Waveform of wireless power transmission using multiple antennas

Abstract

The proposed method is performed by a power transmitting device for wirelessly supplying power to a power receiving device of a communication network, the power transmitting device having M antennas, and for each of the M antennas, transmitting K subcarrier channel estimates h associated with K subcarrier wireless channels to the power receiving device. mk (m=1...M; k=1...K) are obtained (310), and the obtained K subcarrier channel estimates h mk and transmitting a power signal including a single tone per antenna on the selected subcarrier wireless channel within a predefined time frame, the power signal including a single tone per antenna being selected based on the phase of the subcarrier channel estimate.

Description

[Technical Field]

[0001] Generally, there are various examples related to wireless power transfer from a power transmitting device to a power receiving device. [Background technology]

[0002] Modern data transmission relies heavily on wireless communication. In traditional wireless communication, a transmitting device generates a radio signal using components such as a digital-to-analog converter (DAC), mixer, oscillator, and power amplifier, and a receiving device receives the radio signal using components such as a low-noise amplifier, mixer, oscillator, and analog-to-digital converter (ADC). Devices participating in wireless communication are typically battery-powered, and the aforementioned wireless communication components consume a significant amount of the battery's energy. Therefore, the batteries must be periodically charged or replaced. As the number of battery-powered devices participating in wireless communication increases, this may no longer be feasible. For example, assuming there are 1 trillion Internet of Things (IoT) devices worldwide, each with a 10-year battery life, this would mean that 274 billion batteries would need to be replaced every day. However, in some use cases, even a 10-year battery life may not be achievable with known technologies.

[0003] Furthermore, battery recycling remains insufficient: in 2018, 191,000 tonnes of mobile batteries were sold in the European Union, but only 88,000 tonnes, less than half of that, were collected as waste and recycled. Given the limited natural resources needed to manufacture batteries, demand for new batteries must also be reduced.

[0004] To realize long-life, maintenance-free IoT networks, some IoT devices are equipped with rechargeable energy storage devices such as rechargeable batteries, supercapacitors, and capacitors. These rechargeable batteries, supercapacitors, and capacitors can be charged / recharged using environmental energy sources such as light, electromagnetic waves, and thermal energy, as well as thermal energy sources and dedicated energy sources such as electrostatic, acoustic, magnetic, and electromagnetic waves. Among these energy sources, electromagnetic radiation, known as long-distance wireless power transfer (WPT), which is primarily used for communication, is expected to be one of the promising solutions for future ultra-low-power, small-form-factor IoT devices. WPT is easily controllable and available on demand. In contrast to other energy sources, it does not require additional large components to convert RF signals into electrical power. Therefore, several WPT-based methods have been proposed in non-patent literature 1 and non-patent literature 2. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Zeng, Y., Clerckx, B., & Zhang, R. (2017). Communications and signals design for wireless power transmission. IEEE Transactions on Communications, 65(5), 2264-2290. [Non-patent document 2] Ayir, N., Riihonen, T., Allen, M., & Fierro, MFT (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 [Problem to be solved by the invention]

[0006] There is a need for high end-to-end power transfer efficiency, i.e., increasing the ratio of DC power received at the receiver to DC power at the transmitter. [Means for solving the problem]

[0007] The above problem is solved by the subject matter of the independent claims of the present application. Advantageous embodiments are described in the dependent claims. A method is provided by way of example in the detailed description of the invention. A power transmission device is also provided by way of example in the detailed description of the invention. [Brief explanation of the drawings]

[0008] [Figure 1] 1 shows a schematic diagram of a WPT system. [Figure 2] The rectifier efficiency is shown as a function of input amplitude. [Figure 3] 1 is a flowchart illustrating a method for wirelessly providing power. [Figure 4] 1 shows tones transmitted over different subcarrier radio channels. [Figure 5] 1 shows tones transmitted over different subcarrier radio channels. [Figure 6] 1 shows tones transmitted over different subcarrier radio channels. [Figure 7] 1 shows tones transmitted over different subcarrier radio channels. [Figure 8] 1 shows tones transmitted over different subcarrier radio channels. [Figure 9] 1 shows tones transmitted over different subcarrier radio channels. [Figure 10] 1 shows the amplitude of the power signal over time. [Figure 11] 1 shows the amplitude of the power signal over time. [Figure 12] 11 shows the power over time of the power signal of FIG. [Figure 13] 12 shows the power over time of the power signal of FIG. [Figure 14] Indicates the transmission efficiency. DETAILED DESCRIPTION OF THE INVENTION

[0009] FIG. 1 shows a very general block diagram of a WPT system, consisting of a power transmitting device 110 and a power receiving device 120. The power transmitting device 110 and the power receiving device 120 are part of a communication network. In the power transmitting device 110, a direct current (or low frequency) signal is upconverted to a target radio frequency, amplified by a power amplifier 111, and radiated as a power signal 130 by a transmitting antenna 112 of the power transmitting device 110. The power signal 130 then propagates through a radio channel, is picked up by one or more receiving antennas 122 of the power receiving device 120, is converted to usable direct current (DC) via components such as a rectifier 123, and is finally stored in a storage unit 124, such as a battery or capacitor 125. The stored power / energy is used by a load 126 of the power receiving device 120.

[0010] The end-to-end power transfer efficiency depends on the direct current (DC) to radio frequency (RF) conversion efficiency in the power transmitting device 110, the RF transmission efficiency over the wireless channel, and the RF to DC conversion efficiency in the power receiving device 120.

[0011] The power transmitting device 110 may further include a control circuit. The control circuit may include a processor 117 and a memory 118 connected to the processor 117. The control circuit may be used to control an interface 119 that includes a power amplifier 111 connected to the antenna 112.

[0012] Similarly, the power receiving device 120 may include control circuitry. The control circuitry may include a processor 127 and a memory 128 coupled to the processor 127. The control circuitry may be used to control the interface 129.

[0013] The power transmitting device 110 may have more antennas than are actually used to transmit the power signal 130. In some situations, the power transmitting device 110 may use more antennas to transmit the power signal 130 than in other situations.

[0014] In some scenarios, a communication network may include several communication nodes that communicate according to a predefined protocol, the communication nodes including power transmitting devices 110 and / or power receiving devices 120. The predefined protocol may be a protocol defined by 3GPP or IEEE.

[0015] Figure 2 shows an example of rectifier efficiency as a function of input amplitude. Due to the nonlinear characteristics of rectifiers, to achieve high rectifier efficiency, it is advantageous to design the transmitting power signal so that the energy is concentrated in the received power signal and the conversion occurs at a high amplitude. Multi-tone waveforms have been proposed to generate power signals with high peaks. However, the efficiency of the power amplifiers used by power transmitters for RF transmission typically decreases when the power signal contains high peaks.

[0016] Therefore, optimizing the end-to-end power transfer efficiency, i.e., the ratio of DC power received by the power receiving device 120 to the power transmitted by the power transmitting device 110, is a very important and yet very challenging task when designing a WPT system.

[0017] An example disclosed herein provides a method performed by a power transmitting device for wirelessly supplying power to a power receiving device in a communication network, as shown in Figure 3. The power transmitting device includes M antennas.

[0018] At 310, the method provides for obtaining, for each of the M antennas, estimates hmk (m=1...M; k=1...K) associated with K subcarrier radio channels to the powered device. That is, for each of the M antennas, a channel estimate is obtained. This can be achieved by transmitting a reference signal from the powered device, which can be used to estimate an uplink channel, which may be identical to the downlink channel in the case of TDD. In the case of FDD, correlation between duplex bands may be used to obtain the channel estimate. It is also possible to obtain the channel estimate through environmental learning. In some scenarios, a pre-determined channel estimate may be used. For example, the channel estimate may be used to optimize data communication between the powered device and the powered device.

[0019] A single subcarrier radio channel is selected from the K subcarrier radio channels for each antenna based on the obtained K subcarrier channel estimates hmk (320), i.e., the single subcarrier is selected based on its individual contribution to the total amount of energy collected at the receiving device for the obtained channel estimates.

[0020] Next, at 330, the method provides for transmitting, within a predefined time period, a power signal including a single tone per antenna on the selected subcarrier radio channel, i.e., one tone is transmitted over each antenna, the frequency of the tone depending on the subcarrier radio channel selected at 320 for each antenna.

[0021] The tones may correspond to sinusoidal signals of a single frequency. The phase of the transmitted tones is selected based on the phase of the subcarrier channel estimate. In some examples, the predefined time period may correspond to a number of radio frames. In some scenarios, the predefined time period may correspond to one or more OFDM symbols. The predefined time period may be selected according to a predefined rule. In some scenarios, the predefined time period may be selected to match the time-varying characteristics of the subcarrier radio channel. In particular, the predefined time period may be set to be longer than a time period during which the subcarrier radio channel can be considered static. The predefined time period may correspond to a time period during which the same transmission configuration can be maintained.

[0022] 1, the antenna 112 comprises 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.

[0023] The proposed method allows for the construction of efficient energy transmission waveforms for multiple antennas, in some cases in real time, and can further adapt to current channel conditions. Therefore, an end-to-end design is proposed that jointly optimizes transmission, radio propagation, and reception for improved end-to-end conversion efficiency. This proposal can be seen as a low-complexity, highly practical solution to a challenging optimization problem.

[0024] Typically, a power signal may be transmitted using a set of discrete frequencies within a particular bandwidth. Orthogonal frequency division multiplexing (OFDM) systems are a common system type, and OFDM subcarriers can be considered a good example of a set of discrete frequencies. In particular, OFDM subcarriers can be considered a good example of a set of discrete tones. An OFDM-based power transmission system uses K subcarriers, and a power transmission device in such a system may be configured with M antennas.

[0025] A subcarrier channel estimate is obtained for the subcarrier channel from each antenna to the receiving device. This subcarrier channel estimate is obtained through a known channel acquisition procedure. hm,k is the subcarrier channel estimate for subcarrier k at antenna m. hm,k is also called the channel coefficient. Each antenna of the transmitting device is fed by a power amplifier, i.e., a transmitter chain with a limited maximum instantaneous amplitude A.

[0026] Excluding the cyclic prefix, the transmitted baseband power signal in a single OFDM symbol from antenna m is

number

number

[0027] The received power signal after passing through each channel is

number

number

[0028] To limit the peak amplitude fluctuations at the transmitter antennas, transmission can be performed on only one subcarrier per antenna. For a selected subcarrier Km of antenna m, the corresponding portion of the transmit power signal is ax m、Km =Ae jφm and for all other values ​​of k, x m,k =0.

[0029] Therefore, the transmit power signal is:

number

number

[0030] Correspondingly, the received power signal is:

number

[0031] To obtain the highest possible amplitude for efficient rectifier operation in the receiving device, the subcarrier K used at antenna m m , which is the subcarrier channel estimate for the receiving device that is strongest, i.e.,

number

[0032] Furthermore, all terms in the sum can be chosen to have a common phase, i.e.

number

number

[0033] Thus, the terms of the sum are positively added at at least one time instant n0.

[0034] Figures 4 through 11 illustrate the benefits of appropriately selecting the phase of the tones sent over each subcarrier channel. Figures 4 through 9 illustrate the amplitude over time of tones transmitted on different subcarrier channels (i.e., having different frequencies).

[0035] Figures 10 and 12 show typical amplitudes and powers of the power signals obtained from the tones shown in Figures 4 to 9, without considering the phase of each subcarrier channel estimate when transmitting the tones over the antennas.

[0036] Figures 11 and 13 show the amplitude and power of the power signals obtained from the tones shown in Figures 4 to 9, taking into account the phase of each subcarrier channel estimate when transmitting the tones through the antenna.

[0037] The amplitude and power shown in Figures 11 and 13 feature significantly more pronounced peaks that facilitate power harvesting due to increased efficiency of the rectifier in the power receiving device.

[0038] Therefore, the proposed design can provide high transmission efficiency and high reception efficiency in OFDM-based multiple-input multiple-output (MIMO) systems.

[0039] Figure 14 further illustrates the advantages of the proposed approach. Figure 3 shows the complementary CDF (CCDF) of the received amplitude at the receiving device for the three approaches. In each case, the receiving device is configured with 128 antennas and 64 OFDM subcarrier channels are used. The CCDF is generated assuming IID Rayleigh fading channel coefficients.

[0040] Curve a) shows a typical maximum ratio transmission. Curve b) shows a scheme where a single tone is transmitted on a single subcarrier channel per antenna, where the subcarrier channel used by each antenna and the phase of each tone are chosen randomly. Finally, curve c) shows the approach shown above. In both cases, the maximum amplitude at each antenna element is chosen to be the same level.

[0041] The proposed power signal c) outperforms the other two approaches by approximately 7 dB and 14 dB.

[0042] In summary, at least the following examples are described above:

[0043] Example 1 1. A method performed by a power transmitting device for wirelessly powering a power receiving device in a communication network, the power transmitting device comprising M antennas, For each of the M antennas, for the receiving device, K subcarrier channel estimates h associated with the K subcarrier wireless channels. mk (m=1...M;k=1...K) is obtained (310), The acquired K subcarrier channel estimates h mk selecting (320) a single subcarrier radio channel from the K subcarrier radio channels for each antenna based on transmitting (330) a power signal including a single tone per antenna on the selected subcarrier radio channel within a predefined time frame; A method wherein the phase of the transmitted tone is selected based on the phase of the subcarrier channel estimate. Example 2 2. The method of Example 1, wherein the phases of the transmitted tones are selected such that the peak power of the power signal received at the power receiving device is greater than the sum of the powers of each single tone if received individually at the power receiving device. Example 3 3. The method of example 1 or 2, wherein the phase of the transmitted tone is selected such that a single tone sums positively at the receiving device. Example 4 The predefined time frame is: - a number of radio frames, - one or more OFDM symbols The method of any of Examples 1 to 3, corresponding to one or more of: Example 5 5. The method of any of Examples 1 to 4, wherein one antenna includes a single power amplifier connected to one or more antenna elements. Example 6 A power transmitting device that wirelessly supplies power to a power receiving device in a communication network, the power transmitting device including M antennas, the power transmitting device including a control circuit, the control circuit including: For each of the M antennas, for the receiving device, K subcarrier channel estimates h associated with the K subcarrier wireless channels. mk (m=1...M;k=1...K) is obtained (310), The acquired K subcarrier channel estimates h mk selecting (320) a single subcarrier radio channel from the K subcarrier radio channels for each antenna based on - transmitting (330) a power signal comprising a single tone per antenna on the selected subcarrier radio channel via the associated antenna within a predefined time frame; The phase of the transmit tone is selected based on the phase of the subcarrier channel estimate. Example 7 7. The power transmitting device of Example 6, wherein the phases of the transmitted tones are selected such that the peak power of the power signal received at the power receiving device is greater than the sum of the powers of each single tone received individually at the power receiving device. Example 8 8. The power transmitting device of example 6 or 7, wherein the phase of the transmitted tone is selected such that a single tone sums positively at the power receiving device. Example 9 The predefined time frame is: - a number of radio frames, - one or more OFDM symbols 9. The power transmitting device of any of Examples 6 to 8, corresponding to one or more of: Example 10 10. The method of any of Examples 6 to 9, wherein one antenna includes a single power amplifier connected to one or more antenna elements. Example 11 10. A power transmitting device that wirelessly supplies power to a power receiving device in a communication network, the power transmitting device including M antennas, the power transmitting device including control circuitry, the control circuitry configured to implement the method of any of Examples 1 to 5.

Claims

1. 1. A method performed by a power transmitting device for wirelessly powering a power receiving device in a communications network, the power transmitting device comprising M antennas, - for each of the M antennas, K subcarrier channel estimates h associated with the K subcarrier radio channels for the receiving device; ｍｋ (m=1...M; k=1...K) (310), The acquired K subcarrier channel estimates h ｍｋ selecting (320) a single subcarrier radio channel from the K subcarrier radio channels for each antenna based on transmitting (330) a power signal comprising a single tone per antenna on said selected subcarrier radio channel within a predefined time frame; A method wherein the phase of the transmitted tones is selected based on the phase of the subcarrier channel estimates.

2. 2. The method of claim 1, wherein the phases of the transmitted tones are selected so that the peak power of the power signal received at the powered device is greater than the sum of the powers of each single tone if received individually at the powered device.

3. 3. The method of claim 1, wherein the phase of the transmitted tone is selected such that a single tone sums positively at the receiving device.

4. The predefined time period is: - a number of radio frames, one or more OFDM symbols The method according to any one of claims 1 to 3, wherein the method corresponds to one or more of:

5. 5. The method of claim 1, wherein an antenna comprises a single power amplifier connected to one or more antenna elements.

6. A power transmitting device that wirelessly supplies power to a power receiving device in a communication network, the power transmitting device including M antennas, the power transmitting device including a control circuit, the control circuit including: - for each of the M antennas, K subcarrier channel estimates h associated with the K subcarrier radio channels for the receiving device; ｍｋ (m=1...M; k=1...K) (310), The acquired K subcarrier channel estimates h ｍｋ selecting (320) a single subcarrier radio channel from the K subcarrier radio channels for each antenna based on - configured to transmit (330) via said associated antenna a power signal comprising a single tone per antenna on said selected subcarrier radio channel within a predefined time frame; A power transmitting device, wherein the phase of the transmit tone is selected based on the phase of the subcarrier channel estimate.

7. 7. The power transmitting device of claim 6, wherein the phase of the transmitted tone 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 each single tone if received individually at the power receiving device.

8. 8. The power transmitting device according to claim 6, wherein the phase of the transmitted tone is selected such that a single tone is summed positively at the power receiving device.

9. The predefined time period is: - a number of radio frames, one or more OFDM symbols The power transmitting device according to claim 6 , which corresponds to one or more of the following:

10. 10. A method according to any one of claims 6 to 9, wherein an antenna comprises a single power amplifier connected to one or more antenna elements.

11. 6. A power transmitting device for wirelessly supplying power to a power receiving device in a communication network, the power transmitting device including M antennas, the power transmitting device including a control circuit, the control circuit configured to implement the method of any one of claims 1 to 5.

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