Waveform for multi-antenna wireless power transfer

Abstract

An example proposes a method performed by a power transmitting device for wirelessly powering a power receiving device of a communication network, the power transmitting device comprising M antennas, the method comprising: for each of the M antennas, acquiring (310) K subcarrier channel estimates hmk (m = 1... M; k = 1... K); selecting (320) one individual subcarrier wireless channel of the K subcarrier wireless channels for each antenna based on the acquired K subcarrier channel estimates hmk; and transmitting (330) a power signal comprising one individual single tone signal per antenna over the selected subcarrier wireless channel over the associated antenna within a predefined time window, where the phase of the transmitted single tone signal is selected based on the phase estimated by the subcarrier channel. Further, an example discloses a power transfer apparatus.

Description

Technical Field

[0001] Various examples generally relate to wirelessly transmitting power from a power transmitting device to a power receiving device. Background Art

[0002] Modern data transmission relies heavily on wireless communications. Traditional wireless communications require transmitting devices to generate wireless signals using components such as digital-to-analog converters (DACs), mixers, oscillators, and power amplifiers, and receiving devices to receive wireless signals using components such as low-noise amplifiers, mixers, oscillators, and analog-to-digital converters (ADCs). Typically, devices involved in wireless communications are battery-powered, and the components used for wireless communications consume a significant amount of the battery's energy. Consequently, these batteries must be regularly recharged or replaced. As the number of battery-powered devices participating in wireless communications continues to grow, this may no longer be feasible. For example, with 1 trillion Internet of Things (IoT) devices worldwide and a battery life of 10 years per device, this means that 274 billion batteries need to be replaced every day. However, in some application scenarios, even with existing technologies, a 10-year battery life may not be achievable.

[0003] Furthermore, battery recycling remains inadequate. In 2018, 191,000 tons of portable batteries were sold in the EU, but less than half, or 88,000 tons, of used portable batteries were collected as waste for recycling. Given the limited natural resources required for battery production, the demand for new batteries must also be reduced.

[0004] In order to achieve a long-life and maintenance-free IoT network, some IoT devices are equipped with rechargeable energy storage devices such as rechargeable batteries, supercapacitors or capacitors. Ambient energy (such as light, electromagnetic radiation, thermal energy resources) or dedicated energy (such as static electricity, sound, magnetism or electromagnetic radiation) can be used to charge / recharge these rechargeable batteries, supercapacitors or capacitors. Among these energy sources, electromagnetic radiation mainly used for communication (called far-field wireless power transfer (WPT)) is one of the promising solutions for future ultra-low power and miniaturized IoT devices. WPT is easy to control and can be provided on demand. Compared with other energy resources, RF signals can be converted into electrical energy without additional bulky components. Therefore, WPT is very suitable for miniaturized devices. Zeng, Y., Clerckx, B., and Zhang, R. have proposed some methods for WPT (2017). Communications and signals design for wireless power transmission, IEEE Transactions on Communications, 65(5), 2264-2290 and Ayir, N., Riihonen, T., Allen, M., and Fierro, M. F.T. (2021). Waveforms and end-to-end efficiency in RF wireless power transfer using digital radio transmitter, IEEE Transactions on Microwave Theory and Techniques, 69(3), 1917-1931. Summary of the Invention

[0005] High end-to-end power transfer efficiency, ie the ratio of the DC power received at the receiver to the DC power at the transmitter, is required.

[0006] The above needs have been solved by the subject matter of the independent claims. Advantageous embodiments are described in the dependent claims.

[0007] Example providing method##

[0008] Example provides power transmission equipment## BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 A WPT system is schematically shown.

[0010] Figure 2 A graph of the rectifier efficiency as a function of input amplitude is shown.

[0011] Figure 3 is a flow chart illustrating a method for wireless power supply.

[0012] Figures 4 to 9 A single tone signal transmitted through a radio channel with different subcarriers is shown.

[0013] Figure 10 The amplitude of the power signal is shown as a function of time.

[0014] Figure 11 The amplitude of the power signal is shown as a function of time.

[0015] Figure 12 Shown Figure 10 The power of the signal varies with time.

[0016] Figure 13 Shown Figure 11 The power of the signal varies with time.

[0017] Figure 14 The power transmission efficiency is shown. DETAILED DESCRIPTION

[0018] Figure 1 A very general block diagram of a WPT system is shown, which includes a power transmission device 110 and a power receiving device 120. The power transmission device 110 and the power receiving device 120 are part of a communication network. At the power transmission device 110, a DC (or low-frequency) signal is up-converted to a target radio frequency, amplified by a power amplifier 111, and transmitted as a power signal 130 by the transmission antenna 112 of the power transmission device 110. The power signal 130 then propagates through a wireless channel, is picked up by one or more receiving antennas 122 of the power receiving device 120, converted to usable direct current (DC) by components such as a rectifier 123, and ultimately stored in a storage unit 124 such as a battery or capacitor 125. The stored power / energy can then be used by a load 126 of the power receiving device 120.

[0019] End-to-end power transfer efficiency depends on the efficiency of DC to radio frequency (RF) conversion at the power transfer device 110 , the efficiency of RF transmission over the wireless channel, and the efficiency of RF to DC conversion at the power transfer device 120 .

[0020] The power transfer device 110 may further include a control circuit. The control circuit may include a processor 117 and a memory 118 coupled to the processor 117. The control circuit may be used to control an interface 119 including a power amplifier 111 connected to the antenna 112.

[0021] Likewise, the power receiving device 120 may include a control circuit, which may include a processor 127 and a memory 128 coupled to the processor 127. The control circuit may be configured to control the interface 129.

[0022] The power transfer device 110 may include more antennas than are actually used to transmit the power signal 130. In some scenarios, the power transfer device 110 may use more antennas to transmit the power signal 130 than in other scenarios.

[0023] In some cases, the communication network may include several communication nodes communicating according to a predefined protocol, wherein the communication nodes include the power transmitting device 110 and / or the power receiving device 120. The predefined protocol may be a protocol specified by 3GPP or IEEE.

[0024] Figure 2 A graph shows rectifier efficiency as a function of input amplitude. Due to the nonlinear nature of rectifiers, achieving high rectifier efficiency can be advantageous if the power signal providing the energy is designed so that the energy is concentrated in the received power signal and the conversion occurs at high amplitude. Several single-tone signal waveforms have been proposed to generate power signals with high peaks. However, the efficiency of power amplifiers used in RF transmission devices is often reduced by the presence of high peaks in the power signal.

[0025] Therefore, optimizing the end-to-end power transfer efficiency, i.e., the ratio of the DC power received at the power receiving device 120 to the power transmitted by the power transmitting device 110, is a very important and challenging task when designing a WPT system.

[0026] The examples disclosed herein provide Figure 3 The method for wirelessly supplying power to a power receiving device of a communication network, performed by a power transmission device, is shown. The power transmission device includes M antennas.

[0027] At 310, the method provides for obtaining, for each of the M antennas, K subcarrier channel estimates h associated with the K subcarrier wireless channels to the power receiving device. mk(m=1...M; k=1...K). In other words, for each of the M antennas, a channel estimate is obtained. This can be done by transmitting a reference signal from the power receiving device that can be used to estimate the uplink channel, which in the case of TDD may be the same as the downlink channel. In the case of FDD, the channel estimate can be obtained using the correlation between the duplex frequency bands. It is also conceivable to obtain the channel estimate by environmental learning. In some scenarios, a previously determined channel estimate can be used. For example, the channel estimate may have been used to optimize the data communication between the power transmitting device and the power receiving device.

[0028] Based on the obtained K subcarrier channel estimation h mk , selecting (320) a single subcarrier radio channel from the K subcarrier radio channels for each antenna. In other words, for the obtained channel estimate, the single subcarrier is selected based on its single contribution to the total amount of energy collected at the power receiving device.

[0029] Then, at 330, the method provides for transmitting a power signal comprising a separate tone signal for each antenna on the selected subcarrier radio channel within a predefined time window. In other words, a single tone signal is transmitted via each antenna. The frequency of the tone signal depends on the subcarrier radio channel selected for each antenna in 320.

[0030] The single-tone signal may correspond to a sinusoidal signal having a single frequency. The phase of the transmitted single-tone signal is selected based on the phase of the subcarrier channel estimate. In some examples, the predefined time window may correspond to multiple radio frames. Some scenarios may specify that the predefined time window corresponds to one or more OFDM symbols. The predefined time window may be selected according to predefined rules. In some scenarios, the predefined time window may be selected to be a time-varying characteristic of the subcarrier radio channel. Specifically, the predefined time window may be selected to be longer than a period during which the subcarrier radio channel can be considered static. The predefined time window may correspond to a time period during which the same transmission settings can be maintained.

[0031] Also like Figure 1 As shown, one antenna 112 includes a single power amplifier 111 connected to one or more antenna elements. In some examples, an antenna port may be referred to as an antenna.

[0032] In some examples, the proposed method can allow for the real-time establishment of energy-efficient multi-antenna transmission waveforms that can also adapt to current channel conditions. Thus, for improved end-to-end conversion efficiency, an end-to-end design with joint optimization of transmission, wireless propagation, and reception is proposed. This proposal can be considered a very practical, low-complexity solution for challenging optimization problems.

[0033] Typically, a discrete set of frequencies within a specific bandwidth can be used to transmit power signals. Orthogonal frequency division multiplexing (OFDM) systems are a common type of system, and OFDM subcarriers can be considered to be good representatives of discrete frequency sets. Specifically, OFDM subcarriers can be considered to be good representatives of discrete single-tone signals. An OFDM-based power transmission system can use K subcarriers, and the power transmission equipment of such a system can include M antennas.

[0034] The subcarrier channel estimates of the subcarrier channels from each antenna to the power receiving device may be obtained by a known channel acquisition process. mk. It can be the subcarrier channel estimate from antenna m on subcarrier k. mk. It can also be called the channel coefficient. Each antenna of the power transmission device can be fed by a power amplifier, ie a transmission chain with a limited maximum instantaneous amplitude A.

[0035] Excluding any cyclic prefix, the baseband power signal from antenna m transmitted during a single OFDM symbol is

[0036]

[0037] Where n = 0, ..., K-1, and x m,k are complex-valued coefficients representing the amplitude and phase of the transmission on the mth antenna and the kth subcarrier channel. Furthermore, the power amplifier at each transmit antenna may have a finite maximum amplitude, and to avoid clipping of the signal and associated out-of-band radiation, for all transmitters m, the peak transmit amplitude may be considered to be limited to

[0038] max n |s m (n)|≤An.

[0039] The received power signal after passing through each channel becomes:

[0040]

[0041] Here, again, n = 0,…,K-1. This makes the total received power signal from all M antennas be

[0042]

[0043] In order to limit the peak amplitude variation at the antenna of the power transmission device, transmission can be performed on only one subcarrier for each antenna. m , the corresponding part of the transmitted power signal becomes And for all other values ​​of k, x m,k =0.

[0044] Therefore, the transmitted power signal becomes

[0045]

[0046] Among them, max n |s m (n)|=A.

[0047] Accordingly, the received power signal becomes

[0048]

[0049] In order to obtain the highest possible amplitude at the power receiving device so that the rectifier of the power receiving device operates with high efficiency, the subcarrier K used on antenna m is m The one that has the strongest subcarrier channel estimate to the power receiving device may be selected, i.e.,

[0050] k m =argmax k |h m,κ |.

[0051] Furthermore, all terms in the summation can be chosen to have a common phase, i.e.,

[0052]

[0053] where the constant value is arbitrary and can be equal to zero, for example, giving

[0054]

[0055] Therefore, the terms of the sum can produce a constructive superposition at at least one instant n0.

[0056] Figures 4 to 11 The advantage of appropriately selecting the phase of the tone signals to be delivered via the respective sub-carrier channels is shown. Figures 4 to 9 The time variation of the amplitude of single tone signals (i.e., with different frequencies) transmitted on different subcarrier wireless channels is shown.

[0057] Figure 10 and Figure 12It shows that if the phase of the corresponding subcarrier channel estimation is not considered when transmitting a single tone signal through the antenna, then Figures 4 to 9 Example amplitude and power of the power signal produced by a single tone signal are shown.

[0058] Figure 11 and Figure 13 It shows that if the phase of the corresponding subcarrier channel estimation is taken into account when transmitting a single tone signal through the antenna, then Figures 4 to 9 Example amplitude and power of the power signal produced by a single tone signal are shown.

[0059] As shown in the figure, Figure 11 and 13 The amplitude and power shown in have significantly more pronounced peaks, which facilitates energy harvesting due to the higher efficiency of the rectifier in the energy receiving device.

[0060] Therefore, the proposed design can lead to high transmission efficiency and high receiving efficiency in OFDM-based multiple-input multiple-output (MIMO) systems.

[0061] Figure 14 The advantages of the proposed method are also shown. Figure 3 The complementary CDF (CCDF) of the amplitude received at the power receiving device for the three methods is shown. In all cases, the power receiving device includes 128 antennas and uses a 64-subcarrier OFDM channel. The CCDF is generated under the assumption of IID Rayleigh fading channel coefficients.

[0062] Curve a) illustrates classic maximum ratio transmission. Curve b) illustrates the transmission of a single tone signal on a separate subcarrier channel for each antenna, where the subcarrier channel used by each antenna and the phase of each tone signal are randomly selected. Finally, curve c) illustrates the method shown above. In all cases, the maximum amplitude at each antenna element is selected to have the same level.

[0063] The proposed power signal c) outperforms the other two methods by approximately 7dB and 14dB.

[0064] In summary, at least the following examples have been described above:

[0065] Example 1. A method performed by a power transmitting device for wirelessly supplying power to a power receiving device of a communication network,

[0066] The power transmission device includes M antennas,

[0067] The method includes:

[0068] - for each of the M antennas, obtaining (310) K subcarrier channel estimates h associated with the K subcarrier wireless channels to the power receiving devicemk (m=1...M; k=1...K);

[0069] - Based on the obtained K subcarrier channel estimate h mk , selecting (320) a single subcarrier radio channel out of the K subcarrier radio channels for each antenna;

[0070] - transmitting (330) a power signal comprising a separate tone signal per antenna on the selected subcarrier radio channel within a predefined time window,

[0071] The phase of the transmitted single tone signal is selected based on the phase of the subcarrier channel estimate.

[0072] Example 2. According to the method of Example 1,

[0073] The phase of the transmitted single tone signal is selected so that the peak power of the power signal received at the power receiving device is greater than the sum of the powers of the individual single tone signals if they are received at the power receiving device individually.

[0074] Example 3. The method according to Example 1 or 2,

[0075] Therein, the phases of the transmitted tone signals are selected for the individual tone signals so as to produce a constructive superposition at the power receiving device.

[0076] Example 4. The method according to any one of Examples 1 to 3,

[0077] The predefined time window corresponds to one or more of the following:

[0078] - multiple radio frames,

[0079] -One or more OFDM symbols.

[0080] Example 5. The method according to any one of Examples 1 to 4,

[0081] Wherein, an antenna comprises a single power amplifier connected to one or more antenna elements. Example 6. A power transmission device for wirelessly powering a power receiving device of a communication network,

[0082] The power transmission device includes M antennas.

[0083] Among them, the power transmission equipment includes a control circuit,

[0084] The control circuit is configured to:

[0085] - for each of the M antennas, obtaining (310) K subcarrier channel estimates h associated with the K subcarrier wireless channels to the power receiving device mk (m=1...M; k=1...K);

[0086] - Based on the obtained K subcarrier channel estimate h mk , selecting (320) a single sub-carrier radio channel out of the K sub-carrier radio channels for each antenna; and

[0087] - transmitting (330) a power signal comprising a separate tone signal per antenna on the selected subcarrier radio channel over the associated antennas within a predefined time window,

[0088] The phase of the transmitted single tone signal is selected based on the phase of the subcarrier channel estimate.

[0089] Example 7. The power transmission device according to Example 6,

[0090] The phase of the transmitted single tone signal is selected so that the peak power of the power signal received at the power receiving device is greater than the sum of the powers of the individual single tone signals if they are received at the power receiving device individually.

[0091] Example 8. The power transmission device according to example 6 or 7,

[0092] Therein, the phases of the transmitted tone signals are selected for the individual tone signals so as to produce a constructive superposition at the power receiving device.

[0093] Example 9. The power transmission device according to any one of Examples 6 to 8,

[0094] The predefined time window corresponds to one or more of the following:

[0095] - multiple radio frames,

[0096] -One or more OFDM symbols.

[0097] Example 10. The power transmission device according to any one of Examples 6 to 9,

[0098] Wherein, an antenna comprises a single power amplifier connected to one or more antenna elements. Example 11. A power transmission device for wirelessly powering a power receiving device of a communication network,

[0099] The power transmission device includes M antennas.

[0100] Among them, the power transmission equipment includes a control circuit,

[0101] The control circuit is configured to perform the method according to any one of Examples 1 to 5.

Claims

1. A method for wirelessly supplying power to a power receiving device of a communication network, performed by a power transmitting device, The power transmission device includes M antennas, The method comprises: - for each of the M antennas, obtaining (310) K subcarrier channel estimates h associated with the K subcarrier wireless channels to the power receiving device mk (m=1...M; k=1...K); - Based on the obtained K subcarrier channel estimate h mk , selecting (320) a single subcarrier radio channel of the K subcarrier radio channels for each antenna; - transmitting (330) a power signal comprising a separate tone signal per antenna on the selected subcarrier radio channel within a predefined time window, The phase of the transmitted single tone signal is selected based on the phase of the subcarrier channel estimate.

2. The method according to claim 1, in, The phase of the transmitted tone signal is selected so that the peak power of the power signal received at the power receiving device is greater than the sum of the powers of the individual tone signals if received individually at the power receiving device.

3. The method according to claim 1 or 2, in, The phases of the transmitted tone signals are selected for the individual tone signals to produce constructive superposition at the power receiving device.

4. The method according to any one of claims 1 to 3, in, The predefined time window corresponds to one or more of the following: - multiple radio frames, -One or more OFDM symbols.

5. The method according to any one of claims 1 to 4, in, An antenna consists of a single power amplifier connected to one or more antenna elements.

6. Power transmission equipment for wirelessly supplying power to power receiving equipment in communication networks, in, The power transmission device includes M antennas, Wherein, the power transmission device includes a control circuit, Wherein, the control circuit is configured to: - for each of the M antennas, obtaining (310) K subcarrier channel estimates h associated with the K subcarrier wireless channels to the power receiving device mk (m=1...M; k=1...K); - Based on the obtained K subcarrier channel estimate h mk , selecting (320) a single sub-carrier radio channel of the K sub-carrier radio channels for each antenna; and - transmitting (330) a power signal comprising a separate tone signal per antenna on the selected subcarrier radio channel over the associated antennas within a predefined time window, The phase of the transmitted single tone signal is selected based on the phase of the subcarrier channel estimate.

7. The power transmission device according to claim 6, in, The phase of the transmitted tone signal is selected so that the peak power of the power signal received at the power receiving device is greater than the sum of the powers of the individual tone signals if received individually at the power receiving device.

8. The power transmission device according to claim 6 or 7, in, The phases of the transmitted tone signals are selected for the individual tone signals to produce constructive superposition at the power receiving device.

9. The power transmission device according to any one of claims 6 to 8, in, The predefined time window corresponds to one or more of the following: - multiple radio frames, -One or more OFDM symbols.

10. The power transmission device according to any one of claims 6 to 9, in, An antenna consists of a single power amplifier connected to one or more antenna elements.

11. Power transmission equipment for wirelessly supplying power to power receiving equipment in communication networks, in, The power transmission device includes M antennas, Wherein, the power transmission device includes a control circuit, The control circuit is configured to execute the method according to any one of claims 1 to 5.

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