Array-to-array beamforming and iterative time reversal techniques

Abstract

In examples, two arrays of Radio Frequency nodes achieve enhanced beamforming for communications between the arrays by successively sending sounding signals from one array to the other array. Each sounding signal sent by the first of the two arrays is beamformed through time reversal of an immediately preceding sounding signal received by the first array from the second array, and each sounding signal (except the initial sounding signal) sent by the second array is beamformed through time reversal of an immediately preceding sounding signal received by the second array from the first array. The initial sounding signal sent by the second array may be omnidirectional, beamformed through a guesstimate, random, predetermined, or determined through a search of the area where the arrays are located. With sufficient beamfocusing, the arrays may communicate by sending and receiving data from one array to the other array.

What is claimed is: 
     
         1 . A method of radio frequency (RF) communication between arrays of nodes, the method comprising steps of:
 aligning/synchronizing nodes of a first array in time, frequency, and phase, the first array comprising a first plurality of nodes, the first plurality of nodes comprising at least two first array ad hoc nodes, each node of the first array comprising an RF receiver and an RF transmitter, whereby the first array is enabled to operate as a coherent array with coherent RF transmission properties and coherent RF reception properties;   aligning/synchronizing nodes of a second array in time, frequency, and phase, the second array comprising a second plurality of nodes, the second plurality of nodes comprising at least two second array ad hoc nodes, each node of the second array comprising an RF receiver and an RF transmitter, whereby the second array is enabled to operate as a coherent array with coherent RF transmission properties and coherent RF reception properties; and   successively sending RF sounding signals from the first plurality of nodes to the second plurality of nodes and from the second plurality of nodes to the first plurality of nodes, the RF sounding signals comprising a first RF sounding signal from the first plurality of nodes to the second plurality of nodes, each of the RF sounding signals sent by the second plurality of nodes being beamformed through time reversal of an immediately preceding RF sounding signal of the RF sounding signals received by the second plurality of nodes from the first plurality of nodes, and each of the RF sounding signals sent by the first plurality of nodes except the first RF sounding signal being beamformed through time reversal of an immediately preceding RF sounding signal of the RF sounding signals received by the first plurality of nodes from the second plurality of nodes.   
     
     
         2 . The method of  claim 1 , wherein:
 each of the at least two first array ad hoc nodes is free to move in absolute terms and with respect to each other node of the at least two first array ad hoc nodes in at least two dimensions and   each of the at least two second array ad hoc nodes is free to move in absolute terms and with respect to each other node of the at least two second array ad hoc nodes in at least two dimensions.   
     
     
         3 . The method of  claim 2 , further comprising:
 determining whether sufficient focusing between the first plurality of nodes and the second plurality of nodes has been achieved, thereby obtaining a determination;   terminating the step of successively sending in response to the determination indicating that sufficient focusing between the first plurality of nodes and the second plurality of nodes has been achieved; and   transmitting RF data communications in at least one direction selected from the group consisting of from the first plurality of nodes to the second plurality of nodes, and from the second plurality of nodes to the first plurality of nodes, the step of transmitting being performed after the determination indicates that sufficient focusing between the first plurality of nodes and the second plurality of nodes has been achieved.   
     
     
         4 . The method of  claim 3 , wherein the step of determining comprises measuring convergence of Signal-to-Noise Ratio (SNR) in at least one of the first plurality of nodes and the second plurality of nodes. 
     
     
         5 . The method of  claim 3 , wherein the step of determining comprises comparing mean square of aggregated differences of beamforming weights metric in successive sounding iterations to a predetermined limit. 
     
     
         6 . The method of  claim 3 , wherein the step of determining comprises computing a communication performance metric. 
     
     
         7 . The method of  claim 6 , wherein the step of determining further comprises computing a change in the communication performance metric. 
     
     
         8 . The method of  claim 6 , further comprising scatterer nulling by the first plurality of nodes. 
     
     
         9 . The method of  claim 6 , further comprising at least one step selected from the group consisting of beam sweeping and sidelobe sweeping. 
     
     
         10 . The method of  claim 6 , wherein the step of transmitting the RF data communications is performed with beamforming transmit/receive gain. 
     
     
         11 . The method of  claim 9 , further comprising:
 repeating at least one of the steps of aligning/synchronizing the RF nodes of the first array, aligning/synchronizing the RF nodes of the first array, and successively sending in response to a need to maintain link performance between the first plurality of nodes and the second plurality of nodes determined based on an error rate or Signal-to-Noise Ratio.   
     
     
         12 . The method of  claim 6 , wherein first inter-node distances of the first array and second inter-node distances of the second array are greater than inter-array distances between the first array and the second array. 
     
     
         13 . The method of  claim 6 , wherein the at least two first array ad hoc nodes comprise at least three first array ad hoc nodes, and the at least two second array ad hoc nodes comprise at least three second array ad hoc nodes. 
     
     
         14 . A Radio Frequency (RF) communication apparatus comprising:
 a first array of communication nodes comprising a first plurality of nodes, the first plurality of nodes comprising at least two first array ad hoc nodes, each node of the first plurality of nodes comprising an RF receiver and an RF transmitter;   a second array of communication nodes comprising a second plurality of nodes, the second plurality of nodes comprising at least two second array ad hoc nodes, each node of the second plurality comprising an RF receiver and an RF transmitter;   wherein:   the first array is configured to align/synchronize the first plurality of nodes in time, frequency, and phase, whereby the first array is enabled to operate as a coherent array with coherent RF transmission properties and coherent RF reception properties;   the second array is configured to align/synchronize the second plurality of nodes in time, frequency, and phase, whereby the second array is enabled to operate as a coherent array with coherent RF transmission properties and coherent RF reception properties; and   the first array and the second array are further configured to successively send RF sounding signals from the first plurality of nodes to the second plurality of nodes and from the second plurality of nodes to the first plurality of nodes, the RF sounding signals comprising a first RF sounding signal from the first plurality of nodes to the second plurality of nodes, each of the RF sounding signals sent by the second plurality of nodes being beamformed through time reversal of an immediately preceding RF sounding signal of the RF sounding, signals received by the second plurality of nodes from the first plurality of nodes, and each of the RF sounding signals sent by the first plurality of nodes except the first RF sounding signal being beamformed through time reversal of an immediately preceding RF sounding signal of the RF sounding signals received by the first plurality of nodes from the second plurality of nodes.   
     
     
         15 . The RF communication apparatus of  claim 14 , wherein:
 each of the at least two first array ad hoc nodes is free to move in absolute terms and with respect to each other node of the at least two first array ad hoc nodes in at least two dimensions; and   each of the at least two second array ad hoc nodes is free to move in absolute terms and with respect to each other node of the at least two second array ad hoc nodes in at least two dimensions.   
     
     
         16 . The RF communication apparatus of  claim 15 , wherein at least one of the first array and the second array is further configured to:
 determine whether sufficient focusing has been achieved between the first plurality of nodes and the second plurality of nodes, thereby obtaining a determination;   stop successively sending the RF sounding signals in response to the determination indicating to that sufficient focusing; between the first plurality of nodes and the second plurality of nodes has been achieved; and   transmit RF data communications in at least one direction selected from the croup consisting of: from the first plurality of nodes to the second plurality of nodes, and from the second plurality of nodes to the first plurality of nodes, after the determination indicates that sufficient focusing between the first plurality of nodes and the second plurality of nodes has been achieved.   
     
     
         17 . The RF communication apparatus of  claim 16 , wherein said at least one of the first array and the second array is further configured, in the course of determining whether sufficient focusing, has been achieved between the first plurality of nodes and the second plurality of nodes, to measure convergence of Signal-to-Noise Ratio (SNR) in at least one of (1) the first plurality of nodes and (2) the second plurality of nodes. 
     
     
         18 . The RF communication apparatus of  claim 16 , wherein'said at least one of the first array and the second array is further configured, in the course of determining whether sufficient focusing has been achieved between the first plurality of nodes and the second plurality of nodes, to compare mean square of aggregated differences of beamforming weights metric in successive sounding iterations to a predetermined limit. 
     
     
         19 . The RF communication apparatus of  claim 16 , wherein said at least one of the first array and the second array is further configured, in the course of determining whether sufficient focusing has been achieved between the first plurality of nodes and the second plurality of nodes, to compute a communication performance metric. 
     
     
         20 . The RF communication apparatus of  claim 19 , wherein said at least one of the first array and the second array is further configured, in the course of determining whether sufficient focusing has been achieved between the first plurality of nodes and the second plurality of nodes, to compute a change in the communication performance metric. 
     
     
         21 . The RF communication apparatus of  claim 19 , wherein the first array is further configured to null scatterers. 
     
     
         22 . The RF communication apparatus of  claim 19 , wherein the first array is further configured to perform at least one step selected from the group consisting of beam sweeping and sidelobe sweeping. 
     
     
         23 . The RF communication apparatus of  claim 19 , wherein said at least one of the first array and the second array is further configured to transmit the RF data communications with beamforming transmit/receive gain. 
     
     
         24 . The RF communication apparatus of  claim 23 , wherein said at least one of the first array and the second array is further configured, in response to a need to maintain link performance between the first plurality of nodes and the second plurality of nodes determined based on an error rate or Signal-to-Noise Ratio, to repeat at least one of: (1) align/synchronize the RF nodes of the first array, (2) align/synchronize the RF nodes of the first array, and (3) successively send. 
     
     
         25 . The RF communication apparatus of  claim 19 , wherein each inter-node distance of the first array is greater than all inter-array distances between the first array and the second array. 
     
     
         26 . The method of  claim 19 , wherein the at least two first array ad hoc nodes comprise at least three first array ad hoc nodes, and the at least two second array ad hoc nodes comprise at least three second array ad hoc nodes. 
     
     
         27 . An article of manufacture comprising at least one non-volatile machine-readable storage medium with program code stored in the at least one non-volatile machine-readable storage medium, the program code, when executed by processors of nodes of a first array and of nodes of a second array, each node of the first array and each node of the second array comprising an antenna, a radio frequency (RF) receiver coupled to the antenna, an RF transmitter coupled to the antenna, and a processor coupled to the RF receiver and the RF transmitter to control operation of the RF receiver and the RF transmitter, the first array comprising a first plurality of nodes that comprises at least two first array ad hoc nodes, the second array comprising a second plurality of nodes comprising at least two second array ad hoc nodes, configures the nodes of the first array and the nodes of the second array to:
 align synchronize nodes of the first array in time, frequency, and phase, enabling the first array to operate as a coherent array with coherent RF transmission properties and coherent RF reception properties;   align/synchronize nodes of a second array in time, frequency, and phase, enabling the second array to operate as a coherent array with coherent RF transmission properties and coherent RF reception properties; and   successively send RF sounding signals from the first plurality of nodes to the second plurality of nodes and from the second plurality of nodes to the first plurality of nodes, the RF sounding signals comprising a first RF sounding signal from the first plurality of nodes to the second plurality of nodes, each of the RF sounding signals sent by the second plurality of nodes being beamformed through time reversal of an immediately preceding RF sounding signal of the RF sounding signals received by the second plurality of nodes from the first plurality of nodes, and each of the RF sounding signals sent by the first plurality of nodes except the first RF sounding signal being beamformed through time reversal of an immediately preceding RF sounding signal of the RF sounding signals received by the first plurality of nodes from the second plurality of nodes.