Anti-geolocation

Abstract

Methods, apparatus, and articles of manufacture make Geolocation of a source transmitter more difficult or impossible. Scatterers common to a source transmitter and an intended receiver are identified using a variety of techniques, such as iterative time reversal (ITR) and Singular Value Decomposition (SVD) of a scatter matrix. The source transmitter then uses time reversal and knowledge of the signatures of the scatterers to focus its transmissions on one or more of the scatterers, instead of the intended receiver. The source transmitter may have multiple antennas or antenna elements. The source transmitter and/or the intended receiver may include antenna elements with Near-Field Scatterers to enable spatial focusing below the diffraction limit at the frequencies of interest. The source transmitter may be a plurality of ad hoc nodes cooperating with each other.

What is claimed is: 
     
         1 . A method of transmitting data from a first radio frequency communication system to a second radio frequency communication system, the method comprising steps of:
 sounding environment using channel sounding bursts transmitted from a plurality of antennas of the first radio frequency communication system, wherein reflections of the channel sounding bursts are received by the plurality of antennas;   creating a scatter matrix from information obtained in the step of sounding;   applying time-reversal to the scatter matrix to obtain a time-reversed scatter matrix;   performing Singular Value Decomposition (SVD) on the time-reversed scatter matrix to obtain first automatic focusing parameters for focusing radio frequency transmissions of the plurality of antennas on a first scatterer; and   sending a first transmission of the data to the second radio frequency communication system through the plurality of antennas so that the first transmission is focused on the first scatterer using the first automatic focusing parameters.   
     
     
         2 . A method according to  claim 1 , wherein the step of creating the scatter matrix comprises:
 for each antenna of the plurality of antennas,
 transmitting a channel sounding burst from said each antenna; 
 receiving at said each antenna of reflections of the channel sounding burst transmitted from all the antennas of the plurality of antennas; 
 sampling and storing the reflections to obtain stored reflections; and 
 assembling the stored reflections into the scatter matrix. 
   
     
     
         3 . A method according to  claim 1 , wherein the step of creating the scatter matrix comprises a step for creating the scatter matrix. 
     
     
         4 . A method according to  claim 1 , wherein:
 the step of performing Singular Value Decomposition comprises obtaining second automatic focusing parameters for focusing radio frequency transmissions of the plurality of antennas on a second scatterer, the second scatterer being different from the first scatterer;   the method further comprising step of:   sending a second transmission to the second radio frequency communication system through the plurality of antennas so that the second transmission is focused on the second scatterer using the second automatic focusing parameters, the step of sending the second transmission following the step of sending the first transmission.   
     
     
         5 . A method according to  claim 4 , wherein:
 the step of performing Singular Value Decomposition further comprises obtaining third automatic focusing parameters for focusing radio frequency transmissions of the plurality of antennas on a third scatterer, the third scatterer being different from the first scatterer and from the second scatterer;   the method further comprising step of:   sending a third transmission to the second radio frequency communication system through the plurality of antennas so that the third transmission is focused on the third scatterer using the third automatic focusing parameters, the step of sending the third transmission following the step of sending the second transmission.   
     
     
         6 . A method according to  claim 1 , wherein the first communication system comprises a plurality of ad hoc nodes movable relative to each other and synchronized with each other, each ad hoc node of the plurality of ad hoc nodes comprising at least one antenna of the plurality of antennas. 
     
     
         7 . A method according to  claim 1 , further comprising varying shape of the channel sounding burst. 
     
     
         8 . A method of transmitting data from a first radio frequency communication system to a second radio frequency communication system, the method comprising steps of:
 performing iterative time reversal (ITR) at the first radio frequency communication system to obtain information for focusing in space and time transmissions from a plurality of antennas of the first communication system on a scatterer;   sending a transmission of the data to the second radio frequency communication system through the plurality of antennas so that the transmission of data is focused on the scatterer using the information for focusing.   
     
     
         9 . A method according to  claim 8 , wherein the step of performing iterative time reversal comprises a step for performing iterative time reversal. 
     
     
         10 . A method according to  claim 8 , wherein the step of performing iterative time reversal comprises at least two iterations. 
     
     
         11 . A radio frequency communication system, comprising:
 at least one transmitter;   at least one receiver;   a plurality of antennas coupled to the at least one transmitter and the at least one receiver; and   at least one processor coupled to the at least one transmitter and the at least one receiver, to control operation of the at least one receiver and the at least one transmitter, the at least one processor configured to execute code to cause the radio frequency communication system to:
 sound environment using channel sounding bursts transmitted from the plurality of antennas of the radio frequency communication system; 
 receive reflections of the channel sounding bursts by the plurality of antennas; 
 assemble a scatter matrix from information obtained from sounding the environment and receiving the reflections; 
 apply time-reversal to the scatter matrix to obtain a time-reversed scatter matrix; 
 perform Singular Value Decomposition (SVD) on the time-reversed scatter matrix to obtain first automatic focusing parameters for focusing radio frequency transmissions of the plurality of antennas on a first scatterer in the environment; and 
 send a first transmission of data to a destination communication system through the plurality of antennas so that the first transmission is focused on the first scatterer using the first automatic focusing parameters. 
   
     
     
         12 . A radio frequency communication system according to  claim 11 , wherein the at least one processor is further configured to execute code to cause the radio frequency communication system to:
 sound the environment by transmitting a channel sounding burst from each antenna of the plurality of antennas;   receive at said each antenna the reflections of the channel sounding burst transmitted from all the antennas of the plurality of antennas;   sample and store the reflections to obtain stored reflections; and   assemble the stored reflections into the scatter matrix.   
     
     
         13 . A radio frequency communication system according to  claim 11 , wherein the radio frequency communication system comprises means for assembling the scatter matrix. 
     
     
         14 . A radio frequency communication system according to  claim 11 , wherein the at least one processor is further configured to execute code to cause the radio frequency communication system to:
 perform Singular Value Decomposition so that second automatic focusing parameters for focusing radio frequency transmissions of the plurality of antennas on a second scatterer are obtained, the second scatterer being different from the first scatterer;   send a second transmission to the destination communication system through the plurality of antennas so that the second transmission is focused on the second scatterer using the second automatic focusing parameters, the second transmission following the first transmission.   
     
     
         15 . A radio frequency communication system according to  claim 14 , wherein the at least one processor is further configured to execute code to cause the radio frequency communication system to:
 perform Singular Value Decomposition so that third automatic focusing parameters for focusing radio frequency transmissions of the plurality of antennas on a third scatterer are obtained, the third scatterer being different from the first scatterer and from the second scatterer;   send a third transmission to the destination communication system through the plurality of antennas so that the third transmission is focused on the third scatterer using the third automatic focusing parameters, the third transmission following the second transmission.   
     
     
         16 . A radio frequency communication system according to  claim 11 , wherein the radio frequency communication system comprises a plurality of ad hoc nodes movable relative to each other and synchronized with each other, each ad hoc node of the plurality of ad hoc nodes comprising at least one antenna of the plurality of antennas. 
     
     
         17 . A radio frequency communication system according to  claim 11 , wherein the at least one processor is further configured to execute code to cause the radio frequency communication system to vary shape of the channel sounding bursts between at least some soundings. 
     
     
         18 . A radio frequency communication system, comprising:
 at least one transmitter;   at least one receiver;   a plurality of antennas coupled to the at least one transmitter and the at least one receiver; and   at least one processor coupled to the at least one transmitter and the at least one receiver, to control operation of the at least one receiver and the at least one transmitter, the at least one processor configured to execute code to cause the radio frequency communication system to:
 perform iterative time reversal (ITR) at the radio frequency communication system to obtain information for focusing in space and time transmissions from the plurality of antennas of the communication system on a scatterer; 
 send a transmission with data to a destination communication system through the plurality of antennas so that the transmission is focused on the scatterer using the information for focusing. 
   
     
     
         19 . A method according to  claim 18 , wherein the radio frequency communication system comprises means for performing iterative time reversal. 
     
     
         20 . A method according to  claim 18 , wherein the ITR comprises at least two iterations.