Patent Description:
"Light Fidelity," also referred to as "Li-Fi," is a high-speed wireless communication technology, in which data is transmitted over a light channel. Li-Fi devices may operate over the visible and invisible (ultraviolet and infrared) light spectrums.

<CIT> discloses a hybrid communication system based on WiFi and LiFi, comprising a modulation and demodulation device, a WiFi signal transceiver, and a visible light signal transceiver; the modulation and demodulation device being configured to access signals through network cables and modulates the received signals; thereafter, the signals are respectively transmitted to the WiFi signal transceiver device and the visible light signal transceiver device, and are emitted by the WiFi signal transceiver device and the visible light signal transceiver device; the WiFi signal transceiver device being configured to receive the WiFi signal and to transmit the received WiFi signal to the modem device to demodulate the original signal; the visible light signal transceiver device can also convert the received visible light signal into a radio frequency signal and transmit it to the modulation and demodulation device to demodulate the original signal so as to realize the two-way transmission of WiFi communication and LiFi communication.

According to an aspect of the present invention, there is provided a wireless LAN Li-Fi transceiver as set out in the first of the appended independent claims. According to another aspect of the present invention, there is provided a method for wireless communication as set out in the second of the appended independent claims. Features of various embodiments are set out in the appended dependent claims.

These and other embodiments will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which:.

Embodiments that are described herein provide methods and systems for implementing a wireless Li-Fi transceiver by reusing elements designed for Wi-Fi devices.

Wireless light communication may be advantageous compared to radio communication in various aspects. For example, the light spectrum (as used, e.g., in Li-Fi) is much wider compared to the Radio Frequency (RF) spectrum (as used, e.g., in Wi-Fi), offers higher data rates, and is usable in areas susceptible to electromagnetic interference such as aircrafts and hospitals. Moreover, communication over light supports data densities that are significantly higher than in RF, due to the almost unlimited bandwidth of the visible/invisible light spectrum. Light communication also provides enhanced physical layer security by directing a narrow light beam to selected directions. With the advent of the Power-over-Ethernet (PoE) technology and its usage in lighting, backhaul connectivity to the Internet may be implemented using a light source and a Li-Fi modem.

In Li-Fi devices, data is typically communicated over light by (i) driving an optical emitter such as a Light Emitting Diode (LED) with a data-carrying signal in the transmit direction, and (ii) converting a data-carrying light beam into an electrical signal using a photo detector device in the receive direction.

In the present context and in the claims, the term "Wi-Fi RF band, or simply "RF band" for brevity, refers to herein as a frequency band in the RF spectrum specified for Wi-Fi. Similarly, the term "Li-Fi optical band" or simply "optical band" for brevity, refers to herein as a frequency band in the visible or invisible light spectrum specified for Li-Fi.

In the embodiments that will be described below, elements of a Wi-Fi device are reused in implementing a Li-Fi transceiver. The Wi-Fi device operates in accordance with Wi-Fi standards specified, for example, in the IEEE <NUM> family of standards. The IEEE <NUM>. 11bb Task Group on Light Communications focuses on modifications to the base IEEE <NUM> standards required to enable communications in the light medium. A conventional Wi-Fi device typically generates a real Wi-Fi signal by first generating a Base Band (BB) complex signal comprising In-phase and Quadrature (I/Q) signals. The I/Q signals are up-converted to a suitable Wi-Fi RF band, such as the <NUM> band or the <NUM> RF band specified in the IEEE <NUM> family of standards, and are combined to generate the real Wi-Fi signal for transmission via a RF antenna. The Wi-Fi device may be implemented using a Wi-Fi baseband (BB) module that handles the MAC and PHY layers, and a Wi-Fi RF module that handles frequency conversion between baseband and RF.

In contrast, a Li-Fi signal comprises a real baseband signal that drives a light source such as a LED. In principle, a Li-Fi transceiver could generate the real Li-Fi signal directly and independently from any Wi-Fi device or Wi-Fi specifications.

Embodiments that will be described in detail below make use of elements of a Wi-Fi transceiver in implementing a Li-Fi transceiver, which is advantageous, e.g., in terms of cost and design effort.

Consider a Wireless LAN (WLAN) Li-Fi transceiver, comprising a Wi-Fi device and an Analog Front-End (AFE). The Wi-Fi device is configured to produce a spatial stream carrying data, and to produce from the spatial stream In-phase and Quadrature (I/Q) signals for transmission over a radio channel having a predefined Radio Frequency (RF) band. The AFE is configured to modify the I/Q signals, or modify operation of the Wi-Fi device, for producing a real Li-Fi signal in a predefined optical band, and to transmit the data carried by the spatial stream to a remote Li-Fi receiver by driving an optical emitter (e.g., a LED) with the real Li-Fi signal.

As will be described in detail below, the Li-Fi transceiver may be implemented in various embodiments, and each such embodiment may reuse different parts of the Wi-Fi device, as will be described below.

In some embodiments, the Wi-Fi device comprises a frequency converter configurable to produce the I/Q signals in the RF band or in the optical band, and to combine the I/Q signals to produce a real signal in the RF band or optical band. In such embodiments, the AFE is configured to modify operation of the Wi-Fi device by configuring the frequency converter to produce the I/Q signals in the optical band (and not in the RF band). In an embodiment of this sort, a Wi-Fi RF module of the Wi-Fi device is modified to be reused for Li-Fi.

In some embodiments, the Wi-Fi device is configured to produce from the I/Q signals a real Wi-Fi signal in the RF band (using frequency up-conversion), and the AFE comprises a frequency down-converter, configured to down convert the real Wi-Fi signal from the RF band to the optical band. In these embodiments, the Li-Fi transceiver may generate the Wi-Fi real signal by reusing a Wi-Fi RF module of a Wi-Fi device.

In yet other embodiments, the Wi-Fi device is configured to operate in a partial-bandwidth mode, in which the <NUM>/Q signals occupy only part (e.g., half <NUM>/<NUM> or quarter <NUM>/<NUM>) of an allocated channel bandwidth. In these embodiments, the AFE is configured to produce the real Li-Fi signal based only on an I signal component or on a Q signal component of the I/Q signals.

In some embodiments, the Wi-Fi device (e.g., the PHY subsystem of the Wi-Fi device) is configured to produce complex-valued signals comprising OFDM symbols, and to produce the I/Q signals based on respective real and imaginary components of the complex-valued signals.

In some embodiments, the AFE is configured to receive from the remote Li-Fi receiver, via a photo detector, an uplink real Li-Fi signal in the optical band, and to produce from the uplink real Li-Fi signal, uplink I/Q signals, wherein the Wi-Fi device is configured to process the uplink I/Q signals for extracting data carried in the uplink real Li-Fi signal.

In some embodiments, the Wi-Fi device is configured to connect to an optical interface for communicating over Li-Fi, or to a RF interface for communicating over Wi-Fi, wherein the Wi-Fi device is configured to produce a real Wi-Fi signal in the RF band, the optical interface is configured to apply frequency conversion between the RF band of the real Wi-Fi signal and the optical band, and the RF interface is configured to connect between the Wi-Fi device and a RF antenna.

A WLAN transceiver supporting both Li-Fi and Wi-Fi may select communication over Li-Fi and/or over Wi-Fi in various ways. In an example embodiment, the WLAN transceiver operates over Li-Fi, and when communication over Li-Fi fails, e.g., due to blocking the light channel, switches to communicate over Wi-Fi. In some alternative embodiments, the AFE is configured to communicate the real Wi-Fi signal via both the optical interface and the RF interface, in parallel. Other suitable methods for dynamically switching between Li-Fi and Wi-Fi communication based on suitable criteria can also be used.

In the disclosed techniques, a Li-Fi transceiver that communicates over a light channel is implemented by reusing elements of a Wi-Fi device designed to communicate over a radio channel. The Wi-Fi device produces a complex signal comprising I/Q signals. The I/Q signals and/or operation of the Wi-Fi device are modified to produce a real Li-Fi signal suitable for driving a light emitting device. By reusing elements of a Wi-Fi device, development effort and product cost of the Li-Fi transceiver are reduced significantly.

<FIG> is a block diagram that schematically illustrates a wireless Li-Fi system <NUM> implemented by reusing Wi-Fi elements, in accordance with an embodiment that is described herein.

Li-Fi system <NUM> comprises a Li-Fi transceiver <NUM> coupled to an optical interface <NUM> for bidirectional communication with remote Li-Fi devices (not shown) over a wireless light channel <NUM>. Optical interface <NUM> comprises an optical emitter <NUM> that converts electrical signal carrying data into light in a predefined optical band, and a photo detector <NUM> that receives light signal carrying data in the predefined optical band and converts the light signal into an electrical signal. In the present example, optical emitter <NUM> comprises a Light Emitting Diode (LED). Alternatively, other suitable optical emitters can be used, such as, for example, a Laser diode. Photo detector <NUM> may comprise any type of photo detector or photo sensor such as, for example, an avalanche Photo Diode (APD).

In the present context and in the claims, the term "optical band" refers to a frequency range in one or more of the visible-light spectrum, the infrared spectrum and the ultraviolet spectrum, specified for Li-Fi communication.

Li-Fi system <NUM> may be used in various wireless applications such as in environments that are sensitive to electromagnetic interference, indoor secure communications via light and wireless communication, e.g., via streetlights, to name a few. Another example usage of Li-Fi is a lighting system in airplanes that provides both illumination and user access to the Internet.

Li-Fi transceiver <NUM> may comprise an Access Point for wireless communication over light with remote Li-Fi client stations. Alternatively, Li-Fi transceiver <NUM> may comprise a Li-Fi client station that communicates over light with a Li-Fi AP and/or with one or more other Li-Fi devices.

In the example of <FIG>, Li-Fi transceiver <NUM> comprises a Wi-Fi Baseband (BB) <NUM> coupled to a Li-Fi Analog Front End (AFE) <NUM>. In some embodiments, Wi-Fi BB <NUM> is implemented in accordance with the IEEE <NUM> family of standards. In the transmit direction, Wi-Fi BB <NUM> produces TX In-Phase and Quadrature (I/Q) signals, from which Li-Fi AFE <NUM> produces a TX real Li-Fi signal for driving LED <NUM>. In the receive direction, Li-Fi AFE <NUM> receives a RX real Li-Fi signal via photo detector <NUM> and produces from the RX real Li-Fi signal RX I/Q signals to be processed by Wi-Fi BB <NUM> for recovering data carried in the received RX real Li-Fi signal.

In the example of <FIG>, Wi-Fi BB <NUM> and at least part of Li-Fi AFE <NUM> are comprised in a Wi-Fi device <NUM>, depicted in dashed lines. Wi-Fi device <NUM> is designed to communicate Wi-Fi signals over a radio channel having a predefined Wi-Fi RF band, e.g., in accordance with the IEEE <NUM> family of standards. As will be described in detail below, in various embodiments of Li-Fi transceiver <NUM>, relevant elements of Wi-Fi device <NUM> are shared with Li-Fi AFE <NUM>.

Wi-Fi BB <NUM> comprises a MAC subsystem <NUM> comprising a MAC TX <NUM>, a MAC RX <NUM> and a MAC controller <NUM>. Wi-Fi BB <NUM> further comprises a PHY subsystem <NUM> comprising a PHY TX <NUM>, a PHY RX <NUM> and an Automatic Gain Control (AGC) <NUM>. In some embodiments, MAC subsystem <NUM> and PHY subsystem <NUM> implement a MAC sublayer and a PHY sublayer, respectively, e.g., in accordance with the IEEE <NUM> standards.

The MAC sublayer executed by MAC subsystem <NUM> coordinates access to the shared physical air interface for using time and frequency resources effectively. In the present context, the term "air interface" refers to the communication link between Li-Fi system <NUM> and the remote Li-Fi devices over the optical band. As will be described further below, in some transceiver configurations, the "air interface" is used for both light communication over a Li-Fi optical band and for radio communication over a Wi-Fi RF band.

In the transmit direction, MAC TX <NUM> receives data from a higher sublayer, referred to as Logical Link Control (LLC). Alternatively or additionally, MAC TX <NUM> produces the data internally. MAC TX constructs MAC frames containing the data, header and tail fields, and sends the MAC frames to PHY TX <NUM> that produces from the MAC frames packets for transmission via the Li-Fi AFE. The packets are typically protected using a suitable Error Correction Code (ECC), as will be described below. In the receive direction, PHY RX <NUM> provides packets received vi the Li-Fi AFE to MAC RX <NUM>, which processes the packets to recover the MAC frames, and extract data contained in the MAC frames. AGC <NUM> controls the gain along the reception path by controlling the gain of one or more elements in Li-Fi AFE <NUM>, as will be described below. When a packet is received in error at the remote station, MAC subsystem <NUM> may coordinate retransmission of the corresponding MAC frame.

In some embodiments, MAC subsystem <NUM> handles multiple access using methods such as carrier sensing, packet detection and random back-off, to avoid collisions among multiple users of the air interface.

Li-Fi AFE <NUM> comprises an AFE TX <NUM>, an AFE RX <NUM> and a Local Oscillator (LO) <NUM>. AFE TX <NUM> produces from the TX I/Q signals of Wi-Fi BB <NUM>, a TX real Li-Fi signal for driving LED <NUM>. AFE RX <NUM> receives a RX real Li-Fi signal from photo detector <NUM>, and produces from the RX real Li-Fi signal RX I/Q signals to be processed by Wi-Fi BB <NUM>. LO <NUM> generates a LO signal that AFE TX <NUM> and AFE RX <NUM> use for frequency up/down-conversion between baseband and a desired frequency band, as will be described in detail below.

In some embodiments, LO <NUM> is configurable to produce a Li-Fi LO signal for communication over a Li-Fi optical band or a Wi-Fi LO signal for communication over a Wi-Fi RF band. This allows reusing a Wi-Fi device modified to support both modes for Li-Fi communication, by configuring LO <NUM> to generate the Li-Fi LO signal.

<FIG> is a block diagram that schematically illustrates a PHY subsystem <NUM>, implementing the physical layer of Li-Fi transceiver <NUM> of <FIG>, in accordance with an embodiment that is described herein.

PHY subsystem <NUM> comprises a PHY TX <NUM> and a PHY RX <NUM>, which may be used, for example, in implementing PHY TX <NUM> and PHY RX <NUM> of PHY subsystem <NUM>.

The data path in PHY subsystem <NUM> comprises a framing module <NUM>, a Forward Error Correction (FEC) module <NUM>, a frequency-domain processing module <NUM>, a Fast Fourier Transform (FFT) processor <NUM>, a time-domain processing module <NUM>, a Digital to Analog Converter (DAC) <NUM> and an Analog to Digital Converter (ADC) <NUM>.

In the transmit direction (within PHY TX <NUM>) framing module <NUM> receives data from MAC subsystem <NUM>, e.g., in the form of MAC frames. Framing module <NUM> adds to the MAC frames one or more preamble fields to produce packets for transmission. The preamble fields are typically used by the remote receiver for synchronization and channel estimation. The actual preamble fields and their formatting typically depends on the type of the underlying packets.

FEC module <NUM>, encodes the packet payload using a suitable Error Correction Code (ECC). In accordance with some IEEE <NUM> standards, the ECC may be configured to use a Binary Convolutional Code (BCC) or a Large-Density Parity-Check (LDPC) code. Frequency-domain processing module <NUM> maps bits in one or more spatial streams into constellation points and performs spatial expansion. "Nsc" in the figure denotes the number of subcarriers.

Further in the transmit direction, FFT processor <NUM> transforms frequency-domain signals output by frequency-domain processing module <NUM> into time-domain signals, using a complex-to-complex Inverse FFT (IFFT) operation. The signals output by the IFFT are complex-valued signals comprising In-phase and Quadrature components (I/Q) signals. In some embodiments, the I/Q signals carry the transmitted data modulated in symbols referred to as Orthogonal Frequency-Division Multiplexing (OFDM) symbols.

Time-domain processing module <NUM> up-samples the I/Q signals and filters the up-sampled I/Q signals using a TX Front-End (FE) filter, e.g., a Low Pass Filter (LPF), to exclude frequencies outside the frequency band allocated for transmitting the underlying packet. In some embodiments, the TX FE filter has a cutoff frequency of <NUM>, <NUM> or <NUM>. In an embodiment a cutoff frequency <NUM> is also supported, for a <NUM> bandwidth. DAC <NUM> converts the filtered I/Q signals to analog form denoted TX I/Q signals, to be input to Li-Fi AFE <NUM>.

In the receive direction (within PHY RX <NUM>), ADC <NUM> receives from Li-Fi AFE <NUM> I/Q signals denoted RX I/Q signals and converts them into digital form. Time-domain processing module <NUM> filters and down-samples the RX I/Q signals, in accordance with the configured bandwidth (e.g., <NUM>, <NUM> or <NUM>). FFT processor <NUM> converts the down-sampled RX I/Q signals into frequency domain using a complex-to-complex FFT operation. Frequency-domain processing module <NUM> applies equalization operation to the I/Q signals produced by the FFT to recover the underlying constellation points, and de-maps the constellation points into data bits. In some embodiments, the equalization operation is implemented using an equalizer having multiple taps. In such embodiments, frequency-domain processing module <NUM> calculates the equalizer taps, e.g., by performing channel estimation and smoothing, as depicted, for example, in <FIG>.

The RX I/Q signals received via Li-Fi AFE <NUM> carry packets encoded using an ECC comprising, for example, a BCC or a LDPC code. FEC module <NUM> decodes the ECC of the packets to recover the un-coded packets, e.g., using any suitable decoder of the underlying ECC. For example, in some embodiments, when the packets are encoded using BCC, the packets may be decoded using a Viterbi decoder. Alternatively, when the packets are encoded using the LDPC code, the packets may be decoded using a suitable LDPC decoder. Framing module <NUM> identifies packet type, e.g., by inspecting the preamble and/or headers of the received packet and sends the packet with relevant parameters that are based on the packet type to MAC subsystem <NUM>.

In some embodiments, time-domain processing module <NUM> further comprises an AGC <NUM> and a Radio Controller (RC) <NUM> that produce control signal(s) to AFE RX <NUM>. AGC <NUM> may be used in implementing AGC <NUM> of <FIG>. AGC <NUM> receives I/Q signals from ADC <NUM>, down-sampled I/Q signals from time-domain processing module <NUM> or both. AGC <NUM> estimates a reception level from the I/Q signals and produces, based on the estimated reception level, an AGC control signal for adjusting reception gain in AFE RX <NUM>. For example, the AGC control signal may be used for adjusting the gain of one or more amplifiers in RX AFE <NUM>. In some embodiments, RC <NUM> produces a RC control signal for selecting a required bandwidth (e.g., cutoff frequency) for one or more filters within RX AFE <NUM>, as will be described below.

Next are described various example embodiments that may be used for implementing Li-Fi AFE <NUM>. In the description that follows, "Wi-Fi_FREQ" denotes the center frequency of a Wi-Fi RF band, and "Li-Fi_FREQ" denotes the center frequency of a Li-Fi optical band.

<FIG> is a block diagram that schematically illustrates a Li-Fi Analog Front End (AFE) <NUM>, implemented using a modified Wi-Fi Radio Frequency (RF) module, in accordance with an embodiment that is descried herein. <FIG> are diagrams that schematically illustrate spectral density functions of I/Q signals and Li-Fi signals processed in Li-Fi AFE <NUM> of <FIG>, in accordance with an embodiment that is descried herein.

Li-Fi AFE <NUM> of <FIG> comprises an AFE TX <NUM> for Li-Fi transmission and an AFE RX <NUM> for Li-Fi reception, which may be used in implementing respective AFE TX <NUM> and AFE RX <NUM> of <FIG>.

AFE TX <NUM> and AFE RX <NUM> of Li-Fi AFE <NUM> use an architecture that generally resembles that of a Wi-Fi device (such as Wi-Fi device <NUM>), which converts between baseband I/Q signals and Wi-Fi signals in a Wi-Fi RF band. In Li-Fi AFE <NUM>, however, the architecture of the Wi-Fi device (or of a Wi-Fi module comprised in the Wi-Fi device) is modified for generating Li-Fi signals in a Li-Fi optical band instead of Wi-Fi signals in the Wi-Fi RF band.

AFE TX <NUM> comprise a TX filter <NUM>, mixers <NUM>, a signal combiner <NUM> and a TX Power Amplifier (PA) <NUM>. AFE RX <NUM> comprises a RX filter <NUM>, mixers <NUM> and a Low-Noise Amplifier (LNA) <NUM>. Li-Fi AFE <NUM> further comprises a configurable LO <NUM> that supports converting baseband I/Q signals into a real Li-Fi signal in the Li-Fi optical band, as will be described below. LO <NUM> produces a <NUM>-gegree and a <NUM>-degree LO signals having a frequency denoted LO_FREQ.

In a conventional Wi-Fi device, the LO signal is tuned to generate a Wi-Fi signal in the desired Wi-Fi RF band by generating LO signals having a frequency LO_FREQ=Wi-Fi_FREQ. In some embodiments, unlike a conventional Wi-Fi device, LO <NUM> comprises a dual-purpose LO that supports two different LO_FREQ frequencies. In one configuration LO <NUM> generates a Wi-Fi signal in the Wi-Fi RF band centered about Wi-Fi_FREQ. In the other configuration, LO <NUM> generates a Li-Fi signal in a Li-Fi optical band centered about Li-Fi_FREQ. In such embodiments, for Li-Fi communication, dual-purpose LO <NUM> is configured to LO_FREQ=Li-Fi_FREQ.

In the transmit direction, TX filter <NUM> receives TX I/Q signals from PHY subsystem <NUM>. In the present example, the TX I/Q signals together comprise a complex signal in baseband. A spectral density function <NUM> of an example I/Q complex baseband signal having a bandwidth BW is depicted in the <FIG>. Spectral density function <NUM> is centered about the zero frequency, and typically has an asymmetric shape. In the present example, BW may be configured to <NUM>, <NUM>, <NUM>. In some embodiments, BW may be also configured to <NUM>.

TX Filter <NUM> filters the TX I/Q signals to exclude spectral content outside the BW band, e.g., above BW/<NUM> and below -BW/<NUM>. Using the <NUM>-degree and <NUM>-degree LO signals, mixers <NUM> up-convert the filtered TX I/Q signals to Li-Fi_FREQ, by configuring LO <NUM> to LO_FREQ=Li-Fi_FREQ>BW/<NUM>. Signal combiner <NUM> combines the up-converted I/Q signals to produce a real signal, which TX PA <NUM> amplifies to produce a real Li-Fi signal that drives LED <NUM>. A spectral density function <NUM> of the real Li-Fi signal corresponding to the TX I/O signals having spectral density function <NUM>, is depicted in <FIG>. Spectral density <NUM> has positive and negative parts, centered about respective frequencies Li-Fi_FREQ and (-Li Fi_FREQ), and having a bandwidth BW. Note that Li-Fi_FREQ should be larger than BW, as noted above.

In the receive direction, RX LNA <NUM> receives from photo detector <NUM> a real Li-Fi signal in the Li-Fi optical band and amplifies the real Li-Fi signal to be input to mixers <NUM>. The received real Li-Fi signal may have a spectral density function <NUM>, for example. Using the <NUM>-degree and <NUM>-degree LO signals of LO <NUM> configured to LO_FREQ=Li-Fi_FREQ, mixers <NUM> down-convert the real Li-Fi signal to baseband, thus producing an I signal (based on <NUM>-degree LO signal) and a Q signal (based on <NUM>-degree LO signal). RX filter <NUM> filters the down-converted I/Q signals to exclude spectral content outside the relevant band, e.g., having frequencies above BW/<NUM> and below -BW/<NUM>. The filtered I/Q signals, denoted RX I/Q signals, are sent to PHY subsystem <NUM>. In the present example, the RX I/Q signals have a spectral density function <NUM>, corresponding to spectral density function <NUM> of the received Li-Fi signal.

In some embodiments, Li-Fi AFE <NUM> receives (e.g., from the PHY RX <NUM>) control signals <NUM> comprising, for example, an AGC control signal, a RC control signal or both. In some embodiments, the AGC control signal is produced by AGC <NUM> and is used for adjusting the gain of RX LNA <NUM>. In some embodiments, in addition to RX filter <NUM> RX, PHY <NUM> comprises a Variable Gain Amplifier (VGA) (not shown) that amplifies the RX I/Q signals based on the AGC control signal. In some embodiments, the RC control signal is produced by RC <NUM> of PHY RX <NUM>, and is used for selecting a bandwidth cutoff frequency such as BW/<NUM> in RX filter <NUM>, among BW bandwidths <NUM>, <NUM>, <NUM> and possibly <NUM>.

In an embodiment, in which Li-Fi AFE <NUM> comprises a Wi-Fi RF module modified to comprise a LO <NUM> that supports both Wi-Fi and Li-Fi, LO <NUM> is configured to LO_FREQ=Li-Fi_FREQ for generating the Li-Fi signal. Alternatively, Li-Fi AFE <NUM> comprises a Wi-Fi RF module, modified to comprise LO <NUM> that supports producing an LO signal only for Li-Fi communication. In this case, the Wi-Fi RF module is modified by replacing a LO device of the W-Fi RF module that supports producing only a LO signal for W-Fi communication, with LO <NUM> that supports producing a LO signal for Li-Fi communication.

<FIG> is a block diagram that schematically illustrates a Li-Fi AFE <NUM>, implemented using a two-step frequency conversion, in accordance with an embodiment that is descried herein. <FIG> are diagrams that schematically illustrate spectral density functions of respective I/Q signals, Wi-Fi signals and Li-Fi signals processed in Li-Fi AFE <NUM> of <FIG>, in accordance with an embodiment that is descried herein.

In <FIG>, Li-Fi AFE <NUM> comprises an AFE TX <NUM> for Li-Fi transmission and an AFE RX <NUM> for Li-Fi reception, which may be used for implementing respective AFE TX <NUM> and AFE RX <NUM> of <FIG>. In the example of <FIG>, the implementation of AFE TX <NUM> and AFE RX <NUM> is partitioned between a Wi-Fi RF module <NUM> (of a Wi-Fi device) and a RF/Li-Fi converter <NUM>, which together perform a two-step frequency conversion between baseband and a Li-Fi optical band, as will be described below.

In some embodiments, Wi-Fi RF module <NUM> performs frequency conversion between baseband and a selected Wi-Fi RF band, whereas RF/Li-Fi module <NUM> converts between the selected Wi-Fi RF band and the Li-Fi optical band. In the embodiment of <FIG> conversion between baseband and the Li-Fi optical band involves a two-step frequency conversion via the intermediate Wi-Fi RF band.

Wi-Fi RF module <NUM> has a similar architecture to that Li-Fi AFE <NUM> of <FIG>. The data flows in the transmit and received directions described for Li-Fi AFE <NUM> are therefore generally applicable to Wi-Fi RF module <NUM>, as well. Wi-Fi RF module <NUM>, however, supports frequency conversion between baseband and Wi-Fi signals in a selected Wi-Fi RF band, and not between baseband <NUM>/Q signals and a Li-Fi optical band, as in AFE <NUM>. To this end, Wi-Fi RF module <NUM> comprises a LO <NUM> that generates <NUM>-degree and <NUM>-degree LO signals for frequency up-conversion and down-conversion between baseband and the selected Wi-Fi RF band. In the present example, LO <NUM> is tuned to the <NUM> Wi-Fi RF band of the IEEE <NUM> family of standards. Alternatively, other Wi-Fi bands such as the <NUM> band can also be used. In the present embodiment, Wi-Fi RF module <NUM> thus comprises a Wi-Fi RF module of a conventional Wi-Fi device.

<FIG> depicts an example spectral density function <NUM> of TX and RX I/Q signals in baseband having a bandwidth BW (similarly to spectral density <NUM> of <FIG>). <FIG> depicts a spectral density function <NUM> of a Wi-Fi signal corresponding to the baseband TX I/Q and RX I/Q signals having spectral density function <NUM>, in a Wi-Fi RF band centered about Wi-Fi_FREQ.

RF/Li-Fi converter <NUM> mediates between the Wi-Fi RF band and the Li-Fi optical band. RF/Li-Fi converter <NUM> comprises mixers <NUM>, a second LO <NUM>, a TX LPF <NUM> and a RX LPF <NUM>. Second LO <NUM> generates <NUM>-degree and <NUM>-degree LO signals at a frequency Wi-Fi_FREQ-Li-Fi_FREQ. Note that LO_FREQ should satisfy the expression LO_FREQ<Wi-Fi_FREQ-BW/<NUM>.

In the transmit direction, using the LO signal of second LO <NUM>, mixer <NUM> down-converts the real Wi-Fi signal generated by Wi-Fi RF module <NUM> to a Li-Fi signal in the Li-Fi optical band, centered about Li-Fi_FREQ. TX LPF <NUM> filters the down-converted signal to include the spectral content of the Li-Fi signal and exclude frequencies outside the Li-Fi optical band. <FIG> depicts a spectral density <NUM> of the resulting real Li-Fi signal (similar to spectral density function <NUM> of <FIG> above).

In the receive direction, RF/Li-Fi converter receives a real Li-Fi signal from photo detector <NUM>. RX LPF <NUM> filters the real Li-Fi signal to exclude spectral content having frequencies outside the Li-Fi optical band. Using the LO signal of second LO <NUM>, a mixer <NUM> up-converts the Li-Fi signal from the Li-Fi optical band to the Wi-Fi RF band centered about Wi-Fi_FREQ, as depicted in <FIG>. Wi-Fi RF module <NUM> down-converts the Wi-Fi signal to baseband, to produce RX I/Q signals having spectral density function <NUM>.

<FIG> is a block diagram that schematically illustrates a Li-Fi transceiver <NUM> in which a Li-Fi signal is produced from only the I component of a complex signal produced by a PHY subsystem configured to operate in a partial-bandwidth mode, in accordance with an embodiment that is described herein. <FIG> are diagrams that schematically illustrate spectral density functions of complex signals in a partial-bandwidth mode of the PHY subsystem and Li-Fi signals processed in Li-Fi transceiver <NUM> of <FIG>, in accordance with an embodiment that is descried herein.

Li-Fi transceiver <NUM> comprises a Wi-Fi BB <NUM> and a Li-Fi AFE <NUM>. Li-Fi transceiver <NUM> may be used for implementing Li-Fi transceiver <NUM> of <FIG>, in which Wi-Fi BB <NUM> implements Wi-Fi BB <NUM> and Li-Fi AFE <NUM> implements Li-Fi AFE <NUM>.

Wi-Fi BB <NUM> comprises a MAC TX <NUM>, a PHY TX <NUM>, a MAC RX <NUM>, a PHY RX <NUM> an AGC <NUM>, and a MAC controller <NUM>. Wi-Fi BB <NUM> is essentially similar to Wi-Fi BB <NUM> that comprises similar respective elements, as described above with reference to <FIG>.

In Li-Fi transceiver <NUM>, MAC controller <NUM> (or another processor of the Li-Fi transceiver, not shown) configures PHY TX <NUM> and PHY RX <NUM> to operate in a mode referred to herein as a "partial-bandwidth" mode. In the partial-bandwidth mode, PHY TX <NUM> produces, and PHY RX <NUM> receives a complex signal having a bandwidth smaller than the bandwidth BW allocated for the underlying channel. In the present example, the partial bandwidth used is denoted BWH, wherein BWH=BW/<NUM>, and the BWH band is centered about the frequency Li-Fi_FREQ, as depicted, for example, in spectral density function <NUM> in <FIG>. For example, for a channel BW of <NUM>, <NUM> and <NUM>, the respective partial bandwidth BWH is given by <NUM>, <NUM> and <NUM>. Note that in the present embodiment, Li-Fi_FREQ should be larger than BWH/<NUM>. Using half the bandwidth is given by way of example and is not mandatory. In alternative embodiments, other partial-bandwidth configurations can be used, e.g., using a BW/<NUM> partial bandwidth mode. As another example, in a <NUM>/<NUM> partial bandwidth mode, <NUM> out of <NUM> may be used.

Li-Fi AFE <NUM> comprises a TX filter <NUM>, a TX PA <NUM>, a RX filter <NUM> and a RX LNA <NUM>. TX PA <NUM> and RX LNA <NUM> may be identical or similar to TX PA <NUM> and RX LNA <NUM> of <FIG>. TX filter <NUM> and RX filter <NUM> are similar to respective TX filter <NUM> and RX filter <NUM> of <FIG>, but are configured to process a real signal rather than a complex signal comprising I/Q signals as in <FIG>.

In the transmit direction, TX filter <NUM> receives only the I component of the complex signal generated by PHY TX <NUM>. The I component comprises a real Li-Fi signal having a spectral density function <NUM>, as depicted in <FIG>. TX PA <NUM> amplifies the real Li-Fi signal for driving LED <NUM>. In the receive direction, RX LNA <NUM> receives from photo detector <NUM> a real Li-Fi signal having, for example, a spectral density function <NUM> and amplifies the received Li-Fi signal. RX filter <NUM> filters the amplified signal to exclude frequencies outside the Li-Fi optical band and sends the filtered signal as an I component to PHY RX <NUM>, which recovers the corresponding complex signal having a spectral density <NUM>.

The complexity of Li-Fi AFE <NUM> is very low because Li-Fi AFE <NUM> does not perform any frequency conversion, which typically involves using elements such as a LO and mixers.

Although Li-Fi transceiver <NUM> in <FIG> is based on the I component of a complex I/Q signal, a similar Li-Fi transceiver may be implemented based only on the Q component.

<FIG> is a block diagram that schematically illustrates a WLAN transceiver <NUM> that supports both Li-Fi and Wi-Fi communication, in accordance with an embodiment that is described herein.

WLAN transceiver <NUM> comprises a Wi-Fi device <NUM> comprising a Wi-Fi BB <NUM> coupled to a Wi-Fi RF module <NUM>. WLAN transceiver <NUM> further comprises a RF/Li-Fi converter <NUM> and a Wi-Fi antenna interface <NUM>. In some embodiments, Wi-Fi device <NUM> connects to one of RF/Li-Fi converter <NUM> and Wi-Fi antenna interface <NUM>, or to both, e.g., using a switching circuit (not shown) so that at any given time WLAN transceiver <NUM> may communicate over a Li-Fi optical band, over a Wi-Fi RF band, or both.

Wi-Fi BB <NUM> functions similarly to Wi-Fi BB <NUM> of <FIG>, and comprises similar elements such as a MAC TX, a MAC RX, a PHY TX, a PHY RX and an AGC. Wi-Fi BB <NUM> comprises a MAC controller <NUM> that is similar to MAC controller <NUM> of <FIG>. Among other tasks, MAC controller <NUM> selects communication over Li-Fi, Wi-Fi, or both, e.g., using a suitable selection signal <NUM>.

When WLAN transceiver <NUM> is configured to Li-Fi communication, Wi-Fi RF module <NUM> and RF/Li-Fi converter together function as a Li-Fi AFE <NUM>, similarly to Li-Fi AFE <NUM> with Wi-Fi RF module <NUM> and RF/Li-Fi converter <NUM>, as described with reference to <FIG> above.

Wi-Fi antenna interface comprises a TX antenna interface <NUM>, a RX antenna interface <NUM> and an antenna switch <NUM> coupled to one or more RF antennas <NUM>. When WLAN transceiver <NUM> is configured to communicate over Wi-Fi, in the transmit direction, antenna switch <NUM> connects between Wi-Fi TX antenna interface <NUM> and antennas <NUM> for transmitting a Wi-Fi signal generated by Wi-Fi RF module <NUM>. In the receive direction, switch <NUM> connects between antennas <NUM> and Wi-Fi RX antenna interface <NUM> for sending a received Wi-Fi signal to Wi-Fi RF module <NUM>.

In some embodiments, WLAN transceiver <NUM> operates in a Wi-Fi Multiple-In Multiple-Out (MIMO) configuration, in which transmission and reception of Wi-Fi signals is carried out via multiple antennas <NUM>. In such embodiments, Wi-Fi RF module <NUM> comprises multiple TX chains and multiple RX chains, e.g., a pair of a TX chain and a RX chain per Wi-Fi antenna (not shown). In such embodiments, the antenna switch supports switching between the multiple antennas and the relevant TX chains and RX chains.

The configurations of wireless Li-Fi system <NUM> shown in <FIG> and <FIG>, including various Wi-Fi device and AFE configurations shown in <FIG>, <FIG> and <FIG>, and the configuration of WLAN transceiver <NUM> shown in <FIG> are example configurations, which are chosen purely for the sake of conceptual clarity. In alternative embodiments, any other suitable Li-Fi system, Wi-Fi device, AFE and WLAN transceiver configurations can be used.

The division of functions among Wi-Fi device <NUM>, Wi-Fi BB <NUM>, Li-Fi AFE <NUM> and optical interface <NUM> may differ from the division shown in <FIG>. For example, Wi-Fi BB <NUM>, Li-Fi AFE <NUM> and optical interface <NUM> may be integrated in a single device (e.g., on a single silicon die) or implemented in separate devices (e.g., separate silicon dies). Alternatively, the pair - Wi-Fi BB <NUM> and Li-Fi AFE <NUM> and the pair - Li-Fi AFE <NUM> and optical interface <NUM>, may be separately implemented, each pair in a single device. In WLAN transceiver <NUM>, Wi-Fi antenna interface <NUM> may be comprised within or external to Wi-Fi device <NUM>.

The different elements of Li-Fi transceiver <NUM> and the different elements of WLAN transceiver <NUM> may be implemented using suitable hardware, such as in one or more RFICs, Application-Specific Integrated Circuits (ASICs) or Field-Programmable Gate Arrays (FPGAs). In some embodiments, some elements of Li-Fi transceiver <NUM> and some elements of WLAN transceiver <NUM>, e.g., Wi-Fi BB <NUM> including MAC controller <NUM> and Wi-Fi BB <NUM> including MAC controller <NUM>, can be implemented using software, or using a combination of hardware and software elements. Elements of Li-Fi transceiver <NUM> and of WLAN transceiver <NUM> that are not mandatory for understanding of the disclosed techniques have been omitted from the figure for the sake of clarity.

In some embodiments, Wi-Fi BB <NUM> (and/or MAC controller <NUM>), Wi-Fi BB <NUM> (and/or MAC controller <NUM>) or both comprise general-purpose processors, which are programmed in software to carry out the functions described herein. The software may be downloaded to the processors in electronic form, over a network, for example, or it may, alternatively or additionally, be provided and/or stored on non-transitory tangible media, such as magnetic, optical, or electronic memory. This processor may be internal or external to the relevant Wi-Fi BB module.

<FIG> is a flow chart that schematically illustrates a method for switching between Li-Fi and Wi-Fi communication in WLAN transceiver <NUM> of <FIG>, in accordance with an embodiment that is described herein.

The method will be described as executed by various elements of WLAN transceiver <NUM>.

The method begins with MAC controller <NUM> selecting a communication configuration over Li-Fi, at a Li-Fi configuration step <NUM>. In the present example, Li-Fi communication serves as a default communication mode. In some embodiments, MAC controller <NUM> generates a suitable selection signal (<NUM>) for connecting between Wi-Fi RF module <NUM> and RF/Li-Fi converter <NUM>, and disconnecting between Wi-Fi RF module <NUM> and Wi-Fi antenna interface <NUM>.

At a Li-Fi communication step <NUM>, WLAN transceiver <NUM> communicates with one or more remote client stations over the Li-Fi optical band. RF/Li-Fi converter <NUM> converts between Wi-Fi signals generated by Wi-Fi device <NUM> and Li-Fi signals in the Li-Fi optical band, as described above.

At a monitoring step <NUM>, MAC controller <NUM> monitors the communication quality over Li-Fi. For example, MAC controller <NUM> monitors the communication quality by monitoring signal level at one or more points along the Li-Fi reception path. At a quality verification step <NUM>, MAC controller <NUM> checks whether the communication quality over Li-Fi is acceptable. MAC controller <NUM> may detect that the communication quality is unacceptable when one or more monitored signals in the Li-Fi reception path drop below a predefined threshold quality. This may occur, for example, when the light channel between WLAN transceiver <NUM> and remote station(s) becomes blocked, e.g., by some non-transparent or partially transparent physical object.

When at step <NUM> the communication quality is acceptable, the method loops back to step <NUM>, to continue communicating over Li-Fi. Otherwise, the method proceeds to a Wi-Fi configuration step <NUM>, at which MAC controller <NUM> configures WLAN transceiver <NUM> to communicate over Wi-Fi instead of over Li-Fi. In some embodiments, MAC controller <NUM> generates selection signal <NUM> for disconnecting between Wi-Fi RF module <NUM> and RF/Li-Fi converter <NUM>, and connecting between Wi-Fi RF module <NUM> and Wi-Fi antenna interface <NUM>.

At a Wi-Fi communication step <NUM>, WLAN transceiver <NUM> communicates with one or more remote client stations over Wi-Fi via Wi-Fi antenna interface <NUM>, as described above. Following step <NUM> the method terminates.

In the method of <FIG>, the WLAN transceiver communicates over Li-Fi, and switches to communicate over Wi-Fi when Li-Fi communication fails. In this configuration, Wi-Fi communication mode serves as a backup mode for the default Li-Fi communication mode. In alternative embodiments, WLAN transceiver <NUM> communicates over Li-Fi and over Wi-Fi in parallel. By using Li-Fi and Wi-Fi in parallel, higher data rates may be achieved compared to using only Wi-Fi or Li-Fi alone. Parallel operation may also provide fast switching between or fallback to one of the Wi-Fi and Li-Fi systems. Parallel communication over Li-Fi and Wi-Fi may be effective in environments in which both the Li-Fi optical band and the Wi-Fi RF band may suffer from interferences.

The embodiments described above are given by way of example, and other suitable embodiments can also be used. For example, in WLAN transceiver <NUM>, the MAC controller may switch between Li-Fi and Wi-Fi communication dynamically based on identifying varying environmental conditions such as reception quality, interference and the like.

In some of the disclosed embodiments, the LO signal frequency is required to be larger than BW/<NUM>. The LO signal frequency may be selected sufficiently high above BW/<NUM> to avoid light-related interferences that may fall in a frequency range close to the zero frequency.

Although the embodiments described above mainly address signals in baseband at the PHY layer, in alternative embodiments, the PHY layer may handle signals in a suitable Intermediate Frequency (IF). In this case, the spectral density function of the complex I/Q signals may not be centered about zero frequency.

Claim 1:
A Wireless LAN, WLAN, Li-Fi transceiver (<NUM>), comprising:
a Wi-Fi device (<NUM>), configured to:
produce a spatial stream carrying data; and
produce from the spatial stream a complex-valued signal comprising In-phase and Quadrature signal components; and
an Analog Front-End (<NUM>), configured to:
produce a Li-Fi signal in a predefined optical band; and
transmit the data carried by the spatial stream to a remote Li-Fi receiver by driving an optical emitter (<NUM>) with the Li-Fi signal;
characterised in that the Wi-Fi device is configured to produce the complex-valued signal such that the complex-valued signal is centered about a Li-Fi frequency for the predefined optical band; and
in that the Analog Front-End is configured to produce the Li-Fi signal based only on the In-phase signal component or only on the Quadrature signal component of the complex-valued signal.