JP2009194819A - Rfid base station, and rfid system employing the same, and method of transmitting/receiving signals in rfid system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means for effectively suppressing radio noise of a surrounding environment and unwanted radio noise caused by transmission waves of a base station, with respect to a transfer signal from a terminal station. <P>SOLUTION: An RFID base station has two or more time-base modes, converts a part of reception waves and transmission waves into digital signals through an analog/digital converter, and performs different types of digital operations. Namely, the RFID base station has a mode for sending a signal from the terminal station and a mode not to send any signal on a time base and cancels unwanted radio noise superimposed on a reception signal from the terminal station while using a transmission wave of the base station as a reference signal through digital operations over both the modes. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an RFID base station, an RFID system using the RFID base station, and a signal transmission / reception method in the RFID system, and more particularly to an RFID base station suitable for a system having a long distance to a terminal station, and an RFID system and an RFID using the RFID base station. The present invention relates to a signal transmission / reception method in a system.

  Wireless monitoring systems are being developed that employ a wireless system and can be monitored or surveyed from a distance.

  In an actual radio system, a signal having a frequency lower than the frequency of the carrier wave, which is called modulation, is superimposed on an electromagnetic wave responsible for transmitting a signal called a carrier wave, and as a result, detuning that generates a frequency component separated from the frequency of the carrier wave is generated. Used. Therefore, in the base station, unnecessary radio noise having frequency components of radio waves to be transmitted is effectively suppressed, so that the base station is composed of radio waves having a frequency closest to the transmission signal (received signal) from the terminal station, that is, having the greatest influence. Unwanted radio noise can be reduced. Using this principle, the base station transmission wave is used as a reference signal, and its phase and amplitude are adjusted to negatively superimpose the base station reception wave to reduce unwanted radio noise, which has the greatest impact Is described in Patent Document 1, for example.

  The high frequency transmission / reception unit 18 of the wireless tag communication device disclosed in FIGS. 3 to 5 of Patent Document 1 includes a transmission circuit (58), a carrier distributor 60, a transmission / reception separation unit 64, and an antenna 20 coupled in series. . An analog / digital converter 94 is connected to the other terminal side of the transmission / reception separation unit 64 that separates and transmits the reception signal from the antenna 20 via the cancel signal synthesis unit 66, and the digital output of the reception signal is input to the reception memory unit 42. Is done. The output of the transmission circuit is partly branched by the carrier distributor 60 and is input to the cancel memory 40 through the cancel phase controller 72, cancel amplitude controller 78 and distributor 80, and from the antenna by the cancel signal multiplexer 66. The received signal is negatively superimposed. Thereby, a noise signal having the same frequency component as the output of the transmission circuit can be reduced from the received signal and transmitted to the reception memory unit 42. The reception memory unit 42 transmits the reception sensitivity to the adaptive cancel control unit 38, and the adaptive cancel control unit 38 cancels the cancel phase control unit 72 and the cancel amplitude control unit 78 so that the reception sensitivity is maximized. Control the phase and amplitude.

JP 2007-251641 A

  Social infrastructure systems such as electric power, water supply, and communications are becoming more sophisticated and complex year by year in accordance with demands for improving user convenience. Once the system does not operate normally, many direct users are disadvantaged. Ripple effects also occur in other complicatedly related systems, and the damage from difficulties can be transmitted to users of other systems, resulting in confusion for the entire region and society as a whole. Sex has come out. Wide-area catastrophic blackouts and wide-area toxic chemical contamination, which are frequently reported in modern times, have already developed into major social problems. One measure to solve such a problem is to examine the state of the device that is the key of each social infrastructure system and the state of the surrounding environment where the device is placed.

  Once a social infrastructure system becomes inoperable, if it is possible to quickly investigate which devices in this system are not operating normally, the social infrastructure system can be quickly restored. The spread of adverse effects on social infrastructure systems can be minimized. Also, if the operation status of each device in the regular social infrastructure system or the status of the environment where the device is located can be investigated or monitored, it is possible to prevent the social infrastructure system from being inoperative. It becomes possible.

  In modern times, because users are demanding to enjoy advanced services, the devices that form the core of the social infrastructure system are concentrated in a place that is separated from the user's normal residence, The actual situation is that the equipment is operated in an extreme environment that is dangerous or problematic in the vicinity of a normal residence. In terms of electricity, nuclear power plants that are at risk of radiation exposure, thermal power plants that are at risk of burning explosions, hydroelectric power plants that have many high heads, and high-voltage power generated at power plants are transmitted and distributed There are transmission and transformation facilities. In waterworks, people are prohibited from easily accessing each facility in order to eliminate pollution from reservoirs and water treatment plants for safety and hygiene. In communication, in order to realize wireless communication, base station antennas are generally installed at high places, and in optical communication, transmission media such as fibers are installed underground and underground. Access to is not easy.

  Reflecting the above situation, focusing on electromagnetic wave permeability, detour propagation property, and non-contact property, an attempt is made to attach a state detection mechanism to each of the above facilities and detect the state as a radio signal using radio waves. Has been made. However, the distance attenuation characteristics associated with the spherical wave propagation characteristics of electromagnetic waves are orders of magnitude greater than those of wired communications where the energy of the transmission signal is confined and transmitted in the transmission path, so information is transmitted from the base station to the terminal station wirelessly. In the process of transmitting the signal, the transmission signal is mixed with various unnecessary wireless noises from around the wireless transmission path. The transmission signal attenuates in proportion to the square to the third power of the distance between the base station and the terminal station, and the unnecessary radio noise can be arbitrarily mixed in the transmission process of the transmission signal, and is received by the base station Sometimes, the energy ratio of the unnecessary radio noise to the transmission signal becomes large, and it becomes a big problem for the base station to suppress the unnecessary radio noise in order to faithfully demodulate the transmission signal.

  Further, in a wireless system, in order to ensure coexistence with other systems, in other words, compatibility, the frequency band of radio waves that can be used by one system is limited. For this reason, the terminal station transmits a signal using a certain frequency within the same frequency band. Generally, when a signal is superimposed on a radio wave having a frequency used for this transmission, in other words, when modulation is performed, a radio wave having a frequency component slightly separated from the frequency is generated. It goes without saying that this frequency component also needs to be included in the frequency band in which the system is allowed.

  As described above, in the wireless monitoring system, since the distance between the base station that is in charge of monitoring and the terminal station that transmits the information on the object or environment to be monitored and investigated to the base station is long, the radio transmitted by the terminal station There is a need for a function that effectively suppresses the effects of unnecessary radio noise when information is subjected to a lot of unnecessary radio noise from the periphery of the transmission path in the process of transmitting information to the base station.

  In particular, in the case of a wireless monitoring system in which the power consumption of the terminal station needs to be as low as possible, for example, when the terminal station is indispensable to consider the surrounding environment or physical access to the terminal station is not possible at all. In the so-called backscattering method in which the carrier wave of the transmitted wave is directly modulated and the carrier wave frequency of the transmitted wave and the carrier wave frequency of the received wave are the same, interference with the received wave of the transmitted wave inside the base station is also unnecessary. It becomes a more serious problem to exhibit the same effect as noise and to suppress the unnecessary radio noise.

  The prior art disclosed in Patent Document 1 performs analog negative superimposition of a transmission wave on a reception wave using a cancellation phase control unit and a cancellation amplitude control unit. In this conventional technique, the effect of reducing the unnecessary radio noise is not sufficient, and there is a problem that it is difficult to use this conventional technique particularly in the case of a wireless monitoring system in which the distance between the base station and the terminal station is large. .

  An object of the present invention is to provide an RFID base station and an RFID system using the same, which can effectively suppress radio noise in the surrounding environment and unnecessary radio noise due to a transmission wave of the base station with respect to a transmission signal from a terminal station. It is another object of the present invention to provide a signal transmission / reception method in an RFID system.

  Another object of the present invention is to determine whether the operation status of each device in the social infrastructure system or the status of the environment in which the device is located, which is usually installed in a situation where human access is extremely difficult, It is an object of the present invention to provide a wireless monitoring system that is suitable for investigating or monitoring with high reliability without having a power source according to the above and ensuring a distance that allows human beings to be isolated from undesirable effects from the device.

  An example of a representative one of the present invention is as follows. That is, the RFID base station of the present invention includes an antenna, a transmission circuit, a reception circuit, and a circulator that couples any one of the transmission circuit and the reception circuit to the antenna. A digital feedforward circuit is disposed between the circuit and the circulator, and the digital feedforward circuit includes a reception signal determination unit and a digital signal processing unit, and the reception signal determination unit is configured to receive on the time axis. A function of detecting whether or not a reception signal from a terminal station is included in the wave, and the digital signal processing unit uses the transmission wave generated by the transmission circuit as a reference signal to the reception wave. Performs a digital operation to suppress the superimposed unnecessary wave component, and has a function of transmitting the result of the digital operation to the receiving circuit, Serial digital signal processing unit uses the information of the presence or absence of the received signal detected by the reception signal determination unit, and performing the reset of the digital operation and the digital operation.

  According to the present invention, since the base station can subtract the disturbance / interference of the unnecessary radio noise including the transmission wave transmitted by the base station itself from the radio signal transmitted from the terminal station by digital calculation, A highly accurate suppression effect of the disturbance and interference can be realized with little influence of secular change.

  In the present invention, unnecessary radio noise superimposed on the received signal of the base station is subtracted by digital calculation using the transmission wave of the base station as a reference signal. For this purpose, the transmission wave and the reception wave are converted into digital signals by an analog / digital converter and directly subjected to calculation by a digital signal processing unit. Unlike the suppression of this unwanted radio noise by analog circuits, which is essentially an analog circuit in the prior art, subtraction of this unwanted radio noise by digital computation requires considerable computation time, and the processing speed of current digital signal processing hardware Thus, effective real-time processing is impossible. For this reason, in the present invention, once the base station receives a transmission signal (reception signal) from the terminal station for a certain period, it performs a deduction process that subtracts unnecessary radio noise superimposed on the reception signal by digital calculation. A system is used in which a received signal that has been subjected to unnecessary wireless noise removal processing is supplied to a receiving circuit after a certain time lag.

  In general digital calculation, calculation methods called adaptive processing and batch processing are known, but both use pre-processing before performing a calculation on this digitized received signal using a reference signal once digitized. A time zone for performing the preparatory stage operation is indispensable, and the received signal cannot be supplied to the receiving circuit in this time zone. In other words, the technique of the present invention requires at least two different modes, a time zone during which a received signal can be supplied to the receiving circuit and a time zone during which it cannot.

  Even if preprocessing is finished and calculation for supplying the received signal to the receiving circuit is started, the base station receives the transmission signal (received signal) from the terminal station depending on the content of the calculation. Even after this operation is completed, the digital operation result is supplied to the receiving circuit even after shifting to a time zone during which no received signal is received from the terminal station that continuously visits on the time axis, in other words, another mode. It will continue to be done.

  In the technology of the present invention, unnecessary radio noise superimposed on a transmission signal transmitted from a terminal station by digital calculation can be subtracted. Therefore, this unnecessary radio is determined by the dynamic range of the digital / analog converter and the calculation accuracy of the digital calculator. The degree of noise suppression is determined.

  These dynamic range and calculation accuracy are inextricably linked with the miniaturization of semiconductor process technology, and continue to improve day by day according to the so-called Moore's law. In the current technology, a digital processor capable of signal processing of several to several tens of microseconds can be used, and the dynamic range of the digital-analog converter corresponding to the signal processing speed is 11 to 14 bits. It surpasses the accuracy of analog device manufacturing accuracy, temperature variation, and aging variation.

  This means that, in the frequency range of several to several tens of megahertz, the suppression effect of unnecessary radio noise by digital calculation still surpasses the same effect by analog circuits even now, and it will be a frequency suitable for radio communication in the future. Even in the range of 300 to 3000 megahertz, suppression of this unnecessary radio noise by digital calculation is effective. In order to bring out the same effect with the current digital semiconductor technology, the base station transmission wave and the reception wave from the terminal station are down-converted by using a separately installed local oscillator, and a frequency range of several to several tens of megahertz. Can be converted to.

Since the dynamic range of the digital / analog converter is inversely proportional to the frequency to be handled, reducing the power of this unnecessary radio noise in advance for the received wave from the terminal station will alleviate the demand for the dynamic range. The applied frequency of the digital / analog converter can be increased. In order to realize this, an analog feedforward circuit that reduces the unnecessary radio noise having the same frequency as the transmission wave included in the reception wave from the terminal station using the transmission wave of the base station as a reference wave is provided in the digital signal of the present invention. It is also very effective to install it before the digital-analog converter, which is a component of this unnecessary radio noise subtraction circuit by calculation, or before the down-conversion circuit using a separate local oscillator.
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  An embodiment of the present invention will be described with reference to FIGS. 1A is a diagram illustrating a configuration of an RFID base station according to an embodiment of the present invention, FIG. 1B is a diagram illustrating a specific configuration example of a signal determination unit in FIG. 1A, and FIG. It is a figure which shows the specific structural example of the digital signal processing part of 1A.

  In FIG. 1A, 1 is a transmission circuit, 2 is a reception circuit, 3 is a digital feedforward circuit, 6 is an antenna, and 7 is a circulator (directional coupler). The transmission circuit 1 includes a carrier wave generation unit, a modulation unit, an amplifier, and the like. The reception circuit 2 includes a demodulation unit, a waveform equalization unit, a decoding unit, and the like. The digital feedforward circuit 3 includes a power distributor 8 disposed between the transmission circuit 1 and the circulator 7, analog / digital converters 4 </ b> A and 4 </ b> B, a received signal determination unit 50, and a digital signal processing unit 5.

  The circulator 7 couples either the transmission circuit 1 or the reception circuit 2 to the antenna 6. That is, the transmission circuit 1, the power distributor 8, and the circulator 7 are coupled in series, and the circulator 7 and the antenna 6 are coupled so that the signal of the transmission circuit 1 is transmitted from the antenna 7. Further, the circulator 7 and the second analog / digital converter 4B are coupled so that the reception signal of the antenna 6 is transmitted to the reception circuit 2 via the circulator 7.

  The received signal discriminating unit 50 arranged between the circulator 7 and the digital signal processing unit 5 has a function of discriminating whether or not the received wave contains a periodic received signal from the terminal station, that is, the circulator 7. It has a function to detect whether or not a received signal from a certain terminal station is included in a received wave input via. In other words, the received signal discriminating unit 50 has, on the time axis, a reception mode in which a received signal from a certain terminal station includes a received signal and a non-reception mode in which the received signal is not included as one cycle. It has a function to detect periodic mode changes.

  The reception signal determination unit 50 can be constituted by, for example, a band pass filter 51, a detection unit 52, and an analog / digital converter 53 as shown in FIG. 1B. The terminal station normally has a function of modulating the signal received from the base station, that is, sending back the carrier signal to the base station with a phase unique to the terminal station (timing difference = center frequency fc). The presence / absence of a signal having the phase (center frequency fc) (the first rising edge and the last falling edge of the pulse shape received signal from the terminal station) is detected by the band-pass filter 51 and the detecting unit 52, thereby determining the presence or absence of the received signal. What is necessary is just to distinguish. Note that the means for determining the presence or absence of a received signal is not limited to this, and may be realized by other means according to the type of modulation applied to the received signal at the terminal station.

Further, a part of the output of the transmission circuit 1 is coupled to the power distributor 8 of the digital feedforward circuit 3 and input to the first analog / digital converter 4A, and the digital of the first analog / digital converter 4A is input. Both the output (X ⁱ ) and the digital output (Y ⁱ ) of the second analog / digital converter 4 B are input to the digital signal processing unit 5.

  The digital signal processing unit 5 includes, for example, an input memory, a multistage set of a switch / arithmetic circuit unit and an intermediate memory, and an output memory as shown in FIG. 1C. The digital computation is executed by the switch / arithmetic circuit unit of each stage of the digital signal processing unit 5. This digital calculation includes suppression of unnecessary wave components included in the received wave, preparation for the digital calculation, and the like, and is controlled by information on the presence / absence of the received signal detected by the received signal determination unit 50.

For example, a digital calculation such as the following equation (1) is performed, in which digital signals (X ⁱ ) and (Y ⁱ ) relating to a received signal from a specific terminal station are input and Wi is a weight coefficient.

Zi = Xi- (WiYi + Wi-1Yi-1 +----W1Y1) (1)
A digital operation in which the weight coefficient Wi is sequentially increased is executed by the switch / arithmetic circuit unit of each stage. The digital signal obtained by subtracting the radio noise component having the same frequency component as the output signal of the transmission circuit 1 from the digital output of the second analog-to-digital converter 4B by this digital operation is the digital signal processing unit 5. Are sequentially input to the receiving circuit 2 as outputs (Z ⁱ ).

  FIG. 2 shows a configuration example of an RFID system to which the present invention is applied. In this example, there is one base station 100 and one terminal station 110. Note that the present invention is applied to an RFID system including a plurality of terminal stations for one base station. However, in order to simplify the description, the following description will be given of one base station. Description will be made assuming that communication is performed with a terminal station.

  The terminal station 110 includes a rectification unit, a smoothing unit, a microprocessor, a terminal station antenna, and the like. An electromagnetic wave propagating in space is used as a communication medium between the base station and the terminal station. In the base station 100, a carrier wave signal having a center frequency f0 (timing t0) is generated by a carrier wave generator having a transmitter, and this carrier wave signal is input to a modulator via a variable attenuator. In the modulation unit, predetermined modulation such as amplitude modulation or phase modulation is applied to the input wave by the modulation signal. The output of the modulator is coupled to the circulator 7. The output signal 104 output from the base station antenna via the circulator has a constant carrier wave period (repetition period), and becomes a pulse-shaped intermittent waveform having ON and OFF signals with constant peak values on the time axis. . As shown in FIG. 2, the output signal 104 forms a frequency spectrum composed of a plurality of sidebands whose power is attenuated with increasing distance from the center frequency f0 on the frequency axis.

  The terminal station 110 is an RFID tag, and the base station 100 functions as an RFID tag reader. The terminal station does not have a battery power source in the device. Instead, a matching unit is coupled to the terminal station antenna in the terminal station. The output of the matching unit is supplied as the power of the microprocessor through the rectifying unit and the smoothing unit. The rectifying unit includes a diode as a rectifying element. The output signal 104 from the base station reaches the terminal station 110, is taken into the terminal station from the terminal station antenna, and is applied to the rectifying unit via the matching unit. When the applied voltage exceeds the threshold voltage of the diode, the applied power to the rectifying unit is rectified and sent to the smoothing unit and stored as a power source for the microprocessor or the like, and the microprocessor is driven by this power. The output signal 104 is sent to the microprocessor through the rectifier and demodulated there. In response to the output signal, the microprocessor controls modulation applied to transmission power radiated from the base station in order to generate a reflected wave including information on the terminal station. This modulation is amplitude modulation, phase modulation or other digital modulation.

  The base station transmits the transmission wave 104 from the antenna 106 at the timing time t0. When performing phase modulation on the reflected wave, the terminal station 110 performs phase modulation on the radio wave including the signal component of the response information for a predetermined timing time (t1-t0) specific to the terminal station 110 with respect to the transmission wave 104. And sent to the base station. As a result, as a reflected wave 105 from the terminal station, as shown in FIG. 2, on the frequency axis, a new transmission having a frequency spectrum composed of a plurality of sidebands whose power is attenuated with increasing distance from the center frequency fc. A signal is formed.

  This is received as a received wave 105 at the base station. The reflected wave 105 from the terminal station reaches the base station, is taken into the receiving circuit inside the base station 100 from the base station antenna 8, and is subjected to demodulation, waveform equalization, and decoding processes.

  Next, received signal processing in the digital feedforward circuit 3 of the base station will be described with reference to FIGS. FIG. 3 shows a flowchart of received signal processing in the digital feedforward circuit 3 in this embodiment. FIG. 4 is a diagram showing time timing of digital processing performed by the RFID base station according to the present invention. In FIG. 4, the reception signal of the base station, the digital signal processing, and the reception circuit input signal are shown together on the same time axis. In this embodiment, it is assumed that adaptive processing is performed. As shown in FIG. 4A, the reception wave of the base station has a reception period Tp (non-reception mode) that does not include the reception period Ts (reception mode) having the signal component from the terminal station and one period. (= Ts + Tp) is a waveform in which Ts and Tp alternately and periodically appear in each of the first and second sections. The reception signal determination unit 50 detects the first and second sections (modes) in each period of the reception wave as individual modes, and sends the result to the digital signal processing unit 5.

  In the processing flow of the digital signal processing unit 5 shown in FIG. 3, first, a parameter relating to adaptive processing is set to an initial value, for example, zero (S302). Next, based on the output of the received signal discriminating unit 50, a reception period (non-reception mode) Tp in which a received wave does not include a signal component from a corresponding terminal station in a certain period, for example, the first interval. It is determined whether or not this is the case (S304). When it is determined that the first section is in the non-reception mode, the digital signal processing unit 5 performs adaptive training processing (S306). This process is a process for repeatedly executing the calculation of the formula (1) to enhance the system of the calculation.

  Next, based on the output of the received signal determination unit 50, it is determined whether or not the received wave corresponds to the reception period (reception mode) Ts of the first section having the signal component from the terminal station (S308). . If no received signal is detected, the adaptive training process is continued. If a reception signal indicating the reception mode of the first section is detected, adaptive processing is performed in the digital signal processing unit 5 in this reception mode (S310).

Further, based on the output of the received signal discriminating unit 50, it is determined whether or not a reception signal indicating a reception period (non-reception mode) Tp for the next period, for example, the second period has been received (S312). ). If the non-reception mode of the second section is determined, the adaptation process is continued. If it is determined that the reception mode is the second interval, the adaptive processing for the first interval is terminated, and the calculation result (Z ⁱ ) is transmitted to the reception circuit 2 (S314). In addition, parameters relating to the adaptive processing are reset (S316). Thereafter, similarly, adaptive training processing and adaptive processing corresponding to each mode are performed for each period.

  The processing of the present embodiment is adaptive processing, and after a received signal is input to the digital signal processing unit, a period during which the signal from which radio unnecessary noise has been subtracted is output from the digital signal processing unit 5 ( Training period).

Therefore, as shown in FIG. 4B, in the digital signal processing unit 5, in order to perform digital signal processing in a certain period, for example, the first section, first, reset processing is performed, and then second processing is performed. Preliminary signal processing (training processing) necessary for the Tp period (non-reception mode) of one section is performed, and further included in the necessary received wave within the Ts period (reception mode) of the first section Perform digital computation (adaptive processing) on signal components. Then, as shown in FIG. 4C, the digital output (Z ⁱ ) of the signal component included in the received wave from which the radio noise, which is the calculation result, is subtracted is transmitted to the receiving circuit 2.

  Even during the Tp period when the signal is not transmitted from the terminal station (non-reception mode), the base station can receive the unnecessary radio noise that gives disturbance and interference to the signal of this terminal. Therefore, during this Tp period, Do this training. In addition, after receiving the signal from the terminal station, it is necessary to reset the digital calculation in order to eliminate the accumulation of errors in the adaptive processing.

  According to the present embodiment, the digital output of the signal component transmitted from the terminal station can be obtained by subtracting the radio noise mixed in the received wave of the base station by digital calculation, so that the influence of secular change, temperature change, etc. can be obtained. While suppressing, it is possible to achieve a noise component removal effect with respect to a highly accurate signal component.

  In addition, since the digital signal processing unit can be realized with a semiconductor integrated circuit, it also has the effect of reducing the overall size of the base station device, and the manufacturing cost of the base station device can be reduced by the mass production effect of the semiconductor integrated circuit. Is also possible.

  Furthermore, the processing of this embodiment can shorten the period required for the signal from which the wireless unnecessary noise is subtracted after the terminal station equivalently transmits the signal to be output from this digital signal processing unit, The probability on the time axis at which the base station can read the signal transmitted from the terminal station can be increased, and as a result, the sensitivity of receiving the signal from the terminal station of the base station can be improved.

  In addition, even if the RFID system including the RFID base station of the present invention described above is used in a wireless monitoring system where the power consumption of the terminal station needs to be as low as possible, the transmission signal from the terminal station is received by the base station. Sensitivity can be greatly improved and faithfully demodulated. Such a wireless monitoring system allows humans and organisms to be directly in high places, high-concentration hazardous chemical substance-filled areas, radiation handling areas, high-power passing areas, high-temperature areas, high-pressure areas, areas where high-purity sanitary environments should be maintained, etc. It is possible to monitor or investigate the state of an area where it is not appropriate to have access to a person without access to the facility.

  That is, according to the present invention, the operation status of each device in the social infrastructure system or the status of the environment in which the device is placed, which is usually installed in a situation where human access is extremely difficult, is stored in the battery. It is possible to provide a wireless monitoring system that is suitable for investigating or monitoring with high reliability without having a power source according to the above and ensuring a distance that allows human beings to be isolated from undesirable effects from the device.

  Another embodiment of the present invention will be described with reference to FIG. FIG. 5 shows a received wave (FIG. 5A) input from the antenna 6, a digital signal (FIG. 5B) input to the receiving circuit 2, and a receiving circuit input signal (FIG. 5) in this embodiment. FIG. 6C is a diagram showing (c)) in the same time axis. The difference from the embodiment of FIG. 1 is that the digital signal input to the receiving circuit 2 is delayed on the time axis compared to the embodiment of FIG. In this embodiment, the digital calculation for obtaining the digital output of the signal component transmitted from the terminal station by subtracting the radio noise mixed in the reception wave of the base station requires more processing time, and the digital signal processing unit 5 This is a case where the adaptive processing in is not completed within Ts (reception mode) of the first section. As a result, the reception wave of the base station is transmitted from the output of the digital signal processing unit 5 to the reception circuit 2 over a period of Tp (non-reception mode) that does not include the signal component transmitted from the terminal station. Even if the adaptive processing is performed by the digital signal processing unit 5 during the Tp period during which no signal is transmitted from the terminal station (non-reception mode), there is no problem in the operation of the base station.

  In general, in order to increase the effect of subtracting the radio noise mixed in the received wave of the base station, it is necessary to perform an accurate digital operation with a longer processing time. In the present embodiment, using the difference in the mode on the time axis in which the base station receives the received wave, it is possible to realize such accurate digital calculation without affecting the signal transmitted from the terminal station. This has the effect of increasing the effect of subtracting radio noise mixed in the received wave.

  Another embodiment of the present invention will be described with reference to FIGS. FIG. 6 shows a flowchart of received signal processing in the digital feedforward circuit in this embodiment.

  FIG. 7 is a diagram showing the time timing of digital processing performed by the base station in this embodiment. The base station received signal ((a) in FIG. 7) and the digital signal input to the receiving circuit 2 (in FIG. 7). (B)) and the receiving circuit input signal ((c) of FIG. 7) are shown together on the same time axis. As shown in FIG. 7, the reception signal has a reception period Ts (reception mode) having a signal component from the terminal station and a reception period Tp (non-reception mode) that does not include the same signal component in a first interval, It appears alternately alternately in the second section, each section of-and-.

  In the processing flow of the digital signal processing unit 5 shown in FIG. 6, first, parameters relating to batch processing are set to initial values (S602). Next, based on the output of the received signal determination unit 50, whether or not the received wave corresponds to the reception period Ts (reception mode) including the signal component from the corresponding terminal station in the section, for example, the first section. Is determined (S604). If it is determined that the reception period is Ts, the digital signal processing unit 5 performs batch processing (S606).

Further, based on the output of the received signal determination unit 50, whether or not the received wave related to the next section, for example, the second section, corresponds to the reception period Tp (non-reception mode) including the signal component from the corresponding terminal station. Is determined (S608). If it is determined that it is not the reception period Tp of the second interval, the collective processing is continued. If it is determined that it is the reception period Tp of the second section, the adaptation process of the first section is terminated, and the calculation result (Z ⁱ ) is transmitted to the receiving circuit 2 (S610). In addition, parameters related to batch processing are reset (S612). Thereafter, batch processing of each section is performed in the same manner.

  The processing of this embodiment is a batch processing, and is required for a signal from which a radio unnecessary noise is subtracted to be stably output from the digital signal processing unit after the received signal is input to the digital signal processing unit. There is no period (training period). On the other hand, since the batch processing includes a division process, generally, the digital operation amount to be performed by the digital signal processing unit requires a lot of time compared with the adaptive processing. However, since it is possible to continue the digital operation of the batch processing even in the period (Tp) of the next section in which no signal is transmitted from the terminal station, this batch processing is performed even if the period (Tp) of the next section is entered. Perform digital processing. Moreover, it is desirable to reset the digital operation after the reception of the signal from the terminal station in order to keep the operation of the digital signal processing unit stable.

  By the processing of this embodiment, it is possible to realize the subtraction calculation of unnecessary radio noise from the radio signal transmitted from the terminal station, which is more accurate than the adaptive processing, so that the signal from the terminal station of the base station is received as a result. Sensitivity can be improved.

  Another embodiment of the present invention will be described with reference to FIG. FIG. 8 is a diagram showing time timing of digital processing performed by the base station of the present embodiment. The base station received signal (FIG. 8A), digital signal processing (FIG. 8B), and receiving circuit The digital signal ((c) of FIG. 8) input to 2 is also shown on the same time axis. This embodiment is different from the embodiment of FIG. 7 in that the interval of the digital data to be output is increased in the digital calculation with respect to the interval of the input digital data. It is that. Even in such a case, it is possible to continue the digital operation of the batch processing even in the period (Tp) of the next section in which no signal is transmitted from the terminal station. Even if it enters, digital processing of this collective processing can be performed. Moreover, it is desirable to reset the digital operation after the reception of the signal from the terminal station in order to keep the operation of the digital signal processing unit stable. By the processing of this embodiment, it is possible to realize the subtraction calculation of the unnecessary radio noise from the radio signal transmitted from the terminal station with higher accuracy by the high-load digital calculation, and as a result, the signal from the terminal station of the base station is received. Sensitivity can be improved.

  Another embodiment of the present invention will be described with reference to FIGS. FIG. 9 is a diagram showing the configuration of another embodiment of the RFID base station according to the present invention. FIG. 10 is a diagram showing the time timing of digital processing performed by the base station of this embodiment. The base station received signal ((a) of FIG. 10) and the digital signal input to the receiving circuit 2 (( b)) is also shown on the same time axis. This embodiment is different from the embodiment of FIG. 1 in that the digital feedforward circuit 3 includes a local oscillator 9 and mixers 10 and 11. As a result, the output of the power distributor 8 and the output of the circulator 7 are frequency down-converted through the mixers 11 and 10, respectively, and the frequency | fc−fl | () lower than the output frequency fc of the original transmission circuit 1 is obtained. The signal of fl = local oscillator frequency) is input to the analog-to-digital converters 3 and 4.

  Since there is an inversely proportional relationship between the dynamic range of the analog-to-digital converter and the input analog frequency, according to this embodiment, the effective number of signals used for digital signal processing can be expanded. The accuracy can be increased, and as a result, there is an effect of increasing the effect of subtracting the radio noise mixed in the received wave.

  In addition, regarding the type of digital computation and the processing timing in the first section and the second section in the present embodiment (and each of the following embodiments), the same as described in the embodiments of FIGS. Needless to say, various processing patterns can be selected.

  Another embodiment of the present invention will be described with reference to FIGS. FIG. 11 is a diagram showing the configuration of another embodiment of the RFID base station according to the present invention. FIG. 12 is a diagram showing the time timing of digital processing performed by the base station of this embodiment. The base station received signal ((a) in FIG. 12) and the digital signal input to the receiving circuit 2 (( b)) is also shown on the same time axis. This embodiment is different from the embodiment of FIG. 1 in that the digital feedforward circuit 3 includes a power distributor 15 inserted between the power distributor 8 and the circulator 7, and the output of the power distributor 15 is an attenuator. 12 and the phase shifter 13 are negatively superimposed on the received wave from the antenna 6 obtained via the circulator 7 by the synthesizer 14 and become an analog input of the digital / analog converter 14.

  According to this embodiment, a part of the output of the transmission circuit 1 is used to reduce radio noise having the same frequency component as the output frequency of the transmission circuit 1, and the received wave from the antenna 6 is converted into the analog / digital converter 4. And 3 inputs. According to this embodiment, the amount of radio noise to be subtracted by digital signal processing can be reduced in advance, so that the accuracy of digital computation can be increased, and as a result, the effect of increasing the effect of subtracting radio noise mixed in the received wave There is.

  Another embodiment of the present invention will be described with reference to FIGS. FIG. 13 is a diagram showing the configuration of another embodiment of the RFID base station according to the present invention. FIG. 14 is a diagram showing the time timing of digital processing performed by the base station of this embodiment. The base station received signal ((a) of FIG. 14) and the digital signal input to the receiving circuit 2 (( b)) is also shown on the same time axis. The present embodiment is different from the embodiment of FIG. 11 in that the digital feedforward circuit 3 includes a local oscillator 9 and mixers 10 and 11. As a result, the output of the power distributor 8 and the output of the combiner 14 are frequency down-converted through the mixers 11 and 10, respectively, and the frequency | fc-fl | lower than the output frequency fc of the original transmission circuit 1 is obtained. The signal of (fl = local oscillator frequency) is input to the analog / digital converters 3 and 4.

  According to the present embodiment, by performing a kind of adjustment operation for reducing the power of the unnecessary radio noise in advance with respect to the received wave from the terminal station, this dynamic range requirement is alleviated, and the digital-analog converter It is possible to increase the frequency of application. This adjustment operation can be performed, for example, when the product is shipped. Further, since the amount of radio noise to be subtracted by digital signal processing can be reduced in advance, it is possible to increase the accuracy of digital computation, and as a result, there is an effect of increasing the effect of subtracting radio noise mixed in received waves.

  Another embodiment of the present invention will be described with reference to FIGS. FIG. 15 is a diagram showing the configuration of another embodiment of the RFID base station according to the present invention. FIG. 16 is a diagram showing the time timing of digital processing performed by the base station of this embodiment. The base station received signal ((a) of FIG. 16) and the digital signal input to the receiving circuit 2 (( b)) is also shown on the same time axis. This embodiment is different from the embodiment of FIG. 13 in that, in the digital feedforward circuit 3, the attenuator 12 and the phase shifter 13 of FIG. 13 are replaced with the variable attenuator 22 and the variable phase shifter 23, respectively. It is. Further, the detection units 20 and 21 respectively detect the outputs of the combiner 14 and the power distributor 8 by envelope detection, create a difference by the difference unit 24 using the result, and store the data in the memory table 26 in which data is written in advance. The comparison with this data is performed using the comparator 25, and a DC voltage necessary for changing the values of the variable attenuator 22 and the variable phase shifter 23 is supplied by the DC voltage control unit 27. Further, the memory table 26 realizes the state of the variable attenuator 22 and the variable phase shifter 23 that minimizes unnecessary radio noise having the same frequency component as the frequency transmitted by the transmission circuit 1 among the outputs of the synthesizer 14. Therefore, the applied DC voltage to both is stored corresponding to the outputs of the combiner 14 and the power distributor 8.

  According to the present embodiment, the amount of radio noise to be subtracted by digital signal processing in response to changes in external unnecessary radio noise due to temperature changes, aging, and external environment changes is determined in advance at the time of product shipment, etc. Since it can be reduced, the effect of the embodiment of FIGS.

  Another embodiment of the present invention will be described with reference to FIG. FIG. 17 is a diagram showing a system configuration example when there are a plurality of terminal stations in the RFID system including the RFID base station of the present invention. In this system, each terminal station has its own timer, and the transmission wave from the base station is directly modulated, and the transmission signal is sent back at a predetermined timing.

  In the example of FIG. 17, there is one base station 100 and three terminal stations 110, 120, and 130. The base station transmits the transmission wave 104 from the antenna 106 at the timing time t0. The terminal stations 110, 120, and 130 transmit radio waves including signal components to the base station at timing times t1, t2, and t3, respectively, and become the received waves 105 of the base station. In the base station, the signal at the timing time t0 becomes unnecessary radio noise and is subjected to a process of subtracting from the signals at the timing times t1, t2, and t3 by digital calculation. In the time timing example of the present embodiment, the transmission time timings of the signals of the terminal stations 110, 120, and 130 are not overlapped and can be discriminated, but if any of the transmission time timings coincides, these signals are discriminated. It becomes impossible.

  In order to solve this problem, the terminal station adopts a retransmission scheme in which signal transmission is repeated, and the retransmission time interval is unique to each terminal station. That is, each terminal station has a retransmission function that periodically repeats transmission of transmission waves (transmission signals), and the retransmission time interval is set in advance as a unique value that is different for each terminal station. The received signal discrimination unit of the base station is configured to be able to discriminate the transmission signals of all the terminal stations using the difference in retransmission time interval by repeatedly receiving periodic transmission signals from each terminal station. ing.

  By doing in this way, it is possible to distinguish all the transmitted signals of all the terminal stations at some time timing while repeating the retransmission. According to the present embodiment, the number of terminal stations that can be accommodated in the RFID system can be increased without complicating the configuration of the base station. Therefore, the service range of the system can be expanded or the services can be diversified. is there.

It is a figure which shows the structure of one Example of the RFID base station which becomes one Example of this invention. It is a figure which shows the specific structural example of the signal discrimination | determination part of FIG. 1A. It is a figure which shows the specific structural example of the digital signal processing part of FIG. 1A. It is a figure which shows the structural example of the RFID system to which this invention is applied. It is a flowchart of the process of the received signal in the digital feedforward circuit in a present Example. It is a figure which shows the time timing of the digital processing which the RFID base station of a present Example performs. It is a figure which shows the time timing of the digital processing which a base station performs in the 2nd Example of this invention. It is a flowchart of the process of the received signal in the digital feedforward circuit which becomes the 3rd Example of this invention. It is a figure which shows the time timing of the digital processing which a base station performs in the 3rd Example of this invention. It is a figure which shows the time timing of the digital processing which a base station performs in the 4th Example of this invention. It is a figure which shows the structural example of the RFID base station which becomes the 5th Example of this invention. It is a flowchart of the process of a received signal in the digital feedforward circuit of the 5th Example of this invention. It is a figure which shows the structural example of the RFID base station which becomes the 6th Example of this invention. It is a flowchart of the process of a received signal in the digital feedforward circuit of the 6th Example of this invention. It is a figure which shows the structural example of the RFID base station which becomes the 7th Example of this invention. It is a flowchart of the process of a received signal in the digital feedforward circuit of the 7th Example of this invention. It is a figure which shows the structural example of the RFID base station which becomes the 8th Example of this invention. It is a flowchart of the process of a received signal in the digital feedforward circuit of the 8th Example of this invention. It is a figure which shows the system configuration example when two or more terminal stations exist in the RFID system which comprises the RFID base station which becomes the 9th Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Transmission circuit, 2 ... Reception circuit, 3 ... Digital feedforward circuit, 4A, 4B ... Analog-digital converter, 5 ... Digital signal processing part, 6 ... Antenna, 7 ... Circulator, 8 ... Power divider, 9 ... Local transmitter, 10 ... mixer, 11 ... mixer, 12 ... attenuator, 13 ... phase shifter, 14 ... synthesizer, 15 ... power divider, 20 ... detector, 21 ... detector, 22 ... variable attenuator, DESCRIPTION OF SYMBOLS 23 ... Variable phase shifter, 24 ... Difference machine, 25 ... Comparator, 26 ... Memory table, 27 ... DC voltage control part, 50 ... Received signal discrimination | determination part, 51 ... Band pass filter, 52 ... Detection part, 53 ... Analog -Digital converter, 100 ... base station, 104 ... transmission wave, 105 ... reception wave, 106 ... base station antenna, 110 ... terminal station, 120 ... terminal station, 130 ... terminal station.

Claims (20)

Comprising an antenna, a transmission circuit, a reception circuit, and a circulator that couples either the transmission circuit or the reception circuit to the antenna;
A digital feedforward circuit is arranged between the transmission circuit, the reception circuit and the circulator,
The digital feedforward circuit includes a received signal determination unit and a digital signal processing unit,
The received signal determining unit has a function of detecting whether or not a received signal from a terminal station is included in a received wave on a time axis,
The digital signal processing unit performs a digital calculation for suppressing an unnecessary wave component superimposed on the reception wave, using the transmission wave generated by the transmission circuit as a reference signal, and outputs the result of the digital calculation to the reception circuit Has a function to communicate to
The RFID base station, wherein the digital signal processing unit performs the digital calculation and resets the digital calculation using information on the presence / absence of the reception signal detected by the reception signal determination unit. In claim 1,
After the base station receives the received wave from the terminal station, the transmission signal from the terminal station included in the received wave is supplied as a received signal to the receiving circuit of the base station at a predetermined time interval. Have
The received signal discriminating unit uses the time interval to periodically set a reception mode in which the received signal is included in the received wave and a non-reception mode in which the received signal is not included as one cycle. An RFID base station having a function of detecting a mode change. In claim 2,
The RFID base station, wherein the digital signal processing unit performs a digital calculation for suppressing the unnecessary wave component at least in the reception mode, and resets the digital calculation in the non-reception mode. In claim 1,
An RFID base station, wherein the digital operation for suppressing the unwanted wave component contained in the received wave is adaptive processing. In claim 1,
An RFID base station, wherein the digital calculation for suppressing unnecessary wave components included in the received wave is a batch process. In claim 1,
An RFID base station, wherein one of the digital operations is suppression of unnecessary wave components included in the received wave, and the other digital operation is a preparation operation for the digital operation. In claim 2,
The digital operation for suppressing the unwanted wave component included in the received wave is an adaptive process,
The RFID base station, wherein the digital operation starts in the reception mode of one cycle and ends in the non-reception mode of the next cycle. In claim 2,
The digital calculation for suppressing the unwanted wave component included in the received wave is a batch process,
The preparatory operation is performed in the non-reception mode of one period;
The RFID base station, wherein the digital calculation for suppressing the unnecessary wave component starts in the reception mode of one cycle and ends in the non-reception mode of the next cycle. In claim 2,
The digital calculation for suppressing the unwanted wave component included in the received wave is a batch process,
The digital calculation for suppressing the unwanted wave component included in the received wave starts in a mode in which the received signal is included, and the end of the digital calculation continues on the time axis and the reception An RFID base station, which ends in a mode of a next cycle in which no signal is included. In claim 1,
An RFID base station that performs a process of resetting a history of past received waves in a next period that continuously exists on the time axis and does not include the received signal. In claim 1,
The RFID base station, wherein the received signal determining unit includes a bandpass filter that detects whether or not a received signal is included in a transmission signal from a specific terminal station. In claim 1,
The digital feedforward circuit includes a local transmission circuit unit and a mixer, down-converts the transmission wave and the reception wave in an intermediate frequency band that is lower than both frequencies, and performs analog / digital conversion in the intermediate frequency band An RFID base station, wherein a digital signal is generated by a device and the digital operation is performed using the digital signal. In claim 1,
The digital feedforward circuit includes an analog feedforward circuit unit that uses the transmission wave as a reference signal and suppresses an unnecessary wave included in the reception wave having the same frequency component as the reference signal. RFID base station. In claim 1,
An RFID base station, wherein a carrier wave frequency of a transmission wave generated by the transmission circuit is equal to a carrier wave frequency of the reception wave. Consisting of a base station and at least one terminal station,
The base station
Comprising an antenna, a transmission circuit, a reception circuit, and a circulator that couples either the transmission circuit or the reception circuit to the antenna;
A digital feedforward circuit is arranged between the transmission circuit, the reception circuit and the circulator,
The digital feedforward circuit includes a received signal determination unit and a digital signal processing unit,
The received signal discriminating unit has a function of detecting whether or not a periodic transmission signal from the terminal station is included in the received wave on the time axis,
The digital signal processing unit performs a digital calculation for suppressing an unnecessary wave component superimposed on the reception wave, using the transmission wave generated by the transmission circuit as a reference signal, and outputs the result of the digital calculation to the reception circuit Has a function to communicate to
The RFID system, wherein the digital signal processing unit performs the digital operation and resets the digital operation using information on the presence / absence of the reception signal detected by the reception signal determination unit. In claim 15,
A plurality of the terminal stations,
Each terminal station has a retransmission function that periodically repeats transmission of the transmission signal,
The time interval of the retransmission is set in advance as a unique value that differs for each terminal station,
The reception signal determination unit of the base station can determine the transmission signals of all the terminal stations by using the difference in the retransmission time interval by repeatedly receiving the periodic transmission signal from the terminal station. An RFID system comprising: In claim 16,
Each of the terminal stations has a function of directly modulating a transmission wave from the base station and sending back the transmission signal. In claim 16,
The base station receives a reception wave from each terminal station until a transmission signal from the terminal station included in the reception wave is supplied as a reception signal to the reception circuit of the base station. Has a time interval,
The reception signal discriminating unit uses the time interval to set a reception mode in which the reception signal is included in a reception wave of each terminal station and a non-reception mode in which the reception signal is not included as one cycle. , Detect periodic mode changes,
An RFID system having a function of performing digital computation for suppressing unwanted wave components contained in the received wave in the reception mode and performing preparation computation for the digital computation in the non-reception mode. A method for transmitting and receiving signals in an RFID system comprising a base station and at least one terminal station,
The base station
Comprising an antenna, a transmission circuit, a reception circuit, and a circulator that couples either the transmission circuit or the reception circuit to the antenna;
A digital feedforward circuit is arranged between the transmission circuit, the reception circuit and the circulator,
The digital feedforward circuit includes a received signal determination unit and a digital signal processing unit,
The digital signal processing unit performs a digital calculation for suppressing an unnecessary wave component superimposed on a reception wave, using the transmission wave generated by the transmission circuit as a reference signal, and outputs the result of the digital calculation to the reception circuit. Has a function to communicate,
In the received signal discriminating unit, on the time axis, it is detected whether or not the received wave contains a periodic transmission signal from the terminal station,
A signal transmission / reception method in an RFID system, wherein the digital calculation is performed in the digital signal processing unit using information on presence / absence of the reception signal included in the reception wave. In claim 19,
A plurality of the terminal stations,
Each terminal station has a retransmission function that periodically repeats transmission of the transmission signal,
The time interval of the retransmission is set in advance as a unique value that differs for each terminal station,
Each terminal station directly modulates the transmission wave from the base station and sends back the transmission signal,
In the reception signal determination unit of the base station, by repeatedly receiving the transmission signal from the terminal station, the transmission signal of all the terminal stations is determined using the difference in the retransmission time interval,
A signal transmission / reception method in an RFID system, wherein, in the digital signal processing unit, the digital calculation and the digital calculation are reset by using the determined presence / absence of the transmission signal from the terminal station .

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