Handshaking protocol for time-reversal system

1. A method comprising:

at a first device, receiving a handshake signal transmitted from a second device through multiple propagation paths, the handshake signal including a preamble and a training sequence, the training sequence including a sequence of symbols known to the first and second devices;

determining a synchronization index based on the preamble;

identifying the training sequence in the handshake signal based on the synchronization index;

determining a channel response signal based on the received training sequence;

generating a signature waveform that is a time-reversed signal of the channel response signal; and

generating a transmission signal based on transmit data and the signature waveform, the transmit data being data configured to be transmitted to the second device

in which determining a channel response comprises calculating =Cq u, in which represents an estimated channel response, Cq represents a conversion matrix, and u represents a portion of the received handshake signal that is estimated to be the received training sequence;

in which the conversion matrix Cq is determined by calculating Cq=(T′ T) −1 T′ s in which T is a Toeplitz matrix generated based on s q , which represents an effective training sequence sent by the second device.

2. The method of claim 1 in which the handshake signal comprises a first predetermined code.

3. The method of claim 2 in which the first predetermined code comprises a barker code.

4. The method of claim 2 in which the handshake signal comprises a second predetermined code that includes an index for selecting the training sequence from among a list of training sequences.

5. The method of claim 1 in which the preamble comprises pulse signals.

6. The method of claim 1 in which determining a channel response signal comprises determining a channel response signal based on a conversion matrix and the training sequence.

7. The method of claim 6 in which the conversion matrix is constructed based on the training sequence sent by the second device.

8. The method of claim 1 in which determining a channel response signal comprises determining a channel response signal based on a least square method.

9. The method of claim 1 , comprising applying time windows to the received training sequence and determining an estimated channel response based on averaging the samples in the time windows.

10. The method of claim 1 , comprising applying time windows to the received preamble to determine the synchronization index.

11. The method of claim 1 in which the training sequence comprises a first guard band, followed by an effective training sequence, which is followed by a second guard band.

12. The method of claim 1 in which generating a signature waveform comprises generating a signature waveform that is a time-reversed conjugate signal of the channel response signal.

13. A system comprising:

a first device comprising:

an input circuit configured to receive a handshake signal transmitted wirelessly from a second device through multiple propagation paths, the handshake signal including a preamble and a training sequence, the training sequence including a sequence of symbols known to the first and second devices; and

a data processor configured to:

determine a synchronization index based on the preamble;

identify the training sequence in the handshake signal based on the synchronization index;

determine a channel response signal based on the received training sequence;

generate a signature waveform that is a time-reversed signal of the channel response signal; and

generate a transmission signal based on transmit data and the signature waveform, the transmit data being data configured to be transmitted to the second device

in which the data processor is configured to determine a channel response by calculating =Cq u, in which represents an estimated channel response, Cq represents a conversion matrix, and u represents a portion of the received handshake signal that is estimated to be the received training sequence;

in which the conversion matrix Cq is determined by calculating Cq=(T′T) −1 T′ in which T is a Toeplitz matrix generated based on s q , which represents an effective training sequence sent by the second device.

14. The apparatus of claim 13 in which the handshake signal comprises a first predetermined code.

15. The apparatus of claim 14 in which the first predetermined code comprises a barker code.

16. The apparatus of claim 14 in which the handshake signal comprises a second predetermined code that includes an index for selecting the training sequence from among a list of training sequences.

17. The apparatus of claim 13 in which the preamble comprises pulse signals.

18. The apparatus of claim 13 in which the data processor is configured to determine a channel response signal based on a conversion matrix and the training sequence.

19. The apparatus of claim 18 in which the conversion matrix is constructed based on the training sequence sent by the second device.

20. The apparatus of claim 13 in which the data processor is configured to determine a channel response signal based on a least square method.

21. The apparatus of claim 13 , in which the data processor is configured to apply time windows to the received training sequence and determine an estimated channel response based on averaging the samples in the time windows.

22. The apparatus of claim 13 , in which the data processor is configured to apply time windows to the received preamble to determine the synchronization index.

23. The apparatus of claim 13 in which the training sequence comprises a first guard band, followed by an effective training sequence, which is followed by a second guard band.

24. The apparatus of claim 13 in which the data processor is configured to generate a signature waveform that is a time-reversed conjugate signal of the channel response signal.