SEARCH AND RESCUE SYSTEM WITH DOPPLER-NULLING SPATIAL AWARENESS

A Search and Rescue (SAR) system is disclosed. The SAR system may include a receiver or transmitter node. The receiver or transmitter node may include a communications interface with at least one antenna element and a controller. The controller may include one or more processors and have information of own node velocity and own node orientation relative to a common reference frame. The receiver or transmitter node may be time synchronized to apply Doppler corrections associated with the receiver or transmitter node’s own motions relative to the common reference frame. For example, the transmitter node may serve as an emergency locator beacon and mark a location of interest, and the receiver node may determine the marked location of interest based at least on the Doppler corrections.

BACKGROUND

Mobile Ad-hoc NETworks (MANET; e.g., “mesh networks”) are known in the art as quickly deployable, self-configuring wireless networks with no pre-defined network topology. Each communications node within a MANET is presumed to be able to move freely. Additionally, each communications node within a MANET may be required to forward (relay) data packet traffic. Data packet routing and delivery within a MANET may depend on a number of factors including, but not limited to, the number of communications nodes within the network, communications node proximity and mobility, power requirements, network bandwidth, user traffic requirements, timing requirements, and the like.

MANETs face many challenges due to the limited network awareness inherent in such highly dynamic, low-infrastructure communication systems. Given the broad ranges in variable spaces, the challenges lie in making good decisions based on such limited information. For example, in static networks with fixed topologies, protocols can propagate information throughout the network to determine the network structure, but in dynamic topologies this information quickly becomes stale and must be periodically refreshed. It has been suggested that directional systems are the future of MANETs, but the potential of this future has not as yet been fully realized. In addition to topology factors, fast-moving platforms (e.g., communications nodes moving relative to each other) experience a frequency Doppler shift (e.g., offset) due to the relative radial velocity between each set of nodes. This Doppler frequency shift often limits receive sensitivity levels which can be achieved by a node within a mobile network.

Search and Rescue (SAR) systems typically utilize Radio navigation beacons which can mark a desired location and allow direction finding devices to find a relative bearing and/or range of the desired location. A conventional SAR system may include Personal Locator Beacons (PLBS), which are portable radio distress signaling units. These beacons are typically designed to be located on an individual rather than located on a vehicle (e.g., a boat or aircraft). Further, PLBs may only be activated manually and operate exclusively at 406 MHz. PLBs include a built-in, low-power homing beacon that transmits on 121.5 MHz. This allows rescue forces to home in on a beacon once the 406 MHz satellite system has gotten them within a sufficient vicinity. Other PLBs may allow GPS data to be integrated into the distress signal as well. However, these systems may also include pitfalls such as being too large, vulnerable to interference, dependent on high transmission power or large antennas, expensive, and/or require large amounts of spectrum.

SUMMARY

A Search and Rescue (SAR) system is disclosed, in accordance with one or more embodiments of the present disclosure. In some embodiments, the SAR system may include a transmitter node and a receiver node. In some embodiments, each node of the transmitter node and the receiver node may include a communications interface with at least one antenna element. In some embodiments, each of the transmitter node and the receiver node may include a controller operatively coupled to the communications interface. In some embodiments, the controller may include one or more processors. In some embodiments, the controller may have information of own node velocity and own node orientation. In some embodiments, the receiver node may be in motion relative to the transmitter node. In some embodiments, the transmitter node and the receiver node may be time synchronized to apply one or more Doppler corrections associated with said node’s own motions relative to a common reference frame. In some embodiments, each of the transmitter node and the receiver node may know the common reference frame prior to the transmitter node transmitting signals to the receiver node and prior to the receiver node receiving signals from the transmitter node. In some embodiments, the transmitter node may serve as an emergency locator beacon and mark a location of interest. In some embodiments, the receiver node may determine the marked location of interest of the transmitter node based at least on the one or more Doppler corrections.

A method is disclosed, in accordance with one or more embodiments of the present disclosure. In some embodiments, the method may include but is not limited to, providing a transmitter node and a receiver node, where the transmitter node serves as an emergency locator beacon and marks a location of interest. In some embodiments, the receiver node may be in motion relative to the transmitter node. In some embodiments, each node of the transmitter node and the receiver node may include a transmitter node and a receiver node. In some embodiments, each node of the transmitter node and the receiver node may include a communications interface with at least one antenna element. In some embodiments, each of the transmitter node and the receiver node may include a controller operatively coupled to the communications interface. In some embodiments, the controller may include one or more processors. In some embodiments, the controller may have information of own node velocity and own node orientation. In some embodiments, the method may include, but is not limited to, applying, by the transmitter node, one or more Doppler corrections to the transmitter node’s own motions relative to a common reference frame based at least on the time synchronization. In some embodiments, the method may include, but is not limited to, applying, by the receiver node, one or more Doppler corrections to the receiver node’s own motions relative to a common reference frame based at least one the time synchronization. In some embodiments, the receiver node may determine the marked location of interest of the transmitter node based at least on the one or more Doppler corrections. In some embodiments, the transmitter node and the receiver node may know the common reference frame prior to the transmitter node transmitting signals to the receiver node and prior to the receiver node receiving signals from the transmitter node.

DETAILED DESCRIPTION

Broadly speaking, embodiments of the inventive concepts disclosed herein are directed to Search and Rescue (SAR) methods and systems using Doppler Nulling Spatial Awareness (DNSA). For example, the SAR system may include at least one transmitter node and at least one receiver node. The transmitter node may serve as an emergency locator beacon and be configured to mark a location of interest. On the other hand, the receiver node may serve as the tracking device configured to monitor the marked location of interest based at least on one or more Doppler corrections.

In embodiments, DNSA applications in SAR systems and methods may help to overcome some of the pitfalls revealed in the conventional SAR systems and methods such as, but not limited to, allowing for the use of a single omni-antenna as a sufficient receiver; eliminating the need for Global Positioning Systems (GPS) or like positioning equipment; having low Size, Weight, Power, and Cost (SWAP-C) capabilities; providing a low probability of detection or inspection; having anti-jamming protection; covering a larger detection range; and maintaining a longer operating time.

It is noted that U.S. Patent Application No. 17/857,920, filed Jul. 5, 2022, is at least partially reproduced by at least some (or all) of the illustrations ofFIGS.1-7and at least some (or all) of the corresponding language forFIGS.1-7below. For example, at least some examples of doppler nulling methods and systems may be better understood, in a nonlimiting manner, by reference toFIGS.1-7. Such embodiments and examples are provided for illustrative purposes and are not to be construed as necessarily limiting. For instance, in embodiments the transmitter node may be stationary rather than moving and/or vice versa.

Moreover, and stated for purposes of navigating the disclosure only and not to be construed as limiting, descriptions that may relate to other language not necessarily reproduced from U.S. Patent Application No. 17/857,920 include the discussion and figures afterFIGS.1-7.

Referring now toFIGS.1-7, in some embodiments, a stationary receiver may determine a cooperative transmitter’s direction and velocity vector by using a Doppler null scanning approach in two dimensions. A benefit of the approach is the spatial awareness without exchanging explicit positional information. Other benefits include discovery, synchronization, and Doppler corrections which are important for communications. Some embodiment may combine coordinated transmitter frequency shifts along with the transmitter’s motion induced Doppler frequency shift to produce unique net frequency shift signal characteristics resolvable using a stationary receiver to achieve spatial awareness. Further, some embodiment may include a three-dimensional (3D) approach with the receiver and the transmitter in motion.

Some embodiments may use analysis performed in a common reference frame (e.g., a common inertial reference frame, such as the Earth, which may ignore the curvature of Earth), and it is assumed that the communications system for each of the transmitter and receiver is informed by the platform of its own velocity and orientation. The approach described herein can be used for discovery and tracking, but the discussion here focuses on discovery which is often the most challenging aspect.

The meaning of the ‘Doppler Null’ can be explained in part through a review of the two-dimensional (2D) case without the receiver motion, and then may be expounded on by a review of adding the receiver motion to the 2D case, and then including receiver motion in the 3D case.

The Doppler frequency shift of a communications signal is proportional to the radial velocity between transmitter and receiver, and any significant Doppler shift is typically a hindrance that should be considered by system designers. In contrast, some embodiments utilize the Doppler effect to discriminate between directions with the resolution dictated by selected design parameters. Furthermore, such embodiments use the profile of the net frequency shift as the predetermined ‘Null’ direction scans through the angle space. The resultant profile is sinusoidal with an amplitude that provides the transmitter’s speed, a zero net frequency shift when the ‘Null’ direction aligns with the receiver, and a minimum indicating the direction of the transmitter’s velocity. It should be noted that that the transmitter cannot correct for Doppler in all directions at one time so signal characteristics are different in each direction and are different for different transmitter velocities as well. It is exactly these characteristics that the receiver uses to determine spatial awareness. The received signal has temporal spatial characteristics that can be mapped to the transmitter’s direction and velocity. This approach utilizes the concept of a ‘Null’ which is simply the direction where the transmitter perfectly corrects for its own Doppler shift. The same ‘Nulling’ protocol runs on each node and scans through all directions, such as via a scanning sequence of a protocol. Here we arbitrarily illustrate the scanning with discrete successive steps of 10 degrees but in a real system; however, it should be understood that any suitable step size of degrees may be used for Doppler null scanning.

As already mentioned, one of the contributions of some embodiments is passive spatial awareness. Traditionally, spatial information for neighbor nodes (based on a global positioning system (GPS) and/or gyros and accelerometers) can be learned via data communication. Unfortunately, spatial awareness via data communication, referred to as active spatial awareness is possible only after communication has already been established, not while discovering those neighbor nodes. Data communication is only possible after the signals for neighbor nodes have been discovered, synchronized and Doppler corrected. In contrast, in some embodiments, the passive spatial awareness described herein may be performed using only synchronization bits associated with acquisition. This process can be viewed as physical layer overhead and typically requires much lower bandwidth compared to explicit data transfers. The physical layer overheads for discovery, synchronization and Doppler correction have never been utilized for topology learning for upper layers previously.

Traditionally, network topology is harvested via a series of data packet exchanges (e.g., hello messaging and link status advertisements). The passive spatial awareness may eliminate hello messaging completely and provide a wider local topology which is beyond the coverage of hello messaging. By utilizing passive spatial awareness, highly efficient mobile ad hoc networking (MANET) is possible. Embodiments may improve the functioning of a network, itself.

In embodiments, the multi-node communications network100may include any multi-node communications network known in the art. For example, the multi-node communications network100may include a mobile ad-hoc network (MANET) in which the Tx and Rx nodes102,104(as well as every other communications node within the multi-node communications network) is able to move freely and independently. Similarly, the Tx and Rx nodes102,104may include any communications node known in the art which may be communicatively coupled. In this regard, the Tx and Rx nodes102,104may include any communications node known in the art for transmitting/transceiving data packets. For example, the Tx and Rx nodes102,104may include, but are not limited to, radios (such as on a vehicle or on a person), mobile phones, smart phones, tablets, smart watches, laptops, and the like. In embodiments, the Rx node104of the multi-node communications network100may each include, but are not limited to, a respective controller106(e.g., control processor), memory108, communication interface110, and antenna elements112. (In embodiments, all attributes, capabilities, etc. of the Rx node104described below may similarly apply to the Tx node102, and to any other communication node of the multi-node communication network100.)

In embodiments, the controller106provides processing functionality for at least the Rx node104and can include any number of processors, micro-controllers, circuitry, field programmable gate array (FPGA) or other processing systems, and resident or external memory for storing data, executable code, and other information accessed or generated by the Rx node104. The controller106can execute one or more software programs embodied in a non-transitory computer readable medium (e.g., memory108) that implement techniques described herein. The controller106is not limited by the materials from which it is formed or the processing mechanisms employed therein and, as such, can be implemented via semiconductor(s) and/or transistors (e.g., using electronic integrated circuit (IC) components), and so forth.

In embodiments, the memory108can be an example of tangible, computer-readable storage medium that provides storage functionality to store various data and/or program code associated with operation of the Rx node104and/or controller106, such as software programs and/or code segments, or other data to instruct the controller106, and possibly other components of the Rx node104, to perform the functionality described herein. Thus, the memory108can store data, such as a program of instructions for operating the Rx node104, including its components (e.g., controller106, communication interface110, antenna elements112, etc.), and so forth. It should be noted that while a single memory108is described, a wide variety of types and combinations of memory (e.g., tangible, non-transitory memory) can be employed. The memory108can be integral with the controller106, can comprise stand-alone memory, or can be a combination of both. Some examples of the memory108can include removable and non-removable memory components, such as random-access memory (RAM), read-only memory (ROM), flash memory (e.g., a secure digital (SD) memory card, a mini-SD memory card, and/or a micro-SD memory card), solid-state drive (SSD) memory, magnetic memory, optical memory, universal serial bus (USB) memory devices, hard disk memory, external memory, and so forth.

In embodiments, the communication interface110can be operatively configured to communicate with components of the Rx node104. For example, the communication interface110can be configured to retrieve data from the controller106or other devices (e.g., the Tx node102and/or other nodes), transmit data for storage in the memory108, retrieve data from storage in the memory, and so forth. The communication interface110can also be communicatively coupled with the controller106to facilitate data transfer between components of the Rx node104and the controller106. It should be noted that while the communication interface110is described as a component of the Rx node104, one or more components of the communication interface110can be implemented as external components communicatively coupled to the Rx node104via a wired and/or wireless connection. The Rx node104can also include and/or connect to one or more input/output (I/O) devices. In embodiments, the communication interface110includes or is coupled to a transmitter, receiver, transceiver, physical connection interface, or any combination thereof.

It is contemplated herein that the communication interface110of the Rx node104may be configured to communicatively couple to additional communication interfaces110of additional communications nodes (e.g., the Tx node102) of the multi-node communications network100using any wireless communication techniques known in the art including, but not limited to, GSM, GPRS, CDMA, EV-DO, EDGE, WiMAX, 3G, 4G, 4G LTE, 5G, WiFi protocols, RF, LoRa, and the like.

In embodiments, the antenna elements112may include directional or omnidirectional antenna elements capable of being steered or otherwise directed (e.g., via the communications interface110) for spatial scanning in a full 360-degree arc (114) relative to the Rx node104(or even less than a full 360 degree arc).

In embodiments, the Tx node102and Rx node104may one or both be moving in an arbitrary direction at an arbitrary speed, and may similarly be moving relative to each other. For example, the Tx node102may be moving relative to the Rx node104according to a velocity vector116, at a relative velocity VTxand a relative angular direction (an angle α relative to an arbitrary direction118(e.g., due east); θ may be the angular direction of the Rx node relative to due east.

In embodiments, the Tx node102may implement a Doppler nulling protocol. For example, the Tx node102may adjust its transmit frequency to counter the Doppler frequency offset such that there is no net frequency offset (e.g., “Doppler null”) in a Doppler nulling direction120(e.g., at an angle ϕ relative to the arbitrary direction118). The transmitting waveform (e.g., the communications interface110of the Tx node102) may be informed by the platform (e.g., the controller106) of its velocity vector and orientation (e.g., α, VT) and may adjust its transmitting frequency to remove the Doppler frequency shift at each Doppler nulling direction120and angle ϕ.

To illustrate aspects of some embodiments, we show the 2D dependence of the net frequency shift for a stationary receiver as a function of Null direction across the horizon, as shown in a top-down view ofFIG.1, where the receiver node104is stationary and positioned θ from east relative to the transmitter, the transmitter node102is moving with a speed |VT| and direction α from east and a snapshot of the scanning ϕ which is the ‘Null’ direction, exemplarily shown as 100 degrees in this picture.

The Doppler shift is a physical phenomenon due to motion and can be considered as a channel effect. In this example the transmitter node102is the only moving object, so it is the only source of Doppler shift. The Doppler frequency shift as seen by the receiver node104due to the transmitter node102motion is:

ΔfDOPPLERf=VT→ccosθ−α,where c is the speed of light

The other factor is the transmitter frequency adjustment term that should exactly compensate the Doppler shift when the ‘Null’ direction aligns with the receiver direction. It is the job of the transmitter node102to adjust its transmit frequency according to its own speed (|VT|), and velocity direction (α). That transmitter frequency adjustment (ΔƒT) is proportional to the velocity projection onto the ‘Null’ direction (Φ) and is:

The net frequency shift seen by the receiver is the sum of the two terms:

It is assumed that the velocity vector and the direction changes slowly compared to the periodic measurement of Δƒnet. Under those conditions, the unknown parameters (from the perspective of the receiver node104) of α, |VT|, and θ are constants.

Furthermore, it is assumed that the receiver node104has an implementation that resolves the frequency of the incoming signal, as would be understood to one of ordinary skill in the art.

FIG.2Ashows the resulting net frequency shift as a function of the ‘Null’ direction for scenarios where a stationary receiver is East of the transmitter (theta = 0), and with a transmitter speed of 1500 meters per second (m/s).FIG.2Bshows the results for a stationary receiver and for several directions with an Eastern transmitter node velocity direction (alpha = 0). The frequency shifts are in units of parts per million (ppm). As shown inFIGS.2A and2B, the amplitude is consistent with the transmitter node’s102speed of 5 ppm [|VT]/c*(1 × 106)] regardless of the velocity direction or position, the net frequency shift is zero when the ‘Null’ angle is in the receiver direction (when ϕ = θ), and the minimum occurs when the ‘Null’ is aligned with the transmitter node’s102velocity direction (when ϕ = α).

From the profile, the receiver node104can therefore determine the transmitter node’s102speed, the transmitter node’s102heading, and the direction of the transmitter node102is known to at most, one of two locations (since some profiles have two zero crossings). It should be noted that the two curves cross the y axis twice (0 & 180 degrees inFIG.2A, and ±90 degrees inFIG.2B) so there is initially an instance of ambiguity in position direction. In this case the receiver node104knows the transmitter node102is either East or West of the receiver node104.

Referring toFIG.3, a multi-node communications network100is disclosed. The multi-node communications network100may include multiple communications nodes, e.g., a transmitter (Tx) node102and a receiver (Rx) node104. As shown inFIG.3both of the transmitter node102and the receiver node104are in motion in two dimensions.

The simultaneous movement scenario is depicted inFIG.3where the receiver node104is also moving in a generic velocity characterized by a speed |VR| and the direction, β. The protocol for the moving receiver node104incorporates a frequency adjustment on the receiver node’s104side to compensate for the receiver node’s104motion as well. The equations have two additional terms. One is a Doppler term for the motion of the receiver and the second is frequency compensation by the receiver.

Again, the Doppler shift is a physical phenomenon due to motion and can be considered as a channel effect, but in this case both the transmitter node102and the receiver node104are moving so there are two Doppler shift terms. The true Doppler shift as seen by the receiver due to the relative radial velocity is:

The other factors are the transmitter node102and receiver node104frequency adjustment terms that exactly compensates the Doppler shift when the ‘Null’ direction aligns with the receiver direction. It is the job of the transmitter node102to adjust the transmitter node’s102transmit frequency according to its own speed (|VT|), and velocity direction (α). That transmitter node frequency adjustment is proportional to the velocity projection onto the ‘Null’ direction (Φ) and is the first term in the equation below.

It is the job of the receiver node104to adjust the receiver node frequency according to the receiver node’s104own speed (|VR|), and velocity direction (β). That receiver node frequency adjustment is proportional to the velocity projection onto the ‘Null’ direction (Φ) and is the second term in the equation below. The receiver node frequency adjustment can be done to the receive signal prior to the frequency resolving algorithm or could be done within the algorithm.

The net frequency shift seen by the receiver is the sum of all terms:

Again, it is assumed that the receiver node104has an implementation that resolves the frequency of the incoming signal, as would be understood in the art.

Also, it is assumed that the velocity vector and direction changes slowly compared to the periodic measurement of Δƒnet. Again, under such conditions, the unknown parameters (from the perspective of the receiver node104) α, |VT|, and θ are constants. When the velocity vector or direction change faster, then this change could be tracked, for example if the change is due to slow changes in acceleration.

The net frequency shift for the two-dimensional (2D) moving receiver node104approach is shown inFIGS.4A and4Bfor several scenario cases of receiver node location, θ, and transmitter node and receiver node speeds (|VT| & |VR|), as well as transmitter node and receiver node velocity direction (α and β).FIG.4Ahas different speeds for the transmitter node102and receiver node104as well as the receiver node location of θ = 0.FIG.4Bhas the same speed for the transmitter node and receiver node. Similarly, there are three concepts to notice here:* The amplitude is consistent with the relative velocity between transmitter node102and receiver node104[|([VT|cos (α) - |VR|cos (β)) |/c * (1e6)].* The net frequency shift is zero when the ‘Null’ angle is in the receiver direction (when ϕ = θ).* The minimum occurs when the ‘Null’ is aligned with the relative velocity direction angle(|VT|cos (α) - |VR|cos (β))).

Again, there is an initial dual point ambiguity with the position, θ, but the transmitter node’s102speed and velocity vector is known.

Referring now toFIG.5, while the 2D picture is easier to visualize, the same principles apply to the 3D case.FIG.5shows a number of direction sets needed to span 3D and 2D space with different cone sizes (cone sizes are full width). Before diving into the equations, it’s worth commenting on the size of the space when including another dimension. For example, when a ‘Null’ step size of 10 degrees was used in the previous examples, it took 36 sets to span the 360 degrees in 2D. Thus, if an exemplary detection angle of 10 degrees is used (e.g., a directional antenna with 10-degree cone) it would take 36 sets to cover the 2D space. The 3D fractional coverage can be computed by calculating the coverage of a cone compared to the full 4 pi steradians. The fraction is equal to the integral [0094]

The number of sets to span the space is shown inFIG.5for both the 2D and 3D cases which correlates with discovery time. Except for narrow cone sizes, the number of sets is not drastically greater for the 3D case (e.g., approximately 15 times at 10 degrees, 7 time at 20 degrees, and around 5 times at 30 degrees). Unless systems are limited to very narrow cone sizes, the discovery time for 3D searches is not overwhelming compared to a 2D search.

Referring now toFIG.6, a multi-node communications network100is disclosed. The multi-node communications network100may include multiple communications nodes, e.g., a transmitter (Tx) node102and a receiver (Rx) node104. As shown inFIG.6both of the transmitter node102and the receiver node104are in motion in three dimensions.

The 3D approach to Doppler nulling follows the 2D approach but it is illustrated here with angles and computed vectorially for simplicity.

In three dimensions, it is convenient to express the equations in vector form which is valid for 2 or 3 dimensions.FIG.6shows the geometry in 3 dimensions whereDirectionis the unit vector pointing to the receiver from the transmitter, andNullis the unit vector pointing in the ‘Null’ direction defined by the protocol.

The true Doppler shift as seen by the receiver node104due to the relative radial velocity which is the projection onto theDirectionvector:

The nulling protocol adjusts the transmit node frequency and receiver node frequency due to their velocity projections onto theNulldirection

The net frequency shift seen by the receiver node104is the sum of all terms:

The net frequency shift for the 3D moving receiver node104approach is not easy to show pictorially but can be inspected with mathematical equations to arrive at useful conclusions. The first two terms are the Doppler correction (DC) offset and the last two terms are the null dependent terms. Since theNullis the independent variable, the maximum occurs when (VR-VT) andNullare parallel and is a minimum when they are antiparallel. Furthermore, the relative speed is determined by the amplitude,

Lastly, the net frequency is zero when the Null is parallel (i.e., parallel in same direction, as opposed to anti-parallel) toDirection.

For the 3D case:* The amplitude is consistent with the relative velocity between transmitter node102and receiver node104[|VR-VT|/c ].* The net frequency shift is zero when the ‘Null’ angle is in the receiver node direction, (VT-VR) · Direction = (VT-VR) ·Null).* The minimum occurs when the ‘Null’ is aligned with the relative velocity direction.

Referring still toFIG.6, in some embodiments, the system (e.g., the multi-node communications network100) may include a transmitter node102and a receiver node104. Each node of the transmitter node102and the receiver node104may include a communications interface110including at least one antenna element112and a controller operatively coupled to the communications interface, the controller106including one or more processors, wherein the controller106has information of own node velocity and own node orientation. The transmitter node102and the receiver node104may be in motion (e.g., in two dimensions or in three dimensions). The transmitter node102and the receiver node104may be time synchronized to apply Doppler corrections associated with said node’s own motions relative to a common reference frame (e.g., a common inertial reference frame (e.g., a common inertial reference frame in motion or a stationary common inertial reference frame)). The common reference frame may be known to the transmitter node102and the receiver node104prior to the transmitter node102transmitting signals to the receiver node104and prior to the receiver node104receiving the signals from the transmitter node102. In some embodiments, the system is a mobile ad-hoc network (MANET) comprising the transmitter node102and the receiver node104.

In some embodiments, the applying of the Doppler corrections associated with the receiver node’s own motions relative to the common reference frame is based on a common reference frequency. For example, a common reference frequency may be adjusted by a node’s own motions to cancel out those motions in reference to the null angle. This common reference frequency may be known by each node prior to transmission and/or reception of the signals. In some embodiments, calculating the net frequency change seen by the receiver node104is based on the common reference frequency. For example, the net frequency change may be a difference between a measured frequency of the signals and the common reference frequency.

For purposes of discussing the receiver node104, a “source” generally refers to a source of a received signal, multiple sources of multiple signals, a single source of multiple signals, and/or the like. For example, a source may be a transmitter node102configured to apply Doppler corrections as disclosed herein and in applications from which priority is claimed and/or incorporated by reference. In this regard, a receiver node104may determine one or more attributes of the source (e.g., bearing between the receiver node104and the source, bearing of the velocity of the source, amplitude/speed of the velocity, range, and the like). In some embodiments, the receiver node104and the source (e.g., transmitter node102) are configured to use a same, compatible, and/or similar Doppler correction, protocol, common reference frame, common reference frequency, time synchronization, and/or the like such that the receiver node104may determine various attributes of the source. Note, in some embodiments, that one or more of these may be known ahead of time, be determined thereafter, included as fixed variable values as part of the protocol, and/or determined dynamically (in real time) as part of the protocol. For example, the protocol may determine that certain common reference frames should be used in certain environments, such as using GPS coordinates on land and a naval ship beacon transmitter common reference frame location (which may be mobile) over certain areas of ocean, which may dynamically change in real time as a location of a node changes.

In some embodiments, the transmitter node102and the receiver node104are time synchronized via synchronization bits associated with acquisition. For example, the synchronization bits may operate as physical layer overhead.

In some embodiments, the transmitter node102is configured to adjust a transmit frequency according to an own speed and an own velocity direction of the transmitter node102so as to perform a transmitter-side Doppler correction. In some embodiments, the receiver node104is configured to adjust a receiver frequency of the receiver node104according to an own speed and an own velocity direction of the receiver node104so as to perform a receiver-side Doppler correction. In some embodiments, an amount of adjustment of the adjusted transmit frequency is proportional to a transmitter node102velocity projection onto a Doppler null direction, wherein an amount of adjustment of the adjusted receiver frequency is proportional to a receiver node104velocity projection onto the Doppler null direction. In some embodiments, the receiver node102is configured to determine a relative speed between the transmitter node102and the receiver node104. In some embodiments, the receiver node104is configured to determine a direction that the transmitter node102is in motion and a velocity vector of the transmitter node102. In some embodiments, a maximum net frequency shift for a Doppler correction by the receiver node104occurs when a resultant vector is parallel to the Doppler null direction, wherein the resultant vector is equal to a velocity vector of the receiver node104minus the velocity vector of the transmitter node102. In some embodiments, a minimum net frequency shift for a Doppler correction by the receiver node104occurs when a resultant vector is antiparallel to the Doppler null direction, wherein the resultant vector is equal to a velocity vector of the receiver node104minus the velocity vector of the transmitter node102. In some embodiments, a net frequency shift for a Doppler correction by the receiver node104is zero when a vector pointing to the receiver node from the transmitter node102is parallel to the Doppler null direction.

Referring now toFIG.7, an exemplary embodiment of a method700according to the inventive concepts disclosed herein may include one or more of the following steps. Additionally, for example, some embodiments may include performing one or more instances of the method700iteratively, concurrently, and/or sequentially. Additionally, for example, at least some of the steps of the method700may be performed in parallel and/or concurrently. Additionally, in some embodiments, at least some of the steps of the method700may be performed non-sequentially.

A step702may include providing a transmitter node and a receiver node, wherein each node of the transmitter node and the receiver node are time synchronized, wherein each node of the transmitter node and the receiver node are in motion, wherein each node of the transmitter node and the receiver node comprises a communications interface including at least one antenna element, wherein each node of the transmitter node and the receiver node further comprises a controller operatively coupled to the communications interface, the controller including one or more processors, wherein the controller has information of own node velocity and own node orientation.

A step704may include based at least on the time synchronization, applying, by the transmitter node, Doppler corrections to the transmitter node’s own motions relative to a common reference frame.

A step706may include based at least on the time synchronization, applying, by the receiver node, Doppler corrections to the receiver node’s own motions relative to the common reference frame, wherein the common reference frame is known to the transmitter node and the receiver node prior to the transmitter node transmitting signals to the receiver node and prior to the receiver node receiving the signals from the transmitter node.

Further, the method700may include any of the operations disclosed throughout.

The null scanning technique discussed herein illustrates a system and a method for spatial awareness from resolving the temporal spatial characteristics of the transmitter node’s102radiation. This approach informs the receiver node104of the relative speed between the transmitter node102and receiver node104as well as the transmitter node direction and transmitter node velocity vector. This approach includes scanning through all directions and has a high sensitivity (e.g., low net frequency shift) when the null direction is aligned with the transmitter node direction. This approach can be implemented on a highly sensitive acquisition frame which is typically much more sensitive than explicit data transfers which allow for the ultra-sensitive spatial awareness with relatively low power.

This sentence may mark an end to the (at least partially) reproduced language from U.S. Patent Application No. 17/857,920 corresponding to the (at least partially) reproducedFIGS.1-7. However, note that this paragraph is nonlimiting, and changes may have been made and language added or removed, and not all the language above or corresponding figures above are necessarily reproduced from U.S. Patent Application No. 17/857,920.

Examples of doppler nulling methods include, but are not limited to, methods and other descriptions (e.g., at least some theory and mathematical basis) are disclosed in U.S. Patent Application No. 17/233,107, filed Apr. 16, 2021, which is hereby incorporated by reference in its entirety; U.S. Patent Application No. 17/534,061, filed Nov. 23, 2021, which is hereby incorporated by reference in its entirety; and U.S. Patent Application No. 17/857,920, filed Jul. 5, 2022, which is hereby incorporated by reference in its entirety. In embodiments, doppler nulling methods allow for benefits such as, but not limited to, relatively quickly and/or efficiently detecting transmitter nodes and determining transmitter node attributes (e.g., transmitter node speed, transmitter node bearing, relative bearing of transmitter node relative to receiver node, relative distance of transmitter node relative to receiver node, and the like).

FIG.8is a diagrammatic illustration of the Search and Rescue System (SAR)800, according to one or more embodiments of the present disclosure. The SAR system800may include a transmitter node102and a receiver node104. For example, the transmitter node102may be located at a ground-based location. By way of another example, the receiver node104may be configured for operation aboard at least one of a mobile or airborne platform (e.g., aircraft, water-based vehicles, ground-based vehicles, and the like), the mobile platform in motion relative to the transmitter node102. Further, the transmitter node may be configured to serve as an emergency locator beacon and mark a location of interest associated with a user needing to be rescued. In embodiments, the receiver node104may be configured to track the marked location of interest based at least on one or more Doppler corrections.

In embodiments, the transmitter node102may be configured to generate a Pseudo Noise (PN) sequence. For example, the PN sequence may allow for the transmitter node102to transmit at least one alert signal to the receiver node104while maintaining at least one of a low SWAP-C (size, weight, power, and cost), low probability of detection or interference (LPD/LPI), and/or anti-jamming capabilities.

In embodiments, the transmitter node may be configured to transmit an alert signal encoded in one or more channel symbols. For example, the receiver node104may be configured to receive the alert signal within a much larger range when the alert signal includes one or more channel symbols.

In embodiments, the transmitter node may be disposed on at least one ejection seat. For example, the transmitter node may be configured to transmit at least one signal causing the ejection seat to be ejected. By way of another example, the receiver node104may be configured to monitor the position/location of the at least one ejection seat upon triggering of the ejection.

In embodiments, the transmitter node102may be combined with other wireless and geolocation capabilities. For example, the transmitter node102may be combined with Search and Rescue (SAR) systems utilizing GPS to report a target location. By way of another example, DNS may be integrated with such systems to detect spoofing of reported target locations because the bearing from a spoofing node to the SAR does not match the reported bearing from the spoofing node.

In embodiments, the receiver node104may use the DNS information to determine the bearing in order to send a highly directional, and LPI/LPD signal/message to a person in need of rescue. For example, the person in need of rescue may receive the signal/message and begin to prepare for a rescue attempt.