WO2024123222A1

WO2024123222A1 - Spectrally efficient ultra low power transmitter

Info

Publication number: WO2024123222A1
Application number: PCT/SE2022/051154
Authority: WO
Inventors: Miguel Lopez; Henrik Sjöland
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2022-12-07
Filing date: 2022-12-07
Publication date: 2024-06-13

Abstract

The present disclosure relates to methods and apparatus for spectrally efficient low power consumption transmissions. An apparatus (700) is provided which switches an output signal (750) between a first state and a second state based on a sequence of codewords. The apparatus comprises an energy storing component (730), which is charged or discharged 5 using an input current, which magnitude depends on a codeword from the sequence of codewords. Therefore, a duration until the voltage of the energy storing component reaches an upper or lower threshold level depends on the magnitude of the input current, and thus represents the codeword. Once the voltage reaches an upper or lower threshold level, a comparator circuit (740) will switch the output signal between the first state and the second 0 state. This triggers another codeword from the sequence of codewords and switches between charging and discharging the energy storing component.

Description

SPECTRALLY EFFICIENT ULTRA LOW POWER TRANSMITTER

TECHNICAL FIELD

The present disclosure generally relates to the technical field of wireless communication, and particularly to methods and apparatuses for spectrally efficient low power consumption transmissions.

BACKGROUND

The 3GPP DRAFT RP -220182 by OPPO and entitled “Discussion on ambient power- enabled loT” discusses modulation and coding schemes for (Ultra-) low power consumption transmissions and (extremely-) low complexity device form factor interfaces with very low complexity signal waveform. Orthogonal Frequency Division Multiplexing (OFDM) is a type of transmission commonly used in various 3rd Generation Partnership Project (3GPP) related standards. However, OFDM may be improper for Internet of Things (loT) devices with very limited power available, such as ambient power-enabled loT devices which may rely e.g., on harvesting energy from their surroundings. Instead of OFDM, RP-220182 considers using low complexity signal modulation techniques such as On-Off Keying (OOK).

OOK is a simple form of modulation, where data is represented by presence or absence of a carrier wave. One simple type of OOK signal 100 is exemplified in FIG. 1. In this example, if the carrier wave is present for a specific time duration, T, it represents a binary ‘1’, and if is it absent for the same time duration, T, it represents a binary ‘O’. However, the spectral efficiency of OOK is limited since only one symbol is transmitted per time duration, T. Thus, there is a need for low power consumption transmissions which increase the spectral efficiency.

SUMMARY

Embodiments of methods, apparatus, transmitters, receivers etc. are provided herein for addressing one or more of the abovementioned issues.

A first aspect of the disclosure provides embodiments of an apparatus for switching an output signal between a first state and a second state based on a sequence of codewords. The apparatus comprises an input circuit, an energy storing component, and a comparator circuit. The input circuit is configured to charge or discharge the energy storing component using an input current. A magnitude of the input current depends on a codeword from the sequence of codewords. The energy storing component is configured to be connected to the comparator circuit such that, based on that a voltage of the energy storing component reaches an upper or lower threshold level, the comparator circuit switches the output signal between the first state and the second state. A duration until the voltage of the energy storing component reaches the upper or lower threshold level depends on the magnitude of the input current. The apparatus further comprises a feedback path from the comparator circuit. The feedback path is configured to switch the input circuit between charging and discharging the energy storing component based on that the voltage of the energy storing component reaches the upper or lower threshold level. The feedback path is further configured to control the input circuit to update the magnitude of the input current based on a next codeword from the sequence of codewords based on that the voltage of the energy storing component reaches the upper or lower threshold level.

A second aspect of the disclosure provides embodiments of a method for switching an output signal between a first state and a second state based on a sequence of codewords. The method comprises charging or discharging an energy storing component using an input current. A magnitude of the input current depends on a codeword from the sequence of codewords. The method comprises, based on that a voltage of the energy storing component reaches an upper or lower threshold level: switching the output signal between the first state and the second state, switching between charging and discharging the energy storing component, and updating the magnitude of the input current based on a next codeword from the sequence of codewords. A duration until the voltage of the energy storing component reaches the respective upper or lower threshold level depends on the magnitude of the input current.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form part of the specification, illustrate various embodiments.

FIG. 1 illustrates an OOK modulated signal. FIG. 2 illustrates different signals modulated in accordance with some embodiments.

FIG. 3 illustrates an efficient modulator in accordance with an embodiment.

FIG. 4 illustrates an example of the voltage level of a capacitor with balanced delays in accordance with an embodiment.

FIG. 5a illustrates a schematic of merged digital to analog converter (DAC) and charge pump in accordance with an embodiment.

FIG. 5b illustrates a schematic of separate DAC and charge pump in accordance with an embodiment.

FIG. 6 illustrates spectral and link performance in the presence of strong interference from a carrier emitter in an Additive White Gaussian Noise, AWGN, channel.

FIG. 7 illustrates an apparatus for switching an output signal between a first state and a second state based on a sequence of codewords in accordance with some embodiments.

FIG. 8 is a flowchart of a method for switching an output signal between a first state and a second state based on a sequence of codewords in accordance with some embodiments.

FIG. 9 is a flowchart of a method for communicating a sequence of codewords in accordance with some embodiments.

FIG. 10 illustrates a transmitter for use in a wireless communication network in accordance with some embodiments.

FIG. 11 is a flowchart of a method for receiving a sequence of codewords in accordance with some embodiments.

FIG. 12 illustrates a receiver for use in a wireless communication network in accordance with some embodiments.

All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the respective embodiments, whereas other parts may be omitted or merely suggested. Any reference number appearing in multiple drawings refers to the same object or feature throughout the drawings, unless otherwise indicated. DETAILED DESCRIPTION

Some of the embodiments contemplated herein will now be described more fully with reference to the accompanying drawings. Embodiments are provided by way of example to convey the scope of the subject matter to those skilled in the art.

According to an example of the present invention, a transmitter may modulate a signal using independent multi-level durations for on and off time durations, in contrast to the fixed on and off time durations for each 0 and 1 used in traditional OOK. The proposed multi-level on and off time durations allow several information bits to be transmitted in each on/off event, making the transmitter spectrally efficient. For this modulation, the number of symbols per time unit is not fixed, preventing the use of a fixed clock frequency to generate the transmit symbols with one symbol per clock cycle. The time periods are instead determined by the data to transmit in each symbol. This will yield an increased spectral efficiency, e.g., compared to OOK. The proposed methods and apparatuses may be applied to active as well as backscattering transmitters and give an efficient modulator structure suitable for ultra-low power transmitters.

An example signal illustrating this is the signal 210 in FIG. 2. In this example, four different codewords ‘00’, ‘01’, ‘10’, and ‘11’ are represented by the different time durations T1-T4. In this example, codeword ‘00’ is represented by time duration T1 during which the signal 210 is in an ON state, codeword ‘01’ is represented by time duration T2 during which the signal 210 is in the OFF state, codeword ‘10’ is represented by time duration T3 during which the signal 210 is in the ON state, and codeword ‘ 11’ is represented by time duration T4 during which the signal 210 is in the OFF state. The signal will switch back and forth between the ON state, where the transmitter is active, and the OFF state, where the transmitter is inactive. The length of each state will depend on the codeword to be communicated. The relative lengths of the durations T1-T4 shown in FIG. 2 are only exemplary, and there is for example no need for the durations T1-T4 to all be equal to an integer multiple of some common time unit, like a clock cycle.

As will be described further below, the proposed signal format may be generated by an ultra-low power transmitter. In contrast, a receiver of this type of signal can be rather straightforward as it does not need to be ultra-low power. The analog to digital converter of the receiver may be clocked at a much higher rate than the transmitted signal. The transmitter may send out a known sequence (e.g., a pre-amble) as part of the transmitted signal to help the receiver receive the transmitted signal. The receiver correlates for the known sequence, with a number of different sequence lengths, as the rate of the transmitter may be uncertain. When the known sequence is found by the receiver in the transmitted signal, e.g., if the corresponding correlation outputs a value above a certain threshold, the receiver can determine the beginning of the data part of the transmitted signal as well as the rate of the transmitter. The receiver could then measure each ON and OFF period received and relate it to the corresponding data bits sent. The transmitted signal may be traversed by the receiver until all data bits have been found. For the example signal 210, the receiver would detect that the signal is in the ON state for a time duration T1 and may thus determine that the codeword is ‘00’. Further, the receiver detects that the signal is in the OFF state for a time duration T2 and may determine that the codeword is ‘01’. The signal is then switched to the ON state for a time duration T3, and the receiver may determine that this represents codeword ‘10’. Finally, the signal is in the OFF state for a time duration T4, and the receiver may determine that this represents codeword ‘11’.

The example of using an ON state and OFF state is only exemplary and it is appreciated that other techniques may be used to represent the codewords. FIG. 2 illustrates three other signals 220, 230, and 240 where a similar modulation has been used. But instead of switching between an ON and OFF state like the signal 210, the signal 220 switches between being transmitted using a first amplitude and being transmitted using a second amplitude, the signal 230 switches between being transmitted using a first frequency and being transmitted using a second frequency, and the signal 240 switches between being transmitted using a first phase and being transmitted using a second phase. The signal 220 has a relatively higher amplitude in every second duration, and a relatively lower amplitude in the other durations. The signal 230 has a relatively lower frequency in every second duration, and a relatively higher amplitude in the other durations. The signal 240 is phase shifted 180 degrees every second duration compared to for the other durations.

Another example is that the transmitter may switch between using two different antenna impedances, so that the transmitted signal switches back and forth between two states corresponding to these antenna impedances, such that the signal remains in these states during respective durations, similarly to the signals 210-240 shown in FIG. 2. Thus, a codeword would be represented by a duration during which the signal is transmitted using one of the antenna impedances before switching to the other. This may for example be beneficial for a backscattering transmitter that can switch between two different antenna impedances for backscattering a received signal.

A further example is that the transmitter may switch between using two different polarizations, e.g., using two antennas with different polarizations and the transmitter switches between using these for the different durations. Here, the signal switches back and forth between states corresponding to the two polarizations such that the signal remains in these states during respective durations, similarly to the signals 210-240 shown in FIG. 2. Thus, a codeword would be represented by a duration during which the signal is transmitted using one of the polarizations before switching to the other.

An efficient low power circuit to obtain the proposed signal type (such as the signals in FIG. 2) is to use an analog integrator, such as an energy storing component (for example a capacitor). The time periods are then defined by integrator charging/ discharging between two target voltages using a charging/discharging current with a magnitude controlled by the current symbol data. When the integrator reaches one target voltage the carrier is turned on, and when it reaches the other target voltage the carrier is turned off. The data to be transmitted is stored in a buffer (for example a register) with codewords a few bits wide. Every time the integrator reaches a target voltage a new codeword to be transmitted is loaded from the buffer to a digital to analog converter (DAC) setting the charging/discharging current level, and the direction of the charging current is reversed. The current sources may be weighted so that the charging/discharging time becomes linearly proportional to the codeword.

Such a modulator with independent multi-level on and off time durations/periods, allows an increased spectral efficiency compared to, e.g., OOK. This modulator can be applied to active as well as backscattering transmitters. The modulator can be efficiently realized by an analog integrator, where the charging/discharging current is controlled by, e.g., a non-linearly weighted DAC, controlled by the data of the symbol to be transmitted. The state of the output signal is changed every time the integrator reaches one of two end voltages, detected by comparators. The charging current direction is then also reversed, and new data is loaded into the DAC from the buffer where the data to be transmitted is stored. Since the modulator may be self-timed, it will not require any additional symbol clock. FIG. 3 shows an efficient modulator 300 according to an embodiment. The data 301 to be transmitted is loaded into a buffer 302. When the buffer 302 receives a clock signal (denoted by ‘elk’ in FIG. 3) it outputs a new data word (or codeword) to the digital to analog converter (DAC) 303. The output of the DAC 303 is a current signal (denoted by Icp FIG. 3), setting the current of a charge pump (CP) 304. At its output the charge pump 304 will provide either a charging or discharging current with a magnitude equal to the charge pump current. Whether the charge pump 304 is providing charging or discharging, e.g., by switching the sign of its output current, is controlled by the up/dwn signal received by the charge pump 304. As will be described further below with reference to FIG. 5a, the DAC 303 and the charge pump 304 may for example be merged into a single circuit block. The charging current from the charge pump 304 is fed to a capacitor 305, creating a voltage ramp as a function of time when it integrates the current from the charge pump 304. Connected to the capacitor 305 is a set of one or more comparators 306, detecting if the voltage of the capacitor 305 is above one threshold level, and/or below another threshold level. If the signal (denoted by ‘up/dwn’ in FIG. 3) controlling the charge pump 304 should be high to charge the capacitor 305, the latch 307 (e.g., a set/reset (SR) latch) should be set when the voltage of the capacitor 305 is detected to be below the lower threshold level, so then the comparator 306 should assert the set signal of the latch 307. In a similar manner, the reset signal of the latch 307 should be asserted when the capacitor voltage is above the higher threshold level. The capacitor 305 will then be charged up and down between the two threshold levels. The output signal 308 of the latch 307 will be a signal that switches back and forth between a high state and a low state (which can also be referred to as an ON state and an OFF state, respectively) such that the signal remains in these states during respective durations corresponding to the input data word (or codeword). This output signal 308 can be used, for example, to modulate a transmitter to obtain any of the signals 210, 220, 230, or 240, or to switch between two antenna impedances (e.g., in a backscatter transmitter) or to switch between two polarizations.

The output signal 308 may switch between high and low state in a manner that in some ways resembles an OOK signal, but with the difference that the durations of the high and low states of the signal 308 differ depending on the codewords provided from the buffer 302. In other words, in contrast to a traditional OOK signal, the durations of all the high and low states of the signal 308 are not necessarily controlled by a common clock cycle, so different numbers of data bits may be represented by the signal 308 per time unit. The output signal 308 also resembles a Pulse-Width-Modulated (PWM) signal, which switches between an ON state and an OFF state. However, for PWM the duration of the ON duration, or the ratio of the ON duration compared to the OFF duration (referred to as duty cycle) carries the information, while the signal 308 carries information during both the ON/high duration and OFF/low duration. Thus, the spectral efficiency is also increased compared to PWM.

Further, in the modulator 300, when the output signal 308 changes between high and low state, a delay element (dl) 309 and an XOR gate 310 may be used to detect the change and clock the buffer 302, so that the buffer 302 outputs the next data word to be represented in the output signal 308. A further delay element (d2) 311 is introduced to the generated clock signal (denoted by ‘elk’ if FIG. 3), with the purpose of reducing inter-symbol interference. The time delay in the comparator 306, latch 307, and charge pump 304 will result in an overshoot of the capacitor voltage compared to the threshold level applied by the comparator 306, which will be proportional to the charging rate. If the new charging current amplitude is delayed by another time, equal to the time delay causing the overshot, the capacitor voltage will return to the threshold level before the new current level is applied. This way, there will be no inter-symbol interference, as the capacitor start voltage with the new current is independent from the previous symbol and the previous charging rate.

The voltage level of the capacitor 305, with compensation for the delays, is illustrated in FIG. 4. During a first time period 410, there is a high output (giving a positive output current) from the charge pump 304 and the capacitor voltage is increased. At time tl in FIG. 4, the capacitor voltage reaches an upper threshold level (denoted Threshold Level 2), making (e.g., after a delay) the output signal 308 switch between the high and low state, as described above. The up/dwn signal will then configure the charge pump 304 to switch between charging and discharging. This switch will, after the delay induced by e.g., the comparator 306, the latch 307, the charge pump 304 and/or other circuits/connections, occur at time t2 in FIG. 4. The charge pump 304 is now discharging the capacitor, using the same magnitude as was used during time period 410. The delay induced by the delay element d2 311 adapts the timing of when the new codeword should be outputted from the buffer 302 to the DAC 303 such that at time t3, in FIG. 4, when the capacitor voltage is back at the upper threshold level, the discharging amplitude is switched to the new value. This is illustrated by the change of inclination at time t3 in FIG. 4, where the amplitude of the charging/discharging current is reduced after the change such that the time period 420 becomes longer than time period 410. The same procedure for handling the overshoot of the threshold level is also shown at the switch between time period 420 and time period 430.

The time periods will be equal to C*(Threshold Level 1 - Threshold Level 2)/I_cp, where C is the (fixed) capacitance of the capacitor, the two threshold voltage levels are fixed, and ICP is the charging current. Thus, by changing the magnitude of the charging/discharging current ICP, the time period will change. Effectively, the time period will be equal to K/ICP, where K is a constant set by capacitance and voltage thresholds, and ICP is the output of the DAC 303 (assuming that the charge pump 304 only changes the sign and does not scale the current). The characteristics is a 1/x type, which is non-linear, for time delay versus current magnitude. If a magnitude of a certain level provides a certain delay, the delay may be increased by 50% by reducing the current magnitude by 33%. However, to reduce the delay by 50% you have to increase the current magnitude by 100%. That is, the change in current is 3x larger for the same change in time period with different sign.

To compensate for this non-linear current to time period characteristic, the DAC digital to current characteristic may have the opposite non-linearity, so that the overall digital to time period conversion becomes linear. This is accomplished by a non-linear weighting of the DAC cells. The non-linear weighting of the DAC cells will depend on the range of modulation and number of levels. For example, assume that there is a modulation range of 3 times between the longest and shortest time period of the output signal 308, that there are 8 different levels, and that we normalize a first DAC cell to 1 and the longest time period to 1. Then the different time periods/durations become 1, 0.91, 0.81, 0.71, 0.62, 0.52, 0.43, and 0.33 for equidistant time symbols. The charging currents become proportional to the inverse of the time, that is for this example they will be 1, 1.10, 1.23, 1.41, 1.61, 1.92, 2.32 and 3. This is the total charging currents, which is the sum of weights used in the DAC cells, such the DAC cell weights can be calculated as 1, 0.10, 0.13, 0.18, 0.20, 0.30, 0.40, 0.68. As an example, thermometer coded signals could be applied, where each bit of the input signal could control a current cell, such that the least significant bit (LSB) controls the current source with current equal to 1, the next bit controls the current source with 0.10, and so on. Hence in the example above, 8 bits are needed to control the 8 sources in this way, such that for the thermometer coded DAC, we get normalized output current according to: 00000001 -> 1 = 1 00000011 -> 1+0.10 = 1.10 00000111 -> 1+0.10+0.13 = 1.23

00001111 -> 1+0.10+0.13+0.18 = 1.41

00011111 -> 1+0.10+0.13+0.18+0.20 = 1.61 etc.

For minimization of delays and glitches in the modulator 300, when the DAC 303 uses thermometer code, the data could be stored in thermometer form in the buffer 302. Thus, any conversion from binary to thermometer code may be performed prior to storing the transmission data 301 in the buffer 302.

It is possible to select or tune the charging currents to obtain any durations in the output signal 308. In one embodiment, there are fixed ratios between the charging currents, and the data rate of the transmission is tuned by changing the absolute/overall current level but keeping the ratios between the different current levels associated with the different codewords of the data. In another embodiment, programmability in the ratios is introduced by having a number of current cells in the DAC 303, for each bit in the codewords, that can be selectively activated or inactivated. Thus, the current sources could for example be controlled via the input signal, putting an AND gate with a new control signal to one input and the regular control signal to the other. When the new control signal is '0' the current sources become inactive. In another example there can be a series transistor in the current source, which we turn off to inactivate the current source, using the new control signal. This new control signal may be generated by a modulation control unit that programs the current cells of the DAC to set the distances between modulation points.

The DAC 303 and charge pump 304 can be advantageously combined to reduce power consumption and improve speed. Rather than replicating the full DAC output current in current mirrors as would be done in a solution with a separate charge pump, a merged charge pump and DAC design can be realized so that only the reference current needs to be replicated. The signal path will then also be shortened resulting in higher speed. The schematic of a merged charge pump and DAC design can be seen in FIG. 5a, while a schematic of separated charge pump and DAC design can be seen in FIG. 5b.

In FIG. 5b the DAC and charge pump functions are implemented as two separate circuit blocks, where the DAC 550 is indicated by the dotted line. In this separate design, the full DAC output current passes through the input current mirrors 560 of the charge pump 570, which may cause higher power consumption than in the case of a merged charge pump and DAC design as in FIG 5a. In the merged design shown in FIG 5a, the current I_ref instead biases the input current mirrors 510. More important, however, is that the transistors 540 and 541 in FIG 5a operate at a bias current when they are active that is independent of output current control setting (cf DO-DN). Each cell in the combined DAC and charge pump delivers a current, when it is on, that is independent of the digital control word value. This is not the case in the separated design in FIG 5b. In FIG. 5b, the transistors 580 in the charge pump 570 operate with the output current of the DAC 550, so if the output current of the DAC 550 changes by, e.g., a factor of 4, so does the current density of the devices that are active. Important transistor properties such as delay and gain then become dependent on the digital control word. This may require more margins in the design to allow such variations in transistor performance, and increasing margins requires increased power consumption. Hence, the merged design illustrated in FIG. 5a can operate at a lower power consumption than the separate design illustrated in FIG. 5b.

In FIG. 5 a there are a number of bit stages 0, 1, ... , N, each controlled by a digital signal Dx (DO-DN). The width of the transistors in each stage are weighted with respect to each other. For instance, the transistors may have equal width in each stage, they may have unary weighting, or they may be binary weighted. It is also possible to have the (non-linear) weights as indicated before to make the charging times uniformly distributed when successively more stages are activated. Using a larger number of stages can increase flexibility at the cost of complexity. The bit stages may also be referred to as cells.

In the merged design of FIG. 5 a, the charging direction is controlled by up/dwn signal. When the up/dwn signal is high, the output of the NAND gates 520 in the upper part (which may be referred to as a charge up part) can become low, such that the PMOS (P- channel Metal-Oxide-Semiconductor) transistors 540 turn on. When the up/dwn signal instead is low, the output of the AND gates 530 in the lower part (which may be referred to as the charge down part) can become high, such that the NMOS (N-type Metal-Oxide- Semiconductor) transistors 541 turn on. Observe the inverter at the corresponding inputs to the AND gates 530, indicated by the circle, which inverts the up/dwn signal compared to for the NAND gates 520. The NAND gates 520 and AND gates 530 also receive the digital input signals Dx, and if both the direction of charging corresponds to the part controlled and the digital input is asserted, the transistor is activated such that current may flow from/to the stage.

In essence there are two DACs in FIG. 5a, one charge up DAC with PMOS devices 540 and one charge down DAC with NMOS devices 541. Which of the DACs that is active is controlled by the up/dwn signal through the AND and NAND gates 520, 530. The DACs are biased using the current mirrors 510 to the left in FIG. 5a. The current mirrors 510 are designed to resemble the DAC cells when active, so the reference current Iref is accurately replicated (and scaled according to the width ratio) when output by the DAC cells. To achieve this, each current mirror transistor is connected the supply/ground through a second transistor 515 turned on by connecting its gate to ground/supply. The reference current Iref can be used to adjust the charging current level without altering the current ratio between the DAC stages, and it can thus be used to adjust the data-rate without altering other modulation properties. It will be appreciated that the separated DAC and charge pump may correspond to DAC 303 and charge pump 304 in FIG. 3. It will also be appreciated that the combined DAC and charge pump in the merged design can replace the DAC 303 and charge pump 304 in FIG. 3. Thus, the resulting output current lout from both FIG. 5a and 5b may be used to, e.g., charge the capacitor 305.

The proposed modulator (for example the modulator 300 shown in FIG. 3) may be used to generate the signals 210-240 described above in relation to FIG. 2. The output signal 308 that switches between the high (or ON) and low (or OFF) state may be used as a control signal to control a signal to be transmitted. It may, as discussed above, control the amplitude and/or phase and/or frequency and/or antenna impedance and/or polarization of the signal such that the proposed signal format is achieved. In some embodiment, the signal to be transmitted may be the output signal 308 itself.

In some embodiments, the proposed modulator (for example the modulator 300 shown in FIG. 3) may also be used to generate different forms of coded OOK such as Manchester coded OOK, FM0 or Miller encoded OOK. These forms of encoding, sometimes referred to as Run-Length-Limited (RLL) encoding, have in common that there is an a-priori known maximum number (or limitation) of consecutive logical 0’s or l’s giving a limitation of the number of consecutive ON or OFF periods. By applying an auxiliary code to, for example, Manchester coded bits, it is possible to transform them into a sequence of durations according to some embodiments in this disclosure. For example, for Manchester coding a logical ‘0’ is mapped to ON-OFF while a logical ‘1’ is mapped to OFF-ON. Hence, in any sequence of encoded data bits there are at most two consecutive OFF or ON. As an illustration, the data sequence 01001 will be Manchester encoded to ON-OFF - OFF-ON - ON-OFF - ON-OFF - OFF-ON. This sequence may be generated using the disclosed modulator, e.g., by feeding the sequence of durations 1,2, 2, 1,1, 2,1. This may for example be achieved by using a proper choice of input codewords.

In a Manchester code the runs are 0, 1, 00, or 11 so ‘2’ in the example above can represent either 00 or 11 such that the code is well defined. However, if all the bits in the data is flipped, one gets the same durations: 10110 -> OFF-ON - ON-OFF - OFF-ON - OFF-ON - ON-OFF -> 1,2, 2, 1,1, 2,1. This ambiguity may easily be resolved. As a first example, the transmitter may be set to state OFF/ON according to whether the first bit is a 0 or a 1. As a second example, a convention may be added such as always starting with a bit 0, for example by prepending a training sequence or sync word. RLL codes may have longer run-lengths than two, as in the example above, but the idea is the same. For example, the code bits could look like 0 1 1 1 0 0 in which case the duration may be 1 3 2. Note that the difference between the durations in this example is linear, where each duration differs by 1, but it is appreciated that the difference between the durations does not need to be linear.

In some embodiments, the proposed modulator (for example the modulator 300 shown in FIG. 3) may be used to support bandwidth efficient link adaptation. For example, a modulator supporting 8 levels of durations can also be used to generate 4 levels of durations, or 2 levels of duration, while simultaneously controlling the signal bandwidth. Suppose that the modulator supports the durations 1, 0.91, 0.81, 0.71, 0.62, 0.52, 0.43, 0.33. Then, codewords of length 3 may be used if all 8 durations are used, while codewords of length 2 (e.g., 00/01/10/11) could be used with e.g., durations 0.43, 0.62, 0.81, 1, and codeword of length 1 (e.g., 0/1) could be used with e.g., durations: 0.62 and 1. Also, referring to the example of Manchester coding above, the modulator can also be used to generate the Manchester encoded signal ON-OFF-OFF-ON-ON-OFF-ON-OFF-OFF-ON by using the durations 0.33,0.62,0.62,0.33,0.33,0.62,0.33. In addition, it can generate the same signal but with a narrower bandwidth (hence lower data rate) by using the sequence 0.52,1,1,0.52,0.52,1,0.52. Thus, the proposed modulator allows simultaneous fine tuning of the data rate and bandwidth to optimize the data throughput while also controlling the signal bandwidth. Since a transmitter using such a modulator can support several data rates while keeping the bandwidth approximately constant, it enables an improved link adaptation for low power/low complexity devices, where, for example, the transmitter can be designed to transmit up to 3 bits per signaling period in some scenarios but may also be designed to transmit 2 bits or one bit per signaling period in other scenarios.

The link performance of the proposed transmitter has been evaluated by means of simulations for backscatter radio. Backscatter radio is challenging at the receiver (i.e., the device that receives the backscattered radio signal) because there is often strong interference from the carrier emitter (i.e., the device that transmits the original radio signal that is backscattered by the backscattering device). So-called FMO modulation has been used as a benchmark since it is widely used in commercial backscatter radios. This modulation is based on OOK but adds memory in order to introduce a spectral null at the carrier frequency (corresponding to zero baseband frequency) and in this way helps the receiver to mitigate the impact of interference from the carrier emitter. The left-hand side of FIG. 6 shows the spectra of the received signals (after frequency down-conversion to baseband and channel selective filtering) for FMO, a signal modulated according to modulator 300 with 8 levels of duration, and very strong interference from a carrier emitter impaired by phase noise. No special interference mitigation algorithms are used at the receiver. Like FMO, the information in the signal modulated according to modulator 300 with 8 levels of duration is carried by the transitions between signal levels, and hence it also offers robustness to interference around DC. Here, the spectral width (e.g., 20 dB bandwidth) of the signal modulated according to modulator 300 with 8 levels of duration is slightly less than that of FMO. The peak rate of the signal modulated according to modulator 300 with 8 levels of duration is 3 times larger than that of FMO, while having comparable bandwidth. The right-hand side of FIG. 6 shows significant throughput gains of the signal modulated according to modulator 300 with 8 levels of duration with respect to FMO at SNRs above 15 dB.

Figure 7 illustrates an apparatus 700 according to some embodiments. The apparatus 700 may be used for switching an output signal 750 between a first state and a second state based on a sequence of codewords. The apparatus 700 comprises an input circuit 710, an energy storing component 730, and a comparator circuit 740. The apparatus 700 will be described with reference to FIG. 7 and FIG. 3, where the proposed modulator 300 described above in relation to FIG. 3 is a specific example of the apparatus 700. However, it will be appreciated that the apparatus 700 may be realized in other ways than the example given in relation to FIG. 3.

The input circuit 710 (which may also be referred to as e.g., converter, charging circuit, and/or charger) is configured to charge or discharge the energy storing component 730 using an input current linput. The magnitude of the input current linput depends on a codeword from the sequence of codewords. In some examples, the sequence of codewords may be input to the input circuit and/or may be buffered in the input circuit.

The energy storing component 730 is configured to be connected to the comparator circuit 740 such that, based on that a voltage of the energy storing component 730 reaches an upper or lower threshold level, the comparator circuit 740 switches the output signal 750 between the first state and the second state. The duration until the voltage of the energy storing component 730 reaches the upper or lower threshold level depends on the magnitude of the input current linput. The comparator circuit 740 may for example switch the output signal 750 between the first state and the second state when (e.g., immediately, or with some delay) a voltage of the energy storing component 730 reaches an upper or lower threshold level. The comparator circuit 740 may for example be triggered to switch the output signal 750 between the first state and the second state by that a voltage of the energy storing component 730 reaching an upper or lower threshold level. The comparator circuit 740 may in some examples comprise e.g., a Schmitt trigger, or at least one comparator 306 and a latch 307, such as for example an SR latch, as discussed above in relation to FIG. 3. For example, the comparator circuit 740 may be able to detect when a voltage reaches the two thresholds, and may be able to switch the output signal 750 when this happens. This may in some examples be realized using two comparators 306, one comparing the voltage to the lower threshold and one comparing the voltage to the higher threshold. The two comparators may then control the latch 307, such that the output signal 750 is switched.

The apparatus 700 further comprises a feedback path 760 from the comparator circuit 740. The feedback path 760 is configured to switch the input circuit 710 between charging and discharging the energy storing component 730. The switch, caused by the feedback path 760, may be based on that the voltage of the energy storing component 730 reaches the upper or lower threshold level. The switch, caused by the feedback path 760, may be based on that the output signal 750 switches between the first state and the second state. For example, when the voltage of the energy storing component 730 reaches the upper or lower threshold level, the output signal 750 may switch between the first state and the second state (e.g., between a high state and a low state or between an ON state and an OFF state). If the output signal 750 switches between the first state and the second state, the signal of the feedback path 760 may also switch between the first state and the second state. In some examples, the input circuit 710 may be configured to charge the energy storing component 730 when the signal of the feedback path 760 is in the first state and discharge the energy storing component 730 when the signal of the feedback path 760 is in the second state, or vice versa. In some examples, the feedback path 760 may be configured to be connected to, or in connection with, the input circuit 710. It is appreciated that the switch caused by the feedback path 760 might be delayed compared to when the voltage of the energy storing component 730 reaches the upper or lower threshold level. It is also appreciated that the switch caused by the feedback path 760 might be delayed compared to when the output signal 750 switches between the first state and the second state. The delay may for example depend on the delay caused by the different components and/or circuits and/or connections, e.g., between the energy storing component 730 and the input circuit 710.

The feedback path 760 is further configured to control the input circuit 710 to update the magnitude of the input current linput based on a next codeword from the sequence of codewords. The update caused by the feedback path may be based on that the voltage of the energy storing component 730 reaches the upper or lower threshold level. The update, caused by the feedback path 760, may be based on that the output signal 750 switches between the first state and the second state. In some examples, the input circuit 710 may be configured to update the magnitude of the input current linput based on a next codeword from the sequence of codewords when the signal of the feedback path 760 switches between the first state and the second state. It is appreciated that the update caused by the feedback path might be delayed compared to when the voltage of the energy storing component 730 reaches the upper or lower threshold level. It is also appreciated that the update (of the magnitude of the input current linput) caused by the feedback path 760 might be delayed compared to when the output signal 750 switches between the first state and the second state. Furthermore, the update (of the magnitude of the input current linput) caused by the feedback path 760 might be delayed compared to, or occur before, the switch, caused by the feedback path 760, of the input circuit 710 between charging and discharging the energy storing component 730. The delay may for example depend on the delay caused by the different components and/or circuits and/or connections e.g., between the energy storing component 730 and the input circuit 710.

According to some embodiments, the apparatus 700 may provide an output signal 750 such that a duration during which the output signal 750 is in the first state may represent a first codeword from the sequence of codewords. Furthermore, a duration during which the output signal 750 is in the second state may represent a second codeword from the sequence of codewords.

According to some embodiments, the comparator circuit 740 may be configured to switch the output signal 750 back and forth between the first state and the second state based on the voltage of the energy storing component 730, such that the output signal 750 remains in these states during respective durations forming a sequence of durations. Thus, each codeword in the sequence of codewords may be represented by a duration in the sequence of durations. This is illustrated in relation to FIG. 2 above, where there are four codewords (‘00’, ‘OF, ‘10’, ‘11’) represented by a respective duration (Tl, T2, T3, T4).

According to some embodiments, the input circuit 710 may comprise a digital buffer and a digital to analog converter (DAC). This is for example discussed in relation to FIG. 3 above, which shows a digital buffer 302 and a DAC 303. The digital buffer 302 may be configured to buffer codewords from the sequence of codewords and output them to the DAC 303. The DAC 303 may be configured to convert codewords to currents. The magnitude of a current may depend on the value of a respective codewords to be converted by the DAC 303.

According to some examples, when the input circuit 710 comprises a digital buffer and a DAC, the input current linput may be a current provided by the DAC, and the DAC may be configured to be switched by the feedback path 760 between charging and discharging the energy storing component 730. This relates to the integrated design discussed in relation to FIG. 5a above. In the example given in relation to FIG. 5a above, lout and the up/dwn signal may correspond respectively to linput and the signal of the feedback path 760 in FIG. 7. In some examples of the integrated design, the DAC may comprise a plurality of cells, where each cell may be controlled by a respective input which depends on the codeword. Then, each cell may provide a current (if activated by its input bit), which may add/subtract from the total charging/discharging current by the up/down signal. Further, in the example of the integrated design, the DAC may comprise at least one current mirror arrangement, which receive a reference current I_ref and provides bias voltages to the cells, where the reference current Iref may be proportionally replicated as output current of active cells to transistors of the cells. As an example, the DAC may have two inputs and one output. One input may be a codeword from the buffer, and one a control signal (such as the signal of the feedback path 760 in FIG. 7). The control signal may then determine whether the output current lout (providing linput) will be charging or discharging the energy storing component 730. In some examples, the output of the input circuit 710 and/or the output of the DAC may be configured to be connected to, or in connection with, the energy storing component 730. It will be appreciated that the DAC according to this example may replace the DAC 303 and the charge pump 304 in FIG. 3.

According to some examples, when the input circuit 710 comprises the digital buffer 302 and the DAC 303, the input circuit 710 may further comprise a charge pump, such as the charge pump 304 in FIG. 3. The charge pump 304 may be configured to receive a current ICP provided by the DAC 303, and the input current linput may be a current provided by the charge pump 304. The charge pump 304 may be configured to be switched by the feedback loop 760 between charging and discharging the energy storing component 730. This relates to the separate design of the DAC 303 and the charge pump 304, as discussed in relation to FIG. 5b above. As an example, the charge pump 304 may have two inputs and one output. One input may be the current ICP from the DAC 303, and the other a control signal (such as the up/dwn signal in FIG. 3, or the signal of the feedback loop 760 in FIG. 7). The control signal may then determine whether the current ICP will be output to the energy storing component 730 as it is, or if the sign of the input current will be inverted. It will be appreciated that the input current linput might be equal to the current ±ICP from the DAC 303. However, it is also appreciated that the input current linput may be scaled by the charge pump such that the current linput is proportional to ±ICP, e.g., ±alcp, where a may be a scaling coefficient of the charge pump. In some examples, the output of the input circuit 710 and/or the output of the charge pump 304 may be configured to be connected to, or in connection with, the energy storing component 730.

According to some embodiments, the feedback path 760 may comprise a detector 770 configured to detect that the output signal 750 switches between the first state and the second state. The detector 770 may further be configured to control the input circuit 710 to update the magnitude of the input current linput based on that the detector 770 detects that the output signal 750 switches between the first state and the second state. In some examples, the detector 770 may also be configured to switch the input circuit 710 between charging and discharging the energy storing component 730 based on that the detector 770 detects that the output signal 750 switches between the first state and the second state. According to some examples, the detector 770 may comprise a first delay element and an XOR gate. This is further discussed in relation to FIG. 3 above, which shows a first delay element 309 and an XOR gate 310. The signal of the feedback path 760 may be input to the first delay element 309, and the signal of the feedback path 760 and the output from the delay element 309 are input to the XOR gate 310. As long as the signal of the feedback path 760 remains in the same state, the output of the delay element 309 and the signal of the feedback path 760 will be the same. Thus, the output of the XOR gate 310 will be low. However, when the voltage of the energy storing component 730 has reached the upper or lower threshold level and the comparator circuit 740 switches the output signal 750 between the first state and the second state, the first delay element 309 will delay the signal of the feedback path 760 such that the two input signals to the XOR gate 310 will be different for as long as the first delay element 309 delays the signal. Thus, the output of the XOR gate 310 will be high, which may be used to trigger the input circuit 710 to update the magnitude of the input current linput based on a next codeword from the sequence of codewords. It will be appreciated that the output of the XOR gate 310 may similarly be used to trigger the switch of the input circuit 710 between charging and discharging the energy storing component 730. In some examples, the signal of the feedback path 760 is the input signal to the detector 770 and/or the first delay element 309 and/or the XOR gate 310. However, it is appreciated that other components and/or circuits may be located between the signal of the feedback path 760 and the detector 770 and/or the first delay element 309 and/or the XOR gate 310.

According to some examples, the feedback path 760 may comprise a second delay element 780. The second delay element 780 may be configured to delay the update of the magnitude of the input current linput by at least a time. The time may correspond to a delay associated with the comparator circuit 740. As described in relation to FIG. 4 above, once the voltage of the energy storing component 730 reaches the upper or lower threshold, there will be a delay until the input circuit 710 switches between charging and discharging the energy storing component 730. This delay is, e.g., due to the delay induced by the comparator circuit 740. The delay may further depend on delays in the input circuit 710 and/or the feedback path 760 and/or the wired connections and/or other circuits and/or components. Due to this delay the voltage of the energy storing component 730 will continue above the upper threshold or below the lower threshold before the switch takes place. It will be appreciated that the delay until the input circuit 710 switches between charging and discharging the energy storing component 730 may differ from the delay until the input circuit 710 updates the magnitude of input current Lnput. Therefore, the purpose of the second delay element 780 is to compensate for these delays, such that the magnitude of the input current linput is updated once the voltage of the energy storing component 730 has returned to its threshold. This will reduce the intersymbol interference. In the example in FIG. 7, the second delay element is located after the detector 770, but it is appreciated that it may instead be located before the detector 770. It will also be appreciated that the second delay element 780 may be configured to, instead, or also, delay the switch between charging and discharging the energy storing component 730 by at least a time.

In preferred embodiments, the energy storing component 730 comprises a capacitor. However, the same principles as described herein are also possible by using an inductor instead of a capacitor as the energy storing component 730. It is appreciated that if an inductor is used, the other components/circuits need to be adapted such that the inductor is fed with an input voltage from the input circuit 710 and that the comparator circuit 740 instead compares the current of the inductor to an upper and/or lower threshold.

According to some embodiments, the input data provided to the apparatus 700 is an RLL code, and an auxiliary code is applied to the RLL code to generate the sequence of codewords. In an example, a sequence of consecutive bits (representing a run) from the RLL code is represented as a sequence of durations. In an example, each duration represents a respective number of consecutive 0’s or number of consecutive l’s. This may be used to generate different forms of coded OOK such as Manchester coded OOK, FM0 or Miller encoded OOK using the apparatus 700. According to some examples, an initial state (e.g., ON or OFF) of the apparatus 700 may be based on whether the first run in the RLL coded data is a run of zeros, or a run of ones. In some examples, the RLL code may be input to the input circuit, and the auxiliary code may be applied to the RLL code within the input circuit. In some examples, the auxiliary code is applied to the RLL code before the input circuit and the sequence of codewords may be input to the input circuit.

The circuits/components shown in FIG 3, 5a, 5b and 7 may for example be connected or coupled to each other as indicated in these drawings. Some of these circuit/components may for example be configured to be connected/coupled to each other, but may sometimes be temporality disconnected from each other. Two circuits and/or components may be configured to be connected to, or in connection with, each other when there may be a physical connection between them. The physical connection may for example be a physical wire. The connection may for example be a direct connection, such that the two circuits and/or components are connected without any intermediate circuits and/or components. However, it is appreciated that the circuits and/or components may be connected to, or in connection with, each other even when there are one or more intermediate circuits and/or components between them.

FIG. 8 illustrates a method 800 for switching an output signal between a first state and a second state based on a sequence of codewords. The method 800 may for example be performed by the apparatus 700 described above with reference to FIG. 7, or the modulator 300 described above with reference to FIG. 3. The method 800 will be described with reference to FIG. 7 and FIG. 8, but it will be appreciated that the method 800 may for example be performed by other devices than the apparatus 700.

The method 800 comprises charging or discharging 830 an energy storing component 730 using an input current linput, where a magnitude of the input current linput depends on a codeword from the sequence of codewords.

The method 800 comprises switching 850 the output signal 750 between the first state and the second state, based on that a voltage of the energy storing component 730 reaches an upper or lower threshold level. The switching 850 may for example be performed when a voltage of the energy storing component 730 reaches an upper or lower threshold level, or be triggered by that a voltage of the energy storing component 730 reaches an upper or lower threshold level. It will be appreciated that there may be a delay between when the voltage of the energy storing component 730 reaches an upper or lower threshold level and when the switching 850 occurs.

The method 800 comprises switching 860 between charging and discharging the energy storing component 730, based on that a voltage of the energy storing component 730 reaches an upper or lower threshold level. The switching 860 may for example be performed when a voltage of the energy storing component 730 reaches an upper or lower threshold level, or be triggered by that a voltage of the energy storing component 730 reaches an upper or lower threshold level. It will be appreciated that there may be a delay between when the voltage of the energy storing component 730 reaches an upper or lower threshold level and when the switching 860 occurs.

The method 800 comprises updating 870 the magnitude of the input current linput based on a next codeword from the sequence of codewords, based on that a voltage of the energy storing component 730 reaches an upper or lower threshold level. The updating 870 may for example be performed when a voltage of the energy storing component 730 reaches an upper or lower threshold level, or be triggered by that a voltage of the energy storing component 730 reaches an upper or lower threshold level. It will be appreciated that there may be a delay between when the voltage of the energy storing component 730 reaches an upper or lower threshold level and when the updating 870 occurs.

In some embodiments of the method 800, a duration during which the output signal is in the first state represents a first codeword from the sequence of codewords, and a duration during which the output signal is in the second state represents a second codeword from the sequence of codewords.

In some embodiments of the method 800, the output signal switches back and forth between the first state and the second state such that the output signal remains in these states during respective durations forming a sequence of durations, and where each codeword in the sequence of codewords is represented by a duration in the sequence of durations.

The method 800 may, in some embodiments, comprise providing 820 an input current linput and/or converting 810 the codeword from the sequence of codewords to the input current linput. The magnitude of the input current linput depends on the value of the codeword.

The method 800 may, in some embodiments, comprise comparing 840 a voltage of the energy storing component 730 to the upper or lower threshold level. The switching 850, switching 860, and updating 870 may be performed based on that the comparing 840 the voltage to the upper or lower threshold level indicates that the voltage has reached the upper or lower threshold level.

The method 800 may, in some embodiments, comprise detecting 880 that the output signal switches between the first state and the second state. Updating 870 the magnitude of the input current linput may comprise updating 870 the magnitude of the input current linput based on detecting 880 that the output signal switches between the first state and the second state.

The method 800 may, in some embodiments, further comprise delaying 890 the update of the magnitude of the input current linput by at least a time. The time may, for example, correspond to a delay associated with and/or introduced by one or more circuits and/or components of the device implementing the method 800. In one example, the delay may correspond to the delay introduced by the comparator circuit 740 of the apparatus 700. This is further discussed e.g., in relation to FIG. 4 above.

FIG. 9 illustrates a method 900 implemented by a transmitter in a wireless communication network. The method 900 is for communicating a sequence of codewords. The method 900 comprises transmitting 930 a signal. The signal switches between a first state and a second state. A first codeword from the sequence of codewords is represented by a first duration during which the signal is in the first state. A second codeword from the sequence of codewords is represented by a second duration during which the signal is in the second state. The signal may for example be a radio signal which is to be transmitted from the transmitter to a receiver, such that the sequence of codewords is communicated to the receiver. Examples of signals provided in the method 900 are shown above in relation to FIG. 2, such as signals 210-240. In some examples, the output signals 308 and 750 provided by the modulator 300 and apparatus 700, discussed above in relation to FIG. 3 and FIG. 7, may be used to switch the signal of method 900 between the first and second state. In some examples, the transmitter implementing the method 900 may comprise the modulator 300 and/or apparatus 700. The signal provided in the method 900 is a way to convey information in a more spectrally efficient way than, e.g., OOK, and which may be used by ultra-low power transmitters.

In some embodiments of the method 900, the signal switches back and forth between the first state and the second state such that the signal remains in these states during respective durations forming a sequence of durations, and each codeword in the sequence of codewords is represented by a duration in the sequence of durations.

In some embodiments of the method 900, whether a codeword from the sequence of codewords is represented by a duration during which the signal is in the first state or by a duration during which the signal is in the second state, is determined based on whether the codeword is located at an odd or even numbered position in the sequence of codewords. For example, in the example given in relation to FIG. 2, the sequence of codeword is ‘00 01 10 11’. For example, the state used for the first and third codeword (‘00’ and ‘10’) may be denoted the first state, and the state used for the second and fourth codeword (‘01 ’ and ‘11’) may be denoted the second state. Thus, the first and third codeword will, in this example, be located at odd positions (position 1 and 3) in the sequence of codewords, and therefore are represented by durations during which the signal is in the first state. The second and fourth codeword will, in this same example, be located at even positions (position 2 and 4) in the sequence of codewords, and therefore are represented by durations during which the signal is in the second state. If, for example, the sequence of codewords was instead ‘01 00 10 11’, the first state would have been used for the codeword ‘01’ and the second state would have been used for the codeword ‘00’. In some examples, the signal is configured to start in a specific state and/or to end up in a specific state after a predefined training sequence.

In some embodiments of the method 900, a duration during which the signal is in the first state is between two durations during which the signal is in the second state, and a duration during which the signal is in the second state is between two durations during which the signal is in the first state. In some embodiments of the method 900, a duration during which the signal is in the first state extends from a switch from the second state to the first state until a switch from the first state to the second state, and a duration during which the signal is in the second state extends from a switch from the first state to the second state until a switch from the second state to the first state. Thus, the duration, during which the signal is in the first state, may start when the signal switches from the second state to the first state, and end when it switches back, and vice versa. The duration representing a codeword may change somewhat over time so that slightly different durations represent different occurrences of the same codeword, e.g., due to time drifting of hardware components. It is, however, appreciated that if the duration drifts too much, this will affect the performance of the receiver.

In some embodiments of the method 900, in the signal, equal durations represent different occurrences of the same codeword, and different durations represent different codewords. Comparing to the signals in FIG. 2, where there are four codewords (‘00’, ‘01’, ‘10’, and ‘11’), there will be four distinct durations (T1-T4). Equal durations, e.g., Tl, represents different occurrences of the same codeword, e.g., ‘00’. While two different durations, e.g., T1 and T2, represent different codewords, e.g., ‘00’ and ‘01’.

In some embodiments of the method 900, a codeword comprises N bits, and a duration during which the signal is in the first state or in the second state corresponds to a duration from a set of M durations, where N > 0 and N = log2M. In some examples of the method 900, each codeword from the sequence of codewords consists of N bits, where N > 0. As an example, there may be only two codewords, corresponding to the binary values ‘0’ and ‘ 1’ of length N = 1. In this example, there may be M = 2 distinct durations, which respectively represents the ‘0’ and the ‘1’. In another example, the codeword consists of N = 2 bits, e.g., ‘00’, ‘01’, ‘10’, and ‘11’, and these codewords are represented by M = 4 different durations, etc. It will be appreciated that the number of codewords does not have to be a power of two. For example, the codewords may consist of two bits, but there may only be three codewords in the sequence of codewords, each represented by a respective duration. Also, in other examples, the different codewords may consist of different number of bits. However, it is appreciated that each different codeword is related to a unique duration, such that the receiver may decode the signal and obtain the codewords represented by the durations of the signal.

In some embodiments of the method 900, the first state is an on state and the second state is an off state. The on state may correspond to a state where the transmitter is active and energy is transmitted, while the off state may correspond to a state where the transmitter is inactive and little, or no energy is transmitted. This is exemplified by signal 210 in FIG. 2. It is appreciated that the first state may instead be the off state and the second state may be the on state.

In some embodiments of the method 900, in the first state, the signal is transmitted using a first antenna impedance, and, in the second state, the signal is transmitted using a second antenna impedance. In some embodiments of the method 900, in the first state, the signal is transmitted using a first frequency, and, in the second state, the signal is transmitted using a second frequency, as exemplified by the signal 230 in FIG. 2. In some embodiments of the method 900, in the first state, the signal is transmitted using a first amplitude, and, in the second state, the signal is transmitted using a second amplitude, as exemplified by the signal 220 in FIG. 2. In some embodiments of the method 900, in the first state, the signal is transmitted using a first phase, and, in the second state, the signal is transmitted using a second phase, as exemplified by the signal 240 in FIG. 2. In some embodiments of the method 900, in the first state, the signal is transmitted using a first polarization, and, in the second state, the signal is transmitted using a second polarization. As will be appreciated, it would also be possible to combine two or more of the above-mentioned techniques to distinguish between the two states. It is also appreciated that the output signal 750 of FIG. 7 may be used to control the switching between these states. But, in some embodiments, the output signal 750 of FIG. 7 may also be the signal discussed in relation to the method 900.

In some embodiments of the method 900, the signal comprises a detection sequence where the signal switches between the first state and the second state according to a predefined sequence of durations. The detection sequence may for example be a pre-amble, a mid-amble, a training sequence, or a synchronization word. The detection sequence may be known by the receiver and used to detect the signal, by detecting and/or correlating for the detection sequence. The detection sequence may comprise one or more predefined durations. The receiver may use the predefined durations to detect the signal, such that it knows the start and end of the durations. Further, if the durations may drift a bit in time, the receiver may determine the exact length of the predefined duration, and through this it may determine the remaining durations.

In some embodiments of the method 900, the transmitter is an active transmitter. In these embodiments, the method 900 may further comprise generating 910b an input signal and modulating 920 the input signal by switching the input signal between the first state and the second state based on the sequence of codewords. For such embodiments, transmitting 930 the signal may comprise transmitting the modulated version of the input signal. The output signal 750 of FIG. 7 may for example be used to control the modulating 920 of the input signal by switching the input signal between the first state and the second state. The active transmitter may be active in the sense that it generates the input signal itself, rather than relying on receiving a signal and reflecting it, like a backscattering transmitter. The input signal may for example be generated 910b by a signal generator (e.g., an oscillator).

In some embodiments of the method 900, the transmitter is a backscattering transmitter. In these embodiments, the method 900 may further comprise receiving 910a an input signal and modulating 920 the input signal by switching the input signal between the first state and the second state based on the sequence of codewords. For this embodiment, transmitting the signal comprises transmitting the modulated version of the received input signal. The output signal 750 of FIG. 7 may for example be used to control the modulating 920 of the received input signal by switching the input signal between the first state and the second state. For example, the output signal 750 may be used as a control signal to switch an antenna element between two antenna impedances, e.g., to generate a backscattered signal.

FIG. 10 illustrates a transmitter 1000 for use in a wireless communication network. The transmitter 1000 may be configured to perform any embodiment of the methods 800 or 900 described above with reference to FIG. 8 and FIG. 9. The transmitter 1000 may comprise circuitry configured to communicate with a receiver in the wireless communication network. The transmitter 1000 and/or circuitry may for example comprise a modulation circuit 1010 configured to modulate an input signal, and/or a transmitter circuit 1020 configured to transmit a modulated input signal. The circuitry and/or modulation circuit 1010 and/or transmitter circuit 1020 may be configured to cause the transmitter 1000 to perform any embodiment of the methods 800 or 900 described above with reference to FIG. 8 and FIG. 9. The transmitter 1000 may for example comprise one or more of the components/circuits described above with reference to FIG. 3 and FIG. 7. The modulation circuit 1010 may for example comprise one or more switches for switching a signal between the first and second state. The transmitter circuit 1020 may for example comprise one or more antennas for transmitting a signal.

FIG. 11 illustrates a method 1100 implemented by a receiver in a wireless communication network. The method 1100 is for obtaining a sequence of codewords. The method 1100 comprises receiving 1120 a signal. The signal switches between a first state and a second state. A first codeword from the sequence of codewords is represented by a first duration during which the signal is in the first state. A second codeword from the sequence of codewords is represented by a second duration during which the signal is in the second state. The method 1100 further comprises obtaining 1130 the sequence of codewords based on the received signal. The sequence of codewords may for example be obtained 1130 from the received signal by processing and/or decoding the received signal. According to some examples, an analog to digital converter of the receiver may be clocked at a much higher rate than the transmitted signal. Thereby, the transmitter may sufficiently accurately determine how long durations the signal remains in the two states, whereby it can translate the obtained sequence of durations into codewords. The receiver may for example measure each duration the received signal is in the different states and relate it to the corresponding data bits sent. The received signal may then be traversed by the receiver until all data bits have been found.

According to some embodiments, the signal received in the method 1100 may correspond to the signal transmitted in accordance with method 900, discussed above.

According to some embodiments, the signal comprises a detection sequence where the signal switches between the first state and the second state according to a predefined sequence of durations. In some examples, the receiver may use the detection sequence (e.g., a pre-amble) to obtain the sequence of codewords. The detection sequence may for example be known by the receiver. The receiver may then correlate for the known sequence, with a number of different sequence lengths, as the rate of the transmitter may still be uncertain. When the detection sequence is found in the signal, e.g., if the corresponding correlation outputs a value above a certain threshold, the receiver can determine the beginning of the data part of the signal as well as the rate of the transmitter.

According to some embodiments, the method 1100 may further comprise transmitting 1110 an input signal, and wherein receiving 1120 the signal comprises receiving a (backscattered) modulated version of the transmitted input signal, switched between the first state and the second state based on the sequence of codewords. The signal received at step 1120 may for example be a backscattered version of the signal transmitted at step 1110.

FIG. 12 illustrates a receiver 1200 for use in a wireless communication network. The receiver 1200 may be configured to perform any embodiment of the method 1100 described above with reference to FIG. 11. The receiver 1200 may for example comprise processing circuitry 1220 and a memory 1210, said memory 1210 containing instructions executable by said processing circuitry 1220, whereby said processing circuitry 1220 is configured to cause the receiver 1200 to perform any embodiment of the method 1100 described above with reference to FIG. 11. The receiver and/or processing circuitry may be configured to communicate with a transmitter, such as transmitter 1000, in the wireless communication network.

The transmitter 1000 and/or receiver 1200 may for example be implemented in a network node and/or a User Equipment (UE) communicating in the wireless communication network. In some examples, the network node may comprise the transmitter 1000, which is configured to transmit signals to the UE which comprises the receiver 1200. In other examples, the UE may comprise the transmitter 1000, which is configured to transmit signals to the network node and/or other UEs which comprises the receiver 1200. In other examples, the transmitter and/or network node and/or UE may comprise a backscattering transmitter or an active transmitter. The backscattering transmitter may or may not comprise an energy source, such as e.g., a battery. A typical scenario of this disclosure is a massive deployment of loT devices, which transmits using ultra-low power. These devices may be in connection with a network node and/or a wireless device that is not power constrained and therefore does not need to be as energy efficient as the loT devices, so the receiver of the signal can afford to use more energy than the transmitter of the signal.

Semi-passive and passive transmitters, e.g., backscattering transmitters, are very attractive for ultra-low power loT applications. Passive transmitters are powered entirely by the energy received from an incoming radio frequency (RF) signal. Semi-passive transmitters have a battery and consume power to perform baseband processing but lacks a power amplifier and many other components present in a Transmitter RF chain. Backscattering may involve delegating the generation of the RF carrier to a receiving node that is not power constrained. This implies that no power-hungry power amplifiers, filters, mixers and other components are needed in the (semi-)passive device. Instead, the devices generate signals by using an antenna mismatched to the incoming RF carrier, thus reflecting or backscattering the incoming radio waves, and by modulating the reflected electromagnetic waves in order to transmit data to a receiving unit. The modulation may be done using methods 800 and/or 900 discussed above, and/or by the apparatus 300 and/or 700.

In an example scenario, the wireless communication network may comprise a plurality of UEs which communicates with the same network node. The plurality of UEs may for example involve sensors, where the sensor data should be communicated to the network node. The network node may send a signal to one or more of the plurality of UEs, which UEs may in turn reflect or backscatter the signal according to the sequence of durations representing the sensor data to be communicated. The network node may receive the backscattered signal and decode the sensor data by decoding the durations.

An example wireless communication network, over a wireless connection, may include transmitting and/or receiving wireless signals using electromagnetic waves, radio waves, infrared waves, and/or other types of signals suitable for conveying information without the use of wires, cables, or other material conductors. Moreover, in different embodiments, the communication network (or system) may include any number of wired or wireless networks, network nodes, UEs, and/or any other components or systems that may facilitate or participate in the communication of data and/or signals whether via wired or wireless connections. The communication network may include and/or interface with any type of communication, telecommunication, data, cellular, radio network, and/or other similar type of system.

As a whole, the communication system may enable connectivity between UEs and network nodes. In that sense, the communication system may be configured to operate according to predefined rules or procedures, such as specific standards that include, but are not limited to: Global System for Mobile Communications (GSM); Universal Mobile Telecommunications System (UMTS); Long Term Evolution (LTE), and/or other suitable 2G, 3G, 4G, 5G standards, or any applicable future generation standard (e.g., 6G); wireless local area network (WLAN) standards, such as the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards (WiFi); and/or any other appropriate wireless communication standard, such as the Worldwide Interoperability for Microwave Access (WiMax), Bluetooth, Z-Wave, Near Field Communication (NFC) ZigBee, LiFi, and/or any low-power wide-area network (LPWAN) standards such as LoRa and Sigfox.

In some examples, the wireless communication network is a cellular network that implements 3 GPP standardized features. Accordingly, the communications network may support network slicing to provide different logical networks to different devices that are connected to the communication network. For example, the communications network may provide Ultra Reliable Low Latency Communication (URLLC) services to some UEs, while providing Enhanced Mobile Broadband (eMBB) services to other UEs, and/or Massive Machine Type Communication (mMTC)/Massive loT services to yet further UEs.

In some examples, the UEs are configured to transmit and/or receive information without direct human interaction. For instance, a UE may be designed to transmit information to the access network on a predetermined schedule, when triggered by an internal or external event, or in response to requests from the access network. Additionally, a UE may be configured for operating in single- or multi-RAT or multi-standard mode. For example, a UE may operate with any one or combination of Wi-Fi, NR (New Radio) and LTE, i.e. being configured for multi-radio dual connectivity (MR-DC), such as E-UTRAN (Evolved-UMTS Terrestrial Radio Access Network) New Radio - Dual Connectivity (EN-DC). As used herein, network node refers to equipment capable, configured, arranged and/or operable to communicate directly or indirectly with a UE and/or with other network nodes or equipment, in a telecommunication network. Examples of network nodes include, but are not limited to, access points (APs) (e.g., radio access points), base stations (BSs) (e.g., radio base stations, Node Bs, evolved Node Bs (eNBs) and NR NodeBs (gNBs)), O-RAN nodes or components of an O-RAN node (e.g., O-RU, O-DU, O-CU).

As used herein, a UE refers to a device capable, configured, arranged and/or operable to communicate wirelessly with network nodes and/or other UEs. Examples of a UE include, but are not limited to, a smart phone, mobile phone, cell phone, voice over IP (VoIP) phone, wireless local loop phone, desktop computer, personal digital assistant (PDA), wireless cameras, gaming console or device, music storage device, playback appliance, wearable terminal device, wireless endpoint, mobile station, tablet, laptop, laptop-embedded equipment (LEE), laptop-mounted equipment (LME), smart device, wireless customer-premise equipment (CPE), vehicle, vehicle-mounted or vehicle embedded/integrated wireless device, etc. Other examples include any UE identified by the 3rd Generation Partnership Project (3 GPP), including a narrow band internet of things (NB-IoT) UE, a machine type communication (MTC) UE, and/or an enhanced MTC (eMTC) UE.

A UE may support device-to-device (D2D) communication, for example by implementing a 3 GPP standard for sidelink communication, Dedicated Short-Range Communication (DSRC), vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), or vehicle-to-everything (V2X). In other examples, a UE may not necessarily have a user in the sense of a human user who owns and/or operates the relevant device. Instead, a UE may represent a device that is intended for sale to, or operation by, a human user but which may not, or which may not initially, be associated with a specific human user (e.g., a smart sprinkler controller). Alternatively, a UE may represent a device that is not intended for sale to, or operation by, an end user but which may be associated with or operated for the benefit of a user (e.g., a smart power meter).

Claims

CLAIMS What is claimed is:

1. An apparatus (700) for switching an output signal (750) between a first state and a second state based on a sequence of codewords, the apparatus comprising: an input circuit (710), an energy storing component (730), and a comparator circuit (740), wherein the input circuit is configured to charge or discharge the energy storing component using an input current, wherein a magnitude of the input current depends on a codeword from the sequence of codewords, wherein the energy storing component is configured to be connected to the comparator circuit such that, based on that a voltage of the energy storing component reaches an upper or lower threshold level, the comparator circuit switches the output signal between the first state and the second state, wherein a duration until the voltage of the energy storing component reaches the upper or lower threshold level depends on the magnitude of the input current, wherein the apparatus further comprises a feedback path (760) from the comparator circuit, wherein the feedback path is configured to switch the input circuit between charging and discharging the energy storing component based on that the voltage of the energy storing component reaches the upper or lower threshold level, and wherein the feedback path is further configured to control the input circuit to update the magnitude of the input current based on a next codeword from the sequence of codewords based on that the voltage of the energy storing component reaches the upper or lower threshold level.

2. The apparatus of claim 1, wherein a duration during which the output signal is in the first state represents a first codeword from the sequence of codewords, and a duration during which the output signal is in the second state represents a second codeword from the sequence of codewords.

3. The apparatus of any of claims 1-2, wherein the comparator circuit is configured to switch the output signal back and forth between the first state and the second state based on the voltage of the energy storing component such that the output signal remains in these states during respective durations forming a sequence of durations, and wherein each codeword in the sequence of codewords is represented by a duration in the sequence of durations.

4. The apparatus of any of claims 1-3, wherein the input circuit comprises a digital buffer (302) and a digital to analog converter (303), DAC, wherein the digital buffer is configured to buffer codewords from the sequence of codewords and output them to the DAC, and wherein the DAC is configured to convert codewords to currents, where the magnitude of a current depends on the value of a respective codeword to be converted by the DAC.

5. The apparatus of claim 4, wherein the input current is a current provided by the DAC, and wherein the DAC is further configured to be switched by the feedback path between charging and discharging the energy storing component.

6. The apparatus of claim 4, wherein the input circuit further comprises a charge pump (304) configured to receive a current provided by the DAC, wherein the input current is a current provided by the charge pump, and wherein the charge pump is configured to be switched by the feedback path between charging and discharging the energy storing component.

7. The apparatus of any of claims 1-6, wherein the feedback path comprises a detector (770) configured to detect that the output signal switches between the first state and the second state, and wherein the detector is further configured to control the input circuit to update the magnitude of the input current based on that the detector detects that the output signal switches between the first state and the second state.

8. The apparatus of claim 7, wherein the detector comprises a first delay element (309) and an XOR gate (310).

9. The apparatus of any of claims 1-8, wherein the feedback path comprises a second delay element (780) configured to delay the update of the magnitude of the input current by at least a time corresponding to a delay associated with the comparator circuit.

10. The apparatus of any of claims 1-9, wherein the energy storing component comprises a capacitor.

11. The apparatus of any of claims 1-10, wherein the comparator circuit comprises:

- a Schmitt trigger, or

- at least one comparator and a latch.

12. A method (800) for switching an output signal (750) between a first state and a second state based on a sequence of codewords, the method comprising: charging or discharging (830) an energy storing component (730) using an input current, wherein a magnitude of the input current depends on a codeword from the sequence of codewords, and based on that a voltage of the energy storing component reaches an upper or lower threshold level: switching (850) the output signal between the first state and the second state, switching (860) between charging and discharging the energy storing component, and updating (870) the magnitude of the input current based on a next codeword from the sequence of codewords, wherein a duration until the voltage of the energy storing component reaches the respective upper or lower threshold level depends on the magnitude of the input current.

13. The method of claim 12, wherein a duration during which the output signal is in the first state represents a first codeword from the sequence of codewords, and a duration during which the output signal is in the second state represents a second codeword from the sequence of codewords.

14. The method of any of claims 12-13, wherein the output signal switches back and forth between the first state and the second state such that the output signal remains in these states during respective durations forming a sequence of durations, and wherein each codeword in the sequence of codewords is represented by a duration in the sequence of durations.

15. The method of any of claims 12-14, further comprising: converting (810) the codeword from the sequence of codewords to the input current, where the magnitude of the input current depends on the value of the codeword.

16. The method of any of claims 12-15, further comprising: detecting (880) that the output signal switches between the first state and the second state, and wherein updating the magnitude of the input current comprises updating the magnitude of the input current based on detecting that the output signal switches between the first state and the second state.

17. The method of any of claims 12-16, further comprising: delaying (890) the update of the magnitude of the input current by at least a time.