Abstract: In examples, Time-Reversal (TR) Orthogonal Frequency-Division Multiplexing (OFDM) communications employ adaptive filtering on a per-subcarrier basis. Matched filtering is used for subcarriers with poor transmission properties (such as relatively high channel attenuation), while inverse filtering is used for subcarriers with relatively good transmission properties (such as relatively low channel attenuation). Modulation order may be reduced for the subcarriers with poor properties (relative to the subcarriers with good properties). The discovery of subcarrier properties may be performed through the channel state information measured and reconciled from single- and/or bi-directional TR sounding signals. The discovery may be repeated, for example, performed continually. In response to changes in traffic and other environmental conditions, the system may be reconfigured dynamically with different subcarriers selected for matched and inverse filtering.

Abstract: In examples, Radio Frequency nodes of an array are synchronized using Time-Reversal. A Master node (“Master”) of the array receives and captures a sounding signal emitted by a Slave node (“Slave”) of the array, downconverts it to baseband, Time-Reverses the downconverted signal, upconverts the Time-Reversed signal to the carrier frequency using the Master's clock so that the upconverted signal has phase property of the Master's clock, and transmits the resulting signal to the Slave. The Slave receives the signal from the Master, and adjusts the phase of the Slave's clock so that the phases of the two nodes are aligned. Once phases, frequencies, and time references of the array's nodes are aligned, the array may be used for coherent operation. In examples, the array is used to transmit Time-Reversed signals so that the signals from the array's nodes are spatially and temporally focused on a target.

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.

Abstract: In examples, Radio Frequency nodes of an array are synchronized using Time-Reversal. A Master node (“Master”) of the array receives and captures a sounding signal emitted by a Slave node (“Slave”) of the array, downconverts it to baseband, Time-Reverses the downconverted signal, upconverts the Time-Reversed signal to the carrier frequency using the Master's clock so that the upconverted signal has phase property of the Master's clock, and transmits the resulting signal to the Slave. The Slave receives the signal from the Master, and adjusts the phase of the Slave's clock so that the phases of the two nodes are aligned. Once phases, frequencies, and time references of the array's nodes are aligned, the array may be used for coherent operation. In examples, the array is used to transmit Time-Reversed signals so that the signals from the array's nodes are spatially and temporally focused on a target.

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.