Radio frequency (RF) ranging in propagation limited RF environments
The embodiments described herein provide ranging capabilities in RF-opaque environments, such as a jungle, utilizing transponders located on a property line. In particular, the embodiments described herein provide for determining a perpendicular distance to a property line from a ranging device. The transponders are located on the property line and a separated from each other by a known distance. The ranging device transmits RF signals to the transponders, which are received by the transponders and re-broadcasted back to the ranging device on a different frequency. The ranging device uses information about the transmitted and received RF signals and the known distance to calculate a perpendicular distance from the ranging device to the property line.
1. An apparatus comprising:
a transmit antenna configured to transmit Radio Frequency (RF) signals at a first carrier frequency (f1), wherein f1 is selected from frequencies of 30 Megahertz (MHz) to 1 Gigahertz (GHz);
a receive antenna configured to receive RF signals at a second carrier frequency (f2) that is different than f1, wherein f2 is selected from frequencies of 30 MHz to 1 GHz;
an RF transmitter communicatively coupled to the transmit antenna;
an RF receiver communicatively coupled to the receive antenna; and
a controller communicatively coupled to the RF transmitter and the RF receiver and configured to direct the RF transmitter to broadcast a first RF signal at f1, to receive a first RF rebroadcast at f2 of the first RF signal through the RF receiver from a first transponder located on a property line, to perform a first correlation between the first RF signal and the first RF rebroadcast, to calculate a first integer wavelength delay based on the first correlation, and to calculate a first distance from the apparatus to the first transponder based on the first integer wavelength delay,
wherein the controller is further configured to direct the RF transmitter to broadcast a second RF signal at f1, to receive a second RF rebroadcast at f2 of the second RF signal through the RF receiver from a second transponder, wherein the second transponder is located on the property line and is separated from the first transponder by a known distance,
wherein the controller is further configured to perform a second correlation between the second RF signal and the second RF rebroadcast, to calculate a second integer wavelength delay based on the second correlation, to calculate a second distance to the second transponder based on the second integer wavelength delay, and to calculate a perpendicular distance from the apparatus to the property line based on the first distance, the second distance, and the known distance.
2. The apparatus of claim 1 , wherein:
f1 and f2 each have frequency that is selected from a 23 cm band or a 70 cm band.
3. The apparatus of claim 1 , wherein:
the controller is configured to perform at least one of the first correlation and the second correlation at one or more intermediate frequencies.
4. The apparatus of claim 1 , wherein:
the controller is further configured to determine a first phase difference between the first RF signal and the first RF rebroadcast, to calculate a first fractional wavelength delay based on the first phase difference, and to calculate the first distance based on the first integer wavelength delay and the first fractional wavelength delay; and
the controller is further configured to determine a second phase difference between the second RF signal and the second RF rebroadcast, to calculate a second fractional wavelength delay based on the second phase difference, and to calculate the second distance based on the second integer wavelength delay and the second fractional wavelength delay.
5. The apparatus of claim 4 , wherein:
the controller is configured to determine at least one of the first phase difference and the second phase difference at one or more intermediate frequencies.
6. The apparatus of claim 1 , wherein:
the first RF signal and the second RF signal comprise a pulse sequence that is modulated by a Barker code;
the first RF rebroadcast comprises a pulse sequence that is modulated based on the Barker code of the first RF signal; and
the second RF rebroadcast comprises a pulse sequence that is modulated based on the Barker code of the second RF signal.
7. A method comprising:
broadcasting a first Radio Frequency (RF) signal at a first carrier frequency (f1), wherein f1 is selected from frequencies of 30 Megahertz (MHz) to 1 Gigahertz (GHz);
receiving a first RF rebroadcast of the first RF signal from a first transponder that is located on a property line, wherein the first RF rebroadcast is at a second carrier frequency (f2) that is different from f1, wherein f2 is selected from frequencies of 30 MHz to 1 GHz;
performing a first correlation between the first RF signal and the first RF rebroadcast;
calculating a first integer wavelength delay based on the first correlation;
calculating a first distance to the first transponder based on the first integer wavelength delay;
broadcasting a second RF signal at f1;
receiving a second RF rebroadcast at f2 of the second RF signal from a second transponder located on the property line, wherein the second transponder is separated from the first transponder by a known distance;
performing a second correlation between the second RF signal and the second RF rebroadcast;
calculating a second integer wavelength delay based on the second correlation;
calculating a second distance to the second transponder based on the second integer wavelength delay;
calculating a perpendicular distance to the property line based on the first distance, the second distance, and the known distance.
8. The method of claim 7 , wherein:
broadcasting the first RF signal and the second RF signal at f1 further comprises:
broadcasting at a frequency of f1 that is selected from a 23 cm band or a 70 cm band; and
receiving the first RF rebroadcast and the second RF rebroadcast at f2 further comprises:
receiving at a frequency of f2 that is selected from frequencies from the 23 cm band or the 70 cm band.
9. The method of claim 7 , wherein:
at least one of the first correlation and the second correlation is performed at one or more intermediate frequencies.
10. The method of claim 7 , wherein:
calculating the first distance further comprises:
determining a first phase difference between the first RF signal and the first RF rebroadcast;
calculating a first fractional wavelength delay based on the first phase difference; and
calculating the first distance based on the first integer wavelength delay and the first fractional wavelength delay; and
calculating the second distance further comprises:
determining a second phase difference between the second RF signal and the second RF rebroadcast;
calculating a second fractional wavelength delay based on the second phase difference; and
calculating the second distance based on the second integer wavelength delay and the second fractional wavelength delay.
11. The method of claim 10 , wherein:
at least one of the first phase difference and the second phase difference are determined at one or more intermediate frequencies.
12. The method of claim 7 , wherein:
broadcasting the first RF signal and the second RF signal comprises:
modulating a carrier with a Barker code to broadcast a pulse sequence; receiving the first RF rebroadcast comprises:
receiving a carrier that is modulated based on the Barker code of the first RF signal; and
receiving the second RF rebroadcast comprises:
receiving a carrier that is modulated based on the Barker code of the second RF signal.
13. An apparatus comprising:
a controller communicatively coupled to a Radio Frequency (RF) transmitter and an RF receiver and configured to direct the RF transmitter to broadcast a first RF signal at a first carrier frequency (f1), to receive a first RF rebroadcast of the first RF signal at a second carrier frequency (f2) through the RF receiver from a first transponder located above ground on a property line, wherein f1 and f2 are different and are selected to have frequencies of 30 Megahertz (MHz) to 1 Gigahertz GHz,
wherein the controller is further configured to perform a first correlation between the first RF signal and the first RF rebroadcast, to calculate a first integer wavelength delay based on the first correlation, and to calculate a first distance across the ground from the apparatus to the first transponder based on the first integer wavelength delay,
wherein the controller is further configured to direct the RF transmitter to broadcast a second RF signal at f1, to receive a second RF rebroadcast at f2 of the second RF signal through the RF receiver from a second transponder, wherein the second transponder is located above the ground on the property line and is separated from the first transponder by a known distance,
wherein the controller is further configured to perform a second correlation between the second RF signal and the second RF rebroadcast, to calculate a second integer wavelength delay based on the second correlation, to calculate a second distance across the ground from the apparatus to the second transponder based on the second integer wavelength delay, and to calculate a perpendicular distance from the apparatus to the property line based on the first distance, the second distance, and the known distance.
14. The apparatus of claim 13 , wherein:
the controller is configured to perform at least one of the first correlation and the second correlation at one or more intermediate frequencies.
15. The apparatus of claim 13 , wherein:
the controller is further configured to determine a first phase difference between the first RF signal and the first RF rebroadcast, to calculate a first fractional wavelength delay based on the first phase difference, and to calculate the first distance based on the first integer wavelength delay and the first fractional wavelength delay; and
the controller is further configured to determine a second phase difference between the second RF signal and the second RF rebroadcast, to calculate a second fractional wavelength delay based on the second phase difference, and to calculate the second distance based on the second integer wavelength delay and the second fractional wavelength delay.
16. The apparatus of claim 15 , wherein:
the controller is configured to determine at least one of the first phase difference and the second phase difference at one or more intermediate frequencies.
17. The apparatus of claim 13 , wherein:
the first RF signal and the second RF signal comprise a pulse sequence that is modulated by a Barker code;
the first RF rebroadcast comprises a pulse sequence that is modulated based on the Barker code of the first RF signal; and
the second RF rebroadcast comprises a pulse sequence that is modulated based on the Barker code of the second RF signal.