Multi-transceiver system with selective transmit branch combination for optical wireless communication

Abstract

A LiFi system with a plurality of transceivers (11) and a single Multiple Input Multiple Output (MIMO) modem (41) with at least M outputs, wherein the M transmit outputs of the MIMO modem (41) are fed to a linear combiner (42). The linear combiner creates M different linear combinations based on the N MIMO transmit branch signals of the MIMO modem and selects the linear combinations such that when N of the M different output signals are received, they allow decoding each of the N MIMO transmit branch signals.

Description

Technical Field

[0001] This invention relates to the field of communication in optical wireless networks (e.g., but not limited to LiFi networks) for use in a variety of applications in homes, offices, retail, hotels, and industries. Background Technology

[0002] Wireless optical networks, such as LiFi networks (compared to WiFi networks), enable mobile user devices (hereinafter referred to as endpoints (EPs)) – such as laptops, tablets, smartphones, etc. – to wirelessly connect to the internet. WiFi uses radio frequencies to achieve this, but LiFi uses the spectrum, enabling unprecedented data transfer 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. Radio frequency (RF) technologies (like WiFi) are exhausting the spectrum supporting this digital revolution, and LiFi 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 can 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 the array. For example, the light sensor could be a dedicated photocell included in a radar detector inserted into 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 face recognition. Either way, this allows applications running on the endpoint to receive data via light.

[0004] In wireless optical networks, physical access devices (e.g., transceivers) are typically located at lighting fixtures, and logical access points can connect to one or more physical access devices, each located at one or more lighting fixtures. Communication signals can be embedded in optical signals emitted by the lighting sources of the physical access devices, such as everyday lighting fixtures, like indoor or outdoor lighting, thereby allowing the use of lighting from the fixtures as a carrier of information. Thus, the light includes both the visible illumination component used to illuminate a target environment such as a room (often the primary purpose of light) and the embedded signal used to provide 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 only perceives the overall lighting and not the effect of data modulated into that lighting. Physical access devices (such as transceivers) are typically located at light fixtures, and logical access points can connect to one or more physical access devices, each located at one or more light fixtures. In many lighting systems, a continuous and uniform level of brightness is achieved by including numerous light-emitting fixtures and light sources within the same room. This results in uniform illumination of the entire area and prevents sharp shadows from obstructing light. Similarly, if the line of sight (LOS) is blocked, the LiFi system suffers an immediate link interruption, which can often occur if a user leans over their communication device and enters between a ceiling-mounted access device (such as a transceiver) and their own communication device.

[0005] The idea of ​​using multiple optical transmitters, which may have multiple overlapping coverage areas from multiple transmitters, is used here for data transmission. It is not limited to visible light; for example, it can also be used for infrared (IR) light or other radiation. Therefore, the deployment criteria—especially regarding the degree of transmitter overlap—can differ from those required for uniform illumination and can be based, for example, on the goal of achieving a sufficiently uniform achievable bit rate throughout the coverage area, even when the main beam is accidentally blocked.

[0006] Multiple-input multiple-output (MIMO) communication can improve this situation because it allows an alternative transceiver mounted on the ceiling but still having a loss of access (LOS) to immediately take over the link. This can even happen at the lowest physical layer (PHY) of the Open Systems Interconnection (OSI) model without protocol-level intervention. In fact, it even allows simultaneous transmission via multipath links, thus allowing immediate fallback by utilizing another link if one LOS is blocked.

[0007] According to the paper "Joint Optimization of Precoder and Equalizer in MIMO VLC Systems" published by Ying Kai et al. in IEEE Journal on Selected Areas in Communications, Volume 33, Issue 9, MIMO VLC systems using Nt×Nr optical MIMO channels are known, where Nt represents the number of transmitters and Nr represents the number of receivers. This paper proposes using a precoding matrix F on the transmitter side and a linear equalizer G on the receiver side to extract data from the received signal. Thus, the precoding matrix F and the linear equalizer G are jointly optimized to compensate for channel defects.

[0008] The paper "Performance Comparison of MIMO Techniques for Optical Wireless Communications in Indoor Environments" by Thilo Fath et al. was published in IEEE Transactions on Communications, Volume 16, Issue 2. The paper presents a comparison of several MIMO algorithms, including repetitive coding, spatial multiplexing, and spatial modulation used in optical wireless communication systems (assuming different transmitter spacing and different receiver positions), and also addresses the power imbalance between signals.

[0009] However, one problem with high-speed communication is that the propagation time difference from different access devices (i.e., light spots) can be so significant that multipath extinction (zero) occurs through fading in the communication channel. Differences in transceiver cable lengths can also cause these delays. If a client receives a signal midway beneath two ceiling-mounted transmitters at the access device, the lengths of the free-space optical paths are approximately equal, so the signal strengths arriving are almost equal. Although the phase difference due to free-space propagation is small, a two-meter difference in cable length corresponding to a half-wavelength phase difference at 50 MHz (assuming a cable speed of 2 / 3 the speed of light in free space) does not necessarily lead to a zero, but it can. Larger differences in cable length can lead to the first transmission zero at even lower frequencies. This problem could become more severe if future systems use higher bit rates, utilize better transmitters (e.g., vertical-cavity surface-emitting lasers (VCSELs) instead of LEDs), and better amplifiers at the receiver. Summary of the Invention

[0010] Optical wireless communication (or OWC) as envisioned herein is not limited to the visible spectrum. Systems that can additionally or alternatively utilize the infrared and / or ultraviolet spectra are envisioned. Here, the infrared spectrum is generally preferred because it has lower energy quanta compared to the ultraviolet spectrum, and is therefore more suitable for the user's location. A significant advantage of using light outside the visible spectrum is that the problems associated with illumination functions, such as flickering, dimming, and the need to turn on illumination to enable communication alone, are eliminated.

[0011] Integrating such an OWC system into lighting fixtures remains beneficial even when using light outside the visible spectrum. A key reason for this is location; lighting fixtures are typically placed in locations with direct line of sight to where users who need to communicate might reside. Furthermore, it is possible to follow existing infrastructure, such as the lighting light itself; for example, power or even connectivity in the case of Power over Ethernet applications.

[0012] One object of the present invention is to provide an optical wireless communication system with improved robustness to multipath-induced fading.

[0013] This objective is achieved by the apparatus for generating M output signals as described in claim 1 or 10, the OWC system as described in claim 7, the apparatus for providing feedback to the OWC system as described in claim 8, the network access initialization device as described in claim 9, the method for controlling an optical wireless communication system as described in claim 11 or 13, and the computer program product as described in claim 14 or 15.

[0014] According to a first aspect relating to a modem or transceiver, an apparatus for controlling an optical wireless communication system is provided, the apparatus comprising:

[0015] The input terminal is used to receive at least two transmit branch signals for multiple-input multiple-output (MIMO) communication;

[0016] A combiner is used to combine the at least two transmit branch signals via multiple linear combinations to generate multiple output signals to be provided to each spatially separated transmitter, wherein the number of output signals is greater than the number of transmit branch signals;

[0017] The combiner is configured to set linear combinations such that the output signals generated from different linear combinations are received in the overlapping receiving regions of spatially separated transmitters.

[0018] Therefore, the linear combinations used to combine MIMO channel signals to generate transmitter output signals can be selected and updated, such that transmitter output signals generated from different linear combinations are received in the overlapping receiving areas of spatially separated transmitters. Thus, a MIMO system with multiple transceivers and enhanced robustness against multipath fading can be provided. Signals arriving at the endpoint from different transmitters with different delays (e.g., due to different cable lengths) no longer cancel each other out and / or significantly reduce the bit rate, because the signals are now distinct from each other.

[0019] Therefore, a simple MIMO system supporting, for example, two branches can be enhanced to support more transceivers coupled to the same modem by transmitting different output signals. This can alleviate installation problems and provide options for automatically configuring the MIMO system (e.g., via network initialization or a learning / training process).

[0020] According to the first option of the first aspect, the combiner can be configured to apply linear combination by combining at least two transmit branch signals using selected mixing coefficients. Therefore, the linear combination can be flexibly set and modified by changing the corresponding mixing parameters via software parameters of a digital signal processor or via analog or digital circuitry reflecting the mixing parameters.

[0021] In this way, a combiner can be provided to combine N transmit branch signals by using selected mixing coefficients, and then combining the N transmit branch signals via multiple linear combinations to generate multiple M distinct output signals to be provided to corresponding transmitters in M ​​spatially separated transmitters, where M > N. Such a combiner can be configured to set the linear combinations such that the output signals generated from the different linear combinations are received in the overlapping receiving regions of the spatially separated transmitters.

[0022] Preferably, the combiner is configured to form each of M output signals by mixing N transmit branch signals using N mixing coefficients, where the N mixing coefficients of the corresponding output signals represent a point in N-dimensional space, and the square of the distance from each of the corresponding M points to the origin is the same, such that the M transmitters use the same output signal power to output the M output signals. As a result, the probability of zeroing is reduced, and the probability of receiving different linear combinations in the overlapping receiving regions of spatially separated transmitters is increased, leading to a higher probability of recovering the N branch signals from the received signals.

[0023] According to the second option of the first aspect, which can be combined with the first option or the first aspect, the combiner can be configured to combine the two transmit branch signals by using a mixing coefficient matrix of output signals of number M:

[0024] .

[0025] Therefore, a general method can be provided for generating mixed parameters for any number of transceivers to improve robustness against multipath fading in dense optical wireless communication networks.

[0026] According to the third option of the first aspect, which can be combined with the first or second option or with the first aspect, the combiner can be configured to set a linear combination by the corresponding ratio between the feedback resistor and the input resistor of the operational amplifier. This approach provides a simple analog implementation of the proposed coefficient-based combination, wherein the mixing coefficients can be easily adjusted by selecting appropriate resistance values ​​and ratios or by using variable resistors.

[0027] According to the fourth option of the first aspect, which can be combined with any of the first to third options or with the first aspect, the combiner can be configured to provide adaptive settings for linear combination by allowing control of the switching states of switching elements used to provide transmit branch signals to the combiner or to provide output signals to spatially separated transceivers. The use of switching elements provides a flexible and easily implemented solution for introducing adaptive control in combiners implemented by analog or digital circuitry.

[0028] According to the fifth option of the first aspect, which can be combined with any one of the first to fourth options or with the first aspect, the device can be configured to allow control of the switching state of the switching element based on a learning or training algorithm or based on a network initialization process. Therefore, adaptive control via a linear combination of feedback mechanisms can be provided, which can be based on a learning or training or network initialization process.

[0029] According to a second aspect concerning a control device (e.g., a network access initialization device), an apparatus for controlling an optical wireless communication system is provided, the apparatus comprising:

[0030] A receiver is configured to receive from spatially separated transmitters of an optical wireless communication system information indicating a linear combination of corresponding selections of at least two transmit branch signals for multiple-input multiple-output (MIMO) communication, wherein the corresponding linear combination is used to generate a communication signal transmitted by a corresponding one of the spatially separated transmitters based on the at least two transmit branch signals; and

[0031] A comparator is used to compare selected linear combinations received in the overlapping receiving regions of spatially separated transmitters and to determine the linear combination that needs to be changed so that the output signal generated from the different linear combinations is received in the overlapping receiving regions of the spatially separated transmitters.

[0032] Therefore, an apparatus for controlling an optical wireless communication system is provided, the apparatus comprising: a receiver for receiving from M spatially separated transmitters of the optical wireless communication system information indicating corresponding selected linear combinations of N transmit branch signals output by an N-output multiple-input multiple-output (MIMO) modem for communication, N ≥ 2, wherein the corresponding selected linear combinations are used to generate a communication signal transmitted by a corresponding one of the spatially separated transmitters based on the N transmit branch signals; and a comparator for comparing the selected linear combinations of the N transmit branch signals among signals received in overlapping receiving regions of the spatially separated transmitters, and determining the linear combinations that need to be changed, such that N transmit branch signals can be generated from different linear combinations received in the overlapping receiving regions of the spatially separated transmitters.

[0033] According to the first option of the second aspect, the device can be configured to signal a feedback signal with a list of combined states to be updated to spatially separated transmitters. This provides a feedback mechanism for adapting the selected linear combination based on the actual received state, enabling decentralized control of the linear combinations for each spatially separated transmitter.

[0034] According to a third aspect, a modem is provided for generating output signals for multiple-input multiple-output (MIMO) communication in an optical wireless communication system, wherein the modem includes the means according to the first aspect.

[0035] According to a fourth aspect, a transceiver is provided for transmitting output signals of multiple-input multiple-output (MIMO) communication, wherein the transceiver includes the means according to the first aspect.

[0036] According to the first option of the fourth aspect, the transceiver can be configured to transmit information indicating the linear combination used to generate the output signal to a control device for controlling the settings of the linear combination. Therefore, the linear combination of each transceiver can be checked by detecting the linear combinations transmitted by each transceiver and ensuring that different linear combinations are assigned to adjacent transceiver pairs or transceivers with overlapping coverage or lighting areas.

[0037] According to a fifth aspect, an optical wireless communication system is provided, comprising a modem according to a third aspect and a plurality of spatially separated transceivers according to a fourth aspect.

[0038] According to a sixth aspect, a network access initialization device is provided for performing network access initialization on an access point of a wireless optical communication system, wherein the network access initialization device includes the apparatus according to the second aspect.

[0039] According to a seventh aspect relating to a modem or transceiver, a method for controlling an optical wireless communication system is provided, the method comprising:

[0040] Receive at least two transmit branch signals for multiple-input multiple-output (MIMO) communication;

[0041] At least two transmit branch signals are combined via multiple linear combinations to generate multiple output signals to be provided to spatially separated transmitters, wherein the number of output signals is greater than the number of transmit branch signals; and

[0042] Linear combinations are configured such that output signals generated from different linear combinations are received in the overlapping receiving regions of spatially separated transmitters.

[0043] Therefore, a method for controlling an optical wireless communication system is provided, the method comprising: receiving N transmit branch signals, N ≥ 2, output by an N-output multiple-input multiple-output (MIMO) modem for communication; combining the N transmit branch signals by using selected mixing coefficients, and combining the N transmit branch signals via multiple linear combinations to generate multiple M distinct output signals to be provided to corresponding transmitters in M ​​spatially separated transmitters, where M > N; and setting the linear combinations such that the output signals generated from the different linear combinations are received in overlapping receiving regions of the spatially separated transmitters, and providing the M distinct output signals to the M spatially separated transmitters for transmission.

[0044] More preferably, the combination includes forming each of the M output signals by mixing the N transmit branch signals using N mixing coefficients, wherein the N mixing coefficients of the corresponding output signals represent a point in N-dimensional space, and wherein the square of the distance from each of the corresponding M points to the origin is the same, such that the M transmitters use the same output signal power to output the M output signals.

[0045] According to an eighth aspect concerning a device for controlling or network access initialization, a method for controlling an optical wireless communication system is provided, the method comprising:

[0046] Information is received from a spatially separated transmitter of an optical wireless communication system indicating a linear combination of at least two selected transmit branch signals for multiple-input multiple-output (MIMO) communication, wherein the selected linear combination is used to generate a communication signal transmitted by a corresponding one of the spatially separated transmitters based on the at least two transmit branch signals.

[0047] Compare linear combinations of selected receptions in the overlapping receiving regions of spatially separated transmitters; and

[0048] Determine the linear combination that needs to be changed so that the output signals generated from different linear combinations are received in the overlapping receiving regions of spatially separated transmitters.

[0049] Therefore, a method for controlling an optical wireless communication system is provided, the method comprising: receiving from N spatially separated transmitters of the optical wireless communication system information indicating corresponding selected linear combinations of N transmit branch signals output by an N-output multiple-input multiple-output (MIMO) modem for communication, N ≥ 2, wherein the corresponding selected linear combinations are used to generate a communication signal transmitted by a corresponding one of the N spatially separated transmitters based on the N transmit branch signals; comparing the selected linear combinations of the N transmit branch signals in signals received in overlapping receiving regions of the spatially separated transmitters; and determining the linear combinations that need to be changed such that the N transmit branch signals can be generated from different linear combinations received in the overlapping receiving regions of the spatially separated transmitters.

[0050] According to the ninth aspect, a computer program product may be provided, which includes code means for generating the steps of the methods described in the seventh or eighth aspect when run on a computer device.

[0051] Note that the above-described device may be implemented based on an arrangement of discrete hardware circuits, integrated chips, or chip modules with 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).

[0052] It should be understood that the apparatus as claimed in claim 1 or 10, the OWC system as claimed in claim 7, the apparatus as claimed in claim 8, the network access initialization device as claimed in claim 9, the method as claimed in claim 11 or 13, and the computer program product as claimed in claim 14 or 15 may have similar and / or identical preferred embodiments, particularly as defined in the dependent claims.

[0053] 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.

[0054] These and other aspects of the invention will become clear and explained with reference to the embodiments described below. Attached Figure Description

[0055] In the following figures:

[0056] Figure 1 A block diagram of a LiFi architecture in which various embodiments can be implemented is shown schematically;

[0057] Figure 2 The LiFi architecture for multiple-input multiple-output (MIMO) or multiple-input single-output (MIMO) communication is schematically illustrated.

[0058] Figure 3 The frequency diagram of the signal and noise power spectral density at the input amplifier of the dual-ray receiver is schematically shown.

[0059] Figure 4 A block diagram of an optical transmission system with a combination of emission branches according to various embodiments is shown schematically;

[0060] Figure 5 The diagram schematically illustrates a two-dimensional coordinate system according to various embodiments, with mixing coefficients for two input channels having different combinations of emission branches;

[0061] Figure 6 A block diagram of a multi-transceiver access device with a fixed combination configuration according to various embodiments is shown schematically.

[0062] Figure 7 A block diagram schematically illustrates a first example of a multi-transceiver access device with combined adaptive settings according to various embodiments;

[0063] Figure 8 A block diagram schematically illustrates a second example of a multi-transceiver access device with combined adaptive settings according to various embodiments;

[0064] Figure 9 A flowchart is shown of a combined setup process based on network access initialization at a multi-transceiver access device according to various embodiments;

[0065] Figure 10 A block diagram of an adaptive setting for combination according to various embodiments is shown schematically;

[0066] Figure 11 A flowchart is shown of a combined setup process based on network access initialization at a network access initialization device according to various embodiments;

[0067] Figure 12 The architecture of a network access initialization system for adaptive configuration of combinations at a multi-transceiver access device is schematically illustrated according to various embodiments.

[0068] Figure 13 An exemplary arrangement of the transceiver and the combined state is schematically shown; and

[0069] Figure 14 Exemplary embodiments of a multi-transceiver access device with transmit branch combinations according to various embodiments are illustrated schematically. Detailed Implementation

[0070] Various embodiments of the present invention will now be described based on optical wireless lighting and communication (LiFi) systems with multiple transceiver access devices.

[0071] In the following text, luminaires as access devices 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)) light 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. Luminaires can be of conventional types, such as recessed or surface-mounted incandescent, fluorescent, or other discharge lamps. Luminaires can also be of non-conventional types, such as fiber optic components in one location and fiber cores or “light guides” in another.

[0072] It should also be noted that when using optical wireless communication based on the invisible portion of the spectrum (e.g., infrared and / or ultraviolet), the device according to the claimed invention can also be embedded in a separate transceiver node of the optical wireless communication system.

[0073] Figure 1 A block diagram of a LiFi network in which various embodiments can be implemented is shown schematically.

[0074] A LiFi network comprises multiple access points (APs) 12 (e.g., luminaires of 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 (optical sensors)) for optical communication toward endpoints (EPs) EP1 to EP4 10 (e.g., mobile user equipment or other user equipment). Individual beams generated by the TRX 11 and defining coverage areas on the plane(s) of EP 10... Figure 1 The middle part is represented by a dashed trapezoid.

[0075] AP 12 can use 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 different AP 12, then coordination of AP 12 is required to reduce cross-AP interference.

[0076] 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 14 can be connected to a synchronization server 16 for synchronization management and to a router 15 for connecting to the baseboard or backhaul network (e.g., Ethernet) 100.

[0077] Figure 2 Two options for MIMO communication in a LiFi infrastructure are illustrated schematically.

[0078] The LiFi infrastructure includes multiple TRX 11s of various APs (e.g., luminaires of a lighting system) located in a planar area 19 (e.g., the ceiling of a building). Each TRX 11 has an optical coverage area for transmitting and receiving LiFi signals projected onto a second planar area (not shown, e.g., the ground floor of a building), and an EP 10 with an optical front end 101 for receiving the optical LiFi signals transmitted by the TRX is located in this second planar area.

[0079] Figure 1 The system on the left is a MIMO system in which the same LiFi signal is exchanged between at least two different TRX 11 and EP 10 optical front ends 101 of the corresponding ceiling AP.

[0080] Figure 2 The simplified variant shown on the right is a multiple-input single-output (MISO) system in which multiple (at least two) TRX 11 of each ceiling AP communicate with a single optical front end 101 at an EP 10 that receives multiple signals from the multiple TRX 11.

[0081] MISO operation allows the standard optical front-end 101 of the EP 10 (e.g., a dongle) to benefit from processing in the TRX 11 at the ceiling. A single EP 10 can use the corresponding transmit branches of two or more TRX 11s to create a single common signal, which can be used to compensate for delay and phase difference. The MIMO-enabled modem at the AP at the ceiling can actively estimate the two downlink channels separately. This ensures—for example, each frequency bin of Orthogonal Frequency Division Multiplexing (OFDM)—phase adjustment to ensure coherent constructive addition and eliminate multipath fading (e.g., nulling).

[0082] In most cases, this may be sufficient if only one or two LiFi signals contribute significantly to the reception. This means that using a MIMO-enabled modem for MISO transmission may be sufficient, where two optical transmitters from each TRX transmit to one optical receiver at the EP.

[0083] This can be very efficient if the optical receiver is located at the intersection of two optical transmitters, such that the optical path lengths of the two transmission links are almost identical and the amplitudes are the same. However, the residual phase difference of exp{-2πjτf} can still be introduced by the difference in the feed cable lengths of the two (or more) TRXs, where τ represents the time delay caused by the difference in cable length and f represents the frequency of the LiFi signal. When the optical receiver at EP adds the two signals with equal intensity, it results in complete extinction or cancellation (zero) at frequencies where τf = 1 / 2 or an odd multiple thereof.

[0084] For example, if the cable length difference between the modem and the TRX exceeds, say, 2 meters, the receiver in the middle between the TRXs will receive two signals with delays that cause cancellation across most of the spectrum. In a MISO system, the modem can be operated so that the phase of one TRX automatically flips within the relevant frequency range to prevent cancellation. Outside the relevant frequency range, an optimal phase is selected so that the bandwidth gained near the notch due to cancellation can still be utilized.

[0085] Figure 3 The frequency diagram of the signal and noise power spectral density at the input amplifier of the dual-ray receiver is schematically shown.

[0086] More specifically, Figure 3 The frequency plot illustrates the power spectral density (PSD) characteristics of the MISO LiFi signal (S-PSD), amplifier noise signal (AN-PSD), and shot noise signal (SN) generated due to the DC (direct current) of the photocurrent and dark current at the photodetector element at the EP receiver. As can be seen from the frequency plot, notches caused by multipath cancellation (fading) are observed at approximately 25 MHz and 75 MHz. The 25 MHz notch makes the channel less suitable for data communication between 15 and 35 MHz.

[0087] According to various embodiments, multiple transmit branch signals at the modulator output are combined by using selected mixing coefficients to increase robustness against multipath fading effects.

[0088] Figure 4 A block diagram of an optical transmission system with a combination of emission branches according to various embodiments is shown schematically.

[0089] The proposed system allows the use of two or more optical outlets (i.e., TRXs) with the addition of a combiner function or circuit (CB) 42 (hereinafter referred to as the "combiner") to provide a fixed or adaptive linear combination of the transmit branch signals using selected mixing coefficients.

[0090] Therefore, the proposed optical wireless communication system (e.g., a LiFi system) includes a physical layer (PHY) signal processing communication unit (e.g., a MIMO modem) 41 (hereinafter referred to as a "MIMO modem") adapted to generate MIMO signals with N transmit branches (N greater than or equal to 2). The N transmit branch terminals of the signal processing communication unit 41 are connected to a combiner 42, which combines the N transmit branches using multiple mixing coefficients to generate M output signals (M greater than or equal to N) provided to the M optical transmitter units (transmitters) of each TRX 11.

[0091] Combiner 42 connects N transmit branches to M transmitters of TRX 11 and can be composed of a linear combination of N transmit branches, wherein the mixing coefficients of the linear combination are selected to reduce the possibility of cancellation (zeroing) of optical signals transmitted through the wireless space defined by channel matrix 43 and received at the receiver by analog front-end (AFE) 44 (which includes, for example, channel filters, amplifiers, attenuators, mixers, etc.), which is followed by physical layer (PHY) unit 10 (which handles, for example, addressing, collision avoidance, data acknowledgment protocols, etc.).

[0092] As in Figures 6 to 8 As illustrated in the following examples, the parameter-based combination operation of combiner 42 can be fixed or adaptive (e.g., based on a learning algorithm or based on (historical) input from the user to find out which TRXs are neighbors).

[0093] A simple first example of the mixing coefficients for two MIMO transmit branches or channels or paths (N=2) and two TRXs (M = 2) could be simply connecting the first MIMO transmit branch to the first TRX and the second MIMO transmit branch to the second TRX. In this case, the parameter matrix used to combine the two MIMO transmit branches to obtain the input signals for the two TRXs can be represented as follows:

[0094]

[0095] However, the second example below is also a good option:

[0096]

[0097] This means that the input signal of the first TRX corresponds to the sum of the two transmit branch signals, each transmit branch signal multiplied by a mixing coefficient. Furthermore, the input signal of the second TRX corresponds to the difference between the two transmit branch signals, each transmit branch signal being multiplied by a mixing coefficient. .

[0098] Based on the third example of two MIMO transmit branches and four TRXs, the mixing coefficients can be selected, for example, as follows:

[0099]

[0100] This means that the input signal of the first TRX corresponds to the first transmit branch signal; the input signal of the second TRX corresponds to the second transmit branch signal; and the input signal of the third TRX corresponds to the sum of the first and second transmit branch signals, with each transmit branch signal multiplied by a mixing coefficient. Furthermore, the input signal of the fourth TRX corresponds to the difference between the first and second transmit branch signals, with each transmit branch signal multiplied by a mixing coefficient parameter. .

[0101] More generally, consider N MIMO transmit branches and M transceivers, and N-dimensional space. The coordinates of each point in the N-dimensional space represent the N mixing coefficients of the corresponding signal combination, and the square of the distance to the origin represents the signal power.

[0102] In this way, the combiner can be configured to combine the N transmit branch signals of a modem using N mixing coefficients to form each of the M transmitter / transceiver output signals. The N mixing coefficients of the corresponding output signals can be considered as representing a point in N-dimensional space, where the squared distance from each of the M corresponding points in N-dimensional space to the origin is the same. As a result, based on the applicable coefficients, each of the N transmit branch signals (which have the same power) can contribute a fraction of the power to the signal power of the M output signals. By setting the distances of all M output signals to the origin to be equal, the M transmitters will transmit the same output signal power.

[0103] The corresponding M points in N-dimensional space represent points on the real part of N spheres. For N=2, this translates to half a real circle of the unit circle. In the absence of prior knowledge of the receiver, preferably, the points on the real semicircle will be spaced as far apart as possible to facilitate reconstruction at the receiver. Using this method, it is possible to decode N transmit branch signals in a region receiving N of the M output signals. As the probability of transmit branch signal cancellation decreases, this improves the robustness of the transmitter system to delays, for example, from cable lengths from different optical transmitters.

[0104] Figure 5 A two-dimensional coordinate system with coordinates x and y is schematically shown, each coordinate x and y representing one of the two transmit branch signals output by the MIMO modem, having mixing coefficients for different combinations of transmit branches according to various embodiments.

[0105] The two coordinate points 50-1 and 50-2 on the x and y axes correspond to the first example with two TRXs mentioned above.

[0106] Furthermore, the four coordinate points 50-1, 50-2, 51-1, and 51-2 correspond to the third example described above with four TRX.

[0107] Additionally, the eight coordinate points 50-1, 50-2, 51-1, 51-2, 52-1, 52-2, 52-3, and 52-4 correspond to the case with eight TRX.

[0108] As a general example of two emission branches and M output signals (i.e., M TRX), an M-dimensional sphere can be drawn around the origin of the coordinate system. Then, considering only the positive parameters of the x-axis, the following mixing coefficient matrix can be obtained:

[0109] .

[0110] The parameter-based combination described above can be achieved by providing a resistor in the forward path of combiner 42 that is proportional to the reciprocal of the matrix parameter value. If the value is negative, the resistor is connected to an inverting signal, which can be obtained by adding an inverter circuit.

[0111] Figure 6 A block diagram of a multi-transceiver access device with a fixed combination configuration according to various embodiments is shown schematically.

[0112] Note that throughout this disclosure, the structure and / or function of boxes with the same reference numerals as previously described will not be described unless specific additional functionality is involved.

[0113] Figure 6 The multi-transceiver access device includes a MIMO modem 41 with two transmit branches or channels X and Y, and a combiner 42 for combining the two transmit branches using a fixed mixing coefficient to produce three output signals provided to three TRX 11.

[0114] The mixing coefficient is defined by the ratio between each feedback resistor R3a, R3b, and R3c and each input resistor R1a, R2a, R1b, R2b, R1c, and R2c of each operational amplifier OPa, OPb, and OPC. It defines the amplification factors or gains g1a, g2a, g1b, g2b, g1c, and g2c of each operational amplifier from OPa to OPC as the mixing coefficient, as follows:

[0115] .

[0116] Due to the first transmit branch signal X of the MIMO modem 41 ( Figure 6 The fact that the left output (in the circuit) is routed to the input of the operational amplifier OPa above via the inverter circuit INV, therefore Figure 6 The sign of the mixing coefficient of the emitter branch of TRX 11 above is reversed to g1a = +R3a / R1a.

[0117] Therefore, the three output signals Oa to Oc of TRX are obtained by the following combination of the emitter branches X and Y with the respective mixing parameters:

[0118] .

[0119] In the following text, based on Figure 7 and Figure 8 Examples of adaptive and / or self-learning methods for combiner 42 are described.

[0120] Figure 7 A block diagram schematically illustrates a first example of a multi-transceiver access device with combined adaptive settings according to various embodiments.

[0121] Figure 7 The configuration of the adaptive combiner 42 basically corresponds to Figure 6 In the example, except that the inverter circuit INV has been omitted, and each of the transmitted branch signals X and Y is connected to the corresponding one of the input resistors R1a, R2a, R1b, R2b, R1c and R2c via the corresponding one of the switching elements S1a, S2a, S1b, S2b, S1c and S2c, which can be implemented as semiconductor switches (e.g., transistors) or mechanical (micro) switches, etc.

[0122] The switching states of switches S1a, S2a, S1b, S2b, S1c, and S2c can be controlled via corresponding control signals, which can be generated, for example, by an adaptive setting mechanism or algorithm based on feedback from at least one receiver or network access initialization device from at least one corresponding EP. Modem 41 generates two transmit branch signals X and Y, and a suitable combination of the two transmit branch signals X and Y is selected by each TRX 11 or for each TRX 11.

[0123] Figure 8 A block diagram schematically illustrates a second example of a multi-transceiver access device with a combined adaptive configuration according to various embodiments. In the second example, the two transmit branch signals X and Y of the modem 41 are first combined in a combiner 42 by an amplifier-resistor circuit 81, their respective mixing coefficients being defined by a resistor network, to produce three output signals of three TRX 11. These three output signals are then selectively applied to their respective input terminals of the TRX 11 via respective switching elements Sa, Sb, and Sc, which can be implemented as semiconductor switches (e.g., transistors) or mechanical (micro) switches, etc.

[0124] according to Figure 8 If the switching elements Sa to Sc are controlled to select the middle one of their three input terminals, then the first transmit branch signal X (the left output of modem 41) can be directly applied to each of the three TRX 11. The upper and lower portions of their input terminals are connected to the corresponding output signals generated by a specific combination of transmit branch signals X and Y, as defined by the amplifier-resistor circuit 81.

[0125] In the first and second examples of adaptive combination in combiner 42 described above, the connection state of the switching elements can be controlled based on a learning or training algorithm to ensure that adjacent lamps or luminaires at the access point receive different communication signals (i.e., output signals Oa to Oc). In a regular rectangular pattern of TRXs, for example, at the ceiling, two different MIMO signals are sufficient to ensure that adjacent TRXs never receive the same signal.

[0126] To train the system, each TRX 11 can be informed or determined to have a suitable combination of transmission branches for its transmission. The goal could be to ensure that adjacent TRXs (in their respective lamps or luminaires) receive different signals (e.g., different phases and / or amplitudes).

[0127] If the adaptive feedback function is implemented without a central controller, the proposed enhanced network infrastructure can remain simple. In other words, the adaptive combination of the transmit branch signals X and Y of the TRX 11 should be locally controlled.

[0128] The adaptation and / or initial configuration of the combination at combiner 42 can be achieved through the network access initialization process. For the necessary communication associated with the network access initialization process, out-of-band (OOB) signaling can be used, as it can be implemented in the TRX 11 without the need for additional light-emitting diodes (LEDs) and photodetectors. OOB signaling is transmitted outside the defined frequency band of LiFi communication signals (or, metaphorically, outside some other kinds of signaling activity in the LiFi network).

[0129] Figure 9 A flowchart illustrating the combined setup process based on network access initialization at a multi-transceiver access device according to various embodiments is shown.

[0130] In the initial step S901, N MIMO transmit branch signals (e.g., X and Y) are received from the modem 41. Then, in step S902, the initial or default settings of the combinations and their respective mixing coefficients of the combiner 42 are selected, and M corresponding output signals are forwarded to the TRX 11. In the subsequent step S903, information about the selected individual combinations (combination state) is transmitted to the network access initialization device (e.g., via OOB signaling) along with the identifier (ID) of each TRX 11 of the access device. This network access initialization device can be a mobile device that scans the LiFi communication range based on automatic or manual operation.

[0131] Then, in step S904, the access device waits until it has received a feedback message from the network access initialization device—the feedback message indicating whether the selected combination of the identified TRX can be maintained or needs to be updated—for example, due to a conflict with an adjacent TRX using the same or insufficiently differentiated transmit branch combination.

[0132] In the next step S905, the access device checks whether the selected combination must be updated. If not, the process jumps back to step S903 and continues to transmit the ID of the current combination and the corresponding TRX, for example, in response to a trigger received from the network access initialization device. If the required update for the selected combination has been received from the network access initialization device, the process continues to step S906, where a new combination is established based on the corresponding information received from the network access initialization device or based on an arbitrary or predetermined self-selection of the new combination (e.g., by a corresponding control signal applied to the switching element of the combiner 42).

[0133] Figure 10 A block diagram of an adaptive configuration for combination, according to various embodiments, is schematically shown.

[0134] The network access initialization device can be a mobile user equipment of the TRX 101 with network access initialization signaling (e.g., OOB signaling). The OOB signaling can be in the optical frequency range or the RF range.

[0135] Detector circuitry (DET) 102 is configured to detect combined states and IDs signaled via OOB signaling from various access devices, for example, located on a building ceiling, and forwards the received IDs and combined states(s) to comparator (CP) 103. Comparator 103 stores the received IDs and a list of combined states—for example, along with geographic information about the geographic relationships between the various TRXs identified by the received IDs—in memory or database (MEM) 104. This geographic information can simply indicate, for example, which combined state belongs to an adjacent TRX (e.g., via a neighbor flag).

[0136] If comparator 103 determines that two adjacent TRXs have the same or indistinguishable combination states, it initiates the transmission of a feedback signal via its own TRX 101 to the access device of the corresponding TRX. This feedback signal indicates that the combination state of the corresponding TRX needs to be updated. As an additional option, comparator 103 can be configured to select a sufficiently distinguishable combination state for the TRX of interest and initiate the transmission of the selected combination state to the TRX of interest.

[0137] Figure 11 A flowchart illustrating a combined setup process based on network access initialization at a network access initialization device according to various embodiments is shown.

[0138] In the initial step S1101, the network access initialization device receives information about the selected combination status along with the corresponding IDs (e.g., via OOB signaling) of each TRX 11 in the scan range of the network access initialization device (which may be a mobile device scanning the LiFi communication range based on automatic or manual operation) from the corresponding access device in the scan range of the network access initialization device (which may be a mobile device scanning the LiFi communication range based on automatic or manual operation).

[0139] Then, in step S1102, the network access initialization device stores the received combined states(s) along with their corresponding IDs(s) and optional geographic information indicating the adjacent states of the corresponding TRXs (e.g., in the database or memory of the network access initialization device). Based on this, a log or list of all (adjacent) TRX pairs that can be used for MIMO or MISO reception at the EP can be generated. In manual scan mode, logs can be generated as users of the network access initialization device walk through the room until messages from all TRXs have been received. In automatic scan mode, the reception range (e.g., antenna characteristics) of the receiver at the network access initialization device can be mechanically or electronically controlled to scan the entire area where all TRXs are located.

[0140] Then, in step S1103, it is determined which of the received combined states need to be updated (e.g., due to conflicts at relevant TRX pairs), and a corresponding list can be generated. Optionally, an updated combined state can be selected for each TRX in the generated list.

[0141] Finally, in step S1104, a feedback signal with a corresponding list of the combined states to be updated and the corresponding IDs, along with optional suggestions for the new combined states, can be sent to the access device (e.g., via OOB signaling).

[0142] Figure 12 The architecture of a network access initialization system for adaptively setting the mixing coefficient at a multi-transceiver access device is illustrated schematically according to various embodiments.

[0143] exist Figure 12 In the system, the MIMO modem 41 generates two transmit branch signals X and Y, which are provided to four TRX 11 (TRX1 to TRX4). Each TRX 11 includes a combiner (not shown) that combines the two transmit branch signals X and Y as follows:

[0144] TRX1: a1X+b1Y (identified by ID1);

[0145] TRX2: a2X+b2Y (identified by ID2);

[0146] TRX3: a3X+b3Y (identified by ID3); and

[0147] TRX4: a4X+b4Y (identified by ID4).

[0148] As an example, the selection at each combiner of the TRX can be achieved by at least one controllable wavelength selection filter inserted in the signal path of the transmit branch signal.

[0149] Via OOB signaling, each TRX 11 transmits (e.g., broadcasts) its ID and selected XY combination to the network initiation device 120 with receiver 121. To ensure that the network initiation device 120 receives messages from all TRX 11 within its communication range, a random backoff time may be used for transmission.

[0150] Figure 13 An exemplary arrangement of transceivers and their corresponding combinations are illustrated schematically.

[0151] exist Figure 13 In the example, four TRX 11s (TRX1 to TRX4) are arranged in a square pattern on, for example, the ceiling of a room. Therefore, the individual TRX pairs in the log can be TRX1 / TRX2, TRX1 / TRX3, TRX2 / TRX4, and TRX3 / TRX2, as indicated by the bidirectional arrows between the individual TRX 11s. Figure 13 As indicated in the log, TRX1, TRX2, and TRX4 have signaled the combined state "X" (which indicates, for example, the first transmit branch of a MIMO modem), while TRX4 has signaled the combined state "Y" (which indicates, for example, the second transmit branch of a MIMO modem). When the log is complete, the network initialization device is now able to define which transceiver list it should update.

[0152] exist Figure 13 In the example shown, TRX2 should switch to the combination state "Y" to ensure that all identified adjacent TRX pairs transmit their respective optical communication signals in mutually different combination states "X" and "Y". This result is transmitted back by the network initialization device in the feedback signal transmitted via the OOB channel.

[0153] Figure 14 Exemplary embodiments of a multi-transceiver access device with transmit branch combinations according to various embodiments are illustrated schematically.

[0154] exist Figure 14In an exemplary embodiment, the MIMO modem 140 is connected to the mains power grid via a plug 142 and to a communication network (e.g., a local area network (LAN)). The MIMO modem 140 includes a combiner (not shown) as explained in the above embodiments and generates six output signals with different combination states based on, for example, two transmit branch signals generated by the MIMO modem. The six output signals are provided via respective cables 141 to six TRX 11s (e.g., infrared (IR) transceivers) having integrated plugs or interfaces that can be connected to corresponding sockets 146 provided at respective ceiling units (panels) 145, which include one or more lamps or luminaires for the optical transmission of the output signals generated by the respective TRX 11. The ceiling units 145 are driven by driver circuitry 144 (e.g., LED drivers), which is connected to the mains power grid via another plug 142.

[0155] In this way, the optical wireless TRX unit is integrated into the ceiling unit, and a separate transmitter unit is not required. Alternatively, for example, if the spacing between the lighting ceiling units is too far to provide adequate coverage by means of the TRX integrated into the ceiling unit, the TRX can be installed in a separate "standalone" unit (not shown).

[0156] The cable length between the access device 140 and all ceiling units 145 should preferably be the same to minimize the phase delay between the output signals of the different TRX 11.

[0157] For multiple ceiling units 145 (e.g., six or twelve units). Figure 14 Exemplary implementations can be used to enhance MIMO capabilities by increasing the number of transmit branch signals (e.g., two outputs) generated by the MIMO modem to more output signals with different combinations of each other.

[0158] According to various embodiments, a reverse communication direction (i.e., the uplink direction) can also be considered. A communication system using any aspect of the above embodiments in the downlink direction from infrastructure equipment (typically a ceiling-mounted or wall-mounted TRX 11 at access point 12) toward distributed endpoints 10 can be supplemented by an uplink communication link from endpoint 10 back to the infrastructure equipment. This can be achieved by having at least some endpoints 10 transmit at least one uplink radiation beam carrying a data signal, which can be received by uplink signal detectors or receivers located at at least some infrastructure equipment, such as at the ceiling or walls of a building. According to the following non-limiting example, the infrastructure equipment can then combine the data signals received by the uplink signal receiver to optimize the combination process of downlink MIMO or MISO signals.

[0159] In the first example, two analog signal buses (or as many as those used in the downlink allocation) can be provided from the uplink signal receiver to the MIMO-enabled TRX 11. Signals received from the signal buses are combined using a weighting factor (e.g., shared weighting), which is at least substantially the same as the linear combination (e.g., mixed weighting) used in the downlink direction. As an example, the weighting factor can be determined in the same manner as the metrics described in the above embodiments.

[0160] In the second example, all received uplink data signals could be added, although this does involve risk, as phase cancellation can affect the (higher) portion of the uplink data signal and lead to noise accumulation. This approach is particularly attractive if the required downlink data rate (e.g., involving large download files or streaming video) is higher than the data rate in the uplink direction.

[0161] In the third example, noise gating can be applied to the received uplink data signal. For example, only strong copies (e.g., signal-to-noise ratios or bit error rates above a predetermined threshold) or the strongest copies of the received uplink data signal can be processed. This enables adaptive signal operation in the uplink direction. This avoids noise accumulation in large networks.

[0162] In summary, a LiFi system has been described having M multiple TRXs and a single multiple-input multiple-output (MIMO) modem with at least N transmit branch outputs, wherein the N transmit branch outputs of the MIMO modem are fed to a linear combiner. The linear combiner creates M distinct linear combinations based on the N MIMO outputs of the MIMO modem and selects the linear combinations such that when N distinct signals are received from the M transmit signals, they allow decoding of each of the N MIMO signals.

[0163] While the invention has been detailed and described in the accompanying drawings and the foregoing description, such description should be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments. The proposed combination process of MIMO or MISO signals can be applied to other types of wireless networks and may be standardized in other types of wireless networks, with other types of access devices and transceivers. In particular, the invention is not limited to LiFi-related environments, such as ITU-T G.9961, ITU-T G.9960, and ITU-T G.9991 network environments.

[0164] 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 imply that combinations 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, however detailed it may appear in the text, and is therefore not limited to the disclosed embodiments. 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.

[0165] 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 imply that a combination of these measures cannot be used advantageously.

[0166] Similar to Figure 9 and Figure 11 The processes indicated herein can be implemented as program code devices 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, provided together with or as part of other hardware; however, it can also be distributed in other forms, such as via the Internet or other wired or wireless telecommunications systems.

Claims

1. An apparatus for generating M output signals for use in an optical wireless communication (OWC) system. The OWC system includes: - An N-output multiple-input multiple-output modem for communication, where N ≥ 2, used to modulate the modem input signal and output N transmit branch signals. - M spatially separated optical transmitters (11), each transmitter being configured to emit light based on a corresponding one of M output signals, the M transmitters being arranged to have multiple overlapping receiving areas in which light emitted by multiple transmitters of the M transmitters (11) can be received; The device includes: - An input terminal used to receive the signals from the N transmitted branches. - Combiner (42) is used to combine the N transmit branch signals by using selected mixing coefficients, and to combine the N transmit branch signals by multiple linear combinations to generate M output signals, each output signal being a different linear combination, and where M > N; The combiner (42) is configured to: - Select the mixing coefficients for the linear combination to reduce the probability of signal cancellation in the overlapping receiving region, where multiple received light beams from M spatially separated transmitters (11), and - Provide M output signals to M transmitters (11) for transmission, such that each transmitter receives a different one of the M output signals.

2. The apparatus of claim 1, wherein the combiner (42) is configured to form each of M output signals by mixing the N transmit branch signals using N mixing coefficients, wherein the N mixing coefficients of the corresponding output signals represent a point in N-dimensional space, and wherein the square of the distance from each of the corresponding M points to the origin is the same, such that the M transmitters output the M output signals using the same output signal power.

3. The apparatus of claim 2, wherein the combiner (42) is configured to combine two transmit branch signals using the following mixing coefficient matrix of M output signals: 。 4. The apparatus of claim 1, wherein the combiner (42) is configured to set the linear combination by a corresponding ratio between the feedback resistors (R3a, R3b and R3c) and the input resistors (R1a, R2a, R1b, R2b, R1c, R2c) of the operational amplifiers (OPa to OPc).

5. The apparatus of claim 1, wherein the combiner (42) is configured to provide an adaptive setting for linear combination by allowing control of the switching states of switching elements (S1a, S2a, S1b, S2b, S1c, S2c; Sa, Sb, Sc) for providing transmit branch signals to the combiner (42) or for providing output signals to spatially separated transceivers (11).

6. The apparatus of claim 5, wherein the apparatus is configured to allow control of the switching states of switching elements (S1a, S2a, S1b, S2b, S1c, S2c; Sa, Sb, Sc) based on a learning or training algorithm or based on a network access initialization process.

7. An optical wireless communication (OWC) system, comprising: An N-output multiple-input multiple-output modem for communication, where N ≥ 2, is used to modulate the modem input signal and output N transmit branch signals; M spatially separated optical transmitters (11), each transmitter being configured to emit light based on a corresponding one of M output signals, the M transmitters being arranged to have multiple overlapping receiving areas in which light emitted by multiple transmitters of the M transmitters (11) can be received; and An apparatus for generating M output signals, the apparatus comprising: - An input terminal used to receive the signals from the N transmitted branches. - Combiner (42) is used to combine the N transmit branch signals by using selected mixing coefficients, and to combine the N transmit branch signals by multiple linear combinations to generate M output signals, each output signal being a different linear combination, and where M > N; The combiner (42) is configured to: - Select the mixing coefficients for the linear combination to reduce the probability of signal cancellation in the overlapping receiving region, where multiple received light beams from M spatially separated transmitters (11), and - Provide M output signals to M transmitters (11) for transmission, such that each transmitter receives a different one of the M output signals.

8. An apparatus for providing feedback to the OWC system according to claim 7, comprising: A receiver (101) is used to receive information from M spatially separated optical transmitters (11) of an optical wireless communication system, indicating a linear combination of their respective identifiers and corresponding selections of N transmit branch signals; Memory (104) for storing linear combinations of identifiers and selections, as well as geographic information about the geographic relationships between the respective transmitters; and Comparator (103) is used for: - Compare the linear combination of the selected N transmit branch signals in the signals received in the overlapping receive areas of the spatially separated transmitters (11), and - Determine the linear combinations that need to be changed so that the N transmit branch signals can be generated from different linear combinations received in the overlapping receiving regions of spatially separated transmitters (11); The device is configured to send a feedback signal with a combined state list to be updated to M spatially separated transmitters (11).

9. A network access initialization device (120) for performing network access initialization on a wireless optical communication system, the network access initialization device (120) comprising the apparatus as described in claim 8.

10. An apparatus for generating M output signals for use in an optical wireless communication (OWC) system, the OWC system comprising: - M spatially separated optical transmitters (11), each transmitter being configured to emit light based on a corresponding one of M output signals, the M transmitters being arranged to have multiple overlapping receiving areas in which light emitted by multiple transmitters of the M transmitters (11) can be received; The device includes: - An input terminal used to receive modem input signals. - An N-output multiple-input multiple-output modem for communication, where N ≥ 2, used to modulate the modem input signal and output N transmit branch signals. - Combiner (42) is used to combine the N transmit branch signals by using selected mixing coefficients, and to combine the N transmit branch signals by multiple linear combinations to generate M output signals, each output signal being a different linear combination, and where M > N; The combiner (42) is configured to: - Select the mixing coefficients for the linear combination to reduce the probability of signal cancellation in the overlapping receiving region, where multiple received light beams from M spatially separated transmitters (11), and - Provide M output signals to M transmitters (11) such that each transmitter receives a different one of the M output signals.

11. A method for controlling an optical wireless communication system, the system comprising: - M spatially separated optical transmitters (11), each transmitter being configured to emit light based on a corresponding one of M output signals, the transmitters being arranged to have multiple overlapping receiving areas in which light emitted by multiple transmitters of the M transmitters (11) can be received; The method includes: Receive (S901) N transmit branch signals output by an N-output MIMO modem for communication, where N ≥ 2. The N transmit branch signals are combined by using selected mixing coefficients, and then combined via multiple linear combinations (S902) to generate M output signals, each output signal being a different linear combination, where M > N. By selecting a mixing coefficient to set the linear combination (S906), the possibility of signal cancellation in the overlapping receiving region is reduced, where multiple received light beams from M spatially separated transmitters (11) and M different output signals are provided to M spatially separated transmitters (11) for transmission.

12. The method of claim 11, wherein the combination (S902) comprises: - Each of the N transmit branch signals is formed by mixing the N transmit branch signals with N mixing coefficients, where the N mixing coefficients of the corresponding output signal represent a point in N-dimensional space, and the square of the distance from each of the corresponding M points to the origin is the same, such that the M transmitters use the same output signal power to output the M output signals.

13. A method for controlling an optical wireless communication system, the system comprising: - M spatially separated optical transmitters (11), each transmitter being configured to emit light based on a corresponding one of M output signals, the transmitters being arranged to have multiple overlapping receiving areas in which light emitted by multiple transmitters of the M transmitters (11) can be received; The method includes: Information is received (S1101) from M spatially separated transmitters (11) of the optical wireless communication system, indicating their respective identifiers and information of correspondingly selected linear combinations of N transmit branch signals output by an N-output MIMO modem for communication, where N ≥ 2, wherein the correspondingly selected linear combinations are used to generate M output signals based on the N transmit branch signals, and the M output signals are transmitted by the M spatially separated transmitters (11) such that each transmitter transmits a different one of the M output signals. Compare the linear combination of the selected N transmit branch signals in the signals received in the overlapping receive regions of the spatially separated transmitters (11), and Determine the linear combination that needs to be changed, such that the N transmit branch signals can be generated from different linear combinations received in the overlapping receive regions of spatially separated transmitters (11).

14. A computer program product comprising, when run on a computer device, code means for generating the steps of the method of claim 12.

15. A computer program product comprising, when run on a computer device, code means for generating the steps of the method of claim 13.

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