Endpoint proximity pairing using acoustic spread spectrum token exchange and ranging information

Abstract

A first endpoint generates an acoustic spread spectrum signal including a pilot sequence and a data sequence representing a token synchronized to the pilot sequence, transmits the acoustic spread spectrum signal, and records a transmit time at which the acoustic spread spectrum signal is transmitted. A receive time at which a second endpoint received the acoustic spread spectrum signal transmitted by the first endpoint is received from the second endpoint along with an indication of a second token as recovered from the received acoustic spread spectrum signal by the second endpoint. A separation distance between the first endpoint and the second endpoint is computed based on a time difference between the transmit time and the receive time. The first endpoint is paired with the second endpoint when the token matches the second token and the computed distance is less than a threshold distance.

What is claimed is: 
     
       1. A method comprising:
 at a first endpoint device, generating an acoustic spread spectrum signal including a pilot sequence and a spread data sequence representing a token synchronized to the pilot sequence; 
 at the a first endpoint device, transmitting the an acoustic spread spectrum signal and recording a transmit time at which the acoustic spread spectrum signal is transmitted, wherein the acoustic spread spectrum signal is encoded with a token; 
 receiving over a network from a second endpoint device an indication of a receive time at which the second endpoint device received the acoustic spread spectrum signal transmitted by the first endpoint device and a second token as recovered from the received acoustic spread spectrum signal by the second endpoint device; 
 computing a separation distance between the first endpoint device and the second endpoint device ranging information based on a time difference between the transmit time and the receive time; and 
 responsive to the token matching the second token, and a comparison of the ranging information to a threshold value, pairing the first endpoint device with the second endpoint devicewhen the token matches the second token and the computed distance is less than a threshold distance. 
 
     
     
       2. The method of  claim 1 , wherein the pairing includes permitting the second endpoint device access to an information carrying channel between the first endpoint device and the second endpoint device. 
     
     
       3. The method of claim  1  24, further comprising, at the second endpoint device:
 receiving the acoustic spread spectrum signal transmitted by the first endpoint device; 
 correlating the received acoustic spread spectrum signal with a replica of the pilot sequence to produce a correlation peak indicative of a presence of the pilot sequence; 
 decoding the data sequence based on timing of the correlation peak to recover the second token from the data sequence; and 
 determining the receive time based on the timing of the correlation peak. 
 
     
     
       4. The method of  claim 1 , further comprising:
 repeatedly transmitting the acoustic spread spectrum signal and recording a respective transmit time at which each repeated acoustic spread spectrum signal is transmitted; 
 determining which of the recorded transmit times is nearest in time to the receive time; 
 wherein the computing includes computing the separation distance ranging information based on the receive time and the transmit time determined to be nearest in time to the receive time. 
 
     
     
       5. The method of claim  1  24, wherein the data sequence representing the token is based on a Prometheus Orthonormal Set (PONS) code construction and the pilot sequence is based on the PONS code construction and is orthogonal to the data sequence. 
     
     
       6. The method of  claim 5 , wherein each of the data sequence and the pilot sequence includes a respective sequence of PONS coefficients that sum together to a value of zero. 
     
     
       7. The method of  claim 5 , wherein the data sequence includes a sequence of PONS coefficients having a length equal to a first odd power of 2 and the pilot sequence includes a sequence of PONS coefficients having a second length equal to a second odd power of 2. 
     
     
       8. The method of  claim 1 , further comprising:
 initially sending a message carrying the token from a management entity, configured to communicate with the first endpoint device and the second endpoint device over a network, to the first endpoint device to cause the first endpoint device to perform the generating, the transmitting, and the recording. 
 
     
     
       9. The method of  claim 8 , further comprising, at the management entity:
 sending to the first endpoint device a request for the transmit time; 
 receiving from the first endpoint device a message indicating the transmit time, 
 wherein the computing the separation distance ranging information and the pairing are each performed at the management entity. 
 
     
     
       10. The method of  claim 8 , wherein the receiving includes receiving at the management entity the indication of the receive time and the second token, and the method further comprises:
 sending from the management entity to the first endpoint device the indication of the receive time; 
 performing the computing the separation distance ranging information at the first endpoint device; and 
 sending the computed separation distance ranging information from the first endpoint device to the management entity, 
 wherein the pairing is performed at the management entity. 
 
     
     
       11. A system comprising:
 a first endpoint device including: an encoder and a modulator to generate an acoustic spread spectrum signal including a pilot sequence and a spread data sequence representing a token synchronized to the pilot sequence; and a loudspeaker to transmit the a acoustic spread spectrum signal, wherein the first endpoint device is configured to record a transmit time at which the acoustic spread spectrum signal is transmitted, and the acoustic spread spectrum signal is encoded with a token; and 
 a management entity including:
 a network interface to communicate with a network; and 
 a processor coupled with the network interface and configured to:
 receive from a second endpoint device an indication of a receive time at which the second endpoint device received the acoustic spread spectrum signal transmitted by the first endpoint device and a second token as recovered from the received acoustic spread spectrum signal by the second endpoint device; 
 compute a separation distance between the first endpoint device and the second endpoint device ranging information based on a difference between the transmit time and the receive time; and 
 responsive to the token matching the second token, and a comparison of the ranging information to a threshold value, pair the first endpoint device with the second endpoint devicewhen the token matches the second token and the computed separation distance is within a threshold distance. 
 
 
 
     
     
       12. The system of  claim 11 , wherein the processor is configured to pair by permitting the second endpoint device access to an information carrying channel between the first endpoint device and the second endpoint device. 
     
     
       13. The system of claim  11  25, wherein the second endpoint device is configured to:
 receive the acoustic spread spectrum signal transmitted by the first endpoint device; 
 correlate the received acoustic spread spectrum signal with a replica of the pilot sequence to produce a correlation peak indicative of a presence of the pilot sequence; 
 decode the data sequence based on timing of the correlation peak to recover the second token from the data sequence; and 
 determine the receive time based on the timing of the correlation peak. 
 
     
     
       14. The system of claim  11  25, wherein the data sequence representing the token is based on a Prometheus Orthonormal Set (PONS) code construction and the pilot sequence is based on the PONS code construction and is orthogonal to the data sequence. 
     
     
       15. The method system of  claim 11 , wherein the processor is further configure configured to:
 initially send a message carrying the token to the first endpoint device over the network to cause the first endpoint device to perform the operations to generate, transmit, and record. 
 
     
     
       16. A method comprising:
 at a first endpoint device: generating an acoustic spread spectrum signal including a pilot sequence and a spread data sequence synchronized with the pilot sequence, wherein the spread data sequence encodes a token and a future transmit time at which the acoustic spread spectrum signal will be transmitted; and transmitting the an acoustic spread spectrum signal at the a future transmit time, wherein the acoustic spread spectrum signal is encoded with a token and a future time at which the acoustic spread spectrum signal will be transmitted; 
 at a second endpoint device: receiving the acoustic spread spectrum signal; determining from the received acoustic spread spectrum signal a receive time, a second token corresponding to the token, and the future transmit time; computing a separation distance between the first endpoint device and the second endpoint device ranging information based on a difference between the receive time and the future transmit time; and sending to the a network the second token and the computed separation distance ranging information; 
 receiving from the second endpoint device over the network the second token and the computed separation distance ranging information; and 
 responsive to the token matching the second token, and a comparison of the ranging information to a threshold value, pairing the first endpoint device with the second endpoint device when the second token matches the token and the computed separation distance is less than a threshold distance. 
 
     
     
       17. The method of claim  16  26, wherein the spread data sequence encoding the token is based on a Prometheus Orthonormal Set (PONS) code construction and the pilot sequence is based on the PONS code construction and is orthogonal to the data sequence. 
     
     
       18. The method of  claim 16 , further comprising:
 wherein the generating includes encoding acoustic spread spectrum signals encoded with the token and respective incrementally increasing future times into respective acoustic spread spectrum signals into which the token is encoded, and transmitting the respective acoustic spread spectrum signals at the respective incrementally increasing future times. 
 
     
     
       19. The method of  claim 18 , wherein the generating includes generating a sequence of acoustic spread spectrum signals each including a respective token of a sequence of tokens. 
     
     
       20. The method of  claim 16 , wherein the generating further includes encoding acoustic spread spectrum signal is encoded with an indication of a number of remaining times will be transmitted before transitioning to a next token. 
     
     
       21. The method of claim 1, wherein the ranging information is a separation distance between the first endpoint device and the second endpoint device, the threshold value is a threshold distance, and the separation distance is less than the threshold distance. 
     
     
       22. The system of claim 11, wherein the ranging information is a separation distance between the first endpoint device and the second endpoint device, the threshold value is a threshold distance, and the separation distance is less than the threshold distance. 
     
     
       23. The method of claim 16, wherein the ranging information is a separation distance between the first endpoint device and the second endpoint device, the threshold value is a threshold distance, and the separation distance is less than the threshold distance. 
     
     
       24. The method of claim 1, wherein the acoustic spread spectrum signal includes a pilot sequence and a spread data sequence representing the token synchronized to the pilot sequence. 
     
     
       25. The system of claim 11, wherein the acoustic spread spectrum signal includes a pilot sequence and a spread data sequence representing the token synchronized to the pilot sequence. 
     
     
       26. The method of claim 16, wherein the acoustic spread spectrum signal includes a pilot sequence and a spread data sequence synchronized with the pilot sequence, and the spread data sequence encodes the token and the future transmit time.