Beam control for optical wireless communication systems

Abstract

The invention relates to methods and systems for controlling pencil beams in optical wireless communication systems (OWCs) to shorten search time and enable tracking of moving nodes by using different scanning strategies (e.g., slower and faster steering speed, different beam divergence during steering and / or adding a steering pilot light) for different nodes. It is further proposed to use a search algorithm to control the search process.

Description

[0001] BEAM CONTROL FOR OPTICAL WIRELESS COMMUNICATION SYSTEMS

[0002] FIELD OF THE INVENTION

[0003] The invention relates to the field of communication in optical wireless communication (OWC) networks for use in various different applications for home, office, retail, hospitality and industry.

[0004] BACKGROUND OF THE INVENTION

[0005] The number of Internet-connected mobile devices are increasing rapidly. Among others, video streaming and accessing cloud-based services are user activities that consume high amounts of data capacity. The resulting data traffic is expected to grow exponentially and is mostly generated in indoor environments.

[0006] OWC refers to communication in the form of a signal embedded (e.g., by intensity modulation) in light (including for example visible light or invisible light, such as for example infrared light) emitted by a light source. Depending for example on particular wavelengths used, such techniques may also be referred to as coded light, Light Fidelity (LiFi), visible light communication (VLC) or free-space optical communication (FSO). In this context, visible light may be light that has a wavelength in the range 380nm to 780nm and infrared (IR) light may be light that has a wavelength in the range 780nm to 1.5pm, or even longer. It is appreciated that there may be some overlap between these ranges.

[0007] Based on modulations, information in the coded light can be detected using any suitable light sensor. This can be a dedicated photocell (point detector), an array of photocells possibly with a lens, reflector, diffuser of phosphor converter, or a camera comprising an array of photocells (pixels) and a lens for forming an image on the array. E.g., the light sensor may be a dedicated photocell included in a dongle which plugs into the end point, or the sensor may be a general purpose (visible or infrared light) camera of the end point or an infrared detector initially designed for instance for 3D face recognition. Either way this may enable an application running on the end point to receive data via the light.

[0008] OWC can be done with wide field of view (FoV) or with concentrated beams (e.g., pencil beams). In case of concentrated beams, transceivers on both communication ends need to be properly aligned to allow communication in both directions. Thus, in beamed communication or beam-oriented / beam-steered OWC (e.g., for vehicle-to-vehicle (V2V) communication) resulting technical problems in connection with search (aka acquisition phase) and tracking approaches need to be addressed.

[0009] US9876567B2 relates to a bi-directional Free Space Optical (FSO) communication unit that may be used in a multi-node FSO communication system. The bidirectional FSO unit includes a co-boresighted optical unit such that received and transmitted beams are coincident through a common aperture.

[0010] EP4016876A1 relates to a method for acquiring a bi-directional optical link between distant transceivers.

[0011] SUMMARY OF THE INVENTION

[0012] It is an object of the present invention to provide an optical communication system with search and tracking functions for beam-steered OWC systems.

[0013] This object is achieved by a beam steering system as claimed in claim 1, by an optical network node as claimed in claim 9 or 10, by an optical wireless communication network as claimed in claim 11, and by a method as claimed in claim 12.

[0014] According to a first aspect, a beam steering system is provided for searching or tracking nodes of an OWC system by beam steering, wherein the system comprises: a first node configured to apply a first search or tracking procedure with a first search pattern and a slower scanning speed; and a second node configured to apply a second search or tracking procedure with a second search pattern and a faster scanning speed; wherein the first and second search or tracking procedures are configured to ensure that a scanning operation of the first node remains not moving while a scanning operation of the second node scans a whole scan area towards the first node; wherein a total time necessary for the second node to scan with full coverage a total surface area at the first node is selected to be less than a time duration that a viewing cone of the first node rests directed in a direction that covers a current surface area viewed by the viewing cone.

[0015] According to a second aspect, an optical network node is provided for use in a beam steering system of the first aspect, wherein the network node is configured to apply the first search or tracking procedure with the first search pattern and the slower scanning speed.

[0016] According to a third aspect, an optical network node is provided for use in a beam steering system of the first aspect, wherein the network node is configured to apply the second search or tracking procedure with the second search pattern and the faster scanning speed.

[0017] According to a fourth aspect, an OWC network is provided, which comprises a beam steering system of the first aspect.

[0018] According to a fifth aspect, a method of searching or tracking nodes by beam steering in an OWC system is provided, wherein the method comprises: applying a first search or tracking procedure with a first search pattern and a slower scanning speed at a first node; and applying a second search or tracking procedure with a second search pattern and a faster scanning speed at a second node; wherein the first and second search or tracking procedures are configured to ensure that a scanning operation of the first node remains not moving while a scanning operation of the second node scans a whole scan area towards the first node; wherein a total time necessary for the second node to scan with full coverage a total surface area at the first node is selected to be less than a time duration that a viewing cone of the first node rests directed in a direction that covers a current surface area viewed by the viewing cone.

[0019] Accordingly, to shorten the search time and enable tracking of moving nodes, two or more types of nodes with different scanning strategy for their search or tracking procedures are proposed, wherein a first type of node is configured to apply a faster scanning speed while a second type of node is configured to apply a slower scanning speed.

[0020] Thereby, while setting up an optical wireless data communication link, the duration until transmitter-receiver alignments are achieved can be shortened, particularly when pencil beams are used. As a result, search for pencil beam nodes can be made more predictable with respect to duration and search pattern.

[0021] Additionally, additional use of pilot light may improve tracking of moving nodes, since the coverage area of a pilot light is typically larger than the coverage area of a pencil-beam.

[0022] Additionally, the narrow radiation angle of the pilot light allows for realistic radiated power at long distances, compared to wide radiation angle of the pilot light, that would cover the whole area of interest.

[0023] According to a first option which can be combined with any one of the first to fifth aspects, the first and second search or tracking procedures may be configured to ensure that a scanning operation of the first node remains not moving while a scanning operation of the second node scans a whole scan area towards the first node. The whole scan area at the first node may be understood as the total area that can be covered by the pencil beam during the scanning process by the illuminating node, e.g., an entire emission / radiation coverage area of the second node in a direction towards the first node.

[0024] According to a second option which can be combined with the first option or any one of the first to fifth aspects, a total time necessary for the second node to scan with full coverage a total surface area at the first node is selected to be less than a time duration that a viewing cone of the first node rests directed in a direction that covers a current surface area viewed by the viewing cone. The total surface area at the first node may be understood as the area that can be viewed by the viewing cone during the scanning process by the viewing node. The current surface area may be understood as the area portion that is momentarily viewed by the viewing cone of the viewing node during the scanning process.

[0025] According to a third option which can be combined with the first or second option or any one of the first to fifth aspects, at least one of the first and second nodes is configured to generate a diverging pencil beam to reduce the search time.

[0026] According to a fourth option which can be combined with the third option, the at least one of the first and second nodes may be configured to generate the diverging pencil beam by inserting a lens between a light source and a collimator or by shifting the light source out of a focal point of the collimator.

[0027] According to a fifth option which can be combined with the first or second option or any one of the first to fifth aspects, at least one of the first and second nodes may be configured to add a pilot light beam with diverged beam width to a pencil beam.

[0028] According to a sixth option which can be combined with the fifth option, the at least one of the first and second nodes be configured to add the pilot light beam by adding a beam splitter to which pilot light is supplied by an additional light source placed out of a focal point of a collimator of the pencil beam, or by adding an additional light source placed close to a light source of the pencil beam but out of the focal point of the collimator.

[0029] According to a seventh option which can be combined with the fifth option, the at least one of the first and second nodes may be configured to add the pilot light beam by means of an additional modulation of a light source of the pencil beam, wherein the additional modulation is out of the bandwidth of already existing communication light.

[0030] According to an eighth option which can be combined with the fifth option, the at least one of the first and second nodes may be configured to add the pilot light beam by means of additional modulation by interrupting an existing communication light of a light source. According to a ninth option which can be combined with any one of the first to eighth options or any one of the first to fifth aspects, the first and second search patterns may be meandering patterns.

[0031] It is noted that the above apparatuses may be implemented based on discrete hardware circuitries with discrete hardware components, integrated chips, or arrangements of chip modules, or based on signal processing devices or chips controlled by software routines or programs stored in memories, written on a computer readable media, or downloaded from a network, such as the Internet.

[0032] It shall be understood that the beam steering system of claim 1, the optical node of claim 11 or 12, the OWC network of claim 13, and the method of claim 14 may have similar and / or identical preferred embodiments, in particular, as defined in the dependent claims.

[0033] It shall further be understood that a preferred embodiment of the invention can also be any combination of the dependent claims or above embodiments with the respective independent claim.

[0034] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0035] BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In the following drawings:

[0037] Fig. 1 shows schematically an office scenario of a beam-steered OWC system where search and tracking is required;

[0038] Fig. 2 shows schematically a V2V scenario of a beam-steered OWC system where search and tracking is required;

[0039] Fig. 3 shows schematically a two-node beam-steered OWC system where a first node searches for a second node;

[0040] Fig. 4 shows schematically an exemplary search procedure applied at the first node to find the second node of Fig. 3;

[0041] Fig. 5 shows schematically a two-node beam-steered OWC system where two nodes search for each other;

[0042] Fig. 6 shows schematically a first structural example for implementing a communication node with a steered optical pencil beam;

[0043] Fig. 7 shows schematically a viewing angle of a detector of the first structural example of Fig. 6; Fig. 8 shows schematically a two-node beam-steered OWC system where pencil beams of two nodes search for each other;

[0044] Fig. 9 shows schematically a two-node beam-steered OWC system and associated search procedures by which a first node can search for a second node, according to a first embodiment;

[0045] Fig. 10 shows schematically search patterns and scanning signals with time scale indication, according to the first embodiment;

[0046] Fig. 11 shows schematically search patterns and scanning signals with diverging beam of one node, according to a second embodiment;

[0047] Fig. 12 shows schematically a second structural example for implementing a communication node with a steered optical pencil beam and lens-controlled diverging beam option according to the second embodiment;

[0048] Fig. 13 shows schematically a third structural example for implementing a communication node with a steered optical pencil beam and light-source-controlled diverging beam option according to the second embodiment;

[0049] Fig. 14 shows schematically a two-node beam-steered OWC system and associated search pattern and scanning signals for an additional pilot light irradiance, according to a third embodiment;

[0050] Fig. 15 shows schematically a fourth structural example for implementing a communication node with a steered optical pencil beam and additional pilot light source according to the third embodiment;

[0051] Fig. 16 shows schematically a fifth structural example for implementing a communication node with a steered optical pencil beam and additional pilot light source according to the third embodiment; and

[0052] Fig. 17A-17B show flow diagrams of search procedures of a first node and a second node respectively, according to a fourth embodiment.

[0053] DETAILED DESCRIPTION OF EMBODIMENTS

[0054] Various embodiments of the present invention are now described based on a steered-beam OWC system.

[0055] Throughout the following, a luminaire as an access point or node is to be understood as any type of lighting unit or lighting fixture which comprises one or more light sources (including visible or non-visible (infrared (IR) or ultraviolet (UV)) light sources) for illumination and / or communication purposes and optionally other internal and / or external parts necessary for proper operation of the lighting, e.g., to distribute the light, to position and protect the light sources and ballast (where applicable), and to connect the luminaires to a power supply. Luminaires can be of the traditional type, such as a recessed or surfacemounted incandescent, fluorescent or other electric-discharge luminaires.

[0056] A LiFi network, in which various embodiments can be implemented, may comprise multiple access-points (APs), e.g. luminaires of a lighting system, connected via a switch (e.g., an Ethernet switch), whereby each AP may control one or more optical front ends (OFEs) which may comprise transceivers (i.e., combined transmitters (optical emitters) and receivers (light sensors)) for wireless optical communication towards end points (EPs), e.g., mobile user devices. Respective light beams generated by the transceivers and defining coverage areas on the plane(s) of the EPs. Each AP may apply a time-slot schedule for communicating with EP(s) in its coverage area.

[0057] The protocol stack for LiFi communication consists of physical (PHY), media access control (MAC) and upper layers. The PHY layer covers light transceivers and a PHY switch is provided in PHY layer interfaces with an optical service access point (SAP) that connects to the optical medium. The optical medium may be composed of one or multiple optical sources or optical detectors (e.g., laser diodes or photodiodes). There are different modulation schemes used in different PHY layer modes. OOK stands for On Off Keying, VPPM stands for Variable Pulse Position Modulation and CSK stands for Color Shift Keying. The MAC layer takes care of resource management (i.e., allocation of channels, identities (IDs), etc.) as well as entire network management. It thus provides channel access for all types of data and control message transmissions. Upper LiFi layers comprise a network layer and an application layer. The network layer takes care of providing network configuration, network manipulation, message routing etc., while the application layer takes care of providing intended functionality as needed by the VP AN or LiFi device.

[0058] Fig. 1 shows schematically an office scenario of a beam-steered OWC system where search and tracking is required.

[0059] It is noted that - throughout the present disclosure - the structure and / or function of blocks or circuit components with identical reference numbers that have been described before are not described again, unless an additional specific functionality is involved. Moreover, only those structural elements and functions are shown, which are useful to understand the embodiments. Other structural elements and functions are omitted for brevity reasons. The office scenario of Fig. 1 relates to a meeting room situation where a user 10 uses a laptop 11 with an attached first OWC transceiver dongle 12, also known as end device (ED). Two other users also use OWC over their respective second and third transceiver dongles 13, 14. First and second access points (APs) 20, 21 are attached to the ceiling and are in the present case of Fig. 1 even integrated with downlight luminaires. As multiple APs 20, 21 are available, it can make sense to connect the users to different ones of the first and second APs 20,21 in order to reduce the data rates concentrated in (transferred via) each of the two APs 20, 21. The depicted APs 20, 21 are configured to allow for beamed connections. For simplicity reasons, uplink beams from the first to fifth transceiver dongles (EDs) 12-14 to a respective one of the first and second APs 20, 21 are not shown. A first downlink beam 22 generated by the first AP 20 is used to serve (e.g., transfer data to) the first ED 12. A second downlink beam 23 is generated by the second AP 21 to serve the second ED 13 and a fourth downlink beam 24 generated by the same second AP 21 is used to serve the third ED 14.

[0060] This very static application is shown here as an example for indoor use. However also moving objects like vehicles or drones may be connected via directed beams.

[0061] Fig. 2 shows schematically a V2V scenario of a beam-steered OWC system where search and tracking is required.

[0062] The V2V scenario of Fig. 2 corresponds to an on-road situation with a plurality of vehicles 50 to 90 that drive into the same direction. A first vehicle 90 tries to connect via directed beam to a second vehicle 80. The second vehicle 80 has multiple optical frontends (OFEs) 81, 82, 83 of transceivers (endpoints) at multiple positions, which are configured to be directed (aim) into different directions (i.e., directional beam receiving patterns) in order to serve different connections in various directions relative to a driving direction 85.

[0063] Fig. 3 shows schematically a two-node beam-steered OWC system where a first node 200 searches for a second node 100.

[0064] In the system of Fig. 3, the second node 100 is configured to emit a wide optical beam 120 with a wide cone in the direction of the first node 200 and the first node 200 is configured to use the wide optical beam 120 for searching and tracking. At a location of the first node 200 there is a large first surface area 121 irradiated (covered) by the wide optical beam 120 of the second node 100. The first node 200 is configured to search for the second node 100 by scanning (‘looking’ into) the space in the direction of the second node 100. At any moment of time, a small viewing cone (detection cone) 250 of the first node 200 is controlled by the first node 200 to cover (‘see’) a small current first surface 251. By moving itself or its viewing cone 250 (e.g., by a controllable node or node optics steering function) using a predetermined search or scanning pattern, the first node 200 can move (scan) the small first surface 251 over a predetermined total surface area 253 at a location of the second node 100. When the viewing cone 250 of the first node 200 has reached a local surface area 252 in which the second node 100 is located, it will detect (‘see’) the second node 100.

[0065] Fig. 4 shows schematically an exemplary search procedure applied by the first node 200 to detect the second node 100 of Fig. 3.

[0066] The search method of the first node 200 is based on a predetermined meandering scanning pattern applied to the viewing cone 250 over a sequence of local surface areas (1, 2, 3, . . .n) via the current first surface area (i) 251 and the local surface area 252 at the location of the second node 100 to finally cover the total surface area 253 to find the second node 100, as illustrated in Fig. 4.

[0067] Note that many other shapes (e.g., circular or elliptical shapes) and / or paths (e.g., spiral-shaped paths) can be used by the nodes of the embodiments described herein.

[0068] Fig. 5 shows schematically a two-node beam-steered OWC system where two nodes 100, 200 search for each other.

[0069] In addition to the system shown in Fig. 3, the second node 100 of the system shown in Fig. 5 is also searching for the first node 200.

[0070] Furthermore, the first node 200 is configured to also emit a wide optical beam 220 with a wide cone in the direction of the second node 100. At the location of the second node 100, a large second surface area 221 is irradiated (covered) by the wide optical beam 220 of the first node 200.

[0071] Additionally, the second node 100 is configured to search for the first node 200 by controlling a small viewing cone 150 to scan (Took’ into) the space in the direction of the first node 200. At any moment of time, the viewing cone 150 of the second node 100 is controlled by the second node 100 to cover (‘see’) a small current second surface area 151. By moving itself or its viewing cone 150 (e.g., by a controllable node or node optics steering function) using a predetermined search or scanning pattern, the second node 100 can move (scan) its small current second surface area 151 over a predetermined total surface area 153 at a location of the first node 200. When the viewing cone 150 of the second node 100 has reached a local surface area 152 at the location of the first node 200, it will detect (‘see’) the first node 200. Please note that due to the wide angle of the cones of the wide optical beams 220 and 120, each of the first and second nodes 200, 100 is able to see the respective other node at all times.

[0072] Fig. 6 shows schematically a first structural example for implementing a communication node with a steered optical pencil beam.

[0073] Pencil-shaped optical beams or pencil beams can be generated and controlled as shown in Fig. 6. A light source 10 is configured to emit a light beam 11 that is collimated by a collimator (e.g., collimator lens) 20 after having passed a beam splitter 32. When the collimator 20 is implemented as a collimator lens and the light source 10 is configured to be arranged in the focal point of the collimator lens, an output beam 12 that leaves the collimator 20 has non-diverging parallel rays with a predetermined diameter 22, so that it may be called pencil beam.

[0074] In order to implement a detection function with the above-mentioned viewing cone, the beam splitter 32 and a detector 30 (photo detector or the like) with a predetermined size 31 of its detection area are introduced, so that incoming light rays 33 are focused by the collimator 20 on the detection area of the detector 30 in order to generate a detection signal. To achieve this, the detection area of the detector 30 is placed at a focal distance 21 of the collimator lens to be arranged in the focal point of the collimator lens.

[0075] Fig. 7 shows schematically a viewing angle of the detector 30 of the first structural example of Fig. 6.

[0076] The viewing angle 35 of the viewing cone of the detector 30 is determined by the angle between outer rays of the incoming light rays 33, that impinge on the edge of the detection area of the detector 30, and the central axis of the collimator 20. These outer rays are determined by the size of the detection area of the detector 30 and the focal distance 21 of the collimator 20, as shown in Fig. 7.

[0077] Fig. 8 shows schematically a two-node beam-steered OWC system where pencil beams (scanning beams) of two nodes search for each other.

[0078] The system of Fig. 8 comprises a second node 100 configured to emit a second pencil beam 120 that illuminates a small current second illumination surface area 121 at the side of a first node 200, and a first node 200 configured to emit a first pencil beam 220 that illuminates a small current first illumination surface area 221 at the side of the second node 100. Furthermore, there is a detection or viewing cone 150 of the second node 100 that covers a current first surface area 151 at the location of the first node 200. On the other side, the first node 200 has a detection or viewing cone 250 that covers a current second surface area 251 at the location of the second node 100.

[0079] As a result, the first and second nodes 100, 200 of Fig. 8 do not detect (‘see’) each other. They can see each other only when the second pencil beam 120 of the second node 100 is directed exactly to the location of the first node 200 and when the first pencil beam 220 of the first node 200 is directed exactly to the location of the second node 100. If both nodes are searching for the respective other node, it can take a long time until this condition is met and they ‘see’ each other.

[0080] To shorten the search time and enable tracking of moving nodes, it is proposed to use two or more different types of the nodes with different search or scanning strategies. As an example, one node applies a first search pattern with a faster scanning speed and the other node applies a second search pattern with a slower scanning speed.

[0081] Thereby, search duration and patterns of the pencil beam nodes become more predictable.

[0082] The different search or scanning strategies may be implemented by using different search or scanning algorithms (e.g., in software implementation) for different types of nodes, as explained below in connection with examples shown in Figs. 17A and 17B.

[0083] Fig. 9 shows schematically a two-node beam-steered OWC system and associated search procedures by which a first node can search for a second node, according to a first embodiment.

[0084] According to the first embodiment, the first and second nodes 200, 100 are configured to apply two different scanning speeds for their search procedures.

[0085] When the first node 200 searches for the second node 100, the second node 100 is visible to the first node 200 only when the second pencil beam 120 of the second node 100 is directed in a way that its illuminated second illumination surface area 121 covers exactly the location of the first node 200. This is one necessary condition illustrated at the upper half of Fig. 9.

[0086] On the other hand, if the viewing cone 150 of the detector of the first node 200 is at the moment of the above condition directed elsewhere in the space, like illustrated in upper half of Fig. 9, the first node 200 will still not detect the second node 100 (simply because it is looking elsewhere in space), since the viewing cone 150 is looking into the current second surface area 251 while the second node 100 can only be ‘seen’ when the viewing cone 150 is directed to the local surface area 252 of the second node 100 in the total surface area 253. To be certain that the first node 200 will be able to detect the second node 100 at all, the second node 100 must apply a scanning pattern of the pencil beam 120 that will cover a total surface area 122 at the first node 200. This is illustrated in the bottom part of Fig. 9, where the total surface area 122 (i.e., the total emitting coverage of the illumination surface area 121 of the pencil beam 120 of the second node 100) with exemplary search pattern 123 of the pencil beam 120 with higher scanning speed and smaller distance of the meandering scanning paths is shown in the right portion, and the total surface area 253 (i.e., total receiving coverage of the first node 200) with current surface area 251, local surface area 252 of the second node 100 and search pattern with lower scanning speed and larger distance of the meandering scanning paths of the viewing cone 150 is shown in the left portion.

[0087] As already mentioned, the search patterns shown in Fig. 9 are examples of many possible search patterns. What is essential is that both search patterns cover the search areas, for example the search pattern 123 of the pencil beam 120 covers the total surface area 122.

[0088] Fig. 10 shows schematically search patterns and scanning signals with time scale indication, according to the first embodiment.

[0089] As previously mentioned, the scanning pattern 123 of the second node 100 is configured to illuminate all locations within the total surface area (radiated coverage area) 122 at the first node 200 by the illumination surface area 121 of the pencil beam 120 to guarantee that the second node 100 can be visible to the first node 200 at some point in time during the search procedure.

[0090] Assuming for example a scanning pattern 123 of the pencil beam 120 of the second node 100 (as shown in the upper right diagram of Fig. 10) and assigning two coordinates x (horizontal direction) and y (vertical direction) to the total surface area 122, the change of the x and y coordinates of the illumination surface area 121 over time (t) can be presented in respective time diagrams for the x-coordinate and the y-coordinate, as shown in the lower right portion of Fig. 10.

[0091] As shown in Fig. 10, the time-dependent change of the x-coordinate of the illumination surface area 121 corresponds to a periodic triangular waveform, as the illumination surface area 121 of the pencil beam 120 successively moves back and forth over the whole horizontal width of the total surface area 122. Furthermore, the time-dependent change of the y-coordinate of the illumination area 121 corresponds to a stepped sawtooth waveform or slope with duration T100, as the illumination surface area 121 of the pencil beam 120 moves stepwise from the upper end to the lower end of the total surface area 122, wherein the duration of each step corresponds to the duration of one complete forward or backward move of the illumination surface area 121 along the whole horizontal width of the total surface area 122 (i.e., upward or downward slope of the triangular waveform of the x- coordinate).

[0092] Similarly, as shown in the left portion of Fig. 10, the time-dependent change of the x-coordinate of the current surface area 251 of the viewing cone 250 of the first node 200 corresponds to a periodic stepped triangular waveform with step duration T200i, as the current surface area 251 of the viewing cone 250 successively moves stepwise back and forth over the whole horizontal width of the total surface area 253 at the second node 100. Furthermore, the time-dependent change of the y-coordinate of the current surface area 251 of the viewing cone 250 corresponds to a stepped sawtooth waveform or slope with duration T200, as the current surface area 251 of the viewing cone 250 moves stepwise from the upper end to the lower end of the total surface area 253, wherein the duration of each step corresponds to the duration of one complete forward or backward move of the current surface area 251 along the whole horizontal width of the total surface area 253 (i.e., upward or downward slope of the stepped triangular waveform of the x-coordinate).

[0093] According to embodiments, in order to minimize the searching time, the total time necessary for the second node 100 to scan with full coverage the total surface area 122 at the first node 200, i.e., the duration T100 of the stepped sawtooth of the y-coordinate, is selected to be less than the horizontal step duration T200i which is the time that the viewing cone 250 of the first node 200 rests directed in a direction that covers the current surface area 251 (i.e., T100<T200i).

[0094] In this way, during the step duration T200i, when the viewing cone 250 of the first node 200 is directed to the local surface area 252, within which the second node 100 is located, the second node 100 will certainly illuminate with its pencil beam 120 the first node 200.

[0095] In other embodiments, the first node 200 may be configured to scan at a higher speed than the second node 100. As long as the searching procedures are configured to ensure that the scanning operation of the slower-scanning node remains not moving while the faster- scanning node scans the whole scan area, this is feasible. This means that within one scan over the entire area, one node will see the other node at least once.

[0096] Fig. 11 shows schematically search patterns and scanning signals with diverging beam of one node, according to a second embodiment. According to the second embodiment, the second node 100 is configured to control its pencil beam 120 to diverge during the search (i.e., increase the size of the illuminating surface area 121), which reduces the scan time T100, due to the pencil beam’s larger area coverage, as shown in the lower right portion of Fig. 11. Thus, less horizontal backward and forward moves are required until the total surface area 122 at the first node 200 has been completely covered by the pencil beam 120.

[0097] The beam diverging process may be done once before or at the start of the scanning pattern 123 or during the scanning pattern to adaptively control the scan time T100.

[0098] Fig. 12 shows schematically a second structural example for implementing a communication node (e.g., the second node 100) with a steered optical pencil beam (e.g., pencil beam 120) and lens-controlled diverging beam option according to the second embodiment.

[0099] According to the second structural example, the second node 100 is configured to control a divergence (beam cross-section size) of its pencil beam 120 before or during the search procedure by defocusing the pencil beam 120. As shown in Fig. 12, this can be achieved by inserting a lens 25 (or switching between two different lenses) in the optical path between the light source 10 and the collimator 20 (e.g., between the light source 10 and the beam splitter 32) via a controllable actuator element. In the second structural example of Fig. 12, the lens 25 moves to an insertion or active location 26, so that the second node 100 emits a diverging beam before or during the search procedure.

[0100] Fig. 13 shows schematically a third structural example for implementing a communication node (e.g., the second node 100) with a steered optical pencil beam (e.g., pencil beam 120) and light-source-controlled diverging beam option according to the second embodiment.

[0101] In the third structural example, the second node 100 is configured to generate a diverging pencil beam 120 before or during the search procedure by defocusing the pencil beam 120 by moving the light source 10. As shown in Fig. 13, the light source 10 is moved (e.g., via a controllable magnet, piezoelectric or capacitive actuator element) to a second location 13 (that differs from the focal point of the collimator lens) to generate a diverging beam before or during the search procedure.

[0102] Fig. 14 shows schematically a two-node beam-steered OWC system and associated search pattern and scanning signals for an additional pilot light irradiance, according to a third embodiment. In the first and second embodiments, the duration of a random search of the first and nodes 200, 100 is proportional to the square of the number of distinctive positions of the nodes. On the other side, when an additional pilot light is used, it’s intensity drops with the square of the distance between the nodes. Hence, at long distances such pilot lights require high emission powers at adequate beam angles.

[0103] However, for the moving nodes applications like V2V (as explained in connection with Fig. 2), beam tracking efficiency can be improved substantially when pilot lights are used.

[0104] In examples, a pilot light with narrow or middle-angle beam can be used as quadrant detector or other type of position detector, wherein the viewing angle 35 (as explained in connection with Fig. 7) determines the scanning speed. As additional option, a pulsed pilot light may be used to reduce emission power or increase the covered distance.

[0105] According to the third embodiment, the second node 100 is configured to add to its pencil beam 120 a pilot light beam 131, e.g., by means of an additional light source. The pilot light beam 131 may be diverging, thereby reducing the scan time T100.

[0106] As shown in the upper part of Fig. 14, the cone of the pilot light beam 131 covers a pilot illumination surface area 132 in the total surface area 122 at the first node 200.

[0107] As shown in the lower part of Fig. 14, the pilot illumination surface area 132 enhances the illumination surface area 121 of the pencil beam 120 to thereby reduce the scanning duration T100.

[0108] Fig. 15 shows schematically a fourth structural example for implementing a communication node with a steered optical pencil beam and additional pilot light source according to the third embodiment.

[0109] According to the fourth structural example, a pilot light beam 131 can be added to the pencil beam 120 by means of an additional light source 40 and an additional beam splitter 24. The pilot light beam 131 may be diverging as the rays 42 illustrate, thereby reducing the scan time T100, when for example the light source 40 is located out of a focal point 41 of the lens of the collimator 20. If these two beams (i.e., pencil beam and pilot light beam) would be projected on a surface far from the second node 100, they would look like patterns of the illumination surface area 121 of the pencil beam 120 and the pilot illumination surface area 132 of the diverging pilot light beam 131 shown in the left portion of Fig. 15.

[0110] Fig. 16 shows schematically a fifth structural example for implementing a communication node with a steered optical pencil beam and additional pilot light source according to the third embodiment. According to the fifth structural example, the second node 100 can be configured to add to its pencil beam 120 a pilot light beam 131 by means of an additional light source 40, located close to the pencil beam light source 10, as illustrated in Fig. 16. Thereby, the pilot light beam 131 may be diverging and the center of the pilot light beam 131 may be off with respect to the center of pencil beam 120, as the rays 42 illustrate in Fig. 16, as well as the illumination surface area 121 of the pencil beam 120 and the non-concentric pilot illumination area 132 of the pilot light 131 on an imaginary surface far from the second node 100, shown in the left portion of Fig. 16.

[0111] In a further embodiment, the second node 100 may be configured to add to its pencil beam 120 a pilot light beam 131 by means of an additional out-of-band modulation of the light source 10 which is out of the bandwidth of already existing communication light. The additional modulation allows independent processing of the pilot light beam 131 and / or coping with strong stray light during search, that may work as a noise.

[0112] In an alternative embodiment, the second node 100 may be configured to add to its pencil beam 120 an additional pilot light beam 131 by means of additional modulation by interrupting the existing communication light of the light source 10.

[0113] Figs. 17A and 17B show flow diagrams of search procedures of the first node 200 and the second node 100, according to a fourth embodiment.

[0114] The search procedures may be implemented as a software routine that is used to control a processor or controller of the respective node to implement the search procedures by controlling actuator elements of a mechanical tracking, steering or scanning function of the whole node or optics within the node.

[0115] The flow diagram of Fig. 17A relates to a search procedure of the first node 200 with slower (SL) scanning speed, e.g., as shown in the left portion of Fig. 10.

[0116] After the start (ST) of the search procedure, step 301 (MIS) initiates a move of the viewing cone 150 of the first node 200 by one step (e.g., from surface area 1 to surface area 2 in the left upper diagram of Fig. 10). Then, a timer function for counting the step duration T200i is started in step 302. It is then checked in step 303 whether time out (TO) of the timer function has been reached. If so, the procedure jumps back to step 301 and the viewing cone 150 is moved to the next position.

[0117] If timeout has not been reached in step 303, the procedure continues with step 304 where it is checked whether a quadrant photo detector (QPD) or other type of detector has detected a pencil beam (e.g., the pencil beam 120 of the second node 100). If not, the procedure jumps back to step 303 and checks for a time out of the timer function. If a pencil beam has been detected, the procedure continues with step 305 where the viewing cone 150 is moved towards the center of the QPD. In subsequent step 306, the timer function for counting the step duration T200i is started again. Then, in step 307, it is again checked whether time out (TO) of the timer function has been reached. If so, the procedure jumps back to step 301 and the viewing cone 150 is moved to the next horizontal position.

[0118] If timeout has not been reached in step 307, the procedure continues with step 308 where it is again checked whether the QPD or other type of detector has detected a pencil beam (e.g., the pencil beam 120 of the second node 100). If not, the procedure jumps back to step 307 and checks for a time out of the timer function.

[0119] If a pencil beam has been detected in step 308, the procedure jumps back to step 305 where the viewing cone 150 is moved towards the center of the QPD.

[0120] The flow diagram of Fig. 17B relates to a search procedure of the second node 100 with faster (FA) scanning speed, e.g., as shown in the right portion of Fig. 10.

[0121] After the start (ST) of the search procedure, step 401 (MIS) initiates a move of the pencil beam 120 of the second node 200 by one step (e.g., one part of the horizontal width of the total surface area 122 that just overlaps with the previous location of the pencil beam 120; note that all steps taken together should create a full coverage of the total surface area 122). Then, it is checked in step 402 whether a quadrant photo detector (QPD) or other type of detector has detected a pencil beam (e.g., the pencil beam 220 of the first node 200). If not, the procedure jumps back to step 401 and the pencil beam 120 is moved by one step again.

[0122] If a pencil beam has been detected in step 402, the procedure continues with step 403 where the viewing cone 150 is moved towards the center of the QPD. Then, the procedure continues with step 404 where it is again checked whether the QPD or other type of detector has detected a pencil beam (e.g., the pencil beam 220 of the first node 200). If not, the procedure jumps back to step 401 and the pencil beam 120 is moved by one step again.

[0123] If a pencil beam has been detected in step 404, the procedure jumps back to step 403 where the pencil beam 120 is moved again towards the center of the QPD.

[0124] To summarize, methods and systems for controlling pencil beams in optical wireless communication systems (OWCs) to shorten search time and enable tracking of moving nodes by using different scanning strategies (e.g., slower and faster steering speed, different beam divergence during steering and / or adding a steering pilot light) for different nodes have been described. It has further been proposed to use a search algorithm to control the search process.

[0125] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments. The proposed search procedures and node structures can be implemented in different ways with different scanning patterns, shapes and / or paths and different structural elements that fulfil the same functions as described in the embodiments. Furthermore, two or more of the above embodiments may be combined to obtain further embodiments.

[0126] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single processor or other unit may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. The foregoing description details certain embodiments of the invention. It will be appreciated, however, that no matter how detailed the foregoing appears in the text, the invention may be practiced in many ways, and is therefore not limited to the embodiments disclosed. It should be noted that the use of particular terminology when describing certain features or aspects of the invention should not be taken to imply that the terminology is being re-defined herein to be restricted to include any specific characteristics of the features or aspects of the invention with which that terminology is associated.

[0127] A single unit or device may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0128] The described operations can be implemented as program code means of a computer program and / or as dedicated hardware of beam-steering nodes. The computer program may be stored and / or distributed on a suitable medium, such as an optical storage medium or a solid-state medium, supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

Claims

CLAIMS:

1. A beam steering system for searching or tracking nodes of an optical wireless communication, OWC, system by beam steering, the system comprising: a first node (200) configured to apply a first search or tracking procedure with a first search pattern and a slower scanning speed; and a second node (100) configured to apply a second search or tracking procedure with a second search pattern (123) and a faster scanning speed; wherein the first and second search or tracking procedures are configured to ensure that a scanning operation of the first node (200) remains not moving while a scanning operation of the second node (100) scans a whole scan area towards the first node (200); wherein a total time (T100) necessary for the second node (100) to scan with full coverage a total surface area (122) at the first node (200) is selected to be less than a time duration (T200i) that a viewing cone (250) of the first node (200) rests directed in a direction that covers a current surface area (251) viewed by the viewing cone (250).

2. The system of claim 1, wherein at least one of the first and second nodes (200, 100) is configured to generate a diverging pencil beam (120) to reduce the search time.

3. The system of claim 2, wherein the at least one of the first and second nodes (200, 100) is configured to generate the diverging pencil beam (120) by inserting a lens between a light source (10) and a collimator (20) or by shifting the light source (10) out of a focal point of the collimator (20).

4. The system of claim 1, wherein at least one of the first and second nodes (200, 100) is configured to add a pilot light beam (131) with diverged beam width to a pencil beam (120).

5. The system of claim 4, wherein the at least one of the first and second nodes (200, 100) is configured to add the pilot light beam (131) by adding a beam splitter (24) to which pilot light is supplied by an additional light source (40) placed out of a focal point (41)of a collimator (20) of the pencil beam (120), or by adding an additional light source (40) placed close to a light source (10) of the pencil beam (120) but out of the focal point of the collimator (20).

6. The system of claim 4, wherein the at least one of the first and second nodes (200, 100) is configured to add the pilot light beam (131) by means of an additional modulation of a light source (10) of the pencil beam (120), and wherein the additional modulation is out of the bandwidth of already existing communication light.

7. The system of claim 4, wherein the at least one of the first and second nodes (200, 100) is configured to add the pilot light beam (131) by means of additional modulation by interrupting an existing communication light of a light source (10).

8. The system of any one of the preceding claims, wherein the first and second search patterns are meandering patterns.

9. A network node (200) for use in a beam steering system according to any one of claims 1 to 8, wherein the network node (200) is configured to apply the first search or tracking procedure with the first search pattern and the slower scanning speed.

10. A network node (100) for use in a beam steering system according to any one of claims 1 to 8, wherein the network node (100) is configured to apply the second search or tracking procedure with the second search pattern (123) and the faster scanning speed.

11. An optical wireless communication, OWC, network comprising a beam steering system as claimed in any one of claims 1 to 8.

12. A method of searching or tracking nodes by beam steering in an optical wireless communication, OWC, system, the method comprising: applying a first search or tracking procedure with a first search pattern and a slower scanning speed at a first node (200); and applying a second search or tracking procedure with a second search pattern (123) and a faster scanning speed at a second node (100);wherein the first and second search or tracking procedures are configured to ensure that a scanning operation of the first node (200) remains not moving while a scanning operation of the second node (100) scans a whole scan area towards the first node (200); wherein a total time (T100) necessary for the second node (100) to scan with full coverage a total surface area (122) at the first node (200) is selected to be less than a time duration (T200i) that a viewing cone (250) of the first node (200) rests directed in a direction that covers a current surface area (251) viewed by the viewing cone (250).

13. The method of claim 12, further comprising configuring the first and second search or tracking procedures to ensure that a scanning operation of the first node (200) remains not moving while a scanning operation of the second node (100) scans a whole scan area at the first node (200).

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