WO2021209352A1

WO2021209352A1 - Optical wireless transceiver and method of operating an optical wireless transceiver apparatus

Info

Publication number: WO2021209352A1
Application number: PCT/EP2021/059369
Authority: WO
Inventors: Michel Germe; Chin Wan OH; Francisco David ROJAS CALVENTE; Amir Masood KHALID
Original assignee: Signify Holding B.V.
Priority date: 2020-04-14
Filing date: 2021-04-12
Publication date: 2021-10-21

Abstract

An optical wireless transceiver (100) comprises a plurality of light sources (122) and a plurality of photodetectors (112). Each light source (122) has a different respective transmission field of view (510) for transmission of modulated light signals and each photodetector (112) has a different respective reception field of view (210) for reception of modulated light signals. The optical wireless transceiver (100) is configured to test at least one of the photodetectors (112), while receiving a preamble (310) of a data packet (300), to determine whether that photodetector (112) is receiving the preamble (310) with a signal strength above a threshold signal strength (500) and, if the tested photodetector (112) is determined to have received the preamble (310) with a signal strength above the threshold signal strength (500), activate at least one of the light sources (122) that has a transmission field of view (510) corresponding to the reception field of view (210) of the tested photodetector (112).

Description

Optical wireless transceiver and method of operating an optical wireless transceiver apparatus

TECHNICAL FIELD

The present disclosure relates to an optical wireless transceiver and method of operating an optical wireless transceiver apparatus.

BACKGROUND

Light Fidelity (LiFi) refers to techniques whereby information is communicated in the form of a signal embedded in light (including for example visible light, or infrared light) emitted by a light source. Depending for example on the particular wavelengths used, such techniques may also be referred to as coded light, optical wireless communications (OWC), visible light communication (VLC) or free-space optical communication (FSO). In this context: visible light may be light that has a wavelength in the range 380nm to 740nm; and infrared light may be light that has a wavelength in the range 740nm to 1.5mm. It is appreciated that there may be some overlap between these ranges.

International patent application W02019/016024 A1 discloses an illumination system for communicating data, that includes a downlink system comprising a group of luminaires each emitting a light comprising a modulated output signal as well as an uplink subsystem which comprises sensors (e.g. infrared sensors) embedded in each luminaire in the group. The uplink subsystem also comprises a demodulator, and a distribution network for supplying the signals sensed to an adaptor to combine instances of the sensed uplink signal.

United States patent application US2019/0386745 A1 discloses a mobile device that comprises a plurality of transmitters and receivers, each configured for optical wireless communication, wherein the plurality of transmitters and/or receivers are arranged on at least three surfaces of the mobile device such that each of the three surfaces has a respective at least one of the transmitters and/or each of the three surfaces has a respective at least one of the receivers.

SUMMARY

It is an object of the present invention to provide an efficient method to activate or deactivate light sources of an Optical Wireless Communication, OWC, transceiver apparatus, as claimed in claim 13, as well as a corresponding OWC transceiver apparatus as claimed in claim 1 and a computer program product as claimed in claim 14.

According to a first aspect disclosed herein, there is provided an optical wireless transceiver comprising: a plurality of photodetectors for receiving, as modulated light signals, data packets having at least a preamble and a data portion, each photodetector having a different respective reception field of view for reception of modulated light signals; and a plurality of light sources for transmitting modulated light signals, each light source having a different respective transmission field of view for transmission of modulated light signals; wherein the optical wireless transceiver is configured to: test at least one of the photodetectors, while receiving a preamble of a data packet, to determine whether that photodetector is receiving the preamble with a signal strength above a threshold signal strength; and if the tested photodetector is determined to have received the preamble with a signal strength above the threshold signal strength, activate at least one of the light sources that has a transmission field of view corresponding to the reception field of view of the tested photodetector.

The field of view for reception of modulated light signals, whilst different for the different photodetectors, may partially overlap or not overlap at all. Likewise, the field of view for transmission of modulated light signals, whilst different for the different light sources, may partially overlap or not overlap at all.

By using multiple photoreceivers and light sources having different respective fields of view; the optical wireless transceiver (also simply referred to as “transceiver” herein) may receive light from one or more directions and likewise, may transmit light into one or more directions. The invention may enable an improvement of the transceiver’s noise resilience as well as the transceiver’s energy dissipation.

This effect is based on the understanding that the optical wireless communication makes use of line-of-sight. More in particular, through the use of the preambles, the present invention allows the transceiver to lower the perceived noise floor on the incoming signal, for example by only using those photoreceivers for the subsequent communication that are beneficial for the signal quality. If a particular photoreceiver only adds noise; it’s contribution may be switched off for subsequent communication.

Leveraging the reciprocal aspect of optical line of sight communication, subsequently those light sources that will contribute to the signal-to-noise ratio (SNR) at the communication partner site. For example, those light sources whose light most likely will arrive at the communication partner may be used, thereby avoiding unnecessary power dissipation. This allows the transceiver to deactivate light sources that transmit in directions where the intended recipient device (communication partner) is not located.

In line therewith preferably, at least one (or more) light source is activated, that has a transmission field of view corresponding to a reception field of view of a tested photodetector determined to have received a signal (preamble) with a signal strength above the threshold signal strength, light sources not activated in this manner may be de-activated to save power,

Once it has been established from which direction the respective photodetectors receives light (a coarse estimate of the direction where the communication partner is located relative to the transceiver), the communication with the communication partner preferably uses the corresponding light sources of the selected photodetectors for communication, or until re-evaluated again.

By configuring the transceiver based on the preamble of one or more data packets (also referred to as “packets” herein), the transceiver can respond quickly to changes of relative positions of the transceiver and its communication partner.

Once configured (i.e. once the transceiver has performed the analysis of the SNR from one or more of the photodiodes), the transceiver configuration may be used for processing the packet payload of the packet from which the preamble was detected.

The determining and activating take place during reception of the preamble of the message and prior to reception of the data portion of the message.

The light sources may be invisible light sources, such as for example infrared light sources. The light sources may be visible light sources.

The light sources may be light emitting diodes.

The photodetectors may be photodiodes.

In an example, the transceiver comprises a signal strength detector and a switch arrangement for selectively connecting the photodetectors to the signal strength detector, and the transceiver is configured to test a photodetector by operating the switch arrangement to selectively connect only that photodetector to the signal strength detector.

In other examples, the transceiver is configured to test a photodetector by operating the switch arrangement to selectively disconnect that photodetector (leaving all other photodetectors connected) to the signal strength detector. The signal strength for that one photodetector being tested (the disconnect one) can then be determined by observing a resulting drop in signal strength caused by the disconnecting of that photodetector’s contribution. Preferably, the number of photodetectors in the transceiver, here designated as N, is in the range 2 < N < 8. More preferably the number of photodetectors is selected from 2 and 4.

Preferably, the number of photodetectors is the same as the number of light sources. More preferably the respective reception fields of view of every one of the photodetectors overlaps with a transmission field of view of one and only one of the light sources out of the plurality, such that there is a one-to-one relationship for each photo detector with only one of the light sources out of the plurality.

Preferably the photodetectors are segments of a segmented photodetector, substantially on one side of an end-point or access point device, where individual adjacent segments of the segmented photodetector are arranged to face in different adjacent directions, or have optics facing in different adjacent directions, resulting in the combined segmented photodetector having a combined wider reception field of view, than the individual segments.

Likewise, preferably the light sources preferably are segments of a larger light source, substantially on one side of an end-point or access point, where individual light sources of the segmented light source are arranged to face in different adjacent directions, or have optics facing in different adjacent directions, resulting in the combined segmented light source having a combined wider transmission field of view, than the individual segments.

The present invention may thus be used to selectively activate a subset of the photodetector segment(s) and/or light source segment(s), and deactivate the others, to thereby reduce the reception and transmit power requirements of the endpoint and/or access point device.

The switch arrangement may comprise a respective switch for each photodetector which is operable to selectively connect only that photodetector to the signal strength detector.

In an example, the transceiver is configured to test each of the photodetectors in a sequence.

In an example, the sequence is a predefined sequence. The predefined sequence, may for example be the order from highest to lowest SNR as tested in a previous packet (e.g. the most recent packet for which the testing was carried out).

In some examples, it may be assumed that communication is with the same, substantially stationary, device. In some cases, evaluation of photodetectors in the sequence (order) which was previously highest to lowest SNR may, even when part of the preamble is missed, result in the most relevant photodetector and/or light source being used in the communication. Alternatively or additionally, in particular when the fields of view partially of the photodetectors and light sources overlap; it may be beneficial to first process the non overlapping photodetectors, in this manner a faster, more directional coverage may be achieved.

In a further examples, the sequence may be made adaptive, For example, the sequence may initially follow the last-highest-to-lowest-SNR (previously determined order), or the fast-overall coverage, but then the order may be adapted to achieve faster “convergence”. For example, when no signal (preamble) is detected in the output of the previously highest-SNR photodetector, the transceiver may evaluate the photodetectors in a different order that focuses on coverage rather than history. This is advantageous because when the first photodetector in the previously-determined order no longer has the highest SNR, this may be indicative of the communication partner having moved relative to the receiver, or that the currently -received preamble is from a different communication partner.

In an example, the sequence is a random sequence. A random sequence, in contrast to a predefined sequence, does not favour a particular direction. As a result, in case of substantially non-overlapping receiver/transmit field-of-views this approach will favour coverage.

In an example, the transceiver is configured to perform said testing according to a predefined schedule. Although it may be possible to test and evaluate the photodetectors for every packet, it may be possible to use further information present in the system to reduce the need for testing.

In some examples, optical wireless communication may make use of a time- division multiple access (TDMA) approach. In TDMA time-slots or time-channels are allocated to particular communication partners for communication with an access point.

When the transceiver is an access point; it may be advantageous to leverage knowledge of time-slot boundaries. In such a scenario the testing and evaluation of the photodiode contributions should preferably be performed at the start of a time-slot boundary (optionally on both access point as well as endpoint). Additionally, it may be beneficial to also perform further evaluation mid-time slot, for example when substantial variations in SNR are detected.

In an example, the transceiver is comprised in an endpoint device of an OWC network.

In an example, the transceiver is configured to perform said testing in response to a variation in detected signal quality at the transceiver during communication. Such variation may be based SNR, link quality, lack of acknowledgments etc. Such variation may for example be triggered by a change of relative position of the transmitter and receiver. Optionally, such a variation may even be detected in the transceiver frontend itself as a variation in automatic gain control settings during a packet.

In an example, the transceiver is comprised in an access point of an OWC network.

In an example, the transceiver is configured to perform said testing in response to input from a motion sensor of an endpoint device of the OWC network.

According to a second aspect disclosed herein, there is provided a system comprising a transceiver according to the first aspect comprised in an endpoint device, and an access point of the OWC network.

According to a third aspect disclosed herein, there is provided a system comprising a transceiver according to the first aspect comprised in an access point, and an endpoint device of the OWC network.

In an example, both the access point and endpoint device comprise a transceiver in accordance with the first aspect or any example thereof.

According to a fourth aspect disclosed herein, there is provided a method performed by a transceiver, the transceiver comprising a plurality of photodetectors for receiving, as modulated light signals, data packets having at least a preamble and a data portion, each photodetector having a different respective reception field of view for reception of modulated light signals; and a plurality of light sources for transmitting modulated light signals, each light source having a different respective transmission field of view for transmission of modulated light signals; the method comprising: testing at least one of the photodetectors, while receiving a preamble of a data packet, to determine whether that photodetector is receiving the preamble with a signal strength above a threshold signal strength; and if the tested photodetector is determined to have received the preamble with a signal strength above the threshold signal strength, activating at least one of the light sources that has a transmission field of view corresponding to the reception field of view of the tested photodetector.

In an example, testing a photodetector comprises operating a switch arrangement to selectively connect only said photodetector to a signal strength detector. That is, in order to test a particular one of the photodetectors, that photodetector to be tested, and only that one photodetector, may be selectively connected to a signal strength detector. “Signal strength” here means the AC signal strength of the received OWC data signal. In other examples, testing a photodetector comprises operating a switch arrangement to selectively connect all photodetectors except said photodetector to a signal strength detector. The signal strength for said (disconnected) photodetector can then be determined as an observed drop is signal strength. In particular when the previously strongest photodetector signal is tested first using this approach; the resulting combined input signal of subsequent tests will likely contain preamble information and may be used in parallel to perform synchronization (albeit at a higher noise floor resulting from the signals being combined).

According to fifth aspect disclosed herein, there is provided a computer program product for performing the method according to the fourth aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

To assist understanding of the present disclosure and to show how embodiments may be put into effect, reference is made by way of example to the accompanying drawings in which:

Figure 1 shows schematically a transceiver in accordance with examples described herein;

Figure 2a shows schematically the transceiver installed as part of an endpoint device of a LiFi system within an environment;

Figure 2b shows schematically the transceiver installed as part of an access point of a LiFi system within an environment;

Figure 3 shows schematically the structure of an exemplary LiFi data packet;

Figure 4 shows schematically an example method performed by the transceiver;

Figure 5a shows schematically signal strengths for each of the photodetectors in accordance with a first example;

Figure 5b shows schematically the transmission fields of view of the transceiver in accordance with the first example;

Figure 6a shows schematically signal strengths for each of the photodetectors in accordance with a second example; and

Figure 6b shows schematically the transmission fields of the view of the transceiver in accordance with the second example.

The present disclosure relates to a transceiver for use in for example a LiFi network. The transceiver may, for example, be provided in or as an access point of the LiFi network allowing an endpoint device to connect to the LiFi network via the access point using the transceiver. In other examples, the transceiver may be provided in or as the endpoint device itself.

In a LiFi network, modulated light is used to transmit data from a source device (e.g. an access point or an endpoint device) to a destination device (e.g. an endpoint device or an access point) as a series of one or more data packets. Each data packet comprises a plurality of fields providing different functions. In particular, each data packet has at least a preamble and a data portion. The data portion, sometimes referred to as the frame body, holds the actual payload data of the packet. The preamble precedes the data portion and may for example be used to synchronise the device receiving the data packet.

The transceiver provided by the present disclosure comprises a plurality of photodetectors (e.g. photodiodes) for receiving data packets as modulated light signals and a plurality of light sources (e.g. LEDs) for transmitting data packets as modulated light signals. Each of the photodetectors receives signals from a different respective reception field of view. There may be some overlap between the reception field of view of one of the photodetectors and the reception fields of view of one or more others of the photodetectors. Similarly, each of the light sources transmits signals into a different respective transmission field of view. Again, there may be some overlap between the transmission field of view of one of the light sources and the transmission fields of view of one or more of the other light sources.

Each of the reception fields of view of the photodetectors is associated with a corresponding one or more of the transmission fields of view of the light sources. In this regard, the reception field of view may be regarded as corresponding to a transmission field of view if for example the respective fields of view are identical or similar. For example, in the case that the respective fields of view are cones, the fields of view may be regarded as corresponding if the respective cone angles are the same or the same within say 10%, or within 1 or 2% say. It is appreciated that this is not a precise definition.

In some examples, the photodetectors and light sources may be provided as logical pairs, which receive from and transmit to the same or substantially the same field of view, respectively. The transmission field of view of a light source is considered to correspond to the reception field of view of the photodiode of the same logical pair further, the reception field of view may be regarded as corresponding to a transmission field of view if, for example, the reception field of view falls entirely within the transmission field of view or vice versa.

The present disclosure recognises that it may not always be necessary or appropriate to transmit a signal using all of the light sources. For example, in order for the transceiver implemented at an access point to transmit a LiFi signal to an endpoint device, a single light source may be sufficient. This may be the case, for example, when the endpoint device is only located within the transmission field of view of a single light source.

The transceiver disclosed herein is configured to determine one or more of the light sources to activate for transmitting modulated light signals. Because not all the light sources need to be activated, savings are made with regard to both power consumption and heat production. The determination of which one or more light sources to activate is performed during reception of the preamble of a data packet, and for example not during reception of the data portion. In this manner the input to the demodulator is kept substantially constant during the processing of the data portion. This ensures proper reception and decoding of the received OWC data signal.

Specifically, the transceiver is configured to test at least one of the photodetectors, while receiving a preamble of a data packet, to determine whether that photodetector is receiving the preamble with a signal strength above a threshold signal strength. Then, if the tested photodetector is determined to have received the preamble with a signal strength above the threshold signal strength, a corresponding at least one light source is activated, the corresponding light source having a transmission field of view which corresponds to the reception field of view of the tested photodetector.

Referring now to the drawings, Figure 1 shows schematically a transceiver 100 in accordance with examples described herein. The transceiver 100 comprises a receiver circuit 110, a transmitter circuit 120, and a controller 130. The controller 130 is operatively coupled to the receiver circuit 110 and the transmitter circuit 120. The controller 130 may be implemented, for example, as a microcontroller or a field-programmable gate array FPGA.

The transmitter circuit 120 comprises a plurality of light sources 121 for outputting modulated light signals. The light sources 121 may be implemented, for example, as light emitting diodes LEDs, e.g. visible light or infrared LEDs. Each light source 121 may be in an active state (turned ON) or an inactive state (turned OFF). In the active state, the light source 121 is arranged to output light for the purposes of transmitting LiFi signals. In the inactive state, the light source 121 is arranged to not output light. Each light source 121 emits light into a different respective transmission field of view. For example, each light source 121 may transmit light into a specific sector (over a solid angle) and may be oriented in a different direction from the other light sources 121. Alternatively or additionally, the light output of one or more of the light sources 121 may be constrained by part of the body or housing of the transceiver 100. In either case, there may or may not be overlap between the transmission fields of view of each of the light sources 121.

In this example, there are four light sources 121a-d. However, it is appreciated that there may be more or fewer light sources 121. In general, the transmitter circuit 120 comprises at least two light sources 121.

The controller 130 can selectively and independently control each light source 121 to be in either the active state or the inactive state. In this example, the transmitter circuit

120 comprises a plurality of switches 122. The controller 130 is operatively coupled to each of the switches 122. Each switch 122 is operatively coupled to one of the light sources 121.

In the arrangement shown in Figure 1, a light source 121 is in the active state when its respective switch 122 is closed (allowing current to pass through the switch). Correspondingly, a light source 121 is in the inactive state when its respective switch is open (not allowing current to pass through the switch). In operation, the controller 130 is configured to control one or more light sources 121 to be in the active state in order to transmit LiFi signals. In the example shown in Figure 1, this may comprise the controller 130 opening one or more of the switches corresponding to the one or more active light sources

121 and closing all other switches 122. Other arrangements for selectively activating the light sources 121 are possible, including for example using other circuitry so that a drive voltage/current is only provided to the desired one or more of the light source(s) 121.

The receiver circuit 110 comprises a plurality of photodetectors 111. The photodetectors 111 generate an electrical current in response to light incident on the photodetector 111. In this way, each photodetector 111 can be used to receive LiFi signals in the form of modulated light, as described below. The photodetectors 111 may be implemented, for example, as photodiodes.

Each photodetector 111 receives light from a different respective reception field of view. For example, each photodetector 111 may receive light from a specific sector (over a solid angle) and may be oriented in a different direction. Alternatively or additionally, the solid angle over which one or more of the photodetectors 111 can receive light may be constrained by part of the body or housing of the transceiver 100 thereby shaping the direction/beamshape of the emitted light beam. In this example, there are four photodetectors 11 la-d. However, it is appreciated that there may be more or fewer photodetectors 111. In general, the receiver circuit 110 comprises at least two photodetectors 111. In some examples, the number of photodetectors 111 may be the same as the number of light sources 121.

As the photodetectors 111 and light sources 121 are part of the transceiver 100; the respective field-of-views are known by the controller 130, or at least the correspondence among the field-of view of the respective photodetectors 111 and the one or more light sources 121 corresponding thereto.

In operation, the controller 130 is configured to test at least one of the photodetectors 111, while receiving a preamble of a data packet, to determine whether that photodetector 111 is receiving the preamble with a signal strength above a threshold. There are various different ways that this can be achieved. For example, each photodetector 111 may be coupled to a respective signal strength detector. This allows all of the photodetectors

111 to be tested simultaneously. In other examples, a switch arrangement may be provided for selectively connecting one photodetector 111 at a time to a single signal strength detector. In this configuration, only a single photodetector 111 can be checked at once, but the component count and therefore manufacturing costs are lower as only a single signal strength detector is required.

Herein, the term “signal strength” refers to the AC signal strength. For example, the signal strength detection may start at 2MHz. This is advantageous as it allows DC sources (such as sunlight) to be ignored. In some examples, an optical filter may be provided at the photodetectors in order to substantially remove wavelengths of light other than those used for communication (e.g. the photodetectors may be IR photodetectors provided with a wavelength filter for substantially blocking visible light). In some examples, the photodetectors 111 may be differential, which are more immune to visible light that has no modulation (DC). In other words, the SNR/RSSI is based on a filtered signal, where in some examples a DC contribution is filtered out to remove e.g. sunlight, and alternative or additionally a (frequency) bandpass filter could be used to filter out noise components that are outside of the frequency range of that of the preambles.

In the example shown in Figure 1, the receive circuit 110 includes a switch arrangement comprising a plurality of switches 112. In this example, the number of switches

112 is the same as the number of photodetectors 111 such that there is a respective switch 112 for each photodetector 111. The receiver circuit 110 of this example also includes a transimpedance amplifier 113, a detector 114, and a received signal strength indicator RSSI module 115. The switches 112 may be referred to as photodetector switches 112 in order to distinguish them from the light source switches 122 located in the transmitter circuit 120. As noted, because of the switching arrangement, only a single transimpedance amplifier (TIA)

113, a single detector 114, and a single RSSI module 115 are required in this example.

The controller 130 is operatively coupled to each of the photodetector switches

112 to independently control opening and closing of the switches 112. Each switch 112 is operatively coupled to one of the photodetectors 111. The photodetectors 111 are each operatively coupled to the transimpedance amplifier 113. The detector 114 is operatively coupled to the transimpedance amplifier 113 and the RSSI module 115.

Whether or not current generated by a particular photodetector 111 reaches the transimpedance amplifier 113 depends on the state of the respective switch 112: when the switch 112 for a given photodetector 111 is closed (not passing electrical current), any current generated by that photodetector 111 is not passed to the transimpedance amplifier 113; when the switch 112 for a given photodetector 111 is open (passing electrical current), current generated by that photodetector 111 is passed to the transimpedance amplifier 113.

In operation, the controller 130 is configured to control the switches 112 so that the photodetectors 111 can be selectively tested during reception of a preamble of a data packet in order to determine whether at least one photodetector 111 is receiving the preamble with a signal strength greater than a threshold signal strength. In the example shown in Figure 1, this comprises the controller 130 operating the switches 112 in order to selectively connect a single photodetector 111 to the transimpedance amplifier 113 at a time.

When light is incident on a photodetector 111, the transimpedance amplifier

113 receives electrical current from the photodetector 111 when that photodetector 111 is connected to the transimpedance amplifier 113, and converts the received electrical current into an amplified electrical voltage. The transimpedance amplifier 113 may be implemented, for example, using one or more operational amplifiers.

The detector 114 receives the amplified voltage from the transimpedance amplifier 113 and extracts a LiFi signal therefrom. The detector 114 may be implemented, for example, as a radiofrequency detector.

The RSSI module 115 receives a LiFi signal from the detector 114 and determines a signal strength of the LiFi signal. The RSSI module 115 is arranged to provide the determined signal strength to the controller 130. The RSSI module 115 may be implemented, for example, as a comparator which is arranged to compare a signal strength of the LiFi signal to a threshold signal strength and output to the controller 130 an indication of whether the LiFi signal strength is above the threshold signal strength or below the threshold signal strength. In another example, an analogue-to-digital converter in the controller 130 may be used as a comparator to determine and compare the signal strength of the LiFi signal with a threshold signal strength in place of the RSSI module 115.

It is appreciated that when receiving a data packet, the baseband is used to detect and synchronise the packet by analysing the beginning of the packet. The term “signal strength” as used herein may therefore refer to the received signal strength (RSSI) as established for that part of the band where the preambles are present.

Optionally it may be possible to implement two parallel signal path; one for configuration of the transceiver in accordance with the invention and one which sums up all contributions from all photodetectors, having a separate TIA, that is used for synchronization of the system. Although such a solution comes at the price of a further TIA and, by summing, may suffer from a higher noise floor during synchronization; it does enable the transceiver to perform synchronization using the entire preamble in parallel to the configuration of the transceiver.

Figure 2a shows schematically an example in which the transceiver 100 is installed within an environment 200 as part of an endpoint device 250 of a LiFi network. The endpoint device 2250 may be, for example, a user device, including for example a smartphone, a laptop or tablet computer, etc. The environment 200 may be, for example, a room, an office space, etc. The LiFi network comprises an access point 140 and a LiFi controller 150. The LiFi controller 150 is operatively coupled to the access point 140. The LiFi controller 150 may also be operatively coupled to one or more other devices and or one or more networks. An example network 160 is shown schematically in Figure 2a.

The endpoint device 250 is configured to communicate with the access point 140 using the transceiver 100 in order to connect to the LiFi network via the access point. This comprises the access point 140 having at least one light source for transmitting LiFi signals for reception by the transceiver 100 and also the transceiver transmitting LiFi signals for reception by a photodetector of the access point 140. In some examples, an instance of a transceiver 100 may alternatively or additionally be implemented at the access point 140.

This is discussed in more detail below in relation to Figure 2b.

As mentioned earlier, each photodetector 111 of the transceiver 100 is arranged to receive LiFi signals from a different respective reception field of view 210. In this example, a first photodetector 11 la is arranged to receive LiFi signals from a first reception field of view 210a; a second photodetector 11 lb is arranged to receive LiFi signals from a second reception field of view 210b; a third photodetector 11 lc is arranged to receive LiFi signals from a third reception field of view 210c; and a fourth photodetector 11 Id is arranged to receive LiFi signals from a fourth reception field of view 21 Od.

The reception fields of view 210 are illustrated as cones within the environment 200 in Figure 2a, but it is appreciated that the reception fields of view 210 may in general be of any shape or volume. There may or may not be overlap between the reception fields of view 210 of each of the photodetectors 111. In particular, there may be substantially more or less overlap between the reception fields of view 210 than schematically illustrated in Figure 2a.

Also as mentioned earlier, each light source 121 is arranged to emit LiFi signals into a different respective transmission field of view (not shown in Figure 2a). In some examples, the light sources 121 and photodetectors 111 may be logically paired. This is particularly advantageous if the transmission fields of view substantially overlap with the corresponding reception fields of view 210, i.e. if: the transmission field of view of a first light source 121a substantially coincides with the reception field of view of the first photodetector 111a; the transmission field of view of a second light source 121b substantially coincides with the reception field of view of the second photodetector 11 lb; the transmission field of view of a third light source 121c substantially coincides with the reception field of view of the third photodetector 111c; and the transmission field of view of a fourth light source 121 d substantially coincides with the reception field of view of the fourth photodetector 11 Id, etc.

As the endpoint device 250 may move within the environment 200, the access point 140 may, at different points in time, be located within a different one or more transmission fields of view of the transceiver 100. LiFi signals transmitted by the transceiver 100 into the one or more transmission fields of view in which the access point 140 is currently located may be received by the access point 140. On the other hand, LiFi signals transmitted by the transceiver 100 into one or more transmission fields of view in which the access point 140 is not currently located may not be received by the access point 140, or, may be received with lower signal-to-noise ratio than those transmitted into the one or more transmission fields of view in which the access point 140 is currently located.

The present disclosure proposes to save power and heat production by determining a light source 121 which outputs LiFi signals into transmission fields of view in which the access point 140 is currently located by analysing the signal strength of a preamble of a LiFi data packet received by one or more of the photodetectors 111 from the access point 140. This means that the transmitted LiFi signals are directed from the transceiver 100 towards the access point 140 and power may not be wasted and heat may not be unnecessarily produced by generating and emitting LiFi signals in directions other than towards the access point 140.

In Figure 2a, the access point 140 is located within the first reception field of view 210a and not within the second reception field of view 210b, third reception field of view 210c, or fourth reception field of view 21 Od. In this arrangement, the transceiver 100 will activate the first light source 121a and deactivate the second light source 121b, third light source 121c, and fourth light source 121d, thereby saving power and producing less heat.

Figure 2b shows schematically an example in which the transceiver 100 is installed within an environment 200 as part of an access point 140 of a LiFi network. The construction and operation of the transceiver 100 is similar to that described above with reference to Figure 2a.

In this example, the endpoint device 250 may, at different points in time, be located within a different one or more reception fields of view 210 of the transceiver 100. A light source 121 of the transceiver 100 at the access point 140 which outputs LiFi signals into transmission fields of view in which the endpoint device 250 is currently located is determined by analysing the signal strength of a preamble of a LiFi data packet received by one or more of the photodetectors 111 from the endpoint device 250. Again, this means that the transmitted LiFi signals are directed from the transceiver 100 towards the endpoint device 250 and power may not be wasted and heat may not be unnecessarily produced by generating and emitting LiFi signals in directions other than towards the endpoint device 250.

In Figure 2b, the endpoint device 250 is located within the fourth reception field of view 21 Od and not within the first reception field of view 210a, second reception field of view 210b, or third reception field of view 210c. In this arrangement, the transceiver 100 will activate the fourth light source 121 d and deactivate the first light source 121a, second light source 121b, and third light source 121c, thereby saving power and producing less heat.

Whether implemented at the endpoint device 250, access point 140, or another device, the transceiver 100 is configured to determine which one or more light sources 121 to activate using a preamble of one or more data packets received from the endpoint device 250, as described below.

Figure 3 shows schematically the structure of an exemplary LiFi data packet 300 (also called a “frame”). Currently, there is not yet a globally accepted standard for LiFi communication. At present LiFi communications are implemented using G.vlc, (ITU G 9991) which is part of the G.hn family of standards. The G.hn standards are traditionally used for power line communication (PLC), coax, and phoneline communications. There are differences depending on the profile used (PLC, coax, phoneline). For example, the PLC profile requires sending two copies of each data packet. Currently, the coax implementation is generally used for LiFi. For example, a LiFi data packet maybe implemented in accordance with the ITU-T Rec. G.9960 recommendation for the physical layer. In such implementations, the preamble comprises a series of repeated orthogonal frequency-division multiplex (OFDM) symbols prepended to the PHY frame which are used to detect and synchronize the receiver and help it start decoding the frame.

The example data packet 300 shown in Figure 3 comprises a preamble 310 and a data portion 330. The data packet 300 may comprise one or more additional portions (not shown), e.g. a header portion. The preamble 310 comprises a first portion 311, a second portion 312, and athird portion 313. The first portion 311 comprises a series of repeated OFDM symbols Si. The second portion 312 comprises a series of repeated OFDM symbols S2. The third portion 311 comprises a series of repeated OFDM symbols S3. The full preamble 310 may be, for example, on the order of 18-20 microseconds in duration.

In other examples, the preamble 310 may include one or more fields such as a synchronisation field and a start frame delimiter field, SFD. The synchronisation field may be, for example, a string of alternating Is and 0s (e.g. 80 bits long). The SFD comprises a preset code indicating the start of a frame, e.g. a preset 16-bit string.

Figure 4 is a flow diagram illustrating an example method performed by the transceiver 100. For the purposes of explanation, it will be assumed in this example that the transceiver 100 is implemented at an endpoint device 250, though it is appreciated that a corresponding method can be performed when the transceiver 100 is implemented in another device such as an access point 140.

At S401, the transceiver 100 is operating with all four photodetectors 11 la-d connected to the TIA 113. The transceiver 100 begins receiving the preamble 310 of the data packet 300 from the access point 140 using all four photodetectors 11 la-d.

At S402, the controller 130 tests the photodetectors 111 to determine if at least one photodetector 111 is receiving the preamble 310 with a signal strength above the threshold signal strength. If the signal strength for a particular photodetector 111 is above the threshold signal strength, then the reception field of view of that photodetector 111 is used to determine which one (or more) light sources 121 to activate for transmitting modulated light signals. Specifically, the controller 130 determines any light sources 121 having a transmission field of view corresponding to the reception field of view of that photodetector 111 and activates at least one of those one or more light source(s) 121. If for example there is a single light source 121 corresponding to that photodetector 111 for which the preamble is received with a signal strength above the threshold signal strength, the only that single light source 121 is activated. If for example there is are plural light sources 121 corresponding to that photodetector 111, then, in an example, only one of those light sources 121 is activated.

There are a variety of different ways in which this photodetector testing phase can be implemented. Several examples are given later below. Once the photodetector testing phase has concluded, the method proceeds to S403.

At S403, the remaining portion of the preamble 310 may be used by the transceiver 100 as normal, e.g. to synchronise the transceiver 100 ready for receiving the data portion 320 of the data packet 300. The preamble 31 is designed to be very robust, so that, if some of the symbols are noisy or lost, the frame can still be detected and synchronized to be decoded. The inventors have found that if a few microseconds of the preamble 310 are lost the data packet 300 can be still decoded.

At S404, the transceiver 100 begins receiving the data portion 320 of the data packet 300.

As mentioned above, the photodetector testing phase may be implemented in a variety of different ways. In practice, it may take around 2.5 microseconds to test a photodiode. For example, with reference again to Figure 1, the detector 114 may take around 1 microsecond to measure the signal, and determination of whether the signal strength is above the threshold may take another 1.5 microseconds. If the preamble 310 lasts for, e.g., 18 microseconds, four photodetectors 111 could be tested, with 8 microseconds of preamble 310 remaining for synchronisation.

In some example, the transceiver 100 may be configured to test all the photodetectors 111 in sequence during the preamble 310 of a single data packet 300. The transceiver 100 may stop testing the photodetectors 111 once a photodetector has been found that has a signal strength above the threshold. The sequence may for example be a predetermined sequence in which the photodetectors 111 are tested in the same order each time, or a random sequence in which the photodetectors 111 are tested in a random order each time.

In other examples, the transceiver 100 may be configured to test a single photodetector 111 per preamble 310. For example, the transceiver 100 may be configured to test a different one of the photodetectors 111 using the preamble 310 of a different respective data packet 300, e.g. testing a first photodetector 11 la during the preamble of a first received data packet, testing a second photodetector 111b during the preamble of a second received data packet, and so on. The transceiver 100 may be configured to cycle through the photodetectors 111 in a predetermined order or in a random order.

In other examples the testing may be spread out over multiple packets, which is particularly useful when it is known that multiple packets will be received from a single communication partner (e.g. in a TDMA setting as described above). This may in particular be the case, for example, when the transceiver 100 is implemented as part of an endpoint device 250, as there is only one communication partner (the access point) unless the endpoint device 250 is currently located within an interference zone between two access points.

For example, the transceiver 100 may be configured to test a different more than one of the photodetectors 111 using the preamble 310 of a different respective data packet 300, e.g. by testing a first photodetector 11 la and second photodetector 111b using the preamble of a first received data packet, testing a third photodetector 111c and fourth photodetector 11 Id using the preamble of a second received data packet, and so on. The transceiver 100 may be configured to cycle through the sets of one or more photodetectors 111 in a predetermined order or in a random order. The sets of one or more photodetectors 111 tested during each preamble may be the same or may vary from one preamble to another. In the above manner the energy efficiency which may initially be low (as all light sources are used) increases with further packets being received.

The above examples describe ways in which the photodetectors 111 can be tested during the preamble 310 of a received data packet 300. Any of these may be implemented with respect to any data packet received by the transceiver 100. While the transceiver 100 may be configured to test the photodetectors (in any manner described above) when receiving every data packet, this may not be necessary. For example, the other device (e.g. endpoint device 250 or access point 140, depending on where the transceiver 100 is implemented) may not have moved from one transmission field of view to another (because either the other device or the transceiver 100 itself has moved/rotated, etc.). Hence, in examples, the transceiver 100 may normally operate in a mode in which the transceiver 100 does not test photodetectors 111, but switches to a “testing” mode in which it does test one or more photodetectors 111 to determine one or more light sources 121 which can be activated. In other words, the transceiver 100 may continue using a previously determined set of light sources 121 for transmitting LiFi signals until it switches to the testing mode in order to reassess which light sources 121 to use.

In some examples, the transceiver 111 may be configured to switch to the testing mode according to a predefined timescale, e.g. once a second, once every ten seconds, once a minute, etc.

Alternatively or additionally, the transceiver 111 may be configured to switch to the testing mode in response to input from a sensor.

In one example, the sensor may be a motion sensor (e.g. a gyroscopic sensor) indicating that the transceiver 100 itself has moved, rotated, etc. This is particularly advantageous when the transceiver 100 is implemented as part of the endpoint device 250.

In another example, when the transceiver 100 is implemented as part of a device which is not itself mobile (e.g. an access point of the LiFi network), the sensor may be a motion sensor (e.g. a gyroscopic sensor) in an endpoint device. For example, the access point may thereby determine, based on input from the motion sensor at the endpoint device, that the endpoint device has moved and therefore the access point should switch to the testing mode in order to re-analyse which light source(s) are best to use for sending OWC signals to the endpoint device.

In yet another example, the sensor may be implemented as an infrastructural occupancy/motion sensor, e.g. from the lighting infrastructure. Such a sensor may be used to track motion of a user within the environment. Input from this sensor (indicating presence of a user, or that the user has moved) can then be used as a trigger for the transceiver to switch to the testing mode. This has advantages both when the transceiver 100 is implemented at the endpoint device (which may be e.g. held by the user and therefore motion of the user implies motion of the endpoint device) and when the transceiver 100 is implemented at the access point (as the user may be e.g. holding the endpoint device, and therefore motion of the user implies motion of the communication partner).

In some examples, the transceiver 100 may be configured to test the photodetectors 111 according to any example described herein, but starting with a previously-determined one of the photodetectors 111 first. That is, when the transceiver 100 has previously selected a light source 122 to use based on identifying a photodetector 111 which received a previous preamble 310 with a signal strength above the threshold, it may be configured to begin, as part of the next testing phase, by testing that photodetector 111 before testing the other photodetectors 111. This is particularly advantageous because if the other device has not moved, then the first photodetector 111 tested can be expected to be above the threshold and therefore be selected more quickly.

Described now with reference to Figures 5a, 5b, 6a and 6b are two illustrative examples to show the operation of the transceiver 100 when implemented at the endpoint device 250.

Figure 5a shows signal strengths 500 for received preambles for each of the photodetectors 111 as may be the case, for example, when the endpoint device 250 is located within the reception field of view 21 Od of the fourth photodetector 11 Id and not any other reception fields of view 210a-c.

As will be appreciated, although the images presented herein are two- dimensional; actual systems will be operating in three-dimensional space. As a result, photodetectors and their respective field of views, generally will be adjacent in three- dimensional space. For example, when four photodetectors are placed in a square layout, such as shown in Fig. 2a, in a configuration intended to provide a combined larger coverage areas/solid angle than that of the individual photodetectors, their respective fields of view will be adjacent and may partially overlap.

The signal strength for the first photodetector 111a, second photodetector 111b, and third photodetector 11 lc are each below a threshold 500. The signal strength for the fourth photodetector 11 Id is above the threshold 500. It is appreciated that, in practice, the radiation pahem of an emitter does not have a sharp cut off at a specific angle and therefore there may be some amount of power received by a photodetector even when the endpoint device 250 is not in its field of view, as shown in the figures.

The transceiver 100 is configured to activate at least one light source 121 (and in an example, only one light source 121) having a transmission field of view which corresponds to the reception field of view 210 of a photodetector 111 for which the signal strength is above the threshold 500. In this example, this means activating only the fourth light source 121 d to transmit LiFi signals to the endpoint device 250. The other light sources 121a-c may then be deactivated to save power and heat production.

Following on from Figure 5a, Figure 5b shows schematically the transmission fields of view 510 of the transceiver 100. As mentioned earlier, each light source 121 is arranged to emit LiFi signals into a different respective transmission field of view 510. In this example, the first light source 121a is arranged to emit LiFi signals into a first transmission field of view 510a; the second light source 121b is arranged to emit LiFi signals into a second transmission field of view 510b; the third light source 121c is arranged to emit LiFi signals into a third transmission field of view 510c; and the fourth light source 121d is arranged to emit LiFi signals into a fourth transmission field of view 510d.

In this example, based on the signal strengths determined earlier and shown in Figure 5a, the fourth light source 121d is operated in the active state for sending LiFi signals to the endpoint device 250 and the other light sources 121 may be deactivated. Deactivation of a light source 121 is represented in Figure 5b by the respective transmission field of view 510 being shown with a dotted line, whereas activation of a light source 121 is represented in Figure 5b by the respective transmission field of view 510 being shown with a solid line.

The transmission fields of view 510 are illustrated as cones within the environment 200 in Figure 5b, but it is appreciated that the transmission fields of view 510 may in general be of any shape or volume. There may or may not be overlap between the transmission fields of view 510 of each of the light sources 121. In particular, there may be substantially more overlap between the transmission fields of view 510 than as illustrated in Figure 5a, in which the transmission fields of view 510.

Figures 6a and 6b show an example in which the endpoint device 250 is located partially within the third reception field of view 210c and partially within the fourth reception field of view 21 Od. The signal strengths of preambles received by the four photodetectors 111 are illustrated in Figure 6b. The signal strength for the first photodetector 11 la and the second photodetector 11 lb are below the threshold 500 and the signal strength for the third photodetector 111c and the fourth photodetector 11 Id are above the threshold 500. Hence, the transceiver 100 will activate the third light source 121c and the fourth light source 121 d. The transceiver 100 may also deactivate the first light source 121a and the second light source 121b. This is illustrated schematically in Figure 6b in which the first transmission field of view 510a and second transmission field of view 510b are inactive and the third transmission field of view 510c and fourth transmission field of view 51 Od are active.

It will be understood that the controller referred to herein may in practice be provided by an integrated circuit or plural integrated circuits, an application-specific integrated circuit (ASIC), field-programmable gate array (FPGA), digital signal processor (DSP), etc.

Although at least some aspects of the embodiments described herein with reference to the drawings comprise computer processes performed in a controller, the invention also extends to computer programs, particularly computer programs on or in a carrier, adapted for putting the invention into practice. The program may be in the form of non-transitory source code, object code, a code intermediate source and object code such as in partially compiled form, or in any other non-transitory form suitable for use in the implementation of processes according to the invention. The carrier may be any entity or device capable of carrying the program. For example, the carrier may comprise a storage medium, such as a solid-state drive (SSD) or other semiconductor-based RAM; a ROM, for example a CD ROM or a semiconductor ROM; a magnetic recording medium, for example a floppy disk or hard disk; optical memory devices in general; etc. The examples described herein are to be understood as illustrative examples of embodiments of the invention. Further embodiments and examples are envisaged. Any feature described in relation to any one example or embodiment may be used alone or in combination with other features. In addition, any feature described in relation to any one example or embodiment may also be used in combination with one or more features of any other of the examples or embodiments, or any combination of any other of the examples or embodiments. Furthermore, equivalents and modifications not described herein may also be employed within the scope of the invention, which is defined in the claims.

Claims

CLAIMS:

1. A optical wireless communication, OWC, transceiver apparatus (100) comprising: a plurality of photodetectors (111) for receiving, as modulated light signals, data packets having at least a preamble (310) and a data portion (320), each photodetector having a different respective reception field of view (210) for reception of modulated light signals; and a plurality of light sources (121) for transmitting modulated light signals, each light source having a different respective transmission field of view for transmission of modulated light signals; wherein the OWC transceiver apparatus is configured to: test each of the photodetectors using a signal strength detector (114), while receiving a signal, to determine whether that photodetector is receiving the signal with a signal strength above a threshold signal strength; and activate at least one of the light sources that has a transmission field of view corresponding to a reception field of view of a tested photodetector determined to have received the signal with a signal strength above the threshold signal strength and de-activate the light sources not activated, the OWC transceiver apparatus (100) characterized in that it comprises: a switch arrangement (112) for selectively connecting the photodetectors (111) to the signal strength detector (114); the OWC transceiver apparatus configured to test each photodetector in sequence, wherein a photodetector is tested by operating the switch arrangement to selectively connect only said photodetector to the signal strength detector and wherein the signal used for determining whether a photodetector received a signal, correspond to a preamble (310) of a data packet (300) of an OWC protocol.

2. An OWC transceiver apparatus (100) according to claim 1, wherein the plurality of photodetectors (111) consists of N photodetectors, with 2 < N < 8.

3. An OWC transceiver apparatus (100) according to claim 1, wherein the number of photodetectors (111) is the same as the number of light sources (121).

4. An OWC transceiver apparatus (100) according to claim 1, wherein the sequence is a predefined sequence.

5. An OWC transceiver apparatus (100) according to claim 1, wherein the sequence is a random sequence.

6. An OWC transceiver apparatus (100) according to any of claims 1 to 5, wherein the OWC transceiver apparatus is configured to perform said testing according to a predefined schedule.

7. An OWC transceiver apparatus (100) according to any of claims 1 to 6, comprised in an endpoint device (250) of an OWC network wherein each of the plurality of photodetectors represents a segment of a segmented photodetector located on one side of the endpoint device.

8. An OWC transceiver apparatus (100) according to claim 7, wherein the optical wireless transceiver apparatus is configured to perform said testing in response to input from a motion sensor of the endpoint device (250).

9. An OWC transceiver apparatus (100) according to any of claims 1 to 8, comprised in an access point (140) of an OWC network wherein each of the plurality of photodetectors represents a segment of a segmented photodetector located on one side of the access point device.

10. An OWC transceiver apparatus (100) according to claim 9, wherein the OWC transceiver apparatus is configured to perform said testing in response to input from a motion sensor of an endpoint device (250) of the OWC network.

11. A system comprising an OWC transceiver apparatus (100) according to claim 7 or claim 8 and an access point (140) of the OWC network.

12. A system comprising an OWC transceiver apparatus (100) according to claim 9 or claim 10 and an endpoint device of the OWC network.

13. A method performed by an optical wireless communication, OWC, transceiver apparatus (100), wherein the OWC transceiver apparatus (100) comprises: a plurality of photodetectors (111) for receiving, as modulated light signals, data packets having at least a preamble (310) and a data portion (320), each photodetector having a different respective reception field of view (210) for reception of modulated light signals; and a plurality of light sources (121) for transmitting modulated light signals, each light source having a different respective transmission field of view for transmission of modulated light signals; the method comprising: testing each of the photodetectors using a signal strength detector (114), while receiving a signal of a data packet, to determine whether that photodetector is receiving the signal with a signal strength above a threshold signal strength; and activating at least one of the light sources that has a transmission field of view corresponding to a reception field of view of a tested photodetector determined to have received the signal with a signal strength above the threshold signal strength and de-activate the light sources not activated, the method characterized in that: testing each photodetector in sequence, wherin a photodetector is tested by operating a switch arrangement (112) to selectively connect only that photodetector (111) to the signal strength detector (114) and wherein the signal used for determining whether a photodetector received a signal, correspond to a preamble (310) of a data packet (300) of the OWC protocol.

14. A computer program product comprising instructions for performing the method according to claim 13 when executed on a controller (130) of an optical wireless communication, OWC, transceiver apparatus (100) of claim 1.