Direction finding and mapping in multipath environments

• US 20070115174A1
• Filed: 06/30/2006
• Published: 05/24/2007
• Est. Priority Date: 07/06/2005
• Status: Active Grant

• Current Assignee: Herrick Technology Laboratories, Inc.
• Original Assignee: Herrick Technology Laboratories, Inc.
• Inventors: Herrick, David
• Granted Patent: US 7,598,910 B2
• Time in Patent Office: Days
• US Class Current: 342/420
• CPC Class Codes: G01S 3/10 Means for reducing or compensating for quadrantal, site, or like errors
• CPC Class Codes: G01S 3/46 using antennas spaced apart and measuring phase or time difference between signals therefrom, i.e. path-difference systems
• CPC Class Codes: G01S 5/0218 Multipath in signal reception
• CPC Class Codes: G01S 5/04 Position of source determined by a plurality of spaced direction-finders

Abstract

Determining the direction of a direct arrival path between a receiver and a transmitter in a multipath environment by determining a transmitter heading relative to the receiver as proportional to a frequency offset of the direct path signal component relative to a multipath pedestal, an absolute velocity of the transmitter as proportional to a width of the multipath pedestal, a relative velocity between the transmitter and the receiver as proportional to a magnitude and a direction of doppler shift of the direct arrival component of the received signal relative to the doppler pedestal, and an amplitude of the multipath pedestal as proportional to a number and magnitude of scatterers in the multipath environment. The method is applied for continuous wave and modulated signals, for stationary and moving transmitters and for tracking and mapping transmitter paths.

Claims

1. A method for determining a direction of a direct arrival path between a receiver and a transmitter in a multipath environment wherein a received signal at the receiver includes a direct path signal component of a transmitted signal and a plurality of multipath signal components of the transmitted signal and wherein there is relative motion between at least two of the transmitter, the receiver and the scatterers of the multipath environment, comprising the steps of:

identifying in the received signal

a doppler pedestal comprised of a plurality of multipath signal components having a range of doppler shifts, each multipath doppler shift being determined by a relative motion between a scatterer and at least one of the transmitter and the receiver, and

a direct path signal component having a amplitude greater than an average amplitude of the doppler pedestal, and

determining a direction and a magnitude of a doppler shift of the direct path signal component relative to the doppler pedestal as proportional to a relative speed and heading between the transmitter and the receiver.

2. The method of claim 1 for determining a direction of a direct arrival path between a receiver and a transmitter in a multipath environment wherein a received signal at the receiver includes a direct path signal component of a transmitted signal and a plurality of multipath signal components of the transmitted signal and wherein the transmitter is stationary, further comprising the steps of:

receiving the received signal with first and second antennas and a reference antenna wherein

the first and second direction finding antennas are spaced sufficiently closely to eliminate phase ambiguity among the received signal components and

the reference antenna is spaced sufficiently apart from the first and second antennas that the multipath received signal components at the reference antenna are decorrelated with respect to the direct path received signal components at the first and second antennas,

performing a first comparison of the reference antenna received signal with the first antenna received signal,

performing a second comparison of the reference antenna received signal with the second antenna received signal, and

determining a difference between the first and second comparisons to generate a baseline phase angle measurement indicating the direction of the direct arrival path between the transmitter and the receiver.

3. A method for determining a direction of a direct arrival path between a receiver and a transmitter in a multipath environment wherein a received signal at the receiver includes a direct path signal component of a transmitted signal and a plurality of multipath signal components of the transmitted signal and wherein the transmitter is in motion, comprising the steps of:

identifying in the received signal

a doppler pedestal comprised of a plurality of multipath signal components having a range of doppler shifts, each multipath doppler shift being determined by a relative motion between a scatterer and at least one of the transmitter and the receiver, and

a direct path signal component, and

determining at least one of

a transmitter heading relative to the receiver as proportional to a frequency offset of the direct path signal component relative to the multipath pedestal, and

an absolute velocity of the transmitter as proportional to a width of the multipath pedestal.

4. The method of claim 3 for determining a direction of a direct arrival path between a receiver and a transmitter in a multipath environment wherein a received signal at the receiver includes a direct path signal component of a transmitted signal and a plurality of multipath signal components of the transmitted signal and wherein the transmitter is in motion, further comprising the step of:

determining a relative velocity between the transmitter and the receiver as proportional to a magnitude and a direction of doppler shift of the direct arrival component of the received signal relative to the doppler pedestal.

5. The method of claim 3 for determining a direction of a direct arrival path between a receiver and a transmitter in a multipath environment wherein a received signal at the receiver includes a direct path signal component of a transmitted signal and a plurality of multipath signal components of the transmitted signal and wherein the transmitter is in motion, further comprising the step of:

determining a number and magnitude of scatterers in the multipath environment as proportional to an amplitude of the multipath pedestal.

6. The method of claim 3 for determining a direction of a direct arrival path between a receiver and a transmitter in a multipath environment wherein a received signal at the receiver includes a direct path signal component of a transmitted signal and a plurality of multipath signal components of the transmitted signal and wherein the transmitter is in motion, wherein:

the transmitted signal is a continuous wave signal,

7. The method of claim 3 for determining a direction of a direct arrival path between a receiver and a transmitter in a multipath environment wherein a received signal at the receiver includes a direct path signal component of a transmitted signal and a plurality of multipath signal components of the transmitted signal and wherein the transmitter is in motion, further comprising the initial step of:

when the transmitted signal is a modulated signal,

transforming the received modulated signal into a continuous wave signal by demodulation/remodulation processing.

8. The method of claim 3 for determining a direction of a direct arrival path between a receiver and a transmitter in a multipath environment wherein a received signal at the receiver includes a direct path signal component of a transmitted signal and a plurality of multipath signal components of the transmitted signal and wherein the transmitter is in motion, further comprising a method for mapping a path traversed by the receiver, comprising the steps of:

recording successive transmitter headings relative to the receiver and absolute velocities of the transmitter over a sequence of intervals during which the transmitter traverses a path, and

correlating the recorded transmitter headings and absolute velocities with corresponding geographical locations along the path to generate a map of the geographic map expressed in transmitter headings and absolute velocities.

9. The method of claim 3 for determining a direction of a direct arrival path between a receiver and a transmitter in a multipath environment wherein a received signal at the receiver includes a direct path signal component of a transmitted signal and a plurality of multipath signal components of the transmitted signal and wherein the transmitter is in motion, further comprising a method for determining a geographic path traversed by the receiver, comprising the steps of:

determining successive transmitter headings relative to the receiver and absolute velocities of the transmitter over a sequence of intervals during which the transmitter traverses a path, and

correlating the determined transmitter headings and absolute velocities with at least one stored path map representing corresponding geographical locations along a path expressed in transmitter headings and absolute velocities.

10. A method for determining a location of a receiver in a multi-path environment, comprising:

detecting first and second received signals from corresponding first and second transmitters, wherein

there is relative motion between the receiver and the first and second transmitters and

the first and second received signals each include a direct path signal component and multipath pedestal including a plurality of multipath signal components from a corresponding one of the first and second transmitters,

determining first and second directions of first and second direct arrival paths between the receiver and corresponding ones of the first and second transmitters wherein the direction of each direct arrival path is proportional to a corresponding frequency offset of the corresponding direct path signal component relative to the corresponding multipath pedestal of the corresponding received signal, and

determining the location of the receiver as at an intersection of the first and second directions of the first and second direct arrival paths.