communication equipment

Abstract

To reduce the influence of a self-interference signal even if the self-interference signal fluctuates during communication.SOLUTION: A communication device includes first and second generation units, a sharing unit, a synthesis unit, first and second measurement units, and first, second and third control units. The first and the second measurement units measure the levels of the self-interference signals each extracted from an output signal from the synthesis unit with respect to a first band width or a second band width wider than the first band width. The first control unit controls to reduce the level measured by the first measurement unit. in the period of a first duration, whereas the second control unit sets the variation of an amplitude and a phase in the second generation unit in the period of a second duration shorter than the first duration, according to that the level measured by the second measurement unit has increased. The third control unit controls the first control unit before starting the reception of a response signal transmitted from the opposite device, and the second control unit during receiving the response signal, to set the variation of the amplitude and the phase in the second generation unit, respectively.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] FIELD OF THE INVENTION An embodiment of the present invention relates to a communication device. [Background technology]

[0002] In communication devices that share an antenna for both transmission and reception, a portion of the transmission signal may be superimposed on the reception signal and enter the reception system. This superimposed transmission signal component may become a self-interference signal, which may cause saturation of the reception system and increase noise, resulting in a deterioration of communication quality. Therefore, a technique is known in which a cancellation signal having an opposite phase to the self-interference signal is generated from a transmission signal, and this cancellation signal is used to cancel out the self-interference signal. Conventionally, the gain and phase shift required to generate an appropriate cancellation signal are set before communication begins. Then, during communication, the cancellation signal generated with the gain and phase shift set before communication begins cancels out the self-jammer signal. This type of processing is called self-jammer cancellation processing, hereafter abbreviated as SJC control.

[0003] However, during communication, the self-interference signal may fluctuate due to changes in the antenna's surrounding environment. If the self-interference signal fluctuates significantly, there is a risk that the self-interference signal remaining after cancellation may become large. Under these circumstances, it has been desired to be able to minimize the influence of a self-interference signal even if the self-interference signal fluctuates during communication. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-102530 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a communication device that can minimize the influence of a self-interference signal even if the self-interference signal fluctuates during communication. [Means for solving the problem]

[0006] A communication device according to an embodiment includes a first generating unit, a duplexer, a second generating unit, a combining unit, a first measuring unit, a first control unit, a second measuring unit, a second control unit, and a third control unit. The first generating unit generates a transmission signal for wireless transmission. The combining unit receives the transmission signal generated by the first generating unit from an input terminal and outputs it from an input / output terminal, and also outputs the signal input from the input / output terminal from an output terminal. The second generating unit generates a cancellation signal by changing the amplitude and phase of the transmission signal generated by the first generating unit. The combining unit combines the cancellation signal generated by the second generating unit with the signal output from the output terminal. The first measuring unit measures the level of a self-interference signal extracted for a first bandwidth from the output signal from the combining unit. The first control unit sets the amount of change in amplitude and phase in the second generating unit so as to reduce the level measured by the first measuring unit to a level that meets a predetermined condition during a predetermined first time duration. The second measurement unit measures the level of the self-interference signal extracted from the output signal from the combiner unit for a second bandwidth wider than the first bandwidth. In response to an increase in the level measured by the second measurement unit, the second control unit controls the amounts of change in amplitude and phase in the second generation unit so as to reduce the level measured by the second measurement unit for a second time duration shorter than the first time duration. The third control unit causes the first control unit to set the amounts of change in amplitude and phase in the second generation unit before starting to receive a response signal transmitted from the other device, and causes the second control unit to set the amounts of change in amplitude and phase in the second generation unit while receiving the response signal transmitted from the other device. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 2 is a block diagram showing the main circuit configuration of a reading device according to an embodiment. [Figure 2]FIG. 2 is a block diagram showing the configuration of a circuit built in the FPGA in FIG. 1 for controlling SJC processing. [Figure 3] 3 is a diagram showing frequency characteristics of a first LPF and a second LPF in FIG. 2; [Figure 4] 3 is a flowchart of a control process performed by the control circuit in FIG. 2. [Figure 5] 3 is a diagram showing an example of a change in the residual level measured by the measurement circuit in FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments will be described with reference to the drawings. Note that the following description will be made taking as an example a reader that reads data stored in an RFID (radio frequency identification) tag. This reader is an example of a communication device that performs wireless communication with an RFID tag as a partner device when reading the data.

[0009] FIG. 1 is a block diagram showing the main circuit configuration of a reading device 100 according to this embodiment. The reading device 100 includes an oscillator 11, a phase shifter 12, a digital-to-analog (DA) converter 13, a quadrature modulator 14, a band-pass filter (BPF) 15, a power amplifier 16, a low-pass filter (LPF) 17, an antenna duplexer 18, a feeder 19, an antenna 20, a vector modulator 21, a DA converter 22, a power combiner 23, a quadrature detector 24, a baseband filter (BBF) 25, a baseband amplifier 26, an analog-to-digital (AD) converter 27, an LPF 28, an AD converter 29, and a control unit 30. The control unit 30 includes a CPU 301, a field programmable gate array (FPGA) 302, and a memory 303. The antenna 20 may not be included in the reading device 100, and any antenna may be connectable to the feeder 19. Furthermore, the antenna 20 and the power feeder 19 may not be included in the reader 100, and any power feeder connected to any antenna may be connectable to the antenna duplexer 18.

[0010] The oscillator 11 generates a sine wave of a predetermined frequency as a carrier wave. Phase shifter 12 shifts the phase of the carrier wave generated by oscillator 11 by 90 degrees, and outputs a cosine wave as another carrier wave.

[0011] The DA converter 13 converts two systems of transmission baseband signals output in a digital state from the CPU 301 into analog signals. Quadrature modulator 14 receives as input, as modulated waves, two systems of transmission baseband signals that have been converted to analog signals by DA converter 13. Quadrature modulator 14 also receives as input the carrier wave generated by oscillator 11 and the carrier wave output from phase shifter 12. Quadrature modulator 14 then uses these two systems of modulated waves and two systems of carrier waves to obtain a transmission signal through quadrature modulation.

[0012] The BPF 15 removes low-frequency components and high-frequency components from the transmission signal obtained by the quadrature modulator 14 in order to limit the band. The power amplifier 16 amplifies the power of the transmission signal that has passed through the BPF 15 to a level suitable for wireless transmission. The LPF 17 removes harmonic components from the transmission signal amplified by the power amplifier 16 . The transmission signal becomes a signal for wireless transmission through the processes of BPF 15, power amplifier 16, and LPF 17. In other words, BPF 15, power amplifier 16, and LPF 17 form a first generation unit that generates a transmission signal for wireless transmission.

[0013] The antenna duplexer 18 has an input terminal TI, an input / output terminal TIO, an output terminal TOA, and an output terminal TOB. The transmission signal that has passed through the LPF 17 is input to the input terminal TI. The antenna duplexer 18 outputs the transmission signal input to the input terminal TI from the input / output terminal TIO and the output terminal TOB. The antenna duplexer 18 outputs the signal input to the input / output terminal TIO from the output terminal TOA. The signal output from the output terminal TOA of the antenna duplexer 18 is a signal obtained by combining the received signal generated at the antenna 20 and a self-interference signal, which will be described later, and this signal will be simply referred to as the received signal below. The antenna duplexer 18 is an example of a duplexer.

[0014] The feeder line 19 supplies the transmission signal output from the input / output terminal TIO of the antenna duplexer to the antenna 20. The feeder line 19 transmits the reception signal generated at the antenna 20 to the input / output terminal TIO of the antenna duplexer . The antenna 20 emits radio waves corresponding to the transmission signal supplied by the power supply line 19. The antenna 20 generates an electric signal corresponding to the incoming radio waves as a reception signal.

[0015] The vector modulator 21 modulates the transmission signal output from the output terminal TOB of the antenna duplexer 18 so that the signal has an amplitude and gain according to vectors represented by two systems of control signals (hereinafter referred to as I control signal and Q control signal) supplied from the DA converter 22. The transmission signal modulated by the vector modulator 21 will be referred to as a cancellation signal below. In other words, the vector modulator 21 changes the amplitude and phase of the transmission signal to generate a cancellation signal, and corresponds to a second generation unit.

[0016] The DA converter 22 converts the 2I control signal and Q control signal outputted in digital form from the control unit 30 into analog signals, and obtains the I control signal and Q control signal to be supplied to the vector modulator 21 . The power combiner 23 combines the power of the received signal output from the output terminal TOA of the antenna duplexer 18 with the cancellation signal output from the vector modulator 21. In this way, the power combiner 23 reduces the self-interference signal included in the received signal. The power combiner 23 is an example of a combining section.

[0017] The quadrature detector 24 performs quadrature detection on the received signal output from the power combiner 23 using the two carrier waves output from the oscillator 11 and the phase shifter 12. The quadrature detector 24 outputs, in parallel, two systems of analog received baseband signals obtained by quadrature detection. In other words, the quadrature detector 24 is an example of a detection section.

[0018] The BBF 25 extracts a predetermined baseband component from each of the two systems of received baseband signals output from the quadrature detector 24. The passband of the BPF 25 includes a band that includes the response signal from the RFID tag 200. The baseband amplifier 26 amplifies each of the two received baseband signals that have passed through the BBF 25 to a level suitable for digitization by the AD converter 27 . The AD converter 27 digitizes each of the two systems of received baseband signals amplified by the baseband amplifier 26 .

[0019] The LPF 28 extracts low frequency bands corresponding to the self-interference signal components contained in each of the two systems of received baseband signals output from the quadrature detector 24. The signals extracted by the LPF 28 include the self-interference signal components remaining in the output of the power combiner 23. Therefore, the two systems of signals extracted by the LPF 28 will be referred to as an I residual signal and a Q residual signal hereinafter. The AD converter 29 digitizes the I residual signal and the Q residual signal output from the LPF 28 .

[0020] The CPU 301 outputs two systems of transmission baseband signals in accordance with a predetermined sequence when communicating with the RFID tag 200. The CPU 301 reconstructs the data sent from the RFID tag 200 based on the two systems of reception signals digitized by the AD converter 27.

[0021] The FPGA 302 performs pre-programmed signal processing to quickly execute various calculations associated with the information processing by the CPU 301. One of the functions of the FPGA 302 is to control the vector modulator 21 based on the I residual signal and the Q residual signal digitized by the AD converter 29.

[0022] The memory 303 stores an information processing program that describes information processing to be executed by the CPU 301. The memory 303 stores various data required for the CPU 301 to execute various types of information processing. The memory 303 stores various types of data generated or acquired when the CPU 301 executes various types of information processing.

[0023] FIG. 2 is a block diagram showing the configuration of a circuit built in the FPGA 302 for controlling the SJC process. As shown in FIG. 2, the circuits configured in the FPGA 302 include a control circuit 3021, a generation circuit 3022, a conversion circuit 3023, selectors 3024 and 3025, a first LPF 3026, a second LPF 3027, a measurement circuit 3028, and a detection circuit 3029.

[0024] When a start signal for instructing the execution of SJC processing is provided from CPU 301, control circuit 3021 executes processing (hereinafter referred to as control processing) described below for realizing SJC processing. During the control processing, control circuit 3021 instructs generation circuit 3022 to start scanning. During the control processing, control circuit 3021 also controls selectors 3024 and 3025. During the control processing, control circuit 3021 also sets the amplitude and phase of the cancellation signal in accordance with the minimum amplitude point detected by detection circuit 3029. Then, control circuit 3021 outputs a status signal for notifying CPU 301 of the execution status of SJC processing.

[0025] The generation circuit 3022 generates a digital phase signal and an amplitude signal that respectively represent the amplitude and phase of the cancellation signal. During the scan period, the generation circuit 3022 sequentially changes the phase signal and the amplitude signal so as to sweep the amplitude and phase. During periods other than the scan period, the generation circuit 3022 fixes the phase signal and the amplitude signal so as to keep the amplitude and phase constant.

[0026] The conversion circuit 3023 converts the phase signal and amplitude signal provided from the generation circuit 3022 into I control signal and Q control signal which digitally represent vectors according to the phase and amplitude represented by the phase and amplitude signals. The I control signal and Q control signal obtained by the conversion circuit 3023 are supplied to the DA converter 22.

[0027] The selectors 3024 and 3025 selectively enable the first LPF 3026 and the second LPF 3027 under the control of the control circuit 3021. The selector 3024 supplies the I residual signal and the Q residual signal output from the AD converter 29 to the enabled one of the first LPF 3026 and the second LPF 3027. The selector 3025 supplies the I residual signal and the Q residual signal that have passed through the enabled one of the first LPF 3026 and the second LPF 3027 to the measurement circuit 3028.

[0028] The first LPF 3026 and the second LPF 3027 both pass low-frequency components of the I residual signal and the Q residual signal. As a result, the first LPF 3026 and the second LPF 3027 attenuate unwanted signal components that reduce the measurement accuracy of the measurement circuit 3028. The characteristics of the first LPF 3026 and the second LPF 3027 may be determined as appropriate by, for example, the designer of the reader 100. However, the cutoff frequency of the first LPF 3026 is set to be lower than the cutoff frequency of the second LPF 3027. As a result, the first LPF 3026 has a higher ability to attenuate unwanted signal components than the second LPF 3027. Note that the first LPF 3026 and the second LPF 3027 may be, for example, FIR (finite impulse response) filters. The first LPF 3026 is an example of a first filter, and the second LPF 3027 is an example of a second filter.

[0029] FIG. 3 is a diagram showing the frequency characteristics of the first LPF 3026 and the second LPF 3027. 3, the cutoff frequency of the first LPF 3026 is lower than the cutoff frequency of the second LPF 3027. In addition, the order of the first LPF 3026 is higher than the order of the second LPF 3027. As a result, the slope of the attenuation amount of the first LPF 3026 is higher than the slope of the attenuation amount of the second LPF 3027, as shown in FIG.

[0030] Based on the I residual signal and the Q residual signal supplied from the selector 3025, the measurement circuit 3028 measures the amplitude of the residual signal (hereinafter referred to as the residual level). The detection circuit 3029 detects the timing (hereinafter referred to as the minimum amplitude point) at which the residual level measured by the measurement circuit 3028 is minimum. Then, the detection circuit 3029 notifies the control circuit 3021 of the detected minimum amplitude point.

[0031] Next, the operation of the reader 100 configured as described above will be described. Note that the operation for reading the RFID tag 200 may be another known operation that uses, for example, a quadrature modulation method as a modulation method for wireless communication. Therefore, the description of that operation will be omitted here, and the operation related to the SJC processing will be described.

[0032] Before describing the operation, a self-interference signal will be described. The antenna duplexer 18 is designed so that a transmit signal input to the input terminal TI is not output from the output terminal TOA. However, in an actual circuit configuration, it is difficult to completely prevent the transmit signal input to the input terminal TI from leaking out from the output terminal TOA. For this reason, a portion of the transmit signal input to the input terminal TI is output directly from the output terminal TOA. Furthermore, a portion of the transmit signal output from the input / output terminal TIO of the antenna duplexer 18 is reflected at the feed point of the antenna 20 and transmitted to the antenna duplexer 18 via the feed line 19. This reflected signal is output from the output terminal TOA by the function of the antenna duplexer 18. Thus, the signal output from the output terminal TOA of the antenna duplexer 18 includes a component of the transmit signal that leaks out without being output from the input / output terminal TIO and a component of the transmit signal that is input to the input / output terminal TIO as a reflected signal. The signal resulting from the combination of these transmit signal components is a self-interference signal. The reflection characteristics of the transmit signal at the feed point of the antenna 20 vary depending on the environment surrounding the antenna 20, such as the proximity of the RFID tag 200 and other objects to the antenna 20. Therefore, the amplitude and phase of the signal reflected at the feed point of the antenna 20 also vary depending on the environment around the antenna 20. As a result, the amplitude and phase of the self-interference signal also vary depending on the environment around the antenna 20.

[0033] The environment around the antenna 20 is mainly influenced by the item to which the RFID tag 200 is attached. The environment around the antenna 20 is also influenced by the stand on which the item to which the RFID tag 200 is attached is placed. For this reason, the smaller the distance between the antenna 20 and the RFID tag 200, i.e., the shorter the communication distance, the less stable the environment around the antenna 20 tends to be.

[0034] The self-interference signal is a signal derived from the transmission signal. Therefore, by changing the amplitude and phase of a signal branched from the transmission signal, it is possible to generate a signal having the same frequency and amplitude as the self-interference signal but an opposite phase. Then, by combining such a signal with the reception signal output from the output terminal TOA of the antenna duplexer 18, the self-interference signal contained in the reception signal can be canceled. In the reader 100, the cancellation signal obtained by changing the amplitude and phase in the vector modulator 21 is combined with the reception signal output from the output terminal TOA of the antenna duplexer 18 in the power combiner 23, thereby reducing the self-interference signal contained in the reception signal.

[0035] The reader 100 is used, for example, to read data from RFID tags 200 attached to items placed at predetermined locations in a warehouse. For this purpose, a worker carrying the reader 100 moves in front of a shelf and causes the reader 100 to read the RFID tags 200 attached to the items placed on that shelf. In one operation mode, the worker stands in front of the shelf and holds the reader 100 over the shelf to read RFID tags 200 located over a relatively wide area. In another operation mode, the worker holds the reader 100 close to the RFID tags 200 placed on the shelf to read the RFID tags 200 that are in close proximity. In the former operation mode, the communication distance between the reader 100 and the RFID tags 200 is longer than in the latter operation mode. Therefore, the operation mode of the reader 100 that is suitable for a long communication distance, such as the former operation mode, is called a "long-distance mode." The operation mode of the reader 100 adapted to a short communication distance such as the latter operation mode is called the “short-distance mode.” The long-distance mode corresponds to the first communication mode, and the short-distance mode corresponds to the second communication mode.

[0036] When it is time to start reading the RFID tag 200, the CPU 301 starts outputting a predetermined transmission baseband signal such that the radio waves radiated from the antenna 20 become unmodulated carrier waves. The CPU 301 also starts supplying a start signal to the control circuit 3021. Upon receiving the start signal, the control circuit 3021 starts the control process for the SJC process. FIG. 4 is a flowchart of the control process.

[0037] As ACT1, the control circuit 3021 sets the status signal to a state indicating "scanning." In ACT2, the control circuit 3021 sets the long distance mode. At this time, the control circuit 3021 causes the selectors 3024 and 3025 to select the first LPF 3026, for example.

[0038] In ACT3, the control circuit 3021 starts a full-range scan. For example, the control circuit 3021 instructs the generation circuit 3022 to start sweeping. In response to this instruction, the generation circuit 3022 starts generating and outputting an amplitude signal and a phase signal. The generation circuit 3022 then sequentially changes the states of the amplitude signal and the phase signal so that the amplitude and phase represented by the amplitude signal and the phase signal are sequentially changed over the entire range in which the amplitude and phase can be changed by the vector modulator 21. This gradually changes the gain and phase of the cancellation signal generated by the vector modulator 21. The period from when the generation circuit 3022 starts outputting the amplitude signal and the phase signal until the amplitude and phase finish changing over the entire range in which they can be changed is the scan period during which the full-range scan is performed.

[0039] During this scan period, the reduction amount of the self-interference signal due to combining the cancellation signals in the power combiner 23 changes sequentially. Therefore, the I residual signal and the Q residual signal extracted by the LPF 28 also change sequentially. The I residual signal and the Q residual signal are input to the measurement circuit 3028 via the first LPF 3026. The measurement circuit 3028 measures the residual level based on the I residual signal and the Q residual signal that change as described above. The detection circuit 3029 detects the minimum amplitude point as the timing at which the residual level measured by the measurement circuit 3028 becomes minimum within the scan period. However, the minimum amplitude point does not necessarily have to be the timing at which the residual level becomes minimum strictly; it may be the timing at which the residual level becomes sufficiently low, close to the minimum value. The residual level value that is determined as the minimum amplitude point may be determined arbitrarily, for example, by the designer of the reader 100. At this time, the level of the self-interference signal extracted by the first LPF 3026 serving as the first filter is measured by the measurement circuit 3028, and the first LPF 3026 and the measurement circuit 3028 constitute a first measurement unit.

[0040] In ACT4, the control circuit 3021 sets the amplitude and phase for periods other than the scan period to those required to reproduce the operating state of the vector modulator 21 at the amplitude minimum point detected by the detection circuit 3029. The control circuit 3021 then instructs the generation circuit 3022 to fix the amplitude and phase to those values. The generation circuit 3022 then fixes the amplitude and phase signals it generates and outputs to states that represent the instructed amplitude and phase. In response, the vector modulator 21 is set to a state in which it generates a cancellation signal that can effectively cancel out the self-interference signal in the current ambient environment. Through this processing, the control circuit 3021 functions as a first control unit. In ACT5, the control circuit 3021 sets the status signal to a state indicating "canceling." Then, the CPU 301 starts outputting a transmission baseband signal for emitting radio waves from the antenna 20 to read the RFID tag 200 in a predetermined sequence.

[0041] In ACT 6, the control circuit 3021 checks whether the surrounding environment is stable. For example, the control circuit 3021 calculates the stability of the residual level measured by the measurement circuit 3028 within a predetermined period and checks whether the surrounding environment is stable based on the magnitude of this stability. The stability can be calculated, for example, as the difference between the maximum and minimum values. In this case, the smaller the stability value, the more stable the surrounding environment. Therefore, the control circuit 3021 may determine that the surrounding environment is stable if the stability is equal to or less than a predetermined first threshold. If the surrounding environment is stable, the control circuit 3021 determines YES and proceeds to ACT 7. Note that the first threshold may be determined as appropriate by, for example, the designer of the reading device 100. In ACT7, the control circuit 3021 waits for the reading to be completed.

[0042] When the CPU 301 has completed reading all of the RFID tags 200 that should be read, it notifies the control circuit 3021 of this. For example, the CPU 301 notifies the control circuit 3021 of the completion of reading by stopping the supply of a start signal to the control circuit 3021. In this case, the CPU 301 continues to supply the start signal that was started when reading should have started as described above while reading is in progress. Then, for example, when the control circuit 3021 receives this notification of completion, it determines YES in ACT7 and ends the control process.

[0043] On the other hand, if the temperature is not equal to or lower than the first threshold, the control circuit 3021 determines that the surrounding environment is not stable and makes a NO determination in ACT6, and proceeds to ACT8. In ACT8, the control circuit 3021 sets the short distance mode. At this time, the control circuit 3021 causes the selectors 3024 and 3025 to select the second LPF 3027, for example. Thus, by executing the processes of ACT6 and ACT8, the control circuit 3021 functions as a setting unit.

[0044] In ACT 9, the control circuit 3021 checks whether a change in the surrounding environment has occurred. If the control circuit 3021 cannot confirm the occurrence of such an event, it determines NO and proceeds to ACT 10. In ACT 10, the control circuit 3021 checks whether the reading is complete. If the control circuit 3021 cannot confirm the event, it determines NO and returns to ACT 9. Thus, in ACT9 and ACT10, the control circuit 3021 waits for an environmental change to occur or for reading to be completed.

[0045] At this time, since the operation of the vector modulator 21 is fixed, the residual level fluctuates according to fluctuations in the self-interference signal. Therefore, for example, when the residual level becomes equal to or greater than a predetermined second threshold, the control circuit 3021 determines that an environmental change has occurred, determines YES, and proceeds to ACT11. Note that the second threshold may be appropriately determined, for example, by the designer of the reader 100.

[0046] In ACT11, the control circuit 3021 initiates a full-range scan similar to ACT3. However, here, the short-distance mode is set, and the second LPF 3027 is selected by the selectors 3024 and 3025. The second LPF 3027 has a larger cutoff frequency than the first LPF 3026, and therefore a smaller time constant than the first LPF 3026. In other words, the response speed for measuring the residual level is higher during the full-range scan in ACT11 than during the full-range scan in ACT3. Therefore, the control circuit 3021 changes the amplitude and phase of the cancellation signal at shorter time intervals in ACT11 than in ACT3. Note that the amplitude and phase change intervals in ACT3 and ACT11 may be appropriately determined, for example, by the designer of the reader 100, taking into account the response speeds of the first LPF 3026 and the second LPF 3027, so that the measurement circuit 3028 can correctly measure the residual level. At this time, the level of the self-interference signal extracted by the second LPF 3027 serving as the second filter is measured by the measurement circuit 3028, and the second LPF 3027 and the measurement circuit 3028 constitute a second measurement unit.

[0047] Since the second LPF 3027 has a higher cutoff frequency than the first LPF 3026, the S / N ratio of the I residual signal and the Q residual signal supplied to the measurement circuit 3028 is higher when the full range scan is performed in ACT 11 than when the full range scan is performed in ACT 3. As a result, the error in the residual level measured by the measurement circuit 3028 is larger when the full range scan is performed in ACT 11 than when the full range scan is performed in ACT 3. In other words, the error in the minimum amplitude point detected by the detection circuit 3029 is also larger when the full range scan is performed in ACT 11 than when the full range scan is performed in ACT 3.

[0048] As ACT12, the control circuit 3021 sets the amplitude and phase of the vector modulator 21 in the same manner as ACT4. By this processing, the control circuit 3021 functions as a second control unit.

[0049] The control circuit 3021 then returns to the standby state in ACT 9 and ACT 10. Thus, the control circuit 3021 repeats the full range scan in ACT 11 and the amplitude and phase setting in ACT 12 every time a change in the surrounding environment occurs until reading is completed. Then, upon receiving a completion notification from the CPU 301, the control circuit 3021 determines YES in ACT 10 and ends the control process.

[0050] FIG. 5 is a diagram showing an example of the change in the residual level measured by the measurement circuit 3028. As shown in FIG. 5, the residual level is reduced to a sufficiently small value over a relatively long period of time by the control of the vector modulator 21 by ACT3 and ACT4 (hereinafter referred to as initial control).

[0051] In the example of Fig. 5, after the end of the initial control, the residual level gradually increases in response to changes in the surrounding environment. Then, when the residual level becomes equal to or greater than the second threshold, control of the vector modulator 21 by ACT11 and ACT12 (hereinafter referred to as "during reception control") is performed. The during reception control reduces the residual level to below the second threshold again. However, due to the influence of the detection error of the minimum amplitude point as described above, the residual level after the during reception control is higher than the residual level after the initial control. As described above, the control circuit 3021 performs initial control by functioning as a first control unit before reception begins, and performs control during reception by functioning as a second control unit during reception, thereby functioning as a third control unit.

[0052] By the above operation, the reader 100 monitors the residual level even during reception, and if the residual level increases, it continues receiving and readjusts the vector modulator 21. Therefore, even if the self-interference signal fluctuates during communication due to the influence of fluctuations in the surrounding environment, the influence of the self-interference signal can be kept small.

[0053] Furthermore, the reading device 100 performs full range scanning in a short time with reduced accuracy during reception control, which allows the reading device 100 to quickly overcome a state in which the residual level is high and minimize the influence of self-interference signals.

[0054] Furthermore, the reader 100 executes the during-reception control only when the residual level is not stable after the completion of the initial control. If the residual level is stable after the completion of the initial control, it is considered that an object causing a change in the surrounding environment is not close to the antenna 20, and in this case, it is known that the fluctuation of the self-interference signal is small. Therefore, by not executing the during-reception control in such a situation, it is possible to suppress an increase in the processing load associated with the during-reception control.

[0055] Furthermore, depending on the stability of the residual level after the completion of the initial control, the reader 100 switches between a long-distance mode using the first LPF 3026 to adapt to a relatively long communication distance and a short-distance mode using the second LPF 3027 to adapt to a relatively short communication distance. The reader 100 uses the long-distance mode for the initial control and executes the control during reception only in the short-distance mode. Thus, by switching the operating mode to adapt to changes in the communication distance, the operating states for performing the initial control and the control during reception can be switched.

[0056] This embodiment can be modified in various ways as follows. It may also be realized as a communication device that communicates with the RFID tag 200 in order to write to the RFID tag 200. It may also be realized as a communication device that communicates with a communication device other than the RFID tag 200.

[0057] If the residual level after the completion of the initial control is stable, that is, if communication is performed in the long-distance mode, the communication control may also be performed.

[0058] The cancellation signal may be generated without using the vector modulator 21. For example, instead of the vector modulator 21, a variable attenuator and a variable phase shifter may be connected in series.

[0059] Instead of the selectors 3024 and 3025, the first LPF 3026 and the second LPF 3027, an LPF with a changeable cutoff frequency may be used.

[0060] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0061] 10...antenna, 11...oscillator, 12...phase shifter, 13...DA converter, 14...quadrature modulator, 16...power amplifier, 18...antenna duplexer, 19...feed line, 20...antenna, 21...vector modulator, 22...DA converter, 23...power combiner, 24...quadrature detector, 26...baseband amplifier, 27...AD converter, 29...AD converter, 30...control unit, 301...CPU, 302...FPGA, 303...memory, 3021...control circuit, 3022...generation circuit, 3023...conversion circuit, 3024, 3025...selector, 3028...measurement circuit, 3029...detection circuit, 100...reader, 200...RFID tag.

Claims

1. a first generator that generates a transmission signal for wireless transmission; a common unit that receives the transmission signal generated by the first generating unit from an input terminal and outputs the signal from an input / output terminal, and that outputs the signal received from the input / output terminal from an output terminal; a second generator that generates a cancellation signal by changing the amplitude and phase of the transmission signal generated by the first generator; a combining unit that combines the cancellation signal generated by the second generating unit with the signal output from the output terminal; a first measurement unit that measures the level of a self-interference signal extracted from the output signal from the synthesis unit for a first bandwidth; a first control unit that sets amounts of change in amplitude and phase in the second generation unit so as to reduce the level measured by the first measurement unit to a level that meets a predetermined condition during a period of a predetermined first time width; a second measurement unit that measures a level of a self-interference signal extracted from the output signal from the combiner unit for a second bandwidth that is wider than the first bandwidth; a second control unit that controls amounts of change in amplitude and phase in the second generation unit in response to an increase in the level measured by the second measurement unit, during a period of a second time width that is shorter than the first time width, so as to reduce the level measured by the second measurement unit; a third control unit that causes the first control unit to set amplitude and phase change amounts in the second generation unit before starting to receive a response signal transmitted from a counterpart device, and causes the second control unit to set amplitude and phase change amounts in the second generation unit while receiving the response signal transmitted from the counterpart device; A communication device equipped with:

2. The first measurement unit includes a first filter that passes a signal component of the first bandwidth, The second measurement unit includes a second filter that passes a signal component of the second bandwidth and has a response speed higher than that of the first filter, The communication device according to claim 1 .

3. When the degree of stability of the self-interference signal before starting reception of the response signal transmitted from the other device is low enough to meet a predetermined condition, the third control unit enables control by the second control unit during subsequent reception. The communication device according to claim 1 or 2.

4. The communication device has, as operation modes, a first communication mode and a second communication mode adapted to a communication distance shorter than that of the first communication mode, the third control unit enables control by the second control unit when the second communication mode is set; The communication device according to claim 1 or 2.

5. a setting unit that sets the second communication mode when a degree of stability of a self-interference signal before starting to receive a response signal transmitted from the counterpart device is low enough to meet a predetermined condition; The communication device of claim 4 further comprising:

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