmitter;

said components comprising a digitizer circuit means, a modulator circuit means, and an RF oscillator;

said digitizer, digitizing an input telecommand message and presenting a digitized command signal connected to said modulator;

said RF oscillator, operating at one of three selected frequencies, L1;

1575.42 MHz, L2;

1227.6 MHz, or L3;

1381.05 MHz, and having its signal output connected to said modulator circuit;

said modulator, operating on its input digitized telecommand message and oscillator signal to produce a modulated telecommand message signal which is connected to said GPS transmitter circuit wide band amplifier;

said amplifier, amplifying said modulated telecommand signal together with its normal input spread-spectrum GPS NAV information message signal, and transmitting the combined telecommand and GPS NAV signals by antenna.

3. An improvement to the present Global Positioning System (GPS) of transmitters and receivers, to incorporate a capability of transmitting and receiving telecommand messages;

the improvement comprising;

(a) telecommand processing components added to a GPS receiver;

said components comprising a command demultiplexer circuit;

said command demultiplexer being connected to the output of the frame synchronizer circuit in said GPS receiver, and separating out the telecommand message signals from the GPS NAV message for use; and

(b) reformatting the transmitter GPS NAV message subframes software to include telecommand message bits;

said telecommand message bits utilizing two or more bits in each TLM word and two or more bits in each HOW word portion of said GPS NAV message subframes.