Daisy chaining for optical communication systems

Abstract

The invention relates to daisy chaining network topologies for optical communication systems (e.g., LiFi systems) based on a hybrid electric / fiber cable, which are aimed to provide a backbone link for indoor high speed wireless connectivity. The topologies comprise two optical input / outputs (one wireless and one wired) and use a "sum and split" block that loops in / out an optical signal from a wireless optical frontend and passes the optical signal both up-stream and downstream.

Description

[0001] Daisy chaining for optical communication systems

[0002] FIELD OF THE INVENTION

[0003] The invention relates to the field of communication in optical wireless networks, such as - but not limited to - LiFi networks, for use in various different applications for home, office, retail, hospitality and industry.

[0004] BACKGROUND OF THE INVENTION

[0005] The number of Internet-connected mobile devices are increasing rapidly.

[0006] The document titled “G.p2pf Working Text 1.0; TD-5” by Ronald Heron, ITU-T DRAFT; STUDY PERIOD 2021-2024; STUDY GROUP 15; SERIES TD-5, INTERNATIONAL TELECOMMUNICATION UNION, vol. 3 / 15 19 October 2023 (2023- 10-19), represents an initial draft for the Point-to-Point Fibre in the Premises project, G.p2pf The document discloses how a Main Fibre-in-the-Premises Unit (MFU) may be used as a termination point for an access network and the starting point of the in-premise network. It further discloses a Sub Fibre in the Premises Unit (SFU) which may provide wireline (e.g. Ethernet) and wireless (e.g. Wi-Fi) for end user devices. The document further discloses a Daisy-Chained SFU, being an SFU that is connected to the MFU via an intermediary SFU using a P2P fibre.

[0007] The document titled “ Connectivity for Lighting Systems”, IEC TR 63425:2022, IEC, 3, RUE DE VAREMBE, PO BOX 131, CH-1211 GENEVA 20, SWITZERLAND, provides information and guidance on the connectivity aspects of lighting systems to operate and to interconnect with other systems, amongst other things the document discloses that BACnet is a protocol for building automation and control systems, that may define multiple transmission networks, so that different products work together, and a network implementing BACnet may make use of multiple-topologies, which may comprise a daisy chain, star and hybrid topology structured with wired physical layers such as twisted pair and optical fibres.

[0008] Among others, video streaming and accessing cloud-based services are user activities that consume high amounts of data capacity. The resulting data traffic is expected to grow exponentially and is mostly generated in indoor environments. Visible light communication (VLC) makes use of data transmission in the visible optical band (e.g., in 380 nm to 780 nm) hence visible light communication, on account of their strategic placement and for efficiency reasons, sometimes VLC transmitters are integrated in general illumination system. Often times such optical communication systems make use of visible light for the downlink and infrared for the uplink, so as to avoid visible light being emitted by user equipment. To simplify matters some systems also make use of infrared for the downlink, thereby enabling data communication when illumination light is off. Such optical wireless communication systems using visible and / or infrared light are commercially known as LiFi (Light Fidelity) systems. Unique properties of light propagation are seen as a compelling alternative to the increasingly congested radio waves. In fact, the exponential growth of the number of wireless users led to a continuous shrinking of wireless cell sizes, from several kilometers, to microcells, and now to very small cells that cover just a few rooms or a few meters as femtocells. In the light of such higher user densities, the property that light does not travel across walls and stays inside a room comes as a great advantage. Additionally, LiFi has is its un-licensed enormous bandwidth (in the range of THz) and allows reuse of the entire spectrum in every room. Moreover, it avoids interference, that currently limits the user experience that WiFi dramatically deteriorates in crowded areas, subject to the contention-based access protocols.

[0009] LiFi networks enable mobile user devices (called end points (EP) in the following) like laptops, tablets, smartphones or the like to connect wirelessly to the Internet. WiFi achieves this using radio frequencies, but LiFi achieves this using the light spectrum which can enable unprecedented data transfer speed and bandwidth. Furthermore, it can be used in areas susceptible to electromagnetic interference. It’s important to consider that wireless data is required for more than just our traditional connected devices - today televisions, speakers, headphones, printer’s, virtual reality (VR) goggles and even refrigerators use wireless data to connect and perform essential communications. Radio frequency (RF) technology like WiFi is running out of spectrum to support this digital revolution and LiFi can help power the next generation of immersive connectivity. One of the advantages, that LiFi has is its un-licenced enormous bandwidth (in the range of THz).

[0010] Based on modulations, information in the coded light can be detected using any suitable light sensor. This can be a dedicated photocell (point detector), an array of photo cells possibly with a lens, reflector, diffuser of phosphor converter. E.g., the light sensor may be a dedicated photocell included in a dongle which plugs into the end point, or the sensor may be integrated in the end point. Either way this may enable an application running on the end point to receive data via the light.

[0011] A communication signal can be embedded in a light signal emitted by an illumination source of an access device, such as an everyday luminaire, e.g. room lighting or outdoor lighting, thus allowing use of the illumination from the luminaires as a carrier of information. The light thus comprises both a visible illumination contribution for illuminating a target environment such as a room (typically the primary purpose of the light), and an embedded signal for providing information into the environment (typically considered a secondary function of the light). In such cases, the modulation may typically be performed at a high enough frequency to be beyond human perception, or at least such that any visible temporal light artefacts (e.g., flicker and / or strobe artefacts) are weak enough and at sufficiently high frequencies not to be noticeable or at least to be tolerable to humans. Thus, the embedded signal does not affect the primary illumination function, i.e., so the user only perceives the overall illumination and not the effect of the data being modulated into that illumination.

[0012] In the following, the term “access point” is used to designate a logical access device that provides access to a network and that can be connected to one or more physical access devices (e.g., transceivers). Such a physical access device may be located at a luminaire, or may be dedicated device positioned on the ceiling, and the logical access point may be connected to one or more physical access devices. However, compared to RF technology, the range of each access point is smaller, allowing a higher density of access devices.

[0013] Conventional LiFi systems are configured either as centralised systems (i.e., all in one housing) or distributed systema (i.e., with star topology). Centralised configurations can be installed easily but are very limited in their LiFi coverage area. Distributed configurations based on the star topology may solve the problem of coverage to some extend but installation and scalability is limited and difficult. Besides this, the use of wired connections (e.g., copper wire) beyond a certain limit (e.g., 3m) may cause electromagnetic interference (EMI) problems.

[0014] SUMMARY OF THE INVENTION

[0015] It is an object of the present invention to provide an optical communication system that allows flexible extension of the coverage area, that allows easy installation and / or causes little EMI problems. This object is achieved by an optical network node as claimed in claim 1 and an optical network as claimed in claim 12.

[0016] According to a first aspect, an optical network node is provided for use in an optical network, the network node is capable of being daisy chained and having first and second wireline optical interfaces for coupling to an optical fiber, the network node comprising: a first transceiver stage configured to: transmit a first wireless optical signal to an end point and receive a second wireless optical signal from the end point; a second transceiver stage configured to: transmit via the first wireline optical interface a first wireline optical signal to the optical network and receive via the first wireline optical interface a second wireline optical signal from the optical network; a third transceiver stage configured to: receive via the second wireline optical interface a third wireline optical signal from the optical network and transmit via the second wireline optical interface a fourth wireline optical signal to the optical network; a signal generating circuit configured to: generate a first output signal based on the second wireless optical signal and the third wireline optical signal for output using the second transceiver stage; generate a second output signal based on the second wireline optical signal for transmission by the first transceiver stage; and, generate a third output signal based on the second wireline optical signal for output using the third transceiver stage.

[0017] According to a second aspect, an optical communication network is provided, which comprises an access point and a plurality of optical network nodes of the first aspect in a daisy chain topology.

[0018] Accordingly, the proposed chainable optical network node may be used to forward network connectivity, allowing to build a daisy chain network topology which is favorable for implementing larger networks to increase the coverage area in a flexible manner and allows easy installation. At the same time, the network node allows data from the optical network to be transmitted to endpoints and allows data to from endpoints to be routed onto the optical network. The optical network nodes may be incorporated in luminaires, so as to form combined illumination and communication systems.

[0019] Preferably, network nodes are provided with receiving, regenerating and retransmitting (RRR) blocks, allowing to reconstruct the network signal, thereby allowing the daisy-chain to span longer distances. Optionally the network nodes can be pre- and / or reconfigured, in that they are fitted with hardware that allows them to be configured as access point node or as a forwarding / daisy-chain network node, by doing so, it is possible for the installer to use all identical devices when installing the daisy-chain, and once connected, configure the root node of the daisy-chain as access point. In this manner, only one access point is provided in the daisy chain and a large coverage is achieved. When the forwarding network nodes are fitted with RRR blocks that are implemented as PHY (layer-1) repeaters, no security commissioning is required. As a result of the use of the RRR blocks is that the first wireless optical signal, the first wireline optical signal and the fourth wireline optical signal all use the same modulation.

[0020] The proposed optical network can be extended, by daisy chaining multiple network nodes to multiple coverage zones with easy installation. The optical network links may be implemented by a hybrid cable (electric / fiber) for daisy chaining signal distribution and power supply.

[0021] According to a first option which can be combined with any one of the first to third aspects, the signal generating circuit may be configured to: generate the third output signal further based on the second wireless optical signal; and generate the second output signal further based.

[0022] According to a second option which can be combined with the first option or any one of the first to third aspects, the network node comprises a network interface and is reconfigurable as an access point for providing the optical network with access to the further network via the network interface or as a daisy-chain network node for providing access to the optical network to neighbor nodes when present. Thus, the proposed optical network node (e.g., daisy chain node) can be configured either as access point node or as a daisy-chain network node.

[0023] According to a third option which can be combined with the first or second option or any one of the first to third aspects, the signal generating circuit comprises a repeater stage for: receiving the received second optical wireline signal from the second transceiver stage and generating and outputting a first intermediate signal based thereon for use in generating the second output signal and third output signal and receiving an intermediate input signal based on the received second wireless optical signal and the received third wireline optical signal and generating a second intermediate signal based thereon and outputting it as the first output signal.

[0024] In accordance with the third option, it is possible for the network node to perform full bi-directional signal relaying over the optical network, allowing it to pass signals from the optical wireless link to be passed upstream and downstream over the optical (daisychain) network.

[0025] According to a fourth option which can be combined with the third option, the repeater stage may be configured to operate either in the analog domain only, or on the physical protocol layer (e.g., of the ITU-T G.9991 standard) only. Thereby, the system has the capability to recover / refresh optical signals (e.g., G.vlc or G.hn signals) exclusively at physical layer or in the analog domain (signal forwarding).

[0026] According to a fifth option which can be combined with any one of the first to fourth options or any one of the first to third aspects, the signal generating circuit comprises a multiple-input multiple-output access point block wherein a first input / output pair of the access point block is configured to be connected via the second transceiver stage to a first daisy chain and wherein a second input / output pair of the access point block is configured to be coupled via the third transceiver stage to a second daisy chain and the access point block is further configured to be connected to the further network (LAN) via the network interface. In accordance with the fifth option the network node may be operated as an access point node capable of providing access point functionality to two separate daisy-chains. In this manner network nodes can be split over two daisy-chains (resulting in a shorter chain). Moreover, when the coverage areas of the daisy-chains overlap the MIMO function may advantageously help cope with the resulting interference.

[0027] According to a sixth option which can be combined with any one of the first to fifth options or any one of the first to third aspects, the signal generating circuit may comprise a splitting / summing circuit. According to the sixth option, the splitting and summing is implemented as an electrical circuit.

[0028] According to a seventh option which can be combined with any one of the first to sixth options or any one of the first to third aspects, the optical fiber may comprise a wired link for electric power supply to the network node. According to the seventh option, the wireline sections that are used to connect the individual network nodes into the optical (daisy-chain) network, may also be used to provide the respective nodes with power. Thereby simplifying the installation of a network node to attaching one or two wireline links.

[0029] According to an eighth option which can be combined with the third option, the repeater stage may comprise a physical and media access control (MAC) layer functionality and is configured to stop forwarding an incoming wireline optical signal unicast frame received by the second transceiver state when a target address of the incoming unicast frame corresponds to that of the network node. According to the eighth option, the network node may avoid unnecessary relaying of traffic, thereby realizing energy saving.

[0030] According to a nineth option which can be combined with any one of the second option or any one of the first to third aspects, a baseband unit may be provided, that is configurable at runtime to operate as one of an access point or as a physical layer repeater stage.

[0031] According to an tenth option which can be combined with the nineth option, the baseband unit may be manually configurable by a switch or toggle during commissioning. This approach allows an installer to create an optical network using identical network nodes and to switch / toggle one of the nodes to operate as access point.

[0032] According to an eleventh option which can be combined with the nineth or tenth option, the baseband unit may be configured to detect presence of an input signal at an access point interface and to switch between operation as access point and operation as repeater stage based on a result of the detection. This approach allows an installer to create an optical network using identical network nodes and to switch / toggle a network node to operate as access point by first connecting the ethemet / LAN cable and then connecting power.

[0033] It is noted that the above apparatuses may be implemented based on discrete hardware circuitries with discrete hardware components, integrated chips, or arrangements of chip modules, or based on signal processing devices or chips controlled by software routines or programs stored in memories, written on a computer readable media, or downloaded from a network, such as the Internet.

[0034] It shall be understood that the optical network node of claim 1, the optical network of claim 12 may have similar and / or identical preferred embodiments, in particular, as defined in the dependent claims.

[0035] It shall be understood that a preferred embodiment of the invention can also be any combination of the dependent claims or above embodiments with the respective independent claim. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0036] BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In the following drawings:

[0038] Figs. lA to 1C show schematically optical signal distribution topologies including a star topology (Fig. 1 A), a centralized topology (Fig. IB), and a daisy chain topology (Fig. 1 C);

[0039] Fig. 2 shows schematically a hybrid daisy chain topology according to a first embodiment using a daisy chain node with two digital base band blocks;

[0040] Fig. 3 shows schematically a block diagram of a network node according to a second embodiment with predetermined access point connection end;

[0041] Fig. 4 shows schematically an exemplary circuit diagram of a splitting / summing circuit which may be used in the signal processing circuit of the daisy chain node of the second embodiment;

[0042] Fig. 5 shows schematically a block diagram of a signal processing circuit of a daisy chain node according to a third embodiment without predetermined access point connection end;

[0043] Fig. 6A shows schematically a block diagram of an access point with single input / output for wired connection to a daisy chain node according to the prior art;

[0044] Fig. 6B shows schematically a block diagram of an access point with a first input / output to a wireless endpoint and a second input / output for wired connection to a daisy chain node;

[0045] Fig. 7 shows schematically a hybrid daisy chain topology according to a fourth embodiment using a network node with an analog refresh block;

[0046] Fig. 8A shows schematically a hybrid daisy chain topology according to a fifth embodiment using a using a network node with physical-layer processing;

[0047] Fig. 8B shows schematically a daisy chain topology according to a sixth embodiment using configurable network nodes with physical-layer processing;

[0048] Fig. 9 shows schematically a block diagram of a signal processing circuit of a daisy chain node according to a seventh embodiment which allows selective use as access point or repeater; and Fig. 10 shows schematically a block diagram of a signal processing circuit of a daisy chain node according to an eighth embodiment for use as access point at the end of two daisy chains.

[0049] DETAILED DESCRIPTION OF EMBODIMENTS

[0050] Various embodiments of the present invention are now described based on an optical illumination and communication system (LiFi system), preferably based on the ITU-T G.9991 (also known as “G.vlc”) standard developed for indoor line-of-sight optical networking.

[0051] Throughout the following, a luminaire as an access point is to be understood as any type of lighting unit or lighting fixture which comprises one or more light sources (including visible or non- visible (infrared (IR) or ultraviolet (UV)) light sources) for communication purposes and optionally other internal and / or external parts necessary for proper operation, e.g., to distribute the light, to position and protect the light sources, and to connect to a power supply. Optionally, the network nodes may be incorporated in luminaires. Luminaires can be of the traditional type, such as a recessed or surface-mounted incandescent, fluorescent or other electric-discharge luminaires. Luminaires can also be of the non-traditional type, such as fiber optics with the light source at one location and the fiber core or “light pipe” at another. Where the communication downlink makes use of visible light and the light sources of the luminaire are suitable, e.g. when they are LED based, some or all of the illumination LEDs may be used for both illumination and communication.

[0052] A LiFi network, in which various embodiments can be implemented, may comprise multiple access-points (APs), optionally integrated in luminaires of a lighting system, connected via a switch (e.g., an Ethernet switch), whereby each AP may control one or more optical front ends (OFEs) which may comprise transceivers (i.e., combined transmitters (optical emitters) and receivers (light sensors)) for wireless optical communication towards end points (EPs), e.g., mobile user devices. Respective light beams generated by the transceivers and defining coverage areas on the plane(s) of the EPs. Each AP may apply a time-slot schedule for communicating with EP(s) in its coverage area.

[0053] The protocol stack for LiFi communication consists of physical (PHY), media access control (MAC) and upper layers. The PHY layer covers light transceivers and a PHY switch is provided in PHY layer interfaces with an optical service access point (SAP) that connects to the optical medium. The optical medium may be composed of one or multiple optical sources or optical detectors (e.g., laser diodes or photodiodes and photodiodes or photosensors). There are different modulation schemes used in different PHY layer modes. OOK stands for On Off Keying, VPPM stands for Variable Pulse Position Modulation and CSK stands for Color Shift Keying. The MAC layer takes care of resource management (i. e. , allocation of channels, identities (IDs), etc.) as well as entire network management. It thus provides channel access for all types of data and control message transmissions. Upper LiFi layers typically comprise a network layer and an application layer (as defined in the OSI model). The network layer takes care of providing network configuration, network manipulation, message routing etc., while the application layer takes care of providing intended functionality as needed by the VP AN or LiFi device.

[0054] Medium access for the EPs may be scheduled by frame cycles of a data link layer protocol. In example embodiments, scheduling may be based on MAC cycles of the MAC layer. These MAC cycles are continuously following one another and are divided into two or more time intervals, one or more of which are for domain management purposes, while other time intervals are assigned as transmission opportunities for different APs or groups thereof. At least one of the time intervals allotted for domain management purposes may be assigned for transmission of a medium access plan (MAP). The domain management information transmitted in the MAP frame identifies the boundaries of the MAC cycle and includes a list of assigned transmission opportunities (e.g., dedicated time channels of the MAC cycle) for one or more following MAC cycles (e.g., the MAP transmitted in cycle N can describe the timing boundaries and transmission opportunities of cycle N+l).

[0055] A MAC cycle may start at a time published by a previous MAP frame and may end at the end of the last transmission opportunity scheduled for this MAC cycle as described in the MAP frame. The content of the MAC cycle may be determined based on communication resources and parameters required by different APs for communications.

[0056] Figs. lA to 1C show schematically optical signal distribution topologies including a star topology (Fig. 1 A), a centralized topology (Fig. IB), and a daisy chain topology (Fig. 1C).

[0057] In the star topology of Fig. 1 A, a central LiFi module or access point (LiFi ST) 10 (which may play the role of a central coordinator) is connected via respective copper or fiber cables 100 (with a length of e.g. 5-10m) to a plurality of optical front ends (OFEs) 20.

[0058] In the centralized topology of Fig. IB, a centralized LiFi module (LiFi CTR) 12 comprises one or more integrated OFEs 20 without any external cables. It is thus easy to install but provides very limited coverage area. To provide an enhanced coverage area at reduced installation effort, a daisy chain topology as shown in Fig. 1C is proposed in the below embodiments, wherein a LiFi AP 14 (e.g., with an integrated OFE 20) is connected via a copper or fiber cable 100 to a chain of two or more LiFi nodes (LiFi N) 16 with respective integrated OFEs 20. The LiFi nodes 16 are also connected via copper or fiber cables 100.

[0059] In the following, more detailed embodiments of daisy chain topologies for LiFi networks are described, that are suitable for optical networks that use a TDMA approach, such as but not limited to G.hn and / or G.vlc.

[0060] It is noted that - throughout the present disclosure - only those structural elements and functions are shown and described, which are useful to understand the embodiments. Other structural elements and functions are omitted for brevity reasons. Furthermore, the structure and / or function of blocks with identical reference numbers that have been described before are not described again, unless an additional specific functionality is involved.

[0061] Fig. 2 shows schematically a hybrid daisy chain topology according to a first embodiment using daisy chain nodes with two digital base band blocks.

[0062] The topology comprises a LiFi access point (AP) 14 and first optical network node of a chain of LiFi Add / Drop daisy chain nodes (AD / DC-N) 40. The access point 14 and the daisy chain nodes 40 are connected via a hybrid duplex optical fiber (HD-OF) 110 for data transmission including a DC wire 120 for forwarding a DC supply voltage (e.g., 48V which is a standard for Power over Ethernet (PoE) applications) along the daisy chain topology. The fiber cable length may vary based on application (e.g., Im - 50m). Moreover, as an example, 48DC voltage are proposed for the hybrid cable, which is standard to PoE system.

[0063] Thus, a hybrid cable (optical fiber plus electric wire) is used to provide connectivity between the daisy chain nodes 40 and between the access point 14 and the neighboring daisy chain node 40. The daisy chain nodes 40 are configured as add / drop nodes, which means that they can add or drop signals in LiFi zones along the daisy chain topology, e.g., based on addresses / identities of targeted EPs 50, to save energy and reduce communication load.

[0064] The chain length (number of daisy chain nodes) depends on the number of EPs 50 that the access point 14 can serve, with a benefit of cost saving and ease of installation. In a star configuration all cables should have same cable lengths, which is not required in the proposed daisy chain configurations of the embodiments described herein. In the first embodiment, the access point 14 and each of the daisy chain nodes 40 comprise a first electro-optical transceiver as an integrated optical front end (OFE) 20 which may be configured to illuminate a LiFi coverage area 200 that may include one or more end points (EPs) 50.

[0065] Thus, respective wireless optical paths are provided between the EPs 50 and the OFEs 20, while a wired (guided) optical path is provided by the hybrid duplex optical fiber 110 along the daisy chain topology.

[0066] An electrical input signal to be shared throughout the coverage areas 200 may be supplied to an interfacing input / output port (I / F) 31 providing access to a further network (e.g., a physical layer Ethernet, or a USB link or the like) via a first interface connection 310 (e.g., register jack (RJ-45), Universal Serial Bus (USB), etc.) the resulting signals are then fed via a second interface connection 312 (e.g., a reduced gigabit media-independent interface (RGMII) or a serial GMII (SGMII) to a digital G.vlc access point baseband module (DBBA) 32. All external interfaces may be connected to the access point 14.

[0067] The baseband module 32 may be a system on chip (SoC) that implements the above G.vlc standard (further details can be gathered at https: / / www.itu.int / rec / T-REC- G.9991). The PHY layer of G.vlc uses discrete multitone (DMT) modulation and a configurable baseband bandwidth of 50-200 MHz with 512 subcarriers. The individual subcarriers are modulated with multiple quadrature amplitude modulation (QAM) levels with maximum of 12-bits / subcarrier and employ adaptive bit loading based on channel estimation.

[0068] The digital G.vlc signal generated by the access point baseband module 32 is then fed to an analog front end (AFE) 33 for digital to analog conversion, and is then further applied to a splitting / summing circuit (SP / SU) 34 where a first portion thereof is branched off to the integrated OFE 20 and a remaining portion is forwarded to a third electro-optical transceiver (TRX) 35’ that performs conversion between the electrical and optical domains along the daisy chain topology.

[0069] It is noted that signal processing of the above components 31 to 35’ is configured to allow communication in both directions, i.e., from the interfacing input / output port 31 to the EPs 50 and vice versa.

[0070] In an example, the third transceiver 35’ may comprise an LED / laser driver (modulator) and LED(s) / laser(s) for downlink transmission and photo sensor(s) with transimpedance amplifier for uplink reception. The digital G.vlc signal may be directly modulated on the LED(s) / laser(s), e.g., via a bias-tee which is a diplexer with three ports. The modulated light-wave signal guided through the optical fiber 110 may be received by a lensed Si-photo diode and the transimpedance amplifier may have a gain of e.g. 60 dB. The AC output signal from the transimpedance amplifier may be coupled via the splitting / summing circuit 34 to an automatic gain control (AGC) circuit and an analog to digital converter of the analog front end 33 and then further to a digital baseband modem of the baseband module 32, from where it is fed to interfacing input / output port 31 via the second interface connection 312 (e.g., an SGMII or RGMII bus).

[0071] The splitting / summing circuit 34 is configured to split a signal received from a first terminal and forward the obtained split signal portions to respective second and third terminals, and to combine (sum) respective signals received from the second and third terminals and output the combined (summed) signal at the first terminal.

[0072] A most basic form of the splitting / summing circuit 34 may be is a simple "T" connection, which has three terminals (i.e., one input and two outputs, or two inputs and one output). If the "T" is symmetrical, a signal applied to the input will be divided into two output signals, equal in amplitude and phase, while two signals applied to the two inputs will be combined into one output signal, equal in amplitude and phase. As an additional option, a transformer with a (central) tap may be added at the splitting / summing point. Thereby, equal and opposite currents that flow through the internal transformer cancel each other, so that a high isolation between the two input / output ports can be achieved.

[0073] The daisy chain nodes 40 comprise a second transceiver 35 and the third transceiver 35’ at both connection ends to allow connection in a daisy chain topology. Furthermore, it comprises a receive, regenerate and retransmit block (RRR-B) 42 that operates in the digital domain. Therefore, it comprises two analog front ends 33 at both ends, that connect to two connected digital baseband modules 32 of different configurations. The first configuration is an end point baseband module (DBBE) 32 that is configured for communication with the access point baseband module 32 of the access point 14 and that mimics (i.e., plays the role ol) a LiFi end point towards a preceding access point 14 or daisy chain node 40 according to the provisions of the G.vlc standard. The second configuration is an access point baseband module (DBBA) 32 that mimics (i.e., plays the role ol) a LiFi access point towards the succeeding daisy chain node 40 according to the provisions of the G.vlc standard. The two baseband modules 32 of different configuration may be connected via the second interface connection 312 (e.g., an SGMII or RGMII bus).

[0074] More specifically, the access point baseband module 32 and other bases band modules described herein may be digital baseband chips that implement G.vlc standards as a full G.vlc access point (e.g., modem). According to a general block diagram of the G.vlc modem, the input signal may be an SGMII signal and the output signal may be a digital base band (I,Q) signal according to the G.vlc modulation format, which is then forwarded to the analog front end 33 for digital-to-analog conversion and amplification.

[0075] In an example, the splitting / summing circuit 34 may be provided in the analog front end 33 with G.vlc PHY module.

[0076] Similar to the access point 14, the daisy chain node 40 comprises a splitting / summing circuit 34 for branching off a first portion of the analog output signal of the analog front end 33 to the integrated OFE 20 and for forwarding a remaining portion of the analog output signal to the third electro-optical transceiver (TRX) 35’ that performs conversion between the electrical and optical domains along the daisy chain topology.

[0077] For the wireless uplink direction between the OFE 20 and the EP 50, a full duplex communication link may be used. The transmitted optical power in free space for both uplink and downlink should be below the eye safety limit with 40% margin.

[0078] In the first embodiment, the LiFi daisy chain nodes 40 require two digital base band modules 32 (e.g., chips) to connect to a neighboring one of the daisy chain nodes 40, and further require upper-layer communication (e.g., MAC layer, network layer). In this case, each node (access point 14, daisy chain nodes 40) would require resolving Internet Protocol (IP) conflicts and encryption / decry ption for network security. The two digital base band modules 32 (e.g., G.vlc / BB chips) would require to be associated as end point and access point in-order to forward the signal to the next node of the daisy chain topology.

[0079] Fig. 3 shows schematically a block diagram of a signal processing circuit 36 of a daisy chain node according to a second embodiment with predetermined access point connection end.

[0080] The daisy chain node comprises a signal processing circuit 36, a first transceiver (OFE) 20 for providing an optical wireless link to an EP, a second transceiver 35 for providing an optical wireline link to an AP side, and a third transceiver 35’ for providing an optical wireline link to an EP side. The signals on the optical wireline links are here shown as two distinct signals, that represent light in the optical communication medium (here an optical fiber), where the first wireline optical interface receives light in the form of the second wireline optical signal from the fiber, and the first wireline optical interface couples out light in the form of the first wireline optical signal onto the optical fiber. It will be clear to those skilled in the art that the upstream and downstream signals advantageously make use of different wavelengths to ease separation. To this end the second transceiver 35 may comprise an LED or a VCSEL and optical fiber coupling for transmitting the first wireline optical signal at a first wavelength and a photodiode for receiving light corresponding to the second wireline optical signal at a second wavelength from the optical fiber.

[0081] The signal processing circuit 36 comprises a PHY repeater circuit (PHY REP) 42 that may correspond to the receive, regenerate and retransmit block with baseband modules 32 described above in connection with the first embodiment, and further comprises a splitting / summing functionality that may correspond to the functionality of the above splitting / summing circuit 34 of the first embodiment.

[0082] Moreover, the signal processing circuit 36 may comprise other repeater circuits described in connection with later embodiments.

[0083] In the second embodiment, an AP needs to be connected at the AP side of the daisy chain node via an optical fiber for carrying the first and second optical wireline signal wll, wl2 from / to a first interface ifl of the second transceiver 35 to which a first output ol of the PHY repeater circuit 42 is connected.

[0084] The summing / splitting functionality is indicated by a branched output line that splits the other output signal of the PHY repeater 42 into second and third output signals o2 and o3, and by a combining / adding element that adds an input signal received from the third transceiver 35’ and an input signal received from the first transceiver 20. The third transceiver 35’ comprises a second interface if2 that connects to the EP side of the daisy chain via another optical fiber for carrying optical wireline signals wl3 and wl4. The first transceiver 20 is configured to transmit / receive optical wireless signals wsl, ws2 to / from a local EP at the daisy chain node.

[0085] In examples, the AP side (i.e., interface ifl) and / or the EP side (i.e., interface if2) of the daisy chain node may be indicated by a corresponding marking on the housing of a stock-keeping units (SKU) of the daisy-chain node to ensure proper connection of the daisychain node.

[0086] Fig. 4 shows schematically an exemplary circuit diagram of a splitting / summing circuit 34 which may be used in the signal processing circuit 36 of the daisy chain node of the second embodiment.

[0087] The exemplary circuit diagram of the splitting / summing circuit 34 is configured to branch off a first portion of the analog output signal of the analog front end 33 of the PHY repeater 42 to the (integrated) optical front 20 (first transceiver) and for forwarding a remaining portion of the analog output signal to the third transceiver 35’ that performs conversion between the electrical and optical domains along the daisy chain topology. As can be gathered from Fig. 4, the splitting / summing circuit 34 may consist of a splitting circuit comprising a resistor network of three resistors R1 to R3 and a summing circuit configured as a summing amplifier which may be a type of operational amplifier OA circuit configuration that is used to combine the voltages present at outputs of the third transceiver 35’ and the optical front end 20 into a single output voltage that is supplied to an input of the analog front end 33.

[0088] More specifically, the splitting circuit is configured to split the output voltage of the analog front end 33 based on voltage divider ratios defined by the resistors Rl, R2, R3 and respective input resistances of the third transceiver 35’ and the optical front end 20. In the summing circuit, the operational amplifier is configured as a summing inverter where the output voltage at the input of the analog front end 33 becomes proportional to the sum of the input voltages (output voltages of the third transceiver 35’ and the optical front end 20 applied via the resistors R4 and R5) with proportionality factors -R6 / R4 for the input voltage from the third transceiver 35’ and -R6 / R5 for the input voltage from the optical front end 20.

[0089] The basic circuit of Fig. 4 may be implemented either outside an integrated circuit (chip) of the analog front end 33 (e.g., as discrete components (which may be part of or integrated in the optical front end 20)) or integrated in an integrated circuit (chip) of the analog front end 33, e.g., with separate input terminals (pins).

[0090] Fig. 5 shows schematically a block diagram of a signal processing circuit 36 of a daisy chain node according to a third embodiment without predetermined access point connection end.

[0091] In the third embodiment, the AP can be connected at each side of the daisy chain node, i.e., via an optical fiber carrying the first and second optical wireline signals wll, wl2 from / to the first interface ifl of the second transceiver 35 or via the other optical fiber carrying the third and fourth optical wireline signals wl3, wl4 to and from the second interface if2 of the third transceiver 35’. This can be achieved by a modified the splitting / summing functionality of the signal processing circuit 36, which is configured with three adding elements to provide the splitting and adding functions in both directions between the PHY repeater 42 and the third transceiver 35’ to obtain the second and third output signals o2 and o3 supplied to the optical frontend 20 and the third transceiver 35’, respectively.

[0092] The third embodiment of Fig. 5 thus also allows for direct communication between different EPs of the daisy-chained network via the optical frontends 20 and second and third transceivers 35, 35’ respectively. In an example, a controller of the optical wireless communication system may be configured to make reservations so that EPs on the daisy chain are enabled to transmit to one another. This may be achieved by implementing the daisy-chain repeater approach for EP-to-EP communication in a Gigabit Home Networking (G.hn) environment power-line communication (PLC) version, as described in the ITU-T G.9960 standard. In case of peer-to-peer reservations, the controller may further be configured to provide nodes with information about reservations and to optionally indicate power requirements (e.g., who needs to have what powered and when), which allows potential power saving in the backend. In examples, during timeslot's information sharing, the controller may also inform the nodes about power up / down, wherein the nodes may then generate Tx / Rx enable signals which may be used by all components for power on / off control.

[0093] Fig. 6A shows schematically a block diagram of an AP 14 with single input / output for wired connection to a daisy chain node according to various embodiments.

[0094] The AP with single input / output links (e.g., G.hn or G.vlc) comprises the third type of transceiver 35’ for receiving and transmitting the third and fourth wireline signals vl3,wl4 via the second interface over a fiber optic line to thereby provide a Local Area Network LAN access (e.g., Ethernet) to the daisy-chained network. Fig. 6B shows schematically a block diagram of an AP 14 with input / output links (e.g., G.hn or G.vlc) that includes add / drop functionality, here indicated by means of the first and second wireless optical signal wsl, ws2 (via the OFE 20 or first transceiver) to a wireless endpoint and also includes third transceiver 35’ akin to the daisy chain node in Fig. 6A. for optical wireline connection by means of an optical fiber to a daisy chain node according to various embodiments.

[0095] In addition to the AP 14 of Fig. 6A, this AP 14 comprises a splitting / summing functionality (e.g., the splitting / summing circuit 34) as described above to split / combine optical wireline signals of the daisy chain to / with wireless signals of a local EP at the AP 14Fig. 7 shows schematically a hybrid daisy chain topology according to a fourth embodiment using daisy chain nodes with an analog refresh block, which may be combined with the second and third embodiments.

[0096] A further approach to achieve daisy chaining at reduced costs and complexity is to provide a fully analog refresh block (ARB) 60 for use in the add / drop daisy chain nodes 40. The analog refresh block 60 may comprise a fully analog front end (AFE (AA)) 33a for receiving signals in accordance with the G.vlc standard, in which either an AGC amplifier or a fixed-gain amplifier may be used to cope with signal attenuation cause by both fiber channels of the optical fiber cable 110 and the wireless LiFi channels between the EPs 50 and the OFEs 20. Furthermore, a buffer or delay may be provided for timing adaptation.

[0097] In the example of Fig. 7, the access point 14 does not comprise any integrated OFE 20. Note that it could be configured in line with the access point 14 of Fig. 2 or 6B to obtain an additional OFE 20 with coverage area 20.

[0098] Despite being the simplest solution, the performance (e.g., data rate, coverage, etc.) of the fourth embodiment may be limited by noise addition by the respective nodes in the daisy chain along the communication path. Therefore, the daisy chain topology of the fourth embodiment may support smaller numbers of daisy chain nodes 40 than those that perform PHY layer regeneration.

[0099] Further approaches for daisy chain topologies are presented in the following fifth and sixth embodiments depicted in Figs. 8A and 8B and relating to two different scenarios for add / drop-type daisy chaining, which may be combined with the second and third embodiments.

[0100] Fig. 8A shows schematically a hybrid daisy chain topology according to a fifth embodiment using a using a daisy chain node with physical-layer processing.

[0101] Here, the interfacing input / output port 31 (serving as interfacing external interface) may be configured for connecting Ethernet, USB or Power over Ethernet (PoE) signals) via the first interface connection 310 to a dedicated G.vlc access point 14 which connects to the LiFi add / drop daisy chain node 40 via the hybrid duplex cable 110 (e.g., optical fiber (e.g., plastic optic fiber (POF) for data and copper cable for electric DC supply).

[0102] The daisy chain nodes 40 comprise the second and third transceivers 35, 35’ (e.g., optical fiber transceivers) at an input end (I) and an output end (O), a receive, recover and retransmit (RRR) block (RRR-BB) 44b of a second configuration B that operates on the PHY layer, the splitting / summing circuit 34 and the OFE 20.

[0103] As the RRR blocks of the daisy chain nodes 40 are not connected to PHY input signals (e.g., from an Ethernet), no SGMII interface with lower-level processing (RPC, LLLC, MAC) is required. These processing functions are therefore not implemented or not used and the RRR block are merely used to refresh (e.g., equalization and / or regeneration of OFDM constellations) signals received from the analog front end 33 on the input side and forward the refreshed signal to the analog front end 33 on the output side.

[0104] For the downlink direction (AP-EP), the LiFi signal received by the second transceiver 35 is recovered, regenerated and retransmitted by the RRR block 44b. In the third embodiment of Fig 8A, the RRR block 44b comprises a first G.vlc analog front end 33 with an analog AGC for providing signal levels appropriate for PHY layer processing by a G.vlc PHY block 36, where the received signal is regenerated on the PHY layer (e.g., signal processing, equalization, Orthogonal Frequency Division Multiplexing (OFDM) demodulation / modulation, etc.) and forwarded to a second G.vlc analog front end 33. The regenerated analog signal is then delivered to the subsequent LiFi daisy chain node 40 over the optical fiber cable 110 and to the integrated (local) OFE 20 via the splitting / summing circuit 34 (e.g., a passive splitter / combiner).

[0105] An advantage of such a signal refresh (i.e., receive, regenerate and retransmit) on the PHY layer is that costs and complexity can be reduced substantially compared to a full baseband regeneration. Moreover, the system of the fifth embodiment is transparent to the network layer and no additional security encryption is required.

[0106] Fig. 8B shows schematically a daisy chain topology according to a sixth embodiment using configurable daisy chain nodes with physical-layer processing.

[0107] In the sixth embodiment, hardware complexity can be reduced by providing the LiFi daisy chain nodes 40 with an option to be configurable (mutually exclusive in time), either as access point (first configuration A) or as a daisy chain node (second configuration B).

[0108] In Fig. 8B, the first daisy chain node 40 comprises an RRR block 44a (RRR- BA) with the first and second G.vlc analog front ends 33 and the G.vlc PHY block 36 in the first configuration A of an access point according to the G.vlc standard. In the first configuration A, the interfacing input / output port 31 is used for providing external access to the daisy chain topology. The remaining daisy chain nodes 40 comprise the RRR block 44b (RRR-BB) with the first and second G.vlc analog front ends 33 and the G.vlc PHY block 36 in the second configuration B of a normal daisy chain node. In the second configuration, the interfacing input / output port 31 is not used or not provided. The underlying rational being that a device that can operate as an access point, has all the functionality on-board to function as a PHY repeater. But, in the PHY repeater mode, signals received via the second transceiver 35 are received, reconstructed at the PHY Layer (only) and transmitted towards the splitting / summing circuit 34. Likewise, the signals received from the splitting / summing circuit 34 are received, reconstructed at the PHY layer (only) and transmitted towards the side second receiver 35.

[0109] The sixth embodiment thus allows to use a single type of device and to repurpose those devices to create the daisy chain topology for the optical network. As another option of the sixth embodiment, the RRR blocks 44b of the second configuration B may be configured for automatic commissioning, so that an RRR block 44b that detects an input signal via its external interface (e.g., an Ethernet signal) following power-up autoconfigures as an access point.

[0110] Thus, the baseband unit 32 can be configured at installation time to operate as one of an access point or as a physical layer repeater stage.

[0111] As a further option, the baseband unit 32 may be manually configurable by a switch or toggle operation during commissioning. According to the above embodiments, a combined repeater and front-end device (i. e. , combo devices for daisy chain nodes, such as the RRR block 42 of Fig. 2, the analog refresh block 60 of Fig. 7, the RRR blocks 44a and 44b of Figs. 8A and 8B) for daisy chain topologies of optical networks that deliver broadband network access to end point devices of users can be provided. The repeaters of the combo devices may be equipped for analog forwarding (second embodiment with analog amplification and passthrough at the repeater) or MAC -lay er forwarding (first embodiment with full demodulation and remodulation at the repeater) or PHY-layer forwarding (third and fourth embodiment with physical layer processing at the repeater). The combo devices with the different types of repeaters and optical wireless transceivers can be daisy-chained using a fiber optic network. Thereby, a wired optical input / output and a wireless optical input / output can be combined via a "sum and split" block (splitting / summing circuit 34) that loops in / out the signal from the wireless OFE 20 and passes it both upstream (uplink) and downstream (downlink) via the optical fiber 110.

[0112] Fig. 9 shows schematically a block diagram of a signal processing circuit 36 of a daisy chain node according to a seventh embodiment which allows selective use as access point or repeater.

[0113] In the seventh embodiment, the daisy chain node can be implemented as a single SKU solution, which can selectively be used as AP when connected to a wired network (e.g., LAN, Ethernet) or as PHY repeater when not connected to a wired network. Here, the signal processing circuit 36 may be configured to be switchable between the RRR block 44a (AP functionality) and the RRR block 44b (PHY repeater functionality).

[0114] In an example, the input / outputs wll and wl2 of the second transceiver 35 may simply be disregarded (e.g., switched off) when a wired network (e.g., LAN / Ethemet) is present (e.g., detected) at the AP / REP circuit 44b and AP functionality is set. Otherwise, when no wired network (e.g., LAN / Ethemet) is present (e.g., detected) at the AP / REP circuit 44b, the PHY repeater functionality is set. In other embodiments, at least two of the splitting / summing circuit 34, the third transceiver 35’ and the optical front end 20 may be combined to thereby reduce complexity and / or implement splitting and summing in the optical domain with optional optical amplifiers. Optical splitters / combiners may by symmetrical splitters.

[0115] In still further embodiments, the daisy chain topology may be configured to allow EPs 50 of different daisy chain nodes 40 to detect each other (e.g., via addresses, identities etc. conveyed via the data stream) and / or to communicate directly with each other without involving the access point 14.

[0116] In still further embodiments, multiple daisy chains with one or more access points may be provided to reduce the amount of traffic and / or chain length.

[0117] Fig. 10 shows schematically a block diagram of a signal processing circuit of a daisy chain node according to an eighth embodiment for use as access point at the end of two daisy chains.

[0118] In the eighth embodiment, the signal processing circuit 36 comprises an access point block 46 with a 2x2 multi pie-input / multiple-output (MIMO) configuration, where each input / output pair of the MIMO is connected to a distinct daisy chain.

[0119] As shown in Fig. 10, the AP functionality 46 is configured to be connected via the second transceiver 35 to an end of a first daisy chain, via an optical fiber for carrying the first and second optical wireline signals wll, wl2 via the first interface ifl to and from an input / out pair of the access point block 46 and to couple a second input / output pair of the access point block 46 via the third transceiver 35’ to a second daisy chain. The splitting / summing functionality meanwhile can be used to provide a link via the OFE 20 with optical wireless input / output ws2, wsl to a local EP.

[0120] In cases where MIMO needs to provide channel diversity, two different daisy chains may be created which will provide separate channel impairments. A MIMO block can be configured to take care of this (e.g., by matrix inversion).

[0121] In still further embodiments, the PHY / MAC repeaters of Figs. 2, 8A and 8B may be configured to stop forwarding data traffic (e.g., packages) downstream when a target EP has been reached to thereby reduce traffic load and / or save energy.

[0122] To summarize, daisy chaining network topologies for optical communication systems (e.g., LiFi systems) based on a hybrid electric / fiber cable have been described, which are aimed to provide a backbone link for indoor high speed wireless connectivity. The topologies comprise two optical input / outputs (one wireless and one wired) and use a "sum and split" block that loops in / out an optical signal from a wireless optical frontend and passes the optical signal both upstream and downstream.

[0123] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments. The proposed daisy chain topologies can be applied to and possibly standardized in other types of optical wireless networks and with other types of cells and / or reuse patterns.

[0124] In particular, the invention is not limited to the ITU-T G.9991 network environment. The proposed daisy chain topologies with combo repeater devices and splitting / summing circuits may as well be used in other optical network environments, where wireless optical access points can be combined via a wired optical backbone in a daisy chain topology.

[0125] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single processor or other unit may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. The foregoing description details certain embodiments of the invention. It will be appreciated, however, that no matter how detailed the foregoing appears in the text, the invention may be practiced in many ways, and is therefore not limited to the embodiments disclosed. It should be noted that the use of particular terminology when describing certain features or aspects of the invention should not be taken to imply that the terminology is being re-defined herein to be restricted to include any specific characteristics of the features or aspects of the invention with which that terminology is associated.

[0126] A single unit or device may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0127] The described operations can be implemented as program code means of a computer program and / or as dedicated hardware of the daisy chain components. The computer program may 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 may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

Claims

CLAIMS:

1. An optical network node (40) for use in an optical network, the network node capable of being daisy chained and having first and second wireline optical interfaces (ifl, if2) for coupling to an optical fiber (100), the network node (14, 40) comprising: a first transceiver stage (20) configured to: transmit a first wireless optical signal (wsl) to an end point (50) and receive a second wireless optical signal (ws2) from the end point (50); a second transceiver stage (35) configured to:transmit via the first wireline optical interface (ifl) a first wireline optical signal (wll) to the optical network and receive via the first wireline optical interface (ifl) a second wireline optical signal (wl2) from the optical network; a third transceiver stage (35’) configured to: receive via the second wireline optical interface (if2) a third wireline optical signal (wl3) from the optical network and transmit via the second wireline optical interface (if2) a fourth wireline optical signal (wl4) to the optical network; a signal generating circuit (36) configured to: generate a first output signal (ol) based on the second wireless optical signal (ws2) and the third wireline optical signal (wl3) for output using the second transceiver stage (35); generate a second output signal (o2) based on the second wireline optical signal (wl2) for transmission by the first transceiver stage (20); and generate a third output signal (o3) based on the second wireline optical signal (wl2) for output using the third transceiver stage (35’), wherein the signal generating circuit (36) comprises a repeater stage(42, 44b, 60) configured to: receive the received second optical wireline signal (wl2) from the second transceiver stage (35) and generate and output a first intermediate signal based thereon for use in generating the second output signal (o2) and third output signal (o3); receive an intermediate input signal based on the received second wireless optical signal (ws2) and the received third wireline optical signal (wl3) and generate a second intermediate signal based thereon and output it as the first output signal; andwherein the first wireless optical signal, the first wireline optical signal and the fourth wireline optical signal use the same modulation.

2. The network node (40) of claim 1, wherein the signal generating circuit (36) is configured to: generate the third output signal (o3) further based on the second wireless optical signal (ws2) and generate the second output signal (o2) further based on the third wireline optical signal (wl3) for transmission by the first transceiver stage (20).

3. The network node (40) of claim 1 or 2, comprising a network interface, the network node (40) reconfigurable to operate as one of: an access point for providing the optical network with access to a further network (LAN) via the network interface or a daisy-chain network node for providing access to the optical network to neighbor network nodes when present.

4. The network node (40) of claim 1, wherein the repeater stage (60) is configured to operate in the analog domain only, or wherein the repeater stage (44b) is configured to operate on the physical protocol layer only.

5. The network node (40) of claim 1, wherein the signal generating circuit (36) comprises a multiple-input multiple-output access point block (46), wherein a first input / output pair of the access point block (46) is configured to be connected via the second transceiver stage (35) to a first daisy chain and wherein a second input / output pair of the access point block (46) is configured to be coupled via the third transceiver stage (35’) to a second daisy chain and the access point block (46) is further configured to be connected to the further network (LAN) via the network interface.

6. The network node (40) of any one of the preceding claims, wherein the signal generating circuit (36) comprises a splitting / summing circuit (34).

7. The network node (40) of any one of the preceding claims, wherein the optical fiber (110) comprises a wired link (120) for electric power supply to the network node (40).

8. The network node (40) of claim 1, wherein the repeater stage (42; 44b; 60) comprises physical and media access control, MAC, layer functionality and is configured to stop forwarding an incoming wireline optical signal unicast frame received by the second transceiver stage (35) when a target address of the incoming unicast frame corresponds to that of the network node (40).

9. The network node (40) of claim 3, further comprising a baseband unit (32) configurable at runtime to operate as one of an access point or as a physical layer repeater.

10. The network node (40) of claim 9, wherein the baseband unit (32) is manually configurable by a switch or toggle during commissioning.

11. The network node (40) of claim 9, wherein the baseband unit (32) is configured to detect presence of an input signal on the backbone wireline interface (LAN) and to switch following power-up between operation as access point, when a network signal is detected and operation as physical repeater stage when no network signal is detected.

12. An optical communication network comprising an access point (14) and a plurality of optical network nodes (40) of claim 1 in a daisy chain topology.

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