Land-based local ranging signal methods and systems
View Patent ↗To provide sub-meter accuracy in a local positioning system, ranging signals with a high modulation rate of code, such as 30 MHz, or more are transmitted. Code phase measurements may be used to obtain the accuracy without requiring relative motion or real time kinematic processing. The ISM or X-band is used for the carrier of the code to provide sufficient bandwidth within available spectrums. The length of codes used is less than or about a longest length across the region of operation, such as less than 15 kilometers in an open pit mine. The spread spectrum codes from different land-based transmitters are transmitted in time slots pursuant to a time division multiple access scheme for an increase in dynamic range. To avoid overlapping of code from different transmitters, each time slot includes or is separated by a blanking period. The blanking period is selected to allow the transmitted signal to traverse a region of operation. Differential measurements of signals received at a base station and a mobile receiver may improve accuracy.
1. In a method for determining relative position of a receiver from ranging signals transmitted from stationary land-based transmitters, an improvement comprising:
(a) determining the position to within sub-meter accuracy with differential ranging of the ranging signals from the land-based transmitters along line-of-sight to the receiver and ranging signals from the land-based transmitters along line-of-sight to a reference station, the ranging signals being at a substantially same center frequency, the determination being free of required movement of the receiver.
2. The method of claim 1 wherein (a) comprises determining the position to within at least 10 centimeter accuracy.
3. The method of claim 1 wherein the ranging signals have a carrier wave bandwidth of at least 60 MHz in an X-band and a modulation rate of code of at least 30 MHz.
4. The method of claim 1 wherein the ranging signals have a carrier wave in an ISM band and a modulation rate of code of at least 30 MHz.
5. The method of claim 1 wherein (a) comprises determining the position from differential ranging of the ranging signals from at least three stationary land-based transmitters received at the reference station and the receiver.
6. The method of claim 5 wherein (a) comprises determining the position where the receiver is moving.
7. The method of claim 1 wherein (a) comprises determining a position vector from the reference station to the receiver as a function of ranges of the reference station and the receiver to the stationary land-based transmitters.
8. The method of claim 1 wherein (a) comprises determining the position from code of the ranging signals, the sub-meter accuracy being from the code having a chip width of less than ten meters.
9. The method of claim 1 wherein the center frequency of the ranging signals is an X-band frequency.
10. The method of claim 1 wherein the center frequency of the ranging signals is an ISM band frequency.