WO2015023895A1 - Systèmes sans fil à inversion temporelle ayant une architecture asymétrique - Google Patents

Systèmes sans fil à inversion temporelle ayant une architecture asymétrique Download PDF

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Publication number
WO2015023895A1
WO2015023895A1 PCT/US2014/051148 US2014051148W WO2015023895A1 WO 2015023895 A1 WO2015023895 A1 WO 2015023895A1 US 2014051148 W US2014051148 W US 2014051148W WO 2015023895 A1 WO2015023895 A1 WO 2015023895A1
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WIPO (PCT)
Prior art keywords
signal
communication protocol
operations
downlink
frequency band
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Application number
PCT/US2014/051148
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English (en)
Inventor
Feng Han
K. J. Ray Liu
Yan Chen
Original Assignee
Origin Wireless Communications, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US13/969,320 external-priority patent/US9559874B2/en
Priority claimed from US13/969,271 external-priority patent/US9882675B2/en
Application filed by Origin Wireless Communications, Inc. filed Critical Origin Wireless Communications, Inc.
Priority to EP14756197.1A priority Critical patent/EP3033862A1/fr
Priority to US14/912,324 priority patent/US9900794B2/en
Publication of WO2015023895A1 publication Critical patent/WO2015023895A1/fr
Priority to US15/861,422 priority patent/US11025475B2/en
Priority to US15/873,806 priority patent/US10270642B2/en
Priority to US16/101,444 priority patent/US10291460B2/en
Priority to US16/125,748 priority patent/US10833912B2/en

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0212—Channel estimation of impulse response
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0224—Channel estimation using sounding signals
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03006—Arrangements for removing intersymbol interference
    • H04L25/03343—Arrangements at the transmitter end
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03891—Spatial equalizers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/0398—Restoration of channel reciprocity

Definitions

  • This disclosure generally relates to time-reversal wireless systems having asymmetric architecture.
  • transceiver B when a transceiver A intends to transmit information to a transceiver B, transceiver B first sends a waveform that propagates through a scattering and multi-path environment, and the signals are received by transceiver A. Transceiver A transmits time-reversed signals back through the same channel to transceiver B. Based on channel reciprocity, a time-reversal communication system leverages the multi-path channel as a matched filter, i.e., treats the environment as a facilitating matched filter computing machine, and focuses the wave at the receiver in both space and time domains.
  • a method for time-reversal wireless communication comprises at a transceiver, receiving a channel response signal derived from a probe signal sent from a first device to the transceiver through multiple wireless propagation paths; calculating a signature waveform for the first device based on the channel response; receiving combined signals that include a signal from the first device and a signal from a second device; and determining the signal from the first device based on the combined signals and the signature waveform for the first device.
  • Implementations of the method may include one or more of the following features. Determining the signal from the first device comprises performing a convolution operation, or an operation equivalent to the convolution operation, between the combined signals and the signature waveform for the first device.
  • Determining the signal from the first device can include filtering the combined signals using the signature waveform as a filtering parameter.
  • the signature waveform for the first device can be a time-reversed waveform of the channel response signal derived from the probe signal sent from the first device.
  • the channel response signal can be represented as h(t) and the signature waveform for the first device can be represented as h* ⁇ T-t), t representing time, and T representing a delay spread of the multiple propagation paths.
  • the channel response signal can be represented as h[k] and the signature waveform for the first device can be represented as h*[L - k ], k being an integer, and L representing a delay spread of the multiple propagation paths.
  • the method can include transmitting, from the transceiver to the first receiver and a second receiver, a combined downlink signal derived from a combination of a first downlink waveform and a second downlink waveform, the first downlink waveform including data intended for the first device, the second downlink waveform including data intended for the second device.
  • the method can include generating the first downlink waveform based on the data intended for the first device and the signature waveform for the first device.
  • Generating the first downlink waveform can include performing a convolution of the data intended for the first device and the signature waveform for the first device.
  • the combined downlink signal can be configured to enable each of the first device and the second device to receive multipath signals that can be used determine a data signal intended for the device, the first and second devices receiving the downlink signal through different propagation paths and determining different data signals.
  • the transceiver can be part of a base station.
  • Receiving combined signals can include receiving combined signals that include signals from three or more devices communicating with the transceiver, each of the devices being associated with a corresponding signature waveform.
  • the first device does not calculate the signature waveform.
  • the first device does not perform any signal processing that uses the signature waveform.
  • communication comprises an input circuit configured to, during a hand-shake period, receive a channel response signal derived from a probe signal sent from a first device to the apparatus through multiple wireless propagation paths, and during an uplink transmission period, receive combined signals that include a signal from the first device and a signal from a second device; and a data processor configured to calculate a signature waveform for the first device based on the channel response, and determine the signal sent from the first device during the uplink transmission period based on the combined signals and the signature waveform for the first device.
  • the apparatus can include a base station that includes the input circuit and the data processor.
  • the data processor can determine the signal sent from the first device by performing a convolution operation, or an operation equivalent to the convolution operation, between the combined signals and the signature waveform for the first device.
  • the data processor can determine the signal sent from the first device by filtering the combined signals using the signature waveform as a filtering parameter.
  • the data processor can determine the signature waveform for the first device by generating a time-reversed waveform of the channel response signal derived from the probe signal sent from the first device.
  • the channel response signal can be represented as h(t) and the signature waveform for the first device can be represented as h* ⁇ T- t), t representing time, and T representing a delay spread of the multiple propagation paths.
  • the channel response signal can be represented as h[k] and the signature waveform for the first device can be represented as h*[L - k ], k being an integer, and L representing a delay spread of the multiple propagation paths.
  • the data processor can be configured to determine a combined downlink signal derived from a combination of a first downlink waveform and a second downlink waveform, the first downlink waveform including data intended for the first device, the second downlink waveform including data intended for the second device.
  • the data processor can be configured to determine the first downlink waveform based on the data intended for the first device and the signature waveform for the first device.
  • the data processor can determine the first downlink waveform by performing a convolution, or an operation equivalent to the convolution, of the data intended for the first device and the signature waveform for the first device.
  • the combined downlink signal can be configured to enable each of the first device and the second device to receive multipath signals that can be used determine a data signal intended for the device, the first and second devices receiving the downlink signal through different propagation paths and determining different data signals.
  • the input circuit can be configured to receive combined signals that include signals from three or more devices that communicate with the apparatus, and the data processor is configured to calculate a signature waveform for each of the devices.
  • the first device does not calculate the signature waveform.
  • the first device does not perform any signal processing that uses the signature waveform.
  • a method of communication between a transceiver and multiple devices using wireless multi-path signals comprises performing a hand-shake process between the transceiver and the devices, in which for each device, the transceiver receives a channel response signal derived from a probe signal sent from the device to the transceiver through multiple propagation paths;
  • the transceiver can be part of a base station.
  • the devices do not calculate any signature waveform.
  • the devices do not perform any signal processing that uses the signature waveform.
  • the method comprises performing a first hand-shake process between the first and second devices, in which the first device receives a channel response signal derived from a probe signal sent from the second device to the first device through multiple wireless propagation paths; performing a second hand-shake process between the first and third devices, in which the first device receives a channel response signal derived from a probe signal sent from the third device to the first device through multiple wireless propagation paths; at the first device, calculating a signature waveform for the second device based on the channel response derived from the probe signal sent from the second device; at the first device, calculating a signature waveform for the third device based on the channel response derived from the probe signal sent from the third device; at the first device, receiving a combined uplink signal that includes uplink signals from the second and third devices; at the first device, determining the uplink signal from the second device based on the combined uplink signal and the signature waveform for the second device; and at the first device, determining the uplink signal
  • Implementations of the method may include one or more of the following features.
  • the second and third devices do not calculate any signature waveform.
  • the method can include transmitting, from the first device to the second and third devices, a combined downlink signal derived from a combination of a second downlink waveform and a third downlink waveform, the second downlink waveform including data intended for the second device, the third downlink waveform including data intended for the third device.
  • the second downlink waveform can be embedded with the signature waveform corresponding to the second device.
  • the method can include at the second device, receiving a signal intended for the second device without performing any signal processing that uses the signature waveform corresponding to the second device.
  • the method can include at the first device, generating the second downlink waveform based on the data intended for the second device and the signature waveform for the second device.
  • Generating the second downlink waveform can include performing a convolution of the data intended for the second device and the signature waveform for the second device.
  • the combined downlink signal can be configured to enable each of the second and third devices to receive multipath signals that can be used determine a data signal intended for the device, the second and third devices receiving the combined downlink signal through different propagation paths and determining different data signals.
  • Determining the uplink signal from the second device can include performing a convolution operation, or an operation equivalent to the convolution operation, between the combined uplink signal and the signature waveform for the second device.
  • Determining the uplink signal from the second device can include filtering the combined uplink signal using the signature waveform corresponding to the second device as a filtering parameter.
  • the signature waveform for the second device can be a time -reversed waveform of the channel response signal derived from the probe signal sent from the second device.
  • the channel response signal derived from the probe signal sent from the second device can be represented as h(t) and the signature waveform for the second device can be represented as h* ⁇ T-t), t representing time, and T representing a delay spread of the multiple propagation paths.
  • the channel response signal derived from the probe signal sent from the second device can be represented as h[k] and the signature waveform for the second device can be represented as h*[L - k ], k being an integer, and L representing a delay spread of the multiple propagation paths.
  • the first device can include a base station.
  • Receiving a combined uplink signal can include receiving a combined uplink signal that includes signals from the second and third devices, and one or more additional devices communicating wirelessly with the first device, each of the devices being associated with a corresponding signature waveform.
  • FIG. 1 is a diagram showing an exemplary environment for operating a time- reversal system.
  • FIG. 2 A is a graph of an exemplary recorded channel response waveform.
  • FIG. 2B is a graph of an exemplary time-reversed waveform generated by reversing the waveform of FIG. 2A with respect to time.
  • FIG. 3 is a diagram showing an exemplary environment for operating a time- reversal system having multiple receivers.
  • FIG. 4 is a diagram of an exemplary multi-user time reversal communication system.
  • FIG. 5 is a diagram showing a hand-shaking process.
  • FIG. 6 is a diagram showing a down-link transmission process.
  • FIG. 7 is a diagram showing an up-link transmission process.
  • FIG. 8 is a graph showing the bit error rate (BER) performance of the time reversal system for downlink transmission in an outdoor environment.
  • BER bit error rate
  • FIG. 9 is a graph showing the bit error rate performance of the time reversal system for uplink transmission in an outdoor environment.
  • FIG. 10 is a graph showing the bit error rate performance of the time reversal system for downlink transmission in an indoor environment.
  • FIG. 11 is a graph showing the bit error rate performance of the time reversal system for uplink transmission in an indoor environment.
  • FIGS. 12-14 are flow diagrams of exemplary processes for asymmetric time- reversal wireless communication.
  • FIG. 15 is a diagram of an exemplary multi-user time reversal communication system.
  • FIGS. 16A and 16B are diagrams showing an exemplary 2D interference cancelation and decision module.
  • FIG. 17 is a diagram showing a multi-stage 2D interference cancelation and decision module.
  • FIGS. 18A and 18B are graphs showing examples of channel impulse responses.
  • FIGS. 19A and 19B are graphs showing examples of convolutions of channel impulse responses and time-reversal signature waveforms.
  • FIGS. 20 to 23 are graphs showing the bit error rate performances of the time reversal system using 2D parallel interference cancellation under various operation conditions.
  • FIGS. 24 to 26 are flow diagrams of exemplary processes for asymmetric time- reversal wireless communication with interference cancellation.
  • FIG. 27 is a diagram of an exemplary multi-user time reversal communication system that uses multiple communication protocols.
  • FIG. 28A is a diagram of an exemplary transmitter based on Wi-Fi protocol.
  • FIG. 28B is a diagram of an exemplary receiver based on Wi-Fi protocol.
  • FIG. 29A is a diagram of an exemplary transmitter at a base station for downlink transmission based on 4G LTE protocol.
  • FIG. 29B is a diagram of an exemplary receiver at a terminal device for downlink transmission based on 4G LTE protocol.
  • FIG. 30A is a diagram of an exemplary transmitter at the terminal device for uplink transmission based on 4G LTE protocol.
  • FIG. 3 OB is a diagram of an exemplary receiver at the base station for uplink transmission based on 4G LTE protocol.
  • FIG. 31A is a diagram of an exemplary downlink architecture of an asymmetrical time -reversal communication system.
  • FIG. 3 IB is a diagram of an exemplary uplink architecture of the asymmetrical time -reversal communication system.
  • FIG. 32 is a diagram of an exemplary symmetrical time -reversal communication system.
  • FIG. 33 is a diagram of exemplary system architectures of a base station and terminal devices that use both symmetrical and asymmetrical time -reversal
  • FIG. 34 is a diagram of an implementation of a base station and terminal devices that use both symmetrical and asymmetrical time-reversal communication.
  • FIG. 35 is a diagram of an exemplary a mobile device having communication modules using a first communication protocol having a substantially symmetric architecture and a second communication having an asymmetric architecture.
  • FIG. 36 is a diagram of an exemplary group of robots that communicate using a first communication protocol that has a substantially symmetrical architecture and a second communication protocol that has an asymmetrical architecture.
  • FIG. 37 is a diagram of an exemplary vehicle having a communication unit that communicates using a first communication protocol that has a substantially symmetrical architecture and a second communication protocol that has an asymmetrical architecture.
  • This disclosure describes a novel asymmetric multi-user time reversal wireless communication system architecture for both downlink and uplink communication between a base station (BS) and multiple terminal devices (TDs).
  • BS base station
  • TDs terminal devices
  • the complexities of the base station and the terminal devices are asymmetric, such that the base station performs most of the signal processing as both a transmitter (for the downlink) and receiver (for the uplink), allowing the use of low complexity terminal devices.
  • an intelligent house may include one or more computers that communicate with several sensors (e.g., temperature, humidity, light, and motion sensors), meters (e.g., electricity and water meters), appliances (e.g., refrigerator, oven, washing machine), electronic devices (e.g., television, digital video recorder, audio/video system, telephone, digital photo album, intelligent lamp, security system), climate control systems (e.g., fans, thermostats for air conditioning and heating, motorized shades), power generators (e.g., backyard wind turbine, solar panel, geothermal energy system).
  • sensors e.g., temperature, humidity, light, and motion sensors
  • meters e.g., electricity and water meters
  • appliances e.g., refrigerator, oven, washing machine
  • electronic devices e.g., television, digital video recorder, audio/video system, telephone, digital photo album, intelligent lamp, security system
  • climate control systems e.g., fans, thermostats for air conditioning and heating, motorized shades
  • power generators e.g., backyard wind turbine, solar panel
  • the devices communicating with the computer be simple without the need to perform complex signal processing.
  • the computer may function as a base station or be coupled to a base station that performs most of the signal processing when transmitting signals to the devices and receiving signals sent from the devices.
  • an intelligent factory may include one or more computers that communicate wirelessly with robots working in assembly lines, vehicles that move supplies and assembled products, climate control systems, security systems, inventory control systems, and power systems.
  • a laboratory may include one or more computers that communicate wirelessly with instruments that monitor parameters when conducting experiments.
  • the computer can communicate with the devices using time -reversal division multiple access technology that uses the environment to provide spatial filtering, allowing a large number of devices to communicate with the computers simultaneously.
  • time-reversal division multiple access has the advantage that the additional cost for enabling each device to communicate with the computer is small because the device itself does not need to perform complicated signal processing. Most of the signal processing is performed at the computer.
  • the power consumption by each device for enabling wireless communication may also be much smaller compared to previous wireless technologies.
  • the computer may receive the tail end of the signal of an earlier symbol and the front end of a later symbol at the same time, resulting in inter-symbol interference.
  • multiple devices may transmit signals to the computer at the same time, so the computer may receive a combined signal having components from several devices.
  • the time -reversal system may use signature waveforms associated with each device to identify the signal components for each device. After using the signature waveforms as a filtering mechanism to identify individual signal components, there may still be interference among signals from different devices.
  • the computer may perform signal processing to cancel inter-symbol interference and/or inter-user interference.
  • time-reversal divisional multiple access technology leverages the unique temporal and spatial focusing effects of the time reversal phenomenon to provide cost-effective single-carrier broadband multi-user communication.
  • OFDM orthogonal frequency-division multiplexing
  • OFDMA orthogonal frequency-division multiple access
  • the time-reversal division multiple access scheme uses the multi-path channel profile associated with each user's location as a location-specific signature for the user.
  • Each path of the multi-path channel can be treated as a virtual antenna in the time- reversal division multiple access system, which collectively results in very high- resolution spatial focusing with potentially "pin-point" accuracy. Meanwhile, the temporal focusing effect can effectively suppress inter-symbol interference which significantly simplifies the terminal user's complexity and gives rise to higher-speed data transmission.
  • the computer may function as a base station or be coupled to a base station that performs most of the signal processing when transmitting signals to the devices and receiving signals sent from the devices.
  • a 2D parallel interference cancellation scheme may allow multiple devices to communicate with the computer at the same time with reduced interference. For a specified bit error rate and data transmission rate, the 2D parallel interference cancellation scheme can allow more devices to communicate with the computer simultaneously. For a specified bit error rate and number of devices, the 2D parallel interference cancellation scheme can allow the devices to communicate with the computer at higher data transmission rates.
  • a time-reversal system can be used in an environment having structures or objects that may cause one or more reflections of wireless signals.
  • a venue 102 may have a first room 104 and a second room 106.
  • a first device 108 in the first room 104 transmits a signal to a second device 110 in the second room 106
  • the signal can propagate in several directions and reach the second device 110 by traveling through several propagation paths, e.g., 112, 114, and 116.
  • the signal traveling through multiple propagation paths may be referred to as a multipath signal.
  • the signal may become distorted.
  • the multipath signal received by the second device 110 can be quite different from the signal transmitted by the first device 108.
  • the signal received by the second device 110 may have a waveform 120.
  • waveform 120 may be referred to as the channel impulse response signal.
  • a time-reversed waveform 130 can be generated by reversing the waveform 120 with respect to time. If the second device 110 sends a signal having the waveform 130, the signal will propagate in various directions, including through propagation paths 112, 114, and 116 (in reverse direction relative to the propagation direction of the impulse signal), and reach the first device 108.
  • the multipath signal received at the first device 108 may form an impulse signal that is similar to the impulse signal previously sent from the first device 108 to the second device 110.
  • the waveforms 120 and 130 shown in FIGS. 2A and 2B are merely examples.
  • the waveforms in time-reversal systems can vary depending on, e.g., the environment and the information or data being transmitted.
  • the initial signal sent from the first device 108 can be any sort of signal, of which an impulse is just one example.
  • the initial signal can be any waveform.
  • the second device 110 may use a normalized time-reversed conjugate of the signal received from device 108 as a basic transmission waveform.
  • the second device 110 may encode the data stream on the basic waveform and transmit the signal through the wireless channel.
  • the signal received at the device 108 may be described as the convolution of the transmitted signal and the channel impulse response, plus additive white Gaussian noise. Because the transmitted signal has been designed based on a time reversed version of the channel impulse response, the first device 108 may only need to perform a simple adjustment to the received signal and down-sample it to recover the data stream transmitted by the second device 1 10.
  • a transmitting device or base station or access point may send signals to two or more receiving devices at the same time.
  • the transmitted signals travel through multiple propagation paths to each receiver. Because the receivers are positioned at different locations, the multipath signals travel through different propagation paths to reach the receivers.
  • By carefully constructing the waveform of the signal sent from the transmitter it is possible to allow each receiver to receive data intended for the receiver with sufficiently high quality.
  • the first device 108 may communicate with the second device 110 and a third device 140.
  • the second device 110 may send a probe signal that travels through propagation paths 112, 114, and 116 to the first device 108.
  • the probe signal can be, e.g., a pulse signal, a signal that has a predetermined waveform, or a signal that includes symbols.
  • the first device 108 may record the received waveform
  • the third device 140 may send a probe signal that travels through propagation paths 142, 144, and 146 to the first device 108.
  • the first device 108 may record the received waveform representing the channel response for the second multipath channel.
  • the first device 108 may construct a downlink signal based on a first time- reversed multipath channel response, a second time -reversed multipath channel response, a first data stream intended for the second device receiver 110, and a second data stream intended for the third device receiver 140.
  • the first device 108 may transmit the downlink signal so that a first portion of the downlink signal travels through propagation paths 112, 114, and 116 to reach the second device 110.
  • a second portion of the downlink signal may travel through propagation paths 142, 144, and 146 to reach the third device 140.
  • the first signal portion received at the second device 110 may form a first data stream.
  • the second signal portion received at the third device 140 may form a second data stream.
  • the device operating as a transmitter may use either an omnidirectional antenna or a directional antenna for broadcasting the downlink signal, as long as the downlink signal reaches each of the receivers through multiple propagation paths.
  • the transmitting antenna may use beam-forming techniques to launch a signal that undergoes a large number of reflections. That is, the transmitter may launch a wireless signal that preferentially experiences multiple transmission paths.
  • an exemplary multi-user time reversal communication system 150 includes a base station (BS) 152 and multiple terminal devices (e.g., 154a, 154b, 154c, collectively 154).
  • BS base station
  • terminal devices e.g., 154a, 154b, 154c, collectively 154.
  • Each of the terminal devices 154 is associated with a multi-path wireless channel (e.g., 156a, 156b, 156c, collectively 156) between itself and the base station 152.
  • Each multi-path wireless channel 156 in the figure represents two or more multiple signal propagation paths between the corresponding terminal and the base station.
  • all the devices can operate at the same frequency band.
  • the base station 152 can send multiple messages (either independent or non-independent) simultaneously to multiple selected terminals 154.
  • multiple terminals 154 can send their own messages to the base station 152 simultaneously.
  • the following describes an exemplary hand-shaking process between the base station 152 and the terminals 154.
  • a hand-shaking process may occur periodically in a round-robin manner among the registered terminal devices 154 to maintain an up-to-date record of the channel responses associated with the terminal devices 154 at the base station 152.
  • only one selected terminal may send a probe signal 160, and may perform radio frequency modulation 162 to produce a radio frequency signal that propagates through the associated multi-path channel 156a to the base station 152.
  • the probe signal 160 can be, e.g., a pulse signal, a signal that has a predetermined waveform, or a signal that includes symbols to enable the base station to perform synchronization and/or other functions.
  • the probe signal is a pulse signal.
  • other types of probe signals can be used in the system 150.
  • the base station 152 may receive the transmitted radio frequency signal, perform radio frequency demodulation 164 to recover the unique channel response (waveform) 166 and record it.
  • the selected terminal e.g., 154a
  • the other terminals e.g., 154b and 154c
  • the base station 152 calculates a signature waveform g 168 for the terminal 154a based on its channel response received at the base station 152.
  • one of the basic signature waveforms for a terminal associated with a channel response hit can be h * (T - t) , which is a time -reversed waveform of the channel response, with T representing the delay spread of the multi-path channel. If hit) is a complex value, h" (T - 1) is the time reverse and conjugation of the channel response hit) .
  • the channel response can be represented as h[k]
  • the corresponding signature waveform can be h * [L - k] , in which L represents the delay spread of the multi-path channel.
  • the delay spread can be a measure of the multipath richness of a communications channel. In general, it can be interpreted as the difference between the time of arrival of the earliest significant multipath component (typically the line-of-sight component) and the time of arrival of the latest multipath component.
  • the delay spread is L
  • the total channel length is L+l .
  • the system 150 can use any type of waveform design that is designed for a variety of performance metrics, such as designed for reducing or minimizing inter- symbol interference and/or inter-user interference.
  • the calculated signature waveforms can be used for data transmissions during both the downlink and the uplink processes.
  • N active terminal devices 154 receiving data from the base station 152 concurrently.
  • the information bits from the sources may be first encoded by channel-coding using encoders 172.
  • the channel-coding process is optional and may be omitted in some implementations.
  • the encoded bit-stream for any given terminal i ⁇ , 2, ... N] may be represented by a sequence of symbols
  • a parameter referred to as the rate back-off factor D may be used to match the symbol rate (signal bandwidth) with the higher system's sampling rate (channel bandwidth).
  • the rate matching process at the base station 152 may be performed by up-sampling the sequence of symbols by the factor D .
  • the rate matching processes may be performed at rate matching modules 174.
  • l, 2, ... N] can be expressed as
  • the up-sampled sequences may be embedded with the calculated (based on the channel responses obtained in the handshaking process) signature waveform , V/ E ⁇ l, 2, ... N by taking the convolution of the up-sampled symbol sequence and the corresponding signature waveform.
  • signature waveform is the time-reversed (and conjugated if the channel response is of complex values) channel response, i.e.,
  • the output of the signature embedding block 176 for the i -th terminal is the convolution of [ ⁇ 1 ⁇ ] and ⁇ l ⁇ ] ⁇ , i.e. where (*) is the linear convolution.
  • each of the streams may be multiplied by a scalar power gain ⁇ to implement a power control mechanism at the power control module 178.
  • All the streams may be multiplexed together by a summation module 180 to obtain a combined signal S[k]:
  • the combined signal S[k] may be transmitted by the RF module 182 and may propagate through different multi-path channels 156, for all/ E jl, 2, ... N] .
  • the signal received at the / -th terminal 154 is the multi-path channel output plus additive noise .
  • the signal energy can be concentrated in a single time sample or close to a single time sample. Then, the / -th terminal 154 may not need to apply equalization to the received signal to recover the signal.
  • the i-th terminal 154 may down-sample the received signal with the same factor D (to recover the signal's rate from the system's sampling rate to the symbol rate), producing ⁇ [k] , represented as follows:
  • an estimation Xi[k] about can be made based on the value of Y t [k] .
  • the estimated/reconstructed symbol sequence can be fed into the decoder (which corresponds to the encoder) to recover the information bits at each individual terminal device.
  • Each terminal device 154 may have its own information source 190 which may be independent of others.
  • the information bits may be first encoded by the channel coding block 192. Then, the coded symbols ⁇ [ c] ⁇ ( Vz * ⁇ ⁇ l, 2, ... N ) may be up-sampled by the rate back-off factor D for rate matching at the rate matching module 194.
  • the scaling factors ⁇ 3 ⁇ 4 ⁇ may be used to implement power control at the power control module 196. After multiplying with scaling factor, the sequence of a. j ⁇ t/ ] ⁇ , for all z e jl, 2, ... N] , may be transmitted by the RF module 198.
  • the convolution between a. j ⁇ t/ ] and the channel impulse response is automatically taken as the channel output for the z -th terminal. Since each terminal's multi-path channel response is unique, the automatic convolution between the a i ⁇ x) D k ⁇ ⁇ and is mathematically similar to the base station's signature embedding process in the downlink.
  • All of the channel outputs for the N terminal devices 154 may be mixed together in the air plus the additive noise at the base station 152.
  • the mixed signal received at the base station 152 can be written as
  • the base station 152 may pass this mixed signal through an information extraction module that can include a filter bank 200 of the calculated signature waveforms g i , Vz E [l, 2, ... N] , each of which may perform the convolution between its input signal Z[k] and the corresponding terminal device's signature waveform ⁇ [&] ⁇ .
  • an information extraction module can include a filter bank 200 of the calculated signature waveforms g i , Vz E [l, 2, ... N] , each of which may perform the convolution between its input signal Z[k] and the corresponding terminal device's signature waveform ⁇ [&] ⁇ .
  • Such a convolution using the signature waveform may extract the useful signal component and suppress the signals of other terminal devices.
  • the convolution can be represented as
  • the rate matching may be performed by down-sampling (with the same factor D) the filter bank's output signal at the rate matching module 202 to recover the original symbol rate of each terminal 154.
  • the down-sampled symbol sequence ⁇ [&] ⁇ can be obtained as
  • an estimation Xi[k] about ⁇ k] can be made. Then, the estimated/reconstructed symbol sequence can be fed into the corresponding decoder 204 to recover the information bits from each terminal device at the base station 152.
  • the IEEE 802.15.4a (broadband) channel model was used to evaluate the effectiveness of the proposed system.
  • the typical delay spread of the outdoor channels are between 200 ns and 400 ns
  • the typical delay spread of the indoor channels are between 70 ns and 120 ns.
  • a graph 210 shows the predicted bit error rate (BER) performance of the system 150 for downlink transmission in an outdoor environment.
  • a curve 212 represents the predicted bit error rate when the rate back-off factor D is equal to 64, and the number of users Nis equal to 2.
  • a curve 214 represents the predicted bit error rate when the rate back-off factor D is equal to 32, and the number of users Nis equal to 2.
  • a curve 216 represents the predicted bit error rate when the rate back-off factor D is equal to 64, and the number of users N is equal to 4.
  • a curve 218 represents the predicted bit error rate when the rate back-off factor D is equal to 32, and the number of users Nis equal to 4.
  • a graph 220 shows the predicted bit error rate performance of the system 150 for uplink transmission in an outdoor environment.
  • a curve 222 represents the predicted bit error rate when the rate back-off factor D is equal to 64, and the number of users N is equal to 2.
  • a curve 224 represents the predicted bit error rate when the rate back-off factor D is equal to 32, and the number of users Nis equal to 2.
  • a curve 226 represents the predicted bit error rate when the rate back-off factor D is equal to 64, and the number of users Nis equal to 4.
  • a curve 228 represents the predicted bit error rate when the rate back-off factor D is equal to 32, and the number of users Nis equal to 4.
  • a graph 230 shows the predicted bit error rate performance of the system 150 for downlink transmission in an indoor environment.
  • a curve 232 represents the predicted bit error rate when the rate back-off factor D is equal to 32, and the number of users N is equal to 2.
  • a curve 234 represents the predicted bit error rate when the rate back-off factor D is equal to 16, and the number of users Nis equal to 2.
  • a curve 236 represents the predicted bit error rate when the rate back-off factor D is equal to 32, and the number of users Nis equal to 4.
  • a curve 238 represents the predicted bit error rate when the rate back-off factor D is equal to 16, and the number of users Nis equal to 4.
  • a graph 240 shows the predicted bit error rate performance of the system 150 for uplink transmission in an indoor environment.
  • a curve 242 represents the predicted bit error rate when the rate back-off factor D is equal to 32, and the number of users N is equal to 2.
  • a curve 244 represents the predicted bit error rate when the rate back-off factor D is equal to 16, and the number of users Nis equal to 2.
  • a curve 246 represents the predicted bit error rate when the rate back-off factor D is equal to 32, and the number of users Nis equal to 4.
  • a curve 248 represents the predicted bit error rate when the rate back-off factor D is equal to 16, and the number of users Nis equal to 4.
  • an exemplary process 250 for asymmetric time-reversal wireless communication is provided.
  • the process 250 can be implemented using the base station 152 shown in FIGS. 4-7.
  • the process 250 may include, at a transceiver, receiving a channel response signal derived from a probe signal sent from a first device to the transceiver through multiple wireless propagation paths (252).
  • the transceiver can be part of the base station 152.
  • the process 250 may include calculating a signature waveform for the first device based on the channel response (254).
  • the first device can be the first terminal device 154a.
  • the process 250 may include receiving combined signals that include a signal from the first device and a signal from a second device (256).
  • the second device can be the second terminal device 154b.
  • the process 250 may include determining the signal from the first device based on the combined signals and the signature waveform for the first device (258).
  • the base station 152 can receive the combined signals from the first and second terminal devices 154a and 154b and apply the signature waveform for the first terminal device 154a to the combined signals to determine the signal from the first terminal device 154a.
  • a convolution operation or an operation equivalent or similar to the convolution operation, can be performed between the combined signals and the signature waveform for the first device.
  • the signature waveform for the first device can be a time-reversed waveform of the channel response signal derived from the probe signal sent from the first device.
  • the transceiver can be the base station 152, and the multiple devices can be the terminal devices 154 in FIGS. 4-7.
  • the process 270 may include performing a hand-shake process between the transceiver and the devices, in which for each device, the transceiver receives a channel response signal derived from a probe signal sent from the device to the transceiver through multiple propagation paths (272). For example, after each device registers with the transceiver, a hand-shaking process can occur periodically in a round-robin manner among the registered devices to maintain an up-to-date record of the channel responses associated with the devices at the transceiver. In embodiments, the hand-shaking process may occur on a predetermined schedule, or a calculated schedule, or in response to a measured parameter of the receivers or transmitters or system performance, and the like.
  • only one selected device may perform radio frequency modulation to produce a radio frequency signal that propagates through the associated multi-path channel to the transceiver.
  • the transceiver receives the transmitted radio frequency signal and may perform radio frequency demodulation to recover the unique channel response (waveform) and may record it.
  • the selected device when the selected device is performing the hand-shaking process with the transceiver, the other devices may remain silent.
  • the process 270 may include calculating a signature waveform for each of the devices based on the channel response derived from the probe signal sent from the device (274).
  • a signature waveform for a device associated with a channel response hit can be h * (T - 1) , which is a time-reversed waveform of the channel response, with T representing the delay spread of the multi-path channel.
  • the channel response can be represented as h[k]
  • the corresponding signature waveform can be h * [L - k] , which L represents the delay spread of the multi-path channel.
  • the process 270 may include receiving a combined uplink signal that includes uplink signals from two or more devices (276), and determining the uplink signal from each one of the devices based on the combined uplink signal and the signature waveform for the device (278).
  • the base station 152 can receive a combined uplink signal that includes uplink signals from the first and second terminal devices 154a and 154b.
  • the base station 152 can apply the signature waveform for the first terminal device 154a to the combined signals to determine the signal from the first terminal device 154a, and apply the signature waveform for the second terminal device 154b to the combined signals to determine the signal from the second terminal device 154b.
  • a convolution operation or an operation equivalent or similar to the convolution operation, can be performed between the combined signals and the signature waveform for the first or second device.
  • a convolution operation or an operation equivalent or similar to the convolution operation, can be performed between the combined signals and the signature waveform for the first or second device.
  • FIG. 14 an exemplary process 290 for asymmetric time-reversal communication between a plurality of devices using wireless multi-path signals is provided.
  • the devices can include the base station 152 and the terminal devices 154 of FIGS. 4-7.
  • the process 290 may include performing a first hand-shake process between the first and second devices, in which the first device may receive a channel response signal derived from a probe signal sent from the second device to the first device through multiple wireless propagation paths (292).
  • the first device can be the base station 152
  • the second device can be the first terminal device 154a.
  • the process 290 may include performing a second hand-shake process between the first and third devices, in which the first device receives a channel response signal derived from a probe signal sent from the third device to the first device through multiple wireless propagation paths (294).
  • the third device can be the second terminal device 154b.
  • the process 290 may include at the first device, calculating a signature waveform for the second device based on the channel response derived from the probe signal sent from the second device (296); and at the first device, calculating a signature waveform for the third device based on the channel response derived from the probe signal sent from the third device (298).
  • the signature waveform for the second or third terminal devices 154a or 154b can be a time -reversed waveform of the channel response signal derived from the probe signal sent from the second or third terminal devices 154a or 154b, respectively.
  • a signature waveform for the second or third terminal devices associated with a channel response hit can be h * (T - t) , which is a time-reversed waveform of the channel response, with T representing the delay spread of the multi-path channel. If h(t) is a complex value, h * (T - t) is the time reverse and conjugation of the channel response h(t) . In discrete time domain, the channel response can be represented as h[k] , and the corresponding signature waveform can be h * [L - k] , in which L represents the delay spread of the multi-path channel. Note that each terminal device may have a unique, location dependent, signature waveform.
  • the process 290 may include at the first device, receiving a combined uplink signal that includes uplink signals from the second and third devices (300).
  • the base station 152 can receive a combined uplink signal that includes uplink signals from the second and third terminal devices 154a, 154b.
  • the process 290 may include at the first device, determining the uplink signal from the second device based on the combined uplink signal and the signature waveform for the second device (302); and at the first device, determining the uplink signal from the third device based on the combined uplink signal and the signature waveform for the third device (304).
  • the base station 152 can apply the signature waveform for the second terminal device 154a to the combined signals to determine the signal from the second terminal device 154a, and apply the signature waveform for the third terminal device 154b to the combined signals to determine the signal from the third terminal device 154b.
  • a convolution operation or an operation equivalent or similar to the convolution operation, can be performed between the combined signals and the signature waveform for the second and/or third terminal device 154a and/or 154b.
  • the novel time -reversal division multiple access based multi-user uplink architecture described above can also utilize a 2-dimensional (2D) parallel interference cancellation scheme to enhance the system performance.
  • 2D parallel interference cancellation scheme uses the tentative decisions of detected symbols to effectively cancel the interference in both the time dimension (inter-symbol interference or ISI) and the user dimension (inter-user interference (IUI)), which may significantly improve the bit-error-rate performance and achieve a high signal-to-noise-ratio (SNR).
  • a multi-stage processing can be implemented by cascading multiple stages of the proposed 2D interference cancellation, with a total delay that increases linearly with the number of stages, but independent of the number of users. Simulation results are provided for up to 3 stages of interference cancellation and compared with the basic time -reversal division multiple access system without interference cancelation.
  • the term “user” may refer to a device.
  • multi-user uplink refers to the uplink by multiple devices
  • inter- user interference refers to the interference among various devices.
  • a time-reversal division multiple access architecture may be described as having two parts, the downlink part and the uplink part.
  • a base station BS may transmit multiple data streams to several users simultaneously, in which each user may be associated with a unique multi-path profile in a rich-scattering environment.
  • the time-reversal division multiple access downlink scheme may exploit the spatial degrees of freedom of the environment and focus the useful signal power mostly at the intended locations.
  • Time reversal mirrors (TRMs) at the base station may use a time -reversed copy of the channel response of each user's channel as the user's signature waveform, and then embed these signatures into the corresponding data streams.
  • TRMs Time reversal mirrors
  • the transmitted signal from the base station in the time -reversal division multiple access downlink may be a mixed signal that includes the data intended to be sent to several users (including different data intended for different users).
  • the encoded waveform may be temporally and spatially focused at the intended user's location.
  • time -reversal division multiple access framework More sophisticated signature waveforms can be derived based on the multi-path channel responses to further improve the performance of the time -reversal division multiple access downlink system.
  • a 2-dimensional (2D) parallel interference cancellation scheme may be provided by exploring the signal structure of both the inter-symbol interference (ISI) (time dimension) and the inter-user interference (IUI) (user dimension).
  • ISI inter-symbol interference
  • IUI inter-user interference
  • a TRDMA system may experience more severe inter-user interference because the multi-path signature waveforms are not naturally orthogonal.
  • the time-reversal division multiple access system allows overlap between the transmitted signature waveforms to boost system throughput, which may cause inter- symbol interference, depending on the extent of overlapping.
  • the 2D parallel interference cancellation scheme uses the tentative decisions of detected symbols to effectively reduce or cancel both the inter-symbol interference and inter-user interference at the base station.
  • multi-stage processing can be performed by cascading multiple stages of cancellation, with a total delay that increases linearly with the number of stages, but independent of the number of users.
  • an exemplary broadband multi-user time reversal communication system 1550 includes a base station 1552 and multiple users or terminal devices (e.g., 1554a, 1554b, 154c, collectively 1554).
  • all the devices can operate at the same frequency band, and the system operates in multi-path environments.
  • the base station 1552 can send multiple messages (either independent or non- independent) simultaneously to multiple selected terminals 1554.
  • multiple terminals 1554 can send their own messages to the base station 1552 simultaneously.
  • N users 1554 may simultaneously transmit independent bit streams to the base station 1552.
  • binary phase-shift keying (BPSK) modulation is considered, and the polarity of the modulated symbols [Xi [k] E ⁇ — 1, +1 ⁇ carries the binary information for user i.
  • BPSK binary phase-shift keying
  • Other types of modulation formats including ASK, FSK, QAM, and any known variations and combinations of those modulation formats can also be used.
  • the channel hi 1556 between the base station 1552 and user is a multi-path channel that can be characterized by a unique discrete-time channel impulse response (CIR)
  • each user 1554 may take turns sending a probe signal or waveform to the base station 1552.
  • the probe signal can be, e.g., a pulse signal, a signal that has a predetermined waveform, or a signal that includes symbols to enable the base station to perform synchronization and/or other functions.
  • the exemplary probe signal is a pulse signal.
  • other types of probe signals can be used in the system 1550.
  • the probe signals are pulse signals
  • the channel impulse response ⁇ 3/[/f] ⁇ of each user's link can be recorded by a time-reversal mirror 1558 at the base station 1552.
  • the time-reversal mirror 1558 may reverse the recorded waveform in the time domain and normalize it as the unique signature waveform of user .
  • the time-reversed waveform of user may be used in the uplink data transmission phase to extract the desired signal from a combination of the multiple access signals that are mixed in the air.
  • each device 1554 may have a rate matching module 1560 that introduces a rate back-off factor D to match the symbol rate (signal bandwidth) with the higher system sampling rate
  • the scaling factors ⁇ 3 ⁇ 4 for / e l,2,- ⁇ -,N] may be used to implement the transmit power control, whose values are assumed to be instructed by the base station 1552 through a feedback/control channel. After multiplying with scaling factor, the sequence of ⁇ 3 ⁇ 4 ) ⁇ ] [ ] for all ⁇ 1,2,...,N], may be transmitted through the corresponding multi-path channel ⁇ 3/[/f] ⁇ .
  • ⁇ ? ; [/ ] ⁇ may be automatically taken as the channel output for user . All of the channel outputs for the N users are mixed together in the air
  • the base station 1552 may pass this mixed signal through a bank of N time-reversal mirrors 1558, each of which may perform the convolution between its input signal ⁇ S[k] ⁇ and the user's signature waveform
  • Equation 13 Comparing Equation 13 and the received signal at the terminal users in the downlink, the same mathematical structure can be found by switching the roles of the signature waveforms ig l s and the channel impulse responses ⁇ ,-s in the convolution (and ignoring the scaling factor a, and noise term). Therefore, mathematically, a virtual spatial focusing effect as observed in the downlink can be seen in the user's signature domain of the uplink scheme. Unlike the physical spatial focusing effect observed in the downlink in which the useful signal power is concentrated at different physical locations, in the uplink, the signal power concentration in the users'
  • the base station 1552 includes a rate matching module 1566 to perform rate matching by down-sampling (with the same factor D) the time-reversal mirror's output signal to recover the original symbol rate of the modulated symbols of each user.
  • the down-sampled time-reversal mirror output Yi[k] can be represented as
  • Yi[k] which aligns the highest temporal focusing gain (gi * hi)[L ⁇ l] in Yi[k] with the transmitted symbol Xi[k] in time for ease of simple notation.
  • Y i [k] a i (g i *h i )[L-l]X i [k] (Signal) + «, ⁇ (g ⁇ h ⁇ L-l + Dl ⁇ ik-l] (ISI)
  • the basic time-reversal division multiple access uplink scheme uses the signal Yi[k] in Equation 15 to estimate the transmitted symbol Xi[k].
  • MLE maximum-likelihood estimation
  • interference and inter-user interference as a Gaussian random variable with zero mean (because the interference term is a linear combination of the zero-mean binary symmetric symbols Xik] £ ⁇ +1,-1 ⁇ ) and variance
  • the likelihood ratio can be derived as
  • Equation 18 Equation 18
  • PDF conditional probability density function
  • Equation 19 the superscript "fo)" of A' j5 [A:] indicates the initial stage of the interference cancellation procedure. Such a notation is useful in the following discussion of multi-stage interference cancellation schemes.
  • Equation 19 The error probability of the estimator shown in Equation 19 can be calculated based on the Gaussian approximations of the interference as follows
  • SINR ⁇ (0)' is the signal-to-interference-plus-noise ratio (SINR) for user at the initial stage. From Equation 20, one can see that the error probability decreases with the achieved signal-to-interference-plus-noise ratio, i.e., the quality of the signal before the final decision.
  • SINR signal-to-interference-plus-noise ratio
  • the base station 1552 includes a 2D interference cancellation and decision module 1568 that cancels the inter-symbol interference and the inter-user interference.
  • the following describes the 2D interference cancellation scheme that uses the estimated symbols to effectively cancel both the inter-symbol interference and inter-user interference, and significantly improves the performance of the uplink communication.
  • the 2D parallel interference cancellation scheme used by the 2D interference cancelation and decision module 1568 can have one or more stages. A single stage 2D parallel interference cancellation scheme is described first.
  • the time-reversal division multiple access system can be an interference-limited system, especially in the high signal-to-noise ratio (SNR) regime.
  • SNR signal-to-noise ratio
  • Equation 16 have structures that can be exploited to improve the bit error rate performances. Because the channel impulse responses have been obtained at the base station 1552 during the channel probing phase, the interference terms in Equation 16 can be reconstructed if the relevant transmitted symbols are known. Note that the coefficients can be determined by the base station 1552 and sent to the users 1554. In the interference cancellation scheme described here, the estimated symbols from the previous stage can be used to approximate the interference terms in the current stage.
  • the basic TRDMA system (without interference cancelation) may be considered as the initial (0-th) stage of the interference cancellation.
  • the interference cancellation of the TRDMA system includes two parts belonging to two different dimensions; the inter-symbol interference due to the multi-path effect of broadband channels, which is in the time domain, and the inter-user interference caused by the simultaneous transmission of multiple users, which is in the user's signature domain.
  • the 2D parallel interference cancellation scheme for the TRDMA uplink system targets the interference in both dimensions by exploiting the structure of interference in both dimensions.
  • each received symbol may include interference caused by the symbols transmitted before and after the current symbol.
  • Equation 16 in order to ideally cancel the interference for user 's symbol Xi[k], one has to know all the other users' transmitted symbols from time
  • the tentative decision vectors can be obtained in parallel for all the users in the 2D parallel
  • Equation 16 Based on the tentative decisions of the transmitted symbols, the approximated interference terms in Equation 16 can be reconstructed by looking at the structure of the inter- symbol interference and the inter-user interference. In doing so, we first define the row vector Uy for V £ ⁇ 1, 2, N ⁇ as
  • inter-symbol interference canceller vector V Considering the inter- symbol interference to Xi[k] as a linear combination of user 's own symbols, we define the inter-symbol interference canceller vector V,;, for user to be
  • interference term for user 's symbol Xi[k] can be written in a compact form as the product of the inter-symbol interference canceller vector V, ; and the tentative decision vector f' ⁇ k ⁇ as shown below
  • inter-user interference canceller vector for the inter-user interference caused by user j to user U , so that the estimated inter-user interference term to be canceled for user z's symbol Xi[k] can be obtained as
  • a 2D interference cancelation and decision module 1670 may use a single-stage 2D parallel interference cancellation scheme.
  • the 2D interference cancelation and decision module 1670 may include N interference cancelation and decision module units (e.g., 1672a, 1672b, 1672c, collectively 1672) each capable of at least partially canceling the interference associated with symbols sent from one of the users 1554.
  • the interference cancelation and decision module unit 1672a may cancel the inter-symbol interference and the inter-user interference from the symbols sent from the user 1554a
  • the unit 1672b may cancel the interference from the symbols sent from the user 1554b
  • the unit 1672c may cancel the interference from the symbols sent from the user 1554c, and so forth.
  • FIG. 16B shows an enlarged diagram of the exemplary interference cancelation and decision module unit 1672a.
  • Tentative hard decision units 1678 may make tentative hard decisions in parallel for the signal associated with user 1 , and the tentative hard decisions may be concatenated at a concatenation unit 1680 to obtain a vector 1682 using the decision rule of Equation 19.
  • the vector X ⁇ ° ⁇ 1682 represents the tentative hard decisions for user 1.
  • the matrix product of vector 1682 and the inter-symbol interference canceller vector Vn, scaled by a power coefficient a ⁇ , can be calculated to obtain the inter-symbol interference ISIi j (1684a) associated with the symbols sent from user 1.
  • the matrix product of a vector X ⁇ ° ⁇ 1682b and the inter-user interference canceller vector li 1,2, scaled by a power coefficient ⁇ 3 ⁇ 4 can be calculated to obtain the inter-user interference IUI1 2 (1684b) representing the interference of user 2 (1554b) to user 1.
  • the matrix product of a vector and the inter-user interference canceller vector ⁇ , ⁇ , scaled by a power coefficient ON, can be calculated to obtain the inter-user interference mis representing the interference of user N to user 1.
  • An interference cancellation module 1686 may subtract the inter-symbol interference ISI 1; 1 (1684a) and inter-user interferences IUI 1; 2 (1684b) to IUIi ⁇ (1684c) from the time-reversal mirror output Y ⁇ [k] to obtain a soft bit representing a refined estimate of the symbol sent from user 1 , represented as [k].
  • the soft bit may pass through a hard decision unit 1690, which may output a hard decision of the symbol sent from user 1 , represented as X ⁇ [k] .
  • the superscript (1) indicates that this is the hard decision for stage 1 interference cancelation.
  • the input signal Yi[k] associated with the z ' -th user can be buffered by a
  • Tentative hard decision units can make tentative hard decisions in parallel for the signal associated with user i, and the tentative hard decisions can be concatenated at a concatenation unit to obtain a vector
  • the vector x ° ⁇ represents the tentative hard decisions for user i.
  • the matrix product of vector x 0 ⁇ and the inter-symbol interference canceller vector V render, scaled by a power coefficient ⁇ 3 ⁇ 4 can be calculated to obtain the inter- symbol interference ISI ; associated with the symbols sent from the user i.
  • the matrix product of each of vectors X ⁇ 0 ⁇ j ⁇ i) and the inter-user interference canceller vector Uj , scaled by a power coefficient aj, can be calculated to obtain the inter-user interference IUIy representing the interference of user j to user i.
  • An interference cancellation module 1686 may subtract the inter-symbol interference IUI ; - and inter-user interferences IUI ij7 (for all j not equal to i) from the time -reversal mirror output Yi[k] to obtain a soft bit representing a refined estimate of
  • the soft bit may pass through a hard decision unit, which may output a refined hard decision of the symbol sent from user i, represented as X ⁇ [k] .
  • the superscript (1) indicates that this is the hard decision for stage 1 interference cancelation.
  • the interference terms may be reconstructed and then subtracted from the signal Yi[k] with the inter- symbol interference and inter-user interference canceller vectors.
  • Equation 16 Simila e definition in Equ , denoting we can rewrite Equation 16 in a more compact form as
  • a hard decision .X ⁇ fc] — sgn ⁇ J*Q A -'[A:] ) can be made based on J ⁇ ' ⁇ to achieve a more refined estimation for the transmitted symbol.
  • multi-stage processing can be performed by cascading multiple stages of the 2D parallel interference cancellation.
  • a 2D interference cancelation and decision module 400 may use an M-stage interference cancellation scheme. As the interference cancellation procedures proceed in each stage, the same 2D parallel interference cancellation may be performed in an attempt to remove both the inter-symbol interference and the inter-user interference with the updated estimates of the transmitted symbols. Each stage may take the soft-bits from the previous stage as input, based on which tentative decisions are made to estimate the interference and generate the soft-bits of the current stage as the output.
  • the m-th stage's operation can be described as follows: Delay and Buffering: The soft-bits from the previous stage (the (m-l)-th stage) are delayed and buffered to form a soft-bit vector for each user, such that
  • the tentative decisions are made based on the soft-bits from the previous stage (the (m-l)-th stage) in an attempt to estimate the transmitted symbols i.e., for all £ ⁇ 1, 2, N ⁇ ,
  • sgn(-) is the sign function applied element-wise to the operand when the operand is a vector.
  • the soft-bits of the current stage (the m-th stage) are generated by subtracting the estimated interference terms from the original signals ⁇ Yi ⁇ .
  • the soft-bit of user generated by the m-th stage is given by
  • such an -stage scheme is initialized by setting the soft-bits of the initial stage (the 0-th stage) as
  • the final decision is made for each user based on the output of the stage- interference cancellation, llJ , for oil i € ⁇ 1 , 2, . . . ; N ⁇
  • each channel tap is a real number.
  • a graph 420 shows an example of a channel impulse response for user 1 under the IEEE 802.15.4a outdoor non-line-of-sight channel model.
  • a graph 422 shows an example of a channel impulse response for user 2 under the IEEE 802.15.4a outdoor non-line-of-sight channel model.
  • a graph 424 shows the convolution of the channel impulse response for user 1 with the time-reversal signature waveform for user 1.
  • a graph 426 shows the convolution of the channel impulse response for user 2 with the time-reversal signature waveform for user 1.
  • the convolution between user l's channel impulse response hi and its matched time-reversal signature waveform g exhibits a prominent central peak 428 at [hi * gi) [L-l], demonstrating the temporal focusing effect of the time-reversal technique.
  • the amplitude of the convolution between the time-reversal signature waveform and the mismatched channel impulse response hi is significantly smaller than the central peak [hi * gi) [L-l] shown in FIG. 19A, demonstrating the virtual spatial focusing effect in the user's signature domain.
  • the following describes the predicted bit error rate performance versus 3 ⁇ 4/No (the energy-per-bit to noise-power-spectral-density ratio) with various combinations of rate back-off factor D and the total number of users N.
  • the energy-per-bit Eb is normalized to 1 by the assumption that each BPSK symbol Xi[k] £ ⁇ -1,+1 ⁇ has a unit power.
  • a graph 430 shows the predicted bit error rate performances of the 2D parallel interference cancellation scheme (up to 3 stages), compared with the basic time-reversal division multiple access system without interference cancellation.
  • a graph 440 shows the predicted bit error rate performances of the 2D parallel interference cancellation scheme (up to 3 stages), compared with the basic time-reversal division multiple access system without interference cancellation.
  • FIGS. 20 and 21 show that significant bit error rate performance gain can be achieved by the 2D parallel interference cancellation scheme, compared with the baseline time-reversal division multiple access system without interference cancellation.
  • a graph 450 shows how the predicted bit error rate performance changes with the number of users N with a high signal-to-noise ratio.
  • the rate back-off factor D 32.
  • the graph 450 shows that the predicted bit error rate increases with the number of users N due to the increased inter-user interference.
  • the 2D interference cancellation may enable more users to transmit simultaneously and therefore may increase the system capacity.
  • the benefit of using the interference cancellation may diminish when the bit error rate of the baseline system (considered as the initial stage) is above a certain threshold. This is because the interference cancellation scheme at the receiver eventually relies on the tentative decisions of the detected symbols to cancel the interference, whose effectiveness depends on the quality of those tentative decisions.
  • a graph 460 shows how the predicted bit error rate performance is affected by the rate back-off factor D with high signal-to-noise ratio, assuming that there are 5 users accessing the base station simultaneously. Because both the inter-symbol interference and the inter-user interference are reduced with a larger rate back-off factor D, the predicted bit error rate decreases as D increases.
  • the graph 460 shows that by using the 2D parallel interference cancellation scheme, the time -reversal division multiple access system can use a smaller D to achieve the same bit error rate, which translates to higher throughput for each user.
  • an exemplary process 470 for time -reversal wireless communication with interference cancellation is provided.
  • the process 470 can be implemented by the base station 1552 of FIG. 15.
  • the process 470 may include at a transceiver, receiving a combined signal that includes a first signal from a first device and a second signal from a second device, the first signal sent from the first device to the transceiver through first multiple wireless propagation paths, the second signal sent from the second device to the transceiver through second multiple wireless propagation paths, each of the first and second signals including a plurality of symbols (472).
  • the transceiver can be part of the base station 1552, the first device can be the first terminal device 1554a, and the second device can be the second terminal device 1554b.
  • the process 470 may include generating a first set of estimated symbols based on the combined signal and a first signature waveform associated with the first device, the first set of estimated symbols representing a rough estimate of the symbols sent from the first device (474).
  • the base station 1552 can apply a signature waveform associated with the first terminal device 1554a to a combined signal to generate a first set of estimated symbols, e.g., according to Equation 13.
  • the process 470 may include generating a second set of estimated symbols based on the combined signal and a second signature waveform associated with the second device, the second set of estimated symbols representing a rough estimate of the symbols sent from the second device (476).
  • the base station 1552 can apply a signature waveform associated with the second terminal device 1554b to the combined signal to generate a second set of estimated symbols, e.g., according to Equation 13.
  • the process 470 may include determining interference based on at least one of the first set of estimated symbols or the second set of estimated symbols (478).
  • the base station 1552 can determine the interference, which can include inter-symbol interference and/or inter-user interference.
  • the interference can be determined based on the first set of estimated symbols, and the inter-user interference can be determined based on the second set of estimated symbols.
  • the inter-symbol interference can be determined based on the second set of estimated symbols, and the inter-user interference can be determined based on the first set of estimated symbols.
  • the interference can be determined according to Equations 24 and 25.
  • the process 470 may include generating a refined first set of estimated symbols by canceling the interference from the first set of estimated symbols, the refined first set of estimated symbols representing a refined estimate of the symbols sent from the first device (480).
  • the base station 1552 can generate the refined first set of estimated symbols by subtracting the inter-symbol interference and/or the inter-user interference from the first set of estimated symbols, e.g., according to Equation 27.
  • an exemplary process 490 for time -reversal wireless communication with interference cancellation is provided.
  • the process 490 can be implemented by the base station 1552 of FIG. 15.
  • the process 490 may include at a transceiver, receiving a combined signal that includes a first signal from a first device and a second signal from a second device, the first signal sent from the first device to the transceiver through first multiple wireless propagation paths, the second signal sent from the second device to the transceiver through second multiple wireless propagation paths (492).
  • the transceiver can be part of the base station 1552, the first device can be the first terminal device 1554a, and the second device can be the second terminal device 1554b.
  • the process 490 may include estimating the first signal sent from the first device to generate a first estimated signal based on the combined signal and a first signature waveform associated with the first device (494).
  • the base station 1552 can apply a signature waveform associated with the first terminal device 1554a to a combined signal to generate a first estimated signal.
  • the process 490 may include estimating the second signal sent from the second device to generate a second estimated signal based on the combined signal and a second signature waveform associated with the second device (496).
  • the base station 1552 can apply a signature waveform associated with the second terminal device 1554b to the combined signal to generate a second estimated signal.
  • the process 490 may include determining interference based on at least one of the first estimated signal or the second estimated signal (498).
  • the base station 1552 can determine the interference, which can include interference between signals from the same device and/or interference between signals from different devices.
  • the interference between signals from the same device can be determined based on the first estimated signal, and the interference between signals from different devices can be determined based on the second estimated signal.
  • the interference between signals from the same device can be determined based on the second estimated signal, and the interference between signals from different devices can be determined based on the first estimated signal.
  • the process 490 may include determining the signal sent from the first device by subtracting the interference from the first estimated signals (500).
  • the base station 1552 can determine the signal sent from the first device by subtracting the interference between signals from the same device and/or the interference between signals from different devices from the first estimated signal.
  • an exemplary process 510 for time -reversal wireless communication with interference cancellation is provided.
  • the process 510 can be implemented by the base station 1552 of FIG. 15.
  • the process 510 may include at a transceiver, receiving a combined signal that includes signals from a plurality of devices, each device sending a signal to the transceiver through multiple wireless propagation paths (512).
  • the transceiver can be part of the base station 1552, and the plurality of devices can include the first terminal device 1554a and the second terminal device 1554b.
  • the process 510 may include estimating signals sent from each of the devices based on the combined signal and a signature waveform associated with the device (514). For example, for each of the terminal devices 1554, the base station 1552 can apply a signature waveform associated with the terminal device 1554 to a combined signal to generate estimated signals for the terminal device 1554.
  • the process 510 may include determining an interference associated with the estimated signal from each of the devices based on the estimated signals from the devices (516).
  • the base station 1552 can determine the interference, which can include interference between signals from the same device and/or interference between signals from different devices.
  • the interference between signals from the same device can be determined based on the estimated signal for the terminal device 1554, and the interference between signals from different devices can be determined based on the estimated signals for the other devices.
  • the process 510 may include determining the signal sent from each of the devices by subtracting the interference associated with the estimated signal associated with the device from the estimated signal associated with the device (518).
  • the base station 1552 can determine the signal sent from the device by subtracting the interference between signals from the same device and/or the interference between signals from different devices from the estimated signal for the terminal device.
  • a multi-user time-reversal division multiple access uplink architecture and a 2D parallel interference cancellation scheme are provided to enhance the system
  • the TRDMA uplink architecture described above may keep the cost of the communication components of the end-users at a low level, and may reuse the processing power at the base station that has already been made available for the downlink.
  • the 2D parallel interference cancellation scheme may utilize the tentative decisions of detected symbols to effectively reduce or cancel the interference in both the time dimension (ISI) and the user dimension (IUI).
  • ISI time dimension
  • IUI user dimension
  • a multistage scheme may be provided by cascading multiple stages of the 2D interference cancellation, with a total delay that increases linearly with the number of stages, but independent of the number of users.
  • the system 100 can have one or more of the following features and advantages:
  • the system 150 may use a single-carrier wireless broadband communication technology using the time reversal structure and other modified waveforms, which effectively suppress the inter-symbol interference.
  • the system 150 may leverage the time-reversal division multiple access concept to explore the spatial degrees of freedom, and thus enable multiple simultaneous transmissions on the same frequency band.
  • the system architecture described above can accommodate all types of waveform design (as a natural generalization of the time-reversed channel response), and arbitrary channel coding scheme (including the uncoded scheme).
  • the downlink scheme described above can form the spatial focusing effect of time reversal, focusing the signal power only at the locations of the intended terminal devices.
  • Such a physical spatial focusing effect can reduce the co-channel interference and
  • electromagnetic pollution to the environment may enhance the privacy and security of the transmitted message.
  • the asymmetric complexity-distribution between the base station (e.g., 152) (which has the most complexity) and the terminal devices (e.g., 154) (which can be of lower complexity) may make the terminal devices more affordable, which is a desirable feature for systems having a large number of terminal devices that may be limited by size, power, and/or computational capability.
  • the architecture design described above does not require channel equalization at the terminal devices to enable two-way communication.
  • the base station 152 can be part of a mobile or stationary device.
  • the base station 152 can be implemented as part of a sensor module, a controller, a mobile phone, a laptop computer, or an electronic appliance that communicates wirelessly with multiple other devices.
  • a mobile phone or a laptop computer may communicate simultaneously with a television, a printer, a thermometer, a radio, a refrigerator, a lighting control system, and other devices using the techniques described above.
  • the base station may be an access point or a router and may be associated with a wireless hot spot, or wireless cell, or picocell, or nanocell and the like.
  • the base station and the terminal devices can communicate with one another other using multiple communication protocols, including communication protocols that use time-reversal techniques and communication protocols that do not use time-reversal techniques.
  • a mobile phone may have a cellular module configured to communicate with a wireless telephone base station using cellular communication protocols, such as Global System for Mobile Communications (GSM), Code Division Multiple Access (CDMA), Long Term Evolution (LTE), or LTE Advanced protocols,
  • GSM Global System for Mobile Communications
  • CDMA Code Division Multiple Access
  • LTE Long Term Evolution
  • LTE Advanced protocols LTE Advanced protocols
  • the mobile phone may have a Wi-Fi module configured to communicate with a network router using Wi-Fi protocols (e.g., IEEE 802.11, 802.1 la, 802.11b, 802.1 lg, 802.11 ⁇ , 802.1 lac, 802.1 lad).
  • Wi-Fi protocols e.g., IEEE 802.11, 802.1 la, 802.11b, 802.1 lg, 802.11 ⁇ , 802.1 lac, 802.1 lad.
  • the Bluetooth module configured to communicate with Bluetooth enabled devices.
  • the mobile phone may have a time-reversal module configured to communicate with sensors and other devices using the time-reversal communication protocol described above.
  • the mobile phone may route calls through the wireless telephone base station when the mobile phone is in an outdoor location, and switch to routing calls through time-reversal base stations when the mobile phone is in an indoor venue where multipath interference is high.
  • the mobile phone may communicate with the network router using Wi-Fi protocols when executing an application that requires a higher data rate (e.g., when sending image and video data), and switch to using the time -reversal protocol when executing an application that requires a lower data rate (e.g., when sending text or numerical data).
  • a communication system 520 may include a base station 522 and multiple terminal devices (e.g., 524a, 524b, collectively 524).
  • the base station 522 may include a first communication module 526 that uses the time-reversal communication techniques described above, and a second communication module 528 that uses the Wi-Fi, Bluetooth, or cellular communication protocol.
  • the first terminal device 524a may have a first communication module 530a that uses time-reversal communication techniques, and a second communication module 532a that uses the Wi-Fi, Bluetooth, or cellular communication protocol.
  • the second terminal device 524b may have a first communication module 530a that uses time-reversal communication techniques, and a second communication module 532a that uses the Wi-Fi, Bluetooth, or cellular communication protocol.
  • the second terminal device 524b may have a first communication module 530a that uses time-reversal communication techniques, and a second communication module 532a that uses the Wi-Fi, Bluetooth, or cellular communication protocol.
  • the communication modules 528 and 532 may be referred to as a Wi-Fi communication module, a Bluetooth communication module, or a cellular communication module.
  • each of the base station 522 and terminal devices 524 may have two or more modules that comply with two or more of Wi-Fi, Bluetooth, cellular, and other communication protocols.
  • the time -reversal communication module 526 at the base station 522 may communicate with the time-reversal communication modules 530a, 530b at the first and second terminal devices 524a, 524b, respectively.
  • the Wi-Fi (or Bluetooth, cellular) communication module 528 at the base station 522 may communicates with the Wi-Fi (or Bluetooth, cellular) communication modules 532a, 532b at the first and second terminal devices 524a, 524b, respectively.
  • the base station 522 and the terminal device 524a may perform a handshake or channel probing process using the Wi-Fi, Bluetooth, or cellular protocol in order to obtain channel information, then use time -reversal techniques to transmit data.
  • the time-reversal communication module 526 can continuously transmit downlink data packets or receive uplink data packets to or from the time -reversal communication module 530a without the need to periodically perform hand-shake processes to obtain channel information.
  • Another advantage of the system 520 is that existing Wi-Fi and/or cellular communication hardware can be used for channel probing for time-reversal communications.
  • each channel can be, e.g., 5MHz for cellular protocol and 20/40MHz for the Wi-Fi protocol.
  • the channel information for each channel can be obtained according to the respective cellular or Wi-Fi protocol.
  • both communication modules 526, 528 may be used to transmit data.
  • the base station 522 may initially use the Wi-Fi (or Bluetooth, cellular) communication module 528 to establish a Wi-Fi (or Bluetooth, cellular) communication link with the terminal device 524a, then based on certain criteria, switch to using the time-reversal communication module 526 to establish a communication link with the terminal device 524a.
  • the criteria for switching may be based on one or more factors such as
  • the Wi-Fi communication modules 528, 532 may be used when the interference level is below a threshold, and the time-reversal communication modules 526, 530 may be used when the interference level is above the threshold.
  • the Wi-Fi communication modules 528, 532 may be used when the application requires a higher data rate (e.g., when transmitting image or video data), and the time-reversal communication modules 526, 530 may be used when the application requires a lower data rate (e.g., when transmitting text or numerical data).
  • the Wi-Fi communication modules 528, 532 may be used when the terminal device 524 has sufficient battery power, and the time-reversal
  • the time-reversal communication module 530 may consume less power than the Wi-Fi communication module 532, so switching to using the time- reversal communication module 530 may reduce power consumption and allow the terminal device 524 to operate for a longer period of time using battery power.
  • the base station 522 and the terminal device 524 may perform a handoff procedure to terminate the Wi-Fi (or Bluetooth, cellular) communication session between the modules 526, 530, and initiate a time-reversal communication session between the modules 528, 532.
  • the base station 522 may send a command signal to the terminal device 524 to initiate the handoff procedure.
  • the time-reversal communication modules 530 and 526 may perform a hand-shake process to obtain channel and timing information. The switching from using the Wi-Fi (or Bluetooth, cellular) protocol to using the time-reversal communication protocol, or vice versa, can be initiated by either the base station 522 or the terminal device 524.
  • the base station 522 and the terminal device 524 may test the signal quality of the link between the modules 526 and 530, and only switch to using the modules 526 and 530 if the time-reversal communication link meets predetermined quality criteria.
  • the base station 522 and the terminal device 524 may switch back to using the communication modules 528, 532 if certain criteria are met. For example, if switching from Wi-Fi to time-reversal is due to interference the base station 522 and the terminal device 524 may periodically test the communication link between the Wi-Fi
  • the base station 522 and the terminal device 524 perform another handoff procedure to switch to using the Wi-Fi communication modules 528 and 532.
  • the base station 522 may communicate with a first group of terminal devices 524 using the Wi-Fi (or Bluetooth, cellular) protocol, and communicate with a second group of terminal devices 524 using the time-reversal communication protocol.
  • Wi-Fi or Bluetooth, cellular
  • the communication modules 526 and 528 are shown as two separate blocks. In some examples, the modules 526 and 528 can have overlapping components, such as sharing one or more common data processors, controllers, and/or memory components.
  • the Wi-Fi, Bluetooth, and cellular communication protocols each has a substantially symmetric architecture, whereas the time -reversal communication protocol may have an asymmetric architecture.
  • An asymmetric architecture of time -reversal communication can be seen from the examples shown in FIGS. 6 and 7, in which the complex signal processing (e.g., performing convolution computations) is performed at the base station for both uplink and downlink.
  • a device that is configured to communicate according to the Wi-Fi protocol may include both a transmitter 540 as shown in FIG. 28A, and a receiver 550 as shown in FIG. 28B.
  • the Wi-Fi communication module 528 of the base station 522 in FIG. 27 may include both the transmitter 540 and the receiver 550.
  • the Wi-Fi communication module 532 of the terminal device 524 may include both the transmitter 540 and the receiver 550.
  • the transmitter 540 at the base station 522 may send data to the
  • the transmitter 540 at the terminal device 524 may send data to the receiver 550 at the base station 522.
  • the complexity of signal processing at the transmitter 540 may be comparable to that of the signal processing at the receiver 550, except that the operations are
  • channel coding e.g., convolution code
  • channel coding may be applied to binary input data, and mapped according to a specific modulation (such as QPSK, 16QAM, or 64QAM). Pilot symbols may be inserted into the modulated data, and the inserted data may undergo serial-to-parallel (S/P) conversion, forming a vector of symbols.
  • S/P serial-to-parallel
  • An inverse Fourier transform (IFFT) can be performed on the vector of symbols to generate a time-domain vector.
  • P/S parallel-to- serial conversion
  • cyclic prefixes can be added to reduce interference.
  • the output signal can then be modulated by a radio frequency carrier and transmitted through an antenna.
  • a radio frequency signal may be received at the antenna and processed (e.g., including A/D conversion and low-pass filtering), and cyclic prefixes may be removed from the received signal.
  • the signal may go through a serial-to-parallel (S/P) conversion to form a vector.
  • a fast Fourier transform (FFT) may be performed on the vector, generating a frequency- domain vector.
  • FFT fast Fourier transform
  • P/S parallel-to-serial conversion
  • the signal may then go through demodulation and channel decoding to estimate the transmitted binary data.
  • the signal processing at the transmitter 540 and the receiver 550 may be substantially symmetrical, thus the Wi-Fi protocol may be said to have a substantially symmetrical architecture.
  • the signal processing performed by the transmitter 540 at the base station 522 during downlink may be substantially the same as the signal processing performed by the transmitter 540 at the terminal device 524 during uplink.
  • the signal processing performed by the receiver 550 at the terminal device 524 during downlink may be substantially the same as the signal processing performed by the receiver 550 at the base station 522 during uplink.
  • the transmitter 540 (or receiver 550) at the base station 522 may be implemented differently from the transmitter 540 (or receiver 550) at the terminal device 524.
  • the transmitter 540 at the base station 522 may use a data processor that is more powerful than the data processor used by the transmitter 540 at the terminal device 524.
  • the Wi-Fi protocol has a substantially symmetrical architecture, we mean that the signal processing specified by the Wi-Fi protocol for the base station is comparable to that for the terminal device, even though the base station may have circuitry (including, e.g., data processor, memory, active/passive electronic components), software, and/or firmware different from those of the terminal device.
  • FIGS. 29 A and 29B show the substantially symmetric architecture of a 4G LTE downlink.
  • FIGS. 30A and 30B show the substantially symmetric architecture of a 4G
  • an LTE communication module at the base station may include a transmitter 560 as shown in FIG. 29A and a receiver 590 as shown in FIG. 30B.
  • a LTE communication module at the terminal device may include a transmitter 580 as shown in FIG. 30A and a receiver 570 as shown in FIG. 29B.
  • the transmitter 560 at the base station may send data to the receiver 570 at the terminal device.
  • the transmitter 580 at the terminal device may send data to the receiver 590 at the base station.
  • a sequence of bits to be transmitted to a terminal device may undergo a serial-to- parallel (S/P) conversion, forming a vector of symbols.
  • the vector of symbols may be re- organized through a sub-carrier mapping.
  • An inverse Fourier transform (IFFT) can be performed on the re -organized vector to generate a time-domain vector.
  • IFFT inverse Fourier transform
  • P/S parallel-to- serial conversion
  • cyclic prefixes can be added to reduce interference.
  • the output signal can then be modulated by a radio frequency carrier and transmitted through an antenna.
  • a radio frequency signal may be received at an antenna and processed (e.g., including A/D conversion and low-pass filtering), and cyclic prefixes may be removed from the received signal.
  • the signal may go through a serial-to-parallel (S/P) conversion to form a vector.
  • a fast Fourier transform (FFT) can be applied to the vector, generating a frequency-domain vector.
  • FFT fast Fourier transform
  • sub-carrier demapping/equalization can be applied to extract the information for the terminal device.
  • P/S parallel-to-serial conversion
  • the transmitted data can be obtained at the terminal device.
  • the signal processing procedures may be similar to the downlink except that at the transmitter 580 of the terminal device, a fast Fourier transform (FFT) may be applied before the subcarrier mapping, and at the receiver 590 of the base station, an inverse fast Fourier transform (IFFT) may be performed after the subcarrier demapping.
  • FFT fast Fourier transform
  • IFFT inverse fast Fourier transform
  • FIGS. 29 A and 29B show that in the 4G LTE downlink, the signal processing at the transmitter 560 and the receiver 570 may be substantially symmetrical.
  • FIGS. 30A and 30B show that the signal processing at the transmitter 580 and the receiver 590 may be substantially symmetrical.
  • the complexity of signal processing at the terminal device may be comparable to that of the signal processing at the base station.
  • the 4G LTE protocol may be said to have a substantially symmetrical architecture.
  • the above example shows the substantially symmetrical architecture of a communication system based on 4G LTE communication protocol.
  • Other cellular communication protocols such as GSM or CDMA, also may have substantially symmetrical architectures in which for the downlink and uplink, the complexity of signal processing at the base station is similar to that at the terminal device.
  • GSM Global System for Mobile communications
  • CDMA Code Division Multiple Access
  • various modifications can be made to the transmitter and the receiver and the base station and the terminal device, and the transmitter and receiver may be implemented using different electronic components.
  • the 4G LTE protocol or other cellular communication protocol has a substantially symmetrical architecture
  • the signal processing specified by the LTE or other cellular communication protocol for the base station is comparable to that for the terminal device, even though the base station may have circuitry (including, e.g., data processor, memory, active/passive electronic components), software, and/or firmware different from those of the terminal device.
  • the following describes a time -reversal communication system that uses two types of time-reversal communication techniques, one symmetrical and the other asymmetrical.
  • FIG. 31A shows an exemplary downlink architecture 600 of an asymmetrical time -reversal communication system
  • FIG. 3 IB shows an exemplary uplink architecture 610 of the asymmetrical time -reversal communication system.
  • the downlink architecture 600 is a simplified version of that shown in FIG. 6, and the uplink architecture 610 is a simplified version of that shown in FIG. 7.
  • a base station may include a transmitter 602 of FIG. 31A and a receiver 612 of GI. 3 IB
  • a terminal device may include a receiver 604 of FIG. 31A and a transmitter 614 of FIG. 3 IB.
  • the transmitter 602 at the base station may transmit data to the receiver 604 at the terminal device.
  • the transmitter 614 at the terminal device may transmit data to the receiver 612 at the base station.
  • the transmitter 602 at the base station may perform waveform embedding, in which up- sampled sequences are embedded with a signature waveform (calculated based on the channel response obtained in a hand-shaking process).
  • the receiver 604 at the terminal device may not need to perform signal processing that involves the signature waveform.
  • the receiver 612 at the base station may perform information extraction, in which a convolution process may be performed between an input signal and the signature waveform.
  • the transmitter 614 at the terminal device may not need to perform any signal processing that involves the signature waveform.
  • the signal processing may be more complicated at the base station than at the terminal device, for both downlink and uplink.
  • FIG. 32 shows an exemplary symmetrical time-reversal communication system 620, in which a base station includes both a transmitter 602 and a receiver 604.
  • the transmitter 602 and receiver 604 in FIG. 32 are the same as those in FIG. 31 A.
  • a terminal device may also include both a transmitter 602 and a receiver 604.
  • the transmitter 602 of the base station may send data to the receiver 604 of the terminal device.
  • the transmitter 602 of the terminal device may send data to the receiver 604 of the base station.
  • the terminal device may first send a channel probing signal to the base station to allow the base station to obtain channel information and calculate a signature waveform for the terminal device.
  • the base station may first send a channel probing signal to the terminal device to allow the terminal device to obtain channel information and calculate a signature waveform for the base station.
  • the signal processing performed by the base station and the terminal device may be similar.
  • the base station when there are multiple terminal devices, can use time division multiplexing to communicate with each of the terminal devices. Alternatively, the base station can use multiple antennas to receive focused signals from the multiple terminal devices.
  • a time-reversal communication system 630 may include a base station 632 that is configured to communicate with terminal devices 634 using a symmetrical time-reversal architecture and an asymmetrical time -reversal architecture.
  • FIG. 34 shows an exemplary implementation of the architecture shown in FIG. 33.
  • a base station 632 may include a transmitter 602 (FIG. 31 A), a receiver 604, and a receiver 612 (FIG. 3 IB).
  • a terminal device 634 may include a transmitter 602, a transmitter 614 (FIG. 3 IB), and a receiver 604.
  • the transmitter 602 of the base station 632 may send data to the receiver 604 of the terminal device 634.
  • the transmitter 614 of the terminal device 634 may send data to the receiver 612 of the base station 632.
  • the transmitter 602 of the base station 632 may send data to the receiver 604 of the terminal device 634.
  • the transmitter 602 of the terminal device 634 may send data to the receiver 604 of the base station 632.
  • the difference between symmetric time-reversal communication and asymmetric time -reversal communication may be in the uplink.
  • the terminal device may directly transmit the data, and the base station or access point may need to perform convolution to have virtual focusing and to extract uplink data.
  • One advantage of the asymmetric time-reversal communication is that the complexity at the terminal device can be low.
  • the terminal device may need to perform convolution of transmit data with a signature waveform before transmission, which may enable physical focusing of the transmit signal at the base station.
  • Another device that is at a distance from the base station may not be able to receive the uplink data. Therefore, depending on different purposes, the terminal device may switch between different modes (i.e., asymmetric or symmetric time-reversal communication) .
  • Each of the base station and terminal devices can include one or more processors and one or more computer-readable mediums (e.g., RAM, ROM, SDRAM, hard disk, optical disk, and flash memory).
  • the one or more processors can implement functions of the waveform embedding 176 (FIG. 6) and information extraction 200 (FIG. 7).
  • the one or more processors can perform calculations based on one or more of Equations 1 to 32.
  • the waveform embedding 176 and information extraction 200 can also be implemented using application-specific integrated circuits (ASICs).
  • ASICs application-specific integrated circuits
  • “computer-readable medium” refers to a medium that participates in providing instructions to a processor for execution, including without limitation, non-volatile media (e.g., optical or magnetic disks), and volatile media (e.g., memory) and transmission media.
  • Transmission media includes, without limitation, coaxial cables, copper wire and fiber optics.
  • a computer program may be a set of instructions that can be used, directly or indirectly, in a computer to perform a certain activity or bring about a certain result.
  • a computer program can be written in any form of programming language (e.g., C, Java), including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, a browser-based web application, or other unit suitable for use in a computing
  • Suitable processors for the execution of a program of instructions include, e.g., both general and special purpose microprocessors, digital signal processors, and the sole processor or one of multiple processors or cores, of any kind of computer.
  • a processor will receive instructions and data from a read-only memory or a random access memory or both.
  • the essential elements of a computer are a processor for executing instructions and one or more memories for storing instructions and data.
  • a computer will also include, or be operatively coupled to communicate with, one or more mass storage devices for storing data files; such devices include magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and optical disks.
  • Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non- volatile memory, including by way of example semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks.
  • semiconductor memory devices such as EPROM, EEPROM, and flash memory devices
  • magnetic disks such as internal hard disks and removable disks
  • magneto-optical disks and CD-ROM and DVD-ROM disks.
  • the processor and the memory can be supplemented by, or incorporated in, ASICs (application-specific integrated circuits). Flash memory and/or any type of known memory are within the scope of the invention.
  • the system 150 can combine time division multiplexing with frequency division multiplexing to allow a base station to communicate with a first group of terminal devices at a first frequency and a second group of terminal devices at a second frequency.
  • the base station can perform a hand-shaking process with two or more terminal devices at different frequencies.
  • the base station 152 and terminal devices 154 can include more components that are not shown in the figures. For example, standard components such as analog-to- digital converters, digital-to-analog converters, and power amplifiers have been omitted from the figures.
  • a mobile device 640 includes a first communication module 642 using a communication protocol having a substantially symmetric architecture, such as the Wi-Fi, Bluetooth, or cellular (e.g., GSM, CDMA, LTE) communication protocol.
  • the mobile device 640 includes a second communication module 644 using a communication protocol having an asymmetric architecture, such as the asymmetric time-reversal communication protocol.
  • the mobile device 640 uses the first communication module 642 to communicate with a base station 646 that uses the communication protocol having a substantially symmetric architecture.
  • the mobile device 640 uses the second communication module 644 to communicate with devices 648 that use the communication protocol having an asymmetric architecture.
  • the mobile device can be, e.g., a mobile phone, a laptop computer, a tablet computer, a smart watch, or a head-mounted display.
  • the base station 646 can be a Wi-Fi base station or a wireless telephone base station.
  • the devices 648 can be, e.g., sensors mounted at various locations in a building or electronic devices worn on a user (e.g., body temperature sensor, heart rate monitor, insulin level monitor, hearing aid, or smart contact lens).
  • a system 650 includes a group of robots 652 that communicate with devices 646 outside the group of robots using a communication protocol that has a substantially symmetrical architecture (e.g., Wi-Fi, Bluetooth, or cellular protocol, such as GSM, CDMA, or LTE).
  • the device 646 can be, e.g., a Wi-Fi base station, a wireless telephone base station, a Bluetooth peripheral device, or another robot that communicates by Wi-Fi or Bluetooth.
  • the communication within the group of robots 652 is performed using a communication protocol that has an asymmetrical architecture, such as asymmetrical time -reversal communication protocol.
  • the robots 652 can be robotic arms operating at assembly lines in a factory.
  • the robots can be autonomous vehicles, such as autonomous land-based vehicles, aquatic vehicles, or aerial vehicles.
  • the robots 652 can be made small, having the sizes of insects, birds, or small animals, and used to monitor the environment.
  • one or more of the robots 652 can function as the base station, and the other robots 652 can function as terminal devices. Deploying a group of robots as shown in FIG. 36 may be useful for, e.g., search and rescue missions in collapsed buildings or tunnels where there may be severe multipath interference.
  • the group of robots 652 can be scouting robots used to explore mine shafts or underground caves.
  • components of a robot may communicate with one another using the time -reversal communication protocol.
  • a robot can have multiple arms each having multiple fingers, and each arm or finger may have multiple sensors and actuators.
  • the sensors and actuators of the fingers and arms may
  • a central controller may communicate with external devices using symmetrical communication protocols.
  • a vehicle 660 may include a communication unit 662 that communicates with one or more devices 646 outside the vehicle 660 using a communication protocol that has a substantially symmetrical architecture, such as Wi-Fi, Bluetooth, or cellular communication protocol.
  • the communication unit 662 communicates with one or more devices 664 within the vehicle 660 (or attached to the vehicle, or associated with the vehicle) using a
  • the communication unit 662 may communicate with a wireless telephone base station using GSM, CDMA, LTE, or LTE Advanced protocols.
  • the communication unit 662 may communicate with a controller of an electric vehicle charging station using the Wi-Fi or Bluetooth protocol.
  • the devices 664 can be sensors (e.g., temperature sensors, motion sensors, light sensors, acoustic sensors), information display devices, or audio / video devices (playback or recording devices).
  • car seats may be embedded with accelerometers and pressure sensors that measure the forces imparted to passengers and communicate with the communication unit 662 using a time-reversal communication protocol.
  • a controller may use the information from the accelerometers and pressure sensors to control an active suspension system under the seats to provide a smoother ride to passengers.
  • the vehicle 660 can be, e.g., a car, a bus, a ship, or an airplane.
  • a bus may have an electronic library that delivers digital content to e-readers provided to passengers using the time-reversal communication protocol.
  • the terminal device 154 can be a low-power wearable device, such as a body temperature sensor, a heart rate monitor, an
  • the base station 152 can be a health monitor unit such as a electrocardiography recorder, a mobile phone, a tablet computer, a smart watch, a smart wristband, or other wearable fitness device having a data processor that executes a health and fitness program.
  • a health monitor unit such as a electrocardiography recorder, a mobile phone, a tablet computer, a smart watch, a smart wristband, or other wearable fitness device having a data processor that executes a health and fitness program.
  • the base station 152 can be part of a control center of a building, and the terminal devices 154 can be sensors mounted at various locations in the building.
  • the sensors can be, e.g., motion sensors, temperature sensors, humidity sensors, light sensors, or acoustic sensors. Because time-reversal communication requires little power consumption at the terminal devices, the sensors can be powered by photovoltaic devices and made at low costs. Many sensors can be placed at various locations in a building without the need to provide wiring to the sensors. For example, this allows a building manager to conveniently monitor various parameters in the building to help optimize utilization of various facilities in the building.
  • light sensors can be placed near conference room tables, and data from the light sensors can be used to control curtains, shutters, or the transmittance of window panels having variable transmittances, in order to optimize lighting conditions for users sitting around the tables.
  • Various light reflectors and light guides can be adjusted based on data from light sensors to optimize the distribution of natural light in a building.
  • a mobile phone is configured to communicate with a wireless telephone base station using a cellular communication protocol, and
  • the second communication protocol can be an asymmetrical time -reversal communication protocol
  • the third communication protocol can be, e.g., the Wi-Fi or Bluetooth protocol.
  • a mobile device can be configured to communicate with a wireless telephone base station using a cellular communication protocol, and communicate with a network router using a communication protocol having an asymmetrical architecture, such as the asymmetrical time-reversal communication protocol.
  • a communication protocol having an asymmetrical architecture such as the asymmetrical time-reversal communication protocol.
  • this may be useful in a convention center where thousands of attendees may need to use mobile devices to access the Internet wirelessly.
  • Conventional Wi-Fi based network routers may not be able to support thousands of users within a crowded space due to severe interference, whereas a network router using the time- reversal communication protocol may be able to support all the users by taking advantage of the spatial filtering characteristics of the conference rooms.
  • the time-reversal communication system may use a wider bandwidth than Wi-Fi, Bluetooth, and cellular communication systems.
  • the time-reversal communication system may use a 500MHz bandwidth
  • an LTE system may use a 20MHz bandwidth
  • an LTE Advanced system may use a 100 MHz bandwidth.
  • a mobile device may communicate with a server using a first communication protocol having a substantially symmetric architecture, download a map and information about locations of access points that use a second communication protocol having an asymmetric architecture.
  • the mobile device uses the second communication protocol to establish links to the access points.
  • the access points can be network routers that allow the mobile device to access the Internet or a corporate intranet.
  • the first communication protocol can be, e.g., the Wi- Fi, Bluetooth, or cellular communication protocol.
  • the cellular communication protocol can be, e.g., GSM, CDMA, LTE, or LTE Advanced.
  • the second communication protocol can be, e.g., the time-reversal communication protocol.
  • the terms used for various communication protocols are meant to encompass variants of the corresponding protocols.
  • the CDMA protocol is meant to include one or more of Wideband CDMA (WCDMA) and Time Division Synchronous CDMA (TD-SCDMA) protocols.
  • WCDMA Wideband CDMA
  • TD-SCDMA Time Division Synchronous CDMA
  • the Wi-Fi protocol is meant to include one or more of IEEE 802.11, 802.11a, 802.11b, 802.1 lg, 802.11 ⁇ , 802.1 lac, and
  • communications may be between any device that is powered in any way, including by battery power, solar power, wind power, a fuel cell, a capacitor, and energy storage unit, a fly wheel, a power line, the mains and the like.
  • Devices that may implement these protocols include phones, computers, robots, meters, lights, controllers, appliances, vehicles, displays, televisions, entertainment equipment, cooking equipment,
  • heating/cooling equipment safety systems, lighting systems, monitoring systems, tracking systems, and the like.
  • time-reversal communication protocol is meant to cover a
  • the time-reversal communication protocol may not require the system to compute a time-reversed version of a received signal.
  • a time-reversal multiuser downlink system may not necessarily compute a time -reversed version of a signal received from any user.
  • the signature waveform is a time-reversed version of the channel response signal.
  • the signature waveform can be a modified version of the time-reversed channel response signal.
  • the signature waveform can be designed to reduce interference.
  • Another method of generating the signature waveform is to separate the time-reverse operation into many element-swap operations and distribute these operations in the signature waveform design algorithm.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

Selon l'invention, dans un système sans fil à inversion temporelle asymétrique, une station de base comprend un circuit d'entrée configuré pour, au cours d'une période de prise de contact, recevoir un signal de réponse de canal provenant d'un signal de sonde envoyé d'un premier dispositif de terminal à l'appareil par l'intermédiaire de multiples trajets de propagation sans fil, et au cours d'une période d'émission de liaison montante, recevoir des signaux combinés qui comprennent un signal provenant du premier dispositif de terminal et un signal provenant d'un second dispositif de terminal. La station de base comprend un processeur de données configuré pour calculer une forme d'onde de signature pour le premier dispositif de terminal sur la base de la réponse de canal, et déterminer le signal envoyé depuis le premier dispositif de terminal au cours de la période d'émission de liaison montante sur la base des signaux combinés et de la forme d'onde de signature pour le premier dispositif de terminal.
PCT/US2014/051148 2012-12-05 2014-08-14 Systèmes sans fil à inversion temporelle ayant une architecture asymétrique WO2015023895A1 (fr)

Priority Applications (6)

Application Number Priority Date Filing Date Title
EP14756197.1A EP3033862A1 (fr) 2013-08-16 2014-08-14 Systèmes sans fil à inversion temporelle ayant une architecture asymétrique
US14/912,324 US9900794B2 (en) 2013-08-16 2014-08-14 Time-reversal wireless systems having asymmetric architecture
US15/861,422 US11025475B2 (en) 2012-12-05 2018-01-03 Method, apparatus, server, and systems of time-reversal technology
US15/873,806 US10270642B2 (en) 2012-12-05 2018-01-17 Method, apparatus, and system for object tracking and navigation
US16/101,444 US10291460B2 (en) 2012-12-05 2018-08-11 Method, apparatus, and system for wireless motion monitoring
US16/125,748 US10833912B2 (en) 2012-12-05 2018-09-09 Methods, devices, servers, apparatus, and systems for wireless internet of things applications

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US13/969,320 US9559874B2 (en) 2013-08-16 2013-08-16 Multiuser time-reversal division multiple access uplink system with parallel interference cancellation
US13/969,271 US9882675B2 (en) 2013-08-16 2013-08-16 Time-reversal wireless systems having asymmetric architecture
US13/969,320 2013-08-16
US13/969,271 2013-08-16

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US15/004,335 Continuation-In-Part US10009148B1 (en) 2012-12-05 2016-01-22 Time-reversal technologies for hybrid wireless networks

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US14/912,324 A-371-Of-International US9900794B2 (en) 2013-08-16 2014-08-14 Time-reversal wireless systems having asymmetric architecture
US15/861,422 Continuation-In-Part US11025475B2 (en) 2008-09-23 2018-01-03 Method, apparatus, server, and systems of time-reversal technology
US15/861,422 Continuation US11025475B2 (en) 2008-09-23 2018-01-03 Method, apparatus, server, and systems of time-reversal technology
US15/873,806 Continuation-In-Part US10270642B2 (en) 2012-09-18 2018-01-17 Method, apparatus, and system for object tracking and navigation

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US9900794B2 (en) 2013-08-16 2018-02-20 Origin Wireless, Inc. Time-reversal wireless systems having asymmetric architecture
US10163311B2 (en) 2016-02-16 2018-12-25 Above the Fold, LLP Systems for tracking medications
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CN114337751A (zh) * 2021-12-07 2022-04-12 重庆邮电大学 一种时间反转ofdm多用户通信系统的功率分配方法
CN114337751B (zh) * 2021-12-07 2023-11-21 江苏华鹏智能仪表科技股份有限公司 一种时间反转ofdm多用户通信系统的功率分配方法

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