Patent Publication Number: US-2023155664-A1

Title: Methods, Apparatus and Machine-Readable Mediums Related to Wireless Access in Communication Networks

Description:
RELATED APPLICATIONS 
     The present application is a continuation of U.S. Pat. Application Serial No. 17/414,627 filed on Jun. 16, 2021, which is a National Stage Application of PCT/EP2018/086612 filed Dec. 21, 2018, the disclosures of each of which are incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     Embodiments of the disclosure relate to wireless access in communication networks, and particularly relate to methods, apparatus and machine-readable mediums for wireless access in communication networks comprising radio access network nodes and wireless light communication network nodes. 
     BACKGROUND 
     Transmission points for wireless radio communication networks are increasingly being equipped with advanced antenna systems. These antenna systems increase the capacity and/or coverage of existing wireless systems by the addition of antenna arrays. This enables the use of beamforming techniques to increase the received signal strength for signals transmitted in and received from a particular direction. Wireless devices are similarly being provided with multi-antenna transceivers. Thus, they are also able to apply beamforming techniques to benefit from beamforming gain in particular directions both for transmitted and received signals. 
     In order to benefit from beamforming gains, therefore, a transmitting device, whether an Access Point (AP) or a wireless device, should determine an appropriate transmit beam (e.g., shape and/or direction) so as to transmit beams with higher gain in the direction of the receiving device. Similarly, a receiving device, whether an AP or a wireless device, should determine an appropriate receive beam (e.g., shape and/or direction) so as to receive beams with higher gain in the direction of the transmitting device. 
     This outcome is usually achieved through a process known as beamsweeping, in which the transmitting device transmits beams in all predefined directions, e.g., in a burst and/or at a regular interval. The receiving device performs measurements on those beams using all of its receiving beams, and reports the measurements to the transmitting device so that an appropriate transmit-receive beam pair can be determined. To be certain that the most appropriate beam pair is chosen, transmissions and corresponding measurements are performed for all possible transmit-receive beam pairs. 
     This selection of transmit-receive beam pairs may be performed as part of several different processes in the network. For example, the transmit-receive beam pair may be determined in the initial system access to the wireless radio communication network, during handover from one radio access point to another, after radio beam link failure, and/or during an on-going connection (e.g., to ensure that the optimal beam pair continues to be used over time). In the latter case, the beam pair may be re-determined periodically, or on an event-driven basis (e.g., in response to received signal quality or strength falling below a threshold). 
     To be certain that the most appropriate beam pair is chosen, transmissions and corresponding measurements are performed for all possible transmit-receive beam pairs. This can take a considerable amount of time, and involve considerable signalling overhead in the network. If the process could be made quicker or more efficient, radio resources would be freed up for other devices attempting to access the network. 
     SUMMARY 
     Embodiments of the present disclosure seek to address these and other problems. 
     In one aspect, there is provided a method performed by a radio access network node for selecting a transmit or receive beam for communication with a wireless device in a communication network. The radio access network node comprises a plurality of antenna elements configurable to provide a plurality of transmit or receive beams. The communication network further comprises one or more wireless light communication, LC, network nodes. The method comprises: obtaining information identifying a wireless LC network node to which the wireless device is connected; based on the identified wireless LC network node, selecting a subset of the plurality of transmit or receive beams; and initiating a beam-sweeping procedure using the subset of transmit or receive beams to select a transmit or receive beam for communication with the wireless device. 
     Apparatus and non-transitory machine-readable mediums are also provided for performing the method set out above. For example, in one aspect, a radio access network node is provided, configured to perform the method (and other methods set out herein). In another aspect, there is provided a radio access network node, for selecting a transmit or receive beam for communication with a wireless device in a communication network. The communication network further comprises one or more wireless light communication, LC, network nodes. The radio access network node comprises processing circuitry, a non-transitory machine-readable medium and a plurality of antenna elements configurable to provide a plurality of transmit or receive beams. The non-transitory machine-readable medium stores instructions which, when executed by the processing circuitry, cause the radio access network node to: obtain information identifying a wireless LC network node to which the wireless device is connected; based on the identified wireless LC network node, select a subset of the plurality of transmit or receive beams; and initiate a beam-sweeping procedure using the subset of transmit or receive beams to select a transmit or receive beam for communication with the wireless device. 
     In another aspect, there is provided a method performed by a wireless device for selecting a transmit or receive beam for communication with a radio access network node in a communication network. The wireless device comprises a plurality of antenna elements configurable to provide a plurality of transmit or receive beams. The communication network further comprises one or more wireless light communication, LC, network nodes. The method comprises: connecting to a wireless LC network node; based on the wireless LC network node to which the wireless device is connected, selecting a subset of the plurality of transmit or receive beams; and performing a beam-sweeping procedure using the subset of transmit or receive beams to select a transmit or receive beam for communication with the radio access network node. 
     Apparatus and non-transitory machine-readable mediums are also provided for performing the method set out above. For example, in one aspect, a wireless device is provided, configured to perform the method (and other methods set out herein). In another aspect, there is provided a wireless device, for selecting a transmit or receive beam for communication with a radio access network node in a communication network. The communication network further comprises one or more wireless light communication, LC, network nodes. The wireless device comprises processing circuitry, a non-transitory machine-readable medium and a plurality of antenna elements configurable to provide a plurality of transmit or receive beams. The non-transitory machine-readable medium stores instructions which, when executed by the processing circuitry, cause the wireless device to: connect to a wireless LC network node; based on the wireless LC network node to which the wireless device is connected, select a subset of the plurality of transmit or receive beams; and perform a beam-sweeping procedure using the subset of transmit or receive beams to select a transmit or receive beam for communication with the radio access network node. 
     A further aspect provides a method performed by a wireless light communication (LC) network node in a communication network. The communication network further comprises one or more radio access network nodes, each radio access network node forming a respective radio cell. The method comprises: establishing a wireless LC connection with a wireless device; and transmitting, to a radio access network node, an information message comprising an indication that the wireless device is connected to the wireless LC network node. 
     Apparatus and non-transitory machine-readable mediums are also provided for performing the method set out above. For example, in one aspect, a wireless LC network node is provided, configured to perform the method (and other methods set out herein). In another aspect, there is provided a wireless light communication (LC) network node in a communication network. The communication network further comprises one or more radio access network nodes, each radio access network node forming a respective radio cell. The wireless LC network node comprises processing circuitry and a non-transitory machine-readable medium storing instructions which, when executed by the processing circuitry, cause the wireless LC network node to: establish a wireless LC connection with a wireless device; and transmit, to a radio access network node, an information message comprising an indication that the wireless device is connected to the wireless LC network node. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of examples of the present disclosure, and to show more clearly how the examples may be carried into effect, reference will now be made, by way of example only, to the following drawings in which: 
         FIGS.  1   a  and  1   b    are schematic diagrams showing beamforming in a communication network according to embodiments of the disclosure; 
         FIG.  2    is a signalling diagram according to embodiments of the disclosure; 
         FIG.  3    is a flowchart of a method performed by a radio access network node according to embodiments of the disclosure; 
         FIG.  4    is a flowchart of a method performed by a wireless device according to embodiments of the disclosure; 
         FIG.  5    is a flowchart of a method performed by a wireless light communication network node according to embodiments of the disclosure; 
         FIGS.  6  and  7    are schematic diagrams of a radio access network node according to embodiments of the disclosure; 
         FIGS.  8  and  9    are schematic diagrams of a wireless device according to embodiments of the disclosure; 
         FIGS.  10  and  11    are schematic diagrams of a wireless light communication network node according to embodiments of the disclosure; 
         FIG.  12    shows a telecommunication network connected via an intermediate network to a host computer in accordance with some embodiments of the disclosure; 
         FIG.  13    shows a host computer communicating via a base station with a user equipment over a partially wireless connection in accordance with some embodiments of the disclosure; and 
         FIGS.  14  to  17    show methods implemented in a communication system including a host computer, a base station and a user equipment in accordance with some embodiments of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1   a    is a schematic diagram showing a communication network  100  according to embodiments of the disclosure. The illustration shows an example where the network  100  is deployed indoors (with the floor at the bottom of the page and the ceiling at the top); however, those skilled in the art will appreciate that the concepts disclosed herein are applicable to indoor and outdoor environments. 
     The network  100  comprises a radio access network node  102  and a wireless device  104 . 
     The radio access network node  102  is configured to provide wireless radio access to the wireless device  104  implementing any suitable radio telecommunication standard. For example, the radio access network node  102  may form part of a cellular network, and provide radio access conforming to a cellular network radio standard such as those produced by the 3rd Generation Partnership Project (3GPP), e.g., Global System for Mobile Communications (GSM), General Packet Radio Service (GPRS), Enhanced Data Rates for GSM Evolution (EDGE), Universal Mobile Telecommunications System (UMTS), Long Term Evolution (LTE), LTE Advanced, and the 5G standard termed New Radio (NR). Alternatively, the radio access network node  102  may form part of a wireless local area network (WLAN), and provide radio access conforming to the IEEE 802.11 standards, for example. In this latter example, the radio access node may be termed an access point (AP). References to a “radio access network node” herein include at least cellular radio access network nodes and WLAN access points. In the illustrated embodiment, the radio access network node  102  is located on the ceiling; however, it will be understood that the radio access network node  102  may be located at any position. 
     The wireless device  104  is configured to communicate wirelessly with the radio access network node  102 , and thus also implements the same standard as the radio access network node  102 . For example, the wireless device  102  may alternatively be termed a user equipment (UE) or a mobile station (STA). 
     In the illustrated embodiment, the radio access network node  102  and the wireless device  104  each comprise a plurality of antennas or antenna elements (e.g. an antenna array or similar arrangement) for the transmission and/or reception of radio signals. Through the application of beamforming techniques, the radio access network node  102  and the wireless device  104  are thus both able to transmit radio signals having a greater strength and/or to receive radio signals with a higher sensitivity in a particular direction. For example, one or more respective weights or phase-shifts may be applied to signals provided to each antenna element, or received from each antenna element, so that signals from or to a particular direction experience constructive interference while those from other directions experience destructive interference. Those skilled in the art will be well aware of the principles of beamforming techniques. 
     Various beams are shown in the illustrated example. Those beams used by the radio access network node  102  are given the reference numeral  110 , while those used by the wireless device  104  are given the reference numeral  112 . It will be understood that the beams  110 ,  112  may be for the transmission or reception of wireless radio signals. For example, in one embodiment the radio access network node  102  is the transmitting device and the wireless device  104  is the receiving device; in this example the beams  110  are therefore transmit beams, while the beams  112  are receive beams. In another example, the wireless device  104  is the transmitting device and the radio access network node  102  is the receiving device; in this example the beams  112  are therefore transmit beams and the beams  110  are receive beams. 
     In a further example, transmit or receive beams may be utilized by only one of the radio access network node  102  and the wireless device  104 , with the other transmitting or receiving radio signals omnidirectionally. Thus one of the radio access network node  102  and the wireless device  104  may transmit a radio signal using a directional beam, while the other of the radio access network node  102  and the wireless device  104  receives the radio signal without using beamforming. Similarly, one of the radio access network node  102  and the wireless device  104  may transmit a radio signal without using beamforming, while the other of the radio access network node  102  and the wireless device  104  receives the radio signal using a receive beam. The description below assumes that a transmit-receive beam pair is determined for the radio access network node  102  and the wireless device  104 . However, it will be understood that embodiments of the disclosure also relate to the determination of a transmit or receive beam for just one of the radio access network node  102  and the wireless device  104 . 
     As noted above, in order to benefit from beamforming gains, a transmitting device should determine an appropriate transmit beam (e.g., shape and/or direction) so as to transmit beams with higher gain in the direction of the receiving device. Similarly, a receiving device (whether an access point or a wireless device) should determine an appropriate receive beam (e.g., shape and/or direction) so as to receive beams with higher gain in the direction of the transmitting device. Such devices will typically use a process known as beamsweeping, in which the transmitting device transmits beams in all predefined directions, e.g., in a burst and/or at a regular interval. The receiving device performs measurements on those beams using all of its receiving beams, and reports the measurements to the transmitting device so that an appropriate transmit-receive beam pair can be determined. To be certain that the most appropriate beam pair is chosen, transmissions and corresponding measurements are performed for all possible transmit-receive beam pairs. This process is time consuming, and utilizes significant power and radio resources. 
     Embodiments of the disclosure utilize an alternative wireless communication technology to determine the location of a receiving device (whether the radio access network node  102  or the wireless device  104 ) with a reasonable degree of accuracy. The number of transmit and/or receive beams tested as part of a beamsweeping procedure can therefore be reduced, so as to target the known location of the receiving device. 
     In particular, embodiments of the disclosure utilize wireless light communication (sometimes referred to as “LiFi”), and thus the network  100  additionally comprises a plurality of wireless light communication network nodes  106   a ,  106   b ,  106   c ,  106   d  (collectively,  106 ). 
     Recent studies in academia and early prototypes from industry have shown that visible light communication (VLC) has the potential to become a new means of wireless communication. This is also the case for the general light communication (LC) which deploys frequencies that do not belong to the visible optical spectrum, such as infrared light. In particular, several gigabits per second (Gb/s) are anticipated from wireless communication systems that utilize the optical spectrum for communication purposes. 
     The main concept behind LC is to communicate binary data using rapidly varying levels of light intensity. In more detail, one or multiple light emitting diodes (LEDs) are deployed in the transmitting source in order to modulate binary data in different levels of emitted light intensity. The deployed LEDs change the levels of the emitted light intensity at rates that are not perceivable by the human eye. Thus, the incorporation of LC in an illumination system does not affect the quality of illumination. The receiving device detects the changes of the emitted light intensity using photo detectors (PDs), for example. In this way, the receiving device is able to detect the transmitted data. 
     Thus each of the wireless LC network nodes  106  comprises one or more light sources (such as LEDs) for the transmission of light. The light may have a wavelength which is in the visible part of the spectrum, or adjacent to it (e.g., infrared or ultraviolet). The light is subject to modulation with one or more data sources, such that the intensity of the light varies over time in a manner which can be detected and decoded by a receiving device. The line of sight area covered by this light is shown by the dashed lines  107 . The wireless device  104  therefore comprises one or more photo detectors for the detection of the modulated light transmitted by the wireless LC network nodes  106 , and in this way communications can take place in the downlink from the wireless LC network nodes  106  to the wireless device  104 . The wireless device  104  may additionally comprise one or more light sources (such as LEDs), and the wireless LC network nodes  106  may comprise one or more photo detectors, so that communication can also take place in the uplink from the wireless device  104  to the LC network nodes  106 . 
     Annex 1 below describes how the LC channel is dominated by the line of sight component between the transmitter (e.g., the LC nodes  106 ) and the receiver (e.g., the wireless device  104 ). When line of sight no longer exists between the transmitter and the receiver, the SINR of the communication decreases significantly such that a connection between the transmitter and the receiver is no longer viable. Therefore, if a connection is operational between an LC transmitter and an LC receiver, the location of the LC receiver is known; it must be within a line of sight of the LC transmitter. In the context of  FIG.  1   , if an LC connections exists between a wireless LC node  106  and the wireless device  104 , the wireless device must be within the bounds of the transmitted light  107 . This area is termed “an LC cell”  107  herein. 
     The wireless LC network nodes  106  may be independent of each other, providing independent services to wireless devices in a manner akin to separate radio base stations. For example, each wireless LC network node  106  may implement its own respective software protocol stack. Alternatively, the wireless LC network nodes  106  may form part of a larger entity, in a manner akin to different transmission-reception points of a radio base station. For example, each wireless LC network node  106  may implement one or more lower layers of a protocol stack, with a separate network entity implementing the higher layers for multiple wireless LC network nodes  106 . 
     It will further be noted that the wireless LC nodes  106  are communicatively coupled to the radio access network node  102  via a backhaul connection  108 . The backhaul connection  108  will typically be a wired connection, such as an Ethernet connection (e.g., power over Ethernet) or other packet data connection, although in certain embodiments the connection  108  may alternatively be wireless. 
     According to embodiments of the disclosure, the radio access network node  102  obtains information identifying an LC cell  107  or wireless LC network node  106  to which the wireless device  104  is connected. Based on that information, the radio access network node  102  is able to select a subset of the beams  110  which it is capable of producing, and to initiate a beamsweeping procedure using just that subset of beams to select a transmit or receive beam for communicating with the wireless device  104 . Similarly, the wireless device  104  connects to an LC cell  107  or wireless LC network node  106  and, based on the LC cell or wireless LC network node  106 , identifies a subset of the transmit or receive beams which it is capable of producing and performs a beamsweeping procedure using the subset of beams to select a transmit or receive beam for communicating with the radio access network node  102 . 
       FIG.  1   b    shows the network  100  described above, once the selection of the subset of transmit or receive beams has taken place. In this example, the wireless device  104  establishes a connection with the wireless LC node  106   c . Information identifying the wireless LC network node  106   c  or the LC cell  107  formed by it is provided to the radio access network node  102  (e.g., via the backhaul connection  108 , or from a communication by the wireless device  104  itself), and the radio access network node consequently identifies beams  114  (a subset of the beams  110 ) which target just the cell  107 . Similarly, the wireless device  104  identifies beams  116  (a subset of the beams  112 ) which target the radio access network node  102  from the identified cell  107 . A beamsweeping procedure using just these subsets of beams  114 ,  116  therefore requires much less time and resources to complete. 
       FIG.  2    is a signalling diagram according to embodiments of the disclosure, showing signalling between a radio frequency network node or access point (such as the radio access network node  102  described above), a wireless device or STA (such as the wireless device  104  described above) and a wireless light communication network node or access point (such as the wireless LC nodes  106  described above). 
       200 . The wireless device  104  connects to a wireless LC network node  106 . For the reasons discussed above, and below in Annex 1, a connection with a wireless LC network node requires line of sight between the wireless device  104  and the wireless LC network node  106 . 
     The connection to the wireless LC network node may be established using any suitable mechanism and/or according to any suitable standard which may be developed for LC communication in future. For example, the connection may be established using a form of random access, in which the wireless device  104  transmits an identifying code to the LC network node. 
       202 . The radio access network node obtains information identifying the wireless LC network node to which the wireless device connected in step  200 , or the LC cell formed by it. For example, the wireless LC network node may transmit a message to the radio access network node (e.g., via the backhaul link  108 ) containing an indication that the wireless device is connected to it. The indication may comprise an identifier for the wireless device. The message may also comprise an indication of the identity of the wireless LC network node or, alternatively, the identity of the wireless LC network node may be inferred from the source of the message. Alternatively, the wireless device may itself transmit a message to the radio access network node (e.g., via an established radio connection) containing an indication that it has connected to the wireless LC network node. The indication may comprise an identifier for the wireless LC network node or the LC cell. The message may also comprise an indication of the identity of the wireless device or, alternatively, the identity of the wireless device may be inferred from the source of the message. Those skilled in the art will appreciate that alternative methods of informing the radio access network node of the wireless device’s connection are possible. For example, a further node (not illustrated), coupled to the wireless LC network nodes  106 , may collate information as to which wireless devices are connected to which wireless LC network nodes, and provide the information to the radio access network node. 
       204   a . The radio access network node selects a subset of one or more transmit or receive beams of those transmit or receive beams which are available to it, on the basis of the identified wireless LC network node or LC cell in step  202 . For example, the subset of transmit or receive beams may be directed so as to target a geographical area including the geographical area of the LC cell, either to transmit messages to that area or to receive messages from that area. 
     The radio access network node may further utilize knowledge of the geographical location of the LC cell with respect to the radio access network node. For example, the radio access network node may be pre-programmed with the location of the LC cells in its vicinity, and/or respective subsets of beams to be used in order to target those LC cells. Alternatively, the radio access network node may acquire that knowledge over time, through its interactions with wireless devices which are connected to the LC cells in its vicinity. For example, the radio access network node may perform conventional beamsweeping procedures (i.e. using all available beams) to determine an optimal beam for a wireless device which is connected to a particular LC cell. The radio access network node may store an association between the particular LC cell and the optimal beam determined through the conventional method. The determined beam may be added to the subset of beams for that particular LC cell, for example. 
     The latter embodiment, of using historical data to select a subset of beams, may be particularly beneficial when no line of sight exists between the radio access network node and the wireless device. Thus, for example, historical data may be used to select the subset of transmit or receive beams when no line of sight is present between the radio access network node and the wireless device. 
     Those skilled in the art will be aware of several methods for determining whether a line of sight exists between two radio devices. Various papers address this topic, and are not described in further detail herein. For example, such methods may rely on detection of the polarization of wireless transmissions between the devices, to determine whether those transmissions reflected off surfaces between the devices. Alternatively, papers by Benedetto et al (“Dynamic LOS/NLOS Statistical Discrimination of Wireless Mobile Channels”, 2007 IEEE Vehicular Technology Conference) and Borràs et al (“Decision Theoretic Framework for NLOS Identification”, 1998 IEEE Vehicular Technology Conference) take a statistical approach. The present disclosure is not limited in that respect. 
       204   b . The wireless device selects a subset of one or more transmit or receive beams of those transmit or receive beams which are available to it, on the basis of the wireless LC network node to which it connected in step  200 . For example, the subset of transmit or receive beams may correspond to those transmit beams which are directed towards the radio access network node from a coverage area of the identified wireless LC network node (e.g., the LC cell), or those receive beams in the coverage area of the identified wireless LC network node which are directed to receive transmissions from the radio access network node. 
     The wireless device may further obtain and utilize knowledge of the geographical location of the radio access network node with respect to the LC cell. For example, such knowledge may include, or be based on one or more of: angle-of-arrival information for one or more transmissions received from the radio access network node; location information received from the wireless LC network node forming the identified LC cell; and location information received from the radio access network node. Thus the wireless LC network node and/or the radio access network node (or any other node of the network  100 ) may provide the information implicitly or explicitly in a transmission to the wireless device. 
     The wireless device may further obtain and utilize knowledge of its orientation to select the subset of transmit or receive beams. For example, the wireless device may comprise one or more sensors (such as a compass, an accelerometer, a gyroscope, etc) from which it is able to determine its orientation with respect to a defined frame of reference. The wireless device is expected to be more mobile than the radio access network node, so its orientation is liable to change and effect the beams which will be effective in targeting the radio access network node from any given location. Therefore the orientation of the wireless device may also be taken into account when selecting the subset of the transmit or receive beams. 
       206 . The radio access network node and the wireless device perform a beamsweeping procedure, using only the selected subset of transmit or receive beams. As noted above, this procedure may involve the transmitting device (whether the radio access network node or the wireless device) transmitting beams in all of the beams of the subset, e.g., in a burst and/or at a regular interval. The receiving device performs measurements on those beams using all of the receiving beams in the subset, and reports the measurements to the transmitting device so that an appropriate transmit-receive beam pair can be determined. To be certain that the most appropriate beam pair is chosen, transmissions and corresponding measurements may be performed for all possible transmit-receive beam pairs within the selected subsets. However, as only the subset of transmit and receive beams are swept, this process can be expected to be significantly less time-consuming and complex. 
       208   a  and  208   b . The radio access network node and the wireless device select a transmit-receive beam pair based on the measurements performed in step  206 . For example, the transmit-receive beam pair associated with a highest or best signal metric may be chosen, such as the received signal strength or quality. 
       210 . The radio access network node and the wireless device utilize the selected transmit-receive beam pair to communicate with each other. 
       FIG.  3    is a flowchart of a method performed by a radio access network node according to embodiments of the disclosure. The method may correspond in part to the signalling of the radio access network node or access point set out above with respect to  FIG.  2   , for example. The method may be performed by the radio access network node  102  described above with respect to  FIG.  1   . 
     In step  300 , the radio network node obtains information identifying a wireless LC network node to which a wireless device has established a connection or an LC cell formed by the wireless LC network node. For example, the wireless LC network node may transmit a message to the radio access network node (e.g., via the backhaul link  108 ) containing an indication that the wireless device is connected to it. The indication may comprise an identifier for the wireless device. The message may also comprise an indication of the identity of the wireless LC network node or, alternatively, the identity of the wireless LC network node may be inferred from the source of the message. Alternatively, the wireless device may itself transmit a message to the radio access network node (e.g., via an established radio connection) containing an indication that it has connected to the wireless LC network node. The indication may comprise an identifier for the wireless LC network node or the LC cell formed by it. The message may also comprise an indication of the identity of the wireless device or, alternatively, the identity of the wireless device may be inferred from the source of the message. Those skilled in the art will appreciate that alternative methods of informing the radio access network node of the wireless device’s connection are possible. For example, a further node (not illustrated), coupled to the wireless LC network nodes  106 , may collate information as to which wireless devices are connected to which LC cells, and provide the information to the radio access network node. 
     The information may be obtained periodically, on demand from the radio access network node (e.g., in response to a request message transmitted by the radio access network node to the wireless device and/or the wireless LC network node), or on establishment of the connection with the wireless LC network node. 
     In step  302 , the radio access network node determines whether a line of sight exists between the radio access network node and the wireless device. Various methods for determining whether a line of sight exists between two radio devices are discussed above. 
     The method then proceeds to step  304 , in which the radio access network node selects a subset of one or more transmit or receive beams from those transmit or receive beams it is capable of using, based on the identified wireless LC network node. If line of sight does exist, this step involves the substep  306 , in which the radio access network node selects a subset of one or more transmit or receive beams from those transmit or receive beams it is capable of using, based on the identified wireless LC network node and corresponding to the geographical coverage area of the LC cell. For example, the subset of transmit or receive beams may be directed so as to target a geographical area including the geographical area of the LC cell, either to transmit messages to that area or to receive messages from that area. 
     The radio access network node may further utilize knowledge of the geographical location of the LC cell with respect to the radio access network node when selecting the subset of transmit or receive beams. For example, the radio access network node may be pre-programmed with the location of the LC cells in its vicinity, and/or respective subsets of beams to be used in order to target those LC cells. 
     If line of sight does not exist, the step  304  involves substep  308 , in which the radio access network node uses historical data to select a subset of transmit or receive beams. For example, over time, the radio access network node may perform multiple conventional beamsweeping procedures (i.e. using all available beams) to determine optimal beams for wireless devices which are connected to a particular wireless LC network node. The radio access network node may store an association between the particular wireless LC network node and those optimal beams determined through the conventional method. The determined beams may be added to the subset of beams for that particular wireless LC network node. 
     The beams may be generated using analogue, hybrid, or digital techniques, and thus the selection of a subset of beams in step  304  may comprise the selection of one or more beams from: a plurality of analogue beamformers; a plurality of analogue combiners; a digital codebook of beamformers; and a digital codebook of combiners. 
     In step  310 , the radio access network node initiates a beamsweeping procedure using the subset of transmit or receive beams selected in step  304 . As noted above, this procedure may involve the transmitting device (whether the radio access network node or the wireless device) transmitting beams in all of the beams of the subset, e.g., in a burst and/or at a regular interval. The receiving device performs measurements on those beams using all of the receiving beams in the subset, and reports the measurements to the transmitting device so that an appropriate transmit-receive beam pair can be determined. To be certain that the most appropriate beam pair is chosen, transmissions and corresponding measurements may be performed for all possible transmit-receive beam pairs within the selected subsets. 
     In step  312 , the radio access network node selects a transmit or receive beam based on the measurements performed in step  310 . For example, the transmit or receive beam associated with a highest or best signal metric may be chosen, such as the received signal strength or quality. 
       FIG.  4    is a flowchart of a method performed by a wireless device according to embodiments of the disclosure. The method may correspond in part to the signalling of the wireless device set out above with respect to  FIG.  2   , for example. The method may be performed by the wireless device  104  described above with respect to  FIG.  1   . 
     In step  400 , the wireless device connects to a wireless LC network node  106 . For the reasons discussed above, and below in Annex 1, a connection with a wireless LC network node requires line of sight between the wireless device  104  and the wireless LC network node  106 . 
     The connection to the wireless LC network node may be established using any suitable mechanism and/or according to any suitable standard which may be developed for LC communication in future. For example, the connection may be established using a form of random access, in which the wireless device  104  transmits an identifying code to the wireless LC network node. 
     In step  402 , the wireless device obtains knowledge of its orientation. For example, the wireless device may comprise one or more sensors (such as one or more of a compass, an accelerometer, a gyroscope, etc) from which it is able to determine its orientation with respect to a defined frame of reference. 
     In step  404 , the wireless device obtains knowledge identifying the location of a radio access network node relative to the wireless LC network node forming its LC cell. For example, such knowledge may include, or be based on one or more of: angle-of-arrival information for one or more transmissions received from the radio access network node; location information received from the wireless LC network node forming the LC cell; and location information received from the radio access network node. Thus the wireless LC network node and/or the radio access network node (or any other node of the network  100 ) may provide the information implicitly or explicitly in a transmission to the wireless device. 
     In step  406 , the wireless device selects a subset of one or more transmit or receive beams of those transmit or receive beams which are available to it, on the basis of the wireless LC network node to which it connected in step  400 . For example, the subset of transmit or receive beams may correspond to those transmit beams which are directed towards the radio access network node from a coverage area of the identified wireless LC network node (e.g., the LC cell), or those receive beams in the coverage area of the identified wireless LC network node which are directed to receive transmissions from the radio access network node. 
     The selection of the subset of one or more transmit or receive beams may be further based on one or more of: the orientation of the wireless device, determined in step  402 ; and the location of the radio access network node relative to the wireless device or the wireless LC network node, determined in step  404 . 
     In step  408 , the wireless device performs a beamsweeping procedure, using only the selected subset of transmit or receive beams. As noted above, this procedure may involve the transmitting device (whether the radio access network node or the wireless device) transmitting beams in all of the beams of the subset, e.g., in a burst and/or at a regular interval. The receiving device performs measurements on those beams using all of the receiving beams in the subset, and reports the measurements to the transmitting device so that an appropriate transmit-receive beam pair can be determined. To be certain that the most appropriate beam pair is chosen, transmissions and corresponding measurements may be performed for all possible transmit-receive beam pairs within the selected subsets. 
     In step  410 , the wireless device selects a transmit or receive beam based on the measurements performed in step  408 . For example, the transmit or receive beam associated with a highest or best signal metric may be chosen, such as the received signal strength or quality. 
       FIG.  5    is a flowchart of a method performed by a wireless LC network node according to embodiments of the disclosure. The method may correspond in part to the signalling of the wireless LC network node set out above with respect to  FIG.  2   , for example. The method may be performed by the wireless LC network node  106  described above with respect to  FIG.  1   . 
     In step  500 , the wireless LC network node establishes a connection with a wireless device. 
     The connection between the wireless device and the wireless LC network node may be established using any suitable mechanism and/or according to any suitable standard which may be developed for LC communication in future. For example, the connection may be established using a form of random access, in which the wireless device transmits an identifying code to the wireless LC network node. 
     In step  502 , the wireless LC network node transmits a message to a radio access network node (e.g., via the backhaul link  108 ) containing an indication that the wireless device is connected to it. The indication may comprise an identifier for the wireless device. The message may also comprise an indication of the identity of the wireless LC network node or, alternatively, the identity of the wireless LC network node may be inferred from the source of the message. Alternatively, this information may be transmitted indirectly to the radio access network node. For example, a further node (not illustrated), coupled to the wireless LC network node, may collate information as to which wireless devices are connected to which wireless LC network nodes, and provide the information to the radio access network node. 
     The message may be transmitted periodically, on demand from the radio access network node (e.g., in response to a request message transmitted by the radio access network node to the wireless LC network node), or on establishment of the connection with the wireless device in step  500 . 
       FIG.  6    is a schematic diagram of a radio access network node  600  according to embodiments of the disclosure. The radio access network node  600  may be configured to perform the signalling of the radio access network node  102 , described above with respect to  FIG.  2   , and/or the method described above with respect to  FIG.  3   . As noted above, in one embodiment, the radio access network node  600  is a WLAN access point. 
     The radio access network node  600  comprises processing circuitry  602  (such as one or more processors, digital signal processors, general purpose processing units, etc), a machine-readable medium  604  (e.g., memory such as read-only memory (ROM), random-access memory, cache memory, flash memory devices, optical storage devices, etc) and one or more interfaces  606 . The one or more interfaces  606  may comprise a plurality of antenna elements configurable to provide a plurality of transmit or receive beams. The interfaces  606  may additionally comprise an interface for backhaul communications, such as a wireless, wired (e.g., power-over-Ethernet) or optical interface. The components are illustrated coupled together in series; however, those skilled in the art will appreciate that the components may be coupled together in any suitable manner (e.g., via a system bus or suchlike). 
     The radio access network node  600  is operable in a communication network comprising one or more wireless light communication (LC) network nodes. According to embodiments of the disclosure, the computer-readable medium  604  stores instructions which, when executed by the processing circuitry  602 , cause the node  600  to: obtain information identifying a wireless LC network node to which the wireless device is connected; based on the identified wireless LC network node, select a subset of the plurality of transmit or receive beams; and initiate a beam-sweeping procedure using the subset of transmit or receive beams to select a transmit or receive beam for communication with the wireless device. 
     In further embodiments of the disclosure, the node  600  may comprise power circuitry (not illustrated). The power circuitry may comprise, or be coupled to, power management circuitry and is configured to supply the components of node  600  with power for performing the functionality described herein. Power circuitry may receive power from a power source. The power source and/or power circuitry may be configured to provide power to the various components of node  600  in a form suitable for the respective components (e.g., at a voltage and current level needed for each respective component). The power source may either be included in, or external to, the power circuitry and/or the node  600 . For example, the node  600  may be connectable to an external power source (e.g., an electricity outlet) via an input circuitry or interface such as an electrical cable, whereby the external power source supplies power to the power circuitry. As a further example, the power source may comprise a source of power in the form of a battery or battery pack which is connected to, or integrated in, the power circuitry. The battery may provide backup power should the external power source fail. Other types of power sources, such as photovoltaic devices, may also be used. 
       FIG.  7    is a schematic diagram of a radio access network node  700  according to embodiments of the disclosure. The radio access network node  700  may be configured to perform the signalling of the radio access network node  102 , described above with respect to  FIG.  2   , and/or the method described above with respect to  FIG.  3   . As noted above, in one embodiment, the radio access network node  700  is a WLAN access point. 
     The radio access network node  700  comprises an obtaining unit  702 , a selecting unit  704  and a beam-sweeping unit  706 . The radio access network node may additionally comprise one or more interfaces (not illustrated). The one or more interfaces  706  may comprise a plurality of antenna elements configurable to provide a plurality of transmit or receive beams. The interfaces  706  may additionally comprise an interface for backhaul communications, such as a wireless, wired (e.g., power-over-Ethernet) or optical interface. 
     The radio access network node  700  is operable in a communication network comprising one or more wireless light communication (LC) network nodes. According to embodiments of the disclosure, the obtaining unit  702  is configured to obtain information identifying a wireless LC network node to which the wireless device is connected. The selecting unit  704  is configured to, based on the identified wireless LC network node, select a subset of the plurality of transmit or receive beams. The beam-sweeping unit  706  is configured to initiate a beam-sweeping procedure using the subset of transmit or receive beams to select a transmit or receive beam for communication with the wireless device. 
       FIG.  8    is a schematic diagram of a wireless device  800  according to embodiments of the disclosure. The wireless device  800  may be configured to perform the signalling of the wireless device  104 , described above with respect to  FIG.  2   , and/or the method described above with respect to  FIG.  4   . 
     The wireless device  800  comprises processing circuitry  802  (such as one or more processors, digital signal processors, general purpose processing units, etc), a machine-readable medium  804  (e.g., memory such as read-only memory (ROM), random-access memory, cache memory, flash memory devices, optical storage devices, etc) and one or more interfaces 806. The one or more interfaces  806  may comprise a plurality of antenna elements configurable to provide a plurality of transmit or receive beams. The components are illustrated coupled together in series; however, those skilled in the art will appreciate that the components may be coupled together in any suitable manner (e.g., via a system bus or suchlike). 
     The wireless device  800  is operable in a communication network comprising one or more wireless light communication (LC) network nodes. According to embodiments of the disclosure, the computer-readable medium  804  stores instructions which, when executed by the processing circuitry  802 , cause the wireless device  800  to: connect to a wireless LC network node; based on the wireless LC network node to which the wireless device is connected, select a subset of the plurality of transmit or receive beams; and perform a beam-sweeping procedure using the subset of transmit or receive beams to select a transmit or receive beam for communication with the radio access network node. 
     In further embodiments of the disclosure, the wireless device  800  may comprise power circuitry (not illustrated). The power circuitry may comprise, or be coupled to, power management circuitry and is configured to supply the components of wireless device  800  with power for performing the functionality described herein. Power circuitry may receive power from a power source. The power source and/or power circuitry may be configured to provide power to the various components of wireless device  800  in a form suitable for the respective components (e.g., at a voltage and current level needed for each respective component). The power source may either be included in, or external to, the power circuitry and/or the wireless device  800 . For example, the wireless device  800  may be connectable to an external power source (e.g., an electricity outlet) via an input circuitry or interface such as an electrical cable, whereby the external power source supplies power to the power circuitry. As a further example, the power source may comprise a source of power in the form of a battery or battery pack which is connected to, or integrated in, the power circuitry. The battery may provide backup power should the external power source fail. Other types of power sources, such as photovoltaic devices, may also be used. 
       FIG.  9    is a schematic diagram of a wireless device  900  according to embodiments of the disclosure. The wireless device  900  may be configured to perform the signalling of the wireless device  104 , described above with respect to  FIG.  2   , and/or the method described above with respect to  FIG.  4   . 
     The wireless device  900  comprises a connecting unit  902 , a selecting unit  904  and a beam-sweeping unit  906 . The wireless device may additionally comprise one or more interfaces (not illustrated). The one or more interfaces  906  may comprise a plurality of antenna elements configurable to provide a plurality of transmit or receive beams. 
     The wireless device  900  is operable in a communication network comprising one or more wireless light communication (LC) network nodes. According to embodiments of the disclosure, the connecting unit  902  is configured to connect to a wireless LC network node. The selecting unit  904  is configured to, based on the wireless LC network node to which the wireless device is connected, select a subset of the plurality of transmit or receive beams. The beam-sweeping unit  906  is configured to perform a beam-sweeping procedure using the subset of transmit or receive beams to select a transmit or receive beam for communication with the radio access network node. 
       FIG.  10    is a schematic diagram of a wireless light communication network node  1000  according to embodiments of the disclosure. The radio access network node  1000  may be configured to perform the signalling of the wireless light communication network node  106 , described above with respect to  FIG.  2   , and/or the method described above with respect to  FIG.  5   . 
     The wireless light communication access network node  1000  comprises processing circuitry  1002  (such as one or more processors, digital signal processors, general purpose processing units, etc), a machine-readable medium  1004  (e.g., memory such as read-only memory (ROM), random-access memory, cache memory, flash memory devices, optical storage devices, etc) and one or more interfaces  1006 . The one or more interfaces  1006  may comprise one or more light sources (e.g., LEDs), whose output can be modulated with a data source to enable the transmission of wireless data over the light medium. The interfaces  1006  may additionally comprise an interface for backhaul communications, such as a wireless, wired (e.g., power-over-Ethernet) or optical interface. The components are illustrated coupled together in series; however, those skilled in the art will appreciate that the components may be coupled together in any suitable manner (e.g., via a system bus or suchlike). 
     The wireless LC network node  1000  is operable in a communication network further comprising one or more radio access network nodes, each forming a respective radio cell. 
     According to embodiments of the disclosure, the computer-readable medium  1004  stores instructions which, when executed by the processing circuitry  1002 , cause the node  1000  to: establish a wireless LC connection with a wireless device; and transmit, to a radio access network node, an information message comprising an indication that the wireless device is connected to the wireless LC network node. 
     In further embodiments of the disclosure, the node  1000  may comprise power circuitry (not illustrated). The power circuitry may comprise, or be coupled to, power management circuitry and is configured to supply the components of node  1000  with power for performing the functionality described herein. Power circuitry may receive power from a power source. The power source and/or power circuitry may be configured to provide power to the various components of node  1000  in a form suitable for the respective components (e.g., at a voltage and current level needed for each respective component). The power source may either be included in, or external to, the power circuitry and/or the node  1000 . For example, the node  1000  may be connectable to an external power source (e.g., an electricity outlet) via an input circuitry or interface such as an electrical cable, whereby the external power source supplies power to the power circuitry. As a further example, the power source may comprise a source of power in the form of a battery or battery pack which is connected to, or integrated in, the power circuitry. The battery may provide backup power should the external power source fail. Other types of power sources, such as photovoltaic devices, may also be used. 
       FIG.  11    is a schematic diagram of a wireless light communication network node  1100  according to embodiments of the disclosure. The wireless light communication network node  1100  may be configured to perform the signalling of the wireless light communication network node  106 , described above with respect to  FIG.  2   , and/or the method described above with respect to  FIG.  5   . 
     The wireless light communication network node  1100  comprises a connecting unit  1102  and a transmitting unit  1104 . The wireless light communication network node may additionally comprise one or more interfaces (not illustrated). The one or more interfaces  1106  may comprise one or more light sources (e.g., LEDs), whose output can be modulated with a data source to enable the transmission of wireless data over the light medium. The interfaces  1006  may additionally comprise an interface for backhaul communications, such as a wireless, wired (e.g., power-over-Ethernet) or optical interface. 
     The wireless LC network node  1100  is operable in a communication network further comprising one or more radio access network nodes, each forming a respective radio cell. 
     According to embodiments of the disclosure, the connecting unit  1102  is configured to establish a wireless LC connection with a wireless device. The transmitting unit  1104  is configured to transmit, to a radio access network node, an information message comprising an indication that the wireless device is connected to the wireless LC network node. 
     The term “unit” may have conventional meaning in the field of electronics, electrical devices and/or electronic devices and may include, for example, electrical and/or electronic circuitry, devices, modules, processors, memories, logic solid state and/or discrete devices, computer programs or instructions for carrying out respective tasks, procedures, computations, outputs, and/or displaying functions, and so on, as such as those that are described herein. 
     With reference to  FIG.  12   , in accordance with an embodiment, a communication system includes telecommunication network  1210 , such as a 3GPP-type cellular network, which comprises access network  1211 , such as a radio access network, and core network  1214 . Access network  1211  comprises a plurality of base stations  1212   a ,  1212   b ,  1212   c , such as NBs, eNBs, gNBs or other types of wireless access points, each defining a corresponding coverage area  1213   a ,  1213   b ,  1213   c . Each base station  1212   a ,  1212   b ,  1212   c  is connectable to core network  1214  over a wired or wireless connection  1215 . A first UE  1291  located in coverage area  1213   c  is configured to wirelessly connect to, or be paged by, the corresponding base station  1212   c . A second UE  1292  in coverage area  1213   a  is wirelessly connectable to the corresponding base station  1212   a . While a plurality of UEs  1291 ,  1292  are illustrated in this example, the disclosed embodiments are equally applicable to a situation where a sole UE is in the coverage area or where a sole UE is connecting to the corresponding base station  1212 . 
     Telecommunication network  1210  is itself connected to host computer  1230 , which may be embodied in the hardware and/or software of a standalone server, a cloud-implemented server, a distributed server or as processing resources in a server farm. Host computer  1230  may be under the ownership or control of a service provider, or may be operated by the service provider or on behalf of the service provider. Connections  1221  and  1222  between telecommunication network  1210  and host computer  1230  may extend directly from core network  1214  to host computer  1230  or may go via an optional intermediate network  1220 . Intermediate network  1220  may be one of, or a combination of more than one of, a public, private or hosted network; intermediate network  1220 , if any, may be a backbone network or the Internet; in particular, intermediate network  1220  may comprise two or more sub-networks (not shown). 
     The communication system of  FIG.  12    as a whole enables connectivity between the connected UEs  1291 ,  1292  and host computer  1230 . The connectivity may be described as an over-the-top (OTT) connection  1250 . Host computer  1230  and the connected UEs  1291 ,  1292  are configured to communicate data and/or signaling via OTT connection  1250 , using access network  1211 , core network  1214 , any intermediate network  1220  and possible further infrastructure (not shown) as intermediaries. OTT connection  1250  may be transparent in the sense that the participating communication devices through which OTT connection  1250  passes are unaware of routing of uplink and downlink communications. For example, base station  1212  may not or need not be informed about the past routing of an incoming downlink communication with data originating from host computer  1230  to be forwarded (e.g., handed over) to a connected UE  1291 . Similarly, base station  1212  need not be aware of the future routing of an outgoing uplink communication originating from the UE  1291  towards the host computer  1230 . 
     Example implementations, in accordance with an embodiment, of the UE, base station and host computer discussed in the preceding paragraphs will now be described with reference to  FIG.  13   . In communication system  1300 , host computer  1310  comprises hardware  1315  including communication interface  1316  configured to set up and maintain a wired or wireless connection with an interface of a different communication device of communication system  1300 . Host computer  1310  further comprises processing circuitry  1318 , which may have storage and/or processing capabilities. In particular, processing circuitry  1318  may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. Host computer  1310  further comprises software  1311 , which is stored in or accessible by host computer  1310  and executable by processing circuitry  1318 . Software  1311  includes host application  1312 . Host application  1312  may be operable to provide a service to a remote user, such as UE  1330  connecting via OTT connection  1350  terminating at UE  1330  and host computer  1310 . In providing the service to the remote user, host application  1312  may provide user data which is transmitted using OTT connection  1350 . 
     Communication system  1300  further includes base station  1320  provided in a telecommunication system and comprising hardware  1325  enabling it to communicate with host computer  1310  and with UE  1330 . Hardware  1325  may include communication interface  1326  for setting up and maintaining a wired or wireless connection with an interface of a different communication device of communication system  1300 , as well as radio interface  1327  for setting up and maintaining at least wireless connection  1370  with UE  1330  located in a coverage area (not shown in  FIG.  13   ) served by base station  1320 . Communication interface  1326  may be configured to facilitate connection  1360  to host computer  1310 . Connection  1360  may be direct or it may pass through a core network (not shown in  FIG.  13   ) of the telecommunication system and/or through one or more intermediate networks outside the telecommunication system. In the embodiment shown, hardware  1325  of base station  1320  further includes processing circuitry  1328 , which may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. Base station  1320  further has software  1321  stored internally or accessible via an external connection. 
     Communication system  1300  further includes UE  1330  already referred to. Its hardware  1335  may include radio interface  1337  configured to set up and maintain wireless connection  1370  with a base station serving a coverage area in which UE  1330  is currently located. Hardware  1335  of UE  1330  further includes processing circuitry  1338 , which may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. UE  1330  further comprises software  1331 , which is stored in or accessible by UE  1330  and executable by processing circuitry  1338 . Software  1331  includes client application  1332 . Client application  1332  may be operable to provide a service to a human or non-human user via UE  1330 , with the support of host computer  1310 . In host computer  1310 , an executing host application  1312  may communicate with the executing client application  1332  via OTT connection  1350  terminating at UE  1330  and host computer  1310 . In providing the service to the user, client application  1332  may receive request data from host application  1312  and provide user data in response to the request data. OTT connection  1350  may transfer both the request data and the user data. Client application  1332  may interact with the user to generate the user data that it provides. 
     It is noted that host computer  1310 , base station  1320  and UE  1330  illustrated in  FIG.  13    may be similar or identical to host computer  1230 , one of base stations  1212   a ,  1212   b ,  1212   c  and one of UEs  1291 ,  1292  of  FIG.  12   , respectively. This is to say, the inner workings of these entities may be as shown in  FIG.  13    and independently, the surrounding network topology may be that of  FIG.  12   . 
     In  FIG.  13   , OTT connection  1350  has been drawn abstractly to illustrate the communication between host computer  1310  and UE  1330  via base station  1320 , without explicit reference to any intermediary devices and the precise routing of messages via these devices. Network infrastructure may determine the routing, which it may be configured to hide from UE  1330  or from the service provider operating host computer  1310 , or both. While OTT connection  1350  is active, the network infrastructure may further take decisions by which it dynamically changes the routing (e.g., on the basis of load balancing consideration or reconfiguration of the network). 
     Wireless connection  1370  between UE  1330  and base station  1320  is in accordance with the teachings of the embodiments described throughout this disclosure. One or more of the various embodiments improve the performance of OTT services provided to UE  1330  using OTT connection  1350 , in which wireless connection  1370  forms the last segment. More precisely, the teachings of these embodiments may improve latency and power consumption and thereby provide benefits such as reduced user waiting time and extended battery lifetime. 
     A measurement procedure may be provided for the purpose of monitoring data rate, latency and other factors on which the one or more embodiments improve. There may further be an optional network functionality for reconfiguring OTT connection  1350  between host computer  1310  and UE  1330 , in response to variations in the measurement results. The measurement procedure and/or the network functionality for reconfiguring OTT connection  1350   may be implemented in software  1311  and hardware  1315  of host computer  1310  or in software  1331  and hardware  1335  of UE  1330 , or both. In embodiments, sensors (not shown) may be deployed in or in association with communication devices through which OTT connection  1350  passes; the sensors may participate in the measurement procedure by supplying values of the monitored quantities exemplified above, or supplying values of other physical quantities from which software  1311 ,  1331  may compute or estimate the monitored quantities. The reconfiguring of OTT connection  1350  may include message format, retransmission settings, preferred routing etc.; the reconfiguring need not affect base station  1320 , and it may be unknown or imperceptible to base station  1320 . Such procedures and functionalities may be known and practiced in the art. In certain embodiments, measurements may involve proprietary UE signaling facilitating host computer  1310 ′ s  measurements of throughput, propagation times, latency and the like. The measurements may be implemented in that software  1311  and  1331  causes messages to be transmitted, in particular empty or ‘dummy’ messages, using OTT connection  1350  while it monitors propagation times, errors etc. 
       FIG.  14    is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station and a UE which may be those described with reference to  FIGS.  12  and  13   . For simplicity of the present disclosure, only drawing references to  FIG.  14    will be included in this section. In step  1410 , the host computer provides user data. In substep  1411  (which may be optional) of step  1410 , the host computer provides the user data by executing a host application. In step  1420 , the host computer initiates a transmission carrying the user data to the UE. In step  1430  (which may be optional), the base station transmits to the UE the user data which was carried in the transmission that the host computer initiated, in accordance with the teachings of the embodiments described throughout this disclosure. In step  1440  (which may also be optional), the UE executes a client application associated with the host application executed by the host computer. 
       FIG.  15    is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station and a UE which may be those described with reference to  FIGS.  12  and  13   . For simplicity of the present disclosure, only drawing references to  FIG.  15    will be included in this section. In step  1510  of the method, the host computer provides user data. In an optional substep (not shown) the host computer provides the user data by executing a host application. In step  1520 , the host computer initiates a transmission carrying the user data to the UE. The transmission may pass via the base station, in accordance with the teachings of the embodiments described throughout this disclosure. In step  1530  (which may be optional), the UE receives the user data carried in the transmission. 
       FIG.  16    is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station and a UE which may be those described with reference to  FIGS.  12  and  13   . For simplicity of the present disclosure, only drawing references to  FIG.  16    will be included in this section. In step  1610  (which may be optional), the UE receives input data provided by the host computer. Additionally or alternatively, in step  1620 , the UE provides user data. In substep  1621  (which may be optional) of step  1620 , the UE provides the user data by executing a client application. In substep  1611  (which may be optional) of step  1610 , the UE executes a client application which provides the user data in reaction to the received input data provided by the host computer. In providing the user data, the executed client application may further consider user input received from the user. Regardless of the specific manner in which the user data was provided, the UE initiates, in substep  1630  (which may be optional), transmission of the user data to the host computer. In step  1640  of the method, the host computer receives the user data transmitted from the UE, in accordance with the teachings of the embodiments described throughout this disclosure. 
       FIG.  17    is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station and a UE which may be those described with reference to  FIGS.  12  and  13   . For simplicity of the present disclosure, only drawing references to  FIG.  17    will be included in this section. In step  1710  (which may be optional), in accordance with the teachings of the embodiments described throughout this disclosure, the base station receives user data from the UE. In step  1720  (which may be optional), the base station initiates transmission of the received user data to the host computer. In step  1730  (which may be optional), the host computer receives the user data carried in the transmission initiated by the base station. 
     It should be noted that the above-mentioned embodiments illustrate rather than limit the concepts disclosed herein, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended following statements. The word “comprising” does not exclude the presence of elements or steps other than those listed in a statement, “a” or “an” does not exclude a plurality, and a single processor or other unit may fulfil the functions of several units recited in the statements. Any reference signs in the statements shall not be construed so as to limit their scope. 
     Annex a 
     Point-to-Point Light Communication 
     Recent studies in academia and early prototypes from industry have shown that Visible Light Communication (VLC) has the potential to become a new means of indoor wireless communication. This is also the case for the general Light Communication (LC) which deploys frequencies that do not belong to the visible optical spectrum, such as infrared light. In particular, several Gigabits per Second (Gb/s) are anticipated from wireless communication systems that utilize the optical spectrum for communication purposes. 
     The main concept behind LC is to communicate binary data using rapidly varying levels of light intensity. In more detail, one or multiple light-emitting diode (LEDs) are deployed by the transmitting source in order to modulate binary data in different levels of emitted light intensity. The deployed LEDs change the levels of the emitted light intensity at rates which are not perceivable by the human eye. Thus, the incorporation of LC in an illumination system does not affect the quality of illumination. The receiving device detects the changes of the emitted light intensity using, for example, photo detectors (PDs), and in this way, the receiving device is able to detect the transmitted binary data. As implied before, due to the nature of the optical channel, the use of intensity modulation (IM) with direct detection (DD) is used (see, for example, a paper by Kahn and Barry, “Wireless Infrared Communications”, Proceedings of the IEEE, vol 85, pp 265-298). This means that the transmitted/received signal has to be real and strictly positive. This imposes certain constraints in the deployed communication techniques, both in single and multi-carrier transmission. However, due to the relative large physical area of a PD compared to the carrier wavelength, multipath fading is absent. Therefore, LC may use less complex signalprocessing techniques. 
     Assuming a point-to-point LC system with N t  transmitting LEDs and N r  receiving PDs, the optical channel, in the time domain, between the i-th PD, i = 1, ...,N r   LC , and the j-th LED, j = 1,...,N t   LC  is given as: 
     
       
         
           
             
               h 
               
                 i 
                 , 
                 j 
               
               
                 LC 
               
             
             
               t 
             
             = 
             
               h 
               
                 i 
                 , 
                 j 
               
               
                 LOS 
               
             
             + 
             
               h 
               
                 i 
                 , 
                 j 
               
               
                 NLOS 
               
             
             
               t 
             
             , 
           
         
       
     
      where,  represents the Line-of-Sight (LoS) component, while,  , represents the diffuse component. In the academic literature, the LoS component  is also referred as the Direct Current (DC) component. The diffuse component  is the aggregate result of multiple light reflections from the surrounding surfaces. In (1),  represents the LOS optical gain, which is given as: 
     
       
         
           
             
               h 
               
                 i 
                 , 
                 j 
               
               
                 LOS 
               
             
             = 
             
               
                 
                   
                     
                       
                         
                           
                             A 
                             
                               
                                 k 
                                 + 
                                 1 
                               
                             
                           
                           
                             2 
                             π 
                             
                               d 
                               
                                 i 
                                 , 
                                 j 
                               
                               2 
                             
                           
                         
                         
                           
                             cos 
                           
                           k 
                         
                         
                           
                             
                               ϕ 
                               
                                 i 
                                 , 
                                 j 
                               
                             
                           
                         
                         cos 
                         
                           
                             
                               ψ 
                               
                                 i 
                                 , 
                                 j 
                               
                             
                           
                         
                         , 
                       
                     
                     
                       
                         0 
                         ≤ 
                         
                           ψ 
                           
                             i 
                             , 
                             j 
                           
                         
                         ≤ 
                         
                           Ψ 
                           
                             
                               1 
                               2 
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         0 
                         , 
                       
                     
                     
                       
                         
                           ψ 
                           
                             i 
                             , 
                             j 
                           
                         
                         ≥ 
                         
                           Ψ 
                           
                             
                               1 
                               2 
                             
                             , 
                           
                         
                       
                     
                   
                 
               
             
           
         
       
     
      where, A represents the area of each PD and k is the Lambertian factor which denotes the directionality order. The Lambertian factor k is given as: 
     
       
         
           
             k 
             = 
             − 
             
               
                 ln 
                 
                   2 
                 
               
               
                 ln 
                 
                   
                     cos 
                     
                       
                         
                           Φ 
                           
                             
                               1 
                               2 
                             
                           
                         
                       
                     
                   
                 
               
             
           
         
       
     
      with,  being the transmitter semi-angle. Furthermore, d is the distance between the i-th PD and the j-th LED. The angles ϕ i , j  and ψ i , j  denote the angle of emission of the j-th LED to the i-th PD with respect to the transmitter plane and the angle of incidence of the light at the i-th PD from the j-th LED with respect to the orthonormal vector of the receiver plane of the i-th PD, respectively. The field of view (FOV) semi-angle of each PD is denoted as  Given that the LEDs and PDs are placed in a three-dimensional space, their spatial positions can be described by their Cartesian coordinates. Thus, the angle ϕ i , j  and ψ i , j  can be computed as: 
     
       
         
           
             
               ϕ 
               
                 i 
                 , 
                 j 
               
             
             = 
             arccos 
             
               
                 
                   
                     dot 
                     
                       
                         
                           o 
                           t 
                           j 
                         
                         , 
                         
                           p 
                           r 
                           i 
                         
                         − 
                         
                           p 
                           t 
                           j 
                         
                       
                     
                   
                   
                     
                       d 
                       
                         i 
                         , 
                         j 
                       
                     
                   
                 
               
             
             , 
           
         
       
     
      and, 
     
       
         
           
             
               ψ 
               
                 i 
                 , 
                 j 
               
             
             = 
             arccos 
             
               
                 
                   
                     dot 
                     
                       
                         
                           o 
                           r 
                           i 
                         
                         , 
                         
                           p 
                           t 
                           j 
                         
                         − 
                         
                           p 
                           r 
                           i 
                         
                       
                     
                   
                   
                     
                       d 
                       
                         i 
                         , 
                         j 
                       
                     
                   
                 
               
             
             . 
           
         
       
     
     In and (4), dot(x,y) = x T y, represents the inner product between the vectors x and y. Also,  and  are 3 x 1 vectors which represent the Cartesian coordinates of the j-th LED, j= 1,...,  and, i-th PD, i = 1,..., respectively. The orientation of the j-th LED, j= 1,...,N t , is given from the 3 × 1 orthonormal vector,  which is vertical to the plane of the LED. Similarly, the orthonormal vector,  which is vertical to the plane of the i-th PD, represents the orientation of the i-th PD. Finally, the distance, d i,j , between the i-th PD and the j-th LED can be computed as: 
     
       
         
           
             
               d 
               
                 i 
                 , 
                 j 
               
             
             = 
             
               
                 
                   
                     
                       p 
                       r 
                       i 
                     
                     − 
                     
                       p 
                       t 
                       j 
                     
                   
                 
               
               2 
             
           
         
       
     
     In typical indoor LC scenarios, most of the optical signal energy is included in the LOS component. In more detail, the LOS component includes 95% of the energy collected by the PDs. Therefore, based on experimental measurements and academic research, the diffuse component,  can be neglected. Thus, it is quite reasonable to assume that: 
     
       
         
           
             
               h 
               
                 i 
                 , 
                 j 
               
               
                 LC 
               
             
             
               t 
             
             ≈ 
             
               h 
               
                 i 
                 , 
                 j 
               
               
                 L 
                 O 
                 S 
               
             
             ⋅ 
           
         
       
     
     Even though the optical bandwidth is large, LC communication is bandwidth limited due to the frequency selective nature of off-the-shelf LEDs. In more detail, an off-the-shelf LED behaves like a lowpass filter with a frequency response H LED (f) . The specific form of the frequency response of an LED, H LED (f), depends on the specific type of LED (blue or white). Thus, it is expected to be given in the form of specifications from its manufacturer or obtained via experimental measurements. Note that H LED (f) does not depend on the specific positions of the deployed LEDs and PDs. Considering the approximation of the optical channel in (7) and the frequency response of the LED, H LED (f), the composite LC channel, which includes both the LED and the actual physical optical channel, is expressed (approximated) as: 
     
       
         
           
             
               H 
               
                 i 
                 , 
                 j 
               
               
                 LC 
               
             
             
               f 
             
             ≈ 
             
               h 
               
                 i 
                 , 
                 j 
               
               
                 L 
                 O 
                 S 
               
             
             
               H 
               
                 LED 
               
             
             
               f 
             
             . 
           
         
       
     
     Note that, here, without loss of generality, it is indirectly assumed that all LEDs belong to the same family and have the same frequency response. If this is not the case, additional indices in (8) can be used for denoting the different frequency responses of each used family of LEDs. 
     Provided that the transmission rate is set properly for avoiding inter-symbol interference (ISI) or ISI can be neglected, the system equation of a single carrier MIMO LC system is expressed as: 
     
       
         
           
             y 
             = 
             r 
             
               H 
               
                 LED 
               
             
             
               f 
             
             
               H 
               
                 LC 
               
             
             
               
                 x+w 
               
               
                 LC 
               
             
             . 
           
         
       
     
     In , the  × 1 received signal vector is expressed as y; the responsivity of the PD, in A/W, is denoted by r; H LC  is a  ×  matrix which denotes the optical physical MIMO channel; the (i,j) element of H Lc , i = 1,  and, j= 1,  is given by (2); x is the  × 1 transmitted optical signal vector; the elements of x depend from the deployed MIMO transmission scheme and the used constellation for optically modulating binary data; finally, w LC  is a  × 1 vector which represents the composite effect of ambient shot and thermal noise. 
     Due to the nature of the optical channel, the formation of orthogonal frequency division multiplexing (OFDM)-based communication is more challenging compared with radio frequency (RF) communication. In more detail, as mentioned before, the optical channel supports the transmission of real and non-negative signals. Therefore, the design of a multicarrier LC requires the treatment of the previous limitation. A technique for creating real signals from complex signals is the use of inverse fast Fourier transform (IFFT) combined with its Hermitian symmetry in the frequency domain. This technique creates real signals, which can be negative or positive, by sacrificing half of the available subcarriers. As the resulting signals are still negative or positive (bipolar), they can be represented/approximated in a positive form (unipolar). In literature, this has been achieved using different approaches. This resulted in a plethora of optical OFDM based modulation schemes (e.g., as described in a paper by Tsonev, Sinanovic and Haas, “Complete Modeling of Nonlinear Distortion in OFDM-Based Optical Wireless Communications”, Journal of Lightwave Technology, vol 31, pp 3064-3076). One example is the DCO-OFDM which simply introduces a DC bias to resulting bipolar signals combined with clipping (for removing the large values). Despite the plethora of different OFDM based schemes, all schemes aim to create a number of orthogonal sub-carriers which form a flat transmit spectrum. Irrespective of the considered optical OFDM-based modulation scheme, the k-th sub-carrier is described mathematically as: 
     
       
         
           
             
               y 
               k 
             
             = 
             r 
             
               H 
               
                 LED 
               
             
             
               
                 
                   f 
                   k 
                 
               
             
             
               H 
               
                 LC 
               
             
             
               x 
               k 
             
             
               
                 +w 
               
               k 
             
             , 
           
         
       
     
      k = 1  after applying the IFFT and the appropriate representation processing. The last processing depends from the specific optical OFDM-based scheme. Here,  is the number of the created sub-carriers. Note that the previous equation holds as long as any form of linear and non-linear distortion, such as clipping for DC-OFDM, is ignored. 
     Cellular Deployment in LC Networks 
     Similar to RF communication, LC can be used in a cellular deployment where multiple access points (APs) are dedicated for providing wireless coverage in an indoor space. For example, multiple luminaries which act as LC APs can be placed properly in the ceiling of a room for the purposes of illumination and optical wireless communication. Here, it is assumed that the considered LC APs are interconnected using a backhaul connection, such as power-over-Ethernet. The main objective of cellular communication is to increase the number of served stations (STAs) by spatially separating the considered (indoor) space into multiple cells. Each cell is allocated a certain number of STAs which are served in a certain portion of the available optical spectrum. The spectrum allocation in each cell depends from the considered policy and frequency reuse factor. The value of the frequency reuse factor determines the level of interference observed by each cell. In the limit, the whole spectrum is used throughout the cellular network and the highest level of interference is observed. Furthermore, each STA is associated with a specific AP (cell) based on a certain objective function. For example, one method is to associate each STA to the AP which provides the highest value of signal-to-interference-plus-noise ratio (SINR). An alternative method is to associate each STA to the AP with closest spatial proximity. Note that in LC, due to the directional nature of the optical wireless channel, the formation of a LC cellular system is heavily influenced by the geometrical setup of the AP and the spatial positions and orientations of the STAs. This becomes clear by observing (2) and (8). Through (2) and (8), it can be seen that the parameters of the spatial setup of a transceiver along with its optical specifications determine the exact value of its optical channel and consequently its observed receive SINR. 
     Approximate Positioning in LC Cellular Networks 
     A major characteristic of LC is the very directional nature of its optical channel, especially under the use of lenses. In particular, this can be seen clearly from (2) and (8), where the optical wireless channel is approximated in a convenient form. In more detail, (2) and (8) show that the LC channel is determined by the geometric setup of the considered transceiver and the specifications of the deployed LEDs and PDs. 
     The achieved receive SINR of a LC transceiver, in the k-th subcarrier, is given as: 
     
       
         
           
             
               
                 SINR 
               
               k 
             
             = 
             
               
                 
                   r 
                   2 
                 
                 
                   H 
                   
                     LED 
                   
                 
                 
                   
                     
                       
                         
                           f 
                           k 
                         
                       
                     
                   
                   2 
                 
                 
                   
                     
                       
                         
                           H 
                           
                             LC 
                           
                         
                       
                     
                   
                   F 
                   2 
                 
                 
                   P 
                   k 
                   2 
                 
               
               
                 
                   N 
                   k 
                 
                 + 
                 
                   I 
                   k 
                 
               
             
             , 
           
         
       
     
      where, P k  is the transmitted optical power in the k-th subcarrier; N k  is the variance of the Gaussian and shoot noise in the k-th subcarrier; and I k  is the interference power in the k-th subcarrier. Here, || • || F  is the Frobenius norm. 
     In the future cellular LC networks, it can be assumed that interference will be well controlled due to the careful deployment planning of the transmitting LED. Therefore, the effect of interference can be assumed either as negligible  or the value of interference, I k , can be accurately estimated or bounded for any given position in space. In particular, for each considered LC cell, the maximum level of interference, I max , can be computed off-line for the coverage region of each cell. Thus, for each LC cell, the interference, I k , in (11) can be treated as a deterministic quantity which is known. For this reason, the concurrent observation of (2)-(8), and (11) shows that the value of SINR k  can be accurately estimated/bounded from (11) for each position in the three-dimensional space. Thus, if the cell association method used by a LC cellular network is based on the value of SINR k  in (11), for one, a portion, or all the available subcarriers, the coverage area of each cell can be accurately defined and estimated. The direct result of this conclusion is that, when a LC receiver is associated with a certain cell, the network can accurately know the approximate position of this receiver. Obviously, this holds directly when the cell association is based on the spatial position of the LC receiver. 
     In general, it can be concluded that, due to the directional nature of the LC channel, the coverage space of an LC cell can be accurately estimated from the network. Thus, when a LC receiver is associated with a specific LC cell, its approximate position is directly known by the network.