Synchronizing independent FMCW radar / lidar units via doppler-window acquisition and clock lock

Abstract

A system and method for synchronizing electromagnetic transceivers and for measuring distance between the synchronized electromagnetic transceivers.

Description

[0001] SYNCHRONIZING INDEPENDENT FMCW RADAR / LIDAR UNITS VIA DOPPLER- WINDOW ACQUISITION AND CLOCK LOCK

[0002] RELATED APPLICATIONS

[0003] This application claims the benefit of priority under 35 USC §119(e) of U.S. Provisional Patent Application No. 63 / 714,162 filed on 31 October 2024 and U.S. Provisional Patent Application No. 63 / 716,279 filed on 5 November 2024 and, the contents of which are incorporated herein by reference in their entirety.

[0004] FIELD AND BACKGROUND OF THE INVENTION

[0005] The present invention, in some embodiments thereof, relates to a system and method for synchronizing two or more independent electromagnetic transceivers (e.g., FMCW radar, FMCW lidar, etc.), to enable coherent reception between devices.

[0006] United States Patent Publication No. 2020 / 023307 appears to disclose, “Methods and apparatus to implement compact time-frequency division multiplexing for MIMO radar are disclosed. An apparatus includes an antenna array controller to: transmit a first signal via a first transmitter of a radar antenna array, the first signal having a first duration and modulated across a first frequency range; and transmit a second signal via a second transmitter, the second signal having a second duration and modulated across a second frequency range, the first and second durations including an overlapping period of time, the first and second frequency ranges including an overlapping frequency range. The apparatus further includes a signal separation analyzer to: determine a first echo received at a receiver of the radar antenna array corresponds to the first signal; and determine a second echo received at the receiver corresponds to the second signal. “

[0007] United States Patent Publication No. 2016 / 0291120 appears to disclose, “A method for determining a location of remotely emplaced objects. The method including: (a) scanning a field for one or more remotely emplaced objects with a reference source signal from a reference source; (b) detecting the signal at one or more orientation sensors associated with each of the one or more remotely emplaced objects; (c) determining an angular direction of each of the one or more remotely emplaced objects relative to the reference source based on the signal received at the one or more orientation sensors associated with each of the one or more remotely emplaced objects; (d) directing a range signal from the reference source towards each of the remotely emplaced objects at a corresponding determined angular direction; (e) in response to the range signal, transmitting a response signal from each of the remotely emplaced objects to the reference source; and (f) determining a range for each of the one or more remotely emplaced objects relative to the reference source at the determined angular direction based at least partially on the range and response signals.”

[0008] Additional art includes United States Patent No. 11,385,323, United States Patent No. 11,585,889, Chinese Patent No. 11,208,8317, United States Patent No. 11,520,003, United States Patent Publication No. 2019 / 0293748, United States Patent No. 10,651,957, United States Patent No. 9,304,198, United States Patent No. 8,10,287, United States Patent Publication No. 2011 / 0267222, Chinese Patent No. 102890283, United States Patent No. 11,346,959, United States Patent Publication No 2023 / 0384447, United States Patent No. 11,711,254, Chinese Patent Application No. 109725295. United States Patent No. 5.361.277, United States Patent No. 11.656.325, United States Patent No. 8.922.421, United States Patent Publication No. 2023 / 0384416, United States Patent No. 11,546,083, United States Patent No. 10,502,821, and Chinese Patent No. 112134678,

[0009] Therefore, there is a need for a system and method for synchronization of electromagnetic signals.

[0010] BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Some embodiments of the invention are herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of embodiments of the invention. In this regard, the description, taken in conjunction with the drawings, makes apparent to those skilled in the art how embodiments of the invention may be practiced.

[0012] In the drawings:

[0013] Fig. 1 A: A flow diagram describing a method synchronization of two or more transceivers, in accordance with an embodiment of the current invention.

[0014] Fig. IB: A flow diagram describing a method sliding Doppler window frequency searching in accordance with an embodiment of the current invention. Fig. 2 A: A block diagram describing a synchronized signal system, in accordance with an embodiment of the current invention.

[0015] FIG. 2B: A block diagram of a radar transceiver (e.g., a Doppler radar) in accordance with an embodiment of the current invention

[0016] Fig. 3: A schematic diagram illustrating a computation of a time of travel phase shift, in accordance with an embodiment of the current invention.

[0017] Fig. 4: A schematic diagram illustrating a computation of a frequency shift, in accordance with an embodiment of the current invention.

[0018] Fig. 5: A block diagram illustrating an exemplary system for synchronizing electromagnetic transceivers, in accordance with some embodiments of the current invention.

[0019] Fig. 6: A flow chart illustrating an exemplary method of synchronizing independent electromagnetic transceivers, in accordance with some embodiments of the current invention.

[0020] Fig. 7A: A flow chart illustrating an exemplary method for cooperative ranging between synchronized electromagnetic transceivers, in accordance with some embodiments of the current invention.

[0021] Fig. 7B: A flow diagram describing a method for computing a range between not fully synchronized units, in accordance with an embodiment of the current invention.

[0022] Fig. 8: A flow diagram describing a method for computing a firing range, in accordance with an embodiment of the current invention.

[0023] Fig. 9: A schematic diagram illustrating a friendly-fire prevention use case, in accordance with an embodiment of the current invention.

[0024] Fig. 10: A block diagram illustrating a system for calculating a distance in accordance with some embodiments of the current invention.

[0025] Fig. 11 : A flow diagram illustrating a method for measuring distance between independent frequency-modulated continuous-wave (FMCW) transceivers, in accordance with some embodiments of the current invention.

[0026] FIG. 12 is a flow chart illustration of a method 310 of synchronizing independent electromagnetic devices in accordance with an embodiment of the current invention.

[0027] FIG. 13 is a flow chart illustration of a method 410 for calculating a distance between independent transceivers in accordance with an embodiment of the current invention. SUMMARY OF THE INVENTION

[0028] A system of one or more computers can be configured to perform particular operations or actions by virtue of having software, firmware, hardware, or a combination of them installed on the system that in operation causes or cause the system to perform the actions. One or more computer programs can be configured to perform particular operations or actions by virtue of including instructions that, when executed by data processing apparatus, cause the apparatus to perform the actions.

[0029] In one general aspect, system may include a first electromagnetic transceiver and a second electromagnetic transceiver, where each electromagnetic transceiver is configured to transmit a frequency-modulated continuous-wave (FMCW) chirp and to receive a peer’s chirp. System may also include a mixer and intermediate frequency chain at each transceiver configured to produce a beat from the peer’s chirp. System may furthermore include control circuitry configured to compute a cooperative range from the beat and to either: (i) exchange time tags and phase tags to remove inter-device skew, or (ii) exchange and combine a calculated range measured at the first electromagnetic transceiver and a calculated range measured at the second electromagnetic transceiver to cancel skew. System may in addition include thereby determining a distance between the first electromagnetic transceiver and second electromagnetic transceiver without relying on a reflected echo. Other embodiments of this aspect include corresponding computer systems, apparatus, and computer programs recorded on one or more computer storage devices, each configured to perform the actions of the methods.

[0030] Implementations may include one or more of the following features. System where the cooperative range is calculated by combining may include averaging the calculated range measured at the first electromagnetic transceiver and the calculated range measured at the second electromagnetic transceiver. System where the electromagnetic transceivers are configured to exchange time and / or phase tags associated with chirp detection. System where a transceiver is configured to use an artificial IF. System where a transceiver is configured to use different IFs for transmission and mixing. System may include a friendly-fire interlock configured to inhibit firing if cooperative range or line of fire (LoF) criteria are met. Implementations of the described techniques may include hardware, a method or process, or a computer tangible medium.

[0031] In one general aspect, the method may include transmitting a signal from the first FMCW transceiver. The method may also include receiving the first signal at the second FMCW transceiver. The method may furthermore include transmitting a second chirp and a second time tag from the second FMCW transceiver. The method may in addition include receiving the second chirp and the second time tag at the first FMCW transceiver. The method may moreover include combining the second chirp with a local reference of the first FMCW transceiver to obtain a second intermediate frequency beat. The method may also include computing a first apparent range by the first transceiver based on said second intermediate frequency beat and said second time tag. Other embodiments of this aspect include corresponding computer systems, apparatus, and computer programs recorded on one or more computer storage devices, each configured to perform the actions of the methods.

[0032] Implementations may include one or more of the following features. The method may include: transmitting a first time tag and a first chirp from the first FMCW transceiver; receiving first time tag at the second FMCW transceiver; combining the first chirp with a local reference of the second FMCW transceiver to obtain a first intermediate frequency beat; computing a second apparent range by the second FMCW transceiver based on said first intermediate frequency beat and said second time tag; correcting for residual skew based on to yield an accurate distance. The method where the correcting for skew includes exchanging time tags and phase tags. The method where the correcting for skew includes combining the first apparent range and the second apparent range. The method may include said first transceiver searching for said second chirp using a moving search window to cover frequency uncertainty. The method where the first and second transceivers include FMCW lidar devices. The method where the first and second transceivers include FMCW radar devices. Non - transitory computer - readable medium. Implementations of the described techniques may include hardware, a method or process, or a computer tangible medium.

[0033] In one general aspect, the method may include transmitting a signal from a first electromagnetic device. The method may also include sweeping an offset search window of a second electromagnetic device for detecting the signal of the first electromagnetic device by the offset search window within an intermediate frequency acceptance band. The method may furthermore include correlate the signal against a template of the second electromagnetic device. The method may in addition include adjusting a reference clock of the second electromagnetic device until frequency and phase errors satisfy lock criteria. Other embodiments of this aspect include corresponding computer systems, apparatus, and computer programs recorded on one or more computer storage devices, each configured to perform the actions of the methods.

[0034] Implementations may include one or more of the following features. The method where the signal includes a chirp. The method may include moving the offset window during acquisition to extend capture range. The method where the first and second devices include frequency- modulated continuous- wave (FMCW) lidar devices. The method where the devices are frequency- modulated continuous-wave (FMCW) radar devices. The method where a lock criterion is that frequency error is smaller than the smallest increment the second device uses to tune the offset search window. The method where a lock criterion is that the signal remains phase-continuous. The method where subsequent signals remain phase-continuous within a tolerance. The method may include distinguishing a true signal lock from random noise or brief, transient false alarms by a coherency check. The method may include authenticating the signal using a rolling code or message authentication code. Non - transitory computer - readable medium storing instructions. Implementations of the described techniques may include hardware, a method or process, or a computer tangible medium.

[0035] In one general aspect, system may include a first electromagnetic device configured to transmit a signal. System may also include a second electromagnetic device configured to receive the signal, where the second electromagnetic device may include: a receiver having an intermediate-frequency (IF) bandwidth; a controllable reference clock; and control circuitry configured for: (i) sweeping an offset search window across a plurality of frequency offsets; (ii) detecting the signal of the first electromagnetic device in said offset search window; and (iii) tuning the controllable reference clock in response to the detecting to reduce offset and phase error until the received signal is within a lock tolerance, thereby synchronizing the second electromagnetic device to the first electromagnetic device. Other embodiments of this aspect include corresponding computer systems, apparatus, and computer programs recorded on one or more computer storage devices, each configured to perform the actions of the methods.

[0036] Implementations may include one or more of the following features. System where the signal is a wide band signal. System where the signal is a chirp. System where the control circuitry is further configured correlating a received signal against a chirp template. System where the control circuitry is further configured to calculate a beat frequency (F and correlation threshold from said detecting occurs when the correlation Threshold is exceeded for the beat frequency lies within the intermediate-frequency (IF) passband BIF (|(f| < (BIF / 2). System where said first device is a first FMCW transceiver. System where said second device is a second FMCW transceiver. System where said tuning reduces a beat frequency (f and phase error to within a lock tolerance. System where the offset search window spans a frequency band. System where the offset search window is stepped in increment ranging between about 10 and 100 kHz. System where a lock criterion includes that frequency error is smaller than the smallest increment the second electromagnetic device uses to tune the offset search window. System where a lock criterion includes that chirps remain phase-continuous. System where after acquisition, subsequent chirps remain phase-continuous within a tolerance. System where a coherency check distinguishes a true signal lock from random noise or brief, transient false alarms. System where tuning may include digitally resampling. System where tuning may include adjusting a voltage-controlled oscillator or phase-locked loop. System may include a low-band transceiver configured to transmit a wake-up signal or authentication message prior to high-band acquisition. System where the low-band is sub-GHz. System where the wake-up signal or authentication message is authenticated using a rolling code or message authentication code. System where the signal ranges between about 76 to 81 GHz. System where the first electromagnetic device includes an unidirectional antenna. System where the first electromagnetic device includes an omnidirectional antenna. System where the second electromagnetic device includes an unidirectional antenna. System where the second electromagnetic device includes an omnidirectional antenna. System where the signal is authenticated using a rolling code or message authentication code. Implementations of the described techniques may include hardware, a method or process, or a computer tangible medium.

[0037] In one general aspect, system may include a first electromagnetic transceiver configured to transmit a wake-up signal. System may also include a second electromagnetic transceiver, configured to receive said wake-up signal and transmit a response signal and a time tag. System may furthermore include where said first transceiver is configured to receive said response signal. System may in addition include. System may moreover include control circuitry configured to compute a cooperative range from the response signal and time tag. Other embodiments of this aspect include corresponding computer systems, apparatus, and computer programs recorded on one or more computer storage devices, each configured to perform the actions of the methods.

[0038] Implementations may include one or more of the following features. System where said first electromagnetic transceiver is further configured to remove inter-device skew. System where said first electromagnetic transceiver is further configured to transmit a time tag and (i) exchange time tags and phase tags with said second transceiver to remove inter-device skew, or (ii) exchange and combine calculated ranges with said second transceiver to cancel said inter-device skew, thereby determining a distance between the transceivers without relying on a reflected echo. System where said response signal includes a frequency-modulated continuous-wave (FMCW) chirp. System where said control circuitry includes a mixer and intermediate frequency chain to produce a beat from the response signal; and where said range is computed based said beat. Implementations of the described techniques may include hardware, a method or process, or a computer tangible medium.

[0039] DETAILED DESCRIPTION OF THE INVENTION

[0040] The present invention, in some embodiments thereof, relates to a system and method for synchronizing two or more independent electromagnetic transceivers (e.g., FMCW radar, FMCW lidar, etc.), to enable coherent reception between devices. Optionally, the devices are not hardwired or clock-shared. More particularly, but not exclusively, synchronization includes sweeping a frequency-offset “Doppler” search window to capture a peer’s chirp and then tuning the local clock into lock into the identified frequency.

[0041] DEFINITIONS

[0042] A narrowband signal is one whose frequency content is confined to a small range around a central frequency, such that the variation of frequency within the signal does not significantly affect how the signal propagates through the medium or how it interacts with system components. Narrowband signals behave much like a pure tone or carrier wave, whether at radio, millimeter, or optical frequencies, and are typically used for stable transmission, coherent detection, or long- range communication where resolution is less critical. Examples include single-frequency millimeter-wave radar carriers or continuous-wave lasers in optical links.

[0043] A wideband signal is one whose frequency content spans a range large enough that the propagation or system response varies noticeably across that band. In practice, this means that the wide frequency spread is exploited to improve time resolution, spatial resolution, or robustness to interference. At very high frequencies, wideband signals include millimeter-wave FMCW radar chirps or optical LiDAR chirps, where the broad sweep of frequencies enables fine range discrimination and precise measurement.

[0044] Examples of applications typically including narrow band signals include satellite communications, cellular voice channels, continuous-wave and single-frequency lasers used for fiber-optic communication.

[0045] Wideband signals include, for example, millimeter-wave range FMCW radar chirps (which may sweep hundreds of MHz to several GHz) and frequency-modulated LiDAR or chirped pulse LiDAR.

[0046] Continuous wave narrow band doppler radar at millimeter frequencies generally transmits a narrow band signal and may receive a wide band of frequencies (including frequencies with Doppler shift) using a search window. Frequency modulated continuous wave Doppler radar sends and receives wide band signals and also

[0047] As used herein, the term ’’chirp signal” may relate to a signal in which the frequency increases or decreases with time. In some sources, the term chirp is used interchangeably with sweep signal, and is a standard in spread-spectrum communications, sonar, radar, and laser systems.

[0048] As used herein, the term “Doppler radar” may relate to a type of radar that measures the Doppler shift of a reflected signal to determine a target's relative velocity. This shift in frequency is caused by the relative motion between the radar and the target and / or intentionally induced by the transmitter.

[0049] As used herein, the term “high-band” may relate to wave radar / lidar carrier frequencies of about 60-100 GHz; particularly 76-81 GHz.

[0050] As used herein, the term “medium band” may relate to wave radar / lidar carrier frequencies of about 1 GHz-60 GHz.

[0051] As used herein, the term “low-band” may relate to wave radar / lidar carrier frequencies which are sub-GHz (e.g., about 300 kHz-1 GHz).

[0052] As used herein, the term “chirp slope” may relate to the rate of change of frequency in a chirp signal, which is a signal whose frequency increases or decreases over time, i.e., S=df / dt. The chirp slope may be linear.

[0053] As used herein, the terms “IF bandwidth” and “IF passband” and / or “beat” may be used interchangeably, and may relate to a specific range of intermediate frequencies (IF) that a receiver's bandpass filter is designed to pass while blocking others, allowing the desired signal to be separated, amplified, and processed without interference from adjacent channels or noise, that is the passband of the receiver’s IF chain, e.g., BIF is the 3 dB passband of the receiver’s IF chain.

[0054] As used herein, the terms the “intermediate frequency chain” and “IF chain” may relate to a series of electronic components in a receiver (e.g., superheterodyne receiver, etc.) which processes a radio frequency (RF) signal, such as, after it has been down-converted to a fixed, lower frequency. The IF chain may be a core part of the receiver's architecture, and / or may provide signal amplification and / or filtering.

[0055] As used herein, the term “offset search window” may relate to a sweep of receiver mixing conditions configured to accept a peer chirp with a frequency / time offset within a selected range of frequencies, ±Af.

[0056] OVERVIEW

[0057] An aspect of some embodiments of the current invention relates to a system and method for synchronization of electromagnetic signals. Additionally, or alternatively, an aspect of some embodiments of the current invention relates to a system and method to measure distance between independent electromagnetic devices is disclosed and described. Optionally, the system may include at least two transceivers. Optionally, the transceiver may include electromagnetic wave transceivers, for example, a radiofrequency device, and / or a millimeter wave device (e.g., radar), and / or an optical device (e.g., lidar). Optionally, at least one antenna may be dedicated to transmitting and / or receiving a signal unidirectionally. Optionally, at least one antenna may be dedicated to transmitting and / or receiving a signal omnidirectionally. Optionally, the electromagnetic signals may include Doppler radar and / or lidar. Optionally, the electromagnetic signals may include multi-band interrogation signals. For example, signals may include frequency modulated continuous wave (FMCW) radar or FMCW lidar. Optionally, measurements are made without relying on echoes. For example, the measurement may synchronize the devices and / or mix peer-to-peer chirps.

[0058] In order to communicate using radar and / or lidar signals, the signals need to synchronize clocks and / or frequency of different radar sets. Optionally, the reference clocks of the radar and / or lidar units may be controllable and / or adjustable. The reference clocks may be adjusted to synchronize the radar and / or lidar signals. In some embodiments, a window of frequencies (doppler window) of a first device may be caused to drift until it recognizes a signal from a second device. Once the signal from the second device has been detected, the first device may synchronize its clock and / or send a signal to the second device reporting the measured offset. The second device may then compute an exact timing and / or frequency correction.

[0059] In many conventional radar systems and / or lidar systems, the transmitter and receiver are co-located and / or interconnected. Optionally, the system may transmit a signal towards a target and receive an echo of its own signal, e.g., the signal is reflected back to the system by the target. Optionally, the clock of the transmitter and receiver may be automatically synchronized (it is the same clock, therefore, there is no need to synchronize the returned signal). Optionally, the distance to the target may be computed based on the time of travel of the echo and / or change in phase. Optionally, the echo may be shifted and / or offset in frequency with respect to the outgoing transmitted signal due to the Doppler effect, e.g., if the target is moving. Optionally, the system may be configured to search for the incoming signal over a frequency window (Doppler window) for a signal that is frequency offset to find the returning signal even though it is offset from the outgoing signal. Optionally, the speed of the target may be computed based on this frequency shift. Optionally, if the target is moving relative to the radar, the frequency of the reflected signal may be different from the transmitted signal (Doppler shift). Optionally, by measuring the Doppler shift, the radar may determine the target's relative velocity.

[0060] According to some embodiments, the system may include two or more radar and / or lidar transceivers. Optionally, the system may be configured to detect one or more signals. Optionally, the radar and / or lidar transceivers may transmit and / or receive signals. Optionally, two or more radar and / or lidar transceivers may transmit and / or receive signals from each other. Optionally, the frequency and / or phase and / or timing of the signals of the two or more radar and / or lidar transceivers may be synchronized. For example, the signals (e.g., a chirp signal) of one transceiver may be received by another receiver and used to synchronize the clocks of the two receivers. Optionally, the reference clock of the transceivers may be controllable and / or adjustable to synchronize the chirps. For example, the signal (e.g., a chirp signal) of one receiver and / or additionally timing information may be received by another receiver and used to receive information about the first receiver. Optionally, the signals may be radar and / or lidar signals. Optionally, the system may be configured to synchronize the clocks of two or more radar and / or lidar signals.

[0061] According to some embodiments, the system may make use of “off the shelf’ radar and / or lidar. Optionally, the system may include very high band Doppler radar (e.g., about 80 GHz, etc.). Optionally, the system may not make use of the reflected signals. Optionally, the ability of the radar and / or lidar to search over a window of frequencies (the Doppler window) may be configured for other purposes.

[0062] According to some embodiments, since the clocks of two or more radar and / or lidar transceivers may not be synchronized. Optionally, the two or more radar and / or lidar transceivers may each be using a slightly different frequency, therefore, one radar and / or lidar may not detect the signal from another other radar and / or lidar. Optionally, the receiving radar may search for the signal of the transmitting radar. For example, the search may use a Doppler search window (e.g., a search window configured for detecting a frequency shift between an outgoing signal and its echo) to search for the signal sent from a different transceiver. In some embodiments, the range of the search may be expanded using a moving search window. Optionally, the system may be configured for searching for a frequency shift between two or more transceivers. Optionally, the system may assume that the two or more radar and / or lidar are relatively stationary in space.

[0063] According to some embodiments, the system may facilitate searching for the signal e.g., using the Doppler function of the radar and / or lidar which is intended to search for frequency shifts due to the Doppler effect of moving objects on the echo of a radar beam. Optionally, “off the shelf’ radar and / or lidar is not intended to communicate in the frequency range which is being used for communication. For example, a radar band (e.g., a W-band) may be used to transmit information between two radars. In some embodiments, an off the shelf radar system will be used, which does not have a native protocol to detect a signal whose frequency and / or timing and / or phase may not be synchronized with the internal clock of the radar. Optionally, the internal reference clock of the radar may be controllable and / or adjustable. Optionally, the system may be configured to synchronize the frequency and / or timing and / or phase of two or more radar and / or lidar. Optionally, the system may assume that the two or more radars and / or lidars are relatively stationary in space.

[0064] According to some embodiments, a first unit (e.g., a firing unit, an interrogator unit etc.) may transmit a radar signal (e.g., a chirp). Optionally, one or more second units (e.g., a receiving unit) may search for the signal over a range of frequencies (e.g., the exact clock rate of the transmission may not be known). Optionally, the search may include use of a Doppler search window function of a radar and / or lidar to search over a window of frequencies. Optionally, the system may use a moving window (e.g., the window may be moved up and / or down to increase the range of searched frequencies by alternating the beginning and / or the end frequency of the window and / or drift the system clock up and / or down). Optionally, when the receiving radar unit receives the signal, the clock of the receiver unit may be synchronized to that of the incoming unit (e.g., the clock of the second unit is set to equal the base frequency of signal from the first unit by tuning the clock until the received frequency is in the Doppler search window, optionally with a predefined Doppler shift). Optionally, the reference clock of the first unit and / or second unit may be controllable. The reference clock may be adjusted to synchronize the chirps.

[0065] Optionally, the second unit may send a response signal back to the first unit. Optionally, along with the response signal the second unit may send the time and phase on which the signal was received. Optionally, the first unit may receive the response signal and timing information from the second unit. Optionally, the two units may then communicate. For example, synchronization of interrogator (first unit) and transponder (second unit) chirp signals whereby the transponder clock may be drifted until it has synchronized with the interrogator clock within the Doppler frequency offset search window. Advantageously, two or more radars and / or lidars may be synchronized with each other.

[0066] According to some embodiments, the system may be a multi-band interrogation signal system. Optionally, the system may be configured to transmit and / or receive two or more signals at different frequencies. Optionally, the system may be configured to transmit and / or receive a higher frequency signal and a lower frequency signal. Optionally, the higher frequency signal may be higher than the lower frequency signal. Optionally, the bands of the frequencies may be far apart. Optionally, the system may include separate antennas for each band.

[0067] According to some embodiments, the system may include a transceiver. Optionally, the transceiver may include a radar device (e.g., a Doppler radar) and / or a lidar device. Optionally, the transceiver may have a frequency ranging between about 30 GHz to about 120 GHz, and / or between about 60 GHz to about 100 GHz, and / or between about 75 GHz to about 95 GHz, and / or between about 76 GHz to about 81 GHz. Optionally, the bandwidth of the transceiver may range between about 1 GHz to about 10 GHz and / or 10 GHz to 30 GHz. The transmitters wavelength may include radar and / or lidar e.g., in the decimeter range (e.g., between 1 to 0.1 m) the millimeter wave range (e.g., from 1 to 100 mm) and / or the micrometer wave range (e.g., between 1 to 1000 mm) and / or in the nanometer wave range (e.g., between 1 to 1000 nm).

[0068] According to some embodiments, the signals may provide an omnidirectional and / or a unidirectional signal (e.g., angle accuracy less than 0.1 degrees, and / or between 0.1 to 1 degree, and / or between 1 to 10 degrees, and / or between 10 to 45 degrees), and / or resolution, and / or detection accuracy. For example, the directivity of a wake-up signal may range between 1 to 10 m, and / or between 10 to 50 m, and / or between 50 to 150 m, and / or between 150 to 500 m, and / or between 500 to 3000 m. Optionally, the transceiver may include a radar device (e.g., an off the shelf radar, e.g., a doppler radar), e.g., making the system aesthetic and / or lightweight.

[0069] According to some embodiments, the signals may be focused and / or broadcast in all directions (omnidirectional). Optionally, the signals may not penetrate obstacles and / or buildings. Optionally, focused beamed signals may be reflected off some objects and / or may be received behind an obstacle and / or off the intended path (e.g., multipath interference). Optionally, detecting these signals (in high standby mode) may take significant power.

[0070] According to some embodiments, the system may include a lower frequency transceiver. Optionally, the low band transceiver may include a low band radio transceiver. Optionally, the low band signals may include low band radar. Optionally, low band signals may be more power efficient (for transmitting and / or receiving) when compared to higher-frequency radar of similar range. Optionally, the low band signals may have a frequency ranging between about 3 MHz to about 2 GHz, and / or between about between about 300 kHz to about 3 MHz, and / or between about 30 kHz to about 300 kHz, and / or between about 1 Hz to about 100 kHz. Optionally, the low band signals may have a longer wavelength facilitating penetration of the atmosphere without losing strength and / or less susceptible to environmental clutter and atmospheric losses.

[0071] According to some embodiments, the low band signals may be omnidirectional. Optionally, the low band signals may penetrate obstacles (e.g., buildings, vehicles, vegetation, etc.). Optionally, the low band signals may not require significant power to detect in standby mode. Optionally, low band signals may be effective at long-range target detection of challenging targets, e.g., as low and / or high speed and / or small targets and / or targets in cluttered environments.

[0072] According to some embodiments, the system may include various synchronization mechanisms. The receiver may sweep an offset search window in steps of various sizes (e.g., 10- 100 kHz). Optionally, the offset search window may be correlated against an expected chirp template. A candidate lock may be identified. Optionally, a candidate lock may occur when the correlation between the offset search window and the expected chirp template exceeds a threshold value and / or the corresponding difference in frequency between the two signals lies within the IF passband. Upon candidate lock, a control loop may adjust the local reference clock and / or a numerically controlled oscillator (NCO) to reduce the difference in frequency and / or phase error (A ). Optionally, the system may be adjusted until a stable, long-term lock on the target signal is achieved, satisfying both frequency and phase tolerances over a series of measurements. The window may “walk” (move) up / down a frequency band to extend the capture range. Optionally, the frequency may not be perfectly stable and / or may change over time. Optionally, a receiver may find and lock onto a signal with frequency drift. Optionally, when the peer chirp is within the intermediate frequency (IF) passband of a filter, the receiver may compute instantaneous frequency (A / ), from the IF and update the drift estimate until a steady-state lock is achieved. Optionally, the frequency difference between the incoming signal and the receiver's template falls within an acceptable frequency range to be considered a valid signal. If the beat frequency is outside this range, the IF filter may reject it, and the receiver may not be able to achieve a lock. Optionally, the system may include a form of coherency check. Optionally, a coherency check may assist in distinguishing a true signal lock from random noise or brief, transient false alarms. Optionally, a coherency check may provide robustness and / or confidence in the receiver's lock status.

[0073] Some embodiments may relate to a system and method to measure distance between independent electromagnetic devices. According to some embodiments, after synchronization, the system may facilitate computation of a distance between two units without requiring an echo of the signal (e.g., synchronizing the clocks and then computing a time of travel of the signal sent between two units). Optionally, a first unit may synchronize to a second unit. Optionally, the distance between the first unit and the second unit may be calculated from the shift change in the signal phase and / or signal frequency. Optionally, the second unit may communicate the frequency drift and / or error and / or phase to the first unit. Optionally, such communication may remove the error of the clock by adding the drift in order to calculate the distance between the units. For example, the first unit may now know the time and / or phase offset of the signal transmitted between the first unit and the second unit. Optionally, the system may compute the distance to the second unit based on this offset of the response signal without needing to receive a reflected echo. Optionally, the unit may each compute a range independently and send it to the other unit. Optionally, the ranges computed separately by the two devices may be averaged.

[0074] According to some embodiments, the transceivers may be configured to measure the distance between them without reflection, once synchronized. Optionally, a first “off the shelf’ transceiver (e.g., Doppler radar, lidar, etc.) may be used to determine the range to a second synchronized “off the shelf’ transceiver (e.g., Doppler radar, lidar, etc.). Optionally, a “off the shelf’ receiver (e.g., Doppler radar, lidar, etc.) may be used to determine the range to a synchronized “off the shelf’ transmitter (e.g., Doppler radar, lidar, etc.). Optionally, the distance may be computed based on the phase shift of the signal received in relation to the signal transmitted.

[0075] According to some embodiments, the distance between the middle of the search window and the chirp signal may be measured to determine the time offset. Optionally, the offset may be communicated to the interrogator. Optionally, the interrogator may measure the distance of the received signal and / or add to it the feedback from the transponder, e.g., the sum of the frequency distance may be the physical distance between the units. Advantageously, immediate response and / or accurately measured time may not be required prior to responding. Optionally, a parameter without a time critical procedure may be calculated. Optionally, the calculation may be reported to the units.

[0076] According to some embodiments, the system may include Frequency-Modulated Continuous-Wave (FMCW) radar to determine the range of a target by analyzing the frequency difference between the transmitted and received signals. Optionally, the FMCW radar may transmit a chirp signal. Optionally, the signal frequency may linearly increase and / or decrease over time. Optionally, when the signal hits a target, the signal may reflect back to the radar with a slight frequency shift due to the Doppler effect. Optionally, the radar may mix the received signal with a portion of the transmitted signal to obtain the beat frequency. Optionally, the beat signal may be directly proportional to the target's range. Optionally, by measuring the beat frequency and / or using the known chirp parameters, the radar may accurately calculate the distance to the target.

[0077] According to some embodiments, the system may utilize two or more synchronized radars. Optionally, a second radar may transmit a chirp signal identical to the first radar, but with a slight time delay. Optionally, the first radar may receive the signal from the second radar, which may be effectively equivalent to receiving a reflection from a virtual target located between the two radars. Optionally, by analyzing the beat frequency between the transmitted signal and the received signal, the radar may determine the range to this virtual target, providing valuable information for various applications. As used herein, the ‘virtual target’ may not be a physical reflector. Optionally, the two or more synchronized devices may transmit peer chirps. Optionally, each of the synchronized devices may mix the peer chirp with a locally generated chirp template to form the beat (instantaneous frequency difference (Af)).

[0078] According to some embodiments, the system may warn a user when they are pointing a weapon at a friendly transceiver. Optionally, the system may prevent a user from firing at a friendly transceiver. In some embodiments, the system may compute a range to the friendly transceiver and / or the warning and / or action may depend on if the friendly transceiver is in range of the weapon.

[0079] According to some embodiments, the signal may be pulsed, modulated, encoded and / or coded (e.g., encoding and / or coding may be changed to avoid enemy stealing the device and / or spoofing the signal, modulated pulses of any frequency, and / or of any kind of modulation,), modulated and / or non-modulated signals in changing frequencies, spread spectrum, etc. Optionally, the signals may include a digital modulation technique to divide the limited spectrum available, such as time division multiple access (TDMA) and / or frequency division multiple access (FDMA). Optionally, such systems may make it difficult for an enemy to detect and / or locate friendly forces. Optionally, this may prevent and / or make it difficult for the enemy to spoof the signal (e.g., to prevent the enemy from fooling friendly forces into firing on the enemy). Optionally, additional data may be transmitted and / or received (e.g., encourage communication and / or share information between units, individual soldiers, command, etc.).

[0080] According to some embodiments, the system may be configured to avoid unnecessary transmissions, e.g., to avoid exposing units to detection by the enemy. Optionally, the system may be configured to save power (e.g., reducing the demand for battery capacity and / or reducing maintenance e.g., recharging). Optionally, the system may be maintained in standby mode most of the time.

[0081] According to some embodiments, the system, device or method may include a processor. Optionally, the processor may encode and / or decode data. Optionally, the processor may be programmable (e.g., to transmit at a particular frequency, modulate the frequency, pulse the transmission, encode and / or decode a signal, identify friend from foe, assist in the decision to fire or not, provide a warning, provide proximity data, determine signal strength, determine direction and / or range, provide location information, provide information to command, etc.). Optionally, the system may communicate data among compatible devices, similar devices, and / or devices identified as friendly devices. Optionally, signal strength may be used to determine direction and / or range. Optionally, signaling between devices may be used to determine range. Optionally, by communicating with friendly units carrying a similar device, the system may determine the range and direction to one or more units.

[0082] According to some embodiments, the system may facilitate cooperative ranging mechanics. Optionally, the system may facilitate range measurement when dealing with signal reflection from a moving target (e.g. by radar, lidar, etc.). Optionally, the system may be configured to measure the time it takes for a signal to travel and return, i.e., signal reflection. Optionally, each unit may mix a peer’s chirp (e.g., high-band chirp) with its local reference to obtain an IF beat. When a receiver uses a standard FMCW “reflection” mapper on a peer chirp, any residual inter-device skew may bias the apparent range. Optionally, the physical separation may be a one-way delay and / or two-way delay. Optionally, the devices may exchange time and / or phase tags to remove skew. Optionally, the devices may exchange time and / or phase tags to average the two apparent ranges. Optionally, the requirements for acceptance and / or system tolerance may be predefined by a user.

[0083] According to some embodiments, cooperative ranging may occur when chirps are synchronized. Optionally, when synchronized, each radar and / or lidar may transmit the same chirp set. Optionally, when synchronized, each radar and / or lidar may receive the peer’s chirp. Optionally, when synchronized, each chirp may be mixed with its local IF. Optionally, the mixed chirps may be used to compute the ranges. Optionally, the two computed ranges may be exchanged. Optionally, the two computed ranges may be combined to yield the corrected separation. Optionally, the two computed ranges may be averaged to cancel skew.

[0084] According to some embodiments, the method may include interrogation and / or response. Optionally, a first transceiver may transmit an interrogation which may be detected by a second transceiver (e.g., a transceiver may continuously search across a frequency window in standby mode). Optionally, the second transceiver may respond with device ID, and / or time tags, and / or phase tags, and / or optional drift estimate, and a message authentication field (e.g., rolling code, message authentication code (MAC), etc.). Optionally, the first transceiver may verify the authenticity of the signal. Optionally, the first transceiver may compute a time-of-travel and / or a phase shift range from the combined ranges to determine range. Optionally, the first transceiver may apply a policy (e.g., warn, lock, etc.). Optionally, a low-band wake-up signal and / or authorization conde may be transmitted prior to high-band acquisition. Optionally, the low-band wake-up signal may initiate frequency window scanning. Optionally, timeouts and / or randomized back-off may reduce detectability by a third party. Optionally, TDMA / FDMA / hopping may be used for multi-unit operation.

[0085] According to some embodiments, a transceiver may generate the IF beat using an artificial reference. Optionally, the artificial reference may not be used for transmission. Optionally, the transceiver may be a transmit-only device while another device, using an artificial IF, may perform the range computation. Optionally, the IF frequency and / or chirp slope may differ between transmitting and mixing paths. Optionally, cooperative exchange reconciles offsets between transmitting and mixing paths.

[0086] According to some embodiments, the system and / or method may compute a distance between receivers in a line of fire LoF and / or facilitate synchronization and / or communication with another receiver. For example, the system may be used to avoid friendly fire incidents and / or warn a user not to fire when they are pointing a weapon at a friendly transmitter and / or in range of a friendly transmitter. Optionally, the system may assist in making a decision to fire or not to fire a weapon. Optionally, the system may include a subsystem that may provide an audible and / or visual and / or vibration warning to the person handling the weapon to avoid firing on friendly units. Optionally, the firing unit may compute a precise range to a friendly unit along the line of fire (LoF) using the cooperative method. Optionally, the system may signal a warning and / or interlock if range / LoF criteria indicate risk to a friendly in the LoF.

[0087] EXAMPLES

[0088] Example 1 - Synchronization Mechanics

[0089] The receiver sweeps an offset search window [-Fmax,+Fmax] in steps 8f (e.g., 10-100 kHz) while correlating against the expected chirp template.

[0090] A candidate lock occurs when correlation exceeds threshold T and the corresponding beat lies within the IF passband: |A / |<BIF / 2.

[0091] The reference clock may be controllable. Upon candidate lock, a control loop adjusts the local reference clock or numerically compensated oscillator (NCO) to reduce A / and phase error A until: lA / jcb / and I A< > \<( / )T continuously for N chirps.

[0092] Where:

[0093] I Af I is the absolute value of the instantaneous frequency error, and is the difference between the frequency of the received signal and the receiver's internal reference frequency (from the NCO).

[0094] Af is the frequency step size of the receiver's search.

[0095] Since I Af|<8f, the frequency error is smaller than the smallest increment the receiver uses to tune the search, indicating that it has found the correct frequency band and is very close to the true frequency of the signal.

[0096] I A(|) I is the absolute value of the instantaneous phase error, and is the difference between the phase of the received signal and the receiver's internal phase reference. c / )T is a phase threshold.

[0097] The condition I Ac|)| <<j)T means the phase error is within a defined tolerance, confirming a stable phase lock. A small phase error is critical for coherent demodulation and accurate data extraction.

[0098] "Continuously for N chirps” is a crucial temporal condition requiring the frequency and phase stability criteria must be met for a consecutive series of N measurement cycles (or "chirps"). This is a form of coherency check that helps distinguish a true signal lock from random noise or brief, transient false alarms. It provides robustness and confidence in the receiver's lock status.

[0099] For example:

[0100] BIF=1-4MHZ, <5 / =25kHz, <pT=20°, N=4-16.

[0101] Example 2 - Acquisition with drift

[0102] When the peer chirp is within ±BIF / 2, the receiver computes instantaneous A / from the IF and updates a drift estimate e for the VCXO / PLL and / or digital resampler; the loop continues until steady-state lock is achieved. A VCXO / PLL is a common and powerful electronic circuit that combines a Voltage- Controlled Crystal Oscillator (VCXO) with a Phase-Locked Loop (PLL). This combination creates a highly stable and tunable frequency source.

[0103] A VCXO is an oscillator that uses a quartz crystal to generate a precise frequency. The key feature of a VCXO is that its output frequency can be slightly adjusted, or "pulled," by applying a small control voltage. While standard crystal oscillators have a fixed frequency, the VCXO's tunability allows it to be used in feedback loops to make minute corrections to its frequency.

[0104] A PLL is a closed-loop feedback control system that automatically adjusts the phase of a local oscillator to match the phase of a reference signal.

[0105] Example 3 - Cooperative Ranging Mechanics.

[0106] Systems with target motion during the time a signal is traveling to and from it, to determine the true range (R*) and velocity, which is related to 8t.

[0107] Each unit mixes the peer’s high-band chirp with its local reference to obtain an IF beat fb. When a receiver uses a standard FMCW “reflection” mapper R=(cf b) / (2S) on a peer chirp, any residual inter-device skew 8t biases the “apparent range.” If the physical separation is R* (so the one-way delay is T=R* / C), then the two apparent ranges computed at the devices are:

[0108] R

[0109] 1= £ (t+ dt) 2

[0110] Where:

[0111] Ri and R2 are the measured ranges.

[0112] Ri is the range measured at a specific moment in time when the signal's travel time is r+8t which equals the true range at the center of the interval plus half the change in distance due to the target's motion.

[0113] R2 is the range measured at a moment when the travel time is r-8t which is equals the true range minus half the change in distance due to the target's motion. c is the speed of light or the speed of the propagating wave.

[0114] T is the total two-way travel time of the signal. This is the time from when the signal is transmitted to when it is received after reflecting off the target.

[0115] 8t is the change in travel time during the measurement interval due to the target's motion. The positive sign in Ri and negative sign in R2 indicates two separate measurements, possibly at different times. R* is the true range or the range at the center of the measurement interval, a reference point in time. c5t / 2 represents the change in range during the measurement.

[0116] It should be noted that 8t is the change in the two-way travel time, therefore the change in the one-way distance (range) is half of that.

[0117] Averaging cancels the skew: = y. When the receiver’s mapper is configured for one way cooperative mode, the corrected distance is R* = R±+ R2(or R* = 2R).

[0118] Worked example: With 7?*=3OOm => T=1 / IS, and 5t=50ns:

[0119] Example 4 - Acceptance & tolerances.

[0120] The absolute value of the beat frequency (I Af|) must be less than or equal to half of the intermediate frequency (IF) bandwidth (BIF / 2). This condition ensures that the received signal's frequency is within the acceptable range for the receiver to process. Acquisition holds if:

[0121] |Af|<BiF / 2;

[0122] Where:

[0123] I Af| is the beat frequency, which is the frequency difference between the incoming signal and the receiver's local oscillator. In a receiver, this "beat" may be a new signal created when the incoming signal is mixed with a reference signal.

[0124] BIF is the bandwidth of the receiver's intermediate frequency (IF) filter. This filter is designed to pass a specific range of frequencies while blocking all others. The total width of this range is BIF.

[0125] The IF passband is the frequency range that the filter allows to pass. It is cantered around the IF, extending from -BIF / 2 to +BIF / 2.

[0126] The devices may exchange time / phase tags to remove skew or simply average the two apparent ranges.

[0127] Example 5 - Range calculation When the transmitted signal hits a target, it is reflected back to the radar receiver. Due to the time delay between the transmission and reception of the signal, there is a frequency difference between the transmitted and received signals. This frequency difference is called the beat frequency. The received signal is mixed with a portion of the transmitted signal to produce an intermediate frequency (IF) signal. The beat frequency is directly proportional to the time delay, which in turn is proportional to the distance to the target. By measuring the beat frequency, the radar can calculate the range to the target using the formula: where:

[0128] R - the range in meters

[0129] C - speed of light

[0130] Af- the difference between the received and transmitted frequency. df / dt - chirp slope

[0131] The above calculation assumes a transmitted, reflected and received signal.

[0132] SPECIFIC EMBODIMENTS

[0133] Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not necessarily limited in its application to the details of construction and the arrangement of the components and / or methods set forth in the following description and / or illustrated in the drawings and / or the Examples. The invention is capable of other embodiments or of being practiced or carried out in various ways.

[0134] Reference is now made to the exemplary figures.

[0135] Fig. 1A is a flow diagram illustrating a method synchronization of two or more transceivers, in accordance with an embodiment of the current invention. For example, in method 10 (synchronization): a first unit (e.g., a firing unit, etc.) transmits 12 a low-band wake followed by a high-band chirp set. A second unit (e.g., a receiving unit) searches 14 for high band signal over a range of frequencies, by sweeping an offset search window across frequencies. Optionally, the system may use a moving window (e.g., the window may be moved up and / or down to increase the range of searched frequencies). The second unit detects 16 the high-band chirp within BIF. The second unit tunes and / or locks its clock to synchronize 18 with the frequency and / or phase of the first unit’s chirp.

[0136] Optionally, the second unit may send a response signal back to the first unit. Optionally, along with the response signal the second unit may send the time and phase on which the signal was received. Optionally, the first unit may receive the response signal and timing information from the second unit. Optionally, the two units may then communicate. For example, synchronization of interrogator and transponder chirp signals whereby the transponder clock may be drifted until it has synchronized with the interrogator clock within the frequency offset search window. Advantageously, two or more radars and / or lidars may be synchronized with each other and / or may communicate over the radar band.

[0137] Fig. IB is a flow chart illustrating a Doppler- window search and frequency shift used during signal acquisition in accordance with an embodiment of the current invention. For example, in method 20, a moving Doppler window is used to search 22 for a signal from a transmitter. The Doppler window may the window may be shifted 24 up and / or down the frequences to increase the range of searched frequencies. Once the receiving radar receives the signal from the transmitting radar, it begins processing to extract meaningful information signal. Optionally, the second radar uses a mixer stage, where the received signal is combined with a local reference signal (e.g., an expected chirp signal according to the local clock) to form a differential signal. Optionally, this facilitates isolating the differences between the transmitted and expected signal.

[0138] In some embodiments, analysis of the signal includes applying a Fast Fourier Transform (FFT). The FFT breaks down the received signal and / or the differential signal into its constituent frequency components, allowing the second radar to identify distinct frequency shifts that correspond differences in clock between the two radars. The result may include a detailed analysis of the frequency shifts. Optionally a phase and / or phase difference (e.g., between the received signal and the reference signal) is calculated (e.g., from an imaginary portion of the FFT output).

[0139] Fig. 2A is a block diagram describing a synchronized multi-band interrogation signaling system, in accordance with an embodiment of the current invention. For example, in method 30, first unit 32 (e.g., a firing unit and / or an interrogating transceiver) and / or a second unit 40 (e.g., a receiver unit and / or a responding unit) may include a transceiver 34, 42 and / or one or more antennas 36, 38, 44, 46. Optionally, transceiver 34, 42 may include a radar transceiver (e.g., as illustrated as FIG. 2B) one or more antennas. Optionally, transceiver 34, 42 may include a uni- directional antenna 38, 46 and / or an omni-directional antenna 36, 44. Optionally, one of the units (e.g., the second unit) or both of the units may not include a directional antenna.

[0140] First unit 32 may send a directed signal in the direction of the second unit 40 using a directional antenna. 38. Second unit 40 optionally receives the signal on an omni-directional antenna 44 and responds with an omnidirectional signal sent over an omnidirectional antenna 44 to the omnidirectional antenna 36 of the first unit 32. Alternatively, or additionally, second unit 40 may send and / or receive the signal and / or send a response using a directional antenna 46 (optionally, scanning over various directions). In some embodiments, first unit 32 receives the response with an omnidirectional antenna 36. Alternatively, or additionally, the signal may be sent with an omnidirectional antenna 44 and / or the response may be received using a unidirectional antenna 38.

[0141] Protocol & Security.

[0142] After lock, the second unit transmits a short authenticated response (e.g., rolling-code ID, timestamp, phase tag) on high-band. Optionally, the wake-up signal and / or authorization code may be sent on low-band. Optionally, timeouts and retry back-off may reduce detectability by third parties. Optionally, multiple-access (time and / or frequency hopping) may limit interception and / or spoofing. Optionally, responses failing authentication (e.g., message authentication code (MAC) based authentication) and / or rolling code may be ignored.

[0143] FIG. 2B is a block diagram of a radar transceiver (e.g., a Doppler radar) in accordance with an embodiment of the current invention. For example, radar system 50 includes a transmitter chain 62 configured for generating and emitting a signal. Optionally, transmitter chain 62 includes a signal generator 52, e.g., 150 KHz, etc. Optionally, signal generator 52 may be a wave generator. Signal generator 52 may use a voltage-controlled oscillator 54 (VCO), such as a GUNN oscillator, and / or a frequency synthesizer to create a continuous wave (CW) and / or pulsed signal. Transmission chain 62 may include a directional coupler 56, and / or a signal isolator 58, and / or a transmitter antenna (e.g., corrugated horn antenna, etc.). Optionally, due to the time delay between the transmission and reception of the signal, there may be a frequency difference between the transmitted and received signals. Optionally, the received signal may be mixed in a frequency mixer 68 with a portion of the transmitted signal to produce an intermediate frequency (IF) signal.

[0144] Optionally, transmitter chain 62 may include an amplifier (not shown) configured to amplify the signal, e.g., a power amplifier, such as a solid-state amplifier and / or a traveling- wave tube amplifier, and / or low-noise amplifier (LNA). This amplified signal is optionally transmitted through a directional antenna 60, which focuses the RF energy toward the target and / or determines the beam shape and / or range.

[0145] Optionally, the system may include a phase-locked loop (PLL). Optionally, the phase- locked loop may be a feedback control system that uses a voltage-controlled oscillator to generate an output signal that is synchronized in frequency and phase with a reference input signal. Optionally, the phase-locked loop includes a phase detector, and / or loop filter, and / or voltage- controlled oscillator 54.

[0146] System 50 includes a receiver chain 76 configured to receive a transmitted signal. In some embodiments, the same antenna is used for both transmitting and receiving signals. Alternatively, or additionally, the system may use separate antennas for receiving and transmitting. Receiver chain 76 may include a receiver antenna 74. The received signal may be amplified by an amplifier 72. For example, a low-noise amplifier (LNA) is employed to amplify a weak signal without introducing significant noise, preserving signal integrity. The amplified signal is optionally fed through an optional isolator 70 into a frequency mixer 68, which combines the incoming signal with a reference signal. For example, the reference signal may be produced by signal generator 54 and / or coupled to the mixer via directional coupler 56. Optionally, the intermediate frequency (IF) may be amplified by one or more amplifiers 64, 66.

[0147] The signal may be fed into an acquisition system 78. Optionally, system 50 may include multiple amplifiers and / or filters. Optionally, acquisition system 78 may be connected to a computer 80 with a display 82. The amplifiers and / or filters may prepare the received signal and / or the mixed signal for further analysis by a processor of computer 80. The signal is optionally converted from analog to digital (e.g., using an analog-to-digital converter (A / D). In some embodiments, the digitized signal may be analyzed by a processor using digital signal processing, for example using a Fast Fourier Transform (FFT), which transforms the radar signal from the time domain to the frequency domain.

[0148] Optionally, the system includes a display 82 and control unit 80. For example, display 82 may include a graphical and / or numerical interface may show information such as range and / or direction. Optionally, the interface may be used to configure radar settings, including frequency, sensitivity, and pulse repetition frequency (PRF). In some embodiments, a duplexer, (e.g., switch or circulator) may facilitate the radar to use the same antenna for transmitting and receiving signals. The duplexer may reduce interference or damage to sensitive components. Optionally, the system incorporates clutter filters, for example, to reduce the effects of multipath signals.

[0149] In some embodiments, system 50 includes a power supply 84. Optionally, power supply 84 may be AC or DC. Optionally, power supply 84 may be portable. Optionally, power supply 84 may be incorporated into the transmitter chain and / or receiver chain.

[0150] Some embodiments relate to a FMCW-lidar variant of the system. The high-band may be an optical FMCW carrier. Each unit may include a tunable laser, optical splitter, photodiode mixer, and DSP. The offset window may be implemented by detuning the local laser’s chirp center and / or slope while correlating the IF (photocurrent) against a chirp template. Lock may be achieved by trimming the laser’s frequency control and resampling until the frequency error is smaller than the smallest increment the receiver uses to tune the search, thereby indicating that it has found the correct frequency band and is very close to the true frequency of the signal. This may be performed continuously for a number of chirps. The frequency and phase stability criteria may be met for a consecutive series of measurement cycles (or "chirps"). Optionally, a true signal lock may be distinguished from random noise or brief, transient false alarms by a coherency check. Optionally, a coherency check may provide robustness and confidence in the receiver's lock status. Optionally, the similar thresholds and / or loops may be used as used for radar. Optionally, the lidar system may include a low band wake-up signal. Optionally, the lidar system may include authentication (e.g., device ID, and / or time tags, and / or phase tags, and / or optional drift estimate, and a message authentication field, message authentication code (MAC), etc.).

[0151] Fig. 3 is a schematic diagram illustrating how phase encodes the time-of-travel during synchronization between independent transceivers. For example, a first unit (e.g., interrogator) transmits a high-band FMCW chirp, while a second unit (e.g., receiver and / or transponder) sweeps an offset (e.g., Doppler) search window. The second unit acquires the interrogator’s chirp within its IF bandwidth. Once acquired, the second unit responds by reporting the time stamp and / or phase at which the chirp was received. The first unit in turn compares the received response with its local chirp to infer the propagation delay. Optionally, the phase shift may be determined. The reference clock of the first unit and / or second unit may be controllable. The reference clock may be adjusted to synchronize the chirps.

[0152] For example, for a linear chirp with slope S=d / / dt,

[0153] The instantaneous frequency difference at acquisition is: f~S(r+6t)+6fo,

[0154] Where:

[0155] T is the line-of-sight propagation delay,

[0156] 8t is any residual timing skew, and

[0157] 8fo is residual frequency error.

[0158] The corresponding phase difference over an observation interval T satisfies

[0159] By holding I A / | inside the IF passband during acquisition, the control loop can (i) estimate 8fo from A / and (ii) trim clock and / or number-controlled oscillator settings until I A / | and |A | meet lock criteria.

[0160] For example, Fig. 3 illustrates that the transmitted chirp and the response signal to show the measurable phase relationship used by the synchronization loop.

[0161] In some embodiments, the second unit’s response includes a phase tag and / or a time tag derived from its local clock at the instant of detection; after acquisition, subsequent chirps remain phase-continuous within a tolerance (e.g., I A< > \<( / )T for N chirps), enabling robust lock even with small drift.

[0162] Fig. 4 is a schematic diagram of the frequency-offset search window used during acquisition in accordance with some embodiments. For example, the receiver sweeps an offset window between lower and upper bounds Fi and F2 while correlating against a chirp template. When the peer chirp is present, the de-chirped beat appears at a measurable offset A / inside the IF band. The diagram shows the transmitted chirp and two received chirps (received chirp 1 and received chirp 2) at different offsets, along with the search window boundaries FI,F2.

[0163] Detection of a signal is recognized when the correlation of the transmitted chirp with the chirp template exceeds a threshold and / or the absolute beat frequency is less than or equal to the bandwidth of the receiver's intermediate frequency (IF) filter or a portion thereof, e.g., I A / |<BIF / 2. The absolute beat frequency is the frequency difference between the incoming signal and the receiver's local oscillator. In a receiver, this "beat" may be a new signal created when the incoming signal is mixed with a reference signal. The receiver's intermediate frequency (IF) filter may be designed to pass a specific range of frequencies while blocking all others. The total width of this range is BIF. The control loop moves (walks) the search window and / or trims the reference clock to drive the offset A / inside the IF band towards zero (A / — >0). The search window may be moved within a specified step size (8f) and / or may maintain phase continuity. By shifting the window up / down (arrows in the figure) the system extends capture range to accommodate initial clock error and unknown propagation delay while remaining compatible with off-the-shelf FMCW radar and / or lidar front-ends.

[0164] In some embodiments, the receiver alternates the starting edge of the sweep (begin at Fi then F2) to reduce worst-case acquisition time; once a candidate lock is found, the loop refines A / and phase error (A< >) until both fall below predefined tolerances across a certain number (N) of consecutive chirps.

[0165] Typical values include BIF in the 1-4 MHz range with incremental sweep step 8f of 10- 100 kHz, though other values may be used.

[0166] Fig. 5 is a block diagram illustrating an exemplary system for synchronizing electromagnetic transceivers, in accordance with some embodiments. For example, system 90 includes a first electromagnetic transceiver 92 configured to transmit a chirp signal and a second electromagnetic transceiver 94 configured to receive a chirp signal. Optionally, at least one antenna of first electromagnetic transceiver 92 is unidirectional and / or at least one antenna of first electromagnetic transceiver 92 is omnidirectional. Optionally, at least one antenna of second electromagnetic transceiver 94 is unidirectional and / or at least one antenna of second electromagnetic transceiver 94 is omnidirectional. Second electromagnetic transceiver 94 may include a receiver 96 having an intermediate-frequency (IF) bandwidth, and / or a controllable reference clock 98, and / or control circuitry 100. Control circuitry 100 may be configured to sweep an offset search window across a plurality of frequency offsets while correlating received signals against a chirp template. Optionally, the offset search window may span a frequency band. Optionally, the offset search window may be stepped in increment ranging between about 10-100 kHz.

[0167] Control circuitry 100 may be configured to detect the first electromagnetic transceiver’s chirp when a correlation threshold is exceeded and a beat frequency lies within the intermediatefrequency (IF) bandwidth. Control circuitry 100 may be configured to tune the reference clock to reduce offset and phase error until the received chirp is within a lock tolerance, thereby synchronizing the second electromagnetic transceiver to the first electromagnetic transceiver. Optionally, tuning comprises digitally resampling and / or adjusting a voltage-controlled oscillator and / or phase-locked loop. Optionally, lock criteria include frequency error is smaller than the smallest increment the receiver uses to tune the offset search window, and / or chirps remain phase- continuous, and / or after acquisition, subsequent chirps remain phase-continuous within a tolerance. Optionally, the system may include a coherency check to distinguish a true signal lock from random noise and / or brief, transient false alarms. Optionally, the system may include a low- band transceiver configured to transmit a wake-up signal and / or authentication message prior to high-band acquisition. Optionally, the low-band may be sub-GHz. Optionally, the wake-up signal and / or authentication message may be authenticated using a rolling code or message authentication code. Optionally, the high-band ranges between about 76-81 GHz.

[0168] Fig. 6 is a flow chart illustrating an exemplary method of synchronizing independent electromagnetic transceivers, in accordance with some embodiments of the current invention. For example, in method 110, a chirp is transmitted 112 from a first electromagnetic transceiver. At a second electromagnetic transceiver an offset search window sweeps 114 for transmitted chirps. Optionally, the offset window may be moved during acquisition to extend capture range. The first electromagnetic transceiver’s chirp is detected 116 by the offset search window within an intermediate frequency acceptance band, and correlating 118 the transmitted chirp against a chirp template. A reference clock of the second electromagnetic transceiver is adjusted 120 until frequency and phase errors satisfy lock criteria. Optionally, lock criteria include that frequency error is smaller than the smallest increment the receiver uses to tune the offset search window, and / or the chirp remain phase-continuous, and / or subsequent chirps remain phase-continuous within a tolerance. Optionally, distinguishing a true signal lock from random noise or brief, transient false alarms by a coherency check. Optionally, the method includes authenticating the transmitted chirp using a rolling code and / or message authentication code. Optionally, the transceivers are Frequency -Modulated Continuous-Wave (FMCW) lidar devices and / or radar devices. Optionally, for lidar devices, tuning includes trimming a laser frequency and / or resampling the IF photocurrent. Optionally, for radar devices, tuning includes adjusting a voltage- controlled oscillator or phase-locked loop. Optionally, method 110 may be performed by control circuitry of a transceiver executing instructions stored on a non-transitory computer-readable medium. Fig. 7A is a flow chart illustrating an exemplary method for cooperative ranging between synchronized electromagnetic transceivers, in accordance with some embodiments of the current invention. For example, in method 130, a first transceiver transmits 132 a chirp to a synchronized second transceiver. Optionally, each transceiver (e.g., radar, lidar, etc.) transmits the same chirp set. Transceiver 2 receives 134 a chirp from transceiver 1, which is mixed 136 with its local IF. The range is calculated 138. Optionally, the two computed ranges are then optionally exchanged and combined to yield the corrected range.

[0169] Fig. 7B is a flow diagram illustrating an exemplary method for computing a range with residual skew, in accordance with an embodiment of the current invention. For example, in method 140, a first transceiver and a second transceiver transmit 142 similar chirp signals. Each transceiver receives 144 the signal from the other transceiver (i.e., transceiver 1 receives a chirp from transceiver 2, and transceiver 2 receives a chirp from transceiver 1). Each transceiver receives 144 peers’ chirp which is mixed 146, 148 with its local IF. The range is calculated by each transceiver 150, 152. The two computed ranges are exchanged 154 and combined 156 to yield the corrected range. Optionally, each device computes an apparent range, exchanges ranges, and combines and / or averages them to cancel the skew.

[0170] The received signal originates from a second transceiver rather than a reflection. If the second transceiver is perfectly synchronized in time and frequency with the first transceiver , such that their chirps start simultaneously and have exact same chirp parameters (e.g., start of chirp, chirp duration, chirp slope, PRI and number of chirps), the signal transmitted by the second transceiver and received by the first transceiver will be delayed relative to the signal transmitted by the first transceiver by the same delay of a reflection of the first transceiver own signal reflected from a target half way between the two transceivers.

[0171] Additionally, or alternatively, the transceiver may not be perfectly synchronized, but may be synchronized well enough for the first transceiver to receive the second transceiver chirps within its IF bandwidth. The transceiver may communicate their range measurements, which may be identified with a unique identification system.

[0172] Fig. 8 is a flow diagram describing a method for computing a firing range, in accordance with an embodiment of the current invention. For example, in method 160 for interrogation and / or response, a receiving unit stands by 162 to search for an interrogation signal (e.g., a low frequency signal LF and / or high frequency (HF) signal) over a range of frequencies. The firing unit transmits 164 an interrogation signal (e.g., the LF wake-up signal). The receiving unit detects 166 the interrogation signal. Receiving unit sends 168 a response signal, optionally, along with timing information and / or phase information back to the firing unit. Firing unit receives 170 the response signal. Firing unit computes 172 the time of travel and / or phase shift of the response signal. Firing unit computes 174 the range to the receiving unit. Optionally, the clocks of the receiving unit and firing unit are synchronized.

[0173] For example, a first unit (e.g., a firing unit, etc.) transmits a high frequency signal. A second unit (e.g., a receiving unit) searches for the high frequency signal over a range of frequencies (e.g., the exact clock rate of the transmission is not known). Optionally, the search may include use of a Doppler function of a radar and / or lidar to search over a window of frequencies. Optionally, the system may use a moving window (e.g., the window may be moved up and / or down to increase the range of searched frequencies). When the second unit detects the high frequency signal, the clock of the second unit is synchronized to that of the first unit (e.g., the clock is set to equal the frequency of signal from the first unit). The second unit may send a response signal back to the first unit. Optionally, along with the response signal the second unit may send the time and phase on which the signal was received. Optionally, the first unit may receive the response signal and timing information from the second unit. Optionally, the two units may then communicate. For example, synchronization of interrogator and transponder chirp signals whereby the transponder clock may be drifted until it has synchronized with the interrogator clock within the frequency offset search window. Advantageously, two or more radars and / or lidars may be synchronized with each other. Optionally, the first unit may now know the time and / or phase offset of the signal transmitted between the first unit and the second unit. Optionally, the system may compute the distance to the second unit based on this offset of the response signal without needing to receive a reflected echo. Optionally, the system may facilitate computation of a distance between two units without requiring an echo of the signal (e.g., synchronizing the clocks and then computing a time of travel of the signal sent between two units). In some embodiments, the receiving unit will transmit a receive an interrogation signal and send a response signal. Optionally, the responding unit will communicate with the interrogating unit (e.g., the firing unit) the time lapse and / or phase change between the receiving the interrogation signal and sending the response. The interrogating unit knows the time lapse and / or phase change between when it sent the interrogation signal and when it received the response. The time lapse between when the interrogating unit sent the interrogation signal and when it received the response will be greater than time lapse between the receiving unit receiving the interrogation signal and sending the response. The time difference is the time of travel of the interrogation signal from the interrogating unit to the receiving unit plus the time of travel of the return signal from the receiving unit to the interrogating unit. From the time of travel, the interrogating unit computes the distance between the unit.

[0174] The method may include interrogation and / or response. Optionally, a first transceiver may transmit an interrogation which may be detected by a second transceiver (e.g., a transceiver may continuously search across a frequency window in standby mode). Optionally, the second transceiver may respond with device ID, and / or time tags, and / or phase tags, and / or optional drift estimate, and a message authentication field (e.g., rolling code, message authentication code (MAC), etc.). Optionally, the first transceiver may verify the authenticity of the signal. Optionally, the first transceiver may compute a time-of-travel and / or a phase shift range from the combined ranges to determine range. Optionally, the first transceiver may apply a policy (e.g., warn, lock, etc.). Optionally, a low-band wake-up signal and / or authorization conde may be transmitted prior to high-band acquisition. Optionally, the low-band wake-up signal may initiate frequency window scanning. Optionally, timeouts and / or randomized back-off may reduce detectability by a third party. Optionally, TDMA and / or FDMA and / or hopping may be used for multi-unit operation.

[0175] A transceiver may generate the IF beat using an artificial reference. Optionally, the artificial reference may not be used for transmission. Optionally, the transceiver may be a transmit- only device while another device, using an artificial IF, may perform the range computation. Optionally, the IF frequency and / or chirp slope may differ between transmitting and mixing paths. Optionally, cooperative exchange reconciles offsets between transmitting and mixing paths.

[0176] Fig. 9 is a schematic diagram illustrating a friendly-fire prevention use case, in accordance with an embodiment of the current invention. For example, the firing unit computes the precise range to a friendly unit along the line of fire (LoF) using a cooperative method. The system may signal a warning and / or interlock if the range and / or LoF criteria indicate a risk to a friendly unit.

[0177] A friendly unit 182 may be in the line of fire (LoF) from a firing unit 184. The firing unit 184 may determine the precise distance to the friendly unit 182 by a method disclosed herein. The firing unit 184 may receive a synchronized signal taking into account the phase shift 188 and / or time of travel of a high frequency (HF) signal and / or low frequency signal (LF). Optionally, the signal may warn the firing unit 184 that they have a friendly unit 182 in the direct line of fire on an enemy unit 186 and / or within firing range and / or indicate which lines of fire and / or ranges may be safe for firing along.

[0178] Fig. 10 is a block diagram illustrating a system for calculating a distance in accordance with some embodiments of the current invention. For example, system 190 includes a first electromagnetic transceiver 192 and a second electromagnetic transceiver 194, wherein each electromagnetic transceiver 192, 194 is configured to transmit a frequency-modulated continuous- wave (FMCW) chirp and to receive a peer’s chirp. Each electromagnetic transceiver 192, 194 includes a mixer 196, 198 and intermediate frequency chain 200, 202 configured to produce a beat from the peer’s chirp. Each electromagnetic transceiver 192, 194 includes control circuitry 204, 206 configured to compute a cooperative range from the beat and to either (i) exchange time tags and phase tags to remove inter-device skew, or (ii) exchange and combine calculated ranges measured at both devices to cancel skew, thereby determining a distance between the transceivers without relying on a reflected echo. Optionally, the cooperative range is calculated by combining comprises averaging the two apparent ranges. Optionally, the electromagnetic transceivers are configured to exchange time and / or phase tags associated with chirp detection. Optionally, each electromagnetic transceiver 192, 194 includes a low-band transceiver configured for transmitting a wake-up signal or authentication signal prior to high-band ranging. Optionally, each electromagnetic transceiver 192, 194 includes a at least one antenna of the first electromagnetic transceiver is unidirectional and / or at least one antenna of the first electromagnetic transceiver is omnidirectional. Optionally, a transceiver is configured to use an artificial IF. Optionally, a transceiver is configured to use different IFs for transmission and mixing. Optionally, the system includes a friendly-fire interlock configured to inhibit firing if cooperative range or line of fire (LoF) criteria are met.

[0179] Fig. 11 is a flow diagram illustrating a method for measuring distance between independent frequency-modulated continuous-wave (FMCW) transceivers, in accordance with some embodiments of the current invention. For example, in method 210 for measuring distance between independent frequency-modulated continuous-wave (FMCW) transceivers, chirps are transmitted 212 from each transceiver. The peer received chirps are mixed 214 with a local reference to obtain an intermediate frequency beat. An apparent range is computed 216 by each transceiver. The apparent range is exchanging 218 between transceivers, and an accurate distance is determined by correcting 220 for residual skew. Optionally, the correcting 220 for skew includes exchanging time tags and phase tags. Optionally, the correcting for skew includes combining the two apparent ranges.

[0180] Optionally, the method further includes a moving search window during standby to cover frequency uncertainty. Optionally, the transceivers are FMCW lidar devices and / or FMCW radar devices. Optionally, a non-transitory computer-readable medium configured for storing instructions that, when executed by control circuitry of a transceiver, cause execution of method 210.

[0181] FIG. 12 is a flow chart illustration of a method 310 of synchronizing independent electromagnetic devices in accordance with an embodiment of the current invention. Optionally the method 310 facilitates improved communication and coordination between such devices. In some embodiments, the method 310 includes transmitting 312 a signal from a first electromagnetic device. In some embodiments, this signal from the first device may include a specific type of electromagnetic wave, such as a radio frequency (RF) signal, which is emitted by the first device to initiate synchronization. Optionally, this signal can include a chirp.

[0182] Optionally, the method 310 further involves searching 314 by the second device for the signal transmitted by the first device. This searching 314 may be performed by sweeping an offset search window of the second device across an intermediate frequency acceptance band. The offset search window is configured to detect the signal of the first electromagnetic device within this band. In some embodiments, the search window may be dynamically adjusted to optimize the detection process. Optionally, the offset window may be moved during acquisition to extend the capture range, which facilitates the detection of signals over a broader frequency spectrum.

[0183] Optionally a detected signal from the first device is correlated 316 to a template of the second device. This template may be a predefined signal pattern stored within the second device, which is used for comparison purposes. The correlation process involves matching the received signal with the template to identify similarities and differences. This step is crucial for ensuring that the correct signal is being processed and facilitates accurate synchronization.

[0184] In some embodiments, the second device is synchronized 318 to the signal of the first device. This step optionally includes adjusting a reference clock of the second device until frequency and phase errors satisfy lock criteria. For example, the reference clock adjustment is performed to align the timing and frequency of the second device with the signal from the first device. In some embodiments, the lock criteria may include specific thresholds for frequency and phase errors, which must be met to achieve synchronization. For example, a lock criterion may be that the frequency error is smaller than the smallest increment the second device uses to tune the offset search window, or that the signal remains phase-continuous.

[0185] In some embodiments, the synchronization mechanics involve the receiver sweeping an offset search window across a range of frequencies while correlating against an expected chirp template. Optionally, a candidate lock occurs when the correlation exceeds a threshold and the corresponding beat lies within the intermediate frequency (IF) passband. Upon candidate lock, a control loop adjusts the local reference clock to reduce frequency and phase errors until they meet lock criteria. The window may walk up or down to extend the capture range. For example, during acquisition with drift, when the peer chirp is within the IF passband, the receiver computes instantaneous frequency differences from the IF and updates a drift estimate for the voltage- controlled crystal oscillator (VCXO) or phase-locked loop (PLL) and / or digital resampler. Optionally, the loop may continue until steady-state lock is achieved.

[0186] In some embodiments, the method 310 may be implemented in various types of electromagnetic devices such as communication systems, radar systems, or other devices that require precise synchronization. The steps of transmitting 312, searching 314, correlating 316, and synchronizing 318 may be executed in a sequential manner or in parallel, depending on the specific requirements of the devices involved. For instance, frequency-modulated continuous- wave (FMCW) lidar devices or radar devices may utilize this method for synchronization.

[0187] In some embodiments, the system may include two or more radar and / or lidar transceivers configured to detect and synchronize signals. The transceivers may transmit and receive signals from each other, and the frequency, phase, and timing of the signals may be synchronized. For example, the signal of one transceiver may be received by another receiver and used to synchronize the clocks of the two receivers.

[0188] The system may make use of off-the-shelf radar and / or lidar, including very high-band Doppler radar. The ability of the radar and / or lidar to search over a window of frequencies may be configured for synchronization purposes. Since the clocks of two or more radar and / or lidar transceivers may not be synchronized, the receiving radar may search for the signal of the transmitting radar using a Doppler search window. In some embodiments, the system may facilitate searching for the signal using the Doppler function of the radar and / or lidar. The system may use a moving window to increase the range of searched frequencies. When the receiving radar unit receives the signal, the clock of the receiver unit may be synchronized to the incoming unit's clock by tuning the clock until the received frequency is within the Doppler search window.

[0189] The system may also include a multi-band interrogation signal system, configured to transmit and receive signals at different frequencies. The system may include separate antennas for each band, with one antenna dedicated to transmitting and another to receiving signals.

[0190] In some embodiments, the system may include a transceiver with a radar device and / or a lidar device. The transceiver may operate within specific frequency ranges and bandwidths, and the signals may provide omnidirectional or unidirectional detection accuracy.

[0191] The synchronization method may also involve protocol and security measures. After lock, the second unit may transmit an authenticated response using a rolling code or message authentication code. Timeouts and retry back-off reduce detectability, and multiple-access schemes limit interception and spoofing.

[0192] FIG. 13 is a flow chart illustration of a method 410 for calculating a distance between independent transceivers in accordance with an embodiment of the current invention. The method may facilitate synchronization and accurate distance measurement between two electromagnetic transceivers. The process begins with the first transceiver transmitting 412 a wake-up signal. This signal serves as an initial communication to alert the second transceiver of the impending synchronization and distance calculation process. The wake-up signal can be transmitted using an omnidirectional band for example, a low-band frequencies (e.g., sub-GHz, 300 kHz-1 GHz). Alternatively or additionally, a direction signal, for example, a high-band frequencies such as mm Wave radar / lidar carrier frequencies (e.g., 60-100 GHz, commonly 76-81 GHz) may be used.

[0193] Upon receiving 414 the wake-up signal, the second transceiver sends 416 a response. The second transceiver sends 416 a response signal back to the first transceiver. This response signal may include a time tag. For example, the time tag may include a time delay between receiving 414 the wake-up signal and sending 416 the response, providing timing information for accurate distance calculation. Additionally or alternatively, the response signal may include a wide band signal, for example, a frequency-modulated continuous-wave (FMCW) chirp. In some embodiments, the first transceiver receives 418 the response signal from the second transceiver. The first transceiver's control circuitry optionally processes the received response signal and the time tag to compute 420 the distance between the two transceivers. The control circuitry may include a mixer and an intermediate frequency (IF) chain to produce a beat from the response signal. The beat frequency is then used to calculate the cooperative range between the transceivers.

[0194] In some embodiments, the first transceiver is further configured to remove inter-device skew. For example, this may include compensating for any timing discrepancies between the two transceivers, facilitating that the distance calculation is accurate and / or reducing the effect of clock differences. The process of removing inter-device skew may involve exchanging time tags and phase tags between the transceivers or combining calculated ranges to cancel out the skew (e.g., combining a range calculated by the first transceiver with a range calculated by the second transceiver).

[0195] Additionally or alternatively, the first transceiver may transmit a time tag along with the wake-up signal and / or in a further response signal. The wake-up time tag can be used in conjunction with the response signal time tag to further refine the distance calculation and / or remove inter-device skew. By exchanging and combining these time tags and phase tags, the system may determine the distance between the transceivers without relying on a reflected echo.

[0196] The response signal's inclusion of an FMCW chirp, may provide several advantages. FMCW chirps are commonly used in radar and lidar systems due to their ability to provide high- resolution distance measurements. The chirp signal's frequency modulation allows for precise calculation of the time delay and, consequently, the distance between the transceivers.

[0197] In some embodiments, the control circuitry may use of a mixer and / or intermediate frequency chain to produce a beat from the response signal. The beat frequency, may result from mixing the received signal with a local reference signal (e.g., the response from the second transceiver may be mixed with a reverence signal of the first transceiver). Optionally, the beat frequency provides a measurable frequency difference that can be used to calculate the distance. This process is optionally facilitated by the control circuitry's ability to tune the reference clock and adjust for any frequency and phase errors.

[0198] In some embodiments, the method may include additional steps to enhance the accuracy and reliability of the distance calculation. For example, the system may employ a Doppler search window to search for the incoming signal over a range of frequencies. This search window can be adjusted to account for any frequency shifts due to the Doppler effect and / or clock differences between the devices.

[0199] The method may also involve the use of multi-band interrogation signals, where the system transmits and receives signals at different frequencies. This can include a combination of high- band and low-band signals, with separate antennas dedicated to each band. The use of multi-band signals can improve the system's ability to penetrate obstacles and provide more robust communication between the transceivers.

[0200] While the invention has been described in its preferred form or embodiment with some degree of particularity, it is understood that this description has been given only by way of example and that numerous changes in the details of construction, fabrication, and use, including the combination and arrangement of parts, may be made without departing from the spirit and scope of the invention.

[0201] USE CASE EXAMPLES

[0202] According to some embodiments, the system may warn a user when they are pointing a weapon at a friendly transceiver. Optionally, the system may prevent a user from firing at a friendly transceiver. In some embodiments, the system may compute a range to the friendly transceiver and / or the warning and / or action may depend on if the friendly transceiver is in range of the weapon.

[0203] According to some embodiments, the signal may be pulsed, modulated, encoded and / or coded (e.g., encoding and / or coding may be changed to avoid enemy stealing the device and / or spoofing the signal, modulated pulses of any frequency, and / or of any kind of modulation,), modulated and / or non-modulated signals in changing frequencies, spread spectrum, etc. Optionally, the signals may include a digital modulation technique to divide the limited spectrum available, such as time division multiple access (TDMA) and / or frequency division multiple access (FDMA) and / or other multiple access schemes. Optionally, such systems may make it difficult for an enemy to detect and / or locate friendly forces. Optionally, this may prevent and / or make it difficult for the enemy to spoof the signal (e.g., to prevent the enemy from fooling friendly forces into firing on the enemy). Optionally, additional data may be transmitted and / or received (e.g., encourage communication and / or share information between units, individual soldiers, command, etc.).

[0204] For example, a weapon with a multi-band interrogation signaling system may be aimed at a suspected enemy position. If a response to the transmitted low frequency and / or high frequency signal is received from a synchronized friendly device at the location of the suspected enemy position, then the position is identified as friendly. A warning may be provided to the user, who then does not fire on the position. Thereby preventing a friendly fire incident. If no response to the transmitted low frequency and / or high frequency signal is received from the suspected enemy position, then the position is identified as an enemy position, and no warning is provided to the user, who may then fire on the position without fear of a friendly fire incident.

[0205] For example, the firing unit may transmit an interrogation signal. The receiving unit may detect the transmitted signal. Optionally, the receiving unit may continuously scan across a frequency window in a standby search. The receiving unit may respond with time tags and / or phase tags. The firing unit may compute time-of-travel and / or phase shift to determine range. Optionally, a low- band wake-up signal and / or authentication signal may precede high-band acquisition.

[0206] GENERAL

[0207] It is expected that during the life of a patent maturing from this application many relevant building technologies, artificial intelligence methodologies, computer user interfaces, image capture devices will be developed and the scope of the terms for design elements, analysis routines, user devices is intended to include all such new technologies a priori.

[0208] Unless otherwise defined, all technical and / or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the invention, exemplary methods and / or materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and are not intended to be necessarily limiting.

[0209] As will be appreciated by one skilled in the art, some embodiments of the present invention may be embodied as a system, method or computer program product. Accordingly, some embodiments of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro- code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.” Furthermore, some embodiments of the present invention may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon. Implementation of the method and / or system of some embodiments of the invention can involve performing and / or completing selected tasks manually, automatically, or a combination thereof. Moreover, according to actual instrumentation and equipment of some embodiments of the method and / or system of the invention, several selected tasks could be implemented by hardware, by software or by firmware and / or by a combination thereof, e.g., using an operating system.

[0210] For example, hardware for performing selected tasks according to some embodiments of the invention could be implemented as a chip or a circuit. As software, selected tasks according to some embodiments of the invention could be implemented as a plurality of software instructions being executed by a computer using any suitable operating system. In an exemplary embodiment of the invention, one or more tasks according to some exemplary embodiments of method and / or system as described herein are performed by a data processor, such as a computing platform for executing a plurality of instructions. Optionally, the data processor includes a volatile memory for storing instructions and / or data and / or a non-volatile storage, for example, a magnetic hard-disk and / or removable media, for storing instructions and / or data. Optionally, a network connection is provided as well. A display and / or a user input device such as a keyboard or mouse are Optionally, provided as well.

[0211] Any combination of one or more computer readable medium(s) may be utilized for some embodiments of the invention. The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer readable storage medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device.

[0212] A computer readable signal medium may include a propagated data signal with computer readable program code embodied therein, for example, in baseband / or as part of a carrier wave. Such a propagated signal may take any of a variety of forms including, but not limited to, electro-magnetic, optical, or any suitable combination thereof. A computer readable signal medium may be any computer readable medium that is not a computer readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device.

[0213] Program code embodied on a computer readable medium and / or data used thereby may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing.

[0214] Computer program code for carrying out operations for some embodiments of the present invention may be written in any combination of one or more programming languages, including an object-oriented programming language such as Java, Smalltalk, C++ or the like and conventional procedural programming languages, such as the "C" programming language or similar programming languages. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider).

[0215] Some embodiments of the present invention may be described below with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention.

[0216] It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general-purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions / acts specified in the flowchart and / or block diagram block or blocks.

[0217] These computer program instructions may also be stored in a computer readable medium that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions which implement the function / act specified in the flowchart and / or block diagram block or blocks.

[0218] The computer program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing the functions / acts specified in the flowchart and / or block diagram block or blocks.

[0219] Data and / or program code may be accessed and / or shared over a network, for example the Internet. For example, data may be shared and / or accessed using a social network. A processor may include remote processing capabilities for example available over a network (e.g., the Internet). For example, resources may be accessed via cloud computing. The term “cloud computing” refers to the use of computational resources that are available remotely over a public network, such as the internet, and that may be provided for example at a low cost and / or on an hourly basis. Any virtual or physical computer that is in electronic communication with such a public network could potentially be available as a computational resource. To provide computational resources via the cloud network on a secure basis, computers that access the cloud network may employ standard security encryption protocols such as SSL and PGP, which are well known in the industry.

[0220] Some of the methods described herein are generally designed only for use by a computer, and may not be feasible or practical for performing purely manually, by a human expert. A human expert who wanted to manually perform similar tasks might be expected to use completely different methods, e.g., making use of expert knowledge and / or the pattern recognition capabilities of the human brain, which would be vastly more efficient than manually going through the steps of the methods described herein.

[0221] As used herein the term “about” refers to ± 10%

[0222] The terms "comprises", "comprising", "includes", "including", “having” and their conjugates mean "including but not limited to".

[0223] The term “consisting of’ means “including and limited to”.

[0224] The term "consisting essentially of' means that the composition, method or structure may include additional ingredients, steps and / or parts, but only if the additional ingredients, steps and / or parts do not materially alter the basic and novel characteristics of the claimed composition, method or structure.

[0225] As used herein, the singular form "a", "an" and "the" include plural references unless the context clearly dictates otherwise.

[0226] As used herein, the terms “multiple” and “multi” are used interchangeably, and mean one or more, e.g., 1, 2, 3, 4, 5, 10, 20, etc.

[0227] Throughout this application, various embodiments of this invention may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

[0228] Whenever a numerical range is indicated herein, it is meant to include any cited numeral (fractional or integral) within the indicated range. The phrases “ranging / ranges between” a first indicate number and a second indicate number and “ranging / ranges from” a first indicate number “to” a second indicate number are used herein interchangeably and are meant to include the first and second indicated numbers and all the fractional and integral numerals therebetween.

[0229] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.

[0230] Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

[0231] All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention. To the extent that section headings are used, they should not be construed as necessarily limiting.

Claims

CLAIMSWhat is claimed is:

1. A system for calculating a distance comprising: a first electromagnetic transceiver and a second electromagnetic transceiver, wherein each electromagnetic transceiver is configured to transmit a frequency-modulated continuous-wave (FMCW) chirp and to receive a peer’s chirp; a mixer and intermediate frequency chain at each transceiver configured to produce a beat from the peer’s chirp; and control circuitry configured to compute a cooperative range from the beat and to either:(i) exchange time tags and phase tags to remove inter-device skew, or(ii) exchange and combine a calculated range measured at the first electromagnetic transceiver and a calculated range measured at the second electromagnetic transceiver to cancel skew, thereby determining a distance between the first electromagnetic transceiver and second electromagnetic transceiver without relying on a reflected echo.

2. The system of claim 1, wherein the cooperative range is calculated by combining comprises averaging the calculated range measured at the first electromagnetic transceiver and the calculated range measured at the second electromagnetic transceiver.

3. The system of claim 1, wherein the electromagnetic transceivers are configured to exchange time and / or phase tags associated with chirp detection.

4. The system of claim 1, wherein a transceiver is configured to use an artificial IF.

5. The system of claim 1, wherein a transceiver is configured to use different IFs for transmission and mixing.

6. The system of claim 1 , further comprising a friendly-fire interlock configured to inhibit firing if cooperative range or line of fire (LoF) criteria are met.

7. A method for measuring distance between a first frequency-modulated continuous-wave (FMCW) transceiver and a second FMCW transceiver, the method comprising: transmitting a signal from the first FMCW transceiver; receiving the first signal at the second FMCW transceiver; transmitting a second chirp and a second time tag from the second FMCW transceiver;receiving the second chirp and the second time tag at the first FMCW transceiver; combining the second chirp with a local reference of the first FMCW transceiver to obtain a second intermediate frequency beat; computing a first apparent range by the first transceiver based on said second intermediate frequency beat and said second time tag.

8. The method of claim 7 further comprising: transmitting a first time tag and a first chirp from the first FMCW transceiver; receiving first time tag at the second FMCW transceiver; combining the first chirp with a local reference of the second FMCW transceiver to obtain a first intermediate frequency beat; computing a second apparent range by the second FMCW transceiver based on said first intermediate frequency beat and said second time tag; correcting for residual skew based on to yield an accurate distance.

9. The method of claim 8, wherein the correcting for skew includes exchanging time tags and phase tags.

10. The method of claim 8, wherein the correcting for skew includes combining the first apparent range and the second apparent range.

11. The method of claim 7, further comprising said first transceiver searching for said second chirp using a moving search window to cover frequency uncertainty.

12. The method of claim 7, wherein the first and second transceivers include FMCW lidar devices.

13. The method of claim 7, wherein the first and second transceivers include FMCW radar devices.

14. A non-transitory computer-readable medium configured for storing instructions that, when executed by control circuitry of a transceiver, cause execution of the method of claim 7.

15. A method of synchronizing independent electromagnetic devices, the method comprising: transmitting a signal from a first electromagnetic device; sweeping an offset search window of a second electromagnetic device for detecting the signal of the first electromagnetic device by the offset search window within an intermediate frequency acceptance band; correlate the signal against a template of the second electromagnetic device; andadjusting a reference clock of the second electromagnetic device until frequency and phase errors satisfy lock criteria.

16. The method of claim 15, wherein the signal includes a chirp.

17. The method of claim 15, further comprising moving the offset window during acquisition to extend capture range.

18. The method of any one of claims 15, 16 and 17, wherein the sweeping of the offset search window is performed by repurposing a Doppler-search or Doppler- window function of the second electromagnetic device, originally configured for detecting frequency shifts of reflected signals, to detect a peer electromagnetic signal and achieve inter-device clock synchronization.

19. The method of claim 15, wherein the first and second devices include frequency-modulated continuous-wave (FMCW) lidar devices.

20. The method of claim 15, wherein the devices are frequency-modulated continuous-wave (FMCW) radar devices.

21. The method of claim 15, wherein a lock criterion is that frequency error is smaller than the smallest increment the second device uses to tune the offset search window.

22. The method of claim 15, wherein a lock criterion is that the signal remains phase-continuous.

23. The method of claim 22, wherein subsequent signals remain phase-continuous within a tolerance.

24. The method of claim 15, further comprising distinguishing a true signal lock from random noise or brief, transient false alarms by a coherency check.

25. The method of claim 15, further comprising authenticating the signal using a rolling code or message authentication code.

26. A non-transitory computer-readable medium storing instructions that, when executed by control circuitry of a transceiver, cause the circuitry to perform the method of claim 15.

27. A system for synchronizing electromagnetic devices comprising: a first electromagnetic device configured to transmit a signal; and a second electromagnetic device configured to receive the signal, wherein the second electromagnetic device comprises: a receiver having an intermediate-frequency (IF) bandwidth; a controllable reference clock; and control circuitry configured for:(i) sweeping an offset search window across a plurality of frequency offsets;(ii) detecting the signal of the first electromagnetic device in said offset search window; and(iii) tuning the controllable reference clock in response to the detecting to reduce offset and phase error until the signal is within a lock tolerance, thereby synchronizing the second electromagnetic device to the first electromagnetic device.

28. The system of claim 27, wherein the signal is a wide band signal.

29. The system of claim 27, wherein the signal is a chirp.

30. The system of claim 29, wherein the control circuitry is further configured correlating a received signal against a chirp template.

31. The system of claim 30, wherein the control circuitry is further configured to calculate a beat frequency AF and correlation threshold from said detecting occurs when the correlation Threshold is exceeded for the beat frequency lies within the intermediate-frequency (IF) passband BIF(\AJ<BIF / 2).

32. The system of claim 27, where said first device is a first FMCW transceiver.

33. The system of claim 27, where said second device is a second FMCW transceiver.

34. The system of claim 27, wherein said tuning reduces a beat frequency Af and phase error to within a lock tolerance.

35. The system of claim 27, wherein the offset search window spans a frequency band.

36. The system of claim 27, wherein the offset search window is stepped in increment ranging between about 10-100 kHz.

37. The system of claim 36, wherein a lock criterion includes that frequency error is smaller than the smallest increment the second electromagnetic device uses to tune the offset search window.

38. The system of claim 36, wherein a lock criterion includes that chirps remain phase- continuous.

39. The system of claim 38, wherein after acquisition, subsequent chirps remain phase- continuous within a tolerance.

40. The system of claim 27, wherein a coherency check distinguishes a true signal lock from random noise or brief, transient false alarms.

41. The system of claim 27, wherein tuning comprises digitally resampling.

42. The system of claim 27, wherein tuning comprises adjusting a voltage-controlled oscillator or phase-locked loop.

43. The system of claim 27, further comprising a low-band transceiver configured to transmit a wake-up signal or authentication message prior to high-band acquisition.

44. The system of claim 43, wherein the low-band is sub-GHz.

45. The system of claim 43, wherein the wake-up signal or authentication message is authenticated using a rolling code or message authentication code.

46. The system of claim 27, wherein the signal ranges between about 76-81 GHz.

47. The system of claim 27, wherein the first electromagnetic device includes a unidirectional antenna.

48. The system of claim 27, wherein the first electromagnetic device includes an omnidirectional antenna.

49. The system of claim 27, wherein the second electromagnetic device includes a unidirectional antenna.

50. The system of claim 27, wherein the second electromagnetic device includes an omnidirectional antenna.

51. The system of claim 27, wherein the signal is authenticated using a rolling code or message authentication code.

52. A system for calculating a distance comprising: a first electromagnetic transceiver configured to transmit a wake-up signal a second electromagnetic transceiver, configured to receive said wake-up signal and transmit a response signal and a time tag; wherein said first transceiver is configured to receive said response signal and includes control circuitry configured to compute a cooperative range from the response signal and time tag.

53. The system of claim 52, wherein said first electromagnetic transceiver is further configured to remove inter-device skew.

54. The system of claim 52, wherein said first electromagnetic transceiver is further configured to transmit a time tag and(i) exchange time tags and phase tags with said second transceiver to remove inter-device skew, or(ii) exchange and combine calculated ranges with said second transceiver to cancel said inter-device skew, thereby determining a distance between the transceivers without relying on a reflected echo.

55. The system of claim 52, wherein said response signal includes a frequency-modulated continuous-wave (FMCW) chirp.

56. The system of claim 52, wherein said control circuitry includes a mixer and intermediate frequency chain to produce a beat from the response signal; and wherein said range is computed based said beat.

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