DISTRIBUTED CO-OPERATING NODES USING TIME REVERSAL

• US 20140126567A1
• Filed: 05/02/2012
• Published: 05/08/2014
• Est. Priority Date: 05/02/2011
• Status: Active Grant

• Current Assignee: Ziva Corporation
• Original Assignee: Ziva Corporation
• Inventors: Husain, Anis, Rode, Jeremy, Smith, David, Hsu, Mark, Achour, Maha
• Granted Patent: US 9,497,722 B2
• Time in Patent Office: Days
• US Class Current: 370/350
• CPC Class Codes: H04B 7/024 Co-operative use of antennas of several sites, e.g. in co-ordinated multipoint or co-operative multiple-input multiple-output [MIMO] systems
• CPC Class Codes: H04J 3/0638 Clock or time synchronisation among nodes; Internode synchronisation synchronization for ring networks H04L12/422; data switching networks with synchronous transmission H04L12/43
• CPC Class Codes: H04J 3/0682 by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
• CPC Class Codes: H04W 56/001 Synchronization between nodes
• CPC Class Codes: H04W 56/0015 one node acting as a reference for the others
• CPC Class Codes: H04W 56/0025 synchronizing potentially movable access points
• CPC Class Codes: H04W 56/0065 using measurement of signal travel time
• CPC Class Codes: H04W 84/18 Self-organising networks, e.g. ad-hoc networks or sensor networks

Abstract

Methods and systems for coherent distributed communication techniques using time reversal are disclosed. In one aspect, cooperating nodes of a cluster can move relative to each other and relative to an intended receiver of the nodes'"'"' data transmissions. The nodes are synchronized to a common time reference, and data for transmission from the cluster is distributed to the nodes. The intended receiver sends a sounding signal to the nodes. Each node receives the sounding signal, obtains the channel response between the intended receiver and itself, and time-reverses the channel response. Each node then convolves its time-reversed channel response with the data to obtain the node'"'"'s convolved data Each node waits a predetermined time following the time reference signal, as determined based on the common time reference. At the expiration of the predetermined time period, the nodes simultaneously transmit their convolved data

Claims

1. A method of transmitting from a plurality of nodes, the method comprising steps of:

synchronizing each node of the plurality of nodes to a common time reference of all nodes of the plurality of nodes, so that all nodes of the plurality of nodes are enabled to transmit synchronously a predetermined synchronization period after a trigger signal is sent from a trigger node of the plurality of nodes;

obtaining at said each node of the plurality of nodes information sufficient to transmit from said each node a time-reversed signal corresponding to said each node, so that when all nodes of the plurality of nodes synchronously transmit respective time-reversed signals, the time-reversed signals combine spatially and temporally to focus on a subject;

sending the trigger signal from the trigger node of the plurality of nodes; and

transmitting the time-reversed signals from all nodes of the plurality of nodes, a time-reversed signal per node, so that a combination of the plurality of time-reversed signals is spatially and temporally focused on the subject, the step of transmitting being performed in response to expiration of the predetermined synchronization period following the step of sending the trigger signal;

wherein the nodes of the plurality of nodes are untethered ad hoc nodes movable relative to each other, a different physical clock per node of the plurality of nodes.

2. A method according to claim 1, wherein the step of synchronizing comprises determining at said each node frequency offset of the physical clock of said each node other than a selected node of the plurality of nodes from a physical clock of the selected node.

3. A method according to claim 2, further comprising measuring the predetermined synchronization period at said each node based on the common time reference of all nodes of the plurality of nodes.

4. A method according to claim 3, further comprising receiving the trigger signal at all nodes of the plurality of nodes other than the trigger node.

5. A method according to claim 4, wherein the common time reference is based on the physical clock of the trigger node.

6. A method according to claim 5, wherein the subject is an intended receiver of the time-reversed signals, and every node of the plurality of nodes is within radio frequency (RF) Line-of-Sight (LoS) of one or more other nodes of the plurality of nodes.

7. A method according to claim 6, wherein the step of obtaining comprises:

receiving at said each node a sounding signal from the intended receiver; and

time-reversing at said each node the sounding signal received at said each node, resulting in said each node obtaining a time-reversed channel response between said each node and the intended receiver.

8. A method according to claim 5, wherein the subject is a first scatterer, the time-reversed signals are intended for an intended receiver, the intended receiver not being the first scatterer, and every node of the plurality of nodes is within radio frequency (RF) Line-of-Sight (LoS) of one or more other nodes of the plurality of nodes.

9. A method according to claim 8, wherein:

the step of obtaining comprises;

receiving at said each node waveforms that resulted from sounding environment using one or more channel sounding bursts transmitted from the intended receiver, the waveforms comprising reflections of the one or more channel sounding bursts from one or more scatterers, the one or more scatterers comprising the first scatterer, and

processing the waveforms using time-reversal and Singular Value Decomposition to determine first signatures for launching from all nodes of the plurality of nodes a first transmission temporally and spatially focused on the first scatterer, each first signature corresponding to a different node of the plurality of nodes;

the method further comprising;

generating the time-reversed signal corresponding to said each node by convolving data intended for the intended receiver with the signature corresponding to said each node.

10. A method according to claim 9, further comprising comparing one or more of the first signatures to a plurality of stored signatures, wherein the stored signatures are stored in a database together with identifications of objects corresponding to the stored signatures.

11. A method of transmitting from a first node of a plurality of nodes, the method comprising steps of:

synchronizing the first node to a common time reference of the plurality of nodes, so that all nodes of the plurality of nodes are enabled to transmit synchronously a predetermined synchronization period after a trigger signal is sent from a trigger node of the plurality of nodes;

obtaining at the first node information sufficient to transmit from the first node a time-reversed signal corresponding to the first node, so that when all nodes of the plurality of nodes synchronously transmit respective time-reversed signals, the time-reversed signals combine spatially and temporally to focus on a subject;

receiving the trigger signal at the first node; and

transmitting from the first node the time-reversed signal corresponding to the first node in response to expiration of the predetermined synchronization period following the trigger node sending the trigger signal;

wherein all nodes of the plurality of nodes are untethered ad hoc nodes movable relative to each other, a different physical clock per node of the plurality of nodes.

12. A method according to claim 11, wherein the step of synchronizing comprises determining at the first node frequency offset of the physical clock of the first node from a physical clock of a selected node of the plurality of nodes.

13. A method according to claim 12, further comprising measuring the predetermined synchronization period at the first node based on the common time reference, the physical clock of the first node being different from the common clock reference.

14. A method according to claim 13, wherein the subject is an intended receiver of the time-reversed signals, and the first node is within radio frequency (RF) Line-of-Sight (LoS) of one or more other nodes of the plurality of nodes.

15. A method according to claim 14, wherein the step of obtaining comprises:

receiving at the first node a sounding signal from the intended receiver; and

time-reversing at the first node the sounding signal received at the first node, resulting in the first node obtaining a time-reversed channel response between the first node and the intended receiver.

16. A node comprising an antenna, a transceiver coupled to the antenna, and a processor coupled to the transceiver to control operation of the transceiver, wherein the node is part of a plurality of cooperative nodes, the node being configured to:

synchronize the node to a common time reference of the plurality of cooperative nodes, so that all nodes of the plurality of cooperative nodes are enabled to transmit synchronously a predetermined synchronization period after a trigger signal is sent from a trigger node of the plurality of cooperative nodes;

obtain at the node information sufficient to transmit from the node a time-reversed signal corresponding to the node, so that when all nodes of the plurality of cooperative nodes synchronously transmit respective time-reversed signals, the time-reversed signals combine spatially and temporally to focus on a subject;

receive the trigger signal at the node; and

transmit from the node the time-reversed signal corresponding to the node in response to expiration of the predetermined synchronization period following the trigger node sending the trigger signal;

wherein all nodes of the plurality of cooperative nodes are untethered ad hoc nodes movable relative to each other, a different physical clock per node of the plurality of cooperative nodes.

17. A node according to claim 16, wherein the node is further configured to synchronize to the common time reference by determining at the node frequency offset of the physical clock of the node from a physical clock of a selected node of the plurality of cooperative nodes.

18. A node according to claim 17, wherein the node is further configured to measure the predetermined synchronization period at the node based on the common time reference, the physical clock of the node being different from the common clock reference.

19. A node according to claim 18, wherein the subject is an intended receiver of the time-reversed signals, and the node is within radio frequency (RF) Line-of-Sight (LoS) of one or more other nodes of the plurality of cooperative nodes.

20. A node according to claim 19, wherein the node is configured to obtain the information by receiving a sounding signal from the intended receiver, and time-reversing the sounding signal received at the node, resulting in the node obtaining a time-reversed channel response between the node and the intended receiver.

21. A system comprising a plurality of nodes, each node of the plurality of nodes comprising an antenna, a transceiver coupled to the antenna, and a processor coupled to the transceiver to control operation of the transceiver, wherein the plurality of nodes is configured to:

synchronize each node of the plurality of nodes to a common time reference of all nodes of the plurality of nodes, so that all nodes of the plurality of nodes are enabled to transmit synchronously a predetermined synchronization period after a trigger signal is sent from a trigger node of the plurality of nodes;

obtain at said each node of the plurality of nodes information sufficient to transmit from said each node a time-reversed signal corresponding to said each node, so that when all nodes of the plurality of nodes synchronously transmit respective time-reversed signals, the time-reversed signals combine spatially and temporally to focus on a subject;

send the trigger signal from the trigger node of the plurality of nodes; and

transmit the time-reversed signals from all nodes of the plurality of nodes, a time-reversed signal per node, so that a combination of the plurality of time-reversed signals is spatially and temporally focused on the subject, the time-reversed signals being transmitted in response to expiration of the predetermined synchronization period following sending of the trigger signal;

wherein the nodes of the plurality of nodes are untethered ad hoc nodes movable relative to each other, a different physical clock per node of the plurality of nodes.

22. A system according to claim 21, wherein the plurality of nodes is further configured to synchronize by determining at said each node frequency offset of the physical clock of said each node, other than a selected node of the plurality of nodes, from a physical clock of the selected node.

23. A system according to claim 22, wherein the plurality of nodes is further configured to measure the predetermined synchronization period at said each node based on the common time reference of all nodes of the plurality of nodes.

24. A system according to claim 23, wherein the plurality of nodes is further configured to receive the trigger signal at all nodes of the plurality of nodes other than the trigger node.

25. A system according to claim 24, wherein the common time reference is based on the physical clock of the trigger node.

26. A system according to claim 25, wherein the subject is an intended receiver of the time-reversed signals, and every node of the plurality of nodes is within radio frequency (RF) Line-of-Sight (LoS) of one or more other nodes of the plurality of nodes.

27. A system according to claim 26, wherein the plurality of nodes is configured to obtain the information by receiving at said each node a sounding signal from the intended receiver, and time-reversing at said each node the sounding signal received at said each node, resulting in said each node obtaining a time-reversed channel response between said each node and the intended receiver.

28. A system according to claim 25, wherein the subject is a first scatterer, the time-reversed signals are intended for an intended receiver, the intended receiver not being the first scatterer, and every node of the plurality of nodes is within radio frequency (RF) Line-of-Sight (LoS) of one or more other nodes of the plurality of nodes.

29. A system according to claim 28, wherein the plurality of nodes is further configured to

obtain the information by (1) receiving at said each node waveforms that resulted from sounding environment using one or more channel sounding bursts transmitted from the intended receiver, the waveforms comprising reflections of the one or more channel sounding bursts from one or more scatterers, the one or more scatterers comprising the first scatterer, and (2) processing the waveforms using time-reversal and Singular Value Decomposition to determine first signatures for launching from all nodes of the plurality of nodes a first transmission temporally and spatially focused on the first scatterer, each first signature corresponding to a different node of the plurality of nodes;

and

generate the time-reversed signal corresponding to said each node by convolving data intended for the intended receiver with the signature corresponding to said each node.

30. A system according to claim 29, wherein the plurality of nodes is further configured to compare one or more of the first signatures to a plurality of stored signatures, wherein the stored signatures are stored in a database together with identifications of objects corresponding to the stored signatures.

31. A method of transmitting from a plurality of nodes, the method comprising steps of:

step for synchronizing each node of the plurality of nodes to a common time reference of all nodes of the plurality of nodes, so that all nodes of the plurality of nodes are enabled to transmit synchronously a predetermined synchronization period after a trigger signal is sent from a trigger node of the plurality of nodes;

step for obtaining at said each node of the plurality of nodes information sufficient to transmit from said each node a time-reversed signal corresponding to said each node, so that when all nodes of the plurality of nodes synchronously transmit respective time-reversed signals, the time-reversed signals combine spatially and temporally to focus on a subject;

sending the trigger signal from the trigger node of the plurality of nodes; and

step for transmitting the time-reversed signals from all nodes of the plurality of nodes, a time-reversed signal per node, so that a combination of the plurality of time-reversed signals is spatially and temporally focused on the subject, the step of transmitting being performed in response to expiration of the predetermined synchronization period following the step of sending the trigger signal;

wherein the nodes of the plurality of nodes are untethered ad hoc nodes movable relative to each other, a different physical clock per node of the plurality of nodes.