Method for improved line of sight signal detection using time/frequency analysis

Abstract

The time-of-arrival of the line-of-sight component of a received, or incoming, signal is determined by performing a time/frequency analysis of the incoming signal. The term time/frequency analysis refers to an analysis of the frequency components (i.e. the frequency make-up) of the incoming signal at given instants in time. For example, one form of time/frequency analysis according to the present invention is to compare the frequency make-up of the received signal to the frequency make-up of the transmitted signal. Those points in time in which the frequency make-up of the received signal matches the frequency make-up of the transmitted signal are the instants in time at which a multipath component of the transmitted signal is received. In such a time/frequency analysis, the first-identified component, in time, is assumed to be the line-of-sight component of the transmitted signal.

What is claimed:  
     
         1 . A method comprising: 
 receiving an incoming signal comprising at least one multipath component of a signal transmitted by a wireless terminal in an RF environment;    performing a time/frequency analysis on the incoming signal, including comparing a set of waveforms corresponding to frequency components of the incoming signal to a set of waveforms corresponding to expected frequency components of the transmitted signal, to identify a time-of-arrival of a line-of-sight component of the incoming signal; and    identifying a first instant in time at which said set of waveforms corresponding to frequency components of the incoming signal substantially match said set of waveforms corresponding to frequency components of the signal transmitted by the wireless terminal, said first identified instant in time thereby being the time-of-arrival of the line-of-sight component of the incoming signal,    wherein said set of waveforms corresponding to frequency components of the incoming signal substantially matches said set of waveforms corresponding to frequency components of the signal transmitted by the wireless terminal when a number of matching corresponding waveforms from the two sets meets or exceeds a threshold.    
     
     
         2 . The method of    claim 1    wherein said step of performing a time/frequency analysis includes the step of comparing a set of frequency components of the incoming signal to a set of frequency components of the signal transmitted by the wireless terminal.  
     
     
         3 . The method of    claim 1    further comprising 
 identifying a first instant in time at which said set of waveforms corresponding to frequency components of the incoming signal substantially match said set of waveforms corresponding to frequency components of the signal transmitted by the wireless terminal, said first identified instant in time thereby being the time-of-arrival of the line-of-sight component of the incoming signal.  
 
     
     
         4 . The method of    claim 3    wherein said time/frequency analysis is a wavelet analysis.  
     
     
         5 . The method of    claim 4    wherein said incoming signal is a signal received during a regular communication of said wireless terminal.  
     
     
         6 . The method of    claim 1    further comprising adjusting said identified time-of-arrival of the line-of-sight component of the incoming signal by an amount based on the value of a parameter that characterizes the scattering hostility in an RF environment through which said incoming signal traveled.  
     
     
         7 . The method of    claim 1    further comprising: 
 generating the set of waveforms corresponding to frequency components from the incoming signal.  
 
     
     
         8 . The method of    claim 7   , wherein the generating step includes passing the incoming signal through a plurality of linear filters.  
     
     
         9 . The method of    claim 7   , wherein the waveforms corresponding to frequency components of the incoming signal and the waveforms corresponding to expected frequency components of the transmitted signal are wavelets.  
     
     
         10 . The method of    claim 3   , wherein said set of waveforms corresponding to frequency components of the incoming signal substantially matches said set of waveforms corresponding to frequency components of the signal transmitted by the wireless terminal when a number of matching corresponding waveforms from the two sets meets or exceeds a threshold.  
     
     
         11 . A method comprising: 
 receiving an incoming signal comprising at least one multipath component of a signal transmitted by a wireless terminal through an RF environment;    decomposing the incoming signal into a set of decomposed signals, which when superposed constitute the incoming signal;    comparing the set of decomposed signals to a set of expected decomposed signals at instants in time; and    identifying a time-of-arrival of a line-of-sight component of the incoming signal from the comparison, wherein the identifying step includes 
 determining a first instant in time at which the set of decomposed signals substantially match the set of expected decomposed signals, the first instant in time being the time-of-arrival of the line-of-sight component of the incoming signal,  
   wherein the set of decomposed signals substantially match the set of expected decomposed signals when a number of matching corresponding decomposed signals from the two sets meets or exceeds a threshold.    
     
     
         12 . The method of    claim 11    further comprising 
 adjusting said identified time-of-arrival of the line-of-sight component of the incoming signal by an amount based on the value of a parameter that characterizes the scattering hostility in the RF environment through which said incoming signal traveled.  
 
     
     
         13 . The method of    claim 11   , wherein the decomposing step includes 
 passing the incoming signal through a plurality of linear filters.    
     
     
         14 . The method of    claim 11   , wherein the set of decomposed signals is a wavelet representation of the incoming signal.  
     
     
         15 . The method of    claim 11   , wherein the set of expected decomposed signals is a wavelet representation of the signal transmitted by the wireless terminal.  
     
     
         16 . A method comprising: 
 receiving an incoming signal comprising at least one multipath component of a signal transmitted by a wireless terminal through an RF environment;    decomposing the incoming signal into a set of decomposed signals, which when superposed constitute the incoming signal;    comparing the set of decomposed signals to a set of expected decomposed signals at instants in time; and    identifying a time-of-arrival of a line-of-sight component of the incoming signal from the comparison, wherein the identifying step includes 
 determining a first instant in time at which the set of decomposed signals substantially match the set of expected decomposed signals, the first instant in time being the time-of-arrival of the line-of-sight component of the incoming signal,  
 wherein the set of decomposed signals substantially match the set of expected decomposed signals when a number of matching corresponding decomposed signals from the two sets meets or exceeds a threshold.  
   
     
     
         17 . A method for detecting a line of sight signal comprising: 
 receiving one or more incoming multi-path components of a signal transmitted by a wireless terminal through a rich-scattering RF environment;    identifying the time of arrival of a first arriving one of the one or more multi path components using time frequency analysis; and    adjusting the identified time of arrival of the first arriving multi path components to obtain a time of arrival associated with a line of sight component.    
     
     
         18 . The method of    claim 17   , further comprising the step of processing a plurality of adjusted times of arrival associated with a plurality of first arriving multi path components to determine a geolocation of the wireless terminal.  
     
     
         19 . The method of    claim 17    wherein the time frequency analysis includes wavelet analysis.