wireless communication system

Abstract

In this wireless communication system that simultaneously transfers an information signal and an energy signal, the transfer rate and the efficiency of a wireless power supply are appropriately controlled. The wireless communication system comprises a first wireless communication device and a second wireless communication device. The first wireless communication device comprises a transmission circuit that transmits an information signal and an energy signal. The second wireless communication device comprises: a splitter that generates a first reception signal and a second reception signal by splitting a reception signal from the first wireless communication device; an energy receiver that rectifies the energy signal included in the first reception signal to generate direct current; an information receiver that decodes the information signal included in the second reception signal; and a second control unit that generates control information including a request relating to transmission power of the information signal and transmission power of the energy signal. The second wireless communication device transmits the control information to the first wireless communication device. The transmission power of the energy signal and the information signal is controlled on the basis of the control information of the first wireless communication device.

Description

[Technical Field]

[0001] The present invention relates to a wireless communication system capable of wireless power supply. [Background technology]

[0002] In recent years, wireless power supply, which transmits power to wireless communication devices using electromagnetic waves, has been studied. For example, in a mobile communication system, power is transmitted from a base station to a terminal device using electromagnetic waves. In this case, the base station simultaneously transmits an information signal and an energy signal to the terminal device. The terminal device decodes the information signal to obtain information and rectifies the energy signal to charge a battery.

[0003] Fig. 1 shows an example of a wireless communication system capable of wireless power supply. In the wireless communication system 100, as shown in Fig. 1, an information signal and an energy signal are simultaneously transmitted from a base station 1 to a terminal device 3. Here, the terminal device 3 includes a splitter 3a, an energy receiver 3b, and an information receiver 3c. The splitter 3a splits the signal received from the base station 1 at a predetermined ratio and guides it to the energy receiver 3b and the information receiver 3c.

[0004] The energy receiver 3b rectifies the energy signal in the received signal to generate a direct current, which charges the battery. The information receiver 3c down-converts the received signal and then decodes the information signal to recover the information.

[0005] Methods for simultaneously transmitting information and power are described, for example, in Non-Patent Documents 1 and 2. Patent Documents 1 and 2 also describe wireless communication systems capable of transmitting power. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-035257 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-193707 [Non-patent literature]

[0007] [Non-Patent Document 1] X. Zhou, R. Zhang, and CK Ho, Wireless information and power Transfer: Architecture design and rate-energy tradeoff, IEEE Transactions on Communications, Vol.61, No.11, pp.4754-4767, November 2013 [Non-patent document 2] Overview on 5G Radio Frequency Energy Harvesting https: / / www.astesj.com / publications / ASTESJ_040442.pdf Summary of the Invention [Problem to be solved by the invention]

[0008] In the above-described wireless communication system, when the battery of the terminal device 3 is sufficiently charged, the terminal device 3 does not need to receive an energy signal. On the other hand, when the battery of the terminal device 3 is not sufficiently charged, it is preferable for the terminal device 3 to receive an energy signal with high power.

[0009] However, in existing wireless communication systems that simultaneously transmit information signals and energy signals, the ratio of the power of the information signals to the power of the energy signals is predetermined, which creates a trade-off between the information transmission rate and the efficiency of wireless power supply.

[0010] An object of one aspect of the present invention is to appropriately control the information transmission rate and the efficiency of wireless power supply in a wireless communication system that simultaneously transmits an information signal and an energy signal. [Means for solving the problem]

[0011] A wireless communication system according to one embodiment of the present invention includes a first wireless communication device and a second wireless communication device. The first wireless communication device includes a transmission circuit for transmitting an information signal and an energy signal, and a first control unit for controlling the transmission of the information signal and the energy signal. The second wireless communication device includes a splitter for branching a signal received from the first wireless communication device to generate a first received signal and a second received signal, an energy receiver for rectifying the energy signal included in the first received signal to generate a direct current, an information receiver for decoding the information signal included in the second received signal, and a second control unit for generating control information including requests related to the transmission power of the information signal and the transmission power of the energy signal. The second wireless communication device transmits the control information to the first wireless communication device. In the first wireless communication device, the first control unit controls the transmission power of the information signal and the transmission power of the energy signal based on the control information. [Effects of the Invention]

[0012] According to the above-described aspect, in a wireless communication system that simultaneously transmits an information signal and an energy signal, it is possible to appropriately control the information transmission rate and the efficiency of wireless power supply. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram illustrating an example of a wireless communication system capable of wireless power supply. [Figure 2] FIG. 2 is a diagram showing an example of a power supply sequence in the wireless communication system according to the first embodiment of the present invention. [Figure 3] 3 is a diagram illustrating an example of an operation of a terminal device in the power supply sequence illustrated in FIG. 2. FIG. [Figure 4] FIG. 10 is a diagram illustrating an example of a base station according to a second embodiment of the present invention. [Figure 5] FIG. 10 is a diagram illustrating an example of a signal transmitted from a base station to a terminal device. [Figure 6] FIG. 10 is a diagram illustrating an example of a terminal device according to a second embodiment of the present invention. [Figure 7] FIG. 10 is a diagram illustrating power distribution in the second embodiment. [Figure 8] FIG. 10 is a diagram illustrating an example of a power supply sequence according to the second embodiment. [Figure 9] FIG. 1 is a diagram (part 1) showing the relationship between the splitter distribution ratio and transmission power. [Figure 10] FIG. 2 is a diagram (part 2) showing the relationship between the splitter distribution ratio and transmission power. [Figure 11] FIG. 10 is a diagram illustrating a first variation of the second embodiment. [Figure 12] FIG. 10 is a diagram illustrating a second variation of the second embodiment. [Figure 13] FIG. 10 is a diagram illustrating a third variation of the second embodiment. [Figure 14] FIG. 10 is a diagram illustrating a fourth variation of the second embodiment. [Figure 15] FIG. 1 is a diagram showing an example of a frame for transmitting an information signal and an energy signal by time division multiplexing. DETAILED DESCRIPTION OF THE INVENTION

[0014] First Embodiment Fig. 2 shows an example of a power supply sequence in a wireless communication system according to the first embodiment of the present invention. Fig. 3 shows an example of the operation of a terminal device in the power supply sequence shown in Fig. 2. In the example shown in Figs. 2 and 3, a radio signal is transmitted from the base station 10 to the terminal device 30. At this time, the power of the radio signal is assumed to be "100".

[0015] As shown in FIG. 3, the terminal device 30 includes a splitter 31 that splits a received signal and guides it to an energy receiver 32 and an information receiver 33. In the example shown in FIG. 3(a), the ratio of the power of the signal guided to the energy receiver 32 to the power of the signal guided to the information receiver 33 is "10:90." In this case, the power of the signal guided to the energy receiver 32 is "10." The energy receiver 32 uses this power to charge its battery. Furthermore, the power of the signal guided to the information receiver 33 is "90." The information receiver 33 decodes this signal to reproduce the information. Note that in this specification, the numerical values ​​representing the transmission power and the reception power are hypothetical values ​​for the sake of simplicity of explanation, and it is assumed that there is no attenuation between the base station 10 and the terminal device 30.

[0016] When the battery charge rate of the terminal device 30 is low, the terminal device 30 increases the ratio of power distributed to the energy receiver 32 relative to the power distributed to the information receiver 33. In this embodiment, the ratio of power distributed to the energy receiver 32 and power distributed to the information receiver 33 is changed to "90:10." However, if the distribution ratio of the splitter 31 is changed while the power of the radio signal transmitted from the base station 10 is constant, the power of the signal guided to the information receiver 33 will decrease. In this case, the error rate will increase due to a deterioration in the signal-to-noise ratio, and there is a risk of a decrease in the transmission rate.

[0017] Therefore, when changing the distribution ratio of the splitter 31, it is preferable to also change the power of the radio signal transmitted from the base station 10. Specifically, when changing the distribution ratio of the splitter 31, it is preferable to increase the power of the radio signal transmitted from the base station 10 so as to maintain the power of the signal guided to the information receiver 33. In this case, the battery can be charged efficiently without decreasing the transmission rate of wireless communication.

[0018] Therefore, when changing the distribution ratio of the splitter 31, the terminal device 30 transmits a request to the base station 10 to increase the transmission power so that the power of the signal guided to the information receiver 33 is maintained. In the example shown in FIGS. 2 and 3, when the ratio of the power distributed to the energy receiver 32 and the power distributed to the information receiver 33 is "90:10", in order to set the power of the signal guided to the information receiver 33 to "90", the power of the radio signal needs to be "900". Therefore, the terminal device 30 transmits a request to the base station 10 to set the power of the radio signal to "900".

[0019] If the base station 10 can control the transmission power in accordance with this request, it transmits an ACK signal to the terminal device 30. Upon receiving the ACK signal, the terminal device 30 sets the distribution ratio of the splitter 31 so that the ratio of the power distributed to the energy receiver 32 and the power distributed to the information receiver 33 is 90:10. Thereafter, the base station 10 increases the transmission power of the radio signal from 100 to 900. As a result, as shown in FIG. 3(b), the power of the signal guided to the energy receiver 32 is 810. The energy receiver 32 then uses this power to charge the battery. Therefore, the battery can be efficiently charged using a large amount of power. Furthermore, the power of the signal guided to the information receiver 33 remains at 90. In other words, even if the distribution ratio of the splitter 31 is changed, the power of the signal guided to the information receiver 33 does not change. Therefore, the transmission rate does not decrease.

[0020] <Second embodiment> FIG. 4 shows an example of a base station according to the second embodiment of the present invention. The base station 10 shown in FIG. 4 corresponds to the base station 1 shown in FIG. 1. That is, the base station 10 can simultaneously transmit an information signal and an energy signal to a terminal device. Although the information signal and the energy signal are not particularly limited, in this embodiment, they are transmitted by carrier waves of different frequencies. That is, the information signal and the energy signal are simultaneously transmitted by frequency division multiplexing.

[0021] The base station 10 includes an information signal generator 11, a digital-to-analog converter (DAC) 12, a mixer 13, an amplifier 14, an amplifier 15, and a control unit 16. However, Fig. 4 only shows the configuration for transmitting signals to a terminal device. That is, the base station 10 may include other circuits or functions not shown in Fig. 4.

[0022] The information signal generator 11 generates an information signal including data and control information to be received by the terminal device. The information signal generator 11 is realized by, for example, a DSP (Digital Signal Processor). The DAC 12 converts the information signal generated by the information signal generator 11 into an analog signal. The mixer 13 upconverts the output signal of the DAC 12 using the carrier frequency signal f0. In other words, the carrier frequency signal f0 is modulated by the information signal. The amplifier 14 amplifies the output signal of the mixer 13. The gain of the amplifier 14 is controlled by the control unit 16. In the following description, the output signal of the amplifier 14 may be referred to as the "information signal."

[0023] Amplifier 15 amplifies carrier frequency signal f1. Carrier frequency signal f1 is not modulated in the example shown in FIG. 4, but may be modulated by a pseudo signal or a dummy signal. The gain of amplifier 15 is also controlled by control unit 16. In the following description, the output signal of amplifier 15 may be referred to as an "energy signal."

[0024] The control unit 16 controls the operation of the base station 10. Specifically, the control unit 16 controls communication between the base station 10 and the terminal device. However, the following description will focus on control related to the transmission of information signals and energy signals.

[0025] The control unit 16 determines the transmission power of the information signal and the transmission power of the energy signal. At this time, the control unit 16 may determine the ratio between the transmission power of the information signal and the transmission power of the energy signal. Here, the control unit 16 may determine the ratio between the transmission power of the information signal and the transmission power of the energy signal in response to a request from the terminal device. However, the control unit 16 can also determine the ratio between the transmission power of the information signal and the transmission power of the energy signal without receiving a request from the terminal device. Then, the control unit 16 controls the transmission power of the information signal and the transmission power of the energy signal based on the determined ratio. Note that the control unit 16 controls the transmission power of the information signal and the transmission power of the energy signal by controlling the gains of the amplifiers 14 and 15.

[0026] The control unit 16 is realized by, for example, a processor. The processor may control the transmission power of the information signal and the energy signal by, for example, executing a software program. Alternatively, the processor (i.e., the control unit 34) may be realized by a hardware circuit that processes digital signals.

[0027] FIG. 5 shows an example of a signal transmitted from the base station 10 to a terminal device. In this embodiment, the base station 10 transmits an information signal and an energy signal to the terminal device. The carrier frequency of the information signal is f0, and the carrier frequency of the energy signal is f1. The base station 10 can individually control the transmission power of the information signal and the energy signal. In this embodiment, the transmission power of the energy signal is higher than the transmission power of the information signal. The base station 10 controls the transmission power of each signal so that the total transmission power (i.e., the sum of the transmission power of the information signal and the transmission power of the energy signal) is equal to or less than a predetermined maximum power. The base station 10 may also control the transmission power of the information signal depending on the communication environment between the base station 10 and the terminal device. Furthermore, as will be described later, the base station 10 may determine the ratio between the transmission power of the information signal and the transmission power of the energy signal in response to a request from the terminal device.

[0028] Fig. 6 shows an example of a terminal device according to the second embodiment of the present invention. The terminal device 30 shown in Fig. 6 corresponds to the terminal device 3 shown in Fig. 1. That is, the terminal device 30 can receive an information signal and an energy signal simultaneously.

[0029] The terminal device 30 includes a splitter 31, an energy receiver 32, an information receiver 33, and a control unit 34. The terminal device 30 may include other circuits or functions not shown in Fig. 6. For example, the terminal device 30 includes a transmitter (not shown) for transmitting a signal to the base station 10.

[0030] The splitter 31 splits a signal received from the base station 10 at a predetermined ratio and guides the split signal to the energy receiver 32 and the information receiver 33. In the following description, the ratio between the power of the signal guided to the energy receiver 32 and the power of the signal guided to the information receiver 33 may be referred to as the "distribution ratio." The distribution ratio of the splitter 31 is controlled by the control unit 34. That is, when the distribution ratio instructed by the control unit 34 is "X (percent)," the power of the signal guided to the energy receiver 32 is "X" percent of the total power of the signals received by the terminal device 30, and the power of the signal guided to the information receiver 33 is "100-X" percent of the total power of the signals received by the terminal device 30. The distribution ratio of the splitter 31 is set, for example, by controlling the resistance values ​​of the path between the input port and the energy receiver 32 and the path between the input port and the information receiver 33.

[0031] The energy receiver 32 includes a rectifier circuit 32a, a low-pass filter (LPF) 32b, and a battery 32c. The rectifier circuit 32a includes one or more diodes and rectifies the received signal. The LPF 32b filters the output signal of the rectifier circuit 32a. This generates a direct current, which charges the battery 32c. When the terminal device 30 receives an energy signal and an information signal, the energy receiver 32 charges the battery 32c using the power of the energy signal. For example, when the information signal and the energy signal are simultaneously transmitted by frequency division multiplexing, the direct current may be generated by rectifying the frequency components of the energy signal.

[0032] The information receiver 33 includes a mixer 33a, a low-pass filter (LPF) 33b, an analog-to-digital converter (ADC) 33c, and a decoder 33d. The mixer 33a performs downconversion by multiplying the received signal by a carrier frequency signal f0. This converts the information signal from the carrier frequency domain to the baseband domain. The LPF 33b filters the output signal of the mixer 33a. This removes noise components and unwanted high-frequency components. The ADC 33c converts the output signal of the LPF 33b into a digital signal. The decoder 33d decodes the digital signal output from the ADC 33c to recover the information. Note that when the information signal transmitted from the base station 10 includes control information, the control information recovered by the decoder 33d is sent to the control unit 34.

[0033] The control unit 34 controls the operation of the terminal device 30. Specifically, the control unit 34 controls communication between the base station 10 and the terminal device 30. However, the following describes control related to reception of information signals and energy signals.

[0034] The control unit 34 can monitor the charge state of the battery 32c. The charge state of the battery 32c is detected, for example, based on the voltage of the battery 32c. The control unit 34 also monitors the communication state between the base station 10 and the terminal device 30. The communication state may be detected, for example, based on the error rate of the output signal of the decoder 33d. Then, based on these monitoring results, the control unit 34 generates control information including requests related to the transmission power of the information signal and the transmission power of the energy signal. The control information includes, for example, information indicating the ratio between the transmission power of the information signal and the transmission power of the energy signal. Alternatively, the control information may include information indicating a desired value of the transmission power of the information signal and a desired value of the transmission power of the energy signal. Then, the control unit 34 transmits the generated control information to the base station 10. Then, the base station 10 controls the transmission power of the information signal and the transmission power of the energy signal in accordance with the control information received from the terminal device 30. In addition, the control unit 34 may control the distribution ratio of the splitter 31 based on the above monitoring results.

[0035] The control unit 34 is realized by, for example, a processor. The processor may execute, for example, a software program to generate control information and control the splitter 31. Alternatively, the processor (i.e., the control unit 34) may be realized by a hardware circuit that processes digital signals.

[0036] In this way, the base station 10 controls the transmission power of the information signal and the transmission power of the energy signal in accordance with the control information received from the terminal device 30. Therefore, the power used to charge the battery 32c and the power used for wireless communication depend not only on the distribution ratio of the splitter 31 but also on the ratio of the transmission power of the information signal and the energy signal.

[0037] FIG. 7 is a diagram illustrating power distribution in the second embodiment. In the cases shown in FIGS. 7(a) and 7(b), the ratio of the transmission power of the information signal and the energy signal transmitted from the base station 10 is 10:90. Here, when the charging rate of the battery 32c is low, the terminal device 30 preferably increases the distribution rate to the energy receiver 32. In FIG. 7(a), the distribution rate to the energy receiver 32 by the splitter 31 is 90 percent. In this case, the power used to charge the battery 32c is 81 percent of the total power of the received signals. On the other hand, when the charging rate of the battery 32c is high, the terminal device 30 preferably decreases the distribution rate to the energy receiver 32. In FIG. 7(b), the distribution rate to the energy receiver 32 by the splitter 31 is 10 percent. In this case, the power used to charge the battery 32c is 9 percent of the total power of the received signals.

[0038] In this way, when the charging rate of the battery 32c is low, by increasing the distribution rate to the energy receiver 32, most of the power of the received signal is used to charge the battery 32c. That is, efficient power supply is realized. In contrast, in the case shown in FIG. 7(b), 80 percent or more of the total power of the received signal is not used. As a result, despite the low distribution rate to the energy receiver 32, not enough power is distributed to the information receiver 33. Here, when the power of the signal guided to the information receiver 33 is low, the error rate increases due to a deterioration in the signal-to-noise ratio, and the transmission rate decreases. For example, when the error rate is high, it is necessary to reduce the number of bits transmitted per symbol and / or lower the baud rate, and therefore the transmission rate decreases. That is, in the case shown in FIG. 7(b), the efficiency of information communication decreases.

[0039] In the cases shown in Figures 7(c) and 7(d), the ratio of the transmission power of the information signal and the energy signal transmitted from the base station 10 is "90:10." Here, when the charge rate of the battery 32c is high, it is preferable that the terminal device 30 increases the distribution rate to the information receiver 33. In Figure 7(c), the distribution rate to the information receiver 33 by the splitter 31 is 90 percent. In this case, the power used for wireless communication is 81 percent of the total power of the received signal. This reduces the error rate, allowing the transmission rate to be increased. In other words, the efficiency of information communication is increased in the case shown in Figure 7(c).

[0040] On the other hand, when the charging rate of the battery 32c is low, it is preferable that the terminal device 30 increase the distribution rate to the energy receiver 32. In Fig. 7(d), the distribution rate to the energy receiver 32 by the splitter 31 is 90 percent. However, in this case, the power used to charge the battery 32c is 9 percent of the total power of the received signal. In other words, even though the distribution rate to the energy receiver 32 by the splitter 31 is high, the power supply efficiency is low.

[0041] As described above, it may not be possible to achieve a good balance between the power supply efficiency and the communication efficiency simply by controlling the distribution ratio of the splitter 31. Therefore, in an embodiment of the present invention, the ratio of the transmission power between the information signal and the energy signal, and the distribution ratio of the power to the energy receiver 32 and the information receiver 33 are appropriately controlled to achieve a good balance between the power supply efficiency and the communication efficiency.

[0042] 8 shows an example of a power supply sequence according to the second embodiment of the present invention. In this example, two terminal devices (30a, 30b) are connected to the base station 10. The configuration of each of the terminal devices 30a and 30b is the same as that of the terminal device 30 shown in FIG.

[0043] Assume that the charging rate of the battery 32c in the terminal device 30a is low. In this case, the control unit 34 determines the transmission power of the control information and energy signal and the distribution ratio of the splitter 31 so that as much power as possible is distributed to the energy receiver 32. At this time, instead of determining the transmission power of the control information and energy signal, the ratio between the transmission power of the information signal and the transmission power of the energy signal (hereinafter referred to as the transmission power ratio) may be determined. However, in order to maintain a predetermined transmission rate, the power of the signal guided to the information receiver 33 needs to be set to a predetermined threshold level or higher.

[0044] Here, the transmission power and the distribution ratio of the splitter 31 are calculated so as to satisfy the following conditions: In this specification, the numerical values ​​representing the transmission power and the reception power are hypothetical values ​​for the sake of simplicity, and it is assumed that there is no attenuation between the base station 10 and the terminal device 30.

[0045] (a) The maximum value of the transmission power of the base station 10 is "1000". (b) When the power of the signal guided to the information receiver 33 is "50" or more, a predetermined transmission rate can be maintained.

[0046] In this case, in order to shorten the charging time of the battery 32c, the transmission power and the distribution ratio of the splitter 31 are determined so as to satisfy the following conditions. (1) The sum of the transmission power of the information signal and the transmission power of the energy signal is the maximum transmission power of the base station 10 (i.e., "1000"). (2) The power of the signal directed to the information receiver 33 is "50". (3) Maximize the power of the signal directed to the energy receiver 32.

[0047] For example, suppose the distribution ratio of splitter 31 is "I (proportion of power distributed to information receiver 33):E (proportion of power distributed to energy receiver 32) = 50:50." In this case, to satisfy condition (2), the transmission power of the information signal is set to "100." Then, according to condition (1), the transmission power of the energy signal is "900." Furthermore, the power of the signal guided to energy receiver 32 is "450."

[0048] 9 shows the relationship between the distribution ratio of the splitter 31 and the transmission power, calculated to satisfy conditions (1) and (2). Here, condition (3) selects a combination that maximizes the power of the signal guided to the energy receiver 32. In this example, the power of the signal guided to the energy receiver 32 is maximized when the distribution ratio of the splitter 31 is "I:E=20:80" and the transmission power is "I (transmission power of the information signal):E (transmission power of the energy signal)=250:750."

[0049] The control unit 34 generates control information indicating the transmission power of the information signal and the energy signal based on the above calculation. That is, the control information "I:E=250:750" is generated. Alternatively, when the total power when the base station 10 transmits wireless signals to the terminal device 30a is determined, the control unit 34 may generate control information indicating the ratio between the transmission power of the information signal and the transmission power of the energy signal. In this case, the control information "I:E=25:75" is generated. Then, the terminal device 30a transmits this control information to the base station 10.

[0050] The base station 10 determines whether or not it is possible to set the transmission power in accordance with the control information. If it is possible to set the transmission power of the information signal and the energy signal in accordance with the control information, the base station 10 transmits an ACK signal to the terminal device 30a. The ACK signal may be realized by returning the control information received from the terminal device 30a to the terminal device 30a.

[0051] When the terminal device 30a receives the ACK signal from the base station 10, it sets the splitter 31 in accordance with the distribution ratio determined previously. In this embodiment, the splitter 31 is set so that the distribution ratio is "I:E=20:80".

[0052] After this, the base station 10 transmits an information signal and an energy signal in accordance with the control information received from the terminal device 30a. In this embodiment, the base station 10 receives control information "I:E=250:750". Therefore, the base station 10 transmits an information signal with a transmission power of "250" and an energy signal with a transmission power of "750". Note that, even when the base station 10 receives control information "I:E=25:75" which indicates the ratio between the transmission power of the information signal and the transmission power of the energy signal, the base station 10 can similarly transmit an information signal with a transmission power of "250" and an energy signal with a transmission power of "750". However, it is assumed that the maximum transmission power of the base station 10 is "1000".

[0053] In the terminal device 30a, the splitter 31 splits the received signal and guides it to the energy receiver 32 and the information receiver 33. Here, the distribution ratio of the splitter 31 is set by the control unit 34, as described above. Therefore, 80 percent of the total power of the received signal is distributed to the energy receiver 32, and 20 percent of the total power of the received signal is distributed to the information receiver 33. As a result, the battery 32c in the terminal device 30a can be charged with high power supply efficiency while maintaining the transmission rate between the base station 10 and the terminal device 30a.

[0054] Assume that the battery 32c of the terminal device 30b is fully charged. Furthermore, assume that the terminal device 30b desires to receive a large amount of data. In this case, the control unit 34 of the terminal device 30b increases the power distributed to the information receiver 33 according to the desired transmission rate while minimizing the power distributed to the energy receiver 32.

[0055] As an example, the transmission power and the distribution ratio of the splitter 31 are determined so as to satisfy the following conditions. (1) The power distributed to the energy receiver 32 is "50". (2) The power distributed to the information receiver 33 is "100". (3) The transmission power of the base station 10 is minimized.

[0056] For example, assume that the distribution ratio of splitter 31 is "I:E=50:50." In this case, to satisfy condition (1), the transmission power of the energy signal is set to "100." Furthermore, to satisfy condition (2), the transmission power of the information signal is set to "200."

[0057] 10 shows the relationship between the distribution ratio of splitter 31 and transmission power, calculated to satisfy conditions (1) and (2). Here, condition (3) selects a combination that minimizes the sum of the transmission power of the information signal and the transmission power of the energy signal. In this embodiment, the transmission power of base station 10 is minimized when the distribution ratio of splitter 31 is "I:E=60:40" and the transmission power is "I:E=167:125."

[0058] Based on the above calculation, the control unit 34 generates control information that indicates the transmission power of the information signal and the energy signal. In this example, the control information "I:E=167:125" is generated and transmitted to the base station 10.

[0059] The base station 10 determines whether or not it is possible to transmit the information signal and the energy signal in accordance with the control information, and if it is possible to transmit the information signal and the energy signal in accordance with the control information, the base station 10 transmits an ACK signal to the terminal device 30b.

[0060] When the terminal device 30a receives the ACK signal from the base station 10, it sets the splitter 31 in accordance with the distribution ratio determined previously. In this embodiment, the splitter 31 is set so that the distribution ratio is "I:E=60:40".

[0061] After this, the base station 10 transmits the information signal and the energy signal in accordance with the control information received from the terminal device 30b. In this example, the base station 10 transmits the information signal with a transmission power of "167" and transmits the energy signal with a transmission power of "125".

[0062] In the terminal device 30b, the splitter 31 splits the received signal and guides it to the energy receiver 32 and the information receiver 33. At this time, 40 percent of the total power of the received signal is distributed to the energy receiver 32, and 60 percent of the total power of the received signal is distributed to the information receiver 33. As a result, efficient wireless communication and wireless power supply are achieved while suppressing the transmission power of the base station 10.

[0063] If an ACK signal cannot be received from the base station 10, the terminal device 30 changes the distribution ratio of the splitter 31 and determines a combination of transmission powers corresponding to the new distribution ratio. Then, the terminal device 30 notifies the base station 10 of the new combination of transmission powers, and the base station 10 determines whether the new combination of transmission powers can be realized. The determination result is transmitted from the base station 10 to the terminal device 30. This procedure is repeated until an ACK signal is transmitted from the base station 10 to the terminal device 30.

[0064] As described above, according to the second embodiment, when the battery charging rate of the terminal device 30 is low, the transmission power of the information signal and the energy signal and the distribution ratio of the splitter 31 are set so that the power for charging the battery is increased while maintaining a predetermined transmission rate. Therefore, efficient wireless power feeding can be realized while maintaining a predetermined transmission rate. Furthermore, when the battery charging rate of the terminal device 30 is high, the transmission power of the base station 10 can be reduced while continuing the minimum necessary power feeding and achieving a desired transmission rate.

[0065] 11 shows a first variation of the second embodiment. In this example, a terminal device 30 is connected to a base station 10.

[0066] In order to charge the battery 32c as quickly as possible, the terminal device 30 may receive only the energy signal without receiving the information signal. In this case, the terminal device 30 transmits to the base station 10 control information "I:E=0:100" that indicates the ratio between the transmission power of the information signal and the transmission power of the energy signal.

[0067] When the base station 10 receives this control information, it determines whether or not the requested transmission power can be realized. If the requested transmission power can be realized, the base station 10 transmits an ACK signal to the terminal device 30. When the terminal device 30 receives the ACK signal, it controls the splitter 31 so that the total power of the received signal is distributed to the energy receiver 32.

[0068] Thereafter, the base station 10 transmits an energy signal to the terminal device 30. At this time, the base station 10 does not need to transmit an information signal. The power of the energy signal may be a predetermined maximum power. The terminal device 30 then guides this energy signal to the energy receiver 32. The energy receiver 32 charges the battery 32c with the power of the received energy signal. This achieves efficient rapid charging.

[0069] 12 shows a second variation of the second embodiment. In the second variation, the terminal device 30 transmits capability information indicating the capabilities of the terminal device 30 to the base station 10 in addition to control information. The capability information indicates, for example, whether the distribution ratio of the splitter 31 can be changed.

[0070] 8 to 10, the base station 10 determines whether or not the transmission power requested by the terminal device 30 can be realized. Then, if the transmission power requested by the terminal device 30 can be realized, the base station 10 transmits an ACK signal to the terminal device 30. On the other hand, if the transmission power requested by the terminal device 30 cannot be realized, the base station 10 refers to the capability information. Here, if the capability information is "OK: distribution ratio can be changed", the base station 10 transmits a NACK signal to the terminal device 30 indicating that the requested transmission power cannot be realized, and may request the terminal device 30 to change the distribution ratio of the splitter 31. Note that if the capability information is "NG: distribution ratio cannot be changed", the base station 10 simply transmits a NACK signal to the terminal device 30.

[0071] FIG. 13 shows a third variation of the second embodiment. The third variation includes a procedure for changing the transmission power of the base station 10 when decoding of an information signal fails. For example, in the example shown in FIG. 13(a), the powers of the information signal and energy signal transmitted from the base station 10 are "10" and "90," respectively. That is, the transmission power of the information signal is low. As a result, if decoding of the information signal fails, the terminal device 30 transmits a NACK signal indicating the decoding failure to the base station 10. The terminal device 30 also transmits control information to the base station 10 requesting a change in the ratio between the transmission power of the information signal and the transmission power of the energy information. This control information requests, for example, increasing the power of the information signal and decreasing the power of the energy signal. The base station 10 then controls the transmission power in accordance with this control information. As a result, the powers of the information signal and energy signal transmitted from the base station 10 to the terminal device 30 are changed to "20" and "80," respectively.

[0072] In the example shown in FIG. 13(b), if decoding of the information signal fails, the terminal device 30 transmits a NACK signal and control information requesting an increase in transmission power to the base station 10. This control information requests that the power of the information signal and the energy signal be increased. The base station 10 then controls the transmission power in accordance with the control information. In this embodiment, the power of the information signal and the energy signal transmitted from the base station 10 to the terminal device 30 are changed to "20" and "180", respectively.

[0073] FIG. 14 shows a fourth variation of the second embodiment. In the fourth variation, the base station 10 monitors the status of wireless communication with the terminal device 30. As an example, when the base station 10 does not receive a resource allocation request from the terminal device 30 for a predetermined period of time or longer, the base station 10 determines that the terminal device 30 is in an idle state. The resource allocation request is a signal requesting resources to be used in communication between the base station 10 and the terminal device 30, and is transmitted from the terminal device 30 to the base station 10. When the base station 10 detects that the terminal device 30 is in an idle state, the base station 10 stops transmitting an information signal and transmits only an energy signal to the terminal device 30. This allows the terminal device 30 that is not performing wireless communication to efficiently charge the battery 32c using this energy signal. In addition, the power consumption of the base station 10 can be reduced.

[0074] Thereafter, when starting wireless communication, the terminal device 30 transmits a resource allocation request to the base station 10. The base station 10 allocates resources to the terminal device 30 in accordance with the resource allocation request, and controls the transmission power of the information signal and the energy signal. In this embodiment, the power of the information signal and the energy signal transmitted from the base station 10 are set to "50" and "50", respectively.

[0075] In the above embodiment, the splitter 31 splits the received signal to generate a first received signal that is guided to the energy receiver 32 and a second received signal that is guided to the information receiver 33. Here, the splitter 31 is a power splitter, and the contents of the first received signal and the second received signal are the same. However, when an information signal and an energy signal are simultaneously transmitted by frequency division multiplexing, the splitter 31 may extract the frequency component of the information signal from the received signal and guide it to the information receiver 33, and may also extract the frequency component of the energy signal from the received signal and guide it to the energy receiver 32.

[0076] <Third embodiment> In the third embodiment, an information signal and an energy signal are simultaneously transmitted by time division multiplexing. In this case, the base station 10 transmits, for example, a frame shown in Fig. 15 to the terminal device 30. The frame is composed of a header and a payload. The information signal and the energy signal are stored in the payload.

[0077] The base station 10 sets the length of the information signal and the length of the energy signal in the payload based on the control information received from the terminal device 30. For example, when the control information received from the terminal device 30 is "I:E=40:60", the frame is configured so that the ratio between the length of the information signal and the length of the energy signal is "40:60".

[0078] The terminal device 30 receives frames transmitted from the base station 10. Here, it is assumed that the terminal device 30 can detect the beginning of each frame. Furthermore, since the payload is created in the base station 10 according to control information transmitted from the terminal device 30 to the base station 10, the terminal device 30 can recognize the time periods for receiving information signals and energy signals. Therefore, by controlling the splitter 31, the terminal device 30 can guide the information signal to the information receiver 33 and the energy signal to the energy receiver 32. Note that in the third embodiment, the terminal device 30 may include, as the splitter 31, a selector that selectively guides the received signal to the information receiver 33 or the energy receiver 32.

[0079] In the wireless communication system configured as described above, when the charging rate of the battery 32c is low, the terminal device 30 transmits control information to the base station 10 requesting a short information signal and a long energy signal. This improves the efficiency of wireless power supply. On the other hand, when the charging rate of the battery 32c is high, the terminal device 30 transmits control information to the base station 10 requesting a long information signal and a short energy signal. This increases the amount of transmission data. Note that the control information transmitted from the terminal device 30 to the base station 10 may include a desired value of transmission power in addition to information indicating the ratio between the length of the information signal and the length of the energy signal. [Explanation of symbols]

[0080] 10 base station 11 Information signal generator 12 Digital-to-Analog Converter (DAC) 13 Mixer 14, 15 Amplifier 16 Control Unit 30 Terminal Equipment 31 Splitter 32 Energy Receiver 32a rectifier circuit 32b Low-pass filter (LPF) 32c battery 33 Information receiver 33a Mixer 33b Low-pass filter (LPF) 33c Analog-to-Digital Converter (ADC) 33d decoder 34 Control Unit

Claims

1. A wireless communication system including a first wireless communication device and a second wireless communication device, the first wireless communication device, a transmitting circuit for transmitting an information signal and an energy signal; a first control unit that controls transmission of the information signal and the energy signal; the second wireless communication device, a splitter that splits a received signal from the first wireless communication device to generate a first received signal and a second received signal; an energy receiver that rectifies the energy signal included in the first received signal to generate a direct current; an information receiver for decoding the information signal included in the second received signal; a second control unit that generates control information including a request related to the transmission power of the information signal and the transmission power of the energy signal; the second wireless communication device transmits the control information to the first wireless communication device; In the first wireless communication device, the first control unit controls a transmission power of the information signal and a transmission power of the energy signal based on the control information; The second control unit setting a desired value of the power of the information signal included in the second received signal to be guided to the information receiver; calculating a transmission power of the information signal, a transmission power of the energy signal, and a distribution factor representing a ratio between the power of the first received signal and the power of the second received signal so as to satisfy the desired value and maximize the power of the energy signal included in the first received signal directed to the energy receiver; transmitting the control information including information representing transmission power of the information signal and the energy signal to the first wireless communication device; The splitter is configured to split the received signal according to the division ratio. A wireless communication system comprising:

2. The control information includes information representing a ratio between the transmission power of the information signal and the transmission power of the energy signal.

2. The wireless communication system according to claim 1.

3. The control information includes information representing a desired value of transmission power of the information signal and a desired value of transmission power of the energy signal.

2. The wireless communication system according to claim 1.

4. When the information receiver fails to decode the information signal, the second wireless communication device transmits, to the first wireless communication device, control information for increasing a ratio of transmission power of the information signal to transmission power of the energy signal.

2. The wireless communication system according to claim 1.

5. When the information receiver fails to decode the information signal, the second wireless communication device transmits control information to the first wireless communication device to increase transmission power of the information signal and the energy signal.

2. The wireless communication system according to claim 1.

6. When the first wireless communication device detects that the second wireless communication device is in a non-communication state, the first wireless communication device stops transmitting the information signal and transmits only the energy signal to the second wireless communication device.

2. The wireless communication system according to claim 1.

7. The transmitting circuit simultaneously transmits the information signal and the energy signal to the second wireless communication device by frequency division multiplexing.

2. The wireless communication system according to claim 1.

8. The transmitting circuit simultaneously transmits the information signal and the energy signal to the second wireless communication device by time division multiplexing.

2. The wireless communication system according to claim 1.

9. A wireless communication method for transmitting power from a first wireless communication device to a second wireless communication device using a wireless signal, comprising: the first wireless communication device includes a transmitting circuit for transmitting a wireless signal including an information signal and an energy signal; the second wireless communication device, a splitter that splits a received signal from the first wireless communication device to generate a first received signal and a second received signal; an energy receiver that rectifies the energy signal included in the first received signal to generate a direct current; an information receiver that decodes the information signal included in the second received signal; the second wireless communication device transmits control information including a request related to the transmission power of the information signal and the transmission power of the energy signal to the first wireless communication device; the first wireless communication device controls a transmission power of the information signal and a transmission power of the energy signal based on the control information; the second wireless communication device, setting a desired value of the power of the information signal included in the second received signal to be guided to the information receiver; calculating a transmission power of the information signal, a transmission power of the energy signal, and a distribution factor representing a ratio between the power of the first received signal and the power of the second received signal so as to satisfy the desired value and maximize the power of the energy signal included in the first received signal directed to the energy receiver; transmitting the control information including information representing transmission power of the information signal and the energy signal to the first wireless communication device; The splitter is configured to split the received signal according to the division ratio. A wireless communication method comprising:

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