Link establishment in multi-cell wireless networks

Abstract

In a multi-cell wireless communication system (100) with at least one optical access point (120) and at least one radio frequency access point (120), more flexibility is provided for a terminal device (110) in selecting an access point (120) for establishing a data link. Due to the line-of-sight nature of optical links and the limited field of view of optical receivers, optical cells are typically deployed with a relatively high density and adjacent optical cells can have overlapping areas. The invention discloses a method for a terminal device (110) to select a favorable access point (120) with reduced overhead even when the terminal device is located in an overlapping area of two adjacent optical cells.

Description

Technical Field

[0001] This invention relates to the field of optical wireless networks, such as Li-Fi networks. More specifically, this document discloses various methods, apparatuses, systems, and computer-readable media related to end devices for establishing data links in multi-cell wireless networks. Background Technology

[0002] To enable an increasing number of electronic devices, such as laptops, tablets, and smartphones, to wirelessly connect to the internet, wireless communication is placing unprecedented demands on data rates and link quality, and these demands continue to grow year by year, given the emerging digital revolution associated with the Internet of Things (IoT). Radio frequency technologies like Wi-Fi, with their limited spectrum capacity, cannot embrace this revolution. Meanwhile, Light Fidelity (Li-Fi) is attracting increasing attention due to its inherent enhanced security and its ability to support higher data rates across the available bandwidth of the visible, ultraviolet (UV), and infrared (IR) spectra. Furthermore, compared to Wi-Fi, Li-Fi is directional and shielded by light-shielding materials, making it possible to deploy more access points in densely populated user areas by spatially reusing the same bandwidth. These key advantages over wireless radio frequency communication make Li-Fi a promising security solution to alleviate the strain on the congested radio spectrum for IoT applications. Other benefits of Li-Fi include guaranteed bandwidth for specific users and the ability to operate safely in areas otherwise susceptible to electromagnetic interference. Therefore, Li-Fi is a very promising technology for enabling next-generation immersive connectivity.

[0003] Several related terms exist in the field of lighting-based communications. Visible light communication (VLC) transmits data via intensity-modulated light sources such as light-emitting diodes (LEDs) and laser diodes (LDs), which transmit data faster than the persistence of the human eye. VLC is typically used to embed signals into light emitted by lighting sources, such as indoor or outdoor lighting, allowing the use of illumination from the illuminator as an information carrier. Thus, light can include a visible illumination contribution for illuminating a target environment such as a room (often the primary purpose of light), and an embedded signal for providing information to the environment (often considered a secondary function of light). In this case, modulation is typically performed at a sufficiently high frequency to exceed human perception, or at least to make any visible temporal light artifacts (such as flicker and / or stroboscopic artifacts) weak enough and unobtrusive or at least tolerable to humans at a sufficiently high frequency. Therefore, the embedded signal does not affect the primary lighting function; that is, the user only perceives the overall lighting, not the data being modulated into that lighting.

[0004] The IEEE 802.15.7 Visible Light Communication Personal Area Network (VPAN) standard maps intended applications to four topologies: point-to-point, star, broadcast, and coordinated. Optical Wireless PAN (OWPAN) is a more general term than VPAN, as it also allows communication using invisible light such as UV and IR. Therefore, Li-Fi is often considered a derivative of Optical Wireless Communication (OWC) technology, which utilizes a wide range of spectra to support bidirectional data communication.

[0005] In Li-Fi systems, signals are embedded by modulating the light according to the characteristics (typically intensity) of any of a variety of suitable modulation techniques. For high-speed communication, infrared (IR) is typically used instead of visible light. Although ultraviolet and infrared radiation are invisible to the human eye, the techniques utilizing these spectral regions are the same, although variations may occur due to wavelength dependence, such as in the case of refractive index. In many cases, using ultraviolet and / or infrared light is advantageous because these frequency ranges are invisible to the human eye and can introduce greater flexibility into the system. Of course, ultraviolet quanta have higher energy levels than those in infrared and / or visible light, which in turn can lead to situations where the use of ultraviolet light is undesirable.

[0006] Based on modulation, any suitable optical sensor or photodetector can be used to detect information in light. For example, an optical sensor can be a photodiode. An optical sensor can be a dedicated phototube (point detector), an array of phototubes that may have lenses, reflectors, diffusers, or (for lower speeds) phosphor converters, or an array of phototubes (pixels) and lenses for forming an image on the array. For example, an optical sensor can be a dedicated phototube included in a dongle that plugs into a user device such as a smartphone, tablet, or laptop, or the sensor can be integrated and / or dual-purpose, such as an infrared detector array originally designed for 3D face recognition. Either way, this allows applications running on the user device to receive data via light.

[0007] In the following text, the term "access point" in Li-Fi systems is used to specify a logical access device that can connect to one or more physical access devices (e.g., optical transceivers). Such physical access devices are typically, but not necessarily, located at illuminators, and a logical access point can connect to one or more physical access devices, each located at one or more illuminators. The access point can then serve one or more network devices or end devices associated with it, thereby forming an optical cell.

[0008] Tang AIMIN et al.'s "Design and Implementation of an Integrated Visible Light Communication and WiFi System" involves integrating VLC and WiFi systems, where access points (APs) support downlink VLC and bidirectional WiFi communication. The VLC radio access process is triggered on the mobile user's side only when the mobile user receives a VLC beacon frame containing the same Service Set Identifier (SSID) as the WiFi radio with which the mobile user has already established a connection.

[0009] EP2953277B1 relates to a method for switching visible light communication terminals at an access point. Summary of the Invention

[0010] Given IoT applications, optical wireless communication or Li-Fi has been proposed as a supplement or even replacement for wired connections or radio-based wireless communication to enable electronic devices or end devices to support higher data rate communications. Although the line-of-sight characteristic of optical wireless communication provides inherent security for optical links, optical cells are typically deployed at relatively high densities due to the limited field of view (FoV) of optical receivers, resulting in relatively small coverage per cell.

[0011] On the other hand, Wi-Fi is one of the most widely used wireless communication technologies in local area networking. Wi-Fi networks are deployed almost everywhere—in homes, offices, buses, trains, stations, airports, stadiums, etc. Therefore, integrating Li-Fi access points into existing infrastructure (such as Wi-Fi infrastructure) to provide connectivity between Li-Fi access points and the backbone network has advantages.

[0012] The coexistence of radio frequency (RF) and optical networks in the same area also provides greater flexibility for end devices. Depending on application requirements, end devices can prioritize one network and use the other as a backup. End devices can also use a combination of the two networks. Furthermore, when an end device is located in the overlapping area of ​​two adjacent optical cells, it needs to select one of the two adjacent access points to establish an optical data link.

[0013] In view of the foregoing, this disclosure relates to a method, apparatus, system, computer program, and computer-readable medium for providing a mechanism to assist an end device in establishing a data link with one of a plurality of access points in a multi-cell network. More specifically, the objective of the invention is achieved by the end device as claimed in claim 1, the end device as claimed in claim 7, the system as claimed in claim 10, and the computer program as claimed in claim 11.

[0014] According to a first aspect of the invention, a method for establishing a data link by an end device is provided. A method performed by an end device for establishing a data link by selecting one of a plurality of access points in a multi-cell wireless communication network, wherein the plurality of access points includes at least one optical access point and one radio frequency (RF)-based access point, the method comprising the end device: monitoring the occurrence of one or more identification codes in an optical signaling channel; selecting an access point for establishing the data link based on the detection of the one or more identification codes, wherein the data link is established on a channel different in frequency from the optical signaling channel; and the other channel may be an optical data channel or an RF data channel; wherein selecting the access point further includes selecting an RF-based access point when no identification code is detected; and selecting an optical access point when at least one identification code is detected, and performing the further steps of: adjusting one or more settings corresponding to the selected optical access point, wherein the one or more settings include at least one hardware configuration; and establishing a data link on the other channel with the selected optical access point after the adjustment; wherein each of the one or more identification codes is used to uniquely identify the optical access point.

[0015] Multi-cell wireless communication networks can be deployed in various scenarios, such as homes, offices, factories, stadiums, exhibition halls, airports, or other indoor environments. End devices can be portable devices, such as smartphones, tablets, laptops, remote controls, or other mobile devices. End devices can also be less mobile electronic devices, such as home appliances, docking stations, or robotic workstations.

[0016] To select an access point to establish a data link, the method involves an end device monitoring an optical signaling channel for one or more identification codes. The data link is established on a channel other than the optical signaling channel. Each identification code is sent by the optical access point to advertise its presence. Such identification codes are used to uniquely identify a particular optical access point. After detecting at least one identification code on the optical signaling channel, the end device can assess the availability of an optical access point with a direct line-of-sight channel. Therefore, ensuring identical coverage of the optical communication for ID detection and the data link is also beneficial. Note that here, the data link refers to the logical connection between the access point and the end device for data communication, which may include one or more physical channels distinguished from each other by frequency or wavelength.

[0017] In a preferred embodiment, when more than one identification code is detected, an optical access point corresponding to the identification code with better received signal quality is selected to establish a data link.

[0018] By detecting more than one identification code, the end device can identify that it is located in the overlapping area of ​​multiple adjacent optical access points. Signal quality is an indicator of the quality of the received signal, which can be reflected by the received signal strength or the signal-to-noise ratio of the received signal. Therefore, the end device can select an optical access point with optimal channel conditions. And thus, a more robust data link can be established. Better channel conditions may also indicate that a higher data rate can be supported on a data link with a higher-order modulation scheme, or that the same data rate can be supported with lower transmission power. When more than one identification code is detected that unexpectedly has approximately the same received signal quality, the end device can randomly select an optical access point from the more than one candidate optical access point represented by the detected identification codes. The end device can also further consider one or more settings corresponding to each optical access point when making the selection. For example, if a setting of the first optical access point indicates that it should support a higher data rate than the second optical access point, the end device can preferentially select the first optical access point to establish a data link.

[0019] In a more preferred embodiment, one or more identification codes are orthogonal to each other.

[0020] In one example, the optical signaling channel may consist of only a single narrow channel, and one or more optical access points can use the same narrow channel to transmit individual identification codes at a relatively low data rate. The advantage of this option is that it is very energy-efficient for the transmitting and end-user devices of the optical access points to perform detection for signaling exchange on such a narrow channel. However, for end-user devices located in the overlapping area of ​​two adjacent optical access points, the problem of interference detection on the signaling channel also needs to be addressed. Therefore, using orthogonal codes as identification codes is advantageous.

[0021] Advantageously, one or more identification codes are Hadamard codes. Hadamard codes, also known as Walsh codes or Walsh-Hadamard codes, are typically used for error detection and correction when transmitting messages over noisy or unreliable channels. Hadamard codes are a type of code with a low information rate but long distance. Given the very limited number of directly adjacent optical access points, the low information rate is not a problem here, but the long distance between the two codes is a very attractive characteristic. For a length of 2... k The Hadamard code has a distance of 2 between two codewords. k-1 .

[0022] Therefore, as long as the end device is not exactly equidistant from two adjacent optical access points, it is possible for the end device to recognize each of the two overlapping identification codes. Even if the end device detects an equally "strong" identification code from two adjacent optical access points, it may still randomly select one of the two adjacent access points.

[0023] Advantageously, another channel used for the data link can be an optical data channel or a radio frequency (RF) data channel.

[0024] Considering scenarios where wireless optical networks can coexist with existing radio networks deployed in the same area, it is beneficial to allow end devices to flexibly choose between the two networks by using optical data channels and RF data channels.

[0025] In the preferred configuration, a data link is established on the RF data channel when no identification code is detected.

[0026] If the end device fails to detect any identification code, it could indicate that the end device is not within the line of sight of any optical access point, or that the optical channel between the end device and a nearby optical access point is inadequate, for example, when receiving optical signals at a very tilted angle. It could also be that the optical access point is busy with another active link and cannot be used to establish a new link with the end device. In such scenarios, the end device will switch to the RF channel to establish a data link.

[0027] In another embodiment, each of one or more identification codes is also used to designate a sub-channel within the optical communication band for use as an optical data channel of the data link.

[0028] In addition to identifying optical access points, the identification code can also be used to convey other information, such as specifying the sub-channel within the optical communication band to be used for the data link. This is particularly beneficial when adjacent optical access points share the same optical band in frequency division or wavelength division multiplexing (FDM). It is also possible for multiple end devices within the same optical cell to share the optical communication band or specific portions thereof in a FDM or wavelength division multiplexing manner.

[0029] Advantageously, when only one identification code is detected, the optical data channel can be extended to include more than one sub-channel within the optical communication band.

[0030] If only one identifier is detected, the end device can determine that it is not in the overlapping area of ​​two adjacent access points, and therefore it may consider channel bonding by extending the optical data channel to more than one sub-channel. The end device can send a request via uplink communication with the optical access point associated with only one identifier. This request can be sent on the optical signaling channel or on the data link to be established. Using the latter approach, an initial data link can be established on the sub-channel specified by the optical access point, and then extended to multiple sub-channels after the optical access point receives feedback from the end device. If such a request might interfere with other communication links, it may also be rejected by the optical access point.

[0031] In another embodiment, one or more identification codes are also used to specify the configuration to be used on the data link.

[0032] Further configuration information can also be specified by the optical access point via an identification code. As an example, if the end device will only detect one identification code, the optical access point may have already indicated that the end device can perform channel bonding. Alternatively, the optical access point may indicate that the end device can use more than one sub-channel, such as when the optical access point is already aligned with a neighboring optical access point or when there are no other active optical access points nearby. Such further configuration information can be enabled by using a different orthogonal code instead of the access point's default identification code.

[0033] Therefore, an identification code can be used to notify end devices based on one or more aspects, such as identifying the access point, the type of access point, or another configuration setting (e.g., the optical communication band or wavelength to be used for the data link, or a sub-channel in the selected / default optical communication band to be used for the data link). Such information can be embedded in the identification codeword, and the same optical access point can use different codewords through different combinations of one or more aspects. Therefore, the length of the orthogonal code, or the size of the entire codeword, is a design trade-off between energy efficiency, robustness, and the actual amount of information carried by the identification code. Longer codes can transmit more information, but are less energy efficient for transmission and reception.

[0034] Optical signaling channels can be included within optical data channels on a time-sharing or frequency-sharing basis. For example, an optical signaling channel can occupy a small portion of the optical data channel in the frequency domain.

[0035] Advantageously, the optical signaling channel is different from the optical data channel.

[0036] Using a separate or dedicated optical signaling channel, one or more identification codes can be continuously transmitted by one or more access points on the signaling channel to announce their presence. Therefore, the end device can quickly detect one or more identification codes. Alternatively, one or more identification codes can be transmitted periodically by one or more access points, such as during each advertising cycle. The end device may then need to monitor the signaling channel for at least one complete advertising cycle for reliable detection.

[0037] In another example, when an access point is unavailable for new data links—for example, when one or more active data links established by the access point already exist and no additional capacity is available—a separate signaling channel can be used to send another signal, such as a busy tone, to indicate the access point's status. In one example, when the access point receives a message from an end device on the uplink optical data channel, it can send a busy tone on a separate signaling channel. This avoids the hidden node problem. Since optical communication requires a direct line-of-sight (LoS), when there are two or more end devices within the access point's coverage area, the access point can listen to both, but the two or more end devices cannot listen to each other's uplink. Utilizing a busy tone at the access point to suppress potential interference from another end device's uplink optical communication is highly beneficial. In this example, the identification code and busy tone can be sent by the access point on a time-shared basis on a separate signaling channel to invite or reject the end device from establishing a data link based on the access point's status.

[0038] In a preferred embodiment, one or more settings include at least one hardware configuration.

[0039] By selecting an access point, the end device can also prepare itself for the data link by adjusting one or more settings. For example, the selected access point can be an optical access point or an RF access point, and when an optical access point is selected, different sub-channels can be associated. Therefore, the end device may need to adjust one or more hardware-related settings to prepare for the data link. Such settings may be related to connections to the optical front end, connections to the radio front end, switching between the optical and radio front ends, control of the frequency shifter, or another control that enables a part of the communication unit.

[0040] According to a second aspect of the present invention, an end device is provided. An end device for establishing a data link by selecting one of a plurality of access points in a multi-cell wireless communication network, wherein the plurality of access points includes at least one optical access point and one radio frequency (RF)-based access point, the end device comprising:

[0041] - An optical receiver is configured to monitor the presence of one or more identification codes in an optical signaling channel; wherein each of the one or more identification codes is used to uniquely identify an optical access point;

[0042] - A controller configured to select an access point to establish a data link based on the detection of one or more identification codes; wherein an RF-based access point is selected when no identification code is detected, and an optical access point is selected upon detection when at least one identification code is detected; and

[0043] - A wireless communication transceiver is configured to adjust one or more settings corresponding to the selected access point when the selected access point is an optical access point, and establish a data link using the selected access point after adjustment;

[0044] The one or more settings mentioned above include at least one hardware configuration.

[0045] The controller of the end device can be a processor, one or more microprocessors, or special-purpose hardware such as application-specific integrated circuits (ASICs) and field-programmable gate arrays (FPGAs).

[0046] Advantageously, the wireless communication transceiver is also configured to support optical or RF communication when one or more settings are adjusted.

[0047] In one option, the wireless transceiver may include two separate hardware units to independently support optical and RF communications. Adjustments to one or more settings include the choice between the two separate hardware units. In another, more cost-effective option, the wireless transceiver implements optical and RF communications through specific components shared by both communication modes (such as, for example, a common baseband modulator), while other components are dedicated to one communication mode.

[0048] In another example, the optical communication mode reuses the entire hardware unit of the RF communication mode and enables another dedicated hardware unit to convert the signal from the RF communication mode to the optical mode.

[0049] In another embodiment, the optical receiver is part of a wireless communication transceiver.

[0050] An optical receiver can be shared by both the optical signaling channel and the optical data channel. Therefore, the optical receiver is part of the wireless communication transceiver. Alternatively, the optical receiver is a dedicated hardware-based receiver optimized for very low power consumption and low cost. This dedicated hardware-based receiver can be used to wake up the wireless communication transceiver after the controller selects the access point.

[0051] According to a third aspect of the present invention, a system is provided. A multi-cell wireless communication system includes: at least one end device according to the present invention; at least one RF access point configured to establish data communication with the at least one end device; and at least one optical access point configured to establish data communication with the at least one end device; and wherein the at least one optical access point is further configured to transmit an identification code on an optical signaling channel.

[0052] In one example, the optical access point can be coupled to an illuminator that supports coded light (CL) communication. An identification code can be sent as a coded light message and can be detected by an end device, such as a camera or another detector. Optical data communication or a data link can be established between the optical access point and the end device via different optical channels, such as Li-Fi channels in the UV or IR spectrum. Therefore, visible light communication can be used as a signaling channel for Li-Fi communication.

[0053] At least one RF access point and at least one optical access point deployed in the same area can share the same infrastructure to connect to the backbone network, while simultaneously providing end devices with greater flexibility for connectivity in the last few tens of meters. In one example, when both connections are available, the end device can prioritize the optical network over the RF network, keeping the RF network as a backup. Considering the small coverage area of ​​optical cells, when the end device is located in the overlapping area of ​​two adjacent optical cells, it may be necessary for the end device to choose between two adjacent optical and RF access points to establish a reliable data link, such as two adjacent Li-Fi and Wi-Fi access points.

[0054] The present invention can be further embodied in a computer program including code means, which, when executed by an end device including a processing means, causes the processing means to perform the end device method disclosed in the present invention. Attached Figure Description

[0055] In the accompanying drawings, similar reference numerals generally refer to the same parts in different drawings. Furthermore, the drawings are not necessarily drawn to scale; instead, the focus is usually on illustrating the principles of the invention.

[0056] Figure 1 It presents an overview of a multi-cell wireless system and the backbone network to which it is connected;

[0057] Figure 2 The diagram illustrates a frequency-division-based optical multi-cell system with a separate optical signaling channel;

[0058] Figure 3 The diagram illustrates the deployment of multiple optical cells based on frequency division.

[0059] Figure 4 The diagram illustrates a system setup that uses orthogonal identification codes to manage interference between adjacent optical access points.

[0060] Figure 5 A frequency division implementation for data communication and for using ID transmission at two adjacent optical access points is demonstrated;

[0061] Figure 6The figure illustrates a frequency division implementation method between two adjacent optical cells on an optical channel response diagram;

[0062] Figure 7 The illustration shows the use of orthogonal identification codes to distinguish one optical access point from another optical access point of an end device located in an overlapping region;

[0063] Figure 8 The diagram shows... Figure 7 The corresponding selection of the end device based on the identification code detection is shown;

[0064] Figure 9 The illustration shows channel bonding at an optical access point when there are no adjacent optical access points and potential vertical handover between Li-Fi and Wi-Fi networks;

[0065] Figure 10 This demonstrates how to use busy tones to avoid hidden node issues;

[0066] Figure 11 The basic components of the terminal device of the present invention are schematically depicted.

[0067] Figure 12 The basic components of the terminal device of the present invention with another configuration are schematically depicted;

[0068] Figure 13 An example implementation of adjusting the end device corresponding to the selected access point is provided;

[0069] Figure 14 A flowchart of the method for the end device is shown. Detailed Implementation

[0070] Various embodiments of the present invention will now be described based on multi-cell wireless communication systems, such as... Figure 1 As shown, the system can be a combination of one or more RF networks and one or more optical wireless networks, or more specifically, a Li-Fi network. For illustrative purposes, the multi-cell wireless communication system 100 is connected to the backbone network 20 via IP router 15 and Ethernet switch 14. In a real system, more routers and switches can be deployed to connect the backbone network to the multi-cell wireless communication system. Note that Ethernet switch 14 and IP router 15 are also part of the backbone network. Figure 1The symbol 20 for the backbone network is for illustrative purposes and should be considered as the remaining portion of the backbone network excluding the Ethernet switch 14 and IP router 15 shown in the diagram. In this example, the connection between the Li-Fi network and the backbone network is referred to as backbone connection 21. A backbone connection is a stable, high-speed link that can be a wired connection, such as Ethernet, fiber optic, or a radio frequency (RF) or millimeter-wave-based wireless connection. A backbone connection can also be another type of optical wireless link, distinct from the optical wireless links performed by end devices in a multi-cell wireless network. An example of another type of optical wireless link could be a free-space point-to-point optical link.

[0071] A multi-cell wireless communication system 100 includes multiple access points (APs) 120 and one or more network devices or end devices (EDs) 110. Figure 1 In the example shown, AP1 and AP2 are optical access points, or preferably Li-Fi access points, and AP3 is an RF access point, or preferably a Wi-Fi access point, such as WiFi-6, or a cellular network. As a wireless communication technology for local area networking, Li-Fi plays a similar role to Wi-Fi in providing connectivity for the last few meters. However, due to different signal propagation characteristics, Wi-Fi access points typically have a much larger coverage area than Li-Fi access points. Therefore, optical access points are deployed at a relatively higher density compared to RF access points.

[0072] Optical AP 120 can be connected to one or more optical front-ends or optical transceivers (TRXs) to provide access to peer device 110. The trapezoidal diagram shown by the dashed line illustrates the field of view (FoV) or coverage of a single optical front-end. ED 110 can only receive downlink communication from optical AP 120 when it is within the coverage of AP 120 (within the trapezoid of the AP). By assuming bidirectional uplink and downlink in optical communication, a bidirectional optical link can be established under the same conditions. Due to the line-of-sight characteristics of optical communication links, adjacent optical APs 120 do not have a direct optical link to each other, but ED 110 located in the overlapping area of ​​the coverage of adjacent APs 120 can detect optical signals from both access points. Figure 1 In the same example, end device 110 can select AP1, AP2 and AP3 to establish a data link.

[0073] Medium Access Control (MAC) becomes necessary for interference-free optical communication when multiple Li-Fi APs are deployed adjacent to each other, or when multiple ED 110s are associated with the same Li-Fi AP or adjacent Li-Fi APs. For multi-cell wireless networks, different MAC mechanisms can be employed, 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 these mechanisms. TDMA is based on a time-division multiplexing scheme, where radio resource access is scheduled in the time domain and different time slots are assigned to different transmitters in a typical cyclic repeating frame structure or MAC cycle. FDMA is based on frequency division multiplexing, where different frequency bands are allocated to different devices for simultaneous transmission. Furthermore, in optical communication, FDMA can evolve into Wavelength Division Multiple Access (WDMA), which is based on wavelength division multiplexing. Another advanced variant of FDMA is Orthogonal Frequency Division Multiple Access (OFDMA), where each device can use one or more subcarriers across the entire frequency band. OFDMA offers greater flexibility in providing different data rates or qualities of service to different users, while maintaining high resource efficiency despite this diversity. CSMA typically employs a "listen-before-talk" approach, where devices verify the absence of any missing traffic before transmitting over a shared medium. CSMA is widely used in sparse networks, and further collision avoidance techniques emerge as node density scales. CDMA is typically built on spread spectrum, and a common form is direct sequence CDMA based on direct sequence spread spectrum, where different devices simultaneously transmit messages using different orthogonal spreading codes. Given that the FoV of optical links is generally smaller compared to radio links, spatial division multiple access can also be a very attractive solution here.

[0074] In TDMA-based multi-cell networks with multiple optical or Li-Fi APs, adjacent APs may sometimes lack synchronized MAC cycles due to the lack of direct communication. While the duration of a MAC cycle or superframe is typically the same for all APs in the network, the start time of the MAC cycle can differ for each AP. Note that APs use the start time of the MAC cycle as a local time reference to divide the wireless medium into consecutive time slots. This MAC cycle offset between two adjacent APs can interfere with ED 110s located in the overlapping coverage area of ​​these two adjacent Li-Fi APs, even if a time slot is specifically allocated to a Li-Fi AP for communication with ED 110s in the overlapping area. Therefore, optical APs may need to synchronize with a common time base. The common time base can be obtained via a synchronization handshake, via a reference clock distributed across the network (such as a synchronized Ethernet clock), or via a dedicated synchronization server in the network, or derived from a common signal (such as the zero-crossing of the main power supply). However, due to unpredictable delays or interference in the network, the timing synchronization of optical APs relative to a timing reference may still be uncertain.

[0075] FDMA does not require precise time synchronization between APs, nor does it require a master controller or Li-Fi controller for MAC cycle planning, and therefore may be more cost-effective and easier to implement in certain scenarios. To enable the ED to select the correct channel to establish a link with the AP, an automatic channel selection method using a novel identification code (ID) detection is disclosed when the ED enters the coverage area of ​​the optical AP.

[0076] Adjacent access points (APs) in an overlapping area are arranged to emit different IDs. The ED detects the "strongest" ID at a certain location within the overlapping area and decides to operate on the channel corresponding to that "strongest" ID. When the ED moves to another AP with a different ID, it switches to a different channel corresponding to the newly detected ID. Because adjacent APs in the overlapping area operate on different data communication channels, there is no interference in data communication within the overlapping area. When the ED detects only one ID, i.e., in a non-overlapping area, it can operate in full-bandwidth mode to increase data throughput. Furthermore, when no ID is detected, the ED can shut down optical channels, such as Li-Fi channels, and operate in RF mode (e.g., WiFi mode for data communication).

[0077] In one option, the optical AP can be configured to share the same optical data communication channel for both ID transmission and data communication on a frequency-division or time-division basis, allowing a small portion of the frequency of the optical data channel to be allocated to ID transmission, or to schedule ID transmission and data communication on the optical data channel on a time-sharing basis.

[0078] In another option, the optical AP can be configured to continuously or periodically transmit its ID at a low data rate on a separate signaling channel, different from the optical data communication channel. For example... Figure 2 As shown, the ID channel is a separate signaling channel, while AP1 and AP2 share the same optical communication band using FDMA. In this example, data channel 1, centered at F1, is assigned to AP1, while data channel 2, centered at F2, is assigned to AP2.

[0079] Figure 3 This example illustrates the deployment of multiple optical cells in a region. Circles represent the coverage of an optical cell. Cells are indicated by solid or dashed lines. Essentially, it is sufficient to divide the entire optical communication band into two parts, for example, centered at F1 and F2 respectively, to arrange FDMA scheduling between adjacent cells. In this example, the optical cell represented by the dashed line operates at F1, while the optical cell represented by the solid line operates at F2. In some application scenarios, interference suppression in such multi-cell networks may require more than two channels. For example, a third channel may be needed when the solid circles in the first row also overlap with the solid circles in the second row. Furthermore, additional channels may be required if the dashed circles between rows also overlap.

[0080] Optical access points (APs) are pre-configured to operate on a specific frequency channel when they are installed or initialized into the network. This can be achieved through software-based methods, such as using configuration tools. Alternatively, settings can be applied via a DIP switch on the AP device, allowing installers to configure the channel by setting the switch position (either on or off if only two channels are available).

[0081] Figure 4 The diagram illustrates a system setup for managing interference between adjacent optical access points using orthogonal identification codes. For example... Figure 4 In one example shown, AP1 operates on data channel 1 with a center frequency Fif of 12.5 MHz, and AP2 operates on data channel 2 with a Fif of 37.5 MHz. In this example, each data channel occupies a bandwidth of 20 MHz. It should be noted that, depending on hardware characteristics, the available optical communication bandwidth of an optical access point can be much wider, reaching up to several hundred MHz or even GHz. In this example, for illustrative purposes, it is assumed that each channel is 20 MHz, which is the same as a typical Wi-Fi data channel. AP1 is also configured to transmit ID1 (“01111111”) on the optical signaling channel, and AP2 is also configured to transmit ID2 (“10000000”). According to the invention, in different scenarios, the end device side can make the following decisions:

[0082] Scenario 1: The end device receives ID1 "0111 1111" → selects FIF = 12.5MHz; BW = 20MHz

[0083] Scenario 2: The terminal device receives ID2 "10000000" → selects FIF=37.5MHz; BW=20MHz

[0084] Scenario 3: End devices in overlapping areas

[0085] If more "1"s are received than "0"s, select FIF=12.5MHz.

[0086] If more "0"s are received than "1"s, select Fif=37.5MHz.

[0087] Therefore, the end device will select the AP with the stronger ID signal it detects, and then the end device will adjust its own FIF to align with the FIF of the selected AP. Hysteresis can be applied when switching from one FIF to another (such as when receiving the same level ID signal from two APs) to avoid consecutive handovers in overlapping areas. The disclosed interference management mechanism is autonomous. AP synchronization is not required, nor is a central controller needed to align time slots between APs.

[0088] Figure 5 A frequency division multiplexing implementation for data communication and ID transmission at two adjacent optical access points AP1 and AP2 is demonstrated. It can be seen that the center frequencies of the two channels are set separately to reduce the impact of spectral leakage of the signal.

[0089] exist Figure 6 The image illustrates the same example of frequency allocation between two adjacent optical cells, AP1 and AP2, on the optical channel response diagram. Here, it shows the distribution of two 20MHz channels and bit loading (up to 6 bits per symbol) based on the IEEE 802.11g protocol. The blue curve shows the bit loading pattern of G.vlc with adaptive bit loading, where the entire 200MHz bandwidth is used. When the analog and optical front-ends support larger bandwidths (e.g., 100MHz, 200MHz, or higher), it is possible to implement 40MHz or 80MHz channels according to the IEEE 802.11 protocol, accommodating at least two parallel channels for interference suppression between adjacent optical cells.

[0090] Figure 7A detailed example is given of using orthogonal identification codes by an end device located in an overlapping region to distinguish an optical access point (AP) from its neighboring APs. Considering the asynchrony of ID signals from neighboring APs, the end device can detect different patterns in the overlapping region. As explained in the figure, the orthogonality of the codes makes the selected ID pattern robust enough to detect the “strongest” ID in the region even when the ID signals are not synchronized. Figure 7 In the example shown, the amplitude of the received ID2 signal is approximately 50% of the amplitude of the received ID1 signal because AP2 is located further away from the ED than AP1. By choosing an appropriate threshold to decode the received mixed signal, it is still possible to make the correct decision.

[0091] Figure 8 The diagram illustrates the terminal device based on, for example... Figure 7 The identification code shown is used to adjust its FIF. In this example, the end device selects a 12.5MHz FIF to align with the selected access point AP1.

[0092] Figure 9 The illustration shows channel bonding at an optical access point, assuming there are no adjacent optical access points and potential vertical handover between the Li-Fi and Wi-Fi networks. When there is no overlapping area between adjacent APs, the access point can be configured to use two channels, such as 40MHz in this example, and issue a third ID, ID3 = "10101010", to announce this. Accordingly, the end device will make the following decision:

[0093] •Scenario 4: End device receives ID3 = "10101010" → selects FIF = 25MHz; BW = 40MHz.

[0094] It is also possible that an end device detects only one access point transmitting ID1 or ID2, and then the end device may send a request to the access point to suggest possible channel bonding. Such a request can be sent by the end device via the optical signaling channel before establishing a data link, or via the data link. When the request is sent via the data link, the data link can be initialized to the default data channel bandwidth proposed by the access point, and then adapted to a wider bandwidth according to the access point's decision.

[0095] The same ID detection mechanism can also be used to achieve vertical switching between optical and RF networks, such as between Li-Fi APs and Wi-Fi APs. When no ID is detected, such as when the end device is roaming outside the coverage area of ​​the optical cell, the EP can switch to the Wi-Fi network. The advantage of this is that the system can adapt and automatically switch to the RF link when the existing optical link is blocked or listed.

[0096] Scenario 5: The terminal device does not detect any ID code → Select RF channel.

[0097] Note that the examples above are all based on a 20MHz bandwidth. This can be extended to wider bandwidths depending on scheduling between adjacent optical access points, scheduling between multiple end devices with the same access point, and the capabilities of the optical front end and / or the rest of the end devices. A unique Li-Fi AP can be configured with different ID and FIF settings, such as via a mechanical switch or via remote software control. The end device can know in advance the mapping between a certain identification code and the channel center frequency (FIF), and then the end device can adjust its own FIF corresponding to the detected ID signal.

[0098] Alternatively, the ID signal can be transmitted in the form of a (single) frequency tone instead of the digital signal as described above. One AP can transmit a frequency tone at a first frequency (e.g., 500 kHz) in the corresponding signaling channel, while another AP can transmit a different frequency tone at a second frequency (e.g., 1 MHz). End devices can detect and compare the energy of these tones by using a narrow-bandpass filter.

[0099] In addition, other management signals can be sent along the ID signal, such as a "busy" signal when the AP is receiving messages from end devices. Figure 10 As shown, this solves the hidden node problem. When there are two (or more) end devices within the coverage area of ​​an AP, the AP can listen to both EDs, but (due to the LoS requirement of optical signals) the EDs cannot listen to each other. For media access methods such as CSMA / CA in the 802.11 protocol, this leads to collisions in the uplink direction. In this example, the AP has an active data link with ED1. The data link with ED1 runs in parallel, and when ED1 sends a message to the AP, the AP can send a "busy" signal via the signaling channel. ED2 will then be aware of the ongoing uplink from ED1 to the AP and will only attempt to establish a new data link with the AP or a neighboring AP after the "busy" signal is cleared. The "busy" signal can also be implemented implicitly. When there is an active link between the AP and an ED, ID transmission is stopped. Other EDs in the same coverage area of ​​the AP will not be able to detect the ID from the AP and therefore will not be able to connect to the AP. In this way, message collisions in the uplink of the AP can also be reduced.

[0100] Figure 11The basic components of the end device of the present invention are schematically depicted. End device 110 includes at least an optical receiver 116, a wireless transceiver 117, and a controller 118. The optical receiver 116 is configured to detect one or more identification codes on an optical signaling channel, which may be located in a subset of the spectrum, such as infrared, visible, or ultraviolet. The wireless transceiver 117 is configured to support both RF data communication and optical data communication. Two different communication modes can be supported via two separate hardware units. Adjustments to one or more settings include selection between the two separate hardware units. In another, more cost-effective option, the wireless transceiver 117 supports optical and RF communication in a portion shared with both communication modes, while other portions are dedicated to one communication mode. For example, a modem and some analog circuitry may be shared, with two different front-ends, an RF front-end and an optical front-end. The first communication mode may also reuse the entire hardware unit of the second communication mode and enable additional dedicated hardware units to convert signals from the second communication mode to the first mode. Here, the optical communication mode or RF communication mode can be the first communication mode.

[0101] End device 110 may optionally include user interface 119, which can provide users with additional convenience for querying or operating device status. For example, via user interface 119, users can query the status of the data link, such as the actual data rate, or set user preferences when choosing between optical and RF networks.

[0102] Figure 12 Another configuration of the end device is schematically depicted, in which the optical receiver 116 is part of the wireless transceiver 117. As disclosed above, this also indicates that the optical signaling channel can be shared on the optical data communication channel on a frequency-division or time-division basis.

[0103] Figure 13 An example implementation of adjusting the end device corresponding to the selected access point is provided. In this example, the baseband signal from the modem is shifted in frequency to the desired channel or uploaded to the desired intermediate frequency (IF). As illustrated, ID detection can be performed via a dedicated low-power photodiode or via a photodiode used for data communication. The AP can multiplex the ID signal with the data signal because the ID signal is transmitted on a frequency band (close to DC) not used for data communication (such as 1MHz or lower, while data communication starts at 2.5MHz, where IF = 12.5MHz and BW = 20MHz). The ED demultiplexes the detected ID signal by passing it through a filter and then decodes it to determine which access point to select or which channel to use. Then, the IF is shifted to the appropriate frequency.

[0104] Figure 14 A flowchart is shown of a method 500 for an end device 110 to establish a data link with one of a plurality of access points 120 in a multi-cell wireless communication network 100. In step S501, the end device 100 detects one or more identification codes on an optical signaling channel; and in step S502, the end device 100 selects an access point to establish a data link based on the detected one or more identification codes. In a further step S503, the end device 110 adjusts one or more settings corresponding to the selected access point 120; and then in step S504, a data link is established with the adjusted selected access point. The plurality of access points includes at least one optical access point, and each of the one or more identification codes is used to specify one or more settings of an optical access point.

[0105] The method according to the present invention can be implemented on a computer as a computer-implemented method, or implemented with dedicated hardware, or a combination of both.

[0106] The executable code of the method according to the invention can 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 includes non-transitory program code means stored on a computer-readable medium for executing the method according to the invention when the program product is executed on a computer.

[0107] Methods, systems, and computer-readable media (transitory and non-transitory) may also be provided to implement selected aspects of the above embodiments.

[0108] The term "controller" is generally used herein to describe various means relating to functions such as the operation of one or more network devices or coordinators. A controller can be implemented in a variety of ways (e.g., using 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 performing some functions and a processor (e.g., one or more programmed microprocessors and associated circuitry) performing other functions. Examples of controller components that can be employed in various embodiments of this disclosure include, but are not limited to, conventional microprocessors, application-specific integrated circuits (ASICs), and field-programmable gate arrays (FPGAs).

[0109] In various embodiments, the processor or controller may be associated with one or more storage media (generally referred to herein as "memory," such as volatile and non-volatile computer memories, such as RAM, PROM, EPROM and EEPROM, compact disks, optical disks, etc.). 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. Various storage media may be fixed within the processor or controller or may be removable, such that one or more programs stored thereon can be loaded into the processor or controller to implement 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 adopted to program one or more processors or controllers.

[0110] As used herein, the term “network” refers to any interconnection of two or more devices (including controllers or processors) that facilitates the movement of information between any two or more devices and / or multiple devices coupled to the network (e.g., for device control, data storage, data exchange, etc.).

Claims

1. A method (500) performed by an end device (110) for establishing a data link by selecting one of a plurality of access points (120) in a multi-cell wireless communication network (100), wherein, The plurality of access points (120) includes at least one optical access point and one radio frequency (RF)-based access point, and the method includes the end device (110): - Monitor (S501) the occurrence of one or more identification codes in the optical signaling channel, wherein each of the one or more identification codes is used to uniquely identify the optical access point, and wherein each of the one or more identification codes is also used to designate a sub-channel within the optical communication band for use as the optical data channel of the data link; - Based on the detection of one or more identification codes, select (S502) an access point (120) for establishing the data link, wherein the data link is established on a channel with a frequency different from the optical signaling channel; and the other channel includes an optical data channel or an RF data channel; - The selection of the access point (120) further includes: ◦ Select an RF-based access point when no identification code is detected; as well as ◦ When at least one identification code is detected, select an optical access point and perform further steps: ▪ Adjustment (S503) corresponds to one or more settings of the selected optical access point (120), wherein the one or more settings include at least one hardware configuration; and ▪ After the adjustment, establish (S504) a data link on another channel with the selected optical access point (120).

2. The method (500) according to claim 1, wherein, When more than one identification code is detected, the optical access point corresponding to the detected identification code with better received signal quality is selected to establish the data link.

3. The method (500) according to claim 1, wherein, The one or more identification codes are orthogonal to each other.

4. The method (500) according to claim 1, wherein, When only one identification code is detected, the optical data channel can be extended to include more than one sub-channel within the optical communication band.

5. The method (500) according to any one of the preceding claims, wherein, The one or more identification codes are also used to specify the configuration to be used on the data link.

6. An end device (110) for establishing a data link by selecting one of a plurality of access points (120) in a multi-cell wireless communication network (100), wherein the plurality of access points (120) includes at least one optical access point and one radio frequency (RF)-based access point, the end device (110) comprising: - An optical receiver (116) is configured to monitor the presence of one or more identification codes in an optical signaling channel; Each of the one or more identification codes is used to uniquely identify the optical access point, and each of the one or more identification codes is also used to specify a sub-channel within the optical communication band for use as an optical data channel of the data link; - A controller (118) is configured to select an access point (120) for establishing a data link based on the detection of one or more identification codes; and wherein the data link is established on a channel different in frequency from the optical signaling channel; and the other channel includes an optical data channel or an RF data channel; wherein an RF-based access point is selected when no identification code is detected, and an optical access point is selected upon detection when at least one identification code is detected; and - A wireless communication transceiver (117) is configured to adjust one or more settings corresponding to the selected access point (120) when the selected access point (120) is an optical access point, and to establish a data link using the selected access point (120) after adjustment; wherein the one or more settings include at least one hardware configuration.

7. The terminal device (110) according to claim 6, wherein, The wireless communication transceiver (117) is also configured to support optical communication or RF communication when one or more settings are adjusted.

8. The terminal device (110) according to claim 7, wherein, The optical receiver (116) is part of the wireless communication transceiver (117).

9. A multi-cell wireless communication system (100), comprising: - At least one end device (110) as described in claim 6; - At least one RF access point (120) is configured to establish data communication with at least one end device; and - At least one optical access point (120) is configured to establish data communication with at least one end device; The at least one optical access point (120) is also configured to transmit an identification code on an optical signaling channel.

10. A computing program including code means, which, when executed by an end device (110) of claim 6 including a processing means, causes the processing means to perform the method of any one of claims 1-5.

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