Electronic device and method for low power rf ranging

Abstract

Electronic devices and methods to provide wireless ranging are shown. A first electronic device includes a memory containing stored instructions that can perform a method for determining a distance between the first electronic device and a second electronic device. For each frequency in a selected set of frequencies, the method sets the transceiver to the respective frequency, sends a first tone having the frequency and a first phase to the second electronic device and receives a second tone having the first frequency and a second phase. For each selected frequency, the first electronic device determines the phase difference between the second tone and the controllable oscillator, receives a phase difference from the second electronic device, and calculates a phase delay for the frequency. The first electronic device calculates a phase delay difference for pairs of the frequencies; and determines the distance using these phase delay differences.

What is claimed is: 
     
         1 . A first device comprising:
 a processing unit;   a transceiver coupled to the processing unit;   an oscillator coupled to the processing unit and to the transceiver; and   a non-transitory memory coupled to the processing unit and storing instructions, that when executed, cause the processing unit to:   select a set of frequencies for transmitting to a second device via the transceiver;   for each frequency of the set of frequencies:
 set the oscillator to oscillate at the respective frequency; 
 cause the transceiver to transmit an outgoing signal having the respective frequency to the second device; 
 receive a response signal from the second device having the respective frequency; 
 determine a phase delay difference based on the outgoing signal and the response signal for the respective frequency; and 
 determine a set of candidate distance ranges based on the phase delay difference; and 
   determine a distance between the first device and the second device that overlaps each candidate distance range of each frequency in the set of frequencies.   
     
     
         2 . The first device of  claim 1 , wherein the non-transitory memory stores further instructions that cause the processing unit to:
 make a coarse distance measurement between the first device and the second device; and   select the set of frequencies to have a frequency step that is based on the coarse distance measurement.   
     
     
         3 . The first device of  claim 1 , wherein the instructions to make the coarse distance measurement are configured to use at least one of: received signal strength indication (RSSI) or time of flight (TOF) to determine the coarse distance measurement. 
     
     
         4 . The first device of  claim 1 , wherein the non-transitory memory stores further instructions that cause the processing unit to, for each frequency of the set of frequencies:
 receive, from the second device, a phase offset measured between the outgoing signal having the respective frequency and a local oscillator of the second device; and   determine the phase delay difference for the respective frequency further based on the phase offset received from the second device.   
     
     
         5 . The first device of  claim 1 , wherein the instructions cause the processing unit to, for each frequency of the set of frequencies:
 transmit a plurality of outgoing signals having the respective frequency to the second device;   receive a plurality of response signals from the second device;   determine a plurality of phase delay difference based on the plurality of outgoing signals and the plurality of response signals; and   determine the phase delay difference for the respective frequency based on an average of the plurality of phase delay differences.   
     
     
         6 . The first device of  claim 1 , wherein the transceiver and oscillator are configured to switch from transmitting to receiving without affecting a phase of the oscillator. 
     
     
         7 . The first device of  claim 1 , wherein the non-transitory memory stores further instructions that cause the processing unit to perform a synchronization sequence between the first device and the second device that includes the determining of the distance between the first device and the second device. 
     
     
         8 . The first device of  claim 1 , wherein the transceiver is a software-controller transceiver. 
     
     
         9 . The first device of  claim 1 , wherein the transceiver is a low-power transceiver. 
     
     
         10 . A method comprising:
 for each frequency of a set of frequencies:
 transmitting, by a transceiver, an outgoing signal having the respective frequency to a target device; 
 receiving, by the transceiver, a response signal having the respective frequency from the target device; 
 determining a phase delay difference based on the outgoing signal and the response signal; and 
 determining a set of candidate distance ranges based on the phase delay difference; 
   determining a distance between the transceiver and the target device that overlaps each candidate distance range of each frequency in the set of frequencies.   
     
     
         11 . The method of  claim 10  further comprising:
 determining a coarse distance measurement between the transceiver and the target device; and 
 selecting the set of frequencies to have a frequency step that is based on the coarse distance measurement. 
 
     
     
         12 . The method of  claim 10  wherein the determining of the coarse distance measurement is based on at least one of received signal strength indication (RSSI) or time of flight (TOF). 
     
     
         13 . The method of  claim 10  further comprising, for each frequency of the set of frequencies:
 receiving, from the target device, a phase offset measured between the outgoing signal having the respective frequency and a local oscillator of the target device; and 
 determining the phase delay difference for the respective frequency further based on the phase offset received from the target device. 
 
     
     
         14 . The method of  claim 10  further comprising, for each frequency of the set of frequencies:
 transmitting, by the transceiver, a plurality of outgoing signals having the respective frequency to the target device; 
 receiving, by the transceiver, a plurality of response signals from the target device; 
 determining a plurality of phase delay difference based on the plurality of outgoing signals and the plurality of response signals; and 
 determining the phase delay difference for the respective frequency based on an average of the plurality of phase delay differences. 
 
     
     
         15 . The method of  claim 10  further comprising performing a synchronization sequence that includes the determining of the distance between the transceiver and the target device. 
     
     
         16 . A system comprising:
 a first device that includes:
 a processing unit; 
 a transceiver coupled to the processing unit; 
 a first oscillator coupled to the processing unit and to the transceiver; and 
 a non-transitory memory coupled to the processing unit and storing instructions, that when executed, cause the processing unit to:
 select a set of frequencies for transmitting to a second device via the transceiver; 
 for each frequency of the set of frequencies:
 set the first oscillator to oscillate at the respective frequency; 
 cause the transceiver to transmit an outgoing signal having the respective frequency to the second device; 
 receive a response signal from the second device having the respective frequency; 
 determine a phase delay difference based on the outgoing signal and the response signal for the respective frequency; and 
 determine a set of candidate distance ranges based on the phase delay difference; and 
 
 determine a distance between the first device and the second device that overlaps each candidate distance range of each frequency in the set of frequencies; and 
 
   the second device, wherein the second device is configured to, for each frequency of the set of frequencies:
 receive the outgoing signal transmitted by the first device; 
 based on the outgoing signal, set a second oscillator to oscillate at the respective frequency; 
 transmit the response signal using the second oscillator oscillating at the respective frequency. 
   
     
     
         17 . The system of  claim 16 , wherein:
 the second device is further configured to, for each frequency of the set of frequencies:
 measure a phase offset between the outgoing signal and the second oscillator; and 
 transmit the phase offset to the first device; 
   the first device is further configured to, for each frequency of the set of frequencies, determine the phase delay difference for the respective frequency further based on the phase offset transmitted by the second device.