Wake-up receiver, transmitter and method thereof

Abstract

The present disclosure relates to a method of receiving a third signal, such as a radio-frequency, RF, signal in a wireless receiver, the third signal comprising a first modulated signal, the method comprising: demodulating the first modulated signal for extracting a second modulated signal; demodulating the second modulated signal for extracting a first sequence, wherein the second modulated signal is frequency or phase modulated based on a known sequence and on a second carrier signal, wherein the first modulated signal is amplitude modulated based on the second modulated signal and on a first carrier signal, wherein a frequency of the first carrier signal is higher than a frequency of the second carrier signal. The present disclosure further relates to a receiver thereof. The present disclosure further relates to a method for transmitting and a transmitter thereof.

Description

[0001] WAKE-UP RECEIVER, TRANSMITTER AND METHOD THEREOF

[0002] Technical field

[0003] The present invention relates to wake-up receivers and transmitters and methods thereof.

[0004] Background

[0005] Wake-up receivers are used in many loT devices, battery driven wireless devices, devices powered by energy harvesting, and other low-power devices, and also in User Equipment devices, UEs. There are other applications of wake-up receivers in wireless communication such as, for example, smart watches, Virtual Reality (VR) and Augmented Reality (AR) glasses or apparatuses and other power-constrained devices and apparatuses. Wake-up receivers have the advantage of being ultra low-power. They typically detect a wake-up signal (WUS) and, when the wake-up signal is detected, they wake up a main unit, which then turns from an idle or powered-off state to a non-idle state or functional state. Therefore, the main device can operate in idle state saving power for a longer time, and further operate in a functional or fully functional state only after being woken up by the wake-up receiver. Once the main device has finished its operation, it can return to the idle state and wait for a control signal from the wake-up receiver to return in its functional or fully functional state. The overall purpose of the wake-up receiver is to save power by having the main unit idle or off for the inactive time. The wake-up receiver itself shall be ultra low-power, for example it should have a sub-mW power consumption.

[0006] Wake-up receivers are typically configured to receive a sequence from a transmitter. The sequence transmitted by the transmitter may be, for example, a second sequence. If the received sequence, that is the first sequence, matches or correlates to a known sequence, such as a wake-up sequence, then the wake-up receiver wakes up a main unit.

[0007] Wake-up receivers may typically be located in positions surrounded by other devices, for example low power devices, turning on and off at a relevant pace. Wake-up receiver may also be surrounded by other devices, for example base stations, sending wake-up signals, which may be relevant or not be relevant for a specific wake-up receiver. Therefore wake-up receivers are typically affected by interference signals, which may, for example, typically carry non relevant sequences for a given wake-up receiver. Due to interference, detection of the sequence may not be optimal, may take longer time, or may even fail. The problem of interference also applies to any other receiver which is configured to receive a signal from a first transmitter, and the receiver is located in an area where other transmitters are transmitting other signals. Summary

[0008] An object of the present invention is to overcome the above problems, among others the interference problem, in receiving signals. In particular it is an object to the present disclosure to solve the problem of interference in the context of receiving and / or transmitting signals, such as wake-up sequences.

[0009] According to a first aspect, the present disclosure relates to a method of receiving a third signal in a wireless receiver, the third signal comprising a first modulated signal, the method comprising: demodulating the first modulated signal for extracting a second modulated signal; demodulating the second modulated signal for extracting a first sequence, wherein the second modulated signal is frequency or phase modulated based on a known sequence and on a second carrier signal, wherein the first modulated signal is amplitude modulated based on the second modulated signal and on a first carrier signal, wherein a frequency of the first carrier signal is higher than a frequency of the second carrier signal.

[0010] According to a further aspect, the present disclosure relates to a wireless receiver, comprising: at least one antenna configured to capture a third signal comprising a first amplitude modulated signal; an envelope detector or a low-pass filter configured to demodulate the first amplitude modulated signal for extracting a second modulated signal; a frequency or phase modulation demodulator configured to demodulate the second modulated signal for extracting a first sequence.

[0011] According to a further aspect, the present disclosure relates to a method in a wireless transmitter, the method comprising: obtaining a second modulated signal by frequency or phase modulating a second carrier signal with a second sequence; obtaining a first modulated signal by amplitude modulating a first carrier signal with the second modulated signal; transmitting the first modulated signal, wherein a frequency of the first carrier signal is higher than a frequency of the second carrier signal.

[0012] According to a further aspect, the present disclosure relates to a wireless transmitter for transmitting a first amplitude modulated signal, wherein the first amplitude modulated signal is modulated based on a second modulated signal and a first carrier signal, wherein the second modulated signal is frequency or phase modulated based on a second sequence and a second carrier signal, wherein a frequency of the first carrier signal is higher than a frequency of the second carrier signal, the transmitter comprising: an oscillator configured to generate a first oscillating signal; a first circuit configured to generate the first carrier based on the first oscillating signal; a second circuit configured to generate at least two second signals based on the first oscillating signal, wherein the at least two second signals are phase-shifted with respect to each other; a third circuit configured to, based on the second sequence, select one of the at least two second signals at a time, thereby generating the second modulated signal; a fourth circuit (506) configured to generate the first modulated signal (510) based on the second modulated signal (508) and the first carrier (511).

[0013] According to a further aspect, the present disclosure relates to an Orthogonal Frequency Division Multiplexing (OFDM) wireless transmitter for transmitting a first amplitude modulated signal, wherein the first amplitude modulated signal is modulated based on a second modulated signal and a first carrier signal, wherein the second modulated signal is frequency or phase modulated based on a second sequence and a second carrier signal, wherein a frequency of the first carrier is higher than a frequency of the second carrier, the transmitter comprising: a first circuit configured to generate a time domain digitized sinusoidal sequence with an amplitude offset and with a phase offset, wherein the phase offset is based on the second sequence, the time domain digitized sinusoidal sequence being a digitized version of the second modulated signal; a Digital to Analog converter (DAC) configured to generate, based on the time domain digitized sinusoidal sequence, the second modulated signal; a second circuit configured to, based on the second modulated signal and the first carrier signal, generate the first modulated signal; wherein the second circuit is further configured to transmit the first modulated signal.

[0014] According to a further aspect, the present disclosure relates to an Orthogonal Frequency Division Multiplexing (OFDM) wireless transmitter for transmitting a first amplitude modulated signal, wherein the first amplitude modulated signal is modulated based on a second modulated signal and a first carrier signal, wherein the second modulated signal is frequency or phase modulated based on a second sequence and a second carrier signal, wherein a frequency of the first carrier is higher than a frequency of the second carrier, the transmitter comprising: a first circuit configured to generate a time domain (TD) digitized sinusoidal sequence with an amplitude offset; a first control logic configured to control a phase of the TD digitized sinusoidal sequence based on the second sequence, the TD digitized sinusoidal sequence being a digitized version of the second modulated signal; a second circuit configured to perform a Discrete Fourier Transform, DFT, or a Fast Fourier Transform, FFT of the TD digitized sinusoidal sequence, obtaining a frequency domain, FD, digitized sequence; a third circuit configured to perform an Inverse Fast Fourier Transform, IFFT, of the FD digitized sequence to generate a second TD digitized version of the second modulated signal; a Digital to Analog converter (DAC) configured to, based on the second TD digitized version of the second modulated signal, generate the second modulated signal; a fourth circuit configured to modulate the second modulated signal with the first carrier, thereby obtaining the first modulated signal, the fourth circuit further configured to transmit the first modulated signal.

[0015] According to a further aspect, the present disclosure relates to a method, in an Orthogonal Frequency Division Multiplexing (OFDM) wireless transmitter, the method comprising: generating, in a digital frequency domain, a frequency domain digitized second modulated signal, said frequency domain digitized second modulated signal comprising: a central tone, corresponding to a second carrier signal; and two sideband tones, wherein a phase of the sideband tones is based on a second sequence; performing an Inverse Fast Fourier Transform (IFFT) of the frequency domain digitized second modulated signal to obtain a time domain digitized second modulated signal; performing a digital to analog conversion (DAC) operation of the time domain digitized second modulated signal, to obtain a second modulated signal; performing an I / Q modulation of a first carrier signal with the second modulated signal, the first carrier signal having a frequency higher than a frequency of the central tone of the second modulated signal, to obtain a first modulated signal; transmitting the first modulated signal.

[0016] Further embodiments are defined in the dependent claims. It should be emphasized that the term “comprises / comprising” when used in this specification is taken to specify the presence of stated features, integers, steps, or components, but does not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof. Brief description of the drawings

[0017] Fig. 1 illustrates a block diagram of a receiver according to an embodiment of the present disclosure.

[0018] Fig. 2 illustrates a block diagram of a receiver according to an embodiment of the present disclosure.

[0019] Fig. 3 illustrates a block diagram of a receiver according to an embodiment of the present disclosure.

[0020] Fig. 4 illustrates a block diagram of a receiver according to an embodiment of the present disclosure.

[0021] Fig. 5 illustrates a block diagram of a transmitter according to an embodiment of the present disclosure.

[0022] Fig. 6 illustrates a block diagram of a transmitter according to an embodiment of the present disclosure.

[0023] Fig. 7 illustrates a block diagram of a transmitter according to an embodiment of the present disclosure.

[0024] Fig. 8 illustrates a block diagram of a transmitter according to an embodiment of the present disclosure.

[0025] Fig. 9 illustrates a flow chart of a method for receiving a signal according to an embodiment of the present disclosure.

[0026] Fig. 10 illustrates a flow chart of a method for transmitting a modulated signal according to an embodiment of the present disclosure.

[0027] Fig. 11 illustrates a flow chart of a method for transmitting a modulated signal according to an embodiment of the present disclosure.

[0028] Detailed description

[0029] It is submitted that a wireless receiver typically works in cooperation with at least one wireless transmitter. Further, the transmitter typically performs a signal modulation and the receiver performs a signal demodulation.

[0030] Fig. 1 illustrates a block diagram of a receiver according to an embodiment of the present disclosure.

[0031] In this embodiment, the wireless wake-up receiver 100 comprises at least one antenna 101 configured to capture a third signal. The third signal may comprise a first amplitude modulated signal. The first modulated signal may be amplitude modulated based on a first carrier and a second modulated signal. That is the amplitude of the first carrier is modulated by the second modulated signal. The first carrier may have a frequency in the low GHz range, such as between 1GHz and 10 GHz. In another embodiment the first carrier may have a frequency between 1 GHz and 20 GHz. That is the first carrier is a radio-frequency (RF) signal.

[0032] The receiver may further comprise an envelope detector 105 configured to demodulate the first amplitude modulated signal for extracting the second modulated signal.

[0033] The receiver may further comprise a frequency or phase modulation demodulator 116, configured to demodulate the second modulated signal for extracting a first sequence.

[0034] The second modulated signal may be phase or frequency modulated based on a second carrier and a sequence.

[0035] The receiver may advantageously further comprise a first band-pass filter 102. The band pass filter 102 may pass frequencies around the first carrier frequency and may have a center frequency substantially equal to a frequency of the first carrier.

[0036] The receiver may advantageously further comprise a matching network 103 for impedance matching between the band pass filter 102 and the envelope detector 105. The envelope detector 105 may be implemented to include low pass filter functionality at its output. Different implementations of the envelope detector are known to the skilled person in the art and may comprise rectifiers based on diodes and / or transistors.

[0037] The receiver may further comprise a selective filter 109. The selective filter 109 may comprise a resonator 107, and buffers 106 and 107. Resonator 107 may be a ceramic resonator. The resonator 107 may be selected and / or tuned to selectively resonate at a center frequency corresponding to a frequency of the second carrier. Tuning of the resonance frequency of the resonator 107 may be obtained by use of a variable capacitor (not shown in the figure) in parallel to the resonator. The value of the variable capacitor may be selected by measuring the frequency of an oscillating signal across the resonator and comparing it to a known signal to determine a frequency of the oscillating signal: this can be done by use of, for example, a tuning controller (not shown in the figure). Buffer 106 may be a buffer with high output impedance to isolate the resonator 107 from the envelope detector 105. The envelope detector 105 may comprise a rectifier. Buffer 106 isolates the resonator 107 from the rectifier to avoid loading the resonator. A center frequency of the selective filter 109 may correspond to a frequency of the second carrier. The frequency of the second carrier may be below 1 GHz, preferably below 100 MHz, more preferably below 10 MHz. That is the second modulated signal is a signal at a second frequency which is lower than a frequency of the first carrier signal. Buffers 106 and 108 are amplifiers operating around the second frequency.

[0038] The selective filter 109 has the advantage to filter out noise and interference, especially low frequency amplitude-modulation noise. Low frequency amplitude-modulation noise may be generated by other devices in vicinity of the receiver, turning on and off intermittently or radiating low frequency amplitude modulated signals, or other type of noise. The second modulated signal is phase or frequency modulated around a second carrier. The selective filter 109 has a center frequency centered at the frequency of the second carrier. Therefore the selective filter 109 can filter out the low frequency noise and extract a modulated tone, the second modulated signal, centered around the frequency of the second carrier.

[0039] Still with reference to Fig. 1 the receiver 100 comprises a Binary Phase Shift Keying (BPSK) demodulator 116, such as In-Phase / Quadrature (I / Q) BPSK demodulator.

[0040] The BPSK demodulator 116 is advantageously used when the second carrier is modulated using a BPSK modulation. In particular, in this embodiment, the second modulated signal is a BPSK signal. In this example the second carrier is modulated with a sequence, such as a first or second or known sequence. The sequence is a digital sequence and a first phase of the second carrier corresponds to a logic 0 and a second phase of the second carrier corresponds to a logic 1. The BPSK demodulator 116 comprises a clock generator 110. The clock generator 110 generates a first clock signal 111 and a second clock signal 112. The first clock signal 111 and the second clock signal 112 are phase shifted between each other by substantially 90 degrees. The mixers 121 and 122 mix the second modulated signal with the clock signals 111 and 112 respectively. The demodulator 116 further comprises low pass filters 131 and 132, buffers or amplifiers 141 and 142 and comparators 151, 152. The demodulator 116 therefore extracts a first sequence from the second modulated signal. The first sequence is an input of a first circuit 115.

[0041] Still with reference to Fig. 1 the receiver 100 further comprises the first circuit 115 which is configured to compare the first sequence with a known sequence. The demodulator 116 has a filtered second modulated signal as an input and as an output a first sequence. The first circuit 115 may be a correlator and may correlate the first sequence with a known sequence.

[0042] The known sequence may be a sequence that is agreed between a transmitter and the receiver 100. A correlation of the first sequence with the known sequence may indicate a correct reception, in particular it may be indicative of an information between a transmitter and the receiver, such as a wake-up information.

[0043] Fig. 2 illustrates a block diagram of a receiver according to an embodiment of the present disclosure. In the embodiment of Fig. 2, the receiver comprises a Quadrature Phase Shift Keying (QPSK) demodulator 216. The QPSK demodulator 216 may be a first QPSK I / Q demodulator . In this embodiment the second modulated signal is modulated according to a QPSK modulation. In this embodiment, the first QPSK demodulator 216 comprises four mixers (221, 222, 223, 224) and four comparators (251, 252, 253, 254) and a clock generator (210) generating four clock signals (211, 212, 213, 214) to respective mixers (221, 222, 223, 224), wherein a phase difference between consecutive clock signals (211, 212, 213, 214) is substantially 45 degrees. The second modulated signal and the clock signals are fed to respective mixers 221, 222, 223, 224.

[0044] Fig. 3 illustrates a block diagram of a receiver according to an embodiment of the present disclosure. In the embodiment of Fig. 3, the receiver comprises a Quadrature Phase Shift Keying (QPSK) demodulator 316. The QPSK demodulator 316 may be a second QPSK I / Q demodulator . In this embodiment, the second QPSK demodulator 316 comprises two mixers 321, 322 and four comparators 351, 352, 353, 354 and a clock generator 310 generating a first clock signal 311 and a second clock signal 312 to respective mixers 321, 322, wherein the second clock signal 312 is phase-shifted by substantially 90 degrees with respect to the first clock signal 311. The second modulated signal and the clock signals are fed to respective mixers.

[0045] Fig. 4 illustrates a block diagram of a receiver according to an embodiment of the present disclosure. In the embodiment of Fig. 4, the receiver comprises a Quadrature Phase Shift Keying (QPSK) demodulator 416. The QPSK demodulator 416 may be a QPSK I / Q demodulator with interpolation amplifiers 441-446 In this embodiment, the QPSK demodulator 416 comprises two mixers 421, 422 and four comparators 451, 452, 453, 454 and a clock generator 410 generating a first clock signal 411 and a second clock signal 412 to respective mixers 421, 422, wherein the second clock signal 412 is phase-shifted by substantially 90 degrees with respect to the first clock signal 411. In this embodiment the demodulator 416 further comprises one or more interpolation amplifiers 443, 444.

[0046] Frequency Shift Key (FSK) modulation can be regarded as a special case of PSK, where multiple consecutive QPSK symbols constitute one FSK symbol, by rotating the symbol by +90 degrees from QPSK symbol to QPSK symbol to generate one FSK symbol corresponding to one offset frequency, and by -90 degrees for the other FSK symbol with the opposite sign of the frequency offset. The wakeup sequence can then be built up from a larger number of QPSK symbols to receive FSK. Of course, other incremental phase shifts than 90 degrees can also be used, like 45 degrees.

[0047] Therefore, PSK demodulators according to embodiments of this disclosure, in particular QPSK demodulators, may be used as well as FSK demodulators, in particular as Binary FSK (BFSK) demodulators.

[0048] In one embodiment, the third signal is a wake-up signal and the wireless receiver is a wake-up receiver. In this embodiment, the first circuit 115, 215 315, 415 is configured to generate a control signal to wake-up a main unit. The main unit may be connected to the receiver by at least said control signal.

[0049] The receiver may comprise first circuit 115, 215, 315, 415 configured to compare the first sequence with a known sequence.

[0050] In one embodiment the first circuit 115, 215, 315, 415 comprises a correlator.

[0051] In one embodiment, the first circuit 115, 215, 315, 415 is configured to output a control signal to a main unit if a comparison between the first sequence and the known sequence is above a first threshold. Fig. 9 illustrates a flow chart of a method 900 for receiving a third signal according to an embodiment of the present disclosure. According to this embodiment, a method is disclosed of receiving a third signal in a wireless receiver, the third signal comprising a first modulated signal, the method comprising: demodulating the first modulated signal for extracting a second modulated signal, 901; demodulating the second modulated signal for extracting a first sequence, 902, wherein the second modulated signal is frequency or phase modulated based on a known sequence and on a second carrier signal, wherein the first modulated signal is amplitude modulated based on the second modulated signal and on a first carrier signal, wherein a frequency of the first carrier signal is higher than a frequency of the second carrier signal.

[0052] In one embodiment of the presently disclosed method, a third signal is applied to, or received by, or sensed by an antenna of a receiver, such as the antenna 101 of receiver 100, 200, 300 or 400 of Fig. 1, 2, 3 or 4 respectively. The third signal may be a radio frequency (RF) signal or a radio signal or a radio frequency modulated signal. The third signal comprises a first modulated signal. The first modulated signal is an amplitude modulated signal. That is the first modulated signal comprises a first carrier which is amplitude modulated with a second modulated signal. The second modulated signal may comprise a second carrier which is modulated with a sequence, such as a second sequence or a first sequence or a known sequence. In step 901 the first modulated signal is demodulated for extracting the second modulated signal. The demodulation in step 901 may be performed by use of an envelope detector, for example the envelope detector 105 of Fig. 1, 2, 3 or 4. In step 902 the second modulated signal may be demodulated for extracting a first sequence. The demodulation in step 902 may be performed by a Phase / Frequency demodulator 116, 216, 316 or 416 of Fig. 1, 2, 3 or 4 respectively.

[0053] In one embodiment a frequency of the first carrier may be between 1GHz and 10 GHz. In another embodiment the first carrier may have a frequency between 1 GHz and 20 GHz. In one embodiment, a frequency of the second carrier may be less than 1GHz, preferably less than 100 MHz, more preferably less than 10 MHz, even more preferably less than 1 MHz.

[0054] In one embodiment, the third signal is a wake-up signal and the wireless receiver is a wake-up receiver.

[0055] In one embodiment, the second modulated signal is modulated with Binary Phase Shift Keying (BPSK).

[0056] In one embodiment, the second modulated signal is modulated with Quadrature Phase Shift Keying (QPSK).

[0057] In one embodiment, the second modulated signal is modulated with Binary Frequency Shift Keying (BFSK).

[0058] In one embodiment, the method of receiving further comprises band-pass filtering the second modulated signal by means of a resonator 107 of Fig. 1, 2, 3 or 4. The resonator 107 is part of a selective filter 109, which further comprises buffering for impedance isolation.

[0059] In one embodiment, the method of receiving further comprises comparing the first sequence with a known sequence. A known sequence may be a sequence that is agreed between a transmitter and a receiver, such as a wake-up sequence. The comparison may be performed, for example, by circuit 115, 215, 315, 415 of the disclosed receiver of Fig. 1, 2, 3 or 4.

[0060] In one embodiment, comparing the first sequence with the known sequence comprises correlating the first sequence with the known sequence by means of a correlator. In this embodiment, circuit 115, 215, 315, 415 (of the disclosed receiver of Fig. 1, 2, 3 or 4) may comprise a correlator.

[0061] In one embodiment, the method of receiving further comprises, when the comparison or the correlation is above a first threshold, sending a control signal to a main unit to wake-up the main unit. The wireless receiver and the main unit may be part of a same device, such as mobile phone, or a User Equipment (UE), or VR glasses, or AR glasses or any other device which may require a wake-up receiver.

[0062] Fig. 5 illustrates a block diagram of a wireless transmitter according to an embodiment of the present disclosure. The wireless transmitter 500 may be configured for transmitting a first amplitude modulated signal 510, wherein the first amplitude modulated signal 510 is modulated based on a second modulated signal 508 and a first carrier signal 511, wherein the second modulated signal 508 is frequency or phase modulated based on a second sequence and a second carrier signal, wherein a frequency of the first carrier signal 511 is higher than a frequency of the second carrier signal. The wireless transmitter may comprise: an oscillator 501 configured to generate a first oscillating signal 509; a first circuit 502 configured to generate a first carrier 511 based on the first oscillating signal 509. The first circuit 502 may be a Phase Locked Loop (PLL) or a Frequency Locked Loop (FLL). The wireless transmitter may further comprise a control signal (not shown in the figure) from the first circuit 502 to the oscillator.

[0063] The wireless transmitter may further comprise a second circuit 504 configured to generate at least two second signals 513 based on the first oscillating signal, wherein the at least two second signals 513 are phase-shifted with respect to each other. The second signals 513 may be second oscillating signals with phase offset with respect to each other. The second signals 513 may have a same frequency as the first oscillating signal or a frequency based on the frequency of the first oscillating signal. For example the second circuit 504 may generate two signals 513, each phase shifted by substantially 90 degrees from each other.

[0064] The wireless transmitter further comprises a third circuit 505 configured to, based on a second sequence, select one of the at least two second signals 513 at a time, thereby generating the second modulated signal 508. The third circuit may comprise a plurality of switches and may route, based on the second sequence, one of the second signals 513 towards its output 508, so that the signal 508 is a second modulated signal based on a second carrier 509 and on a second sequence. The switches in 505 may be controlled by control logic 503, which may control the switches in circuit 505 based on a second sequence.

[0065] The wireless transmitter may further comprise a fourth circuit 506 configured to generate the first modulated signal 510 based on the second modulated signal 508 and the first carrier In one embodiment, the first circuit 502 comprises a Phase Locked Loop (PLL), or a Frequency Locked Loop (FLL). In this embodiment the PLL 502 or the FLL 502 is controlled by a first control logic 503.

[0066] In one embodiment, the second circuit 504 may comprise a Quadrature Generator, QGEN, and the second phase-shifted signals are phase-shifted by substantially 90 degrees with respect to each other. The second circuit 504 may comprise a frequency divider.

[0067] In one embodiment, the third circuit 505 comprises a plurality of switches. In this embodiment the first control logic 503 is further configured to control the switches based on the second sequence.

[0068] In one embodiment, the fourth circuit 506 comprises a power amplifier.

[0069] In one embodiment the power amplifier 506 receives the first carrier 511 and the second modulated signal 508 as input signals. The power amplifier 506 may comprise a plurality of power amplifier stages and a last power amplifier stage of the power amplifier may be saturated and may operate rail to rail.

[0070] In one embodiment, a supply voltage of the last power amplifier stage of the power amplifier is based on the second modulated signal 508.

[0071] Fig. 6 illustrates a block diagram of a transmitter 600 according to an embodiment of the present disclosure. The embodiment of Fig. 6, with respect to the embodiment of Fig.5, and wherein common elements of Figs 5 and 6 are not repeated here for sake of brevity, further comprises circuit 507. Circuit 507 may be a supply modulator, such as a Low Dropout Regulator (LDO), configured to regulate a supply voltage of a last power amplifier stage of the power amplifier 506.

[0072] The transmitter 500 or 600 of respectively Fig. 5 and Fig.6 may further comprise an antenna (not shown in the figures) for transmission of the first modulated signal. Fig. 7 illustrates a block diagram of a transmitter according to an embodiment of the present disclosure. In this embodiment the transmitter may be a Orthogonal Frequency Division Multiplexing (OFDM) wireless transmitter 700 for transmitting a first amplitude modulated signal, wherein the first amplitude modulated signal is modulated based on a second modulated signal and a first carrier signal, wherein the second modulated signal is frequency or phase modulated based on a second sequence and a second carrier signal, wherein a frequency of the first carrier is higher than a frequency of the second carrier. The transmitter may comprise a first circuit 701 configured to generate a time domain digitized sinusoidal sequence with an amplitude offset and with a phase offset, wherein the phase offset is based on the second sequence, the time domain digitized sinusoidal sequence being a digitized version of the second modulated signal. The phase offset may correspond to the second sequence. The transmitter further comprises a Digital to Analog Converter, DAC, 702 configured to generate, based on the time domain digitized sinusoidal sequence, the second modulated signal. The transmitter may further comprise a second circuit 703 configured to, based on the second modulated signal and the first carrier signal, generate the first modulated signal. The transmitter is further configured to transmit the first modulated signal, for example by means of an antenna.

[0073] In one embodiment, the amplitude offset is such that the digitized sinusoidal sequence has only positive values. Such amplitude offset is advantageous to simplify the reception of the first modulated signal at the receiver side and makes it possible to use a simple envelope detector.

[0074] In one embodiment, the first circuit 701 is a controller of the OFDM transmitter. This has the advantage to use existing hardware of the OFDM transmitter without the need to add additional hardware.

[0075] In one embodiment, the first circuit 701 comprises a memory, at least one adder, a phase offset generator and an amplitude offset generator. This has the advantage to use optimized hardware and not overload the existing hardware of the OFDM transmitter.

[0076] In one embodiment, the second circuit 703 is an In-Phase / Quadrature (I / Q) transmitter and the first modulated signal is transmitted using an In-Phase branch of the second circuit, or a Quadrature branch of the second circuit, or both the In-Phase and Quadrature branches. Fig. 8 illustrates a block diagram of a transmitter according to an embodiment of the present disclosure. In this embodiment, the transmitter is an Orthogonal Frequency Division Multiplexing (OFDM) wireless transmitter 800 for transmitting a first amplitude modulated signal, wherein the first amplitude modulated signal is modulated based on a second modulated signal and a first carrier signal, wherein the second modulated signal is frequency or phase modulated based on a second sequence and a second carrier signal, wherein a frequency of the first carrier is higher than a frequency of the second carrier. In this embodiment the transmitter comprises a first circuit 801 configured to generate a time domain (TD) digitized sinusoidal sequence with an amplitude offset. It further comprises a first control logic 802 configured to control a phase of the TD digitized sinusoidal sequence based on the second sequence, the TD digitized sinusoidal sequence being a digitized version of the second modulated signal. It further comprises a second circuit 803 configured to perform a Discrete Fourier Transform (DFT) or a Fast Fourier Transform (FFT) of the TD digitized sinusoidal sequence, obtaining a frequency domain (FD) digitized sequence. It further comprises a third circuit 804 configured to perform an Inverse Fast Fourier Transform (IFFT) of the FD digitized sequence to generate a second TD digitized version of the second modulated signal. It further comprises a Digital to Analog Converter (DAC) 804 configured to, based on the second TD digitized version of the second modulated signal, generate the second modulated signal. It further comprises a fourth circuit 805 configured to modulate the first carrier with the second modulated signal, thereby obtaining the first modulated signal, the fourth circuit further configured to transmit the first modulated signal.

[0077] Fig. 10 illustrates a flow chart of a method 1000, in a wireless transmitter, for transmitting a modulated signal according to an embodiment of the present disclosure. The method comprises obtaining a second modulated signal by frequency or phase modulating a second carrier signal with a second sequence signal, 1001. The method further comprises obtaining a first modulated signal by amplitude modulating the first carrier signal with the second modulated signal, 1002. The method further comprises transmitting the first modulated signal, 1003. A frequency of the first carrier signal may be higher than a frequency of the second carrier signal. It is understood by a skilled person that the second sequence is equal to the known sequence or, that a correlation of the second sequences with the known sequence is more than a second threshold. The known sequence may be a sequence that is agreed between a transmitter according to embodiments disclosed in the present disclosure and a receiver according to embodiments disclosed in the present disclosure. It is also understood that in an ideal wireless communication system deprived of noise and / or errors, the second sequence (transmitted sequence) is equal to the known sequence (agreed sequence) and to the first sequence (received sequence). In a real system, due to noise and / or errors, the second sequence correlates with the known sequence more than a second threshold, and the first sequence correlates with the known sequence by more than a first threshold.

[0078] In one embodiment, the method is performed at least partly in the digital domain.

[0079] In one embodiment, obtaining a first modulated signal by amplitude modulating the first carrier signal with the second modulated signal, 1002, is performed in the digital domain.

[0080] In one embodiment, obtaining a first modulated signal by amplitude modulating the second modulated signal with a first carrier signal, 1002, is performed using a mixer or an In- Phase / Quadrature, I / Q, modulator.

[0081] In one embodiment, the method is at least partly performed in a frequency domain.

[0082] In one embodiment, obtaining a second modulated signal by frequency or phase modulating a second sequence with a second carrier signal with a second sequence, 1001 is performed in the frequency domain.

[0083] Fig. 11 illustrates a flow chart of a method 1010 for transmitting a modulated signal according to an embodiment of the present disclosure. In this embodiment, the method is in an Orthogonal Frequency Division Multiplexing (OFDM) wireless transmitter. The method comprises: generating, in a digital frequency domain, a frequency domain digitized second modulated signal, said frequency domain digitized second modulated signal comprising, 1011 : a central tone, corresponding to a second carrier signal; and two sideband tones, wherein a phase of the sideband tones is based on a second sequence; performing an Inverse Fast Fourier Transform, IFFT, of the frequency domain digitized second modulated signal to obtain a time domain digitized second modulated signal, 1012; performing a digital to analog conversion, DAC, operation of the time domain digitized second modulated signal, to obtain a second modulated signal 1013; performing an I / Q modulation of a first carrier signal with the second modulated signal, the first carrier signal having a frequency higher than a frequency of the central tone of the second modulated signal, to obtain a first modulated signal 1014; transmitting the first modulated signal, 1015.

[0084] The presently disclosed receiver is configured to carry out the presently disclosed receive method.

[0085] The presently disclosed transmitter is configured to carry out the presently disclosed transmit method.

[0086] Reference has been made herein to various embodiments. However, a person skilled in the art would recognize numerous variations to the described embodiments that would still fall within the scope of the claims. For example, the method embodiments described herein describes example methods through method steps being performed in a certain order. However, it is recognized that these sequences of events may take place in another order without departing from the scope of the claims. Furthermore, some method steps may be performed in parallel even though they have been described as being performed in sequence.

[0087] In the same manner, it should be noted that in the description of embodiments, the partition of functional blocks into particular units is by no means limiting. Contrarily, these partitions are merely examples. Functional blocks described herein as one unit may be split into two or more units. In the same manner, functional blocks that are described herein as being implemented as two or more units may be implemented as a single unit without departing from the scope of the claims.

[0088] Hence, it should be understood that the details of the described embodiments are merely for illustrative purpose and by no means limiting. Instead, all variations that fall within the range of the claims are intended to be embraced therein.

Claims

CLAIMS:

1. A method (900) of receiving a third signal in a wireless receiver, the third signal comprising a first modulated signal, the method comprising:- demodulating the first modulated signal for extracting a second modulated signal (901);- demodulating the second modulated signal for extracting a first sequence (902), wherein the second modulated signal is frequency or phase modulated based on a known sequence and on a second carrier signal, wherein the first modulated signal is amplitude modulated based on the second modulated signal and on a first carrier signal, wherein a frequency of the first carrier signal is higher than a frequency of the second carrier signal.

2. The method according to claim 1, wherein the third signal is a wake-up signal and the wireless receiver is a wake-up receiver.

3. The method according to any one of the preceding claims, wherein the second modulated signal is modulated with one of: Binary Phase Shift Keying, BPSK, Quadrature Phase Shift Keying, QPSK, and Binary Frequency Shift Keying, BFSK.

4. The method according to any one of the preceding claims, further comprising bandpass filtering the second modulated signal by means of a resonator (107).

5. The method according to any one of the preceding claims, further comprising comparing the first sequence with the known sequence.

6. The method according to claim 5, wherein comparing comprises correlating.

7. The method according to any one of claims 5-6, further comprising, when the comparison or the correlation is above a first threshold, sending a control signal to a main unit to wake-up the main unit.

8. A wireless receiver (100, 200, 300, 400) comprising:- at least one antenna (101) configured to capture a third signal comprising a first amplitude modulated signal;- an envelope detector (105) or a low-pass filter configured to demodulate the first amplitude modulated signal for extracting a second modulated signal;- a frequency or phase modulation demodulator (116, 216, 316, 416) configured to demodulate the second modulated signal for extracting a first sequence.

9. The wireless receiver of claim 8, wherein the third signal is a wake-up signal and the wireless receiver is a wake-up receiver.

10. The wireless receiver according to any one of claims 8-9, further comprising a first circuit (115, 215, 315, 415) configured to compare the first sequence with a known sequence.

11. The wireless receiver according to claim 10, wherein the first circuit (115, 215, 315, 415) comprises a correlator.

12. The wireless receiver according to any one of claims 8-11, further configured to output a control signal to a main unit if the comparison is above a first threshold.

13. The wireless receiver according to any one of claims 8-12, wherein the frequency or phase modulation demodulator comprises an In-Phase / Quadrature, IQ, demodulator (116, 216, 316, 416).

14. The wireless receiver (100) according to claim 13, wherein the IQ demodulator (116) comprises two mixers (121, 122), two comparators (151, 152) and a clock generator (110) generating a first clock signal (111) and a second (112) clock signal to respective mixers (121, 122), wherein the second clock signal (112) is phase-shifted by substantially 90 degrees with respect to the first clock signal (111).

15. The wireless receiver (200) according to claim 13, wherein the IQ demodulator (216) comprises four mixers (221, 222, 223, 224) and four comparators (251, 252, 253, 254) and a clock generator (210) generating four clock signals (211, 212, 213, 214) to respective mixers (221, 222, 223, 224), wherein a phase difference between consecutive clock signals (211, 212, 213, 214) is substantially 45 degrees.

16. The wireless receiver (300, 400) according to claim 13, wherein the IQ demodulator (316, 416) comprises two mixers (321, 322, 421, 422) and four comparators (351, 352, 353, 354, 451, 452, 453, 454) and a clock generator (310, 410) generating a first clock signal (311, 411) and a second clock signal (312, 412) to respective mixers (321, 322, 421, 422), wherein the second clock signal (312, 412) is phase-shifted by substantially 90 degrees with respect to the first clock signal (311, 411).

17. The wireless receiver (400) according to claim 16, wherein the IQ demodulator (416) further comprises one or more interpolation amplifiers (443, 444).

18. A method (1000) in a wireless transmitter, the method comprising:- obtaining a second modulated signal by frequency or phase modulating a second carrier signal with a second sequence (1001);- obtaining a first modulated signal by amplitude modulating a first carrier signal with the second modulated signal (1002);- transmitting the first modulated signal (1003), wherein a frequency of the first carrier signal is higher than a frequency of the second carrier signal.

19. The method according to claim 18, at least partly performed in a digital domain.

20. The method according to any one of claims 18-19, wherein obtaining a second modulated signal by frequency or phase modulating a second sequence with a second carrier signal (1001) is performed in the digital domain.

21. The method according to any one of claims 18-20, wherein obtaining a first modulated signal by amplitude modulating the second modulated signal with a first carrier signal (1002) is performed using a mixer or an In-Phase / Quadrature, I / Q, modulator.

22. The method according to any one of claims 18-21, at least partly performed in a frequency domain.

23. The method according to any one of claims 18-22, wherein obtaining a second modulated signal by frequency or phase modulating a second carrier signal with a second sequence (1001) is performed in the frequency domain.2124. A wireless transmitter (500, 600) for transmitting a first amplitude modulated signal (510), wherein the first amplitude modulated signal (510) is modulated based on a second modulated signal (508) and a first carrier signal (511), wherein the second modulated signal (508) is frequency or phase modulated based on a second sequence and a second carrier signal, wherein a frequency of the first carrier signal (511) is higher than a frequency of the second carrier signal, the transmitter comprising:- an oscillator (501) configured to generate a first oscillating signal (509);- a first circuit (502) configured to generate the first carrier (511) based on the first oscillating signal (509);- a second circuit (504) configured to generate at least two second signals (513) based on the first oscillating signal, wherein the at least two second signals (513) are phase-shifted with respect to each other;- a third circuit (505) configured to, based on the second sequence, select one of the at least two second signals (513) at a time, thereby generating the second modulated signal (508);- a fourth circuit (506) configured to generate the first modulated signal (510) based on the second modulated signal (508) and the first carrier (511).

25. The wireless transmitter (500, 600) according to claim 24, wherein the first circuit (502) comprises a Phase Locked Loop. PLL, or a Frequency Locked Loop, FLL.

26. The wireless transmitter (500, 600) according to claim 25, wherein the PLL or the FLL is controlled by a first control logic (503).

27. The wireless transmitter (500, 600) according to any one of claims 24-26, wherein the second circuit (504) is a Quadrature Generator, QGEN, and the second phase-shifted signals are phase-shifted by substantially 90 degrees with respect to each other.

28. The wireless transmitter (500, 600) according to any one of claims 24-27, wherein the third circuit (505) comprises a plurality of switches.

29. The wireless transmitter (500, 600) according to claim 28, wherein the first control logic (503) is further configured to control the switches based on the second sequence.2230. The wireless transmitter (500, 600) according to any one of claims 24-29, wherein the fourth circuit (506) is a power amplifier.

31. The wireless transmitter (500, 600) according to claim 30, wherein the power amplifier (506) receives the first carrier (511) and the second modulated signal (508) as input signals.

32. The wireless transmitter (500, 600) according to claim 31, wherein a last power amplifier stage of the power amplifier is saturated and operates rail to rail and wherein a supply voltage of the last power amplifier stage of the power amplifier is based on the second modulated signal (508).

33. The wireless transmitter (600) according to claim 32, wherein at least the supply voltage of the last power amplifier stage of the power amplifier is regulated by means of a supply modulator (507), such as a Low Dropout Regulator, LDO.

34. The wireless transmitter (500, 600) according to any one of claims 24-33, further comprising at last one antenna for transmitting the first modulated signal.

35. An Orthogonal Frequency Division Multiplexing, OFDM, wireless transmitter (700) for transmitting a first amplitude modulated signal, wherein the first amplitude modulated signal is modulated based on a second modulated signal and a first carrier signal, wherein the second modulated signal is frequency or phase modulated based on a second sequence and a second carrier signal, wherein a frequency of the first carrier is higher than a frequency of the second carrier, the transmitter comprising:- a first circuit (701) configured to generate a time domain digitized sinusoidal sequence with an amplitude offset and with a phase offset, wherein the phase offset is based on the second sequence, the time domain digitized sinusoidal sequence being a digitized version of the second modulated signal;- a Digital to Analog converter, DAC, (702) configured to generate, based on the time domain digitized sinusoidal sequence, the second modulated signal;- a second circuit (703) configured to, based on the second modulated signal and the first carrier signal, generate the first modulated signal; wherein the second circuit is further configured to transmit the first modulated signal.2336. The transmitter according to claim 35, wherein the amplitude offset is such that the digitized sinusoidal sequence has only positive values.

37. The transmitter according to any one of claims 35-36, wherein the first circuit (701) is a controller of the OFDM transmitter.

38. The transmitter according to any one of claims 35-36, wherein the first circuit (701) comprises a memory, at least one adder, a phase offset generator and an amplitude offset generator.

39. The transmitter according to any one of claims 35-38, wherein the second circuit (703) is an In-Phase / Quadrature, I / Q, transmitter and the first modulated signal is transmitted using an In-Phase branch of the second circuit, or a Quadrature branch of the second circuit, or both the In-Phase and Quadrature branches.

40. An Orthogonal Frequency Division Multiplexing, OFDM, wireless transmitter (800) for transmitting a first amplitude modulated signal, wherein the first amplitude modulated signal is modulated based on a second modulated signal and a first carrier signal, wherein the second modulated signal is frequency or phase modulated based on a second sequence and a second carrier signal, wherein a frequency of the first carrier is higher than a frequency of the second carrier, the transmitter comprising:- a first circuit (801) configured to generate a time domain, TD, digitized sinusoidal sequence with an amplitude offset;- a first control logic (802) configured to control a phase of the TD digitized sinusoidal sequence based on the second sequence, the TD digitized sinusoidal sequence being a digitized version of the second modulated signal;- a second circuit (803) configured to perform a Discrete Fourier Transform, DFT, or a Fast Fourier Transform, FFT of the TD digitized sinusoidal sequence, obtaining a frequency domain, FD, digitized sequence;- a third circuit (804) configured to perform an Inverse Fast Fourier Transform, IFFT, of the FD digitized sequence to generate a second TD digitized version of the second modulated signal;24- a Digital to Analog converter, DAC, (804) configured to, based on the second TD digitized version of the second modulated signal, generate the second modulated signal;- a fourth circuit (805) configured to modulate the first carrier with the second modulated signal, thereby obtaining the first modulated signal, the fourth circuit further configured to transmit the first modulated signal.

41. A method (1010), in an Orthogonal Frequency Division Multiplexing, OFDM, wireless transmitter, the method comprising:- generating, in a digital frequency domain, a frequency domain digitized second modulated signal, said frequency domain digitized second modulated signal comprising (1011): a central tone, corresponding to a second carrier signal; and two sideband tones, wherein a phase of the sideband tones is based on a second sequence; performing an Inverse Fast Fourier Transform, IFFT, of the frequency domain digitized second modulated signal to obtain a time domain digitized second modulated signal (1012);- performing a digital to analog conversion, DAC, operation of the time domain digitized second modulated signal, to obtain a second modulated signal (1013);- performing an I / Q modulation of a first carrier signal with the second modulated signal, the first carrier signal having a frequency higher than a frequency of the central tone of the second modulated signal, to obtain a first modulated signal (1014);- transmitting the first modulated signal (1015).

42. The receiver according to any one of claims 8-17, configured to carry out the method according to any one of claims 1-7.

43. The transmitter according to any one of claims 35-40, configured to carry out the method according to any one of claims 18-23, and / or according to claim 41.

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