Trigger-based optical wireless communication system

Abstract

High-speed optical communications are very attractive for meeting high-throughput applications. At the same time, it is also desirable to reduce the energy waste caused by the idle state of the optical transceiver of the communication system. The present invention discloses that both the access point (1200) and the endpoint device (1100) can operate in at least two different operating states: a normal operating state and a low-power state. The low-power state is the default state, and the normal operating state is enabled only when a valid trigger is detected. In order to establish a high-speed optical link (60), the endpoint device (1100) first sends an optical trigger signal (50) to the access point (1200) in the low-power state. The access point (1200) switches to the normal operating state only when it identifies a valid trigger signal after detecting the optical trigger signal (50).

Description

Technical Field

[0001] The present invention relates to the field of optical wireless systems, such as Li-Fi networks. More particularly, various methods, apparatuses, systems, and computer-readable media related to a trigger-based optical wireless communication system having at least two operating states are disclosed herein. Background Art

[0002] To enable wireless connectivity for a growing number of electronic devices, such as laptops, tablets, and smartphones, wireless communications face unprecedented demands for data rates and link quality, and these demands continue to grow annually given the emerging digital revolution associated with the Internet of Things (IoT). Radio frequency technologies, such as Wi-Fi, have limited spectrum capacity to accommodate 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, potentially enabling the deployment of a larger number of access points in a given area by spatially reusing the same bandwidth. These key advantages over wireless RF communications make Li-Fi a promising solution for alleviating the pressure on the crowded radio spectrum for IoT applications. Additional benefits of Li-Fi include guaranteed bandwidth for specific users and its ability to operate securely in areas susceptible to electromagnetic interference. Therefore, Li-Fi is a highly promising technology for enabling the next generation of immersive connectivity.

[0003] There are several related terms in the field of illumination-based communications. Visible light communication (VLC) transmits data faster than the human eye can perceive via intensity-modulated light sources, such as light-emitting diodes (LEDs) and laser diodes (LDs). VLC is typically used to embed signals in the light emitted by an illumination source, such as an everyday light fixture, such as indoor or outdoor lighting, allowing the illumination from the light fixture to be used as a carrier of information. Thus, the light can include a visible illumination contribution used to illuminate a target environment, such as a room (typically the primary purpose of light), as well as an embedded signal used to provide information to the environment (typically considered a secondary function of light). In this case, the modulation is typically performed at a sufficiently high frequency to be beyond human perception, or at least such that any visible temporary light artifacts (e.g., flicker and / or stroboscopic artifacts) are sufficiently weak and / or at a high enough frequency to be imperceptible or at least tolerable to humans. Consequently, the embedded signal does not affect the primary lighting function; that is, the user perceives only the overall illumination, not the effects of the data modulated into that illumination.

[0004] The IEEE 802.15.7 Visible Light Communication Personal Area Network (VPAN) standard maps intended applications to four topologies: peer-to-peer, star, broadcast, and coordinated. Optical Wireless PAN (OWPAN) is a more general term than VPAN, allowing for communication using non-visible light, such as UV and IR. Li-Fi is generally considered an optical wireless communication (OWC) technology that utilizes a broad spectrum of light to support bidirectional data communication.

[0005] In Li-Fi systems, signals are embedded by modulating the properties of light (typically intensity) according to any of a variety of suitable modulation techniques. For high-speed communications, infrared (IR) is typically used rather than visible light communications. Although ultraviolet and infrared radiation are invisible to the human eye, the techniques for utilizing these spectral regions are similar, although variations can occur as a result of wavelength dependence (such as in the case of the refractive index). In many instances, the use of ultraviolet and / or infrared is advantageous because these frequency ranges are invisible to the human eye and can introduce more flexibility into the system. Of course, ultraviolet quanta have higher energy levels compared to the energy levels of infrared and / or visible light, which in turn can render the use of ultraviolet light undesirable in certain situations.

[0006] Based on the modulation, any suitable light sensor can be used to detect information in the light. For example, the light sensor can be a photodiode. The light sensor can be a dedicated photocell (point detector), an array of photocells possibly with a lens, reflector, diffuser or phosphor converter (for lower speeds), or an array of photocells (pixels) and a lens for forming an image on the array. For example, the light sensor can be a dedicated photocell included in a dongle that is inserted into a user device such as a smartphone, tablet or laptop, or the sensor can be integrated and / or dual-purpose, such as an array of infrared detectors originally designed for 3D facial recognition. Either way, this can enable applications running on the user device to receive data via light.

[0007] WO2019111018A1 relates to an optical wireless communication (OWC) receiver, comprising: a photodetector device configured to receive light and generate a detection signal in response to the received light; a receiver circuit configured to receive and process the detection signal to generate a receiver signal; and a wake-up circuit configured to monitor an output from the photodetector device or the receiver circuit for a predetermined frequency or frequency range, and in response to the monitored output indicating that the received light represents an OWC signal, perform a wake-up process to move at least a signal processing circuit from a first, lower power state to a second, higher power state.

[0008] WO2017042593A1 relates to a method for communicating in an optical wireless network, which comprises a first device, a plurality of further devices, and a common communication channel, which can be used by any of the further devices to send data to the first device. Summary of the Invention

[0009] Improving energy efficiency is always desirable, both for economic reasons and as a positive contribution to a green environment. However, solutions that provide enhanced energy efficiency often also result in reduced system performance. For example, one approach to reducing access point energy consumption can be achieved through duty cycling, which means that the access point is periodically turned on and off. The disadvantage of this approach is that the average latency for endpoint devices to connect to the access point increases accordingly. Therefore, the inventors have recognized that a trade-off needs to be made between energy efficiency and system performance when designing optical wireless communication systems.

[0010] In view of the foregoing, the present disclosure is directed to methods, apparatuses, systems, computer programs, and computer-readable media for providing a mechanism for avoiding wasteful energy consumption in an optical wireless communication system. More particularly, the present invention is achieved by the access point method of claim 1, the endpoint device method of claim 8, the access point of claim 10, the endpoint device of claim 11, the optical wireless communication network of claim 12, and the computer program of claim 13.

[0011] Therefore, to improve the energy efficiency of access points and / or endpoint devices used to establish high-speed optical communication links, the access points and / or endpoint devices are configured to operate in at least two operating states. The presence of an endpoint device is required to trigger the access point to switch from a low-power state to a normal operating state, and vice versa. In this way, a balance between energy efficiency and access latency is achieved.

[0012] According to a first aspect of the present invention, a method for operating an access point in an optical wireless communication network is provided. The method comprises the access point: operating in a low-power state to detect a first optical signal from an endpoint device on a first optical channel; generating a trigger signal after detecting the first optical signal; switching from the low-power state to a normal operating state based on the generated trigger signal; operating in the normal operating state to establish a high-speed optical data link with the endpoint device; switching from the normal operating state back to the low-power state when there is no active high-speed optical data link with any endpoint device for a predefined time period; and wherein the access point consumes less power in the low-power state than in the normal operating state and establishes the high-speed optical data link on an optical data channel different from the first optical channel.

[0013] Advantageously, the access point operates in at least two different states: a low-power state and a normal operating state. In the low-power state, the access point cannot support high-speed optical data links, but instead operates primarily in a detection mode to detect the presence of endpoint devices. Instead of using a dedicated presence sensor, such as a PIR sensor or microwave sensor, to detect the motion or presence of a user holding the endpoint device, the presence of the endpoint device is detected upon receiving a first optical signal from the endpoint device. The first optical signal may also include identification information for the endpoint device, allowing the access point to determine whether the endpoint device is a trusted device accessing the optical network.

[0014] Considering different scenarios, where the presence of a user is confirmed but no such endpoint device is present, or where an endpoint device is present but there is no immediate need to establish a high-speed optical data link, the access point may be mistakenly triggered to switch to normal operating mode, resulting in unnecessary energy consumption. In the present invention, the first optical signal is used to submit a clear request from the endpoint device to trigger the access point to switch to normal operating mode.

[0015] The access point enters a normal operating state on an as-needed basis. When there is no active high-speed optical data link with any endpoint device for a predefined period, the access point returns to a low-power state as a default. This predefined period can be preset by the manufacturer, the user, or the device itself. This value can be determined based on the application scenario, performance or user experience requirements, or desired energy savings. Longer predefined periods result in lower efficiency in terms of energy consumption, but also have less impact on data communication performance.

[0016] Advantageously, before generating the trigger signal, the method further comprises the access point negotiating with the endpoint device on the first optical channel the settings of the high-speed optical data link upon detecting the first optical signal; and wherein the step of generating the trigger signal is performed after the settings of the high-speed optical data link are agreed upon between the access point and the endpoint device.

[0017] One option is to immediately identify a valid trigger signal from the detected first optical signal so that the access point can attempt to serve any endpoint device that can send the first optical signal over the first optical channel. Alternatively, the access point and the endpoint device can also use low power and low data rate communication on the first optical channel to exchange signaling information to prepare for the high-speed data link. In a preferred example, the access point and the endpoint device can negotiate the settings for the high-speed optical data link and identify a valid trigger signal only after the settings for the high-speed optical data link are agreed upon between the access point and the endpoint device. The settings can be related to the data rate, bandwidth, data channel index, modulation or coding scheme used for the high-speed optical data link. The settings can also be related to a schedule so that the access point and the endpoint device agree on a delay before establishing the high-speed optical data link. Therefore, the access point may not switch to normal operating mode immediately, but rather switch according to a schedule.

[0018] In a preferred arrangement, the low power state of the access point is achieved by disabling a hardware component or disabling a hardware component and enabling a different hardware component in the access point.

[0019] In one option, the access point disables at least one hardware component when switching from the normal operating state to the low power state. In another option, different hardware components are used in the normal operating state and the low power state. And thus, when switching from the normal operating state to the low power state, a first hardware component or a first group of hardware components associated with the normal operating state is disabled, and a second hardware component or a second group of hardware components associated with the low power state is enabled. In another option, the same set of hardware components is used in both states, and the lower power consumption in the low power state is achieved via different configurations (e.g., lower bias current, lower clock speed, etc.).

[0020] In one example, the first optical signal is an infrared signal.

[0021] Advantageously, the first optical signal is a narrowband infrared signal and therefore, transmitting and receiving such a narrowband signal can be very energy efficient.

[0022] In another example, the method further includes switching, by the access point, between the low power state and the sleep state upon receiving a second trigger signal from another access point; and wherein the access point consumes less power in the sleep state than in the low power state.

[0023] In addition to controlling the power state in response to the presence of a terminal device, an access point can also adjust its power state based on a second trigger signal from another access point. Preferably, to further reduce energy consumption, the access point can switch into or out of a sleep state upon receiving the second trigger signal. In the sleep state, the access point cannot detect the presence of a terminal device and instead relies on another access point to provide a second trigger signal to awaken from the sleep state to a low-power state. Thus, the sleep state is similar to a power-off state, in which the access point responds only to the second trigger signal, and other functions may also be disabled, or preferably are disabled.

[0024] The second trigger signal can be scheduled according to a certain schedule or triggered by an event at another access point. In one example, another access point operating in a low-power state can first send a second trigger signal to the access point to request it to enter a sleep state. Then, upon detecting the presence of an endpoint device, the other access point can send another second trigger signal to wake the access point from its low-power state in the event of a handover of the endpoint device. In this example, the other access point may be located near the room entrance and can therefore obtain presence information earlier.

[0025] Preferably, the access point is a slave access point, and the other access point from which the second trigger signal is received is a master access point.

[0026] Depending on the deployment scenario, a master access point can be connected to more than one slave access point, such as in a daisy-chain configuration. The master access point can also have more advanced presence detection capabilities. In one example, by knowing the potential trajectory of an endpoint device, the master access point can selectively send a second trigger signal to the slave access points.

[0027] In a preferred arrangement, the slave access points are connected to the backbone network via the master access point.

[0028] The master access point may include an interface to the backbone network, such as an Ethernet switch, and all connected slave access points are connected to the backbone network via the same Ethernet switch.

[0029] In another preferred arrangement, the slave access points are powered by the master access point.

[0030] From a system deployment perspective, it can be very convenient for slave access points to be powered by the master access point. Even more advantageously, this setup can be combined with the previous setup, using Power over Ethernet (PoE) technology to provide both data and power over the same twisted-pair Ethernet cable. Thus, the master access point is also configured to operate as a power source equipment (PSE), and the slave access point is configured to operate as a powered device (PD). The PoE standard supports different power levels, and thus the master access point can control power delivery to the slave access point based on its operating state.

[0031] According to a second aspect of the present invention, a method for operating an endpoint device in an optical wireless communication network is provided. A method for operating an endpoint device in an optical wireless communication network, comprising the endpoint device: operating in a low-power state for transmitting a first optical signal on a first optical channel; after transmitting the first optical signal, switching from the low-power state to a normal operating state; operating in the normal operating state for establishing a high-speed optical data link with an access point; switching from the normal operating state to the low-power state when there is no immediate need for the high-speed optical link; and wherein the endpoint device consumes less power in the low-power state than in the normal operating state; and wherein the high-speed optical data link is established on an optical data path different from the first optical channel.

[0032] In another example, when there is no immediate need for a high-speed optical link, the endpoint device may switch from a normal operating state to a low-power state or a sleep state; wherein the endpoint device consumes less power in the sleep state than in the low-power state.

[0033] In order to establish a high-speed optical data link with the access point, for example, when the access point is not in a normal operating state, the endpoint device takes the initiative to send a first optical signal to the access point. Considering that the information to be transmitted in such a wake-up signal is very limited, the first optical signal has a low data rate and a narrow bandwidth and is sent in a low-power state of the endpoint device. The low-power state is the default state of the endpoint device. After sending the first optical signal, the endpoint device then switches to a normal operating state for establishing a high-speed optical data link. When there is no immediate need to execute a high-speed link, the endpoint device switches back to a low-power state or a sleep state to further reduce energy consumption. The decision to switch to a low-power state or a sleep state may depend on an application profile, user preferences, or the battery status of the endpoint device.

[0034] Switching from the sleep state back to the low power state may be triggered by a user command, a predetermined event, or a request from an application, such as a request to send or receive application data over a high-speed optical link.

[0035] Advantageously, after sending the first optical signal and before switching to the normal operating state, the method further includes the endpoint device: negotiating the setting of the high-speed optical data link with the access point on the first optical channel; and determining to switch to the normal operating state after the access point and the endpoint device reach an agreement on the setting of the high-speed optical data link.

[0036] In one example, when the access point and the endpoint device cannot agree on the settings of the high-speed optical data link, the method also includes the endpoint device remaining in a low-power state for sending the second optical signal on the first optical channel; or switching from the low-power state to a sleep state.

[0037] It may happen that the endpoint device needs to establish a high-speed optical data link but has not yet reached an agreement with the access point. For example, due to expected poor channel conditions on the optical data channel, the required data rate cannot be met, which can be derived from the channel quality on the first optical channel. The endpoint device can continue to send additional optical wake-up signals to initiate a new negotiation. Since the endpoint device can also roam in the area, the channel conditions between the endpoint device and the access point may improve in the meantime, or the endpoint device may approach another access point. In this sense, the endpoint device may have a better chance of establishing a high-speed data link.

[0038] According to a third aspect of the present invention, an access point is provided. An access point in an optical wireless communication network, the access point comprising: an optical transceiver, the optical transceiver comprising one or more optical front ends; a power management unit and a controller; and wherein the access point is configured to implement any one of the access point methods of the present invention.

[0039] In a first configuration of the access point, the access point has two dedicated optical front ends, a first optical front end for a narrowband first optical channel and a second optical front end for a wideband optical data channel. The two optical front ends can share the same baseband module or modem. When operating on different channels, different settings of the modem can be applied, resulting in different processing speeds and power consumption levels. A controller is configured to apply different settings to the baseband module depending on the current operating state.

[0040] In a second setup, the access point has two dedicated optical transceivers, each of which includes an optical front-end module and a modem. The first optical transceiver can be a low-power narrowband IR transceiver that performs low-data-rate communications on the first optical channel. The second optical transceiver can be a high-power and high-performance transceiver for data communications. Preferably, the second optical transceiver also includes an LED or vertical-cavity surface-emitting laser (VCSEL) front end.

[0041] In a third setup, the access point may have only a single optical transceiver.Different operating states are achieved via different configuration settings.

[0042] Different settings can be used to balance power efficiency, device form factor, and / or hardware cost.

[0043] As an example, an access point includes: a first optical receiver configured to operate in a low-power state of the access point to detect a first optical signal from an endpoint device on a first optical channel; an optical transceiver configured to operate in a normal operating state of the access point to establish a high-speed optical data link with the endpoint device; a controller configured to determine whether the access point is operating in a low-power state or a normal operating state; and a power management unit configured to control power supply to the optical transceiver based on the determination of the controller; wherein the first optical receiver is further configured to generate a trigger signal after detecting the first optical signal; and the controller is further configured to determine a switch from the low-power state to the normal operating state when the trigger signal is generated; determine a switch from the normal operating state to the low-power state when there is no active high-speed optical data link with any endpoint device within a predefined time period; and wherein the access point consumes less power in the low-power state than in the normal operating state and establishes a high-speed optical data link on an optical data channel different from the first optical channel.

[0044] In this example, a dedicated first optical receiver is used to receive on the first optical channel. Compared to the optical transceiver used for the data link, the first optical receiver has much lower power consumption and low data rate reception capability.

[0045] In another example, an access point includes an optical transceiver configured to operate in a normal operating state of the access point for establishing a high-speed optical data link with an endpoint device; an optical transceiver configured to operate in a low-power state of the access point for detecting a first optical signal from the endpoint device on a first optical channel by disabling a hardware component or disabling a hardware component and enabling different hardware of the optical transceiver; a controller configured to determine whether the access point is operating in the low-power state or the normal operating state; and a power management unit configured to control power supply to the optical transceiver based on the determination of the controller. The optical transceiver is further configured to generate a trigger signal in the low-power state of the access point after detecting the first optical signal; and the controller is further configured to determine a switch from the low-power state to the normal operating state upon generating the trigger signal; the switch from the normal operating state to the low-power state is determined when there is no active high-speed optical data link with any endpoint device for a predefined time period; and wherein the access point consumes less power in the low-power state than in the normal operating state and establishes the high-speed optical data link on an optical data channel different from the first optical channel.

[0046] According to a fourth aspect of the present invention, an endpoint device is provided. An endpoint device in an optical wireless communication network, the endpoint device comprising: an optical transceiver including one or more optical front ends; a power management unit and a controller; and wherein the endpoint device is configured to implement any of the endpoint device methods according to the present invention.

[0047] Similar to access points, endpoint devices can also be implemented using different configurations. Note that endpoint devices may have more stringent requirements for power efficiency, form factor, and / or cost than access points. Therefore, endpoint devices may use different configurations than those used by access points.

[0048] In one example of an endpoint device, the endpoint device includes: a first optical transmitter configured to operate in a low-power state of the endpoint device for transmitting a first optical signal on a first optical channel; an optical transceiver configured to operate in a normal operating state of the endpoint device for establishing a high-speed optical data link with an access point; a controller configured to determine whether the endpoint device is operating in the low-power state or the normal operating state; and a power management unit configured to control power supply to the optical transceiver based on the determination of the controller; wherein the controller is further configured to determine a switch from the low-power state to the normal operating state after the first low-power optical transmitter transmits the first optical signal; and when there is no immediate need for a high-speed optical link, the switch from the normal operating state to the low-power state is determined. The endpoint device consumes less power in the low-power state than in the normal operating state; and wherein the high-speed optical data link is established on an optical data channel different from the first optical channel.

[0049] In another example of an endpoint device, the endpoint device includes: an optical transceiver configured to operate in a normal operating state of the endpoint device for establishing a high-speed optical data link with an access point; the optical transceiver further configured to operate in a low-power state of the endpoint device for transmitting a first optical signal over a first optical channel by disabling a hardware component or disabling a hardware component and enabling different hardware of the optical transceiver; a controller configured to determine whether the endpoint device is operating in the low-power state or the normal operating state; and a power management unit configured to control power supply to the optical transceiver based on the determination of the controller; wherein the controller is further configured to determine a switch from the low-power state to the normal operating state after the first low-power optical transmitter transmits the first optical signal; and the switch from the normal operating state to the low-power state is determined when there is no immediate need for the high-speed optical link. The endpoint device consumes less power in the low-power state than in the normal operating state, and wherein the high-speed optical data link is established over an optical data channel different from the first optical channel.

[0050] According to a fifth aspect of the present invention, there is provided an optical wireless communication network comprising at least one access point according to the present invention and at least one endpoint device according to the present invention.

[0051] The invention may also be embodied in a computer program comprising code means for causing the processing means of the access point to carry out any one of the methods according to the invention when the program is executed by an access point comprising processing means.

[0052] The invention may also be embodied in a computer program comprising code means which, when executed by an endpoint device comprising processing means, causes the processing means of the endpoint device to perform any one of the methods according to the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In the drawings, 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.

[0054] Figure 1 An overview of the OWC network and the backbone networks connected to it is shown;

[0055] Figure 2 Schematic depiction of the basic components of a Li-Fi access point;

[0056] Figure 3 Schematic depiction of the basic components of a Li-Fi access point with multiple optical front ends;

[0057] Figure 4Schematically depicts the basic components of a Li-Fi endpoint;

[0058] Figure 5 Schematically depicts the basic components of an optical front end included in a Li-Fi access point or Li-Fi endpoint;

[0059] Figure 6 A trigger-based Li-Fi system is shown;

[0060] Figure 7 Schematically depicts the basic components of an access point in an optical wireless communication network;

[0061] Figure 8 An embodiment of an access point in an optical wireless communication network is schematically depicted;

[0062] Figure 9 schematically depicts the basic components of an endpoint device in an optical wireless communication network;

[0063] Figure 10 An embodiment of an endpoint device in an optical wireless communication network is schematically depicted;

[0064] Figure 11 A master-slave based Li-Fi system is shown;

[0065] Figure 12 A flow chart illustrating a method for operating an access point in an optical wireless communication network;

[0066] Figure 13 A flow chart illustrating another embodiment of a method for operating an access point in an optical wireless communication network;

[0067] Figure 14 A flow chart illustrating a method for operating an endpoint device in an optical wireless communication network; and

[0068] Figure 15 A flow chart illustrating another embodiment of a method for operating an endpoint device in an optical wireless communication network is shown. DETAILED DESCRIPTION

[0069] We will now describe an optical wireless communication (OWC) network system 100, or more specifically, an optical wireless communication (OWC) network system 100. Figure 1The various embodiments of the present invention are described using the Li-Fi network system shown. For illustrative purposes, the Li-Fi network 100 is connected to the backbone network 20 via an IP router 15 and an Ethernet switch 14, while in actual systems, more routers and switches can be deployed to connect the backbone network to the Li-Fi network. In this example, the connection between the Li-Fi network and the backbone network is called a backbone connection 21. The backbone connection is a stable and high-speed link, which can be a wired connection (such as Ethernet) or a wireless connection based on radio frequency (RF) or millimeter wave. The backbone connection can also be another optical wireless link, which is different from the link performed by the endpoint in the optical multi-cell wireless network. An example of another optical wireless link can be a free space point-to-point optical link.

[0070] Li-Fi system overview and network architecture

[0071] As a wireless communication technology for local area networking, Li-Fi plays a role similar to Wi-Fi, providing connectivity for the last few tens of meters. A Li-Fi network 100 may include multiple optical access points (APs) 120 and network devices or endpoints (EPs) 110. Each endpoint 110 selectively associates and synchronizes with a corresponding one of the access points 120. The Li-Fi AP 120 may be connected to one or more optical front ends or Li-Fi transceivers (TRXs) 121 to provide access to Li-Fi devices or Li-Fi endpoints (EPs) 110. The dotted trapezoids illustrate the field of view (FOV) or coverage of each Li-Fi transceiver 121. Only when an EP 110 is within the coverage area of a Li-Fi AP 120 will it be able to receive downlink communications from that AP 120. By assuming symmetrical uplink and downlink optical communications, a bidirectional optical link can be established under the same conditions. Due to the line-of-sight nature of optical communication links, adjacent access points 120 do not have direct optical links with each other, but endpoints 110 located in the overlapping area of coverage of adjacent access points 120 are able to detect optical signals from both access points.

[0072] In one example, a Li-Fi AP 120 can also operate as a domain master with additional functionality according to G.hn, ITU G.9960, and G.9961 to manage several Li-Fi EPs 110. In one embodiment, handover occurs when an EP roams from one domain to another. In another embodiment, each Li-Fi AP 120 operates as a domain master, managing a separate domain hosting multiple Li-Fi EPs, which can be up to 255. Such Li-Fi APs 120 are typically located on the ceiling. They can, but are not necessarily, collocated with light fixtures, especially when communication is not based on visible light. The main functions of a Li-Fi AP 120 may include advertising the presence of the AP 120 to surrounding Li-Fi EPs 110, registering and deregistering Li-Fi EPs 110, providing media access control (MAC) scheduling between associated Li-Fi EPs 110, collecting interference reports from EPs 110, adjusting local scheduling in response to interference reports, and / or reporting neighbor relations to the Li-Fi controller 13. Some functions of the Li-Fi AP 120 , such as MAC scheduling for interference avoidance, may be implemented by the Li-Fi controller 13 in a centralized manner.

[0073] The Li-Fi EP or Li-Fi device 110 is an end-user modem that facilitates endpoint devices connecting to the Li-Fi network 100. Today, the Li-Fi EP 110 is typically a dedicated entity connected to a laptop or other end device. In the future, the Li-Fi EP 110 may be partially or fully integrated into a smartphone, tablet, computer, remote control, smart TV, display device, storage device, home appliance, or another smart electronic device.

[0074] There may be a Li-Fi controller or central controller 13 connected to multiple access points 120 in the Li-Fi network 100. The Li-Fi controller or central controller 13 is responsible for centrally controlling the Li-Fi system when necessary, such as deriving information about topology and neighbor relationships, and determining the scheduling between different Li-Fi access points (APs) to mitigate interference. Furthermore, the Li-Fi controller 13 can also be used to provide a user interface that allows users or administrators (such as IT managers) to configure schedules between multiple Li-Fi APs, monitor reports from these Li-Fi APs, and / or derive further statistics about system performance. Typically, only one Li-Fi controller 13 is visible to each AP. This is achieved through network configuration such that traffic to and from the Li-Fi controller 13 is isolated within its own network segment via a virtual LAN (VLAN) or the like. Furthermore, protocols such as the Control and Provisioning of Wireless Access Points (CAPWAP) protocol can be used to discover multiple controllers and select a controller with available resources to host / manage access points joining the infrastructure.

[0075] In one exemplary embodiment of the Li-Fi system, a Li-Fi synchronization server 16 is connected to the system, which is responsible for synchronizing (or aligning) the G.vlc media access control (MAC) cycles of different G.vlc domains. This requires aligning some common time slots for detecting neighboring APs 120 and avoiding interference with EPs 110 located in the overlapping area of neighboring APs 120. Due to the line-of-sight nature of optical links, neighboring APs 120 cannot usually directly detect each other's signals. However, if neighboring APs 120 are transmitting simultaneously, EPs 110 located in the overlapping area of two neighboring APs 120 may experience interference. To avoid this situation, it may be necessary to keep neighboring APs 120 synchronized to a common time base and prevent them from transmitting at the same time. A preferred option for network synchronization is to use the Precision Time Protocol (PTP), IEEE 1588v2. PTP provides sub-microsecond accuracy, which is fair enough for MAC alignment of mutual G.vlc domains. To maintain the accuracy of PTP, support from the Ethernet switch is necessary, which should also be a capability of PTP. To maintain PTP accuracy, any element in the Ethernet network must process PTP, so the switches selected for any deployment must support and be configured accordingly to operate in PTP mode.

[0076] It may also happen that the Li-Fi system is to be deployed in a legacy system where PTP is not supported by the existing infrastructure. Therefore, additional measures should be taken to synchronize neighboring APs 120 in a different and possibly suboptimal manner, and a solution should be found for the EP 110 to handle non-ideal synchronization between neighboring APs 120.

[0077] Detailed system description

[0078] Li-Fi AP

[0079] The Li-Fi AP 120 is a key unit for establishing the Li-Fi network 100. In some scenarios, the Li-Fi AP 120 also forms an interface between the existing IT infrastructure and the Li-Fi network 100. Figure 2 A high-level block diagram of the Li-Fi AP 120 is shown in FIG.

[0080] On the one hand, the Li-Fi AP 120 has an interface 124 to the backbone network, which can be a wired connection (Ethernet) or a wireless connection (RF, millimeter wave, or another optical wireless different from the optical wireless being implemented by the Li-Fi AP). And on the other hand, the Li-Fi AP 120 has an optical front end 121 to implement an optical link with one or more Li-Fi APs 110. In addition, in terms of conversion between different modulation schemes and conditioning of analog signals, the Li-Fi AP 120 also performs the function of bidirectional conversion or conversion between data on the backbone network 20 and data on the optical link. Therefore, the Li-Fi AP 120 also includes at least a digital modulator and demodulator component 123 and an analog front end 122. In the transmit path, the analog front end (AFE) 122 may include programmable amplifiers, filters, and drivers to condition and amplify the baseband signal to drive the optical front end. For the receive path, the AFE 122 may include attenuators, low-noise amplifiers, filters, and programmable gain amplifiers to accommodate the received signal for further digital processing.

[0081] The optical front end 121, which includes at least a light source and a light sensor, converts electrical signals into optical signals. In the transmitter chain, the optical front end 121 is used to convert the electrical transmission signal into an output optical signal via the light source. In the receiver chain, the optical front end 121 is used to convert the received optical signal into an output electrical signal via the light sensor for further signal processing. The optical front end 121, also known as the Li-Fi transceiver (TRX), enables:

[0082] Li-Fi transmitter (Tx): converts the electrical signal obtained from the AFE into an optical signal (e.g. to be emitted by an LED), and

[0083] Li-Fi receiver (Rx): converts the received optical signal (e.g. from a photodiode) into an electrical signal for the AFE.

[0084] The Li-Fi AP 120 can be connected to a single Li-Fi TRX 121 or multiple Li-Fi TRXs 121, which allows optical signals to be transmitted on different optical paths. In the case where the Li-Fi AP 120 is connected to multiple Li-Fi TRXs 121, the Li-Fi AP can process them as a single coherent signal or as (partially) independent incoherent signals for establishing a communication link. Figure 3 An example of a Li-Fi AP 120 is shown having multiple Li-Fi TRXs 121. A Li-Fi interface component 125 is employed to separate or combine data sent to or received from the multiple Li-Fi TRXs 121.

[0085] Li-Fi EP

[0086] Figure 4 Shown is a high-level overview of a Li-Fi EP or Li-Fi device 110. Similar to a Li-Fi AP 120, the Li-Fi EP 110 includes at least an optical front end 111, an analog front end 112, a digital modulator / demodulator 113, and an interface 114 to a terminal device or processor.

[0087] The Li-Fi EP 110 can be connected to the end device as a separate entity via a cable, or it can be partially or fully integrated into the end device. For many end devices (such as laptops, smartphones, and remote controls), Ethernet is a recognized interface in the end device's operating system. In addition to or instead of Ethernet, Li-Fi can also be used to provide a communication interface to the end device. To simplify the system integration of the Li-Fi EP or Li-Fi device into the end device's operating system, it is advantageous to use USB Ethernet. Therefore, in one option, the Li-Fi EP or Li-Fi device 110 can be connected to the end device via a standard USB cable or plug. Taking USB Ethernet as an example, the Li-Fi EP 110 can include a USB Ethernet interface 114 and connect to the end device via a USB cable 115. As in the Li-Fi AP 120, the Li-Fi EP 110 can also be connected to one or more client optical TRXs 111. Alternatively, a single optical front end with segmented transmitters / receivers can also be envisioned, where each transceiver / receiver points in a different direction.

[0088] In another example, a different interface 114 may be used to connect the Li-Fi EP to the operating system of the terminal device, and the corresponding interface 114 (USB Ethernet) and / or cable 115 should be replaced accordingly.

[0089] Figure 5 Exemplary components of an optical front end or optical TRX 111, 121 included in or connected to the Li-Fi AP 120 and the Li-Fi EP 110 are provided. The optical TRX 111, 121 includes at least a light source 1211, a light sensor 1212, a driver 1213, and an amplifier 1214. The light source 1211 is used to convert an electrical transmission signal into an output optical signal, which can be a light emitting diode (LED), a laser diode (LD), or a vertical cavity surface emitting laser (VCSEL). The light sensor 1212 is used to convert the received optical signal into an output electrical signal, which can be a pin photodiode, an avalanche photodiode, or another type of light sensor. The driver 1213 is mainly used to adjust the power required by the light source 1211. The amplifier 1214 is mainly used to adjust the signal received by the light sensor 1212 so that the signal is suitable for further processing in the circuit. In one example, amplifier 1214 can be a transimpedance amplifier (TIA), which is a current-to-voltage converter implemented using one or more operational amplifiers. The TIA can be located near the receiving light sensor or photodiode 1212 to amplify the signal with minimal noise.

[0090] Interconnectivity in Li-Fi Systems

[0091] Typically, a Li-Fi AP 120 is deployed on a ceiling. Such an AP 120 must first be powered in order to perform communication activities. Therefore, a connection to the AP 120 provides both power and data. The AP 120 establishes a bidirectional link with the cloud or backbone network 20 via a backbone connection 21 on one side, and on the other side, communicates with one or more associated EPs 110 via optical links. The EPs 110 typically receive power from a terminal device to which they are coupled or integrated, and communicate with the associated AP 120 via optical links.

[0092] Connecting Li-Fi APs to the backbone network

[0093] The Li-Fi AP 120 may adopt different options to connect to the backbone network 20 .

[0094] In one aspect, data and power may be co-delivered to the Li-Fi AP, which may be accomplished via a single power cable with power line communication (PLC) or a single Ethernet cable with Power over Ethernet (PoE).

[0095] PLC uses existing power cables, both for supplying mains power to the equipment and for data communication. Popular PLC communication standards such as or G.hn) utilizes orthogonal frequency division multiplexing (OFDM) technology, which is also widely adopted in Li-Fi systems. Therefore, the physical layer (PHY) of the PLC system and the Li-Fi system may be very similar, such as the modulation method and synchronization method used in the two systems. However, transmission in the optical domain is unipolar, while OFDM typically uses bipolar signals. As a result, some adaptation may be required for transmission in the optical network. A simple solution is to use a DC offset, which does not require demodulation and subsequent remodulation of the OFDM-based PLC signal before optical transmission, or alternatively use a unipolar OFDM modulation technique (such as ACO-OFDM, DCO-OFDM, ADO-OFDM and / or flipped OFDM) for demodulation and subsequent remodulation. Therefore, it may be very convenient for the Li-Fi AP 120, which is typically collocated with a ceiling light fixture, to also obtain a data connection to the backbone network 20 using existing power cables.

[0096] However, it's also recognized that the PLC system's channel is quite noisy, given that the mains power lines can act as antennas, picking up all sorts of unwanted signals that could interfere with the communication signals also present on the mains power lines. Therefore, it's important for Li-Fi over PLC-enabled devices to handle this external interference. Furthermore, the amount of attenuation experienced by communication signals on the mains power lines is unpredictable during manufacturing and can vary throughout the day. Factors affecting this include cable lengths that vary from building to building, power loads that are more or less short-circuited to high frequencies, and being turned on or off, among other factors.

[0097] One known solution to address signal integrity issues introduced by PLC systems is to equip Li-Fi over PLC-enabled devices with a PLC decoder for decoding PLC communication signals received via the mains power line. Impairments to the communication signal are processed digitally. For example, narrowband interference may only cause errors on a single subcarrier of an OFDM modulated signal. Error correction algorithms can be used to correct the reconstructed data. The reconstructed data is then converted back to the analog domain and used to modulate the LED current flowing to at least one LED. This approach can provide a more robust operating device with reduced data loss, although one drawback of this solution is that the device becomes larger, more complex, and more expensive.

[0098] On the other hand, if power can be delivered via Ethernet cables, it may also be convenient for the Li-Fi AP to utilize the existing IT infrastructure to obtain both power and connection to the backbone network 20. Power over Ethernet (PoE) is described in the IEEE802.3af / at standards and is currently being expanded to 4-pair power supply in the IEEE task group P802.3bt. PoE is designed to supply a supply voltage of 40V to 48V from power sourcing equipment (PSE) to powered devices (PDs), alongside data lines for control and communication purposes. PSE devices are also called PoE switches. In a PoE lighting system, PDs can be light sources, user interface devices, and sensors. The PSE is typically powered by a mains power supply, such as according to the IEC / TR 60083 standard. Traditional PoE systems will transport data and power through the network and its endpoints, therefore between the PSE and the PD.

[0099] Thus, data can be received by the control device, for example, via an Ethernet connection using the Ethernet protocol. Data is communicated between devices in a Power over Ethernet system via the Ethernet protocol. Thus, a microchip in the form of an Ethernet controller can be used to establish a communication link between devices, supporting the Media Access Control (MAC) and Physical (PHY) layers of the Open Systems Interconnection model (OSI model).

[0100] The Ethernet connection can be, for example, an optical fiber, an electrical conductor, or a twisted pair cable, such as a Category 3 cable, a Category 4 cable, a Category 5 cable, a Category 5e cable, a Category 6 cable, a Category 6A cable, a Category 7 cable, a Category 7A cable, a Category 8 cable, a Category 8.1 cable, or a Category 8.2 cable. The Ethernet connection can have several pairs of cables, for example 2, 3, 4, or more pairs of cables. The cables can be unshielded or shielded, in particular individually or as a whole shielded. Power and data can be transmitted via the same optical fiber, conductor, or cable of the Ethernet connection, or via different optical fibers, conductors, or cables of the Ethernet connection. In the case of power transmission via optical fiber, the power can be transmitted in the form of photons, which can be received by the solar cell of the data receiving device.

[0101] A data receiving device in a PoE system may include one or more ports. Each port may include one or more pins. The pins may be configured to receive power, data, or both. Additionally or alternatively, the port may also include one or more solar cells for receiving power in the form of photons. Because the port can receive both power and data via an Ethernet connection, some pins may be powered via the Ethernet connection while other pins may be provided with data. Alternatively or additionally, a single pin may be powered and provided with data via the Ethernet connection.

[0102] In another aspect, data and power can be delivered to the Li-Fi AP separately, and the options can be via both a power cable and an Ethernet cable (a wired connection to the backbone network), or a combination of a power cable and a wireless link to the backbone network 20 (either an optical wireless link or a free-space optical link).

[0103] Preferably, the Li-Fi system can be integrated into an existing wireless communication system, such as a Wi-Fi system or a cellular system. Therefore, the Li-Fi AP 120 can be integrated into or directly connected to a Wi-Fi access point or a cellular base station. By converting or translating signals between the Li-Fi AP 120 and the Wi-Fi access point or cellular base station, the existing infrastructure of the Wi-Fi system or cellular system can be used to provide the Li-Fi AP 120 with a connection to the backbone network 20.

[0104] Connecting a Li-Fi EP to a Li-Fi AP

[0105] The Li-Fi EP 110 accesses the Li-Fi system via the Li-Fi AP 120, and the associated Li-Fi AP 120 is generally referred to as the local AP. There are several aspects to consider regarding the connection between the Li-Fi EP 120 and the Li-Fi AP 110:

[0106] - Coverage: A Li-Fi EP may not always be able to see a Li-Fi AP, depending on its location, its orientation, the positioning of the Li-Fi AP, and the size of the transducer / sensor coverage area of the Li-Fi EP.

[0107] - Downlink interference: Li-Fi EPs in the overlapping coverage area of multiple optical downlinks experience interference if these Li-Fi APs transmit simultaneously.

[0108] - Uplink interference: One Li-Fi EP transmits a signal to an associated Li-Fi AP while another Li-Fi EP is transmitting to the same Li-Fi AP, which causes uplink interference at the Li-Fi AP.

[0109] -Handover: Due to the mobility of Li-Fi EPs, handover is required when a Li-Fi EP moves from the coverage area of one Li-Fi AP to a neighboring Li-Fi AP. That is, when a Li-Fi EP (such as connected to or contained in a user device, client device, mobile phone, etc.) moves from a current cell to a neighboring cell, then any active communications must be handed over to the node or access point of the neighboring cell. In order to reduce interference with any ongoing communications or data transfers, handover is intended to be performed as quickly as possible and a preparation period may be included to facilitate this. When there is insufficient time available to prepare and establish a link to the new Li-Fi AP before the link with the existing Li-Fi AP is disconnected, the Li-Fi EP may experience a period in which there is no connection. Given the relatively small size of Li-Fi cells due to the line-of-sight nature of optical links, seamless handover is important to ensure link quality and user experience.

[0110] Basically, the Li-Fi EP 110 can be connected to the Li-Fi AP 120 via a bidirectional optical link or a hybrid downlink and uplink. Note that the downlink here represents the communication link from the Li-Fi AP 120 to the Li-Fi EP 110, and the uplink represents the communication link from the Li-Fi EP 110 to the Li-Fi AP 120. The bidirectional optical link achieves a relatively symmetrical connection between the Li-Fi EP 110 and the Li-Fi AP 120. Therefore, both the downlink and the uplink enjoy the same advantages of Li-Fi communication as described above. However, in some application scenarios (such as for web surfing or video streaming), the link between the Li-Fi AP and the Li-Fi EP can also be a hybrid link, which is a combination of an optical downlink from the Li-Fi AP 120 to the Li-Fi EP 110 and a radio frequency (RF) uplink from the Li-Fi EP 120 to the Li-Fi AP 110. The RF link may be based on a popular short-range wireless communication protocol, such as Wi-Fi, BLE, or Zigbee, or based on a cellular communication protocol, such as 4G or 5G cellular.

[0111] Referring back to the option that the Li-Fi AP 120 can be built via a combination device that supports Li-Fi AP functionality and Wi-Fi access point or cellular base station functionality, this hybrid link can be seamlessly handled by the controller on the Li-Fi AP side. Since the Li-Fi EP 110 is typically connected to or integrated into a terminal device (which can be a smartphone, tablet, computer or other smart device), the terminal device may already have hardware support for the short-range wireless communication protocol or cellular protocol used in the hybrid link. Therefore, this hybrid link can also optimize the use of existing resources of the terminal device and provide a simplified solution for the Li-Fi EP, which only requires a receive path and no transmit path. The cost, power consumption and form factor of the EP 110 can be further reduced in this way. Accordingly, the Li-Fi AP 120 is also simplified by primarily including an optical transmitter to send data to the Li-Fi EP 110 via an optical downlink, while the RF-based uplink from the Li-Fi EP 110 to the AP 120 can be received by optimizing the use of an RF receiver in a combined device or co-located Wi-Fi access point / cellular base station, or via a dedicated RF receiver included in the Li-Fi AP 120 itself.

[0112] Scheduling and interference mitigation in optical multi-cell wireless networks

[0113] When there are multiple Li-Fi APs 120 deployed adjacent to each other, or when there are multiple EPs 110 associated with the same local AP 120 or neighboring APs 120, medium access control (MAC) becomes necessary for interference-free optical communication. Different MAC mechanisms may be employed in optical multi-cell wireless networks, such as time division multiple access (TDMA), frequency division multiple access (FDMA), carrier sense multiple access (CSMA), code division multiple access (CDMA), space division multiple access, or a combination of one or more of the above mechanisms. TDMA is based on a time division multiplexing scheme, in which radio resources are scheduled in the time domain, and different time slots are allocated to different transmitters in a typical cyclically repeating frame structure or MAC cycle. FDMA is based on frequency division multiplexing, in which different frequency bands are allocated to different devices for simultaneous transmission. And in optical communications, FDMA can also evolve into wavelength division multiple access (WDMA) based on wavelength division multiplexing. Another advanced variant of FDMA is orthogonal frequency division multiple access (OFDMA), in which each device can use one or more subcarriers outside the entire frequency band. OFDMA offers greater flexibility in providing different data rates or qualities of service to different users, while at the same time maintaining high resource efficiency despite this diversity. CSMA typically employs a listen-before-talk approach, where a device verifies the presence of any other traffic before transmitting on the shared medium. CSMA is widely used in sparse networks, and further collision avoidance techniques emerge when the node density scales. CDMA is typically built on top of spread spectrum, and a common form is direct sequence CDMA based on direct sequence spread spectrum, where different devices send messages simultaneously using different spreading codes that are orthogonal to each other. Given that the FoV of optical links is typically smaller compared to radio links, spatial division multiple access may also be a very attractive solution here.

[0114] In a TDMA-based multi-cell network with multiple APs 120, adjacent APs 120 may sometimes not have synchronized MAC cycles due to a lack of direct communication. While the duration of a MAC cycle, or superframe, is typically the same for all APs 120 in the network, the start time of a MAC cycle can be different for each AP 120. Note that the start time of a MAC cycle is used by the AP as a local time reference to divide the wireless medium into consecutive time slots. Even when a time slot is allocated exclusively to an AP 120 for communication with an EP 110 in the overlapping area, such MAC cycle offsets between two adjacent APs 120 can cause interference to EPs 110 located in the overlapping coverage area of the two adjacent APs 120. Therefore, it is necessary for the APs 120 to synchronize to a common time base. This common time base can be obtained via a synchronization handshake, a reference clock distributed across the network (such as a synchronous Ethernet clock), a dedicated synchronization server within the network, or derived from a common signal (such as the zero crossing of the mains power). However, due to uncertain delays or interference within the network, there may still be uncertainty in the timing synchronization of the APs relative to the timing reference. The EP 110 located in the overlapping area of at least two adjacent APs 120 may still need to derive timing information related to the MAC cycles of the at least two APs 120 based on downlink communications from these APs, where the downlink communications may be normal data communication links or out-of-band signaling messages. Then, based on the derived timing information related to the MAC cycles of the at least two APs 120, the EP 110 may further assist at least one of the two adjacent APs 120 in adjusting its MAC cycle to align with the other.

[0115] Trigger-based optical wireless communication system

[0116] To deploy a Li-Fi network, Li-Fi systems can be categorized as either non-standalone mode or standalone mode, depending on whether the Li-Fi AP is integrated into the luminaire.

[0117] For the first option, Li-Fi APs are integrated into luminaires in a non-standalone mode using the luminaire's sensor slot. The APs can be powered directly from the mains or PoE, or preferably, directly from the luminaire. Connections between APs can be achieved via one or two wires (e.g., IEEE 100BASE-T1 or 1000BASE-T1), with a distance limit of 15 meters for unshielded twisted pair (UTP) or 40 meters for shielded twisted pair (STP). The APs can be connected to a backbone network or the internet (WAN) via an Ethernet switch. Preferably, a master-slave architecture can be used to organize more than one Li-Fi AP. Only the master AP includes an Ethernet switch, while the slave APs are connected to ports on the master AP's internal Ethernet switch via two wires. The Ethernet switch ports can be turned on or off, and different power levels can be implemented for different ports. The slave APs can primarily operate with a low-power detection circuit to detect a valid trigger signal and can switch to normal operation only when a Li-Fi end device (e.g., a Li-Fi-capable user device such as a dongle, laptop, smartphone, etc.) is detected in the coverage area. Li-Fi end devices can send optical signals over a low-power optical link, for example according to the IR long-range RC5 protocol, to trigger the AP to switch from low-power mode to normal operating mode. Thus, the AP can save power when a high-speed link is not needed.

[0118] For the second option, the Li-Fi AP is placed separately from the luminaire in standalone mode. The connection between APs can also be achieved through two wires (e.g., IEEE PoDL - Ethernet technology with remote power feed) with a distance limit of 15 meters (for UTP) or 40 meters (for STP). Similar to the first option, a master-slave architecture can be used to organize more than one Li-Fi AP, and the slave AP can mainly operate with a low-power detection circuit to detect a valid trigger signal.

[0119] Figure 6A trigger-based Li-Fi system is presented in FIG. Access point 1200 can operate in at least two different operating states: a low-power state and a normal operating state. By default, access point 1200 operates in a low-power state for detecting a first optical signal 50 from endpoint device 1100 on a first optical channel. Only when a valid trigger signal is identified after detecting the first optical signal 50 does access point 1200 switch from the low-power state to a normal operating state for establishing a high-speed optical data link 60 with endpoint device 1100. When there is no active high-speed optical data link 60 with any endpoint device 1100 for a predefined time period, access point 1200 switches back to the low-power state. Because the access point consumes less power in the low-power state, energy waste due to idle operations (e.g., waiting for an active link) is correspondingly reduced using trigger-based operation.

[0120] The high-speed optical data link 60 is established over an optical data channel that is different from the first optical channel. The optical data channel has a large bandwidth to support high data rate communications and can be deployed in the visible, ultraviolet (UV), or infrared (IR) spectrum. The first optical channel has a narrow bandwidth to support low data rate, low power optical communications and can be located in the same or a different frequency band than the optical data channel. Preferably, the first optical channel is a low power, narrowband IR channel.

[0121] Endpoint device 1100 also has at least two different operating states. To initiate a data link, endpoint device 1100 first operates in a low-power state to transmit a first optical signal 50 over a first optical channel, and then switches to a normal operating state to establish a high-speed optical data link 60 with access point 1200. When there is no immediate need for high-speed optical link 60, endpoint device 1100 switches from the normal operating state to a low-power state or sleep state. The decision to switch back to a low-power state or sleep state can be based on the endpoint device's application profile, user preferences, or battery status. For example, if a relatively large gap is expected before the next high-speed data link is established, the endpoint may choose to switch to a sleep state, or even a powered-off state.

[0122] Preferably, before switching to the normal operating mode, a signaling exchange can be implemented on the first optical channel between the access point and the endpoint device in a low-power state. For example, the access point and the endpoint device can negotiate the settings of the high-speed optical data link, and only after the settings of the high-speed optical data link are agreed upon between the access point and the endpoint device, a valid trigger signal is identified. The settings can be related to the data rate, bandwidth, data channel index, modulation or coding scheme used for the high-speed optical data link. The settings can also be related to a schedule, so that the access point and the endpoint device agree on a delay before establishing the high-speed optical data link. Therefore, the access point may not switch to the normal operating mode immediately, but rather according to a schedule. Therefore, the chance of the access point and / or endpoint device erroneously switching to the normal operating mode will be further reduced.

[0123] Figure 7 The basic components of an access point are schematically depicted. The access point includes an optical transceiver 1211, a power management unit 1245, and a controller 128. The optical transceiver 1211 includes one or more optical front ends 121 and 1255. The power management unit 1245 is configured to set the Li-Fi functional block to active mode or sleep mode based on the current operating state of the device. The controller 128 is configured to control the power management unit based on a triggering event. Optionally, the optical transceiver 1211 also includes another dedicated optical receiver 1255, which is used to receive a first optical signal from the endpoint device. According to one embodiment, a bidirectional link is established on a first optical channel to negotiate settings on the high-speed data link. The module 1255 can be a dedicated low-power transceiver, such as a narrowband IR transceiver. If the first optical channel is in the same frequency band as the optical data channel, the low-power state can be achieved by using the same hardware components (e.g., the same optical front end 121) with different configurations.

[0124] As an example, 1255 is a low-power IR receiver that utilizes existing IR remote control protocols such as RC5 or RC6, or even simpler versions because it only needs to detect the presence of an endpoint device (e.g., a dongle). In another example, RC5 or RC6 can be implemented with the Li-Fi IR front end 111 for data communication, so that the Li-Fi IR LED 111 can operate in a low-power mode with reduced features for RC codes.

[0125] Figure 8A detailed embodiment of an access point is provided. The optical transceiver 1211 is implemented as a complete Li-Fi transceiver, comprising at least an optical front end 121, an analog front end 122, a digital modulator / demodulator / modem 123, and an interface 124 to a backbone network. Compared to normal operating mode, the first optical signal can be received by the same optical front end 121 with a different configuration. The power management unit 1245 can be configured to shut down all or some other modules in the optical transceiver 1211, such as the analog front end 122, the modem 123, and the interface 124, in a low-power state. Optionally, in accordance with the aforementioned embodiments of the access point, the optical transceiver 1211 can include an additional dedicated low-power optical receiver or transceiver 1255.

[0126] Figure 9 The basic components of an endpoint device in an optical wireless communication network are schematically depicted. The endpoint device includes an optical transceiver 1111, a power management unit 1145, and a controller 118. The optical transceiver 1111 includes one or more optical front ends 111 and 1155. The power management unit 1145 is configured to set the Li-Fi functional block to active mode or sleep mode based on the current operating state of the endpoint device. The controller 118 is configured to control the power management unit 1145. Optionally, the optical transceiver 1111 also includes another dedicated optical transmitter 1155 for transmitting a first optical signal. According to one embodiment, to establish a bidirectional link on a first optical channel to negotiate settings for a high-speed data link, the module 1155 can be a dedicated low-power transceiver, such as a narrowband IR transceiver. If the first optical channel is in the same frequency band as the optical data channel, the low-power state can be achieved using the same hardware components (e.g., the same optical front end 111) with different configurations.

[0127] Figure 10 One embodiment of an endpoint device is schematically depicted. The optical transceiver 1111 is implemented as a complete Li-Fi transceiver, comprising at least an optical front end 111, an analog front end 112, a digital modulator / demodulator / modem 113, and an interface 114 to a terminal device to which the Li-Fi transceiver is connected or contained. The first optical signal can be transmitted via the same optical front end 111 with a different configuration compared to normal operating mode. A power management unit 1145 can be configured to shut down all or some other modules in the optical transceiver 1111, such as the analog front end 112, the modem 113, and the interface 114, in a low-power state. Optionally, in accordance with the aforementioned embodiments of the endpoint device, the optical transceiver 1111 can include an additional dedicated low-power optical transmitter or transceiver 1155.

[0128] With the option for the access point and / or endpoint device to include a dedicated low-power optical receiver (access point) or transmitter (endpoint device) or transceiver (access point, endpoint device), the following power states can be defined:

[0129] Normal operating state: all components are active (“on”);

[0130] Low power state: the low-power optical receiver (access point) or low-power optical transmitter (endpoint device) or low-power optical transceiver (access point, endpoint device) is active ("on"); the optical transceivers for the high-speed link (optical front ends 111, 121, analog front ends 112, 122, modems 113, 123, endpoint interface 114) are in an "off" or unpowered state; the Ethernet interface 124 of the access point is in sleep mode and is able to receive a periodic synchronization clock signal, for example according to the Energy Efficient Ethernet (EEE) IEEE 802.3az standard;

[0131] Sleep or Power-Off State: The low-power optical receiver (access point) or low-power optical transmitter (endpoint device) or low-power optical transceiver (access point, endpoint device) is off; the optical transceivers used for high-speed links (optical front ends 111, 121, analog front ends 112, 122, modems 113, 123, endpoint interface 114) are off; the access point's Ethernet interface 124 is in deep sleep mode and will be triggered by a second trigger signal from the master access point. Therefore, in the sleep or power-off state, a slave access point can only be awakened by the master access point based on a schedule or trigger event. For an endpoint device, it can only be awakened by a user command, a pre-set timer, or a request from an application.

[0132] Figure 11 An illustration of multiple APs arranged in a master-slave configuration is provided. Compared to the slave APs, the master AP may also include an Ethernet switch that provides access to a backbone network to one or more slave APs, and this access may be provided according to the Ethernet standard, for example, via a 1000BASE-T1 interface. In addition, the master AP may be configured to provide power to one or more slave APs. Using PoE technology, the master AP may transmit power and data to the slave APs via the same cable. Advantageously, PoDL (power over data line) technology may be used for powering the master and slave APs, as it requires only a single twisted pair for data and power.

[0133] In one example, the master AP defaults to operating in a normal operating state, while the slave AP defaults to operating in a low-power state for detecting endpoint devices. The slave AP is powered via a twisted pair cable and consumes very low power (only the low-power IR receiver is active). Once a valid trigger signal is detected, the Ethernet interface 124 is activated to establish an Ethernet link, and the modem 123, analog front end 122, and optical front end 121 are activated to establish a high-speed data link with the endpoint device.

[0134] Another embodiment is to implement a protocol between the master AP and the slave AP to further reduce power. Advantageously, the master AP can turn the slave AP on or off according to a schedule or event through a second trigger signal. For example, the master AP can first send a second trigger signal to the slave AP to instruct the slave AP to switch from a low-power state to a sleep state or a power-off state to further reduce power. In the sleep state, the access point cannot detect the presence of a terminal device, but relies on another access point to provide another second trigger signal to wake up from the sleep state to the low-power state. The second trigger signal is sent via the cable connecting the master AP and the slave AP.

[0135] In another example, both the master AP and the slave APs can enter a low-power state, awaiting a trigger from an endpoint device. The master AP can determine its operational state by further considering the state of the slave APs connected to it. For example, when at least one connected slave AP is in normal operational mode, the Ethernet switch in the master AP will remain in operational mode, while the rest of the master AP can enter a low-power state, pending a trigger from an endpoint device.

[0136] Figure 12 A flow chart of a method 500 for operating an access point in an optical wireless communication network is shown. The method 500 includes the access point 1200 operating in a low-power state to detect a first optical signal 50 from an endpoint device 1100 on a first optical channel in step S501; in step S502, the access point identifying a valid trigger signal after detecting the first optical signal 50. In step S503, upon identifying the valid trigger signal, the access point switches from the low-power state to a normal operating state. Then, in step S504, the access point 1200 operates in the normal operating state to establish a high-speed optical data link 60 with the endpoint device 1100. In step S505, when there is no active high-speed optical data link 60 with any endpoint device 1100 for a predefined time period, the access point switches from the normal operating state back to the low-power state.

[0137] Figure 13A flowchart of another embodiment of method 500 is shown. Step S502 of identifying a valid trigger signal further includes step S506, where the access point 1200 negotiates with the endpoint device 1100 on the first optical channel regarding the configuration of the high-speed optical data link 60 upon detecting the first optical signal 50; and in step S507, after the access point 1200 and the endpoint device 1100 reach an agreement on the configuration of the high-speed optical data link 60, the valid trigger signal in step S502 is then identified.

[0138] Figure 14 A flow chart is shown of a method 600 for operating an endpoint device 1100 in an optical wireless communication network 100. The method 600 includes, in step S601, operating the endpoint device 1100 in a low-power state to transmit a first optical signal 50 on a first optical channel. In step S602, the endpoint device switches from the low-power state to a normal operating state after transmitting the first optical signal 50, and in step S603, operates in the normal operating state to establish a high-speed optical data link 60 with the access point 1200. In step S604, when there is no immediate need for the high-speed optical link 60, the endpoint device 1100 switches from the normal operating state to a low-power state or sleep state.

[0139] Figure 15 A flowchart of another embodiment of a method 600 for operating an endpoint device is shown. After transmitting the first optical signal 50 and before switching to a normal operating state, the method 600 further includes, in step S605, the endpoint device 1100 negotiating with the access point 1200 on the first optical channel the settings of the high-speed optical data link 60; and, in step S606, determining to switch to the normal operating state after the access point 1200 and the endpoint device 1100 have reached an agreement on the settings of the high-speed optical data link 60.

[0140] 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.

[0141] 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 memory 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.

[0142] Methods, systems, and computer-readable media (transitory and non-transitory) may also be provided for implementing selected aspects of the above-described embodiments.

[0143] The term "controller" is used generally herein to describe various devices associated with the operation of (among other functions) one or more network devices or coordinators. A controller can be implemented in a variety of ways (e.g., such as with dedicated hardware) to perform the various functions discussed herein. A "processor" is an example of a controller that employs one or more microprocessors that can be programmed using software (e.g., microcode) to perform the various functions discussed herein. A controller can be implemented with or without a processor, and can also be implemented as a combination of dedicated hardware that performs some functions and a processor (e.g., one or more programmed microprocessors and associated circuitry) that performs other functions. Examples of controller components that may be employed in various embodiments of the present disclosure include, but are not limited to, conventional microprocessors, application specific integrated circuits (ASICs), and field programmable gate arrays (FPGAs).

[0144] In various embodiments, a processor or controller may be associated with one or more storage media (generally referred to herein as "memory," e.g., volatile and non-volatile computer memory, such as RAM, PROM, EPROM, and EEPROM, compact disks, optical disks, and the like). In some embodiments, the storage media may be encoded with one or more programs that, when executed on one or more processors and / or controllers, perform at least some of the functions discussed herein. The various storage media may be fixed within the processor or controller, or may be transportable such that the one or more programs stored thereon can be loaded into the processor or controller in order to implement the various aspects of the invention discussed herein. The terms "program" or "computer program" are used herein in a general sense to refer to any type of computer code (e.g., software or microcode) that can be used to program one or more processors or controllers.

[0145] The term "network" as used herein refers to any interconnection of two or more devices (including controllers or processors) that facilitates the transport of information between any two or more devices and / or between multiple devices coupled to the network (e.g., for device control, data storage, data exchange, etc.).

Claims

1. A method (500) for operating an access point (1200) in an optical wireless communication network (100), the method comprising the access point (1200): - operating in a low power state (S501) for detecting a first optical signal (50) from an endpoint device (1100) on a first optical channel; - after detecting said first optical signal (50), generating (S502) a trigger signal; - switching (S503) from said low power state to a normal operating state based on the generated trigger signal, - operating in the normal operating state (S504) for establishing a high-speed optical data link (60) with the endpoint device (1100); - switching (S505) from the normal operating state back to the low power state when there is no active high-speed optical data link (60) with any endpoint device (1100) for a predefined time period; as well as wherein the access point consumes less power in the low power state than in the normal operating state, The method (500) is characterized in that: Before generating (S502) the trigger signal, the method (500) further includes the access point (1200): - upon detecting the first optical signal (50), negotiating (S506) the settings of the high-speed optical data link (60) with the endpoint device (1100) on the first optical channel; and wherein, after reaching an agreement (S507) between the access point (1200) and the endpoint device (1100) on the settings of the high-speed optical data link (60), the step of generating (S502) the trigger signal is followed; And wherein the high-speed optical data link (60) is established on an optical data channel different from the first optical channel.

2. The method (500) according to any one of the preceding claims, wherein: The low power state is achieved by disabling a hardware component or by disabling a hardware component and enabling a different hardware component in the access point (1200).

3. The method (500) according to any one of the preceding claims, wherein: The first optical signal (50) is an infrared signal.

4. The method (500) according to any one of the preceding claims, further comprising: Upon receiving a second trigger signal from another access point (1200), the access point (1200) switches between the low power state and the sleep state (S508); and wherein the access point consumes less power in the sleep state than in the low power state.

5. The method (500) according to claim 4, wherein: The access point (1200) is a slave access point, and the other access point (1200) from which the second trigger signal is received is a master access point.

6. The method (500) according to claim 5, wherein: The slave access point (1200) is connected to a backbone network via the master access point (1200).

7. The method (500) according to claim 5 or 6, wherein: The slave access point (1200) is powered by the master access point (1200).

8. A method (600) for operating an endpoint device (1100) in an optical wireless communication network (100), the method comprising the endpoint device (1100): - operating in a low power state (S601) for transmitting a first optical signal (50) on a first optical channel; - after sending the first optical signal (50), switching (S602) from the low power state to a normal operating state; - operating in the normal operating state (S603) for establishing a high-speed optical data link (60) with the access point (1200); - switching (S604) from the normal operating state to the low power state when there is no immediate need for the high-speed optical data link (60); as well as wherein the endpoint device consumes less power in the low-power state than in the normal operating state; The method (600) is characterized in that: After transmitting the first optical signal (50) and before switching to the normal operating state, the method (600) further comprises the endpoint device (1100): - negotiating (S605) the setup of a high-speed optical data link (60) with the access point (1200) on the first optical channel, - after reaching an agreement between the access point (1200) and the endpoint device (1100) on the settings of the high-speed optical data link (60), determining (S606) to switch to a normal operating state; And wherein the high-speed optical data link (60) is established on an optical data channel different from the first optical channel.

9. The method (600) of claim 8, wherein when the access point (1200) and the endpoint device (1100) cannot agree on the configuration of the high-speed optical data link (60), the method further comprising the endpoint device (1100) - remaining (S601) in said low power state for sending a second optical signal on said first optical channel; or - Switching (S607) from the low power state to the sleep state.

10. An access point (1200) in an optical wireless communication network (100), the access point (1200) comprising: - an optical transceiver (1211) comprising one or more optical front ends (121, 1255); - a power management unit (1245); and - a controller (128); and The access point (1200) is configured to implement any one of the methods (500) described in claims 1-7.

11. An endpoint device (1100) in an optical wireless communication network (100), the endpoint device (1100) comprising: - an optical transceiver (1111) comprising one or more optical front ends (111, 1155); - a power management unit (1145); and - a controller (118); and The endpoint device (1100) is configured to implement any one of the methods (600) described in claims 8-9.

12. An optical wireless communication network (100) comprising at least one access point (1200) according to claim 10 and at least one endpoint device (1100) according to claim 11.

13. A computing program comprising code means, which, when executed by an access point (1200) comprising processing means, causes the processing means of the access point (1200) to perform any one of the methods of claims 1-7, or a computing program comprising code means, which, when executed by an endpoint device (1100) comprising processing means, causes the processing means of the endpoint device (1100) to perform any one of the methods of claims 8-9, respectively.

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