DIRECTIONAL ENHANCEMENTS FOR MOBILE AD HOC NETWORKS (MANET) VIA DOPPLER NULL SCANNING (DNS)

A system is disclosed. The system may be a directional communications network (e.g., MANET) including at least a receiver or transmitter node. The receiver or transmitter node may include a communications interface with an omnidirectional 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 known to the receiver or transmitter node prior to the receiver or transmitter node receiving signals from a source. 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. The transmitter and receiver nodes may exchange medium access control (MAC) packets prior to establishing directional communications links, determining bearings to each other via Doppler corrections with respect to the packet exchanges.

BACKGROUND

Mobile Ad-hoc NETworks (MANET; e.g., “mesh networks”) are known in the art as quickly deployable, self-configuring wireless networks which may or may not have a 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.

Conventional MANETs may be associated with relatively slow discovery times between nodes, e.g., the time required for nodes within the MANET to discover each other, establish relative positioning among each other, and establish communications links among each other. Further, with respect to some directional MANET implementations, it may be necessary or advisable to limit or preclude transmissions in a particular direction to reduce or prevent detection or interception of a transmission by an adversary. Further still, with respect to some MANET implementations it may be necessary or advisable to reuse frequencies or frequency bands (e.g., if available bandwidth is limited). However, spatial reuse within a MANET can be complicated by the potential of multiple transmissions at a given frequency interfering with one another if the transmitting nodes are not far enough away from each other.

SUMMARY

In a first aspect, a system of at least a transmitter (Tx) node and a receiver (Rx) node in relative motion is disclosed. Each node includes a communications interface with omnidirectional antenna elements and a controller including one or more processors, and each node knows its own-node velocity and own-node orientation. Each node is in relative motion (e.g., one node in motion/one node stationary, both nodes in motion) relative to a common reference frame known to both nodes prior to transmission or reception between nodes. Each node is time synchronized to apply Doppler nulling corrections based on the node's own motion relative to the common reference frame. The Tx node transmits, and the Rx node receives, a control message associated with establishing or initiating a directional communications link to the Rx node. Based on Doppler nulling corrections with respect to the control message, the Rx node determines a relative bearing to the Tx node and establishes a directional communications link to the Tx node based on the determined bearing. The Rx node responds to the transmitted control message with a response control message to the Tx node.

In some embodiments, the control message is a request to tune, and the response control message is a response to tune.

In some embodiments, the control message is a request to send (RTS) and the response control message is a clear to send (CTS).

In some embodiments, the Tx node determines a relative bearing to the Rx node based on Doppler nulling corrections with respect to the response control message, and establishes a directional communications link to the Rx node based on the determined bearing.

In some embodiments, the Tx node determines a range to the Rx node.

In some embodiments, the system includes at least a first and second additional node. Based on Doppler nulling corrections with respect to the control message and/or response control message, the first and second additional node determine a relative bearing to the Tx node, a relative bearing to the Rx node, and/or a relative bearing between the first and second additional nodes.

In some embodiments, the first and second additional nodes establish mutual directional communications links based on the relative bearings to each other.

In some embodiments, the directional communications links between the Tx and Rx nodes are associated with transmission and reception at a particular frequency or frequency band, and the directional communications links between the first and second additional nodes are associated with transmission and reception at the same frequency or frequencies.

In some embodiments, the Tx node has a directional communications link to a silent node, e.g., a high value asset operating under emissions control (EMCON) restrictions or under radio silence. The Tx node, a low value or expendable asset, relays transmissions from the silent node to other nodes to which it has established directional communications links to reduce or preclude detection or interception of transmissions from the silent node.

In some embodiments, the Rx node determines a range to the Tx node.

In some embodiments, the Rx node performs receiver-side Doppler nulling correction by adjusting its receiver frequency according to its own-node velocity vector (e.g., speed, velocity direction).

In some embodiments, the amount of adjustment of the receiver frequency is proportional to an Rx node velocity projection onto the associated Doppler nulling direction.

In some embodiments, the Rx node determines a relative velocity between the Rx and Tx nodes. the Rx node determines a velocity vector (e.g., velocity and direction) of the relative motion of the Tx node.

In some embodiments, the maximum net frequency shift for a receiver-side Doppler nulling correction occurs when the resultant vector (e.g., the Rx node velocity vector minus the Tx node velocity vector) is parallel to the associated Doppler nulling direction.

In some embodiments, the minimum net frequency shift for a receiver-side Doppler nulling correction occurs when the resultant vector (e.g., the Rx node velocity vector minus the Tx node velocity vector) is antiparallel to the associated Doppler nulling direction.

In some embodiments, the relative motion of the Tx and Rx nodes is in two or three dimensions.

DETAILED DESCRIPTION

Broadly speaking, embodiments of the inventive concepts disclosed herein are directed to methods and systems for rapid discovery (e.g., node discovery, link discovery) within a MANET via Doppler nulling (e.g., Doppler null scanning (DNS)) by directional antenna elements (e.g., electronically scanned antennas (ESAs)) of the MANET nodes. In some embodiments, the inventive concepts disclosed herein may be utilized for MANET systems (e.g., to reduce node discovery, relative positioning times, and/or communication interface acquisition times). In some embodiments, the inventive concepts disclosed herein may be utilized to detect whether a node is in a main beam or side lobe of a directional antenna (e.g., ESA antenna).

In some embodiments, the inventive concepts disclosed herein may be utilized with highly directional communication methods to use expendable assets as a relay (e.g., emissions control (EMCON) floating data relay techniques, or other implementations wherein the relay incorporates the inventive concepts disclosed herein). For example, at least one node (e.g., which may transmit signals and/or receive signals) may utilize a directional (rather than omnidirectional) antenna element for improved performance. Embodiments may utilize time synchronized scanning sequences (along with directionality) to improve metrics such as signal-to-noise ratio, signal acquisition time, speed of attaining situational awareness of attributes of surrounding nodes, range, and the like. In some embodiments, synced scanning sequences are used so that all transmitting angles of multiple systems are pointing in the same direction at any point in time during a synced sequence, as well as all the receiving angles, which are pointed in the opposite direction. In this regard, if a pulse happens to be sent towards a particular system, that particular system's receiving angle will be aimed in the opposite direction the pulse was sent from, such that the receiving angle is configured to receive the pulse. Such a configuration may vastly improve the ability to detect a relatively large quantity of nodes in a relatively short period of time over relatively large ranges, over relatively large amounts of noise/interference, and the like. In some embodiments, a zero value or near zero value (e.g., or the like such as a zero crossing) of a calculated net frequency shift of a received signal is used to determine a bearing angle between the source (e.g., Tx node) and the receiving node using a time-of-arrival of the received signal. The bearing angle may be made more accurate by combining (e.g., averaging) it with another bearing angle estimation determined from an angle of peak amplitude gain of the signal. In some embodiments, the inventive concepts disclosed herein may be utilized with spatial reuse of networks (e.g., frequencies or frequency bands of directional MANETs).

For example, in some embodiments, concepts herein are used to reuse frequencies of a network when far enough away from other nodes using that frequency (or when nodes are oriented in sufficiently different directions) so as to not interfere with the signal of other nodes using that frequency. For example, a threshold metric (pre-determined, dynamic, etc.) may be used to determine whether a node is far enough away to use a frequency (and/or frequency bandwidth spectrum) based on relative position of the node relative to the network or other nodes on the network.

It is noted that U.S. patent application Ser. No. 17/857,920, filed Jul. 5, 2022 and which application is herein incorporated by reference in its entirety, provides at least some examples of Doppler nulling methods and systems which may be better understood, in a nonlimiting manner, by reference toFIGS.1-7and accompanying text therein (FIG.1of which, and accompanying text, is included here). 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; similarly, relative motion may be in two dimensions or in three dimensions. As disclosed in detail in U.S. patent application Ser. No. 17/857,920, 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 (and/or less signal to noise ratio (SNR)) compared to explicit data transfers.

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 VTand 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, ||) 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 ||and direction a 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:

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 (), and velocity direction α. That transmitter frequency adjustment (ΔƒT) is proportional to the velocity projection onto the ‘Null’ direction ϕ (120) 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, ||, 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.

This sentence may mark an end to the (at least partially) reproduced language from U.S. patent application Ser. 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 Ser. No. 17/857,920.

Directional radio frequency (RF) networks often must spend significant time scanning the physical space over which potential RF network signals may exist. For example, a system scanning spherical space in azimuth and elevation may require numerous discrete time intervals to accomplish the task. Generally, a receiver dwells for a finite amount of time within each spatial sector looking for a desired signal; hence, total discovery time becomes dwell time multiplied by the number of discrete time intervals needed for the receiver to search the entire physical space. Because scanning may be a lengthy process, often it becomes necessary to sacrifice other important system performance metrics to ensure timely discovery performance.

Omnidirectional doppler nulling may be an enabling technology for reducing discovery time within directional networks, thereby allowing for improvement in other performance metrics as well. Because of the significantly improved discovery time, directional Doppler-nulling may also be enabling technology for low-probability of detection (LPD) directional networks.

Transmission of explicit position information (e.g., GPS coordinates using two-way higher-bandwidth communications) and/or velocity information is not necessarily needed to obtain such information when using Doppler-nulling. In embodiments, Doppler is minimized (or “nulled”) via Doppler corrections in each direction an antenna is pointing based on at least a velocity of a node (e.g., which may be equally true for transmitter and receiver). Further, improved communication between nodes becomes possible whenever antennas are pointing toward each other. In embodiments, range to another node can be determined from the use of precisely-defined transmission intervals, as the transmission time in each can be known, a priori, to both the transmitter and receiver. With bearing angle, range, and relative velocity between nodes known via the Doppler-nulling protocol, it becomes possible to precisely discover and track another node's position without using any explicit data transfer (e.g., WiFi, Bluetooth, longer range similar bandwidth aerospace communication protocols, and/or the like).

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 Ser. No. 17/233,107, filed Apr. 16, 2021, which is herein incorporated by reference in its entirety; U.S. patent application Ser. No. 17/534,061, filed Nov. 23, 2021, which is herein incorporated by reference in its entirety; and U.S. patent application Ser. No. 17/857,920, filed Jul. 5, 2022, which is herein incorporated by reference in its entirety; and U.S. patent application Ser. No. 17/941,907, filed Sep. 9, 2022, which is herein 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).

In embodiments, the Tx node102may be disposed within a cluster202of nodes defined by a transmission range204(e.g., transmission radius), which may be adjustable by the Tx node102(e.g., via adjustments to its transmitting power). With respect to the Tx node102, an Rx node104, and other nodes within the cluster202, the antenna elements (112,FIG.1) of each node may be omnidirectional antenna elements capable of transmission through a 360-degree range around the associated node. In embodiments, the topology of the multi-node communications network100may be substantially two-dimensional or three-dimensional as described above. Further, the multi-node communications network100may be a directional MANET wherein member nodes transmit and receive via narrow-beam directional communications links.

In embodiments, the Tx node102may attempt to discover, and establish directional communications links to, other nodes within its cluster202or transmission range204. For example, the Tx node102may transmit a control message206, e.g., a Request to Tune (RTT) or a Request to Send (RTS) including one or more medium access control (MAC) packets. The Rx node104may detect or receive the control message206and discover the Tx node102via Doppler corrections performed with respect to the control message206, thereby determining a bearing208to the Tx node.

In embodiments, referring also toFIG.3, additional nodes300within the cluster202or within the transmission range204of the Tx node102may likewise detect the control message206. For example, additional nodes300may likewise determine a bearing302to the Tx node102based on Doppler corrections with respect to the control message206. In some embodiments, having discovered the Tx node102and determined a bearing302thereto, the additional nodes300may attempt to establish directional communications links with the Tx node.

Referring also toFIG.4, in embodiments the Rx node104may respond to the RTS206by transmitting a response control message400, e.g., a Response to Tune (RTT) or a Clear to Send400(CTS) comprising one or more MAC packets. For example, having determined a bearing208to the Tx node102, the Rx node104may further establish a narrow-beam directional communications link to the Tx node. In embodiments, additional nodes402within the transmission range404of the Rx node104may likewise detect and/or receive the control message400, determining a bearing406to the Rx node based on Doppler corrections with respect to the control message. For example, the additional nodes402, having established a bearing406to the Rx node104, may further establish directional communications links to the Rx node based on the determined bearing.

Referring also toFIG.5, the cluster (202,FIG.2) relative to the Tx node102(e.g., and including network nodes within the respective transmission ranges204,404of the Tx node102and Rx node104), may include, in addition to the Tx and Rx nodes, additional nodes300(e.g., which may have determined a bearing208to the Tx node102), additional nodes402(e.g., which may have determined a bearing406to the Rx node104), and additional nodes500(e.g., which may have determined a bearing to both the Tx node and Rx node). In some embodiments, the additional nodes300,402,500may likewise discover each other, and/or establish directional communications links among each other, based on additional control message exchanges of MAC packets and Doppler corrections based on said control message exchanges.

Referring also toFIGS.6A and6B, in embodiments the Tx node102may continue transmitting to the Rx node104via narrow-beam directional communications link600, and the Rx node104may likewise continue transmitting to the Tx node102via narrow-beam directional communications link602. In some embodiments, the Tx node102and/or Rx node104may adjust (604) their transmitting power to increase or reduce the size of their transmission range404, e.g., to reduce or eliminate probability of detection or interception (e.g., LPD, LPI) by unknown or unfriendly nodes of signals transmitted between the Rx and Tx nodes. For example, one or both of the Tx node102and Rx node104may additionally determine a range or distance to the other node, e.g., an approximate range based on Doppler corrections with respect to the control messages (206,FIG.2;400,FIG.4); a precise range based on two-way timing and ranging (TWTR) via a zero or near-zero Doppler path, as further disclosed in the co-pending application having docket number 175802US01; or via other appropriate ranging means.

In some embodiments, either the Rx node104(e.g., or the Tx node102, or other nodes within the network100) may establish directional communications links to additional nodes300outside their transmission range404, e.g., via short-flag signaling. For example, when the Rx node104(e.g., as a Tx node) is aligned with a receiver node (e.g., the additional long-range node300outside the transmission range404of the Rx node104) with respect to Doppler null directions (e.g., there existing a zero or near-zero Doppler path606between, and known to, the two nodes) such that sensitivity is maximum, the Rx node104may exchange a flag, or bit, informing the additional node300that the Rx node104is ready to transmit via the zero or near-zero path606. Similarly, when the Doppler null scanning direction is reversed and the additional node300is aligned with the Rx node104with respect to Doppler null directions, the additional node may indicate via flag/bit its readiness to receive transmissions. While, for example, a full DNS cycle may be needed to schedule medium access due to the need for Doppler nulling alignment, and additional information may be needed to distinguish between more than one node aligned with a particular Doppler null scan, signaling range may be extended beyond normal transmission range404, the extended range comparable with beaconing range.

Referring also toFIG.7A, in embodiments the additional node500may have determined bearings (208,FIG.8;406,FIG.10) to the Tx node102and Rx node104respectively (e.g., via Doppler corrections with respect to the RTS (206.FIG.8) and/or CTS (400,FIG.10)) and the additional node and Tx node may likewise establish mutual directional communications links700,702. Referring also toFIG.13B, the additional node704may be implemented and may function similarly to the additional node500ofFIG.7A, except that the additional nodes500,704may likewise have mutually determined bearings706between each other (e.g., via Doppler corrections with respect to RTS and CTS transmitted by either additional node to the Tx node102or Rx node104). Accordingly, the additional nodes500and704, both having determined mutual bearings706, may establish mutual directional communications links708,710. For example, the nodes102,104,500,704may all have determined relative positioning and/or velocity vectors of the other nodes. In some embodiments, the Tx and Rx nodes102,104may maintain directional communications links600,602whereby transmissions are sent and received via a predetermined frequency or frequency band. Similarly, the additional nodes500,704, knowing the relative positioning and/or velocity vector information of the Tx and Rx nodes102,104, may re-use the predetermined frequency or frequency band for their own mutual directional communications links708,710. In embodiments, one or more of the nodes102,104,500,704may determine that spatial re-use of the frequency or frequency band may be possible without interference between the directional communications links600,602,708,710, or one or more of the nodes may adjust, or may be directed to adjust, transmitting power to reduce or eliminate signal interference.

Referring now toFIG.8, the additional node500may be a high-value asset (HVA) operating in a state of radio silence or according to emissions control (EMCON) protocols to reduce or eliminate the probability of detection, interference, or interception of signals transmitted by the additional node. For example, EMCON may include EMCON communication protocols. For instance, EMCON states may include, but are not necessarily limited to, EMCON DELTA, EMCON CHARLIE, EMCON BETA, and EMCON ALPHA states used in the military (e.g., navy). In embodiments, EMCON DELTA may mean no or minimal emission limitations and may be used during normal operations. In embodiments, EMCON CHARLIE may mean only mission-essential equipment is allowed to transmit. For example, sensors unique to the vessel may be turned off to prevent identification or classification by adverse nodes. In embodiments, EMCON BETA may mean even more limitations than EMCON CHARLIE, but some transmissions may still be allowed. In embodiments, EMCON ALPHA may mean complete radio silence, such that no nodes in such a state are allowed to transmit.

In embodiments, the additional node/HVA500may wish to establish directional communications to the Tx node102, but may also wish to avoid detection and/or interception of transmissions by nodes800in the path of a directional communications link802between the additional node/HVA and the Tx node. As noted above, the additional node/HVA700, the Tx node102, and the Rx node104(the latter two nodes having established directional communications links (600,602;FIGS.12A-B)) may each know relative position and/or velocity vector information of the other nodes.

In embodiments, the Rx node104may be a low-value asset (LVA) or expendable asset, e.g., a mobile uncrewed aircraft system (UAS) or uncrewed aerial vehicle (UAV) or other uncrewed mobile platform. Accordingly, the Rx node104may receive transmissions from the additional node/HVA500via directional communications link804, relaying received transmissions to the Tx node102via directional communications link602. Similarly, the Tx node102may communicate with the additional node/HVA500by transmitting to the Rx node104via the directional communications link600; the Rx node may relay transmitted messages to the additional node/HVA via directional communications link806, reducing or avoiding in both directions the probability of signal detection and/or interception by the node800.

CONCLUSION