WO2005027370A2

WO2005027370A2 - Method and apparatus for identification and acquisition of directional wireless communications links to a network

Info

Publication number: WO2005027370A2
Application number: PCT/US2004/029777
Authority: WO
Inventors: Rajesh Krishnan
Original assignee: Bbnt Solutions Llc
Priority date: 2003-09-12
Filing date: 2004-09-10
Publication date: 2005-03-24
Also published as: WO2005027370A3

Abstract

Embodiments of the invention allow the automatic acquisition and tracking of a communications node and the initiation of a communications link with a network through the acquired communications node. Automatic acquisition and tracking reduce or eliminate the need for prior location information in connection with communications nodes that may be used as intermediaries for connection to the network. Further, images taken during acquisition and tracking maybe analyzed to extract authentication information regarding an intermediary communications node, or timing information indicating when the intermediary communications node maybe available for a connection.

Description

METHOD AND APPARATUS FOR IDENTIFICATION AND ACQUISITION OF DDRECTIONAL WIRELESS COMMUNICATIONS LINKS TO A NETWORK

FIELD OF THE INVENTION The present invention relates to automatic acquisition of communications links in wireless communications systems. More particularly, the present invention relates to automatic acquisition and tracking of a communications node, and the initiation of a wireless communications link with a network through the communications node in a dynamic networking environment including mobile nodes.

BACKGROUND OF THE INVENTION Current radio frequency-based directional antennas and free space optical- links require that a transceiver be pointed to the approximate coordinates of a correspondent transceiver or communications node, before a closed-loop control system (using, for example, gimbals or micro-electromechanical system ("MEMS") devices) can acquire and track the correspondent transceiver. These techniques rely on prior knowledge of the approximate location or the ability to bootstrap from an omni-directional radio frequency channel before the closed-loop link acquisition and tracking control can take over. Generally, the number and locations of communications nodes in a network may not be known. The difficulties associated with acquisition of and linking to correspondent communications nodes in such a network may be further compounded if they utilize directional transceivers. U.S. Patent No. 5,307,194 illustrates a UV-frequency system for establishing communications between two stations. This system assumes a priori knowledge of the location of the correspondent communications node. The known location of the correspondent communications node is then tracked using a CCD camera and is used to set up a covert communications channel. The assumption of a priori knowledge of location information for a correspondent communications node as well as the non-network context involving only two communicating nodes are deficiencies of the system disclosed in U.S. Patent No. 5,307,194 that render it inappropriate for use in a dynamic network. U.S. Patent No. 5,282,073 discloses a system for optical communications between two nodes that also requires a priori knowledge of the location of a correspondent communications node. This system additionally involves the use of beacons by each station to transmit location information to the other station with respectively greater precision using an iterative procedure. However, this system also involves communications between only two nodes. Moreover, the system uses a directional pencil beam as a beacon, which means that the system requires at least partial a priori location information regarding correspondent communications nodes. U.S. Patent No. 6,469,815 also illustrates a system for optical communications in which an optical link is established between satellites using sweeping beacons and an acquisition and tracking system. U.S. Patents No. 5,801,866 and 5,999,299 each disclose a system for optical communications involving two nodes in which the location of a correspondent node is determined through manual sighting by an operator. This system can only be implemented in a non-network situation, because of the requirement that a pair of communicating nodes point at each other. Moreover, the orientation of a transceiver on the basis of determined location information for a correspondent receiver requires human assistance and may not be done automatically. U.S. Patent No. 6,347,001 discloses an optical communications system in which a communications node uses a laser beacon to advertise its location to another node. The laser beacon, for purposes of covering a large solid angle of space, uses a signal with larger beam divergence compared to a separate communications laser. However, the fact that a directional source such as a laser is used for a beacon implies that at least partial a priori location information need be known or ascertained in the system. The requirement that a communications node have complete or partial a priori location information for a correspondent communications node renders the implementation of a dynamic communications network more difficult. In a network with mobile nodes, connections between pairs of nodes may be continually established and broken. Thus, the ability of a given communications node to establish a communications link with the network may often depend on its ability to form a connection with an arbitrary correspondent communications node that is already linked to the network. However, the mobility of a correspondent communications node in a dynamic network may make it difficult to predict its location. Moreover, the use of directional transmitters on correspondent communications nodes to increase the range of communications and/or the range of beacons for advertising position information may render searches for the correspondent communications node more difficult. Other features of prior known systems are also inadequate in the context of ad hoc networking in a system with dynamic communications nodes. For example, prior known systems do not allow for a way for a communications node to determine whether a correspondent communications node is able to authenticate itself, before establishing a communications link to a network through a connection with the correspondent communications node. Moreover, prior known systems do not allow for a way for a communications node to determine the time at which a correspondent communications node is available for a connection. Thus, there is a need for a system in which a communications node may form a communications link with a network through a correspondent communications node without a priori location information regarding the correspondent communications node. Such a system should be robust enough to allow reliable acquisition and tracking of communications nodes even where directional transmitters are used on the nodes. Further, there is a need for a system in which the correspondent communications node may authenticate to the communications node before a communications connection is established between the two. Finally, there is a need for a system in which the correspondent communications node may indicate when it is available for forming a communications connection for purposes of establishing a communications link with the network. SUMMARY OF THE INVENTION Embodiments of the invention allow the automatic acquisition and tracking of a communications node and the initiation of a communications link with a network through the acquired communications node. In one aspect of the invention, a method is provided for initiating a communications link with a network. In this method, at least one image is captured. The location of at least one candidate communications node is determined, based on a comparison of a predetermined signature and information included within the at least one image. A transceiver is oriented, based on the determined location of the at least one candidate communications node. A communications link is initiated with the network through the at least one candidate communications node. In another aspect of the invention, a method is provided for initiating a communications link with a network. In this method, at least one image is captured using a device that is responsive to electromagnetic radiation within a predetermined frequency range. The location of a candidate communications node is determined, based on the at least one image and based on electromagnetic radiation reflected from the candidate communications node that is within the predetermined frequency range. A transceiver is oriented, based on the determined location of the candidate communications node. A communications link is initiated with the network through the candidate communications node. In another aspect of the invention, a method is provided for initiating a communications link with a network. At least one image is captured using an element that is responsive to electromagnetic radiation within a predetermined frequency range. A location of a candidate communications node that is emitting electromagnetic radiation within the predetermined frequency range is determined, based on the at least one image. The electromagnetic radiation emitted from the candidate communications node includes timing information. A transceiver is oriented, based on the determined location of the candidate communications node. A communications link is initiated with the network through the candidate communications node. Other aspects of the invention are disclosed and discussed in the following written description, drawings and claims, including apparati and computer-readable media capable of performing methods of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows an example of a communications network that may be used with embodiments of the present invention. FIG. 2 shows an example of a transceiver apparatus that may be used with embodiments of the present invention. FIG. 3 shows a flow diagram of an embodiment of a method in accordance with the present invention in which a link is established with a communications network through a node by tracking and authenticating the node. FIG. 4 shows a flow diagram of an embodiment of a method in accordance with the present invention in which a link is established with a communications network through a node by additionally receiving timing information regarding the connection to the node. FIG. 5 shows a computer-implemented apparatus embodiment of the present invention and an embodiment incorporating a computer-readable medium.

DETAILED DESCRIPTION OF THE INVENTION Currently used techniques in link acquisition are often inadequate in dynamic networks containing mobile nodes. One possible technique requires a priori knowledge of the absolute or relative coordinates of a correspondent node to localize a search to a small solid angle. However, such location information may not be available in dynamic network settings where communications nodes are mobile. In another link acquisition technique, the correspondent node may use an omni-directional radio frequency-transceiver to explicitly convey its coordinates. This requires that each communications node know or be able to ascertain its coordinates, which poses limitations in. some environments where access to Global Positioning System or other coordinate systems may not be available. Moreover, an omni-directional radio frequency channel will require considerably more energy to span the same range as a directional link and thus may not be practical. In yet another link acquisition technique, radio-frequency locating techniques may be used to locate an omni-directional radio frequency transceiver co- located with the correspondent node. While this removes the need for knowledge of or the ability to ascertain coordinates, a high-power omni-directional radio frequency channel would still be required. Embodiments of the invention allow the automatic acquisition and tracking of a communications node and the initiation of a communications link with a network through the acquired communications node. Automatic acquisition and tracking reduces or eliminates the need for prior location information in connection with communications nodes that may be used as intermediaries for connection to the network. Further, images taken during acquisition and tracking may be analyzed to extract authentication information regarding an intermediary communications node, or timing information indicating when the intermediary communications node may be available for a connection. In embodiments of the invention, a communications node will usually include a transceiver, comprising a receiver and a transmitter. A transmitter may transmit information including communications by modulating electromagnetic waves of a given range of frequencies. Similarly, a receiver may receive electromagnetic waves of a given range of frequencies with embedded information or communications and extract these. The particular structure or configuration of a transceiver will generally vary depending on the band or frequency range of electromagnetic waves used as the carrier medium and the method for modulating these waves for embedding information or communications. However, transceivers are known for use in communications over a wide range of the electromagnetic spectrum, including the radio band, the microwave band, the infrared band, the optical band, the ultraviolet band and the x-ray band. Known transceivers operating in any band or frequency range of the electromagnetic radiation may be used in embodiments of the invention. FIG. 1 illustrates an example of a communications network suitable for use with embodiments of the present invention. In this network, a number of stationary and mobile transceivers or communications nodes establish and/or maintain communications links with each other. The mobile transceivers may be carried in or on, or be part of, a vehicle, such as an automobile, truck, airplane, helicopter, boat or ship, submarine or satellite. In the example communications network of FIG. 1, User 50 is using his mobile transceiver to establish a communications link with the network of FIG. 1 through a connection with Base Station 20. The term "establishing a communications link with the network" as used herein means that a first node in the network, using or through a direct connection with a second node, is establishing or has established a communications link or channel with at least one other node (i.e., at least a third node) of the communications network. For example, in the communications network of FIG. 1, user 50's mobile transceiver is shown as having established a direct connection with Base Station 20, which in turn is shown as having an additional direct connection with Geosynchronous Satellite Transceiver 40. Because user 50's mobile transceiver has established a communications link with Geosynchronous Satellite Transceiver 40 through Base Station 20, user 50's mobile transceiver may be said to have established a communications link with the network of FIG. 1 in the sense used in this written description. The example communications network of FIG. 1 is shown as comprising (in addition to User 50's mobile transceiver, Base Station 20 and Geosynchronous Satellite Transceiver 40) one of each of a variety of types of nodes: Airplane Transceiver 70, Land Vehicle Transceiver 60, Base Station 10, Low Earth Orbiter Transceiver 30, Ship Transceiver 80 and Submarine Transceiver 90. In general, a communications network having at least three nodes comprising one or more types may be used with embodiments of the invention. Moreover, the types of nodes shown in FIG. 1 are not exhaustive; other types of nodes, including stationary underwater transceivers, moon or planet-based transceivers and so on may be used in communications networks for use with embodiments of the invention. In certain embodiments, each of a pair of transceivers in a direct connection use electromagnetic waves of a specific frequency range as a carrier medium in which communications data is embedded by modulation of the electromagnetic radiation. For example, frequency or amplitude modulation of radio waves may be used to carry communications data between a pair of directly connected nodes. However, other methods for modulating electromagnetic waves to carry communications data are known to those skilled in the art, and may be used with embodiments of the invention. In an embodiment, the same range of frequencies of electromagnetic radiation can be used as a carrier medium for establishing direct connections to other nodes by each node in the communications system. In another embodiment, different nodes may use different ranges of frequencies. For example, Geosynchronous Satellite 40 may use optical frequencies for communications in a direct connection, whereas User 50's mobile device may use radio frequencies. In this example, Base Station 20 may have both a radio-frequency transceiver and an optical-frequency transceiver so that User 50's mobile device and Geosynchronous

Satellite 40 can establish a two-way communications link through Base Station 20. The apparatus of FIG. 2 may be used with embodiments of the invention to determine the location of a correspondent communications node and to initiate a communications link with the correspondent communications node based on the determined location. The configuration of the apparatus of FIG. 2 will vary with the frequency range of electromagnetic waves used for acquiring the location of a communications node and for establishing communications. However, appropriate configurations that may be used are known to those skilled in the art. In the apparatus of FIG. 2, Acquisition Detector 210 is sensitive to electromagnetic radiation of a certain frequency range and may be used to capture images in that frequency range. For example, Acquisition Detector 210 may be a segmented semiconductor diode detector for applications in which images in the high-frequency range (for example, x-rays or gamma rays) of the electromagnetic spectrum are desired to be taken. On the other hand, Acquisition Detector 210 may be a parabolic-shaped receiver (not shown in Fig. 2) for applications in which images in the radio-frequency range are desired to be taken. Appropriate configurations for Acquisition Detector 210 for taking images in different ranges of the electromagnetic spectrum are known and will be apparent to those skilled in the art. In general, Acquisition Detector 210 produces electronic signals that correspond to the image of electromagnetic radiation impinging on it in the range of its sensitivity. Acquisition Detector Electronics and Control 250, which is coupled to Acquisition Detector 210, performs signal shaping functions and amplifies the signals from Acquisition Detector 210 for input into Communications Computer 280. Appropriate configurations for Acquisition Detector Electronics and Control 250 are known to those skilled in the art. For example, U.S. Patent No. 5,235,176, which describes an optical radiation sensing assembly and associated signal-shaping electronics including preamplifiers, exemplifies some of the functions that may be performed by Acquisition Detector Electronics and Control 250. Similarly, U.S. Patent No. 4,027,837, which illustrates an optical missile guidance system, also illustrates some of the functions performed by Acquisition Detector Electronics and Control 250. U.S. Patent No. 6,469,815 illustrates an optical acquisition and tracking system and associated electronics that may also be used as a basis for implementing Acquisition Detector 210 and Acquisition Detector Electronics and Control 250. Each of the foregoing patents in this paragraph is incorporated herein by reference in its entirety. Acquisition Detector Electronics and Control 250 may also include mechanical, electro-mechanical, hydraulic and/or pneumatic systems for changing and controlling the orientation of Acquisition Detector 250. Such systems are known by those skilled in the art. For example, U.S. Patent No. 4,328,789 illustrates a system for orienting a light-collecting device using a hydraulic actuator and gear motor. Similarly, U.S. Patent No. 6,469,815 illustrates a gimbal-based system for orienting an optical detector. Each of the foregoing patents in this paragraph is incorporated herein by reference in its entirety. These and other known means for orienting detectors may be used in embodiments of the invention. Communications Computer 280 may be used to store the images obtained by Acquisition Detector 210. Further, Communications Computer 280 may be programmed to analyze one or more images obtained by Acquisition Detector 210 for predetermined patterns - for example, Communications Computer 280 may be programmed to determine whether one or more images captured by Acquisition Detector 210 contain the signature of a communications node in the range of electromagnetic radiation to which Acquisition Detector 210 is sensitive. Configurations appropriate for Communications Computer 280, as well as pattern- recognition software that may be executed on Communications Computer 280, will be apparent to those skilled in the art. For example, the techniques for automatic target recognition described or referred to in Digital Image Processing (2nd edition), R.C. Gonzalez and R.E. Woods, Addison Wesley (2002) (incorporated herein by reference) and/or known to those skilled in the art may be used with embodiments of the invention. FIG. 2 also shows Transceiver 220, which comprises a Receiver 230 and a Transmitter 240, that may be used to establish connections with communications nodes similar to those shown in FIG. 1. The particular configurations for Receiver 230 and Transmitter 240 will depend on the frequency range of electromagnetic radiation that is selected for communications; for example, for communications in the radio-frequency range, each of Receiver 230 and Transmitter 240 may be parabolic-shaped antennae with conducting surfaces. For communications in the optical-range of frequencies, on the other hand, Transmitter 230 may be a laser, whereas Receiver 240 may be a charge-coupled device (CCD) with a focusing lens. Configurations appropriate for Transmitter 230 and Receiver 240 for communications in different frequency ranges of the electromagnetic spectrum are known to those skilled in the art. In one embodiment, Acquisition Detector 210 is sensitive to electromagnetic radiation in the same range of frequency as Receiver 240. In other embodiments, Acquisition Detector 210 is sensitive to electromagnetic radiation in a different range of frequency from Receiver 240. In the latter embodiments, the frequency ranges may be substantially different. For example, Acquisition Detector 210 may be sensitive to a range of frequencies within a first band of electromagnetic radiation selected from the group consisting of radio band radiation, microwave band radiation, infrared band radiation, optical band radiation, ultraviolet band radiation and x-ray band radiation, whereas Receiver 240 may be sensitive to a range of frequencies within a different band selected from the same group. Although FIG. 2 shows an acquisition detector that is separate from the transceiver, embodiments of the invention include those in which the acquisition detector and the receiver are the same device, or are part of the same device. In these embodiments, the same receiver apparatus is used to also capture images for locating and tracking communications nodes. The receiver apparatus in such embodiments may also be used to receive and extract timing and authentication information in connection with a communications node, as is discussed in greater detail below. In certain embodiments, a separate receiver and transmitter may not be required, and the same device may be able to perform the functions of both the receiver and the transmitter. References in this written description to FIG. 2 are intended to include these alternate embodiments and other variations of the system shown in FIG. 2. Signals received by Receiver 240 may be shaped and amplified in Receiver Electronics and Control 270 before they are input into Communications Computer 280. Similarly, signals including communications data may be shaped and amplified by Transmitter Electronics and Control 260 before transmission by Transmitter 230. Appropriate configurations for Receiver Electronics and Control 270 and Transmitter Electronics and Control 260 are known to those skilled in the art. For example, in particular embodiments, Receiver Electronics and Control 270 may be implemented by the same means as or means similar to those described above in connection with Acquisition Detector Electronics and Control 250. However, other known means may also be used in implementing Receiver Electronics and Control 270. Receiver Electronics and Control 270 and Transmitter Electronics and Control 260 may also (either singly or jointly) include mechanical, electromechanical, hydraulic and/or pneumatic systems for changing and controlling the orientation of Receiver 240 and/or Transmitter 230. Such systems are known by those skilled in the art. For example, U.S. Patent No. 4,328,789 illustrates a system for orienting a light-collecting device using a hydraulic actuator and gear motor. Similarly, U.S. Patent No. 6,469,815 illustrates a gimbal-based system for orienting an optical detector. Each of the foregoing patents in this paragraph is incorporated herein by reference in its entirety. These and other known means for orienting detectors may be used in embodiments of the invention. FIG. 3 shows a flow chart illustrating the steps in an embodiment of the present invention. In this embodiment, the location of a candidate communications node is initially determined on the basis of captured images. Whether a link may actually be established with the candidate communications node may be determined based on the presence or absence of authentication information received from the candidate communications node. A communications link with a communications network may then be established if authentication information received indicates that the candidate communications link is appropriate for forming a communications link. In step 310, one or more images are captured. For example, Acquisition

Detector 210 may capture one or more images of a section of three-dimensional space. These images may then be electronically transferred to and stored in Communications Computer 280. In step 320, the location of a candidate communications node connected to a communications network is determined based on the one or more images obtained in step 310. Known pattern recognition or automatic target recognition techniques may be used to carry out this step. For example, a predetermined signature corresponding to a communications node may be compared against the content of the one or more images taken in step 310. In particular, Communications Computer 280 may compare the contents of the one or more images taken in step 310 against the predetermined signature to identify one or more objects in the images as candidate communications nodes. In an embodiment, the predetermined signature may be an emission of electromagnetic radiation from an object - for example, the reflection of sunlight from an object in a given region of three-dimensional space may be the basis for identifying, and determining the location of, a candidate communications node. The predetermined signature may incorporate other threshold tests for identifying and determining the location of a candidate! communications node, such as the shape of a , detected object or its velocity. The content of the images taken in step 310 may be searched for a predetermined shape corresponding to a candidate communications node. Objects captured in the images having the predetermined shape may be identified as candidate communications nodes. Alternatively, the predetermined signature of a candidate communications node may be an object that has a velocity or angular velocity that is large relative to the background in the images taken in step 310. For example, a plurality of images taken in step 310 may be used to identify candidate communications nodes as those objects in the images that move relative to the background. More generally, any characteristic of a communications node that projects onto images in the range of frequencies of electromagnetic radiation to which Acquisition Detector 210 is sensitive may be used as a signature for identifying a set of one or more candidate communications nodes within the one or more images taken in step 310. In step 330, a signal is transmitted as a probe to at least one candidate communications node identified in step 320. For example, transmitter 230 may transmit a signal at a particular frequency or range of frequencies of electromagnetic radiation as a query to a candidate communications node identified in step 320. In step 340, a determination is made as to whether authentication information is received from the candidate communications node in response to the probing signal of step 330. Decisional step 340 may be executed by Communications Computer 280. In the embodiment shown in FIG. 3, authentication information includes any information transmitted by a communications node following or in response to the probing signal of step 330 that identifies the communications node as such (including, possibly, identification of the communications node as a means to establish a communications link with a network). The authentication information may be embedded in an electromagnetic signal transmitted from the communications node that is received by one or both of Acquisition Detector 210 and Receiver 240. Authentication information that is received may identify the communications node by the substantive information included in a message, or by other means, For example, a message encoded by the communications node using a secret private key not known publicly will contain authentication information by virtue of the fact that decryption using the corresponding public key (known, for example, to the system shown in FIG. 2 and possibly publicly) yields a substantive message, even where the message that is encoded does not itself contain any substantive identification information. In one embodiment, authentication information comprises a symmetric key encrypted using a private key known to the communications node. In this embodiment, Communications Computer 280, may decrypt the encoded message using the non-secret public key corresponding to the private key (which may be publicly available), and may establish a secure communications channel using the symmetric key with the communications node. Authentication information may also include other information besides identification information such as timing information identifying the temporal availability of the communications node for linking. For example, authentication information may additionally include information for synchronizing communications transmissions between the system of FIG. 2 and the communications node. If at step 340 authentication information is not received, then the candidate communications node is determined to not actually be a communications node suitable for a communications link. In that case, the search for a communications node to link to may be continued by returning to step 320 and analyzing the one or more images taken in step 310 for other candidate communications nodes. Alternatively, a further search for a communications node to link to may be commenced by returning execution to step 310 and taking a new image or set of images for analysis. The dashed lines shown in Fig. 3 correspond to these two discussed alternatives. As a further alternative, execution may simply be terminated (not shown) in this case. If, at step 340, authentication information is determined to be received, a determination is made at decisional step 350 as to whether the authentication information received indicates that the candidate communications node is available or appropriate for a communications link. For example, Communications Computer 280 may store a predetermined list of identification tags for communications nodes that are appropriate for a connection to a network. If the received authentication information identifies the corresponding candidate communications node as having an identification tag that is on the predetermined list, then a connection may be formed with the candidate communications node. If the authentication information indicates that the candidate communications node is not available or appropriate for a link, execution may be terminated (not shown), or returned to step 310 or step 320 for further searches for candidate communications nodes as discussed earlier. If, at step 350, the authentication information that is received is determined to indicate that the communications node is suitable for a link, the transceiver is oriented in step 360 in a way allowing a satisfactory connection with the communications node, based on the location information determined in step 320. A communications link may then be initiated at step 370 with a network through the communications node. In some embodiments, step 350 and/or step 360 may be skipped or be optional. For example, the reception of authentication information in step 340 may be sufficient to establish that the candidate communications node is suitable for a link, without requiring a separate step 350. Additionally or alternatively, the transceiver may not require any orientation in step 360, either because the transceiver is already oriented in a manner allowing the adequate exchange of communications with the communications node, or because the transceiver (or the platform attached to the transceiver) is not orientable. In this application, "orienting a transceiver" may be interpreted to include systems in which the transceiver is determined to be already aligned in a manner allowing an adequate exchange of communications with the communications node, or in which a fixed transceiver is aligned by positioning the structure (or satellite) to which the transceiver is fixed. In yet another embodiment, step 330 may be skipped; in these embodiments, the communications node may transmit authentication information periodically or on an ad hoc basis without requiring any prompting by way of the transmission of a probing signal. FIG. 4 shows a flow chart illustrating the steps in another embodiment of the present invention. In this embodiment, the system of FIG. 2, in initiating a communications link with a network through a communications node, initially determines the location of the communications node and authentication information (and possibly timing information) in connection with the communications node by extracting this information from one or more images that are taken. Additionally, the images may be taken at a range of frequencies of electromagnetic radiation that is substantially different from the range of frequencies used for communications with the communications node. In step 410, one or more images are captured. For example, Acquisition Detector 210 may capture one or more images of a section of three-dimensional space in a first range of frequencies of electromagnetic radiation. These images may then be electronically transferred to and stored in Communications Computer 280. In steps 420, 430 and 440, location information, authentication information and timing information in connection with a candidate communications node are respectively extracted from the one or more images captured in step 410. For example, Communications Computer 280 may determine the location of a candidate communications node using known pattern recognition or automatic target recognition techniques as discussed in connection with the embodiments of FIG. 3. Further, authentication information and timing information in connection with a candidate communications node may be extracted from the one or more images taken in FIG. 3 using such techniques. For example, if a communications node indicates its identity as a node available for immediate communications links by modulating an electromagnetic signal in the first range of frequencies of step 410 in a predetermined pattern, then location information, authentication information and timing information in connection with the communications node may be extracted from the images taken in step 410 by analyzing the images for the pattern. In the embodiment of FIG. 4, authentication information is not transmitted from a communications node in response to a probing signal from the system of FIG. 2; rather, the communications node transmits authentication information periodically or on an ad hoc basis without any prompting by way of a probing signal. Such authentication information at least includes information identifying the object as a communications node (including, possibly, identification of the object as a means to establish a communications link with a network). However, "authentication information" as used in connection with these embodiments does not include signals or beacons emitted by an object merely for purposes of advertising its location. In step 450, a determination is made as to whether any extracted authentication information and any timing information indicate that the candidate communications node is available for a link. In an implementation of the embodiment of FIG. 4, Communications Computer 280 may perform decisional step 450. If extracted authentication information indicates that the candidate communications node is not available for a link, no authentication information can be extracted, or timing information indicates that the candidate communications node will not be timely available for a communications link, then execution may be terminated (not shown), or returned to step 410 or step 420 (shown as dashed lines in Fig. 4 to indicate alternative execution paths) for further searches for candidate communications nodes. If the authentication information and timing information indicate that the candidate object is a communications node available for a connection, then the transceiver is oriented in step 460 based on the determined location information. In an embodiment, the transceiver is oriented to face or track the determined location. A communications link may then be initiated at step 470 with a network through the communications node. The communications link may be established using a second range of electromagnetic radiation that is different from the first range discussed above in connection with step 410. The first range of frequencies may be different from the second range. In some embodiments of the invention, the first range of frequencies may be \ substantially different from the second range. For example, in one embodiment, the first range is within a first band of electromagnetic radiation selected from the group consisting of radio band radiation, microwave band radiation, infrared band radiation, optical band radiation, ultraviolet band radiation and x-ray band radiation, whereas the second frequency range is within a second band selected from the same group that is different from the first band. In some embodiments, step 460 may be skipped or be optional. For example, the transceiver may not require any orientation in step 460, either because the transceiver is already oriented in a manner allowing the adequate exchange of communications with the communications node, or because the transceiver (or the platform attached to the transceiver) is not orientable. FIG. 5 shows an example of an apparatus used in some embodiments of the present invention. In FIG. 5, a medium 540 containing Instructions 545 may be operatively coupled to a Computer 500. For example, Instructions 545 may contain the steps in an embodiment of a method of the present invention. For example, Instructions 545 may comprise the instructions corresponding to the steps shown in FIGs. 3 or 4 in specific implementations. In the example depicted in FIG. 5, Computer 500 contains a Processor 510 which is connected to an Input/Output Unit 530 and a Memory 520. Memory 520 may also have Instructions 525, which correspond to the steps in an embodiment of a method of the present invention. In a specific implementation, Instructions 545 of Medium 540 may be copied into Memory 520. The embodiments of the invention discussed here may be used in many different contexts as can be appreciated by one skilled in the art. Three implementations are discussed below for purposes of exemplification only.

A. Underwater Optical Networks In an underwater optical network scenario, a number of underwater optical- frequency transceivers (synapses) that use blue-green lasers for transmissions are deployed along a coastline. A stealthy underwater vehicle must locate synapses in its vicinity before it can point to and acquire a synapse, for example, for forming a communications link with a network connected to the synapse. The vehicle uses a CCD camera to capture images and then simply searches for the location of bright spots on the images to locate a synapse. Image processing is considerably simpler here than in the general case since one needs to only track light points on the image rather than objects. Using this approach, the underwater vehicle has the benefit of low probability of detection from using a passive CCD rather than actively scanning for synapses with a beacon. Unless there is an optical enemy sensor directly in the line of sight of a synapse, the associated beam will not be detected. Moreover, the CCD is useful for visual surveillance. Because a bi-directional radio frequency link is not used to bootstrap the acquisition of the communications link, radio frequency silence is another benefit afforded by this approach. In any case, radio frequency communications would be inefficient in an underwater environment. In a further refinement, the approach described above may be extended by providing the synapse with the ability to signal timing information for linking and for providing authentication information. For example, each synapse may emit a slightly wider beam during intervals when it is available to form a link with the vehicle. For example, the synapse may be in this mode during slots in a time- division multiplexing schedule when it is not communicating with any other peer. Furthermore, these timing signals may be modulated with a specific sequence to provide authentication or identity information in connection with the synapse. In this example, the incoming underwater vehicle would simply need to capture a series of images from which it would determine the locations of the synapses, the time slots for forming a connection with the synapse, as well as the authentication information. The vehicle could then selectively connect to friendly synapses.

B. Tracking Low Earth Orbiter Satellites Low Earth Orbiter Satellites ("LEO") that are illuminated by their reflections of sunlight appear as very bright objects against a dark background, because there are usually no other reflectors of light near them having the same apparent luminosity and/or apparent velocity. A ground node may use a CCD camera pointed at the sky to capture images that may be analyzed using known digital image processing techniques to determine location information for one or more LEOs. Such location information may be used to establish a ground-to-satellite link by, for example, narrowing the acquisition and tracking search to a small solid angle. No a priori knowledge of the satellite location or trajectory is required by this approach.

C. Tracking Links to Aerial Vehicles In an implementation, dynamic links between high altitude platforms (e.g., aircraft) and a ground station may be provided in an ad hoc network. Aircraft are clearly visible across the sky and have easily recognizable signatures. Image processing techniques to automatically recognize and track aircraft targets exist. Once the ground station locates an aircraft using such techniques, it may establish a communications connection with the aircraft for purposes of communications with the aircraft or, for example, to establish a communications link with a network connected to the aircraft. In an extension of this implementation, the ground station may prompt the aircraft for timing and/or authentication information after locating and tracking the aircraft. Such information may be transmitted by the aircraft by modulating a beam of electromagnetic radiation that is sourced at the ground station. For example, the ground station may direct a laser beam onto the aircraft, which may modulate and reflect the laser beam using active reflection systems such as corner cube reflectors, gimbal-mounted mirrors or other micro-electromechanical devices including mirrors or reflective surfaces. Other means for generating such "active" reflections are known to those skilled in the art. The modulations may contain authentication information identifying the aircraft as well as timing information indicating the aircraft's temporal availability for a communications connection. Many variations of the embodiments described in this specification are possible. All of these variations are within the scope and spirit of the invention and the appended claims. For example, the embodiments above have been described in connection with communications links using electromagnetic radiation as the medium carrying communications information. However, embodiments of the invention are possible in which other carrier media are used such as sound or pressure waves in gas (e.g., the atmosphere) or a liquid (e.g., water - oceans or lakes). Known receivers and transmitters operating using sound or pressure waves may be used with these embodiments. The present invention has been described in terms of several embodiments solely for the purpose of illustration. Persons skilled in the art will recognize from this description that the invention is not limited to the embodiments described, and may be practiced with modifications and alterations limited only by the spirit and scope of the appended claims which are intended to cover such modifications and alterations, so as to afford broad protection to the invention and its equivalents.

Claims

CLAIMS:

1. A method for initiating a communications link with a network comprising:

(a) capturing at least one image;

(b) determining a location of at least one candidate communications node based on a comparison of a predetermined signature for a communications node and information included within the at least one image;

(c) orienting a transceiver based on the determined location of the at least one candidate communications node; and (d) initiating the communications link with the network through the at least one candidate communications node.

2. The method of claim 1 wherein the step of determining the location of the at least one candidate communications node is carried out using an automatic target recognition technique.

3. The method of claim 1 wherein the predetermined signature includes authentication information identifying the communications node.

4. The method of claim 3 wherein the authentication information is encrypted.

5. The method of claim 3 wherein the authentication information is carried on reflected electromagnetic radiation from the at least one candidate communications node and is captured in the at least one image.

6. The method of claim 5 wherein the reflected electromagnetic radiation is generated by directing a laser source at an active reflection system on the at least one candidate communications node.

7. The method of claim 1 wherein the step of initiating the communications link is carried out using timing information included in the predetermined signature.

8. The method of claim 7 wherein the timing information indicates availability of the communications node for linking.

9. The method of claim 1 wherein the step of initiating the communications link is caπied out using electromagnetic radiation within a first frequency range and wherein the at least one image is captured using at least one detector that is sensitive to electromagnetic radiation within a second frequency range.

10. The method of claim 7 wherein the first frequency range is different from the second frequency range.

11. The method of claim 7 wherein the first frequency range is within a first band of electromagnetic radiation selected from the group consisting of radio band radiation, microwave band radiation, infrared band radiation, optical band radiation, ultraviolet band radiation and x-ray band radiation, and wherein the second frequency range is within a second band selected from the group, and wherein the second band is different from the first band.

12. A method for initiating a communications link with a network comprising:

(a) capturing at least one image using a device that is responsive to electromagnetic radiation within a predetermined frequency range;

(b) determining a location of a candidate communications node based on the at least one image and based on electromagnetic radiation reflected from the candidate communications node that is within the predetermined frequency range;

(c) orienting a transceiver based on the determined location of the candidate communications node; and

(d) initiating the communications link with the network through the candidate communications node.

13. The method of claim 12 wherein the step of determining the location of the candidate communications node is carried out using an automatic target recognition technique.

14. The method of claim 12 further comprising: (e) receiving authentication information from the candidate communications node.

15. The method of claim 14 wherein the authentication information is received in response to a signal transmitted to the candidate communications node.

16. The method of claim 15 wherein the signal is emitted from a laser source.

17. The method of claim 16 wherein the authentication information is included within a reflection of the signal off the candidate communications node.

18. The method of claim 17 wherein the reflection of the signal is generated by an active reflection system on the candidate communications node.

19. The method of claim 14 wherein the authentication information comprises timing information.

20. The method of claim 19 wherein the timing information indicates availability of the candidate communications node for the communications link.

21. The method of claim 20 wherein the step of initiating the communications link is carried out using the timing information.

22. A method for initiating a communications link with a network comprising:

(a) capturing at least one image using an element that is responsive to electromagnetic radiation within a predetermined frequency range;

(b) determining a location of a candidate communications node that is emitting electromagnetic radiation within the predetermined frequency range based on the at least one image;

(c) orienting a transceiver based on the determined location of the candidate communications node; and (d) initiating the communications link with the network through the candidate communications node;

(e) wherein the electromagnetic radiation emitted from the candidate communications node includes timing information.

23. The method of claim 22 wherein the step of determining the location of the candidate communications node is carried out using an automatic target recognition technique.

24. The method of claim 22 wherein the timing information indicates availability of the candidate communications node for a communications link.

25. The method of claim 22 wherein the electromagnetic radiation emitted from the candidate communications node is a reflection off the candidate communications node.

26. The method of claim 25 wherein the electromagnetic radiation emitted from the candidate communications originates from a source other than the candidate communications node.

27. The method of claim 25 wherein the reflection is generated by directing a laser source at an active reflection system on the candidate communications node.

28. The method of claim 22 wherein the timing infonnation is encrypted.

29. The method of claim 22 wherein the step of initiating the communications link is carried out using the timing information.

30. A method for initiating a communications link with a network comprising:

(a) capturing at least one image in a first frequency range of electromagnetic radiation, wherein the at least one image includes at least one communications node that is emitting electromagnetic radiation within the first frequency range;

(b) based on the at least one image, determining a location of the at least one communications node;

(c) orienting a transceiver based on the determined location; and

(d) initiating the communications link with the network through the at least one communications node using a second frequency range of electromagnetic radiation, wherein the second frequency range is different from the first frequency range.

31. The method of claim 30 wherein the step of determining the location of the at least one candidate communications node is carried out using an automatic target recognition technique.

32. The method of claim 30 wherein the first frequency range is within a first band of electromagnetic radiation selected from the group consisting of radio band radiation, microwave band radiation, infrared band radiation, optical band radiation, ultraviolet band radiation and x-ray band radiation, and wherein the second frequency range is within a second band selected from the group, and wherein the second band is different from the first band.

33. The method of claim 30 wherein the step of initiating the communications link is carried out using timing information.

34. The method of claim 33 wherein the timing information is extracted from the at least one image.

35. The method of claim 34 wherein the timing information indicates the availability of the at least one communications node for the communications link.

36. The method of claim 30 wherein the emitted electromagnetic radiation is a reflection off the at least one communications node.

37. The method of claim 36 wherein the emitted electromagnetic radiation is from a source other than the at least one communications node.

38. A method for initiating a communications link with a network comprising:

(a) capturing at least one image; (b) determining a location of at least one candidate communications node based on the at least one image;

(c) orienting a transceiver based on the detennined location of the at least one candidate communications node;

(d) receiving authentication information from the at least one candidate communications node; and

(e) initiating the communications link with the network through the at least one candidate communications node based on the authentication information.

39. The method of claim 38 wherein the step of determining the location of the at least one candidate communications node is carried out using an automatic target recognition technique.

40. The method of claim 38 wherein the authentication information is received in response to a signal transmitted to the at least one candidate communications node.

41. The method of claim 38 wherein the authentication infonnation is carried on a reflection that is generated by an active reflection system on the at least one candidate communications node.

42. The method of claim 38 wherein the received authentication information is extiacted from the at least one image.

43. The method of claim 38 wherein the authentication information is encrypted.

44. The method of claim 38 further comprising

(f) receiving timing information from the at least one candidate communications node.

45. The method of claim 44 wherein the step of initiating the communications link is carried out using the timing information.

46. The method of claim 45 wherein the timing information indicates availability of the at least one communications node for linking.

47. The method of claim 38 wherein timing information is extracted from the at least one image.

48. The method of claim 47 wherein the step of initiating the communications link is carried out using the timing information.

49. The method of claim 48 wherein the timing information indicates availability of the at least one communications node for linking.

50. An apparatus for initiating a communications link with a network comprising:

(a) means for capturing at least one image;

(b) means for determining a location of at least one candidate communications node based on a comparison of a predetermined signature for a communications node and information included within the at least one image;

(c) means for orienting a transceiver based on the determined location of the at least one candidate communications node; and

(d) means for initiating the communications link with the network through the at least one candidate communications node.

51. The apparatus of claim 50 wherein the predetermined signature includes authentication information identifying the communications node.,

52. The apparatus of claim 51 wherein the authentication information is earned on reflected electromagnetic radiation from the at least one candidate communications node and is captured in the at least one image.

53. The apparatus of claim 50 wherein the means for initiating initiates the communications link based on timing information included in the predetermined signature.

54. The apparatus of claim 53 wherein the timing information indicates availability of the communications node for linking.

55. The apparatus of claim 50 wherein the means for initiating initiates the communications link using electromagnetic radiation within a first frequency range and wherein the at least one image is captured using at least one detector that is sensitive to electromagnetic radiation within a second frequency range.

56. The apparatus of claim 55 wherein the first frequency range is within a first band of electromagnetic radiation selected from the group consisting of radio band radiation, microwave band radiation, infrared band radiation, optical band radiation, ultiaviolet band radiation and x-ray band radiation, and wherein the second frequency range is within a second band selected from the group, and wherein the second band is different from the first band.

57. An apparatus for initiating a communications link with a network comprising:

(a) means for capturing at least one image using a device that is responsive to electromagnetic radiation within a predetermined frequency range;

(b) means for determining a location of a candidate communications node based on the at least one image and based on electromagnetic radiation reflected from the candidate communications node that is within the predetermined frequency range;

(c) means for orienting a transceiver based on the determined location of the candidate communications node; and

(d) means for initiating the communications link with the network through the candidate communications node.

58. The apparatus of claim 57 further comprising:

(e) means for receiving authentication information from the candidate communications node.

59. The apparatus of claim 58 wherein the means for receiving receives the authentication information in response to a signal transmitted to the candidate communications node.

60. The apparatus of claim 59 wherein the signal is emitted from a laser source.

61. The apparatus of claim 60 wherein the authentication information is included within a reflection of the signal off the candidate communications node.

62. The apparatus of claim 58 wherein the authentication information comprises timing information.

63. The apparatus of claim 62 wherein the timing information indicates availability of the candidate communications node for a communications link.

64. An apparatus for initiating a communications link with a network comprising:

(a) means for capturing at least one image using an element that is responsive to electromagnetic radiation within a predetermined frequency range;

(b) means for determining a location of a candidate communications node that is emitting electromagnetic radiation within the predetermined frequency range based on the at least one image;

(c) means for orienting a transceiver based on the determined location of the candidate communications node; and (d) means for initiating the communications link with the network through the candidate communications node. wherein the electromagnetic radiation emitted from the candidate communications node includes timing information.

65. The apparatus of claim 64 wherein the timing information indicates availability of the candidate communications node for a communications link.

66. The apparatus of claim 64 wherein the electromagnetic radiation emitted from the candidate communications node is a reflection off the candidate communications node.

67. The apparatus of claim 66 wherein the electromagnetic radiation emitted from the candidate communications node originates from a source other than the candidate communications node.

68. The apparatus of claim 64 wherein the means for initiating initiates the communications link using the timing information.

69. An apparatus for initiating a communications link with a network comprising: (a) means for capturing at least one image in a first frequency range of electromagnetic radiation, wherein the at least one image includes at least one communications node that is emitting electromagnetic radiation within the first frequency range; (b) means for determining a location of the at least one communications node based on the at least one image;

(c) means for orienting a transceiver based on the determined location; and

(d) means for initiating the communications link with the network through the at least one communications node using a second frequency range of electromagnetic radiation, wherein the second frequency range is different from the first frequency range.

70. The apparatus of claim 69 wherein the first frequency range is within a first band of electromagnetic radiation selected from the group consisting of radio band radiation, microwave band radiation, infrared band radiation, optical band radiation, ultiaviolet band radiation and x-ray band radiation, and wherein the second frequency range is within a second band selected from the group, and wherein the second band is different from the first band.

71. The apparatus of claim 70 wherein the means for initiating initiates the communications link using timing information.

72. The apparatus of claim 71 wherein the timing information is extracted from the at least one image.

73. The apparatus of claim 72 wherein the timing information indicates the availability of the at least one communications node for the communications link.

74. An apparatus for initiating a communications link with a network comprising:

(a) means for capturing at least one image;

(b) means for determining a location of at least one candidate communications node based on the at least one image;

(c) means for orienting a transceiver based on the determined location of the at least one candidate communications node;

(d) means for receiving authentication information from the at least one candidate communications node; and

(e) means for initiating the communications link with the network through the at least one candidate communications node based on the authentication information.

75. The apparatus of claim 74 wherein the authentication information is received in response to a signal transmitted to the at least one candidate communications node.

76. The apparatus of claim 75 wherein the received authentication information is extiacted from the at least one image.

77. The apparatus of claim 76 further comprising

(f) means for receiving timing information from the at least one candidate communications node.

78. The apparatus of claim 77 wherein the means for initiating initiates the communications link using the timing information.

79. The apparatus of claim 78 wherein the timing information indicates availability of the at least one communications node for linking.

80. A computer-readable medium having stored thereon instructions which when executed by a processor, cause the processor to perform a method comprising:

(a) capturing at least one image;

(c) orienting a transceiver based on the determined location of the at least one candidate communications node; and

(d) initiating a communications link with the network through the at least one candidate communications node.

81. The computer-readable medium of claim 80 wherein the step of determining the location of the at least one candidate communications node is carried out using an automatic target recognition technique.

82. Tlie computer-readable medium of claim 80 wherein the predetermined signature includes authentication information identifying the communications node.

83. The computer-readable medium of claim 82 wherein the authentication information is encrypted.

84. The computer-readable medium of claim 82 wherein the authentication information is carried on reflected electromagnetic radiation from the at least one candidate communications node and is captured in the at least one image.

85. The computer-readable medium of claim 84 wherein the reflected electromagnetic radiation is generated by directing a laser source at an active reflection system on the at least one candidate communications node.

86. The computer-readable medium of claim 80 wherein the step of initiating the communications link is carried out using timing information included in the predetermined signature.

87. The computer-readable medium of claim 86 wherein the timing information indicates availability of the communications node for linking.

88. The computer-readable medium of claim 80 wherein the step of initiating the communications link is carried out using electromagnetic radiation within a first frequency range and wherein the at least one image is captured using at least one detector that is sensitive to electromagnetic radiation within a second frequency range.

89. The computer-readable medium of claim 88 wherein the first frequency range is different from the second frequency range.

90. The computer-readable medium of claim 88 wherein the first frequency range is within a first band of electromagnetic radiation selected from the group consisting of radio band radiation, microwave band radiation, infrared band radiation, optical band radiation, ultraviolet band radiation and x-ray band radiation, and wherein the second frequency range is within a second band selected from the group, and wherein the second band is different from the first band.

91. A computer-readable medium having stored thereon instructions which when executed by a processor, cause the processor to perform a method comprising:

(a) capturing at least one image using an element that is responsive to electiomagnetic radiation within a predetermined frequency range; (b) determining a location of a candidate communications node that is emitting electiomagnetic radiation within the predetermined frequency range based on the at least one image; (c) orienting a transceiver based on the determined location of the candidate communications node; and

(d) initiating a communications link with the network through the candidate communications node. wherein the electromagnetic radiation emitted from the candidate communications node includes timing information.

92. The computer-readable medium of claim 91 wherein the step of determining the location of the candidate communications node is carried out using an automatic target recognition technique.

93. The computer-readable medium of claim 91 wherein the timing information indicates availability of the candidate communications node for a communications link.

94. The computer-readable medium of claim 91 wherein the electromagnetic radiation emitted from the candidate communications node is a reflection off the candidate communications node.

95. The computer-readable medium of claim 93 wherein the electromagnetic radiation emitted from the candidate communications originates from a source other than the candidate communications node.

96. The computer-readable medium of claim 93 wherein the reflection is generated by directing a laser source at an active reflection system on the candidate communications node.

97. The computer-readable medium of claim 91 wherein the timing information is encrypted.

98. The computer-readable medium of claim 91 wherein the step of initiating the communications link is carried out using the timing information.

99. A computer-readable medium having stored thereon instructions which when executed by a processor, cause the processor to perform a method comprising:

(a) capturing at least one image in a first frequency range of electromagnetic radiation, wherein the at least one image includes at least one communications node that is emitting electromagnetic radiation within the first frequency range; (b) based on the at least one image, determining a location of the at least one communications node;

(c) orienting a transceiver based on the determined location; and

(d) initiating a communications link with the network through the at least one communications node using a second frequency range of electromagnetic radiation, wherein the second frequency range is different from the first frequency range.

100. The computer-readable medium of claim 99 wherein the step of determining the location of the at least one candidate communications node is carried out using an automatic target recognition technique.

101. The computer-readable medium of claim 99 wherein the first frequency range is within a first band of electromagnetic radiation selected from the group consisting of radio band radiation, microwave band radiation, infrared band radiation, optical band radiation, ultiaviolet band radiation and x-ray band radiation, and wherein the second frequency range is within a second band selected from the group, and wherein the second band is different from the first band.

102. The computer-readable medium of claim 99 wherein the step of initiating the communications link is carried out using timing information.

103. The computer-readable medium of claim 102 wherein the timing infonnation is extracted from the at least one image.

104. The computer-readable medium of claim 103 wherein the timing information indicates the availability of the at least one communications node for the communications link.

105. The computer-readable medium of claim 99 wherein the emitted electromagnetic radiation is a reflection off the at least one communications node.

106. The computer-readable medium of claim 105 wherein the emitted electromagnetic radiation is from a source other than the at least one communications node.