Method for optical wireless beam alignment in short range narrow beam P2P systems

Abstract

An apparatus (301) comprising: an optical transceiver (307) configured to perform bidirectional optical wireless data communication with a remote apparatus (302); two auxiliary beacon transmitters (305, 306) configured to transmit optical wireless beacon signals having the same amount of optical power for assisting a beam alignment process in the remote device (302); two auxiliary four-quadrant photodetectors (303, 304) configured to detect an optical wireless beacon signal from a remote device (302); wherein the optical transceiver (307), the two auxiliary beacon transmitters (305, 306) and the two auxiliary four-quadrant photodetectors (303, 304) are all mounted on the same surface of the device (301), and the two auxiliary beacon transmitters (305, 306) and the two auxiliary four-quadrant photodetectors (303, 304) are symmetrically placed on both sides of the optical transceiver (307), respectively. The apparatus (301) further comprises a controller configured to derive a control signal for controlling the actuator based on the optical wireless beacon signals detected by the two auxiliary four-quadrant photodetectors (303, 304); and an actuator configured to adjust the position of the surface based on a control signal derived by the controller to align the device (301) with a remote device (302) for optical wireless data communication.

Description

Technical Field

[0001] The present invention relates to the field of optical wireless communications, such as Li-Fi communications. More particularly, various devices, systems, and methods related to secure optical wireless communications systems are disclosed herein. Background Art

[0002] To enable a growing number of electronic devices (such as laptops, tablets, and smartphones) to connect wirelessly to the internet, wireless communications are facing unprecedented demands for data rates and link quality, and given the emerging digital revolution associated with the Internet of Things (IoT), these demands continue to grow year by year. Radio frequency technologies (such as Wi-Fi) have limited spectrum capacity and are unable to meet this revolution. Meanwhile, light-fidelity (Li-Fi) is attracting increasing attention due to its inherent security enhancements and its ability to support higher data rates across the available bandwidth of the visible, ultraviolet (UV), and infrared (IR) spectrums. Furthermore, compared to Wi-Fi, Li-Fi is directional and shielded by light-blocking materials, making it possible to deploy a larger number of access points in densely populated areas by spatially reusing the same bandwidth. These key advantages over wireless RF communications make Li-Fi a promising and secure solution for alleviating the pressure on the crowded radio spectrum for IoT applications and indoor wireless access. Other potential benefits of Li-Fi include guaranteed bandwidth for specific users and the ability to operate securely in areas otherwise susceptible to electromagnetic interference. Therefore, Li-Fi is a highly promising technology for enabling the next generation of immersive connectivity.

[0003] To achieve high data throughput in short-range point-to-point optical links, narrow-beam transmitter sources and small, low-capacitance optical receivers are used. Due to the narrow beam characteristics, precise alignment between the transmitter and receiver is essential. For non-static systems, this can be addressed using different types of electromechanical actuators and beam tracking methods.

[0004] A low-cost and compact approach to beam tracking can be implemented using an additional low-frequency beacon transmitter. The system operates normally when there is a long separation distance between the optical transmitter and the optical receiver. For short distances, since the high-speed optical transceiver is physically separated from the low-frequency beacon-based tracking system, deviations in tracking can be significant due to near-field transmission characteristics. To address this issue, the unit can be calibrated to compensate for the deviation for a specific communication distance d. However, this calibration will only work for systems operating at a fixed communication distance and will not work for fully dynamic systems. Summary of the Invention

[0005] The present invention aims to solve the misalignment problem in high-speed narrow-beam optical communication systems when using auxiliary beacon transmitters for beam tracking and alignment. Due to the near-field characteristics, when the distance between two communicating units is short (such as less than 1m or even in the cm range), the offset between the auxiliary beacon transmitter and the high-speed data transceiver in each unit introduces alignment errors, which can degrade the performance of the optical communication link.

[0006] In view of the foregoing, the present disclosure is directed to methods, apparatuses, and systems for providing an effective beam alignment solution in a point-to-point narrow-beam optical wireless communication system. More particularly, the present invention is achieved by an optical wireless communication system as claimed in claim 1, an apparatus as claimed in claim 8, and a method for an apparatus as claimed in claim 14.

[0007] According to a first aspect of the present invention, an optical wireless communication system is provided. The optical wireless communication system comprises:

[0008] A first device comprising:

[0009] - an optical transmitter configured to transmit an optical wireless data signal to a remote second device;

[0010] - two auxiliary beacon transmitters configured to transmit optical wireless beacon signals having approximately the same amount of optical power for assisting in a beam alignment process in the second device; wherein the optical transmitter and the two auxiliary beacon transmitters are mounted on a first surface of the first device, with the two auxiliary beacon transmitters symmetrically placed on either side of the optical transmitter;

[0011] A second device comprising:

[0012] - an optical receiver configured to receive an optical wireless data signal from the first device;

[0013] - two auxiliary four-quadrant photodetectors configured to detect the optical wireless beacon signal from the first device; wherein the optical receiver and the two auxiliary four-quadrant photodetectors are mounted on the second surface of the second device, with the two four-quadrant photodetectors symmetrically placed on either side of the optical receiver;

[0014] - a controller configured to derive a control signal for controlling the actuator based on the optical wireless beacon signal detected by the two auxiliary four-quadrant photodetectors; and

[0015] - an actuator configured to adjust the position of the surface on which the optical receiver and the two auxiliary four-quadrant photodetectors are mounted based on a control signal derived from the controller to align the second device with the first device for optical wireless data communication.

[0016] In order to solve the above-mentioned problem, instead of including a single auxiliary beacon transmitter and a single auxiliary four-quadrant photodiode receiver in the device, two identical auxiliary beacon transmitters are deployed at the transmitting unit (first device) and two auxiliary four-quadrant photodiode receivers are deployed at the receiving unit (second device) to align the two communication units and also fully compensate for the offset caused by the physical spacing between the auxiliary beacon transmitter and the optical transmitter and the physical spacing between the auxiliary four-quadrant photodiode receiver and the optical receiver.

[0017] A control signal is derived based on the beacon signals detected by the two auxiliary four-quadrant photodetectors, respectively, and then used to control an actuator to adjust the position of the second unit for precise beam alignment.

[0018] Optical wireless communication can be performed in the visible, ultraviolet (UV) and infrared (IR) light spectrum. Therefore, optical wireless communication can also be called Li-Fi communication or visible light communication (VLC).

[0019] Each optical transmitter or emitter includes at least a light source for optical data transmission. The light source can be one of a light emitting diode (LED), a laser diode, a vertical cavity surface emitting laser (VCSEL), or an edge emitting laser diode (EELD). Preferably, the optical transmitter includes at least one of an LED and a VCSEL, and each auxiliary beacon transmitter includes an LED.

[0020] Optical transmitters used for high-speed data communications preferably include narrow-beam light sources. The beam angle, or beam width, is the aperture angle from which most of the power is radiated. For example, the half-power beam width is the angle between the half-power (-3dB) points of the main lobe of the radiation pattern. Beam angle or beam width is typically expressed in degrees relative to the horizontal plane. A beam angle of 10 degrees or less is generally considered narrow.

[0021] The optical receiver includes at least one photodiode. A photodiode may also be referred to as a light detector, a photodetector, or a photoelectric sensor, and may be a PIN diode, an avalanche photodiode (APD), or a photomultiplier tube.

[0022] It is necessary to place two auxiliary beacon transmitters symmetrically on either side of the optical transmitter and two auxiliary four-quadrant photodetectors symmetrically on either side of the optical receiver. Different arrangements are possible.

[0023] Advantageously, the first surface has a first axis parallel to the horizontal plane and a second axis perpendicular to the first axis, and the second surface has a third axis parallel to the horizontal plane and a fourth axis perpendicular to the third axis;

[0024] wherein the optical wireless communication system is arranged such that

[0025] - two auxiliary beacon transmitters and an optical transmitter are placed along a first axis of a first surface, and two auxiliary four-quadrant photodetectors and an optical receiver are placed along a fourth axis of a second surface, or

[0026] - two auxiliary beacon transmitters and an optical transmitter are placed along a second axis of the first surface, and two auxiliary four-quadrant photodetectors and an optical receiver are placed along a third axis of the second surface, or

[0027] - two auxiliary beacon transmitters and an optical transmitter are placed along a first axis of a first surface, and two auxiliary four-quadrant photodetectors and an optical receiver are placed along a third axis of a second surface, or

[0028] - Two auxiliary beacon transmitters and an optical transmitter are placed along the second axis of the first surface, and two auxiliary four-quadrant photodetectors and an optical receiver are placed along the fourth axis of the second surface.

[0029] Preferably, the control signal is derived based on a comparison between four signals, each signal representing the sum of the optical wireless beacon signals detected in a corresponding quadrant of two auxiliary four-quadrant photodetectors.

[0030] Advantageously, the control signal is used to control the actuator to adjust the position of the second surface along the third axis and / or the fourth axis, or to rotate the second surface around the third axis and / or the fourth axis.

[0031] Thus, by adjusting the position of the second surface in two axes via roll and / or pitch, the second device may be aligned with the first device for optical data communication.

[0032] In one example, the first device further includes a local calibration loop to calibrate the optical power transmitted by the two auxiliary beacon transmitters.

[0033] Although it is important to keep the two auxiliary transmitters emitting approximately the same amount of optical power, this requirement may not always be met due to the sorting and aging of light sources (such as LEDs or lasers). Therefore, it is beneficial to deploy a local calibration loop to calibrate the optical power emitted by the two auxiliary beacon transmitters, and then this requirement can be guaranteed.

[0034] Advantageously, the local calibration loop comprises two photodiodes configured to detect leakage optical powers of the two auxiliary beacon transmitters, respectively, to estimate actual transmission signal strengths of the individual auxiliary beacon transmitters.

[0035] In this preferred setup, an additional photodiode is placed close to each auxiliary beacon transmitter to detect the leakage optical power of the corresponding auxiliary beacon transmitter and then estimate the actual transmission signal strength of the auxiliary beacon transmitter. Thus, a local optical feedback loop is deployed to compensate for the output power difference between the two auxiliary beacon transmitters due to sorting and aging, and more precise output power control of the two auxiliary beacon transmitters can be achieved.

[0036] In a preferred arrangement, the first device and the second device are configured to perform bidirectional optical wireless data communication, wherein the optical transmitter of the first device and the optical receiver of the second device are both optical transceivers, and the first device and the second device further comprise all other modules of each other.

[0037] In order to perform bidirectional high-speed optical wireless data communications, it is beneficial that the two telecommunication units are identical so that the beam alignment process can be performed by both sides.

[0038] According to a second aspect of the present invention, a device is provided. The device comprises:

[0039] - an optical transceiver configured to perform bidirectional optical wireless data communications with a remote device;

[0040] - two auxiliary beacon transmitters configured to transmit optical wireless beacon signals having the same amount of optical power for assisting a beam alignment process in a remote device;

[0041] - two auxiliary four-quadrant photodetectors configured to detect optical wireless beacon signals from a remote device;

[0042] wherein the optical transceiver, the two auxiliary beacon transmitters and the two auxiliary four-quadrant photodetectors are all mounted on the same surface of the device, and the two auxiliary beacon transmitters and the two auxiliary four-quadrant photodetectors are symmetrically placed on both sides of the optical transceiver;

[0043] The device also includes:

[0044] - a controller configured to derive a control signal for controlling the actuator based on the optical wireless beacon signal detected by the two auxiliary four-quadrant photodetectors; and

[0045] - an actuator configured to adjust the position of the surface based on a control signal derived by the controller to align the device with a remote device for optical wireless data communication.

[0046] Thus, the device includes all the key components for performing narrow beam alignment and bidirectional data communication. Preferably, the optical wireless transceiver or high-speed data transceiver includes a narrow beam transmitter and a receiver. Two auxiliary beacon transmitters are placed around the high-speed transceiver to transmit beacon signals with approximately the same amount of output power. The beacon signals can be transmitted at a lower frequency and a lower data rate as compared to the optical data communication performed by the optical wireless transceiver. Two auxiliary four-quadrant optical receivers are also placed around the high-speed data transceiver to detect beacons from a remote communication partner for beam alignment. Control signals derived by a controller based on the beacon signals detected by the two auxiliary four-quadrant optical receivers are used to control actuators, preferably on two axes (roll and pitch), to align the device towards the remote communication partner.

[0047] Advantageously, the surface has a first axis parallel to the horizontal plane and a second axis perpendicular to the first axis;

[0048] wherein the apparatus is arranged such that the optical transceiver is placed at the intersection of the first axis and the second axis, and

[0049] - two auxiliary beacon transmitters placed along a first axis and two auxiliary four-quadrant photodetectors placed along a second axis, or

[0050] - Two auxiliary beacon transmitters are placed along the second axis, and two auxiliary four-quadrant photodetectors are placed along the first axis.

[0051] Advantageously, the control signal is derived based on a comparison between four signals, each signal representing the sum of the optical wireless beacon signals detected in a corresponding quadrant of two auxiliary four-quadrant photodetectors.

[0052] Preferably, the control signal is used to control an actuator to adjust the position of the surface along the first axis and / or the second axis.

[0053] In one example, the apparatus further includes a local calibration loop to calibrate the optical power transmitted by the two auxiliary beacon transmitters.

[0054] Advantageously, the local calibration loop comprises two photodiodes configured to detect leakage optical powers of the two auxiliary beacon transmitters, respectively, to estimate the actual transmission signal strength of the individual auxiliary beacon transmitters.

[0055] According to a third aspect of the present invention, a method of an apparatus is provided. A method of an apparatus for performing optical wireless communication with a remote apparatus, the apparatus comprising an optical transceiver, two auxiliary beacon transmitters, and two auxiliary four-quadrant photodetectors mounted on the same surface of the apparatus, wherein the two auxiliary beacon transmitters and the two auxiliary four-quadrant photodetectors are symmetrically placed on either side of the optical transceiver, respectively;

[0056] The method comprises the following steps of the apparatus:

[0057] - transmitting an optical wireless beacon signal at approximately the same amount of optical power by two auxiliary beacon transmitters for assisting the beam alignment process in the remote device;

[0058] - Detection of optical wireless beacon signals from remote devices via two auxiliary four-quadrant photodetectors;

[0059] - deriving a control signal based on an optical wireless beacon signal detected by two auxiliary four-quadrant photodetectors; and

[0060] - adjusting the position of the surface based on the control signal to align the device with a remote device for optical wireless data communication; and

[0061] -Perform bidirectional optical wireless data communication with a remote device. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] In the drawings, similar reference numerals are used throughout the different Figure 1 Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention.

[0063] Figure 1 Figure shows an example of a beam tracking setup according to the prior art;

[0064] Figure 2 FIGURE 1 shows another example of a beam tracking arrangement according to the prior art;

[0065] Figure 3 A block diagram of an optical wireless communication system according to the present invention is shown;

[0066] Figure 4 Figure shows an example of a beam alignment arrangement according to the present invention;

[0067] Figure 5 An example of an implementation of a control loop in a device is shown;

[0068] Figure 6 The figure shows the situation when two optical communication units are aligned;

[0069] Figure 7 An example implementation of a local calibration loop for calibrating the optical power transmitted by an auxiliary beacon transmitter is shown; and

[0070] Figure 8 A flow chart showing a method performed by the apparatus according to the present invention is shown. DETAILED DESCRIPTION

[0071] The embodiments set forth below represent information to enable those skilled in the art to practice the embodiments. After reading the following description in light of the accompanying drawings, those skilled in the art will understand the concepts of the present disclosure and will recognize applications of these concepts not specifically set forth herein. It should be understood that these concepts and applications fall within the scope of the present disclosure.

[0072] To achieve high data throughput in short-range, point-to-point optical wireless communications, a narrow-beam transmitter source and a small, low-capacitance optical receiver are typically used. Due to the narrow beam characteristics, precise alignment between the transmitter and receiver is essential. For non-static systems, this requires different types of electromechanical actuators and beam tracking methods.

[0073] Figure 1 The figure shows an example of a beam tracking setup according to the prior art. In this example, a low-cost and compact method for beam tracking can be implemented using an additional low-frequency beacon transmitter 001, which is received by a four-quadrant photodiode receiver 003 with an imaging lens in the opposing unit. Depending on the orientation toward the receiver, the transmitter source will produce different signal levels in each quadrant of receiver 002. By operating on the received signal strength of the four sectors, the xy axis error vector can be calculated and fed to the actuator to correct the position of the receiving unit in pitch and roll rotation. The same is true for the opposing unit.

[0074] Such a system generally operates normally if there is a long separation distance between the two communicating units. However, for short separation distances (such as below 1 m or even in the cm range), since the high-speed transceiver is physically separated from the low-frequency beacon-based tracking system, deviations in tracking can be significant due to near-field transmission characteristics.

[0075] Figure 2The figure shows another example of a beam tracking setup according to the prior art, in which two symmetrical point-to-point units 203 and 204 are separated by a distance d. The circle in the middle of unit 203 represents a high-speed optical transceiver 205. A four-quadrant photodiode receiver or auxiliary tracking receiver 201 and an auxiliary beacon transmitter 202 are placed around the high-speed optical transceiver 205, separated by distances a and b, respectively. The shorter the distance d between the units, the greater the impact of the separation distances a and b on the beam alignment accuracy of the high-speed transceivers. Misaligned transceivers will also be affected by unit rotation (yaw) about the z-axis.

[0076] In order to solve Figure 2 The problem with the setup is shown in , the unit can be calibrated to compensate for this deviation for a specific distance d. However, calibration will only work for systems operating only at fixed standoff distances, and will not work for fully dynamic systems.

[0077] The proposed solution discloses the following key contributions to improving alignment accuracy:

[0078] - Deploy two identical auxiliary beacon transmitters and two 4-quadrant photodiode receivers to compensate for offsets in the xy axis.

[0079] - Create an internal optical feedback mechanism in each unit’s beacon transmitter to automatically compensate for optical power differences due to LED / laser sorting and aging, thus creating two identical beacon transmitters to ensure accurate detection.

[0080] Figure 3 A block diagram of an optical wireless communication system 100 according to the present invention is shown. The optical wireless communication system 100 includes a first device 110 and a second device 120.

[0081] As a basic setup, the first device 110 includes an optical transmitter 111 and two auxiliary beacon transmitters 115, 116. The optical transmitter 111 is configured to transmit an optical wireless data signal to a remote second device 120. The two auxiliary beacon transmitters 115, 116 are configured to transmit optical wireless beacon signals having the same amount of optical power for assisting the beam alignment process in the second device 120. The optical transmitter 111 and the two auxiliary beacon transmitters 115, 116 are mounted on a first surface of the first device 110, with the two auxiliary beacon transmitters 115, 116 symmetrically placed on either side of the optical transmitter 111.

[0082] As a basic configuration, the second device (120) includes an optical receiver 122, two auxiliary four-quadrant photodetectors 123, 124, a controller 125, and an actuator 126. The optical receiver 122 is configured to receive an optical wireless data signal from the first device 110. The two auxiliary four-quadrant photodetectors 123, 124 are configured to detect an optical wireless beacon signal from the first device 110. The optical receiver 122 and the two auxiliary four-quadrant photodetectors 123, 124 are mounted on a second surface of the second device 120, with the two four-quadrant photodetectors symmetrically placed on either side of the optical receiver 122. The controller 125 is configured to derive a control signal for controlling the actuator 126 based on the optical wireless beacon signal detected by the two auxiliary four-quadrant photodetectors 123, 124. The actuator 126 is configured to adjust the position of the surface on which the optical receiver 122 and the two auxiliary four-quadrant photodetectors 123, 124 are mounted based on control signals derived from the controller 125 to align the second device 120 with the first device 110 for optical wireless data communication.

[0083] Figure 4 The figure shows an example of a beam alignment setup according to the present invention. In this setup, two devices or optical wireless units 301, 302 are placed opposite each other. The main components of the first unit or device 301 are shown. A high-speed optical transceiver 307 is placed in the center of the plate or surface of the device 301. Auxiliary beacon transmitters 305, 306 are placed next to the optical transceiver 307 at an equal distance b=b' from the optical transceiver 307, while two auxiliary four-quadrant receivers 303, 304 are placed next to the optical transceiver 307 at an equal distance a=a' from the optical transceiver 307. Mechanical actuators (not shown in the figure) will move each complete unit 301, 302 independently on the xy axis (roll / pitch) based on the received signals from the opposing unit 302 tracked in the two auxiliary four-quadrant receivers 303, 304.

[0084] The key components of device 301 are:

[0085] - an optical wireless high-speed transceiver 307 comprising a narrow beam transmitter and receiver;

[0086] - Two auxiliary beacon transmitters 305, 306, which are placed around the high-speed transceiver 307 and transmit low-frequency beacon signals with the same amount of output power;

[0087] - an optical compensation feedback mechanism for auxiliary transmitters, which consists of a photodiode placed next to each transmitter;

[0088] - Two auxiliary four-quadrant optical receivers 303, 304 placed around the high-speed transceiver 307 to detect beacons from the opposing unit 302 for beam alignment;

[0089] - Mechanical actuators on two axes (roll and pitch) for aligning the optical transceiver 307 towards the opposing unit 302 .

[0090] Figure 5 An example implementation of the control loop in devices 301 and 302 is shown. As illustrated in this implementation, the signals received on corresponding quadrants of the two auxiliary four-quadrant optical receivers are summed. This, along with the use of two auxiliary beacon transmitters in the opposing unit 302 to generate the same beacon, compensates for tracking errors caused by the physical separation between the auxiliary beacon transmitters / auxiliary four-quadrant optical receivers and the high-speed optical transceiver.

[0091] The sum of the signals from the two four-quadrant optical receivers generates four signals that are fed to an analog-to-digital converter (ADC) in the controller 401 of the device 301. The controller 401 processes these signals to generate an error vector and creates a closed-loop control with the mechanical actuator 402. When the error falls below a certain threshold or approaches zero with a predefined tolerance, the actuator stops and the two units 301, 302 are aligned.

[0092] Figure 6 The figure shows the situation when two optical communication units 501, 505 are aligned. For simplicity, only the high-speed optical transceiver 504 and the auxiliary beacon transmitters 502, 503 are shown in the first unit 501, and only the high-speed optical transceiver 506 and the auxiliary four-quadrant receivers 507, 508 are shown in the second unit 505. Since the auxiliary beacon transmitters 502, 503 of the first unit 501 and the auxiliary four-quadrant receivers 507, 508 of the second unit 505 are aligned on the x-axis, after operating on the measurement signals of the four-quadrant sector, the spot image will produce a zero point on the x-axis obtained from the two auxiliary receivers. For the y-axis, due to the spacing between the transmitters 502, 503, an offset (+A) will be produced on the total output of the first auxiliary receiver 507, and an equal opposite offset (-A) will be produced on the second auxiliary receiver 508. The resulting sum of the two vectors will be (0,0), which indicates that the system is aligned. Although in Figure 5 In , the signals from each individual sector of each four-quadrant PD are summed in analog fashion, but the total output is processed digitally to generate the xy vector and error. Figure 6 In order to better illustrate the concept, it is represented as the xy vector of each four-quadrant PD and then summed.

[0093] It's necessary to ensure that both auxiliary transmitters emit the same amount of optical power, which may not always be satisfactory due to LED / laser binning and aging. This problem can be solved by adding an additional photodiode next to the two auxiliary transmitters. This will add an additional optical loop to ensure approximately the same amount of transmitted optical power. This photodiode, placed on the board near the transmitter lens, will pick up enough leaked optical power to detect the transmitted signal strength.

[0094] Figure 7 An example implementation of a local calibration loop for calibrating the optical power emitted by auxiliary beacon transmitters is shown. An auxiliary beacon signal is generated by 604, amplified by a current driver 601, and emitted by an LED / laser 602. A low-pass filter 605 forms a current feedback path. A photodiode 603 detects the emitted signal, which is fed back through a high-pass filter 606 forming optical feedback. When the signals obtained by the photodiode 603 and from the optical feedback path 606 are equal (or within a predefined tolerance level) in both auxiliary beacon transmitters, any changes in the emitted optical power of either transmitter will be corrected by the optical feedback, thereby adjusting the current in the amplifier.

[0095] Figure 8 A flow chart of a method 800 performed by an apparatus 301 according to the present invention is shown. A method 800 of an apparatus 301 for performing optical wireless communication with a remote apparatus 302 is provided, wherein the apparatus 301 includes an optical transceiver, two auxiliary beacon transmitters 305, 306, and two auxiliary four-quadrant photodetectors 303, 304 mounted on the same surface of the apparatus 301, wherein the two auxiliary beacon transmitters 305, 306 and the two auxiliary four-quadrant photodetectors 303, 304 are symmetrically placed on either side of the optical transceiver, respectively; the method 800 includes the following steps of the apparatus 301:

[0096] In step S801 , optical wireless beacon signals having the same amount of optical power are transmitted by two auxiliary beacon transmitters 305 , 306 for assisting the beam alignment process in the remote device 302 ;

[0097] - In step S802, the optical wireless beacon signal from the remote device 302 is detected by two auxiliary four-quadrant photodetectors 303, 304;

[0098] - in step S803 , deriving a control signal based on the optical wireless beacon signal detected by the two auxiliary four-quadrant photodetectors 303 , 304 ; and

[0099] - in step S804, adjusting the position of the surface based on the control signal to align the device 301 with the remote device 302 for optical wireless data communication; and

[0100] - In step S805 , bidirectional optical wireless data communication with the remote device 302 is performed.

[0101] The method according to the present invention can be implemented on a computer as a computer-implemented method, or in dedicated hardware, or in a combination of both.

[0102] The executable code of the method according to the present invention may be stored on a computer / machine-readable storage device. Examples of computer / machine-readable storage devices include non-volatile storage devices, optical storage media / devices, solid-state media, integrated circuits, servers, etc. Preferably, the computer program product comprises non-transitory program code means stored on a computer-readable medium for performing the method according to the present invention when the program product is executed on a computer.

[0103] Methods, systems, and computer-readable media (transitory and non-transitory) may also be provided for implementing selected aspects of the above-described embodiments.

Claims

1. An optical wireless communication system (100), comprising: A first device (110) comprising: - an optical transmitter (111) configured to transmit an optical wireless data signal to a remote second device (120); - two auxiliary beacon transmitters (115, 116) configured to transmit optical wireless beacon signals having approximately the same amount of optical power for assisting a beam alignment process in the second device (120); wherein the optical transmitter (111) and the two auxiliary beacon transmitters (115, 116) are mounted on a first surface of the first device (110), with the two auxiliary beacon transmitters (115, 116) being symmetrically placed on either side of the optical transmitter (111); A second device (120) comprising: - an optical receiver (122) configured to receive an optical wireless data signal from the first device (110); - two auxiliary four-quadrant photodetectors (123, 124) configured to detect an optical wireless beacon signal from the first device (110); wherein the optical receiver (122) and the two auxiliary four-quadrant photodetectors (123, 124) are mounted on a second surface of the second device (120), with the two four-quadrant photodetectors symmetrically placed on either side of the optical receiver (122); - a controller configured to derive a control signal for controlling the actuator based on the optical wireless beacon signal detected by the two auxiliary four-quadrant photodetectors (123, 124); and - the actuator being configured to adjust the position of a surface on which an optical receiver (122) and two auxiliary four-quadrant photodetectors (123, 124) are mounted based on a control signal derived from a controller to align the second device (120) with the first device (110) for optical wireless data communication.

2. The optical wireless communication system (100) according to claim 1, wherein the first surface has a first axis parallel to a horizontal plane and a second axis perpendicular to the first axis, and the second surface has a third axis parallel to the horizontal plane and a fourth axis perpendicular to the third axis; wherein the optical wireless communication system (100) is arranged such that - two auxiliary beacon transmitters (115, 116) and an optical transmitter (111) are positioned along a first axis of the first surface, and two auxiliary four-quadrant photodetectors (123, 124) and an optical receiver (122) are positioned along a fourth axis of the second surface, or - two auxiliary beacon transmitters (115, 116) and an optical transmitter (111) are positioned along a second axis of the first surface, and two auxiliary four-quadrant photodetectors (123, 124) and an optical receiver (122) are positioned along a third axis of the second surface, or - two auxiliary beacon transmitters (115, 116) and an optical transmitter (111) are positioned along a first axis of the first surface, and two auxiliary four-quadrant photodetectors (123, 124) and an optical receiver (122) are positioned along a third axis of the second surface, or - Two auxiliary beacon transmitters (115, 116) and an optical transmitter (111) are placed along a second axis of the first surface, and two auxiliary four-quadrant photodetectors (123, 124) and an optical receiver (122) are placed along a fourth axis of the second surface.

3. The optical wireless communication system (100) according to claim 1 or 2, wherein the control signal is derived based on a comparison between four signals, each signal representing the sum of the optical wireless beacon signals detected in a corresponding quadrant of two auxiliary four-quadrant photodetectors (123, 124).

4. An optical wireless communication system (100) according to any one of the preceding claims, wherein the control signal is used to control the actuator to adjust the position of the second surface along the third axis and / or the fourth axis, or to rotate the second surface around the third axis and / or the fourth axis.

5. The optical wireless communication system (100) according to any one of the preceding claims, wherein the first device (110) further comprises a local calibration loop for calibrating the optical power transmitted by the two auxiliary beacon transmitters (115, 116).

6. The optical wireless communication system (100) according to claim 5, wherein the local calibration loop comprises two photodiodes, the two photodiodes being configured to respectively detect the leakage optical power of the two auxiliary beacon transmitters (115, 116) to estimate the actual transmission signal strength of the individual auxiliary beacon transmitters.

7. The optical wireless communication system (100) according to any one of the preceding claims, wherein the first device (110) and the second device (120) are configured to perform bidirectional optical wireless data communication, wherein the optical transmitter (111) of the first device (110) and the optical receiver (122) of the second device (120) are both optical transceivers, and the first device (110) and the second device (120) further include all other modules of each other.

8. A device (301), comprising - an optical transceiver (307) configured to perform bidirectional optical wireless data communication with a remote device (302); - two auxiliary beacon transmitters (305, 306) configured to transmit optical wireless beacon signals having the same amount of optical power for assisting a beam alignment process in a remote device (302); - two auxiliary four-quadrant photodetectors (303, 304) configured to detect an optical wireless beacon signal from a remote device (302); wherein the optical transceiver (307), two auxiliary beacon transmitters (305, 306) and two auxiliary four-quadrant photodetectors (303, 304) are all mounted on the same surface of the device (301), and the two auxiliary beacon transmitters (305, 306) and the two auxiliary four-quadrant photodetectors (303, 304) are symmetrically placed on both sides of the optical transceiver (307); The device (301) further comprises: - a controller configured to derive a control signal for controlling the actuator based on the optical wireless beacon signal detected by the two auxiliary four-quadrant photodetectors (303, 304); and - the actuator being configured to adjust the position of the surface based on a control signal derived from a controller to align the device (301) with a remote device (302) for optical wireless data communication.

9. The apparatus (301) of claim 8, wherein the surface has a first axis parallel to the horizontal plane and a second axis perpendicular to the first axis; wherein the apparatus (301) is arranged such that the optical transceiver (307) is placed at the intersection of the first axis and the second axis, and - two auxiliary beacon transmitters (305, 306) are placed along a first axis and two auxiliary four-quadrant photodetectors (303, 304) are placed along a second axis, or - Two auxiliary beacon transmitters (305, 306) are placed along the second axis, and two auxiliary four-quadrant photodetectors (303, 304) are placed along the first axis.

10. The device (301) according to claim 8 or 9, wherein the control signal is derived based on a comparison between four signals, each signal representing the sum of the optical wireless beacon signals detected in a corresponding quadrant of two auxiliary four-quadrant photodetectors (303, 304).

11. The device (301) according to any one of the preceding claims 8-10, wherein the control signal is used to control the actuator to adjust the position of the surface along a first axis and / or a second axis.

12. The apparatus (301) according to any of the preceding claims 8-11, wherein the apparatus (301) further comprises a local calibration loop for calibrating the optical power transmitted by the two auxiliary beacon transmitters (305, 306).

13. The apparatus (301) according to claim 12, wherein the local calibration loop comprises two photodiodes, the two photodiodes being configured to detect leakage optical power of two auxiliary beacon transmitters (305, 306), respectively, to estimate actual transmission signal strength of the individual auxiliary beacon transmitters.

14. A method (800) for a device (301) for performing optical wireless communication with a remote device (302), the device (301) comprising an optical transceiver (307), two auxiliary beacon transmitters (305, 306), and two auxiliary four-quadrant photodetectors (303, 304) mounted on the same surface of the device (301), wherein the two auxiliary beacon transmitters (305, 306) and the two auxiliary four-quadrant photodetectors (303, 304) are symmetrically placed on both sides of the optical transceiver (307), respectively; The method (800) comprises the following steps of the apparatus (301): - transmitting (S801) an optical wireless beacon signal at approximately the same amount of optical power by two auxiliary beacon transmitters (305, 306) for assisting a beam alignment process in a remote device (302); - detecting (S802) an optical wireless beacon signal from a remote device (302) by two auxiliary four-quadrant photodetectors (303, 304); - deriving (S803) a control signal based on an optical wireless beacon signal detected by two auxiliary four-quadrant photodetectors (303, 304); and - adjusting (S804) the position of the surface based on the control signal to align the device (301) with the remote device (302) for optical wireless data communication; and - performing (S805) bidirectional optical wireless data communication with a remote device (302).

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