A method for initiating a handover of a LiFi module, a mobile device containing a LiFi module, and a user device.

Abstract

A LiFi module for operatively connecting to a WiFi communication module supporting both Wi-Fi and Li-Fi connections is disclosed. The LiFi module includes an optical front end (OFE) and a connection circuit for communicatively connecting the OFE to the WiFi communication module. The connection circuit includes a switching element electrically connected to the LiFi signal strength detector and configured to enable or disable a connection between the OFE and the WiFi communication module under the control of the LiFi signal strength detector, and a LiFi signal strength detector electrically connected to the switching element and a receive path of the OFE and configured to detect a strength of an optical signal received on the receive path of the OFE and to control the switching element based on the detected strength of the optical signal.

Description

Technical Field

[0001] The present disclosure generally relates to the field of wireless communications, and more specifically relates to a LiFi module, a mobile device including the LiFi module, and a method for initiating handover of a user device.

Background Art

[0002] Nowadays, more and more devices are connected to the Internet, and most of these devices connect wirelessly. For this reason, conventional wireless communication technologies that use Radio Frequency (RF) technology are facing great pressure. There are two reasons for this. First, the RF spectrum has become quite crowded, and furthermore, there are areas where RF wireless communication is not permitted or does not fit well.

[0003] Recently developed LiFi technology is a wireless communication technology that uses light to transmit data or communicate between devices via, for example, visible light, ultraviolet, and infrared spectra.

[0004] Wireless LiFi communication can be advantageous over wireless RF communication in various aspects. For example, the optical spectrum used by LiFi is much wider than the RF spectrum, provides higher data rates, and can be used in areas that are susceptible to electromagnetic interference such as aircraft. Furthermore, communication over light supports a significantly higher data density than RF, due to the nearly unlimited bandwidth of the visible / non-visible optical spectrum.

[0005] On the other hand, LiFi communication has limited coverage because light cannot penetrate objects such as walls. Furthermore, most currently available devices only use hardware for WiFi (registered trademark) networking, and thus are not compatible with LiFi technology.

[0006] Therefore, it is more desirable to use both WiFi and LiFi technologies in combination, allowing users to experience the advantages of both WiFi and LiFi communication.

[0007] Proposed solutions for simultaneous use of WiFi and LiFi require a combiner at a higher layer, i.e., the TCP / IP layer, to transmit signals via both RF and LiFi signal paths, either by utilizing both WiFi and LiFi network interfaces or by using a MIMO chip. Such solutions handle communication between the two devices using MIMO technology and a mixed use of RF and optical frequencies.

[0008] In another conventional solution, the LiFi module is designed as an integrated part of the WiFi chip, and the signal required to select between WiFi and LiFi networks comes from the MAC layer. This signal is from the digital domain and is based on the Received Signal Strength Indicator (RSSI) calculated within the WiFi chip. To utilize this MAC signal, an additional connection between the Optical Front End (OFE) and the WiFi chip is required.

[0009] According to another known system, an access point (AP) can connect to both Wi-Fi and LiFi, as can user terminal devices. In this case, handover between LiFi and Wi-Fi networks occurs within the same network, and there is no roaming or handover from one LiFi AP to another Wi-Fi AP, or vice versa. This handover involves only physical (PHY) layer handover and is sometimes called intra-AP handover.

[0010] Recent developments have proposed 802.11 WiFi-based LiFi systems that enable the possibility of integrating LiFi with existing WiFi networks. Advantages of using WiFi chips for LiFi communication include the reuse of rich WiFi network management and security protocols and resources.

[0011] A well-designed WiFi-based LiFi system, with convenience in mind, allows the LiFi front-end to remain transparent to the higher-layer WiFi protocol, enabling the reuse of existing mechanisms such as high-speed roaming. In this way, the LiFi network becomes an integral part of the wireless access network, for example, in a building, alongside the existing WiFi network.

[0012] US2020 / 195342A1 discloses a WLAN Li-Fi transceiver including a Wi-Fi device and an analog front end. Paragraphs 101 and 102 disclose that a MAC controller 420 configures the WLAN transceiver to communicate via Wi-Fi instead of Li-Fi if the Li-Fi signal quality is unacceptable. The MAC controller 420 generates a selection signal 424 to disconnect the Wi-Fi RF module 408 from the RF / Li-Fi converter 412 and to connect the Wi-Fi RF module 408 from the Wi-Fi antenna interface 416.

[0013] SANUSI JAAFARU et al.'s "Handover in hybrid LiFi and WiFi networks" (2019-12-10) provides an overview concept of hybrid handover in LiFi / WiFi networks. It discloses the concept of soft handover and considers various QoS parameters, including RSSI, in hybrid handover.

[0014] "Hard and soft switching for indoor hybrid VLC / RF systems" by Ashimbayeva Aigerim et al. (2017-09-20) is dedicated to the analysis of hard switching (HS) and soft switching (SS) methods for hybrid VLC / RF systems. It demonstrates that SS outperforms HS when power is optimally shared between the VLC link and the RF link.

[0015] Figure 1 schematically shows a communication system 10 deployed using both a LiFi network and a WiFi network. The communication system 10 may be a local area network (LAN) including a LAN switch 11, a WiFi access point (AP) 12 connected to the LAN switch 11, and two LiFi APs 13 and 14. The LiFi APs 13 and 14 have coverage areas 15 and 16, respectively, indicated by solid triangles, and the WiFi AP has a coverage area 17, indicated by a dashed triangle.

[0016] As can be seen from Figure 1, LiFi APs have relatively small coverage areas 15 and 16, and therefore, blind spots may exist between the coverage areas of two LiFi APs. In contrast, WiFi signals, which are widely present in commercial buildings, can achieve wider coverage 17, but WiFi throughput can be significantly slower than LiFi due to interference.

[0017] Due to the facts described above, user devices operating in a network environment like the one shown in Figure 1 may need to hand over between WiFi and LiFi networks from time to time. In an office environment, users may need to move from one room to another during an online meeting. In the case of a LiFi network, the connection link may be temporarily lost if the user enters or passes through a blind area. It may take several seconds to disconnect from the LiFi AP and reconnect to the WiFi AP, which results in a poor user experience. [Overview of the project] [Problems that the invention aims to solve]

[0018] Therefore, a seamless handover method between LiFi and WiFi networks is truly needed to improve the user experience in WiFi-based LiFi networks. [Means for solving the problem]

[0019] In a first aspect of this disclosure, a LiFi module for operationally connecting to a WiFi communication module that supports both Wi-Fi and LiFi connectivity, the LiFi module comprising an optical front end (OFE) for transmitting and receiving data via an optical medium, and a connection circuit for communicatively connecting the OFE to the WiFi communication module, the connection circuit being A switching element electrically connected to a LiFi signal strength detector and configured to enable or disable the connection between the OFE and the WiFi communication module under the control of the LiFi signal strength detector, A LiFi signal intensity detector is electrically connected to the switching element and the OFE receiving path, and is configured to detect the intensity of the optical signal received in the OFE receiving path and to control the switching element based on the detected intensity of the optical signal. A LiFi module including this is presented.

[0020] This disclosure is based on the insight that by utilizing a LiFi module that works with a WiFi communication module that supports dual antenna connectivity, a seamless transition between LiFi and WiFi networks can be achieved by using only one wireless link for data communication.

[0021] The LiFi module connection circuit for connecting a LiFi module to a WiFi communication module includes a switching element that operates under the control of a LiFi signal strength detector, or simply a signal strength detector, and enables or disables the connection between the LiFi module's OFE and the WiFi communication module based on the intensity of the optical signal detected by the LiFi signal strength detector. This enables seamless handover between the LiFi network and the WiFi network, depending on the availability of the LiFi network indicated by the intensity of the optical signal detected by the LiFi module's LiFi signal strength detector.

[0022] Compared to conventional technologies that rely on simultaneously enabling WiFi and LiFi connectivity for data communication and therefore require complex protocols at the TCP / IP layer to combine RF and optical data paths with two baseband chips, the LiFi module of this disclosure remains simple from a circuit design standpoint and does not require any changes to existing TCP / IP protocols.

[0023] A signal required for selecting between a WiFi network and a LiFi network comes from the MAC layer. Therefore, compared with the prior art which requires an extra connection between an OFE and a WiFi chip, the optical signal used in the present disclosure is an analog signal generated locally inside the OFE. As a result, LiFi module communication remains completely independent of the WiFi module, which makes the LiFi module "universal", that is, the LiFi module can operate with a standard off-the-shelf WiFi communication module supporting dual antenna connection without an extra connector.

[0024] In an example of the present disclosure, the switching element comprises a first switch and a second switch, wherein a control terminal of the first switch is connected to a first output terminal of the LiFi signal strength detector, and a control terminal of the second switch is connected to a second output terminal of the LiFi signal strength detector.

[0025] The LiFi signal strength detector for detecting an optical signal outputs two control signals for separately controlling two switches. The two switches operate to ensure a smooth transition in a so-called "make before break" mode, which means that a connection with one network is established before the connection with the other network is disconnected, thereby preventing connection interruption.

[0026] In one example of the present disclosure, the signal strength detector is configured to output an enabling signal at its second output signal when the detected intensity of the optical signal is lower than a threshold, and output a disabling signal at its first output terminal after a delay period; the first switch is configured to disable the connection between the OFE and the WiFi communication module in response to the disabling signal received at its control terminal from the first output terminal of the LiFi signal strength detector; the second switch is configured to enable the connection between the WiFi communication module and a radio frequency (RF) antenna in response to the enabling signal received at its control terminal from the second output terminal of the LiFi signal strength detector.

[0027] When the detected intensity of the optical signal is lower than a threshold indicating that a user is near the edge of LiFi coverage, the RF antenna of the WiFi network is enabled by the second switch. In this way, the WiFi communication module can prepare to connect to the WiFi network and prepare for fast roaming, for example, through a WiFi access point (AP) within the coverage area of the RF antenna.

[0028] In practice, the first switch operates to disable the connection between the OFE and the WiFi communication module with a slight delay, thereby securing a certain amount of "overlap" time between the WiFi network and the LiFi network. This ensures that in a "make and break" manner, the WiFi network is connected before the LiFi network is disconnected, thereby enabling a smooth transition from the LiFi network to the WiFi network.

[0029] Furthermore, if the connection between the OFE and the WiFi communication module is disabled, the first switch may also be configured to enable the connection between the WiFi communication module and an additional RF antenna.

[0030] Therefore, the WiFi communication module is connected to two antennas operating on the same or different frequencies, which allows for more communication resources.

[0031] Those skilled in the art may conceive that it is also possible to connect the WiFi communication module to a load such as a 50-ohm terminator in order to disable the connection to the WiFi communication module controlled by the first switch.

[0032] In one example of the present disclosure, a LiFi signal intensity detector is configured to output an enabling signal at its first output terminal when the detected intensity of an optical signal is higher than a threshold, and to output a disabling signal at its second output terminal after a delay period; a first switch is configured to enable the connection between the OFE and the WiFi communication module in response to the enabling signal received at its control terminal from the first output terminal of the LiFi signal intensity detector; and a second switch is configured to disable the connection between the WiFi communication module and the RF antenna and enable the connection between the WiFi communication module and the 50-ohm terminator in response to the disabling signal received at its control terminal from the second output terminal of the LiFi signal intensity detector.

[0033] This concerns a handover scenario from a WiFi network to a LiFi network. When a user enters a LiFi coverage area, the detected intensity of the optical signal rises above a threshold. Therefore, the signal strength detector outputs a control signal to the first switch, enabling the connection between the OFE and the WiFi communication module. The second switch is also controlled by the signal strength detector to disconnect the RF antenna from the WiFi communication module with a delay.

[0034] This enables smooth handover between LiFi and WiFi networks, as well as seamless connectivity, through a LiFi module that works in conjunction with a WiFi communication module that supports both WiFi and LiFi connectivity.

[0035] In further examples of this disclosure, the first switch and the second switch are single-pole double-throw switches.

[0036] These readily available switches can be conveniently used to implement the connection circuitry for LiFi modules. The cost of LiFi modules is kept low, and implementation is simple.

[0037] In one example of the present disclosure, the LiFi module further includes an RF-LiFi converter connected between the OFE and a first switch of the connecting module, configured to perform frequency conversion between the RF band and the LiFi optical baseband.

[0038] The RF-LiFi converter upconverts or downconverts RF signals, such as 2.4GHz or 5GHz, to optical baseband frequencies at the connection port of a WiFi communication module, and then interfaces with the OFE (Optical Field Energy).

[0039] In one example of this disclosure, a third switch is connected between the RF-LiFi converter and the first switch of the connection module and is configured to separate the transmit signal and the receive signal from the WiFi communication module.

[0040] Since the OFE communication module operates in full-duplex mode and the WiFi communication module operates in half-duplex mode, the third switch functions with an RF detector to separate the TX and RX signals from the WiFi communication module by detecting the RF signal on the TX path.

[0041] A second aspect of the present disclosure provides a wireless communication module for providing network services to both a WiFi network and a LiFi network connected to the same LAN, the wireless communication module comprising a LiFi module according to the first aspect of the present disclosure and a WiFi communication module operably connected to the LiFi module and supporting both WiFi and LiFi connections. The WiFi communication module includes a first connection port and a second port, the first connection port being switched between an RF antenna and a terminator under the control of a LiFi signal strength detector of the LiFi module, and the second connection port being switched between the OFE of the LiFi module and a second RF antenna or terminator.

[0042] The LiFi module of this disclosure may be used in a user device. In addition to including a LiFi module according to a first aspect of this disclosure, the user device further includes a WiFi communication module that supports both WiFi and LiFi connectivity and is operably connected to the LiFi module, the connection between the OFE of the LiFi module and the WiFi communication module being enabled or disabled under the control of the signal strength detector of the LiFi module.

[0043] Such user devices can seamlessly hand over between WiFi and LiFi networks, thereby improving the user experience in terms of network connectivity.

[0044] A third aspect of this disclosure is a method for initiating a handover of a user device between a WiFi network and a LiFi network, both of which are connectable to a user device and both connected to the same local area network (LAN), wherein the user device includes a LiFi module according to the first aspect of this disclosure, and the user device further includes a WiFi communication module that supports WiFi and LiFi connections on two connection ports, respectively, and the method is performed by a control software routine of the WiFi communication module of the user device. The steps include detecting a change in state at one of the connection ports of the WiFi communication module, The steps include initiating a handover between the WiFi network and the LiFi network using the fast roaming procedure, This provides a method that includes [something].

[0045] For example, when initiating a handover between a WiFi communication network and a LiFi communication network using high-speed roaming, it is crucial for the WiFi module to know when the switching action between the two networks should occur. A LiFi module according to a first aspect of this disclosure, when operating with a WiFi communication module, provides an indication to the WiFi communication module when a state change occurs at one of the connected ports, under the control of the LiFi module's signal strength detector.

[0046] When a WiFi module detects a change in state, it recognizes that it's time to initiate or start the handover procedure. Because fast roaming is typically achieved in a very short time, around 40 milliseconds, the user device successfully connects to the new network before losing its connection to the current network, resulting in a seamless handover between networks.

[0047] In one example of the present disclosure, a user device is connected to a LiFi network, the detection step includes detecting that a WiFi beacon message is received on a second connection port of a WiFi communication module, and the initiation step includes initiating a handover from the LiFi network to the WiFi network.

[0048] When a user device is accessing a LiFi network, the WiFi module can receive a WiFi beacon message as a result of the user device about to lose its connection to the LiFi network, for example, because the user device is at the edge of the LiFi network. At this point, a handover from the LiFi network to the WiFi network begins.

[0049] Specifically, in one example of this disclosure, the WiFi beacon message is received at the second connection port of the WiFi communication module as a result of enabling the connection between the second connection port of the WiFi communication module and the RF antenna, in response to an enabling signal received at the control terminal of a second switch from the second output terminal of the signal strength detector of the LiFi module.

[0050] If a user device is about to lose its connection to the LiFi network, the signal strength detector will detect this situation and control a second switch to enable the connection between the second port of the WiFi communication module and the RF antenna, thereby allowing the WiFi communication module to receive WiFi beacon messages.

[0051] Except for two connection ports, direct communication between the LiFi module and the WiFi communication module is not required.

[0052] In one example of the present disclosure, the user device is connected to a WiFi network, the discovering step includes detecting that a LiFi beacon message is received at a first connection port of a WiFi communication module, and the initiating step includes initiating a handover from the WiFi network to the LiFi network.

[0053] This relates to a scenario where a user is accessing a WiFi network and moves into a LiFi network coverage area, meaning the WiFi communication module should now initiate a handover from the WiFi network to the LiFi network.

[0054] In one example of this disclosure, the LiFi beacon message is received at the first connection port of the WiFi communication module as a result of enabling the connection between the first connection port of the WiFi communication module and the OFE, in response to an enabling signal received at the control terminal of a first switch from the first output terminal of the signal strength detector of the LiFi module.

[0055] In this case as well, the LiFi module's signal strength detector triggers a state change, allowing high-speed roaming to begin at the appropriate time.

[0056] In one embodiment of this disclosure, an indicator is included in the WiFi beacon message and the LiFi message to distinguish between a WiFi network and a LiFi network.

[0057] The indicator may also be a special code to identify the LiFi AP, which is inserted into the appropriate field of the beacon message, allowing the user device to determine which network is reachable.

[0058] A fourth aspect of the present disclosure provides a computer program product that, when executed on at least one processor, includes a computer-readable storage medium that stores instructions causing at least one processor to perform the method according to the third aspect of the present disclosure.

[0059] The above-mentioned and other features and advantages of this disclosure will be best understood from the following description with reference to the attached drawings. In the drawings, similar reference numerals indicate the same part or a part that performs the same or equivalent function or operation. [Brief explanation of the drawing]

[0060] [Figure 1] This diagram outlines a communication system deployed using both LiFi and Wi-Fi networks. [Figure 2] A schematic block diagram of the LiFi module described herein is shown. [Figure 3] This is a schematic timing diagram illustrating the control of a switch that enables or disables a LiFi or WiFi network based on the detected intensity of an optical signal. [Figure 4] A schematic representation of an 802.11 beacon frame is shown below. [Figure 5] A flowchart-type diagram schematically illustrates how to initiate a handover of a user device, including the LiFi module of this disclosure, between a WiFi network and a LiFi network. [Figure 6] A schematic diagram of the complete operation procedure using the method shown in Figure 5 with a user device or EP is provided below. [Modes for carrying out the invention]

[0061] Herein, embodiments contemplated by this disclosure are described in more detail with reference to the accompanying drawings. The subject matter disclosed should not be construed as being limited only to the embodiments described herein. Rather, the illustrated embodiments are provided as examples to convey the scope of the subject matter to those skilled in the art.

[0062] In the following explanation, the terms "handover," "handoff," and "roaming" are used interchangeably, as are the terms "user device" and "EP."

[0063] Seamless handoff between a WiFi network and a LiFi network is achieved by using the LiFi module proposed in this disclosure. Application scenarios for the LiFi module may include user devices such as laptops or mobile phones, which may also be called endpoints (EPs), deployed in a local area network (LAN).

[0064] The LAN may be an Extended Basic Service Set (BSS) including multiple BSSs, including LiFi APs and WiFi APs. The LiFi APs and WiFi APs are independent of each other and are both connected to the same LAN. Furthermore, the LiFi AP is a module that is detachably connected to the WiFi AP, and the two APs may function independently of each other. In other words, the LiFi AP and WiFi AP may be physically packaged together, or even on the same PCB, but logically they are two separate APs connected to the same LAN.

[0065] Both LiFi APs and WiFi APs implement IEEE 802.11r. IEEE 802.11r is a revision of the IEEE 802.11 standard that allows continuous connectivity for wireless devices in transit through fast and secure client migration from one BSS or AP to another, with near-seamless transitions. Switching or transitioning from one AP to another is also known as handoff or roaming.

[0066] 802.11r introduces a new roaming concept called Fast Transition (FT), in which an initial handshake takes place with a new AP before the client, i.e., the EP or user device, roams to the target AP. This initial handshake allows the client and AP to calculate a Pairwise Transient Key (PTK) in advance. These PTK keys are then applied to the client and AP after the client has exchanged a re-association request or response with the new target AP.

[0067] FT compliant with 802.11r may also be called the “Make Before Break” procedure. Specifically, an FT originator, which may be an EP or user device, determines that it needs to migrate to a new or target AP while still connected to the current AP. The FT originator then exchanges Authentication-Request and Authentication-Response messages with the target AP before exchanging Reassociation Request and Reassociation Response messages with the target AP. Successful reassociation occurs only if the time between the Authentication Request and the Reassociation Request does not exceed the Reassociation Deadline Time.

[0068] Therefore, for an EP's WiFi chip that performs a migration or switching action from one AP to another, it is crucial to know the moment when the switch to the other network will begin.

[0069] The LiFi module proposed in this disclosure operates in conjunction with a dual-antenna WiFi communication module to enable smooth and seamless handoff between the LiFi network and the WiFi network.

[0070] Figure 2 schematically shows a block diagram of the LiFi module 20 according to this disclosure. The LiFi module 20, sometimes referred to as an analog front end, is suitable for operation with an existing WiFi communication module 200 that supports both WiFi and LiFi connectivity.

[0071] The WiFi communication module 200 may be configured in a popular M.2 module form factor, for example, via a PCIe interface, enabling easy connection to the motherboard of the user device. The WiFi communication module 200 has two connection ports 201 and 202, which means that the WiFi communication module 200 supports dual antennas. The WiFi chip 205 of the WiFi communication module 200 is configured to work in conjunction with the operation of the LiFi module 20 to perform high-speed roaming between the WiFi network and the LiFi network.

[0072] The LiFi module 20 includes an optical front end (OFE) 21, which includes a transmit path 22 and a receive path 23, respectively, arranged to transmit and receive data via an optical medium such as the visible light, ultraviolet, and infrared spectra.

[0073] The transmission path 22 of OFE21 includes a driver and a light-transmitting device, which may be, for example, a vertical-cavity surface-emitting laser (VCSEL) or a light-emitting diode (LED). The reception path 23 of OFE21 includes a light-receiving device, such as a photodiode, and a transimpedance amplifier (TIA).

[0074] The LiFi module 20 further includes a connection circuit for communicatively connecting OFE 21 to one of the connection ports of the WiFi communication module 200. In an example as shown in Figure 2, the connection 26 between OFE 21 of the LiFi module 20 and the connection port 201 of the WiFi communication module 200 via the connection circuit may be enabled or disabled.

[0075] The connection circuit includes a switching element 24 and a LiFi signal strength detector or simply a signal strength detector 25. The switching element 24 is electrically connected to the signal strength detector 25 and is configured to enable or disable connection 26, which is a communication connection between OFE 21 and the WiFi communication module 200, under the control of the signal strength detector 25.

[0076] The signal strength detector 25 is electrically connected to the switching element 24 and the receiving path 23 of the OFE 21, and is configured to detect the intensity of the optical signal received in the OFE's receiving path 23 and to control the switching element 24 based on the detected intensity of the optical signal.

[0077] The switching element 24 includes a first switch S1 and a second switch S2, which are controlled by a first control signal K1 and a second control signal K2 output by a signal strength detector 25, respectively. Specifically, the control terminal of the first switch S1 is connected to the first output terminal of the signal strength detector 25, and the control terminal of the second switch S2 is connected to the second output terminal of the signal strength detector 25.

[0078] The two switches S1 and S2 may be single-pole double-throw (SPDT) switches that work together to control the routing of communication signals from the WiFi communication module 200 to the OFE 21 of the LiFi module 20 or to the RF antenna 203, and optionally to an additional RF antenna 204, depending on the detected optical signal intensity.

[0079] Specifically, the first switch S1 is controlled by a first control signal K1 and switches the first connection port 201 of the WiFi communication module 200 between position 1, which is connected to OFE 21, and position 0, which is connected to an additional RF antenna 204. It can be understood that the output terminal of position 0 of S1, which is connected to the RF antenna 204, may be terminated with a 50-ohm load (not shown). In this case, the WiFi communication module 200 operates on only one RF band via the RF antenna 203.

[0080] The second switch S2 is controlled by the second control signal K2 and switches the second connection port 202 of the WiFi communication module 200 between position 1, which is connected to the RF antenna 203, and position 0, which is terminated by a 50-ohm load R1.

[0081] Due to the fact that the signal at the connection port of the WiFi communication module 200 is a radio frequency signal, the LiFi module 20 further includes an RF mixer for down / up conversion of the RF signal transmitted through the connection port 201 of the WiFi communication module 200, and then interface with the OFE 21 of the LiFi module 20.

[0082] Since OFE21 is a full-duplex module while the WiFi communication module 200 operates in half-duplex mode, the LiFi module 20 further includes an RF detector 28 and a third switch S3, which work together to separate the TX and RX signals from the WiFi communication module 200 by detecting the RF signal on the TX path.

[0083] The operation of the LiFi module 20 is described in detail below.

[0084] The signal strength detector 25 measures the intensity of the optical signal received via the receiving path 23 of the LiFi module 20, indicating whether the user device, including the LiFi module 20, is within the LiFi coverage area.

[0085] Depending on the comparison result between the measured intensity of the received optical signal and a predetermined threshold, the signal intensity detector 25 outputs two control signals K1 and K2 to control the first switch S1 and the second switch S2 separately, respectively.

[0086] For example, if the measured intensity of the received optical signal is higher than a threshold, the signal intensity detector 25 may output a control signal with a high level "1" from one of its output terminals and a further control signal "0" from the other output terminal. When the control signal is high "1", the controlled switch is connected to position 1, and when the control signal is low "0", the switch is connected to position 2.

[0087] Those skilled in the art can expect that the above examples are not limiting to the implementations of the disclosure. In practice, other controller methods may be defined.

[0088] In the steady-state operating mode of the user device, which includes LiFi and WiFi communication modules 20 and 200, the WiFi chip processor 205 in the WiFi communication module 200 is enabled to detect state transitions or state changes, so that either the RF connection or the optical connection is active and the other medium is disabled, which is used by the user device to initiate high-speed roaming.

[0089] All user devices are connected to the same LAN, which includes LiFi APs and WiFi APs.

[0090] Currently, assume that the first switch S1 is in position 1 and switch S2 is in position 0, i.e., the connection between the WiFi communication module 200 and the OFE 21 of the LiFi module 20 is enabled. At this point, the user device is connected to the LAN via the LiFi AP. As the user device moves toward the edge of the LiFi coverage area, the intensity of the optical LiFi signal detected by the signal strength detector 25 begins to decrease and falls below a threshold.

[0091] In this case, the second switch S2 is controlled by a control signal K2 received at the input terminal of the second switch S2 from the signal strength detector 25 to switch to position 1, which enables the connection between the RF antenna 203 and the WiFi communication module 200 via the connection port 202. In this way, the WiFi communication module 200 can establish contact with WiFi APs within the coverage area of ​​the RF antenna 203 and prepare for high-speed roaming.

[0092] At the same time, the user device is still associated with the LiFi AP via connection port 201 and a signal path through the first switch S1. As soon as the WiFi chip 205 realizes that the WiFi AP is accessible, it initiates, for example, an 802.11 fast roaming procedure.

[0093] From this point onward, the control signal K1 is set to level "0" after a predetermined amount of "overlap" time, or when the detected LiFi signal becomes nearly zero. Therefore, the first switch S1 is controlled by K1 to switch to position 0. From that point onward, the connection between the WiFi communication module 200 and OFE21 is disconnected, and the user device operates in WiFi mode.

[0094] In practice, the "overlap" time or delay between switching the second switch S2 to position 1 and switching the first switch S1 to position 0 may be set to a predetermined time, such as 100 ms, which is sufficient for the fast roaming procedure to complete.

[0095] Alternatively, the control signal K1 may be triggered by an even lower threshold value for the intensity of the optical LiFi signal detected by the signal intensity detector 25. The same applies to the switching procedure from the WiFi network to the LiFi network.

[0096] When position 0 of switch S1 is connected to the additional antenna 204, the WiFi chip 205 operates with dual antennas. Alternatively, position 0 of S1 can be connected to a 50-ohm terminator, allowing the WiFi chip to operate with only one antenna.

[0097] On the other hand, if a user device enters a LiFi coverage area while still connected to a WiFi network, the connection between the OFE of the LiFi connection module 20 and the WiFi communication module 200 is enabled before the (multiple) RF antennas are disconnected.

[0098] Specifically, the intensity of the optical LiFi signal detected by the signal intensity detector 25 exceeds the threshold. Therefore, the signal intensity detector 25 outputs a control signal K1 "1" to switch switch S1 to position 1. Thus, connection port 202 of the WiFi communication module 200 remains connected to the RF antenna 203, while connection port 201 of the WiFi communication module 200 is connected to OFE 21.

[0099] The WiFi chip 205 maintains its association with the WiFi AP, while the fast roaming procedure is initiated to start the association with the LiFi AP.

[0100] When a user device is associated with a LiFi AP, the second switch S2 is controlled by the signal strength detector 25 to switch to position 0, which connects the connection port 202 to a 50-ohm terminator, i.e., the reception of WiFi signals is completely disabled. This serves the purpose of allowing the WiFi chip 205 to detect WiFi / LiFi operating mode state transitions without any extra signal connections between the LiFi and WiFi communication modules.

[0101] Since a user device is associated with only one AP at a time, the LiFi module 20 proposed by this disclosure can enable smooth handover between LiFi and WiFi networks, thereby achieving seamless connectivity.

[0102] Figure 3 is a schematic timing diagram showing the control of switches S1 and S2, which use control signals K1 and K2 to enable or disable a LiFi or WiFi network based on the detected intensity of an optical signal.

[0103] Curve 31 represents the intensity of the optical signal detected by the signal intensity detector 25. At time point A, the detected optical signal intensity is below the threshold 39. The control signal K2 at this point 32 enables switch S2 to connect the RF antenna to the WiFi communication module and triggers the start of the fast roaming procedure for roaming on the WiFi network.

[0104] At time point 33, the user device connects to the WiFi network. Then, at time point 34, the control signal K1 controls switch S1 to disconnect OFE from the WiFi communication module. As described above, the time period between 32 and 34 may be set to a predetermined value. Alternatively, time point 34 may be determined by a further threshold 310 lower than the first threshold 39.

[0105] Meanwhile, at point B, the intensity of the optical signal detected by the signal intensity detector 25 exceeds the threshold 39. At this point 36, the control signal K1 enables switch S1 to connect OFE to the WiFi communication module and triggers the start of a fast roaming procedure for roaming to the LiFi network.

[0106] At time point 37, the user device is connected to the LiFi AP. Then, at time point 38, the control signal K2 controls switch S2 to disconnect the RF antenna from the WiFi communication module and connect connection port 202 to a 50-ohm terminator. Again, the delay period between 36 and 38 may be set to have a predetermined length. Alternatively, time point 38 may be determined based on a further threshold (not shown) higher than the first threshold 39.

[0107] A method for initiating a handover of a user device including the LiFi module of this disclosure between a WiFi network and a LiFi network is described below in detail.

[0108] IEEE 802.11r provides two roaming methods: Over-the-Air and Over-the-DS (Distribution System). For completeness, the Over-the-Air message exchange procedure compliant with IEEE, "Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications," IEEE, 2016, is briefly described below. In all high-speed roaming operations, the FT Originator (FTO) is the client.

[0109] Initially, the FTO performs data transmission if it determines that it is connected to the current AP in a secure session and needs to migrate to the target AP. The FTO then sends an 802.11 authentication request to the target AP and receives an authentication response from the target AP. Subsequently, a reassociation request is sent from the FTO to the target AP, and a reassociation response may be sent from the target AP to the FTO. Successful reassociation occurs only if the time between the authentication request and the reassociation request does not exceed the reassociation deadline. If reassociation is successful, the 802.1X controlled port is unblocked, and a successful (secure) session and data transmission may be performed.

[0110] To ensure successful high-speed roaming, the WiFi chip in the user device maintains a record of neighbor APs and recognizes the transition trigger when both WiFi and LiFi APs become visible. The user device then immediately decides to hand over to the new AP.

[0111] To distinguish between WiFi APs and LiFi APs, during the installation phase, LiFi APs are given a special code in their beacon frames so that user devices can always distinguish between WiFi APs and LiFi APs. This information allows user devices to know the exact moment when they should trigger the fast roaming procedure.

[0112] A special code for identifying a LiFi AP can be implemented, for example, in the Vendor Specific field of the 802.11 beacon frame, as shown in Figure 4, or in any other convenient field of the beacon frame. In this way, after decoding the beacon frame, the user device will know whether the AP is a WiFi AP or a LiFi AP.

[0113] Figure 5 schematically illustrates a method 50 of initiating a handover of a user device including the LiFi module of this disclosure between a WiFi network and a LiFi network, in a flowchart-type diagram.

[0114] Aside from the two connection ports on the WiFi communication module, there is no direct communication between the LiFi module and the WiFi chip in this disclosure.

[0115] Method 50 enables the WiFi chip to know when the switching action, i.e., the transition triggers K1 and K2 shown as "A" and "B" in Figure 3, will occur, and thereby enable it to initiate high-speed roaming at the appropriate time.

[0116] In step 51, the WiFi chip detects a change in state at one of the connection ports of the WiFi communication module.

[0117] This may include the WiFi chip detecting whether the RF antenna is connected to connection port 202 of the WiFi communication module, or whether the OFE is connected to connection port 201 of the WiFi communication module.

[0118] In one example, a user device performs a network scan in the conventional way to find out if there is an AP within its communication range. When the user device "sees" a LiFi AP, that is, when the user device can connect to or attach to a LiFi AP, the user device will connect to the LiFi AP.

[0119] In this operating state, the RF antenna is disabled under the control of the LiFi signal strength detector via control signals K1 and K2. Therefore, although the WiFi chip may still be physically within the WiFi coverage area, it will no longer be able to see the WiFi access point.

[0120] When a user device approaches the edge of the LiFi coverage area, the LiFi signal detector enables the connection of the RF antenna to connection port 202. At this point, the WiFi chip realizes that the WiFi AP is within its communication range because a WiFi beacon message is received at connection port 202 of the WiFi communication module.

[0121] This state change allows the WiFi chip to see both LiFi and WiFi AP simultaneously, as active data communication still exists between the connection port and OFE. The state change is a direct result of the LiFi signal strength detector's action (changing K2 from "0" to "1"). This state change will be used by the WiFi chip as a trigger to initiate the fast roaming procedure and hand over to the WiFi network in the next step.

[0122] In step 52, the WiFi chip initiates a handover from the LiFi network to the WiFi network using a fast roaming procedure.

[0123] The fast roaming procedure is very quick, typically completing in about 40ms. It is expected that the user device will already be associated with a WiFi AP before the LiFi signal is completely lost.

[0124] In another example, the user enters a LiFi zone while still associated with a WiFi AP. At this point, the LiFi signal detector changes the control signal K1 to "1" at time point "B" (see Figure 3). This allows the WiFi chip to notice or detect the state change (step 51) because it can see both the WiFi and LiFi APs. This state change is used as a trigger to hand over to the LiFi network via a fast roaming procedure.

[0125] Subsequently, the WiFi chip initiates a handover from the WiFi network to the LiFi network using a fast roaming procedure (step 52).

[0126] This procedure is less time-critical than a LiFi-to-WiFi handover because the WiFi signal remains available in the LiFi zone, and therefore the transition can be performed slowly if necessary.

[0127] Furthermore, signal K1 may be used to turn off the OFE TX circuit for power saving purposes when the user device is outside of LiFi coverage.

[0128] To avoid frequent transitions or false detections by the LiFi signal strength detector, a signal quality assessment circuit ensures that switching to the optical medium only occurs when the signal received by the OFE is of sufficient connection quality, for example, exceeding a defined signal-to-noise ratio (SNR) or RSSI threshold.

[0129] This can be achieved in combination with well-thought-out thresholds, as shown in Figure 3, and possibly hysteresis, to avoid frequent switching between LiFi and WiFi when the user device is stationary near the edge of LiFi coverage. Hysteresis can be implemented with two different thresholds (not shown in Figure 3), for example, a higher threshold for time point A than for time point B (instead of using the same threshold).

[0130] In real-world application scenarios, user devices on a LAN with both WiFi and LiFi networks are expected to connect to the WiFi network by default upon startup. Since there is no direct communication between the LiFi module and the WiFi chip in the user device, except for the two antenna ports of the WiFi chip, the method described above is used to prompt the WiFi chip to begin roaming as soon as the LiFi signal strength detection changes state (in or out of coverage area).

[0131] Figure 6 schematically shows a complete operation procedure 60 using the above method by a user device or EP.

[0132] After starting up in step 601 by powering up the user device, the user device connects to the WiFi AP in step 602. While still connected to the WiFi AP, the EP performs a network scan in step 603. This is a standard feature implemented in WiFi devices to determine which APs are within range.

[0133] In step 604, as soon as the user device detects a LiFi AP within its reach, it initiates a fast roaming procedure in step 605 and connects to the LiFi AP in step 606.

[0134] If this occurs, RF antenna 203 will be disabled by the LiFi signal strength detector circuits (K1, K2). In this operating state, both RF antennas are disconnected, so the WiFi chip will not be able to see the WiFi AP, although it is still physically within the WiFi coverage area.

[0135] When connected to a LiFi AP, if the user moves near the edge of the LiFi coverage, the LiFi signal detector enables RF antenna 203 (K2 goes high "1" at time 32, see Figure 3). If the EP scans the network (607), its WiFi chip will find at 608 that there is a WiFi AP that it can reach. At this point, active data communication is still taking place via port 201 connected to the OFE, while a WiFi beacon is being received via port 202.

[0136] This state change is used as a trigger to initiate the fast roaming procedure (609) and hand over to the WiFi network (602). With both LiFi and WiFi APs visible, this state change is a direct result of the LiFi signal strength detector's action (changing K2 from "0" to "1").

[0137] In another scenario, if a user device enters a LiFi zone while still associated with a WiFi network, the WiFi chip will notice the change in state because it can see both WiFi and LiFi APs. This is because the LiFi signal detector changes K1 to "1" at time 36 (see Figure 3).

[0138] This state change is used as a trigger to hand over to the LiFi network via a fast roaming procedure. This procedure is less time-critical than a LiFi-to-WiFi handover because the WiFi signal remains available in the LiFi zone, and therefore the transition can be performed slowly if necessary.

[0139] This disclosure is not limited to the examples disclosed above and can be modified and extended by those skilled in the art beyond the scope of this disclosure disclosed in the appended claims for use in any data communication, data exchange, and data processing environment, system, or network without the need to apply inventive skills.

Claims

1. A LiFi module for operationally connecting to a Wi-Fi communication module that supports both Wi-Fi and Li-Fi connectivity, the LiFi module comprising an optical front end (OFE) for transmitting and receiving data via an optical medium, and a connection circuit for communicatively connecting the OFE to the Wi-Fi communication module, the connection circuit comprising: A switching element including a first switch configured to enable or disable the connection between the OFE and the Wi-Fi communication module, and a second switch configured to enable or disable the connection between the Wi-Fi communication module and the radio frequency (RF) antenna, A LiFi signal intensity detector is electrically connected to the switching element and the receiving path of the OFE, and is configured to control the switching element based on the detection intensity of the optical signal received in the receiving path of the OFE. Includes, A LiFi module in which the control terminal of the first switch is connected to the first output terminal of the LiFi signal strength detector, and the control terminal of the second switch is connected to the second output terminal of the LiFi signal strength detector.

2. The LiFi signal intensity detector is configured to output an enabling signal at a second output signal when the detected intensity of the optical signal falls below a threshold, and to output a disabling signal at the first output terminal after a delay period. The first switch is configured to disable the connection between the OFE and the Wi-Fi communication module in response to the disabling signal it receives. The LiFi module according to claim 1, wherein the second switch is configured to enable the connection between the Wi-Fi communication module and the RF antenna in response to the enabling signal it receives.

3. The LiFi signal intensity detector is configured to output an enabling signal at a first output terminal when the detected intensity of the optical signal exceeds a threshold, and to output a disabling signal at a second output signal after a delay period. The first switch is configured to enable the connection between the OFE and the Wi-Fi communication module in response to the enabling signal it receives. The LiFi module according to claim 1, wherein the second switch is configured to disable the connection between the Wi-Fi communication module and the RF antenna and enable the connection between the Wi-Fi communication module and the terminator in response to the disabling signal it receives.

4. The LiFi module according to claim 1 or 2, wherein the first switch and the second switch are single-pole double-throw switches.

5. The LiFi module according to claim 1 or 2, wherein the LiFi module includes an RF-LiFi converter connected between the OFE and the first switch of the connection module, and configured to perform frequency conversion between the RF band and the LiFi optical baseband.

6. The LiFi module according to claim 5, wherein the LiFi module includes a third switch connected between the RF-LiFi converter and the first switch of the connection module, and configured to separate the transmit signal and the receive signal from the Wi-Fi communication module.

7. A wireless communication module for providing network services to both Wi-Fi and Li-Fi networks connected to the same LAN, the wireless communication module comprising a Li-Fi module according to any one of claims 1 to 3, and a Wi-Fi communication module operably connected to the Li-Fi module and supporting both Wi-Fi and Li-Fi connections, wherein the Wi-Fi communication module includes a first connection port and a second connection port, the second connection port being switched between an RF antenna and a terminator under the control of a Li-Fi signal strength detector of the Li-Fi module, and the first connection port being switched between the OFE of the Li-Fi module and a second RF antenna or terminator.

8. A method for initiating a handover of a user device between a Wi-Fi network and a Li-Fi network, both of which are connectable to the user device and both connected to the same local area network, wherein the user device includes a Li-Fi module as described in any one of claims 1 to 3, and the user device further includes a Wi-Fi communication module that supports Wi-Fi and Li-Fi connections on two connection ports, respectively, and the method is performed by a control software routine of the Wi-Fi communication module of the user device. The steps include detecting a change in state at one of the connection ports of the Wi-Fi communication module, The steps include: initiating a handover between the Wi-Fi network and the LiFi network using a roaming procedure; Methods that include...

9. The user device is connected to the LiFi network, The detection step includes detecting that a Wi-Fi beacon message is received at the second connection port of the Wi-Fi communication module. The aforementioned initiating step includes initiating a handover from the LiFi network to the Wi-Fi network. The method according to claim 8.

10. The method according to claim 9, wherein the Wi-Fi beacon message is received at the second connection port of the Wi-Fi communication module as a result of the connection between the second connection port of the Wi-Fi communication module and the RF antenna being enabled in response to an enabling signal received at the control terminal of the second switch from the second output terminal of the Li-Fi signal strength detector of the Li-Fi module.

11. The method according to claim 9, wherein the indicator is included in the Wi-Fi beacon message to distinguish between the Wi-Fi network and the Li-Fi network.

12. The user device is connected to the Wi-Fi network, The detection step includes detecting that a LiFi beacon message is received at the first connection port of the Wi-Fi communication module. The method according to claim 8, wherein the initiating step includes initiating a handover from the Wi-Fi network to the Li-Fi network.

13. The method according to claim 12, wherein the LiFi beacon message is received at the first connection port of the Wi-Fi communication module as a result of the connection between the first connection port of the Wi-Fi communication module and the OFE being enabled in response to an enabling signal received at the control terminal of a first switch from the first output terminal of the LiFi signal strength detector of the LiFi module.

14. The method according to claim 12, wherein an indicator is included in the LiFi message to distinguish between the Wi-Fi network and the LiFi network.

15. A computer program product comprising a computer-readable storage medium that, when executed on at least one processor, stores instructions causing the at least one processor to perform the method according to claim 8.

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