Jonathan L Ladd

US Patent:

8085201, Dec 27, 2011

Filed:

Nov 13, 2008

Appl. No.:

12/270405

Inventors:

Jonathan Ladd - Bridgewater NH, US
Patrick C. Fenton - Calgary, CA

Assignee:

NovAtel Inc. - Calgary, Alberta

International Classification:

G01S 3/02

US Classification:

342464, 342463

Abstract:

A system to determine position, frequency and clock offsets over a network utilizing signals of opportunity transmitted by one or more transmitters with known locations, the system includes a base receiver with a clock and a known position that determines ranges to the transmitters, takes a series of samples of the signals of opportunity and time tags the series with times of receipt, calculated times of transmission based on the calculated ranges, or both. The base receiver transmits the time tagged series and, as appropriate, computed ranges to the remote receivers. A given remote receiver saves and time tags samples of the signals of opportunity, correlates the time-tagged series with the saved samples, and calculates a time offset as a time difference of the times of receipt at the remote receiver and either the time of receipt at the base receiver or the time of transmission calculated at the base receiver. The remote receiver calculates position based on the time offsets, and as appropriate, the ranges provided by the base receiver. The elevations of the remote receivers may be calculated as part of the position calculations, determined iteratively based on constraining the Z coordinate to an average elevation, or determined from differences in air pressure sensor readings at the base and remoter receivers.

US Patent:

8558738, Oct 15, 2013

Filed:

May 22, 2009

Appl. No.:

12/471046

Inventors:

Jonathan Ladd - Bridgewater NH, US
Patrick C. Fenton - Calgary, CA

Assignee:

NovAtel Inc. - Calgary

International Classification:

G01S 19/23
G01S 19/24
G01S 19/26
G01S 19/31

US Classification:

34235762, 34235763, 34235765, 34235771

Abstract:

A GNSS receiver reduces the time to first fix by utilizing the properties of existing radiated signals of opportunity, such as AM or FM radio signals, television signals and so forth, to reduce the uncertainties associated with oscillator frequency and phase, and further utilizing an Almanac and battery backed-up date and time to determine the satellites in view and reduce the uncertainties associated with Doppler. The receiver may use multiple signals of opportunity to determine the city or local area in which the receiver is located based on the set of frequencies of the signals, and also to reduce search uncertainties for oscillator frequency by estimating an offset based on the differences between the frequencies of the respective signals of opportunity at the receiver and the nominal broadcast frequencies of the signals.

US Patent:

20090117928, May 7, 2009

Filed:

Nov 3, 2008

Appl. No.:

12/263940

Inventors:

Jonathan Ladd - Bridgewater NH, US
Patrick C. Fenton - Calgary, CA

International Classification:

H04B 7/00

US Classification:

455502

Abstract:

A system to distribute accurate time and/or frequency over a network utilizing signals of opportunity transmitted by one or more local transmitters with known locations, the system includes a base receiver with a clock synchronized to a reference time scale such as GNSS or UTC time that saves a series of samples of the signals of opportunity and time tags the series with a calculated time of broadcast. A remote receiver saves samples of the signals of opportunity and correlates the series with the saved samples. The remote receiver calculates a time of transmission of saved samples that correspond to the series, determines a time offset as a difference in the time of broadcast calculated at the remote receiver and the time of broadcast calculated at the base receiver, and determines the time offset with respect to the base receiver. The base receiver further or instead phase locks to the signal opportunity and at predetermined intervals determines phase measurements of the integrated carrier frequency of the signal of opportunity and provides the phase information to the remote receiver. The remote receiver, which is also phase locked to the same signal of opportunity, uses the phase measurement information to frequency lock its clock to the base receiver clock by determining a frequency error based on the rate of change of phase measurements made at the base receiver and the remote receiver.