Fast handover for optical multi-cell communication systems

Abstract

An optical wireless communication system, a method and an apparatus for use in an optical wireless communication system, which enables data communication, e.g. LiFi, and wherein fast switching can be achieved by having neighboring access points (AP1, AP2) announce themselves using very short frames, which are picked up by a user equipment (EP1) detecting the identity of the neighbor access point (AP2) and then communicating it to the current access point (AP1) to share information about the user equipment (EP1) with its neighbor access point (AP2) so that the neighbor access point (AP2) can be preconfigured to allocate resources and / or synchronize.

Description

Technical Field

[0001] This invention relates to the field of communication in optical wireless networks (such as, but not limited to, Li-Fi networks) for use in a variety of different applications in homes, offices, retail, hotels, and industries. Background Technology

[0002] Wireless optical networks such as Li-Fi networks (named similarly to Wi-Fi networks) enable mobile user devices (hereinafter referred to as endpoints (EPs)) such as laptops, tablets, and smartphones to wirelessly connect to the internet. While Wi-Fi uses radio frequency (RF) to achieve this, Li-Fi uses the spectrum, which allows for unprecedented data transmission speeds and bandwidth. Furthermore, it can be used in areas susceptible to electromagnetic interference. It's important to consider that wireless data is not just needed for our traditional connectivity devices; today, televisions, speakers, headphones, printers, virtual reality (VR) goggles, and even refrigerators use wireless data to connect and perform vital communications. RF technologies like Wi-Fi are exhausting the spectrum supporting this digital revolution, while Li-Fi can help drive the next generation of immersive connectivity.

[0003] Based on modulation, any suitable light sensor can be used to detect information in the encoded light. This could be a dedicated photocell (point detector), a photocell array possibly with lenses, a reflector, a diffuser with a phosphor converter, or a camera comprising an array of photocells (pixels) and lenses for forming an image on that array. For example, the light sensor could be a dedicated photocell included in a radar detector inserted at the endpoint, or the sensor could be a general-purpose (visible or infrared) camera at the endpoint or an infrared detector originally designed for, for example, 3D facial recognition. Either way, this allows applications running on the endpoint to receive data via light.

[0004] Communication signals can be embedded in light signals emitted by a lighting source of the access device, such as a common luminaire, for example, indoor or outdoor lighting, thereby allowing the use of lighting from the luminaire as a carrier of information. Thus, light comprises a visible illumination component 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 can typically be performed at a sufficiently high frequency to exceed human perception, or at least make any visible transient light artifacts (e.g., flicker and / or stroboscopic artifacts) sufficiently weak and not noticeable 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 perceives only the overall lighting, not the effect of the data modulated into that lighting.

[0005] US Patent Application US2019 / 0261239 A1 discloses a method for controlling communication between a LiFi access point and user equipment (UE) by a coordinating node. The method includes receiving peer connectivity reports from LiFi access points having at least partially overlapping coverage areas, and developing a handover path data structure based on the peer connectivity reports. This handover path data structure identifies a LiFi access point from which communication handover can be received from another identified LiFi access point. The method involves determining an identifier for a first access point providing service to the UE, and using the first access point identifier to access a data structure to determine a second LiFi access point to which the service provider role should switch.

[0006] International patent application WO2011 / 137100 A1 discloses a visible light communication medium for providing communication coupling between two or more devices. The communication coupling supports various functions, including seamless transmission of the medium between the two or more devices.

[0007] In the following text, the term "access point" is used to refer to a logical access device that can be connected to one or more physical access devices (e.g., transceivers). Such physical access devices are typically located at light fixtures, and a logical access point can connect to one or more physical access devices, each located at one or more light fixtures. However, compared to RF technology, each access point has a smaller coverage area, allowing for a higher density of access devices. In such a dense network, interference handling can become complex if the overlapping areas of access points are not well organized. Due to the small coverage area of ​​each access point and the need to prevent excessive interference between access points, the overlapping areas in such a system are small. Therefore, mobile endpoints in such a network will require much faster switching (e.g., handover) between access points than in RF networks or other types of cellular networks with large coverage areas and large overlapping areas per access point. Summary of the Invention

[0008] The purpose of this invention is to provide an optical multi-cell communication system that allows for faster switching between access points.

[0009] This objective is achieved by the system as claimed in claim 1, the apparatus as claimed in claim 5, the endpoint as claimed in claim 12, the method as claimed in claim 13 or 14, and the computer program product as claimed in claim 15.

[0010] According to a first aspect, a system for fast handover in an optical multi-cell communication system is provided, comprising:

[0011] Multiple access points are configured to announce their presence by transmitting shortened frames without a payload portion in a predefined portion of the allocation of a common channel during the frame period of a link layer or physical layer protocol, wherein each shortened frame contains an identifier of the corresponding advertised access point; and

[0012] At least one endpoint is configured to search for neighboring access points among a plurality of access points to predict an upcoming handover by detecting shortened frames advertised in a common channel, and to transmit a pre-registration request for initial registration to the detected neighboring access points before deciding on the handover.

[0013] Therefore, dedicated shortened frames without a payload portion are provided in the dedicated public channel for neighbor detection and fast access to detected neighbors. These shortened frames can be picked up by endpoints to detect the identity of neighboring access points, enabling pre-configuration of neighboring access points for resource allocation and allowing for fast handover at a later time.

[0014] According to the first option of the first aspect, the first access point among the multiple access points can be configured to transmit shortened frames in each frame period. This allows for very rapid detection of adjacent access points within a single period of a signaling frame.

[0015] According to the second option of the first aspect, which can be combined with the first option of the first aspect, the first access point among multiple access points can be arranged to transmit shortened frames and default frames for media access planning in a common channel, followed by transmission of active frames for media access planning in different channels during the frame period. This provides the advantage that existing signaling structures with default and active media access planning frames (e.g., MAP-D and MAP-A frames of the MAC protocol) can be used to achieve the desired fast handover.

[0016] According to the third option of the first aspect, which can be combined with the first or second option of the first aspect, a predefined portion of the allocation of the common channel for the first access point can be reserved. Thus, default signaling capacity is allocated to each access point to ensure that individual announcements are not blocked.

[0017] According to the fourth option of the first aspect, which can be combined with any of the first to third options of the first aspect, the first access point is configured to pre-register the endpoint, reserve transmission resources for the first access point for the endpoint, and, in response to a pre-registration request received from the endpoint, transmit an acceptance message to the endpoint including timing information of the reserved transmission resources. Thus, resources can be reserved before handover, thereby allowing for a rapid handover at a later time.

[0018] According to the fifth option of the first aspect, which can be combined with any of the first to fourth options of the first aspect, the accept message may include an endpoint identifier assigned by the first access point. This measure ensures that the endpoint can be identified during a subsequent handover process.

[0019] According to the sixth option of the first aspect, which can be combined with any of the first to fifth options of the first aspect, the first access point can be configured to remove the pre-registration of the endpoint at the first access point after a predetermined time period. This ensures that sufficient resources are maintained for new pre-registrations, enabling rapid switching to new endpoints.

[0020] According to the seventh option of the first aspect, which can be combined with any of the first to sixth options of the first aspect, the first access point can be configured to prioritize the reservation of transmission resources by assigning higher priority to endpoints already registered with the first access point and unregistered endpoints in the domain requesting entry into the first access point, and lower priority to endpoint pre-registrations, wherein the priority assigned to newer pre-registration requests is higher than the priority assigned to older pre-registration requests. Therefore, fast handover can be provided while still maintaining sufficient transmission resources for registered and newly arriving endpoints.

[0021] According to a second aspect concerning the endpoint, an apparatus is provided for use in an endpoint for fast handover in an optical multi-cell communication system. The apparatus is arranged to search for neighboring access points among a plurality of access points to predict an upcoming handover by detecting shortened frames of announcements that do not contain a payload portion in a predefined portion of the common channel allocated to the access points in a frame period of a link layer or physical layer protocol, and to transmit a pre-registration request for initial registration to the detected neighboring access points prior to determining the handover.

[0022] According to the first option of the second aspect, the device can be configured to report detected neighboring access points to the associated local access point and transmit pre-registration to neighboring access points via the local access point. This measure ensures rapid pre-registration via the local access point.

[0023] According to the second option of the second aspect, which can be combined with the first option of the second aspect, the device can be arranged to store timing information of transmission opportunities received from detected access points in an acceptance message in response to a pre-registration request, so as to achieve rapid synchronization with detected neighboring access points in the event of a rapid handover.

[0024] According to the third option of the second aspect, which can be combined with the first or second option of the second aspect, the device can be arranged to apply timing or synchronization information received in the receiving message during pre-registration and to decode the default media access planning frame to derive information that enables decoding of the actual media access planning frame following the default media access planning frame, thereby obtaining resources pre-allocated by adjacent access points for performing fast handover.

[0025] According to the fourth option of the second aspect, which can be combined with any of the first to third options of the second aspect, the device can be arranged to periodically update pre-registrations. Thus, the access point can delete the pre-registration after a predetermined timeout to free up resources for new pre-registrations.

[0026] According to the fifth option of the second aspect, which can be combined with any of the first to fourth options of the second aspect, the device can be arranged to pre-register simultaneously to several detected access points. This measure ensures that rapid handover is possible, even if it is unclear at the time of pre-registration which detected adjacent access point will later be selected for handover.

[0027] According to the sixth option of the second aspect, which can be combined with any of the first to fifth options of the second aspect, the device can be arranged to determine the access point to which it is pre-registered based on determined signal quality parameters. Therefore, the detected neighboring access point with the best signal quality can be selected for rapid handover.

[0028] According to another option, which can be combined with any of the options in the first and second aspects, the shortened frame can be limited to a preamble and a header containing an identifier of the access point. Thus, the length of the shortened frame can be minimized to maximize the available resources allocated to the access point in the common channel.

[0029] According to yet another option, which can be combined with any of the options in the first and second aspects, the shortened frame can be the shortened default media access planning frame of the MAC protocol. Therefore, existing signaling frames of the MAC protocol can be used for the desired fast handover.

[0030] According to another option, which can be combined with any of the options in the first and second aspects, the active media access planning frame includes scheduling information for transmission opportunities. Thus, the existing active media access planning frame can signal the scheduling information for rapid handover.

[0031] According to another option, which can be combined with any of the options in the first and second aspects, the common channel of the shortened frame can be separated from the normal data traffic in the frame period. This measure ensures that fast handover is not blocked or interfered with by normal data traffic.

[0032] Optionally, the access point in the system according to the first aspect is included in the corresponding luminaire.

[0033] According to a third aspect, an endpoint for accessing an optical multi-cell communication system is provided, the endpoint including means according to any one of the above options of the second and third aspects.

[0034] According to a fourth aspect concerning communication systems, a method is provided that allows for rapid handover in optical multi-cell communication systems, the method comprising:

[0035] The presence of multiple access points is announced by transmitting shortened frames that do not contain a payload portion in the predefined portion of the allocation of the common channel in the frame period of the link layer or physical layer protocol from multiple access points, wherein each shortened frame contains an identifier of the corresponding announced access point.

[0036] The endpoint searches for neighboring access points among multiple access points to predict upcoming handovers by detecting shortened frames advertised in the common channel; and

[0037] Before deciding to switch over, the endpoint transmits a pre-registration request for initial registration to the detected neighboring access point.

[0038] According to the fifth aspect concerning the endpoint, a method for enabling fast handover in an optical multi-cell communication system is provided, the method comprising:

[0039] By detecting shortened frames of announcements that lack a payload portion in the predefined portion of the common channel allocated to access points within the frame period of the link layer or physical layer protocol, neighboring access points among multiple access points are searched to predict upcoming handovers; and

[0040] Before deciding to switch, a pre-registration request for initial registration is transmitted to the detected adjacent access points.

[0041] According to the sixth aspect, a computer program product may be provided, which includes code means for generating the steps of the method described in the fifth aspect when run on a computer device.

[0042] Note that the above-described device may be implemented based on an arrangement of discrete hardware circuits, integrated chips, or chip modules having discrete hardware components, or based on a signal processing device or chip controlled by software routines or programs stored in memory, written on a computer-readable medium, or downloaded from a network such as the Internet.

[0043] It should be understood that the system of claim 1, the apparatus of claim 5, the endpoint of claim 12, the method of claim 13 or 14, and the computer program product of claim 15 may have similar and / or identical preferred embodiments, particularly as defined in the dependent claims.

[0044] It should be understood that the preferred embodiments of the present invention may also be any combination of the dependent claims or the above embodiments with the corresponding independent claims.

[0045] These and other aspects of the invention will become clear and explained with reference to the embodiments described below. Attached Figure Description

[0046] In the following figures:

[0047] Figure 1 A block diagram of a LiFi network in which various embodiments can be implemented is shown schematically;

[0048] Figure 2 A LiFi infrastructure with first and second planar regions is schematically illustrated, in which various embodiments can be implemented;

[0049] Figure 3 schematically shown Figure 2 A top-view illustration of the LiFi infrastructure;

[0050] Figure 4 schematically illustrates examples of aligned frame periods for two access devices according to various embodiments;

[0051] Figure 5 An example of a common channel with time slot allocation for two access devices is illustrated schematically according to various embodiments;

[0052] Figure 6 A flowchart illustrating the pre-registration process of an access device according to various embodiments is shown;

[0053] Figure 7 Flowcharts illustrating the pre-registration and fast handover process of user equipment according to various embodiments are shown; and

[0054] Figure 8 The pre-registration signaling and processing sequences in a LiFi network according to various embodiments are schematically illustrated. Detailed Implementation

[0055] Various embodiments of the present invention will now be described based on optical multi-cell lighting and communication (LiFi) systems.

[0056] Throughout this text, "luminaire as an access point" should be understood as any type of lighting unit or lighting equipment, including one or more light sources (including visible or invisible (infrared (IR) or ultraviolet (UV)) sources) for lighting and / or communication purposes, as well as optional other internal and / or external components necessary for the proper operation of the lighting—for example, distributing light, positioning and protecting the light source and ballast (where applicable), and connecting the luminaire to a power source. The luminaire can be of conventional type, such as recessed or surface-mounted incandescent lamps, fluorescent lamps, or other discharge lamps. The luminaire can also be of non-conventional type, such as fiber optic devices with a light source in one location and an optical fiber core or "light guide" in another.

[0057] Figure 1 A block diagram of a LiFi network in which various embodiments can be implemented is shown schematically.

[0058] A LiFi network comprises multiple access points (APs) 12 (e.g., luminaires in a lighting system) connected via a switch (e.g., an Ethernet switch) 14, whereby each AP 12 controls one or more transceivers (TRXs) 11 (i.e., combined transmitters (optical transmitters) and receivers (light sensors)) for optical communication toward endpoints (EPs) 10 (e.g., mobile user equipment). A corresponding beam of light generated by the TRX 11 and defining a coverage area on the plane(s) of EP 10... Figure 1 The middle section is indicated by a dashed trapezoid.

[0059] AP 12 can apply time-slot scheduling to communicate with (multiple) EP 10s in its coverage area. In cases where TRX 11 coverage areas overlap (e.g.) Figure 1 (As shown in EP1), if the relevant TRX 11 belongs to a different AP 12, then coordination of AP12 is required.

[0060] A LiFi controller 13, configured to manage the LiFi network, is connected to a switch 14 and can provide coordination to support interference handling and handover when one of the EPs 10 moves into or out of the overlapping coverage area of ​​the AP 12. The controller 13 is connected to the AP 12 via the switch 14. The switch 13 can be connected to a synchronization server 16 for synchronization management and to a router 15 for connecting to a backplane or backhaul network (e.g., Ethernet) 100.

[0061] Media access to endpoint 10 can be scheduled by frame periods of a data link layer protocol. In an example embodiment, scheduling can be based on Media Access Control (MAC) periods of a MAC protocol. These MAC periods are consecutive to each other and are divided into two or more time intervals, one or more of which are used for domain management purposes, while other time intervals are allocated as transmission opportunities for different APs 12 or groups thereof. At least one time interval allocated for domain management purposes can be allocated for transmitting Media Access Planning (MAP). The domain management information transmitted in the MAP frame identifies the boundaries of the MAC period and includes a list of transmission opportunities allocated for one or more subsequent MAC periods (e.g., dedicated time channels for the MAC period). (For example, a MAP transmitted in period N could describe the timing boundaries and transmission opportunities of period N+1.)

[0062] A MAC cycle can begin at the time announced in a previous MAP frame and end when the last transmission opportunity scheduled for that MAC cycle ends, as described in the MAP frame. The content of the MAC cycle can be determined based on the communication resources and parameters required for communication between different APs.

[0063] Controller 13 can determine the provisions for providing indications of AP 12's presence during the MAC cycle, thereby enabling EP 10 to detect whether they are within the coverage area of ​​neighboring APs. EP 10 reports the detection of neighboring APs to the local AP (e.g., to AP 12 to which EP 10 is registered). The local AP then forwards these reports to controller 13.

[0064] Based on the neighbor AP detection report received from EP 10, controller 13 can determine the limit on the use of MAC cycles for each AP 12 in order to handle interference via time-division access.

[0065] There may be situations where the EP 10 detects a neighboring AP and, depending on the received signal strength, may want to register and move it to the neighboring AP. Similar to the IEEE 802.11 specification, the communication for this transition can be directly with the neighboring AP, for example, on a direct path (i.e., "over-the-air") or via a local AP in a distributed system (DS) (i.e., "over-the-DS"). Furthermore, the EP 10 may want the neighboring AP to reserve resources prior to the transition, for example, based on the Fast Transition (FT) Resource Request Protocol (Fast BSS Transition) according to Section 13 of the IEEE 802.11 (2016) specification.

[0066] To this end, two FT protocols are defined. These are the FT protocols executed when a transformation to the target AP is performed and no resource requests are required prior to the transformation, and the FT resource request protocol executed when a resource request is required prior to the transformation.

[0067] For EP 10 to perform a fast transition / switching from its current AP to a target AP using the FT protocol, message exchange can be performed using either an over-the-air method (where EP 10 communicates directly with the target AP using IEEE 802.11 authentication with an FT authentication algorithm) or a method on the DS (where EP 10 communicates with the target AP via its current local AP). Communication between EP 10 and the target AP can occur within FT action frames between EP 10 and its current local AP. Communication between the current AP and the target AP can be achieved via encapsulation methods (such as those described in section 13.10.3 of the IEEE 802.11 (2016) specification). The current local AP can switch between the two encapsulation methods.

[0068] Figure 2 A LiFi infrastructure having first and second planar regions 200, 220 is schematically shown, in which various embodiments can be implemented.

[0069] The LiFi infrastructure comprises multiple LiFi infrastructure TRX 22 located in a first planar region 200 (e.g., a ceiling wall in a building) with corresponding APs (e.g., luminaires of a lighting system). Each LiFi infrastructure TRX 22 has an optical coverage area for transmitting and receiving LiFi signals projected onto a second planar region 220 (e.g., the ground floor of a building), where two projections are as follows: Figure 2 The shaded and gray areas are shown in Figure 222.

[0070] In addition, the LiFi infrastructure includes the LiFi device TRX 24 of the EP located in the second planar region 220. The LiFi device TRX 24 moves in the direction indicated by the arrow and has an optical coverage area 242 for transmitting and receiving LiFi signals projected onto the first planar region 200.

[0071] exist Figure 2 In the example, it is assumed that the first planar region 200 and the second planar region 220 are parallel.

[0072] Figure 3 schematically shown Figure 2 A top-view illustration of the LiFi infrastructure, where the boundaries of coverage area 222 are indicated by corresponding circles drawn around the multiple LiFi infrastructure TRX 22. Similarly, the coverage area 242 of the mobile EP's LiFi device TRX 24 is shown as a circle with dashed lines. Figure 3 As indicated, the overlapping areas of the LiFi infrastructure TRX 22 and their AP coverage areas 222 are well organized into a regular pattern.

[0073] Because the coverage area of ​​each AP is small (222), and the overlap area in a LiFi infrastructure is small to prevent excessive interference between APs, mobile EPs will require much faster switching between APs compared to other cellular networks (such as RF networks) with large coverage areas and large overlap areas per AP.

[0074] According to various embodiments, by anticipating upcoming transitions, the transition time between APs can be reduced and preferably minimized. In examples, this can be achieved by detecting at least one of a decrease in the received signal strength of the local AP, a signal from a neighboring AP, or an increase in the signal from a neighboring AP.

[0075] In various embodiments, before a moving EP decides to switch to a neighboring AP, it can pre-register itself with the neighboring AP to prepare for actual registration. This pre-registration can be performed when the EP detects a neighboring AP, even if the received signal strength of the neighboring AP is weaker than that of its local AP.

[0076] In the example, registration to the AP can be performed based on the steps defined in the specifications ITU-G 9960, G.9961, and ITU-G 9991 for LiFi networks. Because in a LiFi network, the AP always acts as a Domain Master (DM), the DM can be considered as an AP. The DM is the node that manages (coordinates) all other nodes in the same network domain (e.g., allocates bandwidth resources and manages user priorities) and can act as a relay node. For registration, the EP can detect potential DM candidates, select a suitable DM candidate, perform coarse synchronization and initial payload detection, then perform fine synchronization and reception of Active Media Access Planning (MAP-A) frames for Media Access Planning, and finally issue a registration request and wait for acceptance.

[0077] When an EP (Employer Provider) has visibility over one or more DMs (i.e., APs), the EP identifies all potential DM candidates. This is achieved by configuring a default indicator or seed for the receiver. The default indicator or seed is an indicator or seed used by all nodes to transmit frames that need to be received by any node in the same domain or other domains without prior information being available. Each DM uses the default seed to generate a preamble for Default Media Access Planning (MAP-D) frame transmission, regardless of its media type. MAP-D frames are used for media access planning and contain basic information that allows nodes (such as EPs) to configure themselves to receive the remaining frames in the domain. For this stage, receiving only the header is sufficient, as it contains enough information to create a list of visible DMs.

[0078] The final selection of an AP for registration depends on factors such as the technology used. Generally, an EP (Extended Premises Provider) has a configured domain name and searches for APs configured with the same domain name. In this case, once the EP has been able to synchronize with the AP, decode the payload, and obtain the AP's domain name, it checks if it matches the desired AP. If not, the process restarts, trying another AP until a suitable AP is found. This process becomes longer for each different AP that needs to be checked.

[0079] Synchronization is the process of adjusting the local clock of the EP (Engineer) to the local clock of the AP (Access Point). These small frequency variations reduce the signal-to-noise ratio (SNR), necessitating that this synchronization be performed as quickly as possible and continuously tracked. Poor synchronization causes received frames to malfunction near the end and typically results in poor performance.

[0080] Frames like MAP-D and MAP-A can be transmitted in robust communication modes that allow their payloads to be decoded even with coarse synchronization between nodes. In an example embodiment, the payload can be encoded as RCM (robust communication mode) transmission with NREP 3 and FEC rate 2 / 3 (see ITU standard G.9960 for details).

[0081] Several fields obtained from the MAP-D payload can be used to decode the MAP-A frame and obtain additional information, such as the scheduling of transmission opportunities. Once the scheduling information is obtained, the MAC protocol allows the EP to begin transmitting the frame, which is not permitted before this point.

[0082] Once an EP is granted permission to transmit, it can send a registration request (e.g., an ADM_NodeRegistrRequest.req message) to the selected AP. Once a registration slot is found, the registration request can be sent. This type of slot may not appear in all MAP cycles. If this is the case, message transmission is delayed until a registration slot is found.

[0083] Therefore, the above registration process involves several obstacles to a rapid conversion or switching process.

[0084] The first obstacle to achieving fast handover is the time required to detect neighboring APs, which depends on receiving MAP-D frames from these neighboring APs. Detection time can be long due to the following facts: according to ITU-G.9961, the DM does not need to send MAP-D frames in every MAC cycle; MAP-D frames from neighboring APs may interfere with ongoing data processing at the local AP and therefore may not be recognized; reception of MAP-D frames requires a default seed, which the EP does not use when registering to the AP; the Inter-Domain Communication Channel (IDCC) is a dedicated time slot for processing neighboring domains and is based on contention-based access unsuitable for LiFi networks, as APs cannot see each other and therefore suffer collisions on the IDCC; and reserving contention-free time for MAP-D frames can reduce the efficient use of available time.

[0085] Furthermore, the second obstacle relates to synchronization. The EP needs to synchronize with the AP before it can exchange frames. It can only do this after correctly receiving MAP-D frames, which, as mentioned above, can take too long.

[0086] Finally, the third obstacle relates to registration. Before an EP can register with a neighboring AP, it needs to know the scheduling (transmission opportunities) carried by the MAP-A frame. However, correct reception of MAP-A frames can suffer from the same problems as MAP-D frames. Furthermore, it relies on receiving MAP-D frames first to obtain the information needed to decode the MAP-A frame.

[0087] According to various embodiments, the transition or handover process is accelerated by announcing a shortened MAP-D frame (which may be referred to as "SMAP-D") in a dedicated portion of the MAC cycle and by performing pre-registration based on anticipated actions. More specifically, SMAP-D may reside in the common channel (CC) of the MAC cycle, while normal MAP-D and MAP-A frames reside elsewhere in the MAC cycle. SMAP-D may contain only a frame header carrying the AP identifier. The physical layer (PHY) frame header of the ITU-G 9960 specification contains a source node identifier (SID) and a destination node identifier (DID). Combined with a domain identifier (DOD), this can adequately identify nodes within a local area network. Therefore, this header is suitable for use as SMAP-D. SMAP-D can be sent in every MAC cycle, for example, to neighboring APs with minimal collision probability. This allows the EP to quickly detect and report neighboring APs for interference handling and pre-registration.

[0088] The MAP-D frame contains a payload carrying information for decoding the MAP-A frame. The EP needs the information provided in the MAP-A frame before it can register with a detected neighboring AP. Therefore, for fast registration, both MAP-A and MAP-D frames are sent in each MAC cycle. MAP-D frames are primarily needed for initial and re-registration with the AP, such as when the EP has lost connection.

[0089] For the proposed fast handover process, the EP can detect SMAP-D frames from neighboring APs. However, due to potential interference with its local AP, it may not yet be able to detect MAP-D and / or MAP-A frames from neighboring APs. Then, after pre-registration, the EP deciding to handover can immediately decode MAP-D and MAP-A frames using timing or scheduling information derived from the pre-registration. Simultaneously, the LiFi controller, having received reports from the EP regarding the detection of neighboring APs, coordinates with the APs to ensure that the EP can receive MAP-D and MAP-A frames from neighboring APs without interfering with its local AP.

[0090] As a result, shortened frames (i.e., SMAP-D frames) allow for time-efficient detection of neighboring APs. They can be transmitted over separate common channels with minimal interference and are short so as not to waste too much time. Furthermore, once an EP decides to register with a neighboring AP, the proposed pre-registration (i.e., initial registration before handover) provides timing information that enables immediate decoding of MAP-D and MAP-A frames (containing the necessary scheduling information).

[0091] Figure 4 schematically illustrates examples of aligned frame periods (i.e., MAC periods) of two APs (i.e., AP1 and AP2) according to various embodiments.

[0092] In the example in Figure 4, the MAC cycle (MAC-c) includes a registration channel (Reg), four transmission channels (i.e., time channels TC1 to TC4), and a common channel (CC). To handle interference through coordinated time-division access, the APs in a LiFi system have aligned MAC cycles. The common channel (CC) is reserved as part of the MAC cycle for the APs to announce their presence. It can be provided in each consecutive MAC cycle.

[0093] For the remainder of the MAC cycle, the LiFi controller allocates a time channel (TC) to each AP. This allocation can be controlled by the LiFi controller so that adjacent APs have different time channels.

[0094] Furthermore, in the example, the LiFi controller could restrict each AP to communicating only in the assigned time channel, but this would not be very efficient.

[0095] In other examples, according to a more advanced approach, if an EP associated with a first AP (e.g., AP1) is within the coverage area of ​​a second AP (e.g., AP2), the first AP will restrict communication with the EP to the time channel allocated to the first AP, and the second AP will restrict communication with the EP associated with it by excluding the time channel allocated to the first AP.

[0096] In the exemplary MAC cycle shown in Figure 4, the LiFi controller has allocated a first time channel (TC1) to the first AP (AP1) and a second time channel (TC2) to the second AP (AP2). Assuming that the first EP has registered with the first AP and the second EP has registered with the second AP, the LiFi controller can control the first AP to restrict its communication with the first EP to the first time channel, and can control the second AP to restrict its communication with the second EP by excluding the first time channel.

[0097] To accelerate the detection of neighboring APs, APs can announce their presence in the common channel (CC) with short MAP-D frames (SMAP-D) during each MAC cycle. This allows for better interference handling (e.g., no mixing of normal data with management information) and enables EPs to apply a default seed to receive SMAP-D frames at the correct time. To efficiently utilize the available time in the MAC cycle, SMAP-D can be limited to a preamble and header, where the header contains the AP's identifier.

[0098] Figure 5 An example of a common channel (CC) according to various embodiments is illustrated, which has exemplary time slot allocation for two APs. Thus, within the time period of the common channel, the LiFi controller can allocate a sub-period to each AP to reduce advertising conflicts, whereby the AP can determine when (e.g., at a random time) to send its advertising message within its allocated sub-period.

[0099] exist Figure 5 In the example shown, the common channel contains eight time slots CC-S1 … CC-S8, where the first two time slots CC-S1 and CC-S2 have been allocated to the first AP (AP 1), and the subsequent two time slots CC-S3 and CC-S4 have been allocated to the second AP (AP 2). Note that this diagram shows only one example. The number of time slots and which time slots are allocated to which AP is determined by, for example, the LiFi controller, and the AP decides which of these allocated time slots will transmit shortened SMAP-D frames.

[0100] Figure 6 A flowchart illustrating the pre-registration process of an AP according to various embodiments is shown.

[0101] After the process begins in step S600, in step S601, the AP announces its presence using a short SMAP-D frame (short message) in a predefined portion of the allocation of the common channel, which is separated from normal data traffic in each MAC cycle. This allows the EP to detect neighboring APs in a single MAC cycle without being interfered with by data traffic.

[0102] To reduce collisions and enable efficient use of available time in the MAC cycle, the MAP-D frame was shortened to an SMAP-D frame consisting only of a preamble and a physical layer (PHY) header, whereby the PHY header carries the AP identifier.

[0103] In step S602, the AP checks whether a pre-registration request has been received. If not, the process jumps back to step S601. Otherwise, if a pre-registration request was received in step S602, the AP checks in step S603 whether it can accept the pre-registration request (e.g., whether there are sufficient resources available for the requesting EP and / or whether it can perform the handover procedure). If not, the process branches to step S604, where a rejection message is transmitted to the requesting EP. Otherwise, if it is determined in step S603 that the pre-registration request can be accepted, the process continues to step S605, where resources (e.g., pre-allocated time slots) are reserved for the requesting EP. Then, in step S606, an acceptance message including timing information of the reserved resources is transmitted to the EP. Finally, the process jumps back to step S601 and starts again.

[0104] Therefore, upon successful pre-registration, neighboring APs include timing information in their acceptance messages. Other information that may be included in the acceptance message may be the identifier of the EP to be assigned by the neighboring AP, and at least one of the seed and / or preamble encoding.

[0105] In the example, the EP can pre-register with detected neighboring APs via the local AP, thereby allowing the neighboring APs to reserve corresponding resources for the requesting EP. Furthermore, the EP is informed of the timing information of the neighboring APs to prepare for rapid synchronization with them.

[0106] In the example, according to the ITU-G.9961 standard, the AP can broadcast a shortened MAP-D frame once every n MAC cycles and a MAP-A frame once in each MAC cycle. To speed up the registration process, the AP can send a MAP-D frame directly in each MAC cycle, followed by a MAP-A frame.

[0107] Figure 7 A flowchart illustrating the pre-registration and fast switching process of an EP according to various embodiments is shown.

[0108] After the process begins in step S700, the EP continuously searches for neighboring APs in the loop of steps S702 and S701 by monitoring short messages (i.e., SMAP-D frames) in the common channel during the MAC cycle. If it detects a neighboring AP in step S702, it reports the detection to its local AP (i.e., the AP to which the EP is registered) in step S703. The local AP then updates the LiFi controller accordingly, and in response, the LiFi controller can update the restrictions for the AP to handle interference, such as the allocation of time channels and time slots in the common channel.

[0109] Then, in step S704, the EP requests pre-registration from the neighboring AP via the local AP. The local AP can relay this pre-registration request to the neighboring AP directly or via the LiFi controller. The neighboring AP replies to the EP with an accept or reject message via the local AP. If it accepts, it reserves the corresponding resources for the EP. The neighboring AP can send an accept or reject message to the local AP directly or via the LiFi controller. In any case, the local AP forwards the message to the EP.

[0110] In step S705, the EP checks whether it has received an acceptance message within a predetermined time period. If not, the process jumps back to step S701, and the EP searches for new neighboring APs. Otherwise, if an acceptance message has been received in step S705, the EP stores the timing information of the acceptance message in step S706 to achieve rapid synchronization with neighboring APs in a possible later handover.

[0111] Subsequently, in step S707, the EP checks the signal quality of the neighboring AP, for example by comparing the Received Signal Strength Indicator (RSSI) of the SMAP-D frame received from the neighboring AP in the common channel of the MAC cycle or another quality or error indicator, to determine in step S708 whether it will switch to the selected neighboring AP.

[0112] If the EP decides to switch to the neighboring AP in step S708, then in step S709, the EP applies the timing or synchronization information it received in the accept message during pre-registration. Then, in step S710, the EP is able to seamlessly decode the MAP-D frame of the neighboring AP and can also derive seed information that enables the decoding of MAP-A frames following the MAP-D frame. Then, in step S711, the EP can begin performing a fast handover using the resources (e.g., time slots) pre-allocated to it by the neighboring AP in the MAC cycle.

[0113] The EP can further utilize a new identifier assigned by the neighboring AP and seed and / or preamble encoding used by the neighboring AP. The neighboring AP enables frame transmission and can trigger a handover of the LiFi network to establish a new path to the EP.

[0114] Note that an EP can attempt to pre-register with all detected neighboring APs in anticipation of potential handovers. An EP may pre-register with several APs simultaneously.

[0115] Figure 8 The pre-registration process for signaling and processing sequences in a LiFi-based network according to various embodiments is illustrated schematically.

[0116] exist Figure 8 In the signaling and processing sequence, the vertical direction from top to bottom corresponds to the time axis, such that messages or processing times / steps shown above other messages or processing times / steps appear at earlier times.

[0117] like Figure 8 As indicated in the top section, the processing time and messages occur at or between the LiFi controller (LC) 13, one EP10, and two APs (AP1, AP2) 12.

[0118] The sequence begins at processing time 801, where EP 10 registers with the first AP (AP1). Subsequently, at processing time 802, EP 10 registers with the first AP (i.e., DM1), but is unaware of the adjacent second AP (AP2). Furthermore, at processing time 803, the LiFi controller 13 learns that EP 10 has registered with the first AP.

[0119] Then, at processing time 804, EP 10 detects a neighboring second AP. In response, EP 10 sends a pre-registration request message 805 (e.g., LIFI_FastHandoverPrepare.req) for the neighboring second AP to LC 13, for example, using the Configuration and Management Protocol (LCMP) defined in ITU-T G.9961. This allows external application entities to interact with the management of one or more ITU-T nodes to read / write parameters within the nodes. This request message is then relayed by LC 13 as request message 806 to the detected neighboring AP (AP2).

[0120] In step 807, upon accepting a pre-registration request, the detected neighboring AP prepares resources to accept the new node and pre-establish a connection. It can add the information locally, but this can be avoided by sending it in the topology packet (because the node (i.e., the requesting EP) is not yet in the domain).

[0121] Then, the neighboring AP sends a notification message 808 (e.g., LIFI_FastHandoverPrepare.cnf) to LC 13 to indicate whether the request from EP 10 is accepted (e.g., allocation of Domain ID (DOD) and / or Destination ID (DID)) or rejected. In the case of pre-registration being rejected, the neighboring AP sends a code indicating the reason for the rejection (e.g., no available resources or handover not supported (functionally limited AP)).

[0122] LC 13 relays the acceptance or rejection notification as notification message 809 to requesting EP 10. If accepted, at processing time 810, the adjacent AP has the resources to prepare for the handover of EP 10, and requests EP 10 to create the necessary resources for possible link negotiation at processing time 811.

[0123] If the requesting EP 10 receives a rejection indicating that no resources are available, the requesting EP 10 may retry pre-registration after a timeout. Otherwise, if the rejection indication does not support handover (i.e., the adjacent AP is a functionally limited AP), the requesting EP 10 may mark the AP as unable to handover.

[0124] However, if EP 10 does not receive a response to the pre-registration request after a predetermined time period, it can retry the pre-registration after a timeout (e.g., 200 ms).

[0125] If the requesting EP 10 detects in processing time 812 that the power received from any neighboring AP is higher than the power of the currently neighboring AP, then EP 10 can release the created resources in processing step 813 and can start a handover process targeting a new AP that has been pre-registered with EP 10.

[0126] After the scheduled timeout at processing time 814, the selected adjacent AP can remove EP 10's pre-registration due to aging in processing step 815. Therefore, it is not necessary to issue a cancellation message. However, if this aging option is implemented, requesting EP 10 may require periodic updates to the pre-registration.

[0127] During the subsequent switchover process ( Figure 8 (Not shown in the image), the EP can decide to change its configuration (e.g., DOD, DID, seed) to a newly selected AP (new LiFi domain). Therefore, it can create new resources (e.g., transmit and receive queues), change synchronization to adjust to the new AP (because each AP informs of its MAP duration, so the clock offset between the current AP and neighboring APs can be calculated), enable transmission paths, and change from the synchronization phase to the tracking phase.

[0128] Neighboring APs can send fake transport packets (e.g., Ethernet packets) with the source MAC addresses of devices connected to an EP (as previously known from the pre-registration phase), allowing switches to change the port location of those MAC addresses. APs can prioritize resource allocation by assigning the highest priority to their current slave devices (i.e., EPs already registered with the AP), the second highest priority to normally registered (i.e., unregistered EPs requesting entry into the domain), and the lowest priority to pre-registered requests. The most recent pre-registration request can have the highest priority among nodes with the lowest priority.

[0129] Furthermore, as indicated above, all pre-registered EPs may need to update their pre-registration from time to time. In cases where the AP needs to release resources for pre-registered nodes, it will select the node with the earliest pre-registration timestamp priority.

[0130] In summary, a communication system, method, and apparatus have been described that implements combined lighting and data communication (e.g., LiFi) and enables rapid handover by allowing neighboring access points to announce themselves using very short frames. These frames are acquired by user equipment that detects the identity of the neighboring access point and then communicated to the current access point to share information about the user equipment with its neighboring access points, allowing the neighboring access points to be pre-configured for resource allocation (and / or synchronization).

[0131] While the invention has been detailed and described in the accompanying drawings and the foregoing description, such description is to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments. The proposed detection and / or selection process can be applied to other types of wireless networks and may be standardized in other types of wireless networks, and may have other types of cell and / or reuse modes.

[0132] For example, in many protocols, a beacon is sent at the beginning of a frame period. The beacon can indicate not only the start of a frame, but also other information such as the identifier of the access point (e.g., the coordinator in IEEE 802.15.7 terminology) and information for the construction and use of the rest of the frame.

[0133] Specifically, this invention is not limited to ITU-T G.9961, ITU-T G.9960, and ITU-T G.9991 network environments. The proposed shortened frames for presence announcements can also be used in network environments according to IEEE 802.15.7, where the concept of beacon frames is applied at the beginning of a superframe. These beacon frames can be shortened to be limited to the Media Access Control header (MHR), where the addressing field contains the source address. As an example, shortened beacons (S-beacons) can be used in addition to normal beacons. The S-beacons can then appear in an S-beacon period corresponding to the Common Channel (CC) explained above.

[0134] Furthermore, the above sample embodiments are based on time division of available channels. However, frequency division can be used in other types of network environments. Therefore, control channels (e.g., D channels in Integrated Services Digital Network (ISDN)) can also be established using frequencies different from those used for data. Thus, in principle, the common channels (CC) described in conjunction with the above sample embodiments can also appear at different frequencies (e.g., out-of-band (OOB) channels with limited bandwidth).

[0135] By studying the accompanying drawings, the disclosure, and the appended claims, those skilled in the art can understand and implement other variations of the disclosed embodiments in practicing the claimed invention. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude a plurality. A single processor or other unit can perform the functions of several items listed in the claims. The mere fact that certain measures are referenced in mutually different dependent claims does not indicate that a combination of these measures cannot be used advantageously. The foregoing description has detailed certain embodiments of the invention. However, it will be appreciated that the invention can be practiced in many ways, and is therefore not limited to the disclosed embodiments, however detailed it may be in the foregoing text. It should be noted that the use of particular terms when describing certain features or aspects of the invention should not be construed as implying that the term is redefined herein to be limited to include any specific characteristic of the feature or aspect of the invention associated with that term.

[0136] A single unit or device can perform the functions of several items listed in the claims. The mere fact that certain measures are referenced in mutually different dependent claims does not indicate that a combination of these measures cannot be used advantageously.

[0137] Similar to Figure 6 and Figure 7The indicated operations can be implemented as program code of a computer program and / or dedicated hardware of a receiver or transceiver device. The computer program can be stored and / or distributed on a suitable medium, such as an optical storage medium or a solid-state medium, supplied together with or as part of other hardware; but it can also be distributed in other forms, such as via the Internet or other wired or wireless telecommunications systems.

Claims

1. A system for fast handover in an optical multi-cell communication system, comprising: a plurality of access points (12) arranged for announcing their presence by transmitting shortened frames without payload portion in an allocated predefined portion of a common channel of a frame period of a link layer or physical layer protocol, wherein each shortened frame contains an identifier of the respective announcing access point; and at least one end point (10) arranged for searching for a neighboring access point of the plurality of access points (12) by detecting the announced shortened frames in the common channel, to predict an upcoming handover, and for transmitting a pre-registration request for a preliminary registration to the detected neighboring access point before deciding on a handover.

2. The system according to claim 1, wherein a first access point among the plurality of access points is arranged for transmitting the shortened frame in each frame period.

3. The system according to claim 1, wherein a first access point among the plurality of access points is arranged for pre-registering an end point (10), reserving transmission resources of the first access point (12) for the end point (10), and in response to a pre-registration request received from the end point (10), transmitting an acceptance message to the end point (10) including timing information of the reserved transmission resources and an end point identifier.

4. The system according to claim 3, wherein the first access point is arranged for prioritizing the reservation of resources by assigning a higher priority to end points (10) already registered at the first access point (12) and to unregistered end points (10) requesting to enter the domain of the first access point (12), and assigning a lower priority to pre-registrations of end points (10), and wherein a newer pre-registration request is assigned a higher priority than an older pre-registration request.

5. An apparatus for fast handover in an optical multi-cell communication system for use in an end point (10), the apparatus being arranged for searching for a neighboring access point of a plurality of access points (12) by detecting announced shortened frames without payload portion in a predefined portion of a common channel allocated to the access points (12) in a frame period of a link layer or physical layer protocol, to predict an upcoming handover, and for transmitting a pre-registration request for a preliminary registration to the detected neighboring access point before deciding on a handover.

6. The apparatus according to claim 5, wherein the apparatus is arranged for reporting the detected neighboring access point to an associated local access point, and for transmitting the pre-registration to the neighboring access point via the local access point.

7. The apparatus according to claim 5 or 6, wherein the apparatus is arranged for storing timing information of transmission opportunities received from the detected access point in an acceptance message in response to the pre-registration request, to enable a fast synchronization with the detected neighboring access point in a possible fast handover.

8. The apparatus according to any of claims 5 to 7, wherein the apparatus is arranged for periodically updating the pre-registration.

9. The apparatus according to any of claims 5 to 8, wherein the apparatus is arranged for deciding to switch to an access point it is pre-registered to based on the determined signal quality parameter.

10. The apparatus according to any of claims 5 to 9, wherein the shortened frame is limited to a preamble and a header containing an identifier of the announcing access point (12).

11. The apparatus according to any of claims 5 to 10, wherein the common channel of the shortened frame is separated from normal data traffic in the frame period.

12. An endpoint (10) for accessing an optical multi-cell communication system, the endpoint (10) comprising an apparatus according to any of claims 5 to 11.

13. A method of allowing fast handover in an optical multi-cell communication system, the method comprising: announcing (S601) the presence of a plurality of access points (12) by transmitting shortened frames without payload parts from the plurality of access points (12) in an allocated predefined part of a common channel of a frame period of a link layer or physical layer protocol, wherein each shortened frame contains an identifier of the respective announcing access point; searching (S701) by an endpoint (10) for a neighboring access point of the plurality of access points (12) by detecting the announced shortened frames in the common channel to predict an upcoming handover; and transmitting (S704) by the endpoint (10) a pre-registration request for preliminary registration to the detected neighboring access point before deciding to handover.

14. A method of allowing fast handover of an endpoint (10) in an optical multi-cell communication system, the method comprising: searching (S701) by the endpoint (10) for a neighboring access point of a plurality of access points (12) by detecting announced shortened frames without payload parts in a predefined part of a common channel allocated to the access points (12) in a frame period of a link layer or physical layer protocol to predict an upcoming handover; and transmitting (S704) by the endpoint (10) a pre-registration request for preliminary registration to the detected neighboring access point before deciding to handover.

15. A computer program product comprising code means for producing the steps of claim 14 when run on a computer device of an endpoint (10). ​ ​

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