WO2021259807A1

WO2021259807A1 - Wireless communication modulator

Info

Publication number: WO2021259807A1
Application number: PCT/EP2021/066689
Authority: WO
Inventors: Matthias Wendt; Johan Paul Marie Gerard LINNARTZ; Andreas Felix Alfred BLUSCHKE
Original assignee: Signify Holding B.V.
Priority date: 2020-06-26
Filing date: 2021-06-18
Publication date: 2021-12-30

Abstract

A wireless communications modulator (100) comprises a baseband processor (110), a transmit radio frequency, RF, block (201) and an output pin (120). The baseband processor (110) generates a baseband signal. The transmit RF block (201) generates an RF signal by modulating the baseband signal generated by the baseband processor (110) onto a RF carrier. The RF signal and the baseband signal are multiplexed to generate a combined signal which is output via the output pin (120).

Description

WIRELESS COMMUNICATION MODULATOR

TECHNICAL FIELD

The present disclosure relates to a wireless communication modulator.

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.

United States patent application US2020/0044349 A1 discloses a system for providing full-duplex communications comprises a first transceiver for simultaneously transmitting first signals having a first orthogonal angular momentum function on a channel and simultaneously receiving second signals having a second orthogonal angular momentum function applied thereto at a same time on the same channel. In this manner full-duplex optical communication or full-duplex radio frequency communication is enabled that reduces or avoids self-interference through the use of orbital angular momentum functions.

Figure 1 shows schematically a known arrangement for use in transmitting and receiving both RF and LiFi signals which comprises both a radio frequency (RF) chipset 10 and a LiFi chipset 20. The RF chipset 10 as shown in Figure 1 may be part of a WiFi chipset located in a mobile device.

The RF chipset 10 comprises an RF baseband processor 11, a transmit RF block 12, an RF power amplifier 13, an RF output pin 14, an RF input pin 15, an amplifier 16, and a receive RF block 17. The RF baseband processor 11 handles RF communication.

On the transmit-side, the baseband signal generated and output by the RF baseband processor 11 is modulated onto an RF carrier by the transmit RF block 12, amplified by the RF power amplifier 13, and output via the RF output pin 14 where it can be supplied to an antenna for transmission. On the receive-side, RF signals are received via the RF input pin 15, amplified by the amplifier 16, and demodulated or down-converted by the receive RF block 17 and the down-converted signal provided to the RF baseband processor 11.

The LiFi chipset 20 comprises a LiFi baseband processor 21, a driver 22, an LiFi output pin 23, an LiFi input pin 24, and a transimpedance amplifier 25. The LiFi baseband processor 21 handles LiFi communication. On the transmit-side, the baseband signal generated by the LiFi baseband processor 21 is provided to a driver 22 which generates a driving signal which is output by the LiFi output pin 23 where it can be supplied to a light source to cause the light source to transmit the LiFi signal as modulated light (visible or invisible). On the receive-side, LiFi signals (e.g. captured by a photodetector) are received via the LiFi input pin 24, amplified by transimpedance amplifier 25, and provided to the LiFi baseband processor 21.

SUMMARY

It is an object of the invention to improve on the prior art, this object is achieved by a wireless communications Orthogonal Frequency-Division Multiplexed,

OFDM, modulator device (100) as claimed in claim 1, a wireless communication method as claimed in claim 13 and a network device as claimed in claim 15.

According to a first aspect disclosed herein, there is provided a wireless communications modulator, in the form of a device, comprising: a baseband processor for generating a baseband signal; a transmit radio frequency, RF, block for generating an RF signal by modulating the baseband signal generated by the baseband processor onto a (single) RF carrier wave; and an output pin of the device; the modulator being constructed and arranged to multiplex the RF signal and the baseband signal to generate a combined signal and to output the combined signal via the output pin.

The RF signal may be for example a WiFi signal. The baseband signal may be for example a LiFi signal.

The baseband signal is preferably an OFDM signal. In the latter case the baseband OFDM signal has a first frequency range bounded by a lowest and highest frequency. Likewise, the RF OFDM signal has a second frequency range bounded by a respective lowest and highest frequency, wherein a highest frequency of the first frequency range is below a lowest frequency of the second frequency range.

As a result, a single modulator device output pin may be used to output both the baseband and RF signals at the same time. In an example, the wireless communications modulator comprises a transmit baseband block for generating a modulated baseband signal by modulating the baseband signal generated by the baseband processor onto a (single) mid-carrier; and the modulator is constructed and arranged to multiplex the RF signal and the modulated baseband signal to generate the combined signal.

In an example, the mid-carrier has a frequency equal to or at least half the bandwidth of the baseband signal. When the mid-carrier frequency is higher than half the bandwidth of the baseband signal, it preferably is lower than or equal to the bandwidth of the baseband signal. The rational being that a smaller gap between OHz and the lowest frequency component of the baseband signal allows for a better usage of the available modulation bandwidth, which is particularly relevant for LED which have a relatively low bandwidth as compared to VCSELs.

Alternatively, the mid-carrier has a frequency equal to a clock frequency of the baseband processor, as a result the clock signal may be repurposed further saving cost.

In an example, the wireless communications modulator is configured to transmit real parts and imaginary parts separately.

In an example, the real and imaginary parts may be transmitted by the wireless communications modulator sequentially. In such cases, any particular time sample may either contain a real or an imaginary sample (thus not linear combinations). In some examples, such sequencing preferably comprises sending all real samples first, followed by all imaginary parts, or v.v., or alternating real and imaginary samples with a sign-flip. In a specific example, the real (Re) and Imaginary (Im) parts may be transmitted in the following sequence: Re[0], lm[0], -Re[l], -Im[l], etc.

In an example, the wireless communications modulator has a digital chip and an analogue chip, and: the transmit RF block is an analogue transmit RF block implemented on the analogue chip; and the baseband processor is a digital baseband processor implemented on the digital chip for generating a digital baseband signal, the digital chip comprising a digital-to-analogue converter for converting the digital baseband signal generated by the digital baseband processor to an analogue baseband signal for output from the digital chip to the analogue transmit RF block.

In an example, the wireless communications modulator has a digital chip and an analogue chip, and: the baseband processor is a digital baseband processor implemented at the digital chip for generating a digital baseband signal; and the transmit RF block is an analogue transmit RF block implemented at the analogue chip, the analogue chip comprising a digital-to-analogue converter for converting the digital baseband signal generated by the digital baseband processor into an analogue baseband signal use by the analogue transmit RF block.

In an example, the wireless communications modulator comprises: an input pin for receiving a wireless signal; a high pass filter constructed and arranged to extract any RF part from the received wireless signal; a receive RF block for generating a demodulated baseband signal by demodulating the extracted RF part; a low pass filter constructed and arranged to extract any baseband part from the received combined signal; and a multiplexer constructed and arranged to selectively pass the demodulated baseband signal or the extracted baseband part to the baseband processor.

In an example, the multiplexer is configured to selectively pass the demodulated baseband signal or the extracted baseband part based on input from the baseband processor.

In an example, the multiplexer is configured to selectively pass the demodulated baseband signal or the extracted baseband part based on input from at least one signal strength detector.

The at least one signal strength detector may be arranged to determine a respective signal strength of the extracted RF part and the extracted baseband part. Separate signal strength detectors may be used for each part. In an example, multiplexer, the signal strength detector, or a separate module is configured to determine which of the demodulated baseband signal or the extracted baseband part has the highest signal strength, and the multiplexer is configured to pass that signal to the baseband processor.

In an example, the wireless communications modulator has a digital chip and an analogue chip, and: the transmit RF block is an analogue transmit RF block implemented at the analogue chip; the receive RF block is an analogue receive RF block implemented at the analogue chip; the baseband processor is a digital baseband processor implemented at the digital chip for generating a digital baseband signal; and wherein the digital chip comprises: a digital-to-analogue converter for converting the digital baseband signal generated by the digital baseband processor into an analogue baseband signal for output from the digital chip to the analogue transmit RF block; and an analogue-to-digital converter for converting analogue signals to digital signals for use by the baseband processor.

In an example, the wireless communications modulator has a digital chip and an analogue chip, and: the baseband processor is a digital baseband processor implemented at the digital chip for generating a digital baseband signal; the transmit RF block is an analogue transmit RF block implemented at the analogue chip; the receive RF block is an analogue receive RF block implemented at the analogue chip; wherein the analogue chip comprises: a digital-to-analogue converter for converting the digital baseband signal generated by the digital baseband processor into an analogue baseband signal use by the analogue transmit RF block; and an analogue-to-digital converter for converting analogue signals to digital signals for use by the baseband processor.

According to a second aspect disclosed herein, there is provided a wireless communication method performed by a wireless communications modulator having a baseband processor, an output pin and an input pin, the method comprising: generating, by the baseband processor, a baseband signal; generating an RF signal by modulating the baseband signal onto a RF carrier; and multiplexing the RF signal and the baseband signal to generate a combined signal; and outputting the combined signal via the output pin.

In an example, the method comprises: receiving a wireless signal via the input pin; extracting any RF part from the received wireless signal; generating a demodulated baseband signal by demodulating the extracted RF part; extracting any baseband part from the received combined signal; and selectively passing the demodulated baseband signal or the extracted baseband part to the baseband processor.

According to a third aspect disclosed herein, there is provided a network device, such as an access point and/or an endpoint device for an optical wireless communications, OWC, network comprising the wireless communications modulator according to the first 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:

Fig. 1 shows schematically a known arrangement for use in transmitting and receiving both RF and LiFi signals;

Fig. 2 shows schematically a wireless communication modulator chipset in accordance with examples disclosed herein;

Fig. 3 is a schematic representation of a frequency spectrum of the combined signal in accordance with an example disclosed herein;

Fig. 4 shows schematically an example of external transmit circuitry;

Fig. 5 shows schematically an example of external receive circuitry; Fig. 6a shows schematically a first example implementation of the wireless communications modulator chipset;

Fig. 6b shows schematically a second example implementation of the wireless communication modulator chipset; and

Fig. 7 shows schematically an example implementation of the transmit functionality.

DETAILED DESCRIPTION

In prior art arrangements, such as the arrangement shown in Figure 1, two separate chipsets (10, 20), each with its own respective baseband processor (11, 21), are required in order to handle both RF and LiFi communication functionality. Additionally, four pins (14, 15, 23, 24) are required in order to manage output and input of signals from and to the two separate chipsets.

The present invention provides an integrated wireless communication modulator. In examples, only a single chipset (the wireless communication modulator chipset described below), having only a single baseband processor and two pins, is required in order to provide both RF and LiFi communication functionality. The present arrangement thereby provides a “universal modulator” for both RF and LiFi communication. The universal modulator as provided herein may also be referred to as a “circuit with a combination of integrated semiconductors”, a wireless communication modulator chipset, or simply “chipset”.

Historically, the word “chip set” or “chipset” in the context of an RF chipset is used to refer to the realization of an RF system involving multiple semiconductor dies respectively performing different parts of the functions, e.g. RF signal generation, or mixed signal generation, and baseband processing, that were often offered in a common package, a so-called multi-chip module (MCM). Often, not the die size per se but the number of pins is the limiting factor. The word chipset here is understood to refer to a multitude of functions, even though these may be performed in a single integrated circuit (IC or package). While a “chipset” may be intended to refer to a device manufactured from a single source, examples described herein may utilize further integrated circuits from different manufacturers or even circuits built partly discrete (e.g. the high frequency part). In examples, specific embodiments are also described which comprise separate analogue and digital dies inside an MCM.

On the transmit-side, the chipset generates a “combined signal” at a single output pin. The combined signal comprises a superposition of both a baseband part and an RF part. Filters can be used to extract the baseband part or the RF part, as required, for use in LiFi communication and RF communication, respectively. For example, a low pass filter can extract the baseband part which can then be used to drive a light source (e.g. LED), and a high pass filter can extract the RF part which can then be transmitted using an antenna. In other examples, one or more of the high pass and low pass filters may be implemented using (different) band pass filters.

On the receive-side, the chipset has a single input pin for receiving both RF and LiFi (baseband) signals. Similarly, on the transmit side, filters are used to separate the signals for use by the (single) baseband processor.

One advantage of the present invention is a saving in costs and component count and space on a circuit board for the components, as only a single chipset is required. Another advantage is the ability to provide seamless handover between communication via the RF and LiFi communication modes because a single chipset can handle both modes using the same baseband modulator.

Figure 2 shows schematically an example wireless communication modulator chipset 100 (referred to herein simply as modulator chipset 100) according to the present disclosure. The modulator chipset 100 comprises a baseband processor 110, a transmit portion 200, an output pin 120, a receive portion 300, and an input pin 130. The transmit portion 200 is operatively coupled to the baseband processor 110 and the output pint 120.

The receive portion 300 is operatively coupled to the baseband processor 110 and the input pin 130.

The wireless communication modulator 100 may be comprised in any electronic device. For example, an optical wireless communications (OWC) access point may comprise the wireless communication modulator 100 for communicating with endpoint devices of the OWC network. An endpoint device may comprise the wireless communication modulator 100 for communicating with e.g. access point of the OWC network.

The baseband processor 110 of this example is a digital circuit for handling baseband communication in accordance with techniques known in the art. On the transmit- side, the baseband processor 110 receives digital data for transmission and generates a baseband signal therefrom. On the receive-side, the baseband processor 110 receives a baseband signal and extracts digital data therefrom. Techniques for handling the baseband signals, per se, are known in the art. For example, the baseband processor 110 may perform one or more operations including but not limited to a (inverse) Fast Fourier Transform (FFT), segmentation or de-segmentation of the data into packets, scrambling or descrambling of the data, serialization or deserialization of the data, insertion or removal of a cyclic prefix, etc. The transmitter gets data to be placed on subcarriers (=frequency domain) to be inverse- Fourier Transformed into the time domain as samples to be sent sequentially. As the FFT and inverse (IFFT) are mathematically operations, the term “FFT” may be used to refer generally to a butterfly signal operation (as used in, for example, the Cooley-Tukey FFT Algorithm). The baseband processor 110 may perform other operations such as, for example, a discrete cosine transform (DCT), modified discrete cosine transform (MDCT), discrete sine transform (DST), etc.

The transmit portion 200 comprises a transmit RF block 201, a transmit baseband block 202, and a summation block 203. The transmit RF block 201 is operatively coupled to the baseband processor 110 and to the summation block 203. The transmit baseband block 202 is operatively coupled to the baseband processor 110 and to the summation block 203. The summation block 203 is operatively coupled to the output pin 120.

The transmit RF block 201 is an analogue circuit for modulating the baseband signal generated by the baseband processor 110 into a form suitable for transmission by an antenna. Specifically, the transmit RF block 201 is configured to modulate the baseband signal onto an RF carrier wave.

The transmit baseband block 202 is optional and, when present, may be implemented in various different ways. Examples are described in more detail later below. In some examples, the transmit baseband block 202 may modulate the baseband signal onto a mid-carrier wave. In some example, the transmit baseband block 202 may convert a digital baseband signal into an analogue baseband signal.

The receive portion 300 comprises a high pass filter 301, a receive RF block 302, a multiplexer 303, and a low pass filter 304. The high pass filter 301 is operatively coupled to the input pin 130. The receive RF block 302 is operatively coupled to the high pass filter 301 and the multiplexer 303. The multiplexer 303 is operatively coupled to the baseband processor 110. The low pass filter 304 is operatively coupled to the input pin 130 and the multiplexer 303.

In the following, the transmit portion 200 and corresponding transmit functionality will be described first, followed by a description of the receive portion 300 and corresponding receive functionality.

The baseband processor 110 and the transmit RF block 201 may be substantially the same as those already present in a conventional baseband chips, such as for example a baseband chip in accordance with WiFi-6 (supporting IEEE 802.1 lax) or other WiFi or radio frequency wireless communication standards. However, in the prior art, the baseband processor and transmit RF block are only used for the purposes of providing RF communication (e.g. WiFi). With an arrangement as described herein, on the other hand, the transmit portion 200 allows the single baseband processor 110 and single output pin 120 to be used for transmitting both LiFi and RF communication signals, as described herein. Similarly, the receive portion 300 allows the single baseband processor 110 and single input pin 130 to be used for receiving both LiFi and RF communication signals, as described herein.

The transmit functionality will now be described.

In operation, the baseband processor 110 generates a baseband signal based on digital data to be transmitted. The baseband signal generated by the baseband processor 110 comprises only frequency components in the region of OHz. For example, the baseband signal may occupy a band of frequencies up to around 200MHz which starts at or is close to 0 Hz.

The transmit RF block 201 receives the baseband signal from the baseband processor 110 and generates an RF signal by modulating the baseband signal onto an RF carrier. The RF signal thereby occupies a band of frequencies around the carrier frequency. The carrier frequency may be, in examples, around 2.4GHz, or around 5GHz or some other radio frequency.

The operation of the transmit RF block 201 described above is substantially the same process as applied by an RF chip known in the art (e.g. by transmit RF block 12 in Figure 1). The difference (on the transmit side) of the modulator chipset 100 of the present disclosure is that the RF signal generated by the transmit RF block 201 is multiplexed with a second signal which is also derived from the baseband signal generated by the baseband processor 110 to generated a combined signal. As mentioned, the second signal may be the baseband signal itself, or it may be a version of the baseband signal which has been processed by the transmit baseband block 202.

In Figure 2, both a transmit RF block 201 and transmit baseband block 202 are present. The summation block 203 receives a signal from each of the transmit RF block 201 and transmit baseband block 202 and multiplexes the two signals to generate a combined signal. The resulting combined signal is passed from the summation block 203 to the output pin 120 for output from the modulator chipset 100.

Figure 3 is a schematic representation of a frequency spectrum 400 of the combined signal 150 output by the summation block 203. The frequency spectrum 400 comprises both the baseband part 410, for use in LiFi communications, and the RF part 420, for use in WiFi or other radio frequency communications.

The RF part 420 of the frequency spectrum 400 results from the RF signal generated by the transmit RF block 201. The RF part 420 comprises the RF carrier 422 extending to sidebands 421a, 421b and has an RF bandwidth 425.

In this example, the baseband signal, as generated by the baseband processor 110, has been modulated onto a mid-carrier by the transmit baseband block 202. The baseband modulated onto the mid-carrier appears as the baseband part 410 of the frequency spectrum 400. The baseband part 410 comprises the mid-carrier 412 extending to sidebands 41 la, 441b and has a baseband bandwidth 415 as shown in Figure 3.

In this example, the bandwidth 425 of the RF part 420 is the same as the bandwidth 415 of the baseband part 410. In this example, the mid-carrier 410 has a frequency which is more than half the baseband bandwidth 415 which results in a non-zero frequency gap 430 between OHz and the baseband part 410 (i.e. the baseband signal comprises no DC component). When the base band part 410 is used for LiFi transmission, a bias DC current through the LED/VCSEL is typically generated separately and superposed to the AC modulation by the LED/VCSEL driver to ensure a non-negative current through the LED/VCSEL. On receiving side, the DC component is removed, e.g. using a decoupling capacitor, to give only AC components for use in the amplification. This is advantageous because e.g. it removes any background light e.g. from the sun.

The Non-zero frequency gap is preferably kept small as it allows better use of the available modulation bandwidth of the light source, in particular when using an LED based light source. When using an infrared optical emitter, the gap can be small as there is no risk of visible flicker. When using a visible light emitter, the gap preferably is wider than 100Hz, more preferably wider than 200 Hz, or wider than 500 Hz, in this manner the baseband signal is less likely to result in human perceivable flicker in the visible light output.

The baseband part 410 and the RF part 420 are well-separated (e.g. by around three or four octaves or more). This means that the baseband part 410 and RF part 420 can be easily separated or extracted using filters. Figure 3 shows schematically an example low pass filter LPF which may be used to extract the baseband part 410, and an example high pass filter HPF which may be used to extract the RF part 420.

The (single) output pin 123 of the modulator chipset 100 may be connected to external transmit circuitry which can use the combined signal to output one or both RF signals and LiFi signals. An example of external transmit circuitry is shown schematically in Figure 4. The external transmit circuitry comprises RF transmit circuitry 510 and LiFi transmit circuitry 520.

The RF transmit circuitry 510 comprises, in this example, a high pass filter 511, an RF power amplifier 512, and an antenna 315. The RF power amplifier 512 is operatively coupled to the high pass filter 511 and the antenna 513. The RF transmit circuitry 510 is connectable to the output pin 123 via the high pass filter 511.

In operation, the combined signal from the output pin 123 is filtered by the high pass filter 511 to extract the RF part 420. The RF part 420 is then amplified by the RF power amplifier 512. The amplified RF signal is then provided to the antenna 513 for transmission.

The LiFi transmit circuitry 520 comprises, in this example, a low pass filter 521, a light source driver 522, and a light source 523. The light source driver 522 is operatively coupled to the low pass filter 521 and the light source 523. The LiFi transmit circuitry 520 is connectable to the output pin 123 via the low pass filter 521.

In operation, the combined signal from the output pin 123 is filtered by the low pass filer 521 to extract the baseband part 410. The baseband part 410 is then provided to the light source driver 522 which drives the light source 523 is accordance with the baseband part 410 to output the baseband signal as modulated light. The light source should be selected based on the bandwidth requirements represented by the application. In exemplary situations the light source 523 may be implemented as an LED light source (preferably without phosphors in case higher speeds are required). For higher speed applications VCSELs based light sources might be more appropriate.

The receive functionality will now be described.

The (single) input pin 130 of the modulator chipset 100 may be connected to external receive circuitry, allowing the input pin 130 to be used for receiving both RF signals and LiFi signals.

An example of external receive circuitry is shown schematically in Figure 5. The external receive circuitry comprises RF receive circuitry 610, LiFi receive circuitry 620, and a combiner 630. The external receive circuitry is connectable to the input pin 130 via the combiner 630.

The RF receive circuitry 610 comprises, in this example, an antenna 611, a high pass filter 612, and an amplifier 613. The high pass filter 612 is operatively coupled to the antenna 611 and the amplifier 613. The amplifier 613 is operatively coupled to the combiner 630.

In operation, an RF signal received via the antenna 611 is filtered by the high pass filter 612 before being passed to the amplifier 613. The amplifier 613 amplifies the filtered signal before passing it to the combiner 630. An advantage of the high pass filter 612 is to cut out potential noise (e.g. signals at different frequencies other than the desired carrier or carriers, or other sources of noise). The antenna 611 itself may provide some filtering (e.g. bandpass filtering), but providing the high pass filter 612 advantageously limits the bandwidth of the RF signals to only frequencies of interest, meaning that amplification power is only used where needed. Hence, although the high pass filter 612 may be placed before or after the amplifier 613, it is advantageous for it to be placed before. Another advantage is the avoidance of intermodulation of first stages (e.g. amplifiers, optionally with filtering).

The LiFi receive circuitry 620 comprises a photodetector 621, a transimpedance amplifier 622, and a low pass filter 623. The transimpedance amplifier 622 is operatively coupled to the photodetector 621 and the low pass filter 623. The low pass filter 623 is operatively coupled to the combiner 630. The photodetector 621 may be, for example, a photodiode, a PIN photodiode, an avalanche photodiode, etc.

In operation, a LiFi signal received via the photodetector 621 is amplified by the transimpedance amplifier 622 before being passed to the low pass filter 623. The low pass filter 623 filters the amplified signal and passes the filtered signal to the combiner 630. An advantage of the low pass filter 623 is the removal or reduction of potential noise (similarly to the high pass filter 612 in the RF receive circuitry 610). For example, the transimpedance amplifier 622 may pick up from RF signal which is removed by the low pass filter 623. Hence, although the low pass filter 623 may be placed before or after the transimpedance amplifier 622, it is advantageous for it to be placed afterwards.

The combiner 630, as described above, receives both RF signals from the RF receive circuitry 610 and LiFi signals from the LiFi receive circuitry 620. The combiner 630 combines the two signals (e.g. as a summation) to generate a combined signal at the input pin 130. Hence, it is appreciated that the signal received at the input pin 130 from the external receive circuitry may comprise both a baseband part 415 and an RF part 425 (e.g. as shown in Figure 3). The received signal is processed in two different ways, and both results are provided to the multiplexer 303, as described below.

On the one hand, the received signal is passed from the input pin 130 to the high pass filter 301 of the receive portion 300 of the modulator chipset 100, which extracts the RF part 420 by filtering out low frequency components including, in particular, the baseband part 415. The RF part 420 extracted by the high pass filter 301 is passed to the receive RF block 302. The receive RF block 302 demodulates the RF part 420 to produce a demodulated baseband signal. The demodulated baseband signal is then passed from the receive RF block 302 to the multiplexer 303.

On the other hand, the received signal is passed from the input pin 130 to the low pass filter 304 of the receive portion 300 of the modulator chipset 100, which extracts the baseband part 410 by filtering out high frequency components including, in particular, the RF part 425. The baseband part 410 extracted by the low pass filter 304 is passed to the multiplexer 303.

It is appreciated that the baseband part 410 may be processed before being passed to the multiplexer 303. Preferably the sampling rate of the ADC sufficiently exceeds twice the bandwidth of the analogue signal (to satisfy Nyquist criteria), while oversampling by at least a factor of e.g. 4 can allow most signal processing in the digital domain. Usually the sampling clock runs independently of the signal clock as synchronization is performed in the digital domain.

In some examples, the sampling may be run in sync with the incoming signal. In particular, when the transmit portion 200 is configured to modulate the baseband signal onto a mid-carrier before multiplexing, the receive portion 300 may demodulate the baseband part 410 by the same mid-carrier frequency before the demodulated baseband part is passed to the multiplexer 303. Separate in-phase (I) and quadrature (Q) sampling may be applied.

In short, the multiplexer 303 is configured to receive two forms of baseband signal: one demodulated from the extracted RF part 420 (for WiFi or other radio frequency received signals) and one extracted directly from the received signal (for received signals LiFi received signals). In operation, the multiplexer 303 selectively passes one or more form of the baseband signal to the baseband processor 110.

The multiplexer 303 may in examples by switch that selects a LiFi or WiFi mode. The multiplexer 303 may be controlled, for example, based on output from a signal strength detector or the BBP 110. For example, a signal strength detector (or separate signal strength detectors for each of the RF-side and the LiFi-side, e.g. after the HPF 301 and the LPF 304, respectively) may determine a respective current signal strength for each of the RF and LiFi signals and control the multiplexer 303 to pass the signal having the highest current signal strength. A similar decision may be made by the baseband processor 110. For example, the baseband processor 110 may determine which of the RF of LiFi signals currently provides the best signal and control the multiplexer 303 to pass that determined signal.

Figures 6a and 6b show schematically two examples in which the modulator chipset 100 is implemented as a Multiple Chip Module (MCM) comprising a digital chip 101 and an analogue chip 102. In these examples, the baseband processor 110 is a digital circuit implemented as part of the digital chip 101 and the transmit RF block 201 and receive RF block 302 are analogue circuits implemented as part of the analogue chip 102.

In the example of Figure 6a, analogue signals are passed between the digital chip 101 and the analogue chip 102. The digital chip 101 comprises the baseband processor 110, a digital -to-analogue converter (DAC) 210, and an analogue-to-digital convertor (ADC) 310. The analogue chip 102 comprises the transmit RF block 201 and the receive RF block 302.

On the transmit side, the baseband signal generated by the baseband processor 110 is passed through to the DAC 210 before leaving the digital chip 101 to be converted to an analogue baseband signal. This analogue baseband signal is passed to the summation block 203 both via the transmit RF block 201 and directly (or with intermediate processing) as described above.

On the receive side, signals received via the input pin 130 are passed to the ADC 301 both via the receive RF block 302 and directly (or with intermediate processing) as described above. The ADC 310 converts the received signals into a digital format and passes the converted signals to the baseband processor 110.

It is appreciated that not all the elements of the modulator chipset 100 described above are shown in Figure 6a. For example, the multiplexer 303 described earlier could be implemented as part of the analogue chip 102. The baseband transmit block 202 could be implemented as part of the analogue chip 102.

In the example of Figure 6b, digital signals are passed between the digital chip 101 and the analogue chip 102. The digital chip 101 comprises the baseband processor 110. The analogue chip 102 comprises the DAC 210, transmit RF block 120, summation block 203, receive RF block 203, and ADC 310.

On the transmit side, the (digital) baseband signal generated by the baseband processor 110 is sent from the baseband processor to the DAC 210 of the digital chip 102. The analogue signal output by the DAC 210 is passed to the summation block 203 both via the transmit RF block 120 and directly (or with intermediate processing) as described above. On the receive side, signals received via the input pin 130 are passed to the ADC 310 both via the receive RF block 302 and directly (or with intermediate processing) as described above. The digital signal output by the ADC 310 is passed from the digital chip 102 to the baseband processor 110 on the digital chip 101.

It is again appreciated that not all the elements of the modulator chipset 100 described above are shown in Figure 6b. For example, the multiplexer 303 described earlier could be implemented as part of the digital chip 102.

Figure 7 shows schematically an example implementation of the transmit functionality. In this example, the baseband processor 110 is configured to generate an Orthogonal Frequency-Division Multiplexed (OFDM) baseband signal, as known per se. A transmit baseband block 202 is provided for processing the OFDM baseband in-phase (real) and quadrature (imaginary) signals and appropriately merging (e.g. interleaving) these before multiplexing these with the RF signal, as described below.

The baseband processor 110 uses an (inverse) FFT operation to generate a real part and an imaginary part of the baseband signal, in accordance with known techniques. For example, the baseband processor 110 may demultiplex a serial stream of digital data to construct a set of parallel streams. Each stream may then be mapped to a respective symbol stream using constellation mapping (e.g. QAM, PSK, etc.). The (inverse) FFT operation may then be performed on the symbol streams to generate the real and imaginary parts of the baseband signal.

The real and imaginary parts of the baseband signal are sent from the baseband processor 110 to both the transmit RF block 201 and the transmit baseband block 202.

In the transmit RF block 201, the baseband signal gets modulated onto the carrier as generated by a local oscillator 321. Again, this may be implemented using known techniques, e.g. Frequency Modulation (FM), Amplitude Modulation (AM), etc.

In the transmit baseband block 202, the baseband signal is processed before being provided to the summation block 203 for multiplexing with the RF signal. There are various different types of processing which may be applied.

In a first example, the transmit baseband block 202 may modulate the baseband signal onto a mid-carrier. In such cases, the layout of the baseband block 202 may be substantially the same as the transmit RF block 201, but using a local oscillator (also referred to as the mixing oscillator) which generates a carrier with a much lower frequency (the mid-carrier). Denote the input subcarrier signals to the N-sized FFT as X_k, and the outcoming time samples as x_n. The oscillator cosine (in-phase) and sine (quadrature) are given as: gi(n) = cos(2 ft) and g_q(n) = sin(2 ft).

The output of the baseband block 202 (to be multiplexed with the RF signal) is then of the form:

Where P() is the pulse shape.

In a specific example, the LiFi mixing frequency in the baseband block 202 (i.e. the frequency of the mid-carrier) is f > 1/(2T_S ) (i.e. more than half the bandwidth). This creates a gap 430 between the baseband part and OHz, which is particularly advantageous as it avoids aliasing. The mixing frequency is preferably not orders of magnitude larger than the Nyquist rate. This would create a large unused gap between DC and the lowest used frequency. In particular when using LEDs for generating the LiFi output, this is not ideal as it operates the output LEDs in a frequency band where the response is attenuated by the junction capacitance. An example starting from 10 MHz wide real and imaginary data signals (creating 20 MHz bandwidth) and mixing these with a 16 MHz mid-carrier, creating a LiFi signal from 6 to 26 MHz. In some examples, multiple Wi-Fi (RF) signals may be placed at different bands (using, e.g. FDMA) to avoid interference. In such examples, the mixing frequencies can be as large as 100 MHz. E.g. if the modulation bandwidth is 20MHz, a 25MHz local oscillator may be used to achieve a shift of 25MHz, giving a quiet gap of 5MHz.

In examples, the lower e.g. 5MHz of the band may be kept free. In other examples, the lower 2MHz may be kept free. It will be appreciated that the mixing frequency required to achieve a given gap 430 depends on the bandwidth of the signal.

Specifically, the gap 430 will generally be equal to the mixing frequency minus half the bandwidth. For example, if a signal with a bandwidth of 20MHz gets mixed with 25 MHz local oscillator, the gap will be 5 MHz. If, on the other hand, the same signal is mixed with a 22MHz local oscillator, the gap will be 2MHz. If the same signal is mixed with a 30MHz local oscillator frequency the resulting gap would be lOMHz, etc. This also means that the extreme mixing frequency for a given bandwidth signal (e.g. 20MHz BW signal) is a frequency equal to half that bandwidth (e.g. 10MHz) as this would result in no gap, i.e. the resulting signal would touch DC (OHz). In a specific example, the mixing frequency of the local oscillator may be 15MHz, meaning that a 20MHz-bandwidth signal would have a gap 430 of 5MHz. A 5MHz gap is particularly advantageous as it can ensure that on spurious signals fold around DC. In another specific example, the mixing frequency of the local oscillator may be 12MHz, meaning that a 20MHz-bandwidth signal would have a gap 430 of 2MHz. 2MHz is still large enough to substantially avoid signals folding around DC.

Mixing with a local frequency to shift the signal up has an advantage of avoiding the generation of alias frequencies for the bandwidth which would fall into a “negative” frequency (which is a somewhat theoretical figure, physical frequencies are always positive).

In another example, the layout of the transmit baseband block 202 may again be substantially the same as the transmit RF block 201, but the mixing oscillator inside the baseband block 202 is locked to the clock of the data coming out of the FFT (i.e. the mid carrier has the same frequency as the baseband signal coming from the baseband processor ). In such cases, the gap 430 is zero (there is a DC component). This may lead to a loss of one, or a few subcarrier frequencies because the DC component is blocked inside the processing. The other bands, however, can still be received and therefore this loss of one or more subcarrier frequencies can be mitigated by error correction coding or subcarrier loading that avoids the outermost subcarriers of the OFDM signal. In practice however, RF radio standards often do not use a number of the outer subcarriers so as to allow filtering of the entire signal, for instance to prevent aliasing.

To accommodate the real and imaginary parts of the baseband signal, this baseband signal clock runs at f=l/T_s.

The pulse shape is such that inter-symbol interference is avoided, i.e. n(jT_s-nT_s )=0 for integer j not equal to n. In this example, the signal is of the form:

This corresponds to using the cosine branch 1, 0, -1, 0 and the sine branch 0, 1,

0, -1.

The transmit sequence then becomes: Re[xo], Im[xo], - Re[xi], - Im[xi],

Re[x2], Im[x₂], - Re[x₃], - Im[x₃], Re[x4], Im[x ], etc. In a third example, the real values of the time samples generated by the baseband processor 110 by the FFT operation may be transmitted first, and then the imaginary (quadrature) time samples may be transmitted later.

The examples given above may be combined. For example, the second and third examples may be implemented in combination by re-shuffling the time samples of the output of the transmit FFT, possibly treating real and imaginary parts separately. That is, the mixing oscillator may be locked to the clock of the data coming out of the FFT, and the real part may be transmitted first, followed by the imaginary part.

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 wireless communications Orthogonal Frequency Division Multiplexed, OFDM, modulator device (100) comprising: a baseband processor (110) arranged to generate a baseband OFDM signal having a first frequency range; a transmit radio frequency, RF, block (201) arranged to generate an RF OFDM signal having a second frequency range by modulating the baseband OFDM signal generated by the baseband processor (110) onto a RF carrier wave; and a device output pin (120); the OFDM modulator device (100) being constructed and arranged to combine the RF OFDM signal and the baseband OFDM signal to generate a combined signal and to output the combined signal via the device output pin (120) wherein a highest frequency of the first frequency range is below a lowest frequency of the second frequency range.

2. The wireless communications OFDM modulator device (100) according to claim 1, comprising a transmit baseband block (202) arranged to generate a modulated baseband OFDM signal by modulating the baseband OFDM signal generated by the baseband processor (110) onto a mid-carrier wave; and wherein the OFDM modulator device (100) is constructed and arranged to multiplex the RF OFDM signal and the modulated baseband OFDM signal to generate the combined signal.

3. The wireless communications OFDM modulator device (100) according to claim 2, wherein the mid-carrier wave has a frequency equal to or at least half the bandwidth of the baseband OFDM signal.

4. The wireless communications OFDM modulator device (100) according to claim 2 or claim 3, wherein the mid-carrier wave has a frequency equal to a clock frequency of the baseband processor (110).

5. The wireless communications OFDM modulator device (100) according to any of claims 1 to 5, wherein the wireless communications OFDM modulator device (100) is arranged to transmit real parts and imaginary parts separately.

6. The wireless communications OFDM modulator device (100) according to any of claims 1 to 5, having a digital chip (101) and an analogue chip (102), wherein: the transmit RF block (201) is an analogue transmit RF block (201) implemented on the analogue chip (102); and the baseband processor (110) is a digital baseband processor implemented on the digital chip (101) arranged to generate a digital baseband OFDM signal, the digital chip (101) comprising a digital-to-analogue converter (210) arranged to convert the digital baseband OFDM signal generated by the digital baseband processor (110) to an analogue baseband OFDM signal for output from the digital chip (101) to the analogue transmit RF block (201).

7. The wireless communications OFDM modulator device (100) according to any of claims 1 to 5, having a digital chip (101) and an analogue chip (102), wherein: the baseband processor (110) is a digital baseband processor implemented at the digital chip (101) arranged to generate a digital baseband OFDM signal; and the transmit RF block (201) is an analogue transmit RF block (201) implemented at the analogue chip (102), the analogue chip (102) comprising a digital-to- analogue converter (210) arranged to convert the digital baseband OFDM signal generated by the digital baseband processor (110) into an analogue baseband OFDM signal for use by the analogue transmit RF block (201).

8. The wireless communications OFDM modulator device (100) according to any of claims 1 to 7, comprising: a device input pin (130) for receiving a signal from a wireless interface; a high pass filter (301) constructed and arranged to extract an RF part from the received signal from the device input pin (130); a receive RF block (302) arranged to generate a demodulated baseband OFDM signal by demodulating the extracted RF part; a low pass filter (304) constructed and arranged to extract a baseband part from the received signal from the device input pin (130); and a multiplexer (303) constructed and arranged to selectively pass the demodulated baseband OFDM signal or the extracted baseband part to the baseband processor (110).

9. The wireless communications OFDM modulator device (100) according to claim 8, wherein the multiplexer is arranged to selectively pass the demodulated baseband OFDM signal or the extracted baseband part based on input from the baseband processor.

10. The wireless communications OFDM modulator device (100) according to claim 8, wherein the multiplexer is arranged to selectively pass the demodulated baseband OFDM signal or the extracted baseband part based on input from at least one signal strength detector.

11. The wireless communications OFDM modulator device (100) according to any of claims 8 to 10, having a digital chip (101) and an analogue chip (102), wherein: the transmit RF block (201) is an analogue transmit RF block (201) implemented at the analogue chip (102); the receive RF block (302) is an analogue receive RF block (302) implemented at the analogue chip (102); the baseband processor (110) is a digital baseband processor implemented at the digital chip (101) arranged to generate a digital baseband OFDM signal; and wherein the digital chip (101) comprises: a digital -to-analogue converter (210) arranged to convert the digital baseband OFDM signal generated by the digital baseband processor (110) into an analogue baseband OFDM signal for output from the digital chip (101) to the analogue transmit RF block (201); and an analogue-to-digital converter (310) arranged to convert analogue signals to digital signals for use by the baseband processor (110).

12. The wireless communications OFDM modulator device (100) according to any of claims 8 to 10, having a digital chip (101) and an analogue chip (102), wherein: the baseband processor (110) is a digital baseband processor implemented at the digital chip (101) for generating a digital baseband OFDM signal; the transmit RF block (201) is an analogue transmit RF block (201) implemented at the analogue chip (102); the receive RF block (302) is an analogue receive RF block (302) implemented at the analogue chip (102); wherein the analogue chip (102) comprises: a digital -to-analogue converter (210) arranged to convert the digital baseband OFDM signal generated by the digital baseband processor (110) into an analogue baseband OFDM signal use by the analogue transmit RF block (201); and an analogue-to-digital converter (310) arranged to convert analogue signals to digital signals for use by the baseband processor (110).

13. A wireless communication method performed by a wireless communications

Orthogonal Frequency Division Multiplexed, OFDM, modulator device (100) comprising a baseband processor (110), a device output pin (120) and a device input pin (130), the method comprising: generating, by the baseband processor (110), a baseband OFDM signal having a first frequency range; generating an RF OFDM signal having a second frequency range by modulating the baseband OFDM signal onto a single RF carrier wave; and combining the RF OFDM signal and the baseband OFDM signal to generate a combined signal; and outputting the combined signal via the device output pin (120) wherein a highest frequency of the first frequency range is below a lowest frequency of the second frequency range.

14. The wireless communication method according to claim 13, comprising: receiving on the device input pin (130) a signal from a wireless interface; extracting any RF part from the signal from the device input pin (130); generating a demodulated baseband OFDM signal by demodulating the extracted RF part; extracting any baseband part from the signal from the device input pin (130); and selectively passing the demodulated baseband OFDM signal or the extracted baseband part to the baseband processor (110).

15. A network device for use in an optical wireless communication, OWC, network comprising the wireless communications OFDM modulator device (100) according to any of claims 1 to 12.