Electronic apparatus and method

According to one embodiment, an electronic apparatus includes transmitter circuitry and processing circuitry. The transmitter circuitry transmits a first transmission signal during a first period via a transmission frequency band defined by a first wireless communication standard. The processing circuitry performs carrier sensing in a first frequency band during a second period following the first period. The transmitter circuitry further transmits, if a wireless signal is not detected in the carrier sensing, a second transmission signal during a third period following the second period. The processing circuitry performs, if the wireless signal is detected in the carrier sensing, carrier sensing in the first frequency band during a fourth period following the second period.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2018-229102, filed Dec. 6, 2018, the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a wireless power transfer technique.

BACKGROUND

In recent years, wireless power transfer systems that perform wireless power supply with an electromagnetic wave have been developed. In general, the electromagnetic wave used for power supply in the wireless power transfer systems has transmit power or equivalent isotropically radiated power (EIRP) greater than that of an electromagnetic wave used for communication. Thus, there is a high possibility that the electromagnetic wave of the wireless power transfer systems interferes with the electromagnetic wave of other wireless communication systems.

Therefore, a novel technique to reduce the interference with other wireless communication systems is required.

DETAILED DESCRIPTION

In general, according to one embodiment, an electronic apparatus includes transmitter circuitry and processing circuitry. The transmitter circuitry is configured to transmit a first transmission signal for power supply during a first period via a transmission frequency band defined by a first wireless communication standard. The processing circuitry is configured to perform carrier sensing in a first frequency band comprising at least the transmission frequency band during a second period following the first period. The second period is equal to or longer than a length of the first frame. The transmitter circuitry is further configured to transmit, if a wireless signal is not detected in the carrier sensing performed during the second period, a second transmission signal for power supply during a third period following the second period. The processing circuitry is configured to perform, if the wireless signal is detected in the carrier sensing performed during the second period, carrier sensing in the first frequency band during a fourth period following the second period.

First Embodiment

Firstly, the structure of an electronic apparatus of an embodiment will be explained with reference toFIG. 1. The electronic apparatus is a wireless power transmission apparatus1that supplies power wirelessly using an electromagnetic wave. The electromagnetic wave is, for example, a microwave, and is a wireless signal for power transmission (hereinafter may be referred to as a power transmission signal). A power reception apparatus2includes a circuit and the like to receive the power transmission signal. The power transmission signal, which is transmitted by the wireless power transmission apparatus1, is received by the power reception apparatus2. Thus, the power is supplied to the power reception apparatus2.

In general, as compared to a wireless signal used for communication (hereinafter may be referred to as a communication signal), the power transmission signal has a greater transmission power or a greater EIRP. Thus, the power transmission signal may possibly interfere with a communication signal of a frequency band that is transferred in another wireless communication system3. That is, the wireless power transmission apparatus1may become an interfering apparatus that interferes with the wireless communication system3, and the wireless communication system3may be an interfered system with which the wireless power transmission apparatus1interferes.

Thus, the wireless power transmission apparatus1of the present embodiment has a power transmission control function to reduce the interference with the wireless communication system3. The wireless power transmission apparatus1reduces the interference with the wireless communication system3using the power transmission control function if the wireless power transmission apparatus1is newly provided, if the wireless communication system3is newly established, or if at least one of the directivity of a radio signal (i.e., a wireless signal) transmitted/received by the wireless power transmission apparatus1and the directivity of a radio signal transmitted/received by the wireless communication system3is changed.

Hereinafter, for better understanding of the description, a case where the wireless communication system3conforms to an ARIB STD-75, that is, a standard of a dedicated short-range communication (DSRC) system will be mainly explained. The DSRC system is used in, for example, an electronic toll collection (ETC) system. The radio frequency band used in the DSRC system is, for example, 5.8 GHz.

The wireless communication system3includes a roadside apparatus3A that is a wireless communication apparatus fixed to a roadside site or the like (that is, a base station) and an in-vehicle apparatus3B that is a wireless communication apparatus mounted in a vehicle or the like (that is, a mobile station). The roadside apparatus3A periodically transmits a radio signal used for transfer of a communication frame. The communication frame includes a specific communication signal that contains predetermined bits (hereinafter may be referred to as a known signal) in order to allow the in-vehicle apparatus3B to detect the roadside apparatus3A. Note that the wireless communication system3may conform to other wireless communication standards such as a wireless LAN communication standard.

As illustrated inFIG. 1, the wireless power transmission apparatus1includes a controller11, a transmitter12, a detector13, one or more antenna transmission/reception duplexers14, and one or more antennas15. Each component may be realized as a circuit. The controller11, the transmitter12, and the detector13may be provided with one chip, or may be provided with multiple chips. Now, the operation of each component used to realize the above-mentioned power transmission control function will be explained.

The one or more antenna transmission/reception duplexers14-1,14-2, . . . , and14-M are connected to one or more antennas15-1,15-2, . . . ,15-M, respectively. Each pair of an antenna transmission/reception duplexer14and an antenna15(for example, the pair of the antenna transmission/reception duplexer14-1and the antenna15-1) may transmit a power transmission signal to the power reception apparatus2and receive a communication signal transmitted by the wireless communication system3to input the communication signal to the wireless power transmission apparatus1.

The controller11controls the operation of each component in the wireless power transmission apparatus1. The controller11controls a power transmission signal, which is transmitted by the transmitter12through the antenna transmission/reception duplexer14and the antenna15, and the timing of transmission of the signal. The controller11designates a time (period) for which power is transmitted and requests the transmitter12to start power transmission for the time, for example. Alternatively, the controller11may request the transmitter12to start power transmission, and may request the transmitter12to stop the power transmission after a certain time from the start.

The transmitter12transmits a power transmission signal for power supply through the antenna transmission/reception duplexers14and the antennas15in accordance with the request by the controller11. For example, the transmitter12generates a power transmission signal and transmits the power transmission signal to the power reception apparatus2through the antenna transmission/reception duplexers14and the antennas15from the time of receipt of the request of a start of power transmission until a designated time has passed.

Furthermore, the controller11controls carrier sensing performed by the detector13through the antenna transmission/reception duplexers14and the antennas15. In the carrier sensing, the detector13detects, based on an amplitude of an input radio signal of a specific frequency band, an occurrence of transmission/reception of radio signals by a terminal and the like in the wireless communication system3. Alternatively, in the carrier sensing, the detector13may detect the occurrence of transmission/reception duplexer of radio signals by a terminal and the like in the wireless communication system3by further signal processing like decoding the input radio signal of the specific frequency band. The specific frequency band is a frequency band including at least a transmission frequency band of a communication frame4defined in a wireless communication standard.

The controller11designates a time (period) of carrier sensing during which the detector13monitors an occurrence of transmission/reception of a radio signal by the wireless communication system3(more specifically, an occurrence of a communication signal transmitted by the roadside apparatus3A), and requests the detector13to start monitoring for the designated time. Alternatively, the controller11may request the detector13to start monitoring, and may request the detector13to stop the monitoring after a certain time from the start.

In accordance with the request by the controller11, the detector13monitors a radio signal received through the antenna transmission/reception duplexers14and the antennas15and detects (carrier-senses) an occurrence of a communication signal transmitted by the wireless communication system3. The detector13detects an occurrence of a communication signal transmitted by the wireless communication system3from the time when the controller11requests the start of monitoring until a designated time has passed from the start, for example. The communication signal to be detected is, for example, a radio signal of a frequency band that includes at least the transmission frequency band of the communication frame4defined in a specific wireless communication standard, and the radio signal has a power equal to or larger than a threshold power. Note that the detector13may detect the occurrences of multiple types of communication signals transmitted by multiple types of wireless communication systems3.

The controller11further controls the directivity of the transmitted power transmission signal and the directivity of the received communication signal by beam forming to control patterns of radio signals transmitted and received through each pair of an antenna transmission/reception duplexer14and an antenna15(hereinafter may be referred to as antenna patterns). In order to perform the beam forming, the controller11selects one or more pairs used for the transmission/reception from the pairs of an antenna transmission/reception duplexer14and an antenna15. When, for example, requesting the transmitter12to start power transmission, the controller11designates an antenna pattern by determining a power transmission signal transmitted through each of the one or more selected pairs.

The transmitter12may include an antenna pattern adjuster121. The antenna pattern adjuster121generates a power transmission signal based on an antenna pattern designated by the controller11. The transmitter12transmits the generated power transmission signal through the designated pair of the antenna transmission/reception duplexer14and the antenna15. Thus, the power transmission signal having a specific directivity can be transmitted.

FIG. 2is a time chart illustrating an example of an operation by the wireless power transmission apparatus1.

Initially, the detector13performs initial monitoring (carrier sensing) during a period T0through the antenna transmission/reception duplexers14and the antennas15(A1). If a communication signal (for example, a DSRC signal) transmitted by the wireless communication system3has not been detected within the period T0for which the initial monitoring has been performed, the transmitter12performs power transmission during a period T1(A2).

After the power transmission performed during the period T1, the detector13performs monitoring (carrier sensing) during a period T2(A3). If a communication signal transmitted by the wireless communication system3has not been detected within the period T2for which the monitoring is performed, the transmitter12performs power transmission during the period T1(A4).

Then, after the power transmission performed during the period T1, the detector13performs monitoring during the period T2(A5). If a communication signal transmitted by the wireless communication system3has been detected within the period T2for which the monitoring is performed, the transmitter12does not perform power transmission during the period T1(A6). That is, the power transmission performed during the period T1is stopped. If the power transmission is not performed, the detector13performs initial monitoring during the period T0. The detector13may wait for the start of the initial monitoring, which is performed during the period T0, for a designated time after the stop of the power transmission.

As can be understood from the above, while a communication signal is not detected, the power transmission performed during the period of T1and the monitoring performed during the period T2are repeated, and if a communication signal transmitted by the wireless communication system3is detected during the monitoring performed during the period T2, the power transmission during the period T1is not performed, and the process returns to the initial monitoring performed during the period T0. Thus, interference, which is caused by the power transmission by the wireless power transmission apparatus1, with the communication performed by the wireless communication system3can be reduced.

As illustrated inFIG. 3, the roadside apparatus3A of the wireless communication system3may transmit communication frames4, which specified by the wireless communication standard, constantly and successively, for example. As described above, the wireless communication standard is a standard of the DSRC system, for example. Furthermore, the communication frame4defined in the wireless communication standard includes, for example, a frame control message slot (FCMS) defined in the standard of the DSRC system. Each communication frame4includes a known signal defined by the wireless communication standard. The detector13of the wireless power transmission apparatus1performs carrier sensing during the initial monitoring during the period T0and the monitoring during the period T2to detect the existence of the wireless communication system3based on whether or not a radio signal, which is input (received) through the antennas15and the antenna transmission/reception duplexers14, includes a known signal.

FIG. 4illustrates an example of a format of a communication frame4transferred in the wireless communication system3. In this example, slots mainly transmitted by the roadside apparatus3A in the wireless communication system3will be explained.

The communication frame4has a variable frame structure including one FCMS and multiple message data slots (MDSs). One communication frame4includes, for example, three slots, five slots, or nine slots. Each slot has the same time length, and is defined to be 100 octets (800 bits) based on the data transmission rate of 1024 kbps, for example.

The FCMS is used to transfer a frame control message channel (FCMC) including, for example, slot allocation information, frame control information, and the like. The MDS is used for data transfer.

FIG. 4(A)indicates a communication frame4-1composed of three slots. An FCMS411is provided at the head of the communication frame4-1, and two MDSs412and413following the FCMS411are provided.

FIG. 4(B)indicates a communication frame4-2composed of five slots. An FCMS421is provided at the head of the communication frame4-2, and four MDSs422,423,424, and425following the FCMS421are provided.

FIG. 4(C)indicates a communication frame4-3composed of nine slots. An FCMS431is provided at the head of the communication frame4-3, and eight MDSs432,433,434,435,436,437,438, and439following the FCMS431are provided.

The FCMS411,421, and423include a preamble (PR) signal and a unique word (UW) signal411A,421A, and431A, respectively. The preamble signal is used in symbol synchronization, and the unique word signal is used in slot synchronization or the like. The preamble signal is a known signal preliminarily defined as a signal of specific bits. The unique word signal is a known signal preliminarily defined as a signal of specific bits.

For example, in the standard of the DSRC system (ARIB STD-T75), in a case where a modulation method is ASK, the preamble signal is defined as 16 bits of “1010101010101010”, and the unique word signal is defined as 32 bits of “00011011101010000100101100111110”.

If a radio signal, which is input the wireless power transmission apparatus1through the antenna15and the antenna transmission/reception duplexer14by the carrier sensing performed in the initial monitoring during the period T0or in the monitoring during the period T2, includes a known signal that is at least one of the preamble signal and the unique word signal, the detector13in the wireless power transmission apparatus1determines that the communication signal transmitted by the wireless communication system3is detected, that is, the wireless communication system3exists. In order to securely detect the existence of the wireless communication system3, a period for which at least one known signal (that is, the preamble signal and/or the unique word signal) can be detected must be set as the period T2for monitoring. Thus, the period T2is set to be equal to or longer than a time corresponding to the length (that is, the frame length) of one communication frame4.

FIG. 5illustrates an example of a time corresponding to the frame length of one communication frame4(that is, the time length of one communication frame4). As explained above, each slot has the same time length, and is defined as 100 octets based on the data transmission rate of 1024 kbps, for example. In that case, the time length of one slot corresponds to 0.78125 milliseconds (ms).

Thus, the time length (i.e., the frame period) of the communication frame4-1composed of three slots is 2.34375 ms (=3×0.78125 ms). The time length of the communication frame4-2composed of five slots is 3.90625 ms (=5×0.78125 ms). Furthermore, the time length of the communication frame4-3composed of nine slots is 7.03125 ms (=9×0.78125 ms).

In this example, the longest frame length is the frame length of the nine slots, and thus, if the frame structure of the communication frame4is unknown, the period T2for monitoring is equal to or longer than 7.03125 ms that is a time corresponding to the frame length of the longest nine slots. Thus, for example, 8 ms is set as the period T2.

Note that the period T0for the initial monitoring is, for example, a time in units of second that is longer than the period T2for which the monitoring after the power transmission is performed, in order to detect a communication signal transmitted by the wireless communication system3with higher accuracy. Furthermore, the period T1for the power transmission is, for example, shorter than the period T0and longer than the period T2. For example, 60 ms is set as the period T1.

Thus, as illustrated inFIG. 2, before the transmitter12starts the power transmission, the detector13performs, through the antenna transmission/reception duplexers14and the antennas15, carrier sensing in a first frequency band including at least the transmission frequency band of the communication frame4during the period T0that precedes the period T1for which the power transmission signal will be transmitted and is longer than each of the period T1and the period T2(A1). Specifically, the detector13is capable of detecting a known signal, which is at least one of the preamble signal and the unique word signal, from the radio signal input during the period T0. If a known signal has been detected, the detector13determines that a communication signal to transmit the communication frame4is input (received) within the period T0.

If any communication signal has not been detected by the carrier sensing performed during the period T0, the transmitter12transmits a power transmission signal during the period T1(for example, 60 ms) following the period T0(A2). Then, the detector13performs carrier sensing in the first frequency band during the period T2(for example, 8 ms) through the antenna transmission/reception duplexers14and the antennas15(A3). The first frequency band includes at least the transmission frequency band of the communication frame4. The period T2follows the period T1for which the power transmission signal is transmitted, and is equal to or longer than the time corresponding to the length (that is, the frame length) of the communication frame4. Specifically, the detector13is capable of detecting a known signal, which is at least one of the preamble signal and the unique word signal, from the radio signal input during the period T2. If the known signal has been detected, the detector13determines that a communication signal to transmit the communication frame4has been input (received) during the period T2.

Then, if a communication signal has not been detected through the carrier sensing performed during the period T2, the transmitter12transmits a power transmission signal during the period T1following the period T2(A4). On the other hand, if a communication signal has been detected through the carrier sensing performed during the period T2, the transmitter12does not transmit a power transmission signal for at least the period T1that follows the period T2(A5) for which the communication signal has been detected (A6). That is, power transmission during the period T1is stopped.

Note that the detector13may monitor several types of communication signals during the monitoring during the period T2. The several types of communication signals are radio signals to transfer communication frames4based on the different wireless communication standards. That is, the detector13performs carrier sensing in a second frequency band, which includes at least the transmission frequency bands of the frames, through the antenna transmission/reception duplexers14and the antennas15during the period T2. The period T2follows the period T1and is equal to or longer than a time corresponding to any one of the lengths of the communication frames4that are defined by the different wireless communication standards, respectively. In that case, the period T2is, for example, set to be equal to or longer than a time corresponding to a length of the longest frame of the communication frames4.

For example, the detector13performs carrier sensing in a second frequency band during the period T2following the period T1. The second frequency band includes at least the transmission frequency band of a first communication frame defined in a first wireless communication standard (for example, the standard of DSRC) and the transmission frequency band of a second communication frame defined in a second wireless communication standard (for example, the wireless LAN communication standard). If a communication signal has not been detected by the carrier sensing performed during the period T2, the transmitter12transmits a power transmission signal during the period T1following the period T2. Since several types of communication signals are monitored during the monitoring performed during the period T2, an affect that the period T1for the power transmission is shortened can be reduced.

Furthermore, as illustrated inFIG. 6, if the communication frame4has been detected by carrier sensing (initial monitoring) performed during the period T0(A1-1), the antenna pattern adjuster121may change at least one of the directivity of a power transmission signal transmitted by the transmitter12through one or more of the antenna transmission/reception duplexers14and one or more of the antennas15and the directivity (antenna pattern) of a communication signal received by the detector13through one or more of the antenna transmission/reception duplexers14and one or more of the antennas15. The detector13performs carrier sensing in the first frequency band, which includes at least the transmission frequency band of the communication frame4, during the period T0after the change of the directivity (A1-2).

If the antenna pattern has been changed, the interference with the wireless communication system3is changed. Thus, by performing the initial monitoring during the period T0again after the change, the interference with the wireless communication system3caused by a power transmission signal with the appropriate changed antenna pattern can be reduced.

Through the above structure, the interference with the wireless communication system3caused by the wireless power transmission apparatus1can be reduced.

With reference to a flowchart ofFIG. 7, an example of the procedure of a power transmission control process executed by the wireless power transmission apparatus1will be explained.

Firstly, the wireless power transmission apparatus1monitors, through the antenna transmission/reception duplexers14and the antennas15, a communication signal transmitted by the wireless communication system3during a period T0for initial monitoring (step S11). That is, the wireless power transmission apparatus1performs carrier sensing in a first frequency band, which includes at least a transmission frequency band of a communication frame4, during the period T0. In other words, the antenna transmission/reception duplexers14and the antennas15receive the communication signal transmitted by the wireless communication system3during the period T0to input the signal to the wireless power transmission apparatus1(specifically, the detector13).

The wireless power transmission apparatus1determines whether a communication signal transmitted by the wireless communication system3has been detected during the period T0(step S12). The wireless power transmission apparatus1determines that a communication signal transmitted by the wireless communication system3has been detected if, for example, a radio signal, which has a power level equal to or larger than a threshold value and includes a known signal, is input to the wireless power transmission apparatus1through the antenna transmission/reception units duplexer14and the antennas15.

If a communication signal transmitted by the wireless communication system3has been detected (YES in step S12), the process returns to step S11, and the initial monitoring of a communication signal is continued. Note that the directivity of a radio signal transmitted/received by the wireless power transmission apparatus1may be changed before the process returns to step S11.

On the other hand, if a communication signal transmitted by the wireless communication system3has not been detected (NO in step S12), the wireless power transmission apparatus1performs power transmission during the period T1(step S13). That is, the wireless power transmission apparatus1transmits a power transmission signal through the antenna transmission/reception duplexers14and the antennas15during the period T1.

Then, the wireless power transmission apparatus1monitors a communication signal transmitted by the wireless communication system3during the period T2following the period T1through the antenna transmission/reception duplexers14and the antennas15(step S14). That is, the wireless power transmission apparatus1performs carrier sensing in the first frequency band including at least the transmission frequency band of the communication frame4during the period T2following the period T1. In other words, the antenna transmission/reception duplexers14and the antennas15may receive a communication signal transmitted by the wireless communication system3during the period T2to input the signal to the wireless power transmission apparatus1.

Then, the wireless power transmission apparatus1determines whether a communication signal transmitted by the wireless communication system3has been detected during the period T2(step S15). If a communication signal transmitted by the wireless communication system3has not been detected (NO in step S15), the process returns to step S13, and power transmission is performed during the period T1.

On the other hand, if a communication signal transmitted by the wireless communication system3has been detected (YES in step S15), the process returns to step S11, and the initial monitoring of a communication signal is performed again.

Through the above process, if the communication signal transmitted by the wireless communication system3is detected, power transmission is stopped, and therefore, interference with the wireless communication system3caused by the wireless power transmission apparatus1can be reduced.

Furthermore,FIG. 8illustrates the structure of a test apparatus7that verifies whether the wireless power transmission apparatus1includes a power transmission control function to reduce the interference with the wireless communication system3. The test apparatus7establishes a wired or wireless connection to the wireless power transmission apparatus1.

The test apparatus7includes a processor71, a communication signal transmitter72, an antenna73, and a power transmission detector74. Each component may be realized as a circuit. Furthermore, the processor71, the communication signal transmitter72, and the power transmission detector74may be provided with one chip or may be provided with multiple chips.

The power transmission detector74detects a start and a stop of the power transmission by the wireless power transmission apparatus1based on a power transmission signal input (received) through the antenna73. The power transmission detector74may notify the processor71that the wireless power transmission apparatus1starts the power transmission, that the wireless power transmission apparatus1stops the power transmission, or the like.

The processor71controls a transmission time of a communication signal, which includes a known signal and is transmitted by the communication signal transmitter72and the antenna73, in accordance with a state of the power transmission by the wireless power transmission apparatus1. The communication signal including the known signal is a radio signal to transmit a communication frame4including an FCMS, for example. As mentioned above, the FCMS includes a preamble signal and a unique word signal that are known signals.

If the start of the power transmission by the wireless power transmission apparatus1has been detected, the processor71instructs the communication signal transmitter72to start transmission of the communication signal including the known signal, and starts a timer711. The known signal is periodically transmitted until the stop of the power transmission by the wireless power transmission apparatus1is detected. Then, the processor71stops the timer711if the power transmission detector74has detected the stop of the power transmission by the wireless power transmission apparatus1. The processor71records the measured time t by the timer711. The measurement time t by the timer711indicates a period of time from the start of transmission of the communication signal including the known signal until the detection of the stop of power transmission by the wireless power transmission apparatus1.

The processor71, the communication signal transmitter72, and the power transmission detector74perform the operation to measure the measurement time t repeatedly, for example, for N times to acquire N measurement times t.

The processor71calculates a ratio of measurement times t, which exceed a threshold time Td, to the N measurement times t (that is, an error ratio), and determines whether the calculated ratio exceeds a specific ratio p. The threshold time Td is the sum of the period T1for power transmission and the period T2for monitoring, for example. If the calculated ratio is equal to or smaller than the specific ratio p, the processor71determines that the wireless power transmission apparatus1performs at least the monitoring during the period T2and has the power transmission control function. On the other hand, if the calculated ratio exceeds the specific ratio p, the processor71determines that the wireless power transmission apparatus1does not perform the monitoring during the period T2and does not have the power transmission control function.

Alternatively, the processor71may calculate a ratio of measurement times t, which are equal to or shorter than the threshold time Td, to the N measurement times t (that is, a pass ratio), and determines whether the calculated ratio exceeds a specific ratio p′. If the calculated ratio exceeds the specific ratio p′, the processor71determines that the wireless power transmission apparatus1performs at least the monitoring during the period T2and has the power transmission control function. On the other hand, if the calculated ratio is equal to or smaller than the specific ratio p′, the processor71determines that the wireless power transmission apparatus1does not perform the monitoring during the period T2and does not have the power transmission control function.

The flowchart ofFIG. 9illustrates an example of the procedure of a test process executed by the test apparatus7. The test apparatus7determines whether the wireless power transmission apparatus1has the power transmission control function by performing trials a specific number of times (for example, N times).

Firstly, the test apparatus7sets zero as each of the number of trials i and the number of errors err, for initialization (step S201). Then, the test apparatus7adds one to the number of trials i (step S202).

Then, the test apparatus7determines whether a start of power transmission by the wireless power transmission apparatus1has been detected (step S203). If a start of power transmission has not been detected (NO in step S203), the process returns to step S203, and whether a start of a power transmission has been detected is again determined.

On the other hand, if a start of power transmission has been detected (YES in step S203), the test apparatus7starts transmitting a communication frame4including an FCMS (specifically, a preamble signal and a unique word signal) and starts the timer711(step S204). Slots other than the FCMS in the communication frame4to be transmitted may be empty.

Then, the test apparatus7determines whether a stop of the power transmission by the wireless power transmission apparatus1has been detected (step S205).

If a stop of the power transmission has not been detected (NO in step S205), the test apparatus7transmits a communication frame4including an FCMS (step S206). In step S206, the communication frame4is transmitted following the communication frame4in step S204, for example.

If a stop of the power transmission has been detected (YES in step S205), the test apparatus7stops the timer711(step S207) and determines whether the measurement time t measured by the timer711exceeds the threshold time Td (step S208).

If the measurement time t exceeds the threshold time Td (YES in step S208), the test apparatus7adds one to the number of errors err (step S209). That is, in the i-th trial, the wireless power transmission apparatus1has not transitioned to a power transmission stop state within the threshold time Td since the FCMS was transmitted. Therefore, the test apparatus7determines that a function to stop the power transmission in accordance with detection of an FCMS is not operated, and increases the number of errors err by one. Note that, if the measurement time t is equal to or shorter than the threshold time Td (NO in step S208), step S209is skipped.

Then, the test apparatus7determines whether the number of trials i is smaller than the maximum number of trials N (step S210). If the number of trials i is smaller than the maximum number of trials N (YES in step S210), the process returns to step S202, and the next trial is started.

If the number of trials i is equal to or larger than the maximum number of trials N (NO in step S210), the test apparatus7calculates a ratio of the number of errors err to the maximum number of trials N (=err/N), and determines whether the calculated ratio exceeds a specific ratio p (step S211). If the calculated ratio exceeds the specific ratio p (YES in step S211), the test apparatus7determines that the wireless power transmission apparatus1does not have the power transmission control function that satisfies the specification (NG determination) (step S213). On the other hand, if the calculated ratio is equal to or smaller than the specific ratio p (NO in step S211), the test apparatus7determines that the wireless power transmission apparatus1has the power transmission control function that satisfies the specification (PASS determination) (step S213).

From the above, the test apparatus7can verify whether the wireless power transmission apparatus1has the power transmission control function to reduce the interference with the wireless communication system3.

Second Embodiment

In the first embodiment, in the period T2after the power transmission performed during the period T1, the carrier sensing to monitor the existence of a communication signal transmitted by the wireless communication system3is performed. In contrast, in a second embodiment, a candidate of a communication signal is detected in monitoring performed during the period T2, and in a period T3after the period T2in which the candidate is detected, carrier sensing to further verify the existence of a communication signal is performed.

The structure of a wireless power transmission apparatus1of the second embodiment is similar to that of the wireless power transmission apparatus1of the first embodiment, and between the first and second embodiments, only the structure for the carrier sensing to verify the existence of a communication signal in the period T3is different. Hereinafter, the points different from the first embodiment will be mainly explained.

FIG. 10is a time chart illustrating examples of operations by the wireless power transmission apparatus1.FIG. 10(A)illustrates an example of a case where a communication signal is detected in the verifying of the existence of a communication signal in the period T3. On the other hand,FIG. 10(B)illustrates an example of a case where a communication signal is not detected in the verifying of the existence of a communication signal in the period T3. In each of periods of B1to B4inFIG. 10(A)and periods of C1to C4inFIG. 10(B), an operation similar to the operation performed in the periods of A1to A4, which is explained above with reference to the time chart ofFIG. 2, is performed.

In the example ofFIG. 10(A), after the power transmission during the period T1(B4), the detector13monitors the existence of a candidate of a communication signal (for example, a DSRC signal) transmitted by the wireless communication system3during the period T2(B5). If a candidate of a communication signal transmitted by the wireless communication system3has been detected within the period T2for the monitoring, power transmission during the period T1is not performed, and the detector13verifies the existence of a communication signal transmitted by the wireless communication system3during the period T3(B6).

The period T3is equal to or longer than the period T2, and, for example, is substantially n times as long as the sum of the periods T1and T2. Note that n is a natural number. For example, if the period T1is 60 ms, the period T2is 8 ms, and n=1, the period T3is set to 68 ms. By setting a length of the period T3to be n times as long as the sum of the periods T1and T2, the operation of verifying can be added without disturbing the cycle of the power transmission during the period T1and the monitoring during the period T2.

If the communication signal transmitted by the wireless communication system3has been detected in the verifying during the period T3, the wireless power transmission apparatus1does not perform power transmission during the period T1(B7). That is, the power transmission during the period T1is stopped. If the power transmission is not performed, the wireless power transmission apparatus1returns to the initial monitoring during the period T0, for example.

Furthermore, In the example ofFIG. 10(B), after the power transmission during the period T1(C4), the wireless power transmission apparatus1monitors the existence of a candidate of a communication signal (for example, a DSRC signal) transmitted by the wireless communication system3during the period T2(C5). If a candidate of a communication signal transmitted by the wireless communication system3has been detected within the period T2for the monitoring, the power transmission during the period T1is not performed, and the detector13verifies the existence of a communication signal transmitted by the wireless communication system3during the period T3(C6).

If a communication signal transmitted by the wireless communication system3has not been detected during the verifying during the period T3, it is determined that the candidate of the communication signal detected in the monitoring during the period T2(C5) was erroneously detected, and the transmitter12performs power transmission during the period T1(C7).

That is, before the transmitter12starts power transmission, the detector13performs the carrier sensing in the first frequency band, which includes at least the transmission frequency band of the communication frame4, during the period T0that is longer than each of the period T2and the period T3. Then, if any communication signal has not been detected by the carrier sensing performed during the period T0, the transmitter12transmits a power transmission signal during the period T1.

Furthermore, if a communication signal has been detected by the carrier sensing performed during the period T2, the detector13performs carrier sensing in the first frequency band, which includes at least the transmission frequency band of the communication frame4, during the period T3following the period T2. Then, if a communication signal has not been detected by the carrier sensing performed during the period T3, the transmitter12transmits a power transmission signal during the period T1following the period T3. Furthermore, the detector13performs carrier sensing in the first frequency band during the period T2following the period T1. On the other hand, if a communication signal has been detected by the carrier sensing performed during the period T3, power transmission during the period T1is not performed, and the process returns to the initial monitoring during the period T0.

Furthermore, the detector13may perform carrier sensing in a second frequency band during the period T2. The second frequency band includes at least a transmission frequency band of a first communication frame defined by a first wireless communication standard (for example, the standard of DSRC) and a transmission frequency band of a second communication frame defined by a second wireless communication standard (for example, the wireless LAN communication standard). In that case, if a communication signal has not been detected by the carrier sensing performed during the period T2, the transmitter12transmits a power transmission signal during the period T1following the period T2. Furthermore, if a communication signal has been detected by the carrier sensing performed during the period T2, the detector13performs carrier sensing in the second frequency band during the period T3following the period T2. Since several types of communication signals are monitored during the monitoring performed during the period T2, an affect that the period T1for the power transmission is shortened can be reduced.

As can be understood from the above, the monitoring during the period T2is performed after the power transmission during the period T1, and if a candidate of a communication signal transmitted by the wireless communication system3is detected during the monitoring, power transmission during the period T1is not performed and the verifying is performed during the period T3. The communication signal may be erroneously detected in the period T2. If power transmission is not performed and the process returns to the initial monitoring performed during the period T0based on the communication signal erroneously detected, it takes a long time to restart the power transmission because the period T0is longer than each of the period T1, the period T2, and the period T3. The wireless power transmission apparatus1handles the communication signal detected in the monitoring during the period T2as a candidate and verifies the existence of the communication signal during the period T3, which follows period T2and is equal to or longer than the period T2, in order to reduce such an erroneous detection.

In the monitoring of the period T2, a communication signal may be detected based on one known signal while a communication signal may be detected based on several known signals in the verifying of the period T3. Thus, in the verifying of the period T3, the existence of the communication signal transmitted by the wireless communication system3can be determined with higher accuracy than the monitoring of the period T2.

If it is determined that a communication signal has not been transmitted in the verifying of the period T3, the wireless power transmission apparatus1resumes the power transmission (that is, performs the power transmission during the period T1). Thus, even if an erroneous detection is generated in the monitoring of the period T2, the power transmission is only suspended during the period T3that is shorter than the period T0of the initial monitoring and is then resumed.

With reference to the flowchart ofFIG. 11, an example of the procedure of a power transmission control process executed by the wireless power transmission apparatus1will be explained. Steps S31to S34in the flowchart ofFIG. 11are the same as above-explained steps S11to S14in the flowchart ofFIG. 7.

After the monitoring of a communication signal performed during the period T2in step S34is finished, the wireless power transmission apparatus1determines whether a candidate of a communication signal transmitted by the wireless communication system3has been detected within the period T2(step S35). If a candidate of a communication signal transmitted by the wireless communication system3has not been detected (NO in step S35), the process returns to step S33, and the power transmission is performed during the period T1.

On the other hand, if a candidate of a communication signal transmitted by the wireless communication system3has been detected (YES in step S35), the wireless power transmission apparatus1verifies, during the period T3following the period T2, a communication signal transmitted by the wireless communication system3through the antenna transmission/reception units14and the antennas15(step S36). That is, the wireless power transmission apparatus1performs carrier sensing in the first frequency band, which includes at least the transmission frequency band of a communication frame4, during the period T3following the period T2. Thus, the wireless power transmission apparatus1verifies the existence of a communication signal more accurately by monitoring a communication signal transmitted by the wireless communication system3during the period T3that is equal to or longer than the period T2.

Then, the wireless power transmission apparatus1determines whether a communication signal transmitted by the wireless communication system3has been detected within the period T3(step S37). If the communication signal transmitted by the wireless communication system3has not been detected (NO in step S37), the process returns to step S33.

On the other hand, if the communication signal transmitted by the wireless communication system3has been detected (YES in step S37), the process returns to step S31, and the initial monitoring of the communication signal is again performed.

As can be understood from the above, the interference with the wireless communication system3can be reduced and an effect on the power transmission because of an erroneous detection of a communication signal can be reduced as well.

As explained above, according to the first and second embodiments, interference with other wireless communication systems can be reduced. The transmitter12transmits a first transmission signal for power supply during a period T1via a transmission frequency band defined by a first wireless communication standard (for example, the standard of DSRC system). The detector13performs carrier sensing in a first frequency band including at least the transmission frequency band during a period T2following the period T1. The period T2is equal to or longer than the length of a communication frame4. If a wireless signal is not detected in the carrier sensing performed during the period T2, the transmitter12transmits a second transmission signal for power supply during the period T1following the period T2. If the wireless signal is detected by the carrier sensing performed during the period T2, the detector13performs carrier sensing in the first frequency band during a period T3following the period T2.

As above, if a wireless signal (a communication signal) transmitted by other wireless communication systems3is not detected by the carrier sensing performed during the period T2, the transmission signal is transmitted during the period T1after the period T2, and on the other hand, if a wireless signal transmitted by the other wireless communication systems3is detected in the carrier sensing performed during the period T2, carrier sensing is further performed during the period T3following the period T2. Therefore, interference with the communication signal transmitted in the wireless communication system3caused by the power transmission signal transmitted by the wireless power transmission apparatus1can be reduced.

Each of the various functions described in the first and second embodiments may be realized by a processing circuit. The processing circuit includes a programmed processor such as a central processing unit (CPU). This processor performs each of the above functions by executing a computer program (instructions) stored in a memory. The processor may be a microprocessor including an electronic circuit. For example, the processing circuit may be a digital signal processor (DSP), an application specific integrated circuit (ASIC), a microcontroller, a controller and other electronic circuit components. Each of other components described in the first and second embodiments other than the CPU may be realized as a processing circuit.