Automatically Determining Locations of Signal Sources in Areas with Limited Satellite Coverage

Abstract

To automatically determine geographic positions of signal sources statically disposed along a path in a geographic area with limited satellite coverage, a system generates an initial estimate of the geographic positions of the signal sources. To this end, the system receives signal data collected by a receiver moving along the path, the signal data being indicative of changes, over a period of time, in strength of respective signals emitted by the signal sources and detected by the receiver and, and generates an initial estimate of the geographic positions of the signal sources using the signal data and an average speed at which the receiver moves along the path. The system then revises the initial estimate of the geographic positions of the plurality of signal sources by determining, for a signal source associated with a segment of the path, a segment-specific average speed of the receiver.

What is claimed is: 
     
         1 . A method for automatically determining geographic positions of signal sources statically disposed along a path in a geographic area with limited satellite coverage, the method comprising:
 generating an initial estimate of the geographic positions of the signal sources, including:
 receiving signal data collected by a receiver moving along the path, the signal data being indicative of changes, over a period of time, in strength of respective signals emitted by the signal sources and detected by the receiver and, and 
 generating an initial estimate of the geographic positions of the signal sources using the signal data and an average speed at which the receiver moves along the path; and 
   revising the initial estimate of the geographic positions of the plurality of signal sources by determining, for a signal source associated with a segment of the path, a segment-specific average speed of the receiver.   
     
     
         2 . The method of  claim 1 , wherein the determining of the segment-specific average speed for the signal source includes:
 determining an amount of time during which the moving receiver detects a signal from the signal source at a strength above a threshold value.   
     
     
         3 . The method of  claim 1 , wherein the revising of the initial estimate includes using a speed reported by a vehicle in which the receiver is disposed. 
     
     
         4 . The method of  claim 1 , wherein the revising of the initial estimate includes using an acceleration reported by a vehicle in which the receiver is disposed. 
     
     
         5 . The method of  claim 1 , further comprising:
 receiving indications of a first position of the receiver at a first time prior to entering the geographic area and a second position of the receiver at a second time subsequent to leaving the geographic area; and   determining the average speed based at least in part on a difference between a first position and the second position, and a difference between the first time and the second time.   
     
     
         6 . The method of  claim 1 , wherein the generating of the initial estimate includes:
 determining, for each of the signal sources, a time at which the strength of the signal emitted by the signal source reaches its peak value at the receiver, and
 determining an order in which the signal sources are arranged along the path using the determined times at which the signals reach their corresponding peak values. 
   
     
     
         7 . The method of  claim 6 , wherein the generating of the initial estimate includes:
 determining the positions for the signal sources using the received signal data and the determined order in which the signal sources are arranged along the path.   
     
     
         8 . The method of  claim 6 , wherein the generating of the initial estimate includes:
 determining a length of the path,   determining a number of the signal sources,   determining an average distance between the signal sources using the length of the path and the determined number; and   determining the positions for the signal sources using the received signal data and the determined order in which the signal sources are arranged along the path.   
     
     
         9 . The method of  claim 6 , wherein the determining of the time at which the strength of the signal emitted by the signal source reaches its peak value at the receiver includes:
 identifying, within the signal data detected by the receiver, a pair of peak values in the strength of the signal, the pair of peak values separated in time approximately by how long it takes for a length of a car to pass by the signal source at the determined speed, and   extrapolating the time at which the strength of the signal reaches its peak value at the receiver from the pair of peak values.   
     
     
         10 . The method of  claim 1 , wherein the signal data further includes data collected by multiple receivers moving along the path; and wherein
 the generating of the initial estimate includes using combining the data collected by multiple receivers.   
     
     
         11 . A system for automatically determining geographic positions of signal sources statically disposed along a path in a geographic area with limited satellite coverage e, the system comprising:
 one or more processors;   a non-transitory computer-readable memory coupled to the one or more processors and storing thereon instructions that, when executed by the one or more processor, cause the system to:
 generate an initial estimate of the geographic positions of the signal sources, including (i) receive signal data collected by a receiver moving along the path, the signal data being indicative of changes, over a period of time, in strength of respective signals emitted by the signal sources and detected by the receiver and, and (ii) generate an initial estimate of the geographic positions of the signal sources using the signal data and an average speed at which the receiver moves along the path; and 
 revise the initial estimate of the geographic positions of the plurality of signal sources by determining, for a signal source associated with a segment of the path, a segment-specific average speed of the receiver. 
   
     
     
         12 . The system of  claim 11 , wherein the determining of the segment-specific average speed for the signal source includes:
 determining an amount of time during which the moving receiver detects a signal from the signal source at a strength above a threshold value.   
     
     
         13 . The system of  claim 11 , wherein the revising of the initial estimate includes using a speed reported by a vehicle in which the receiver is disposed. 
     
     
         14 . The system of  claim 11 , wherein the revising of the initial estimate includes using an acceleration reported by a vehicle in which the receiver is disposed. 
     
     
         15 . The system of  claim 11 , wherein the instructions further cause system to:
 receive indications of a first position of the receiver at a first time prior to entering the geographic area and a second position of the receiver at a second time subsequent to leaving the geographic area; and   determine the average speed based at least in part on a difference between a first position and the second position, and a difference between the first time and the second time.   
     
     
         16 . The system of  claim 11 , wherein the generating of the initial estimate includes:
 determining, for each of the signal sources, a time at which the strength of the signal emitted by the signal source reaches its peak value at the receiver, and   determining an order in which the signal sources are arranged along the path using the determined times at which the signals reach their corresponding peak values.   
     
     
         17 . The system of  claim 16 , wherein the generating of the initial estimate includes:
 determining the positions for the signal sources using the received signal data and the determined order in which the signal sources are arranged along the path.   
     
     
         18 . The system of  claim 16 , wherein the generating of the initial estimate includes:
 determining a length of the path,   determining a number of the signal sources,   determining an average distance between the signal sources using the length of the path and the determined number; and   determining the positions for the signal sources using the received signal data and the determined order in which the signal sources are arranged along the path.   
     
     
         19 . The system of  claim 16 , wherein the determining of the time at which the strength of the signal emitted by the signal source reaches its peak value at the receiver includes:
 identifying, within the signal data detected by the receiver, a pair of peak values in the strength of the signal, the pair of peak values separated in time approximately by how long it takes for a length of a car to pass by the signal source at the determined speed, and   extrapolating the time at which the strength of the signal reaches its peak value at the receiver from the pair of peak values.   
     
     
         20 . The system of  claim 11 , wherein the signal data further includes data collected by multiple receivers moving along the path; and wherein
 the generating of the initial estimate includes using combining the data collected by multiple receivers.