JP2009033486A - Radio communications equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio communications equipment capable of reducing consumed power to the utmost, without impairing responsiveness. <P>SOLUTION: The radio communications equipment include a plurality of antennas 7 for communicating a wireless tag; an antenna switching part 6 for selecting and switching one antenna 7 from among the plurality of the antennas 7; a sensor 14 for detecting a reading object and detecting the distance between it and the reading object; an antenna information part 16a for associating any one antenna 7 among the plurality of the antennas 7 as a predetermined antenna 7 corresponding to its distance, based on the distance which the sensor 14 detects; and a control part 13 for communicating with the wireless tag, by switching the antennas by the antenna switching part 6, referring to the antenna information part 16a based on the distance detected by the sensor 14. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention is a wireless communication device that sends a transmission signal to a wireless tag or the like, receives a response signal, and decodes the response signal. The wireless communication device transmits a suitable power regardless of the distance from the wireless tag or the like to perform communication. The present invention relates to a wireless communication device that can be used.

  In recent years, non-contact wireless tags such as RFID (Radio Frequency Identity) tags have attracted attention. And it is expected that the RFID tag and the like will be affixed to any article in the future and distributed. For this reason, the request | requirement with respect to radio | wireless communication apparatuses, such as a reader-writer apparatus which communicates with an RFID tag non-contactingly, is growing further.

  As a communication method between the RFID tag and the wireless communication device, there are communication methods as follows. The first type is a communication system using electromagnetic induction. There are also two types of electromagnetic induction methods. The frequency used is 400 kHz to 530 kHz, the degree of electromagnetic coupling is high, and communication is performed mainly by mutual induction / electromagnetic induction between the RFID tag coil and the reader coil. Alternatively, there are those that use electromagnetic waves of 13.56 MHz, have a relatively low degree of electromagnetic coupling, and communicate using an induced voltage between both coils.

  On the other hand, there is a radio wave system as a second type. A microwave radiated from an antenna of a wireless communication apparatus is received by a plane wave antenna of an RFID tag, and data is transmitted using the reflected wave. There are also two types of microwave systems: a system that communicates using 2.45 GHz microwaves and a system that communicates using radio waves in the UHF (860 MHz to 960 MHz) band. The former communication distance is about 1 m at the maximum, but the latter communication distance is relatively long and about 8 m at the maximum.

  Now, when communicating by the latter second type radio wave system, the wireless communication device performs automatic gain control based on RSSI (Received Signal Strength Indication) indicating the received electric field strength. In a wireless communication device for a passive wireless tag, the wireless communication device must continue to transmit a question signal so that communication can be performed whenever the wireless tag enters the communication area. If the electric field strength of the interrogation signal is increased, the communicable distance between the wireless communication device and the wireless tag can be increased. However, the electric field strength of the interrogation signal is made larger than the value specified by the Radio Law. It is not possible. Therefore, although there is a limitation on the transmission electric field intensity, it is necessary to communicate with a distance as long as possible, and it is necessary to continuously emit radio waves so that communication can be performed at any time.

  For this reason, the wireless communication apparatus consumes a considerable amount of power even in a standby state, and a reduction in power consumption is required. However, reducing the output power means that the power level for operating the passive wireless tag is lowered, which includes a contradiction that the communication distance becomes short and communication becomes impossible. Therefore, a wireless communication apparatus has been proposed that can maintain the communication distance as usual and can reduce power consumption without impairing responsiveness (see, for example, Patent Document 1).

  This is provided with a control circuit for setting the antenna output power of the interrogation signal of the wireless communication apparatus as follows according to the state when the response signal is received or not received from the wireless tag. That is, (1) When the response signal from the wireless tag is not received, the antenna output power of the interrogation radio wave is alternately output at two predetermined power intervals at predetermined time intervals, and (2) the response from the wireless tag When a signal is received, it continues to be set to a strong power necessary for the transmission / reception of the identification information, and when the transmission / reception of the identification information is completed, the output power is reduced by half.

  However, the wireless communication device of (Patent Document 1) continues to supply strong power during a period required for transmission / reception of identification information only when a response signal is received, and always uses two types of power at the time of non-reception. Must be supplied. Although the wireless tag is not in the communication area, the power consumption cannot be sufficiently reduced if such power must be constantly supplied although it is two types of strength and weakness. The greatest reduction in power consumption is not to emit radio waves from the antenna when not in use.

  That is, in the case of a wireless communication apparatus that includes a plurality of antennas and switches by detection of a sensor, if only the antenna at the position where the sensor detects a person can communicate with the person's wireless tag, power consumption can be reduced (for example, Patent Document 2). However, the output of the wireless communication apparatus of (Patent Document 2) becomes large because it is necessary to normally perform communication after detecting a person (for example, Patent Document 3). Therefore, (Patent Document 3) determines an antenna and an output to be used in association with a region where a person is detected.

  In addition, it is inappropriate to simply reduce the output without considering the communication environment as in the wireless communication device of (Patent Document 1). This is because RSSI depends on the quality of the radio wave environment. It is reasonable to increase this if the RSSI is appropriate and it is determined that it is necessary to increase the transmission power when retrying. And the technique of measuring the distance between objects with a sensor is conventionally known (for example, patent documents 4).

  The reception request for the reception power level is transmitted to the wireless tag, the wireless tag notifies the wireless communication device of the reception power level, and the wireless communication device transmits the transmission power to the wireless tag according to the notified reception power level. A system for adjusting the level has also been proposed (Patent Document 5).

That is, when the wireless communication apparatus determines that the received power level notified from the wireless tag is lower than an appropriate level, the wireless communication apparatus adjusts the transmission power level to be larger, and conversely, the notified received power level. When it is determined that the level is higher than an appropriate level, the transmission power level is made smaller.
JP 2000-009654 A JP 2000-020648 A JP 2006-268695 A JP 2001-074855 A JP 2003-008481 A

  As described above, the wireless communication apparatus performs automatic gain control based on RSSI. However, as in the wireless communication device of (Patent Document 1), when there is no response signal from the wireless tag, the interrogation radio wave is alternately output at two predetermined power intervals at predetermined time intervals, When there is a response signal, continuing to supply power for the period required to send and receive identification information means that such power must be supplied at all times, even if the wireless tag is not in the communication area, This cannot reduce power consumption. Also, it is not effective to reduce the output uniformly without considering the radio wave condition.

  Further, as in (Patent Document 2), if only the antenna designated by the sensor detecting a person can communicate with the wireless tag of this person, it is possible to reduce power consumption, but (Patent Document 2). Since the wireless communication apparatus performs communication at a normal level after detecting a person, the output is still large when viewed in total. Moreover, when the output is reduced uniformly only by the position of the person as in (Patent Document 3), the radio wave condition is overlooked.

  If possible, it is desirable to cut off the power supply by radio waves when the wireless tag is not present in the area, and the power is increased when it is determined that the RSSI is within an appropriate range and the output can be increased within this range. Is reasonable. If it is possible to switch to the best antenna among a plurality of antennas as necessary, there is a possibility that even if communication with one antenna cannot be performed with the same power, communication with a wireless tag can be performed with another antenna. In addition, even if the distance sensor itself is conventionally known as in (Patent Document 4), it has nothing to do with reducing power consumption.

  Also, as in the wireless communication device of (Patent Document 5), a notification request for the received power level is transmitted to the wireless tag, and the wireless tag is notified of the received power level from the wireless tag. There is also a conventional wireless communication apparatus that adjusts the transmission power level according to the received power level. However, a notification request and a response of a reception power level notification request and a reception power level notification are required, and power is separately consumed for this communication. If possible, it is desirable that the transmission power level can be adjusted and the antenna can be switched only by the wireless communication device.

  Therefore, the present invention has been made in view of such circumstances, and an object thereof is to provide a wireless communication apparatus that can reduce power consumption as much as possible without impairing responsiveness.

  In order to solve such a problem, the wireless communication apparatus of the present invention transmits a transmission signal to a wireless tag that can move together with a reading target, receives a response signal from the wireless tag, A wireless communication device that reads information stored in the wireless tag, and a plurality of antennas for communicating with the wireless tag, an antenna selection unit that selects and switches one antenna from the plurality of antennas, A sensor for detecting a reading target and detecting a distance to the reading target, and any one of the plurality of antennas as a predetermined antenna corresponding to the distance according to the distance detected by the sensor Based on the antenna information part for matching and the distance detected by the sensor, the antenna selecting part refers to the antenna information part and the antenna is selected by the antenna selecting part. Switching, and major further comprising a control unit which communicates with the RFID tag.

  According to the wireless communication apparatus of the present invention, power consumption can be reduced as much as possible without impairing responsiveness.

  In order to solve the above-mentioned problem, a first invention of the present invention transmits a transmission signal to a wireless tag that can move together with a reading object, receives a response signal from the wireless tag, and wireless tags in the response signal A wireless communication device that reads information stored in the wireless tag, a plurality of antennas for communicating with the wireless tag, an antenna selection unit that selects and switches one antenna from the plurality of antennas, and a reading target A sensor for detecting a distance to the reading object, and an antenna information unit for associating any one of a plurality of antennas as a predetermined antenna corresponding to the distance according to the distance detected by the sensor; Based on the distance detected by the sensor, with reference to the antenna information unit, the antenna selection unit switches the antenna and communicates with the wireless tag. Is a wireless communication apparatus characterized. With this configuration, power consumption can be reduced as much as possible without impairing responsiveness.

  A second invention of the present invention is an invention subordinate to the first invention, wherein when the sensor detects the reading object and detects the distance to the reading object, the control unit uses transmission power corresponding to the distance. A wireless communication apparatus is characterized by transmitting. With this configuration, when a reading target is detected, a transmission signal can be transmitted with the minimum power consumption scheduled for this distance.

  A third invention of the present invention is an invention dependent on the first or second invention, wherein a response signal is received from the wireless tag when the sensor detects the reading object and detects the distance to the reading object. When it is impossible, the wireless communication apparatus is characterized in that the control unit increases the transmission power. With this configuration, when the reading target is detected and the response signal cannot be received, the transmission power is increased, so that the transmission signal can be transmitted with the minimum power consumption.

  A fourth invention of the present invention is an invention dependent on any one of the first to third inventions, comprising an electric field level detection unit for detecting a received electric field strength of a response signal, and the control unit detects the electric field level. The wireless communication apparatus is characterized in that the reception gain and transmission power are adjusted based on the received electric field strength detected by the unit. With this configuration, transmission and reception can be performed with minimum power consumption without impairing responsiveness.

  A fifth invention of the present invention is an invention dependent on the fourth invention, and when the response error rate of the wireless tag is equal to or less than a threshold value, the control unit repeats the transmission signal until one round of transmission is completed. If the response error rate exceeds the threshold, the control unit increases the transmission power and repeats transmission until one round of transmission is completed. If there is no response signal of the wireless tag, the control unit The wireless communication device is characterized in that a sensor detects a reading target and a distance from the reading target. With this configuration, the transmission power is increased only when the response error rate is bad, and when there is no response signal, the object to be read is detected again. Therefore, transmission / reception can be performed with minimum power consumption without impairing the responsiveness.

  A sixth invention of the present invention is an invention dependent on the first or second invention, wherein the control unit transmits to the wireless tag when a response signal cannot be received from the wireless tag even if the reading object is detected by the sensor. The wireless communication apparatus is characterized in that a transmission signal to be transmitted is stopped. With this configuration, leakage electromagnetic waves radiated from the wireless communication device can be minimized.

  A seventh invention of the present invention is an invention dependent on the first invention, and is a setting for setting any one of a plurality of antennas as a predetermined antenna corresponding to the distance detected by the sensor A wireless communication apparatus characterized in that a unit is provided. With this configuration, a condition for determining an antenna to be selected by the user can be set, and an antenna associated with this condition can be set as a default antenna.

(Embodiment 1)
A radio communication apparatus according to Embodiment 1 of the present invention will be described. The wireless communication apparatus according to Embodiment 1 is a reader / writer apparatus that communicates with a communication target such as an RFID tag by radio waves, and is a wireless apparatus that includes a duplexer. FIG. 1 is an overall configuration diagram of a wireless communication apparatus according to Embodiment 1 of the present invention, FIG. 2 is a format explanatory diagram of a response signal from a wireless tag to the wireless communication apparatus according to Embodiment 1 of the present invention, and FIG. FIG. 3 is an explanatory diagram when there is no response to the read request from the wireless communication apparatus according to the first embodiment of the present invention, and FIG. 3B is an explanatory diagram when there is a response to the read request of FIG. FIG. 3C is an explanatory diagram when a low level response and a high level response are mixed with respect to the read request of FIG. 3B, and FIG. 4 is a wireless communication device and a wireless tag according to Embodiment 1 of the present invention. It is a flowchart of communication with.

  First, the structure of the main part which comprises the radio | wireless communication apparatus of Embodiment 1 is demonstrated based on FIG. In FIG. 1, reference numeral 1 denotes a transmission signal generator that generates a baseband signal such as a read request toward a passive wireless tag such as an RFID tag. 2 is a modulation unit (orthogonal modulation unit) that orthogonally modulates the baseband signal generated by the transmission signal generation unit 1 using an ASK (Amplitude shift keying) method or the like, and 3 is a predetermined frequency (860 MHz˜ This is a carrier generation unit that generates a local oscillation signal (carrier wave) of 960 MHz UHF band), for example, 900 MHz. This is composed of a local oscillator circuit (Local Oscillator) or the like. Furthermore, 4 is a variable power amplifier (Power Amplifier) that amplifies a transmission signal in which the local oscillation signal and the baseband signal are modulated by the ASK method.

  Reference numeral 5 denotes a transmission / reception shared unit that transmits a transmission signal only to the antenna side and transmits a reception signal only to a reception system circuit. Reference numeral 6 denotes an antenna that selects one of a plurality of provided antennas based on an input from a sensor 14 described later. A switching unit (antenna selection unit of the present invention) and 7 are a plurality of antennas that perform radio communication with a radio tag at a frequency in the UHF band. Therefore, the antenna 7 of Embodiment 1 is a planar antenna. The transmission signal from the transmission system circuit is output to the antenna 7 side, but does not wrap around the reception system circuit described later from the transmission / reception shared unit 5, and conversely, the reception signal received by the antenna 7 is transmitted / received. Does not sneak into the transmission system circuit.

  The transmission system circuit of the wireless communication apparatus that transmits a transmission signal from the antenna 7 has been described above. Next, the reception system circuit will be described. In FIG. 1, 8 is a low noise amplifying unit that receives a reflected wave as a response from the wireless tag and amplifies the received signal with low noise, and 9 is a demodulator that orthogonally demodulates the output that has been low noise amplified by the low noise amplifying unit 8. Part (orthogonal demodulator). In the demodulator 9, the local oscillation signal of the carrier wave generator 3 is input with the same phase as the received signal and with a phase shifted by 90 ° (π / 2) at the same time, and is mixed with the received signal from the antenna 7 to be orthogonal. Demodulated.

  Therefore, the demodulator 9 outputs two orthogonal signals of an I (In-phase) signal having the same phase as the received signal and a Q (Quadrature-phase) signal delayed by 90 ° from this. An automatic gain control unit 10 is a VGA (Variable Gain Amplifier) that amplifies the I signal and the Q signal, and 11 is an RSSI detection unit that detects a Received Signal Strength Indication (RSSI) indicating the received electric field strength.

  Reference numeral 12 denotes a signal decoding unit, a signal decoding unit, which can convert each signal of the I signal and Q signal whose gain is adjusted by the automatic gain control unit 10 into a digital signal and decode the response information returned from the wireless tag. 12 includes an arithmetic unit for synthesizing each of the I and Q signals and a decoding unit for decoding the response information from the wireless tag based on the output calculated here.

  Subsequently, in FIG. 1, 13 is a control unit that controls the system of the wireless communication device, and 14 is a reading target (14) that moves together with an object such as a pallet or container attached to a wireless tag, a forklift, or a person or other wireless tag. This is a sensor for detecting an object. The sensor 14 is a sensor that detects a distance using ultrasonic waves, electromagnetic waves, light, or the like, and a predetermined (predetermined) antenna 7 that is provided in plural or one and should be at the closest position can be selected. Reference numeral 15 denotes a distance detection unit that detects the distance to the reading object based on the signal detected by the sensor 14. The correspondence between the predetermined antenna 7 and the distance detected by the sensor 14 will be described later.

  Based on the distance information detected by the distance detection unit 15, the control unit 13 selects an antenna 7 that is determined to be closest to the wireless tag (calculation which selection condition is met). And a switching signal is sent to the antenna switching unit 6 based on the information of the selected antenna 7 to switch to one antenna 7. At the same time, the control unit 13 transmits a read request transmission signal from the antenna 7 to the wireless tag with power corresponding to the distance between the antenna 7 and the wireless tag.

  In FIG. 1, 16 is a memory unit for the control unit 13, and 16 a is an antenna information unit which is a reference table provided in the memory unit 16. The antenna information unit 16 a stores conditions for determining the antenna 7 according to the distance detected by the sensor 14, and the control unit 13 selects the antenna 7 based on the distance detected by the sensor 14. A calculation is performed, and the result and the condition are compared, and the predetermined antenna 7 is determined as the antenna 7 corresponding to the distance. Reference numeral 17 denotes a setting unit for setting a condition for determining the antenna 7 of the antenna information unit 16a and the antenna 7 associated therewith. With the setting from the setting unit 17, a condition for the user to determine the antenna 7 can be set, and one antenna 7 can be set as a predetermined antenna associated with this condition. A detailed description of this association will be given later.

  FIG. 2 shows a communication format of a response signal sent from the wireless tag to the wireless communication apparatus. Here, 21 is the preamble of this response signal. If the standard is the same, the preamble 21 has common data, and an SFD (Start Frame Delimiter) indicating that response data continues is placed after a field having a repetition of the same pattern in a plurality of octets. Reference numeral 22 denotes a data portion for storing response data, which stores a response request command for the wireless tag. Reference numeral 23 denotes a 16-bit CRC (Cyclic Redundancy Check) code having a bit width of 16 bits, 32 bits, 8 bits, 12 bits, and the like, and is used to detect whether an error has occurred in communication data by cyclic redundancy check. belongs to. Although the above description is about the response signal sent from the wireless tag to the wireless communication device, the communication format of the read request sent from the wireless communication device to the wireless tag is basically different only by the preamble 21 being different. There is no.

  As described above, the wireless communication apparatus according to the first embodiment can detect a reading target such as a person with the sensor 14 and simultaneously measure the distance to the reading target. Also, based on this information, the control unit 13 refers to the antenna information unit 16a, selects the antenna 7 that is related as being closest to the reading target, and depends on the distance detected from the antenna 7 The transmission signal is transmitted to the wireless tag with minimum power from the beginning. When a response signal is returned from the wireless tag, the RSSI detection unit 11 detects the RSSI. If the level is low, the power amplifier 4 is controlled to increase the transmission power gain of the transmission signal, and the automatic gain control unit 10 Increase the receiving gain. Conversely, if the RSSI is high, each is lowered.

  Further, in the wireless communication apparatus according to the first embodiment, (1) whether the preamble 21 of the response signal decoded by the signal decoding unit 12 is normal, and (2) whether the check by the CRC code is normal. Therefore, it is determined whether the communication state is normal or there are many errors. Only when both the conditions (1) and (2) are satisfied is normal, and other cases are determined as errors.

This will be described in detail. In order to ensure the quality of communication QoS between the wireless communication device and the wireless tag, what is the number of reading requests in one round (number of transmissions N = 2 ^Q (Q = 0 to 16))? If this is received, the wireless tag transmits a response signal, or designates the number of transmissions Q to perform communication. That is, in the case of Q = 1, the number of transmissions is N = 2 ¹ = 2 times in ^one round, and response signals are transmitted from the wireless tag up to twice in response to these two requests. In the case of Q = 2, N = 2 ² = 4 times in one round, N = 2 ³ = 8 times in the case of Q = 3, and N = 2 ⁴ = 16 times in the case of Q = 4. When the wireless tag can receive the communication frame specified by the transmission count Q, the wireless tag starts transmitting a response signal. However, all of the response signals sent in this way are not normal signals, and the response frame may be checked by the wireless communication device due to a change in the wireless environment and may be determined as an error.

  In the first embodiment, when both of the conditions (1) and (2) are satisfied, it is determined that the normal response signal has been received (communication success), and when only (1) is satisfied or when only (2) is satisfied, Alternatively, if both (1) and (2) are not satisfied, it is determined that there is an error (communication failure). When the error ratio E / N (response error rate of the present invention), which is the ratio of the number of errors E to the number N of transmissions, is, for example, E / N ≦ 0.5 (50% in terms of%) The control unit 13 according to the first embodiment controls the power amplifier 4 to increase the gain of the transmission power of the transmission signal. The threshold of the error ratio E / N is set to 0.5 (50%) or the like in advance, or the threshold is determined from the number N of transmission requests of one round of read requests and the error ratio E / N ≦ 0.5 (50%). The error count E may be set directly.

  However, in the above description, the case where the above (1) and (2) are satisfied at the same time is determined as reception of a normal response signal. However, if only (1) is satisfied, it is determined as normal or only (2) is satisfied. It may be determined as normal. It can be easily determined.

  As described above, in the first embodiment, RSSI is detected by the action of the RSSI detection unit 11 to adjust the gain of the transmission power and the reception gain of the automatic gain control unit 10, and the error ratio of the response signal is 0. When it becomes less than 5 (50%), the gain of the transmission power is adjusted. As a result, transmission power can be minimized. If the RSSI and the error rate are not improved by the above gain adjustment, the control unit 13 switches the antenna 7 that is determined to be closest, switches to the adjacent antenna 7 with reference to the sensor information, and repeats this.

  FIG. 3A shows a case where there is no response from the wireless tag in response to the reading request from the wireless communication apparatus. On the other hand, FIG. 3B shows a case where there are three responses from the wireless tag to the read request. In FIG. 3 (c), there are three responses from the wireless tag, but a response with a low RSSI level (below a predetermined threshold) is once and a relatively high level response is mixed. Is shown. These are cases where the gain adjustment of the transmission power is performed in response to this result.

  Next, a wireless tag communication flowchart executed by the wireless communication apparatus according to the first embodiment will be described. In FIG. 4, when a reading target such as a person carrying a wireless tag or an object with a wireless tag attached enters the reading area (step 1), the sensor 14 which is a distance sensor detects the distance from the reading target. (Step 2).

  Next, in this detection operation, it is determined whether or not there is a reading target such as a human or an object with a wireless tag attached (step 3). If this reading target does not exist, the process ends. However, when there is an object to be read at step 3, the control unit 13 controls the antenna switching unit 6 to select the predetermined antenna 7 of the antenna information unit 16a set as the antenna 7 closest to the object to be read (step 4). ).

  Subsequently, the control unit 13 selects transmission power (power level) corresponding to the distance between the antenna 7 and the reading target and performs gain adjustment of the power amplification unit 4 (step 5). As a result, communication with minimum electric power is possible from the beginning. In this gain adjustment state, a transmission signal (read request command) is transmitted (step 6). On the other hand, it is determined whether or not a response signal from the wireless tag is detected (step 7). If a wireless tag is not detected in this determination, the transmission power level is increased (step 8), and the process returns to step 6. If a wireless tag is detected in this determination, it is determined whether the RSSI level is appropriate. (Step 9).

  If the RSSI level is not appropriate in step 9, the reception gain and transmission power gain adjustment is performed from the next transmission round, and the process returns to step 6. If the RSSI level is appropriate, the error rate is equal to or less than a predetermined threshold. Is determined (step 11). If this error rate is equal to or less than a predetermined threshold, the communication round is repeated by returning to step 6 as a normal communication state. In step 11, if the error rate exceeds a predetermined threshold, it is abnormal as a communication state, and it is determined whether or not a wireless tag is present (step 12). Even if there is one response signal, the wireless tag is present. If so, the level of transmission power is increased (step 13), and the process returns to step 6.

  If it is determined in step 12 that there is no response signal and no wireless tag is present, the process returns to step 2, and the sensor 4 detects the distance from the reading target again. If the reading object is not detected in this second detection, the transmission of the transmission signal is terminated. When the reading target is detected, step 4 to step 13 are repeated, and the transmission of the transmission signal is ended when the reading target is finally not detected.

  If the sensor 14 detects that the reading target exists but the wireless tag is not detected in step 7, the transmission power level is increased up to several rounds. Power stop control is performed. Thereby, leakage electromagnetic waves (EMF) emitted from the wireless communication device can be minimized.

  Now, sensor arrangement and antenna selection of the wireless communication apparatus according to Embodiment 1 of the present invention will be described. FIG. 5A is an explanatory diagram when a plurality of antennas of the wireless communication apparatus according to Embodiment 1 of the present invention are arranged on the upper side surface of the reading object and one sensor is provided for distance detection, and FIG. FIG. 6 is an explanatory diagram when distance detection is performed by arranging a plurality of antennas of the wireless communication apparatus according to the first embodiment of the present invention on the upper side surface of the reading target and two sensors facing each other on the side surface, FIG. FIG. 7 is an explanatory diagram when distance detection is performed by arranging a plurality of antennas of the wireless communication device in Embodiment 1 in a row on the upper surface of a reading target and arranging two sensors facing each other on the side surface, FIG. 2 is an explanatory diagram when a plurality of antennas of the wireless communication device in FIG. 1 are arranged on the upper and lower surfaces of a reading target, and two sensors are arranged opposite to each other to perform distance detection.

  FIG. 5A shows one cross section in the case where a person who brings a wireless tag as a reading target advances along a passage. The antennas (1) and (4) are provided on the side of the traveling person, and the antennas (2) and (3) are arranged side by side on the ceiling. Among these, the antenna (2) is disposed near the antenna (1), and the antenna (3) is disposed near the antenna (4). The sensor (1) is arranged near the antenna (1) on the side of the person so as to detect the distance to the person in parallel along the floor and the ceiling.

  When a wireless tag is placed between the antenna (1) and the antenna (2) and the distance from the sensor (1) at this time is a distance A, the antenna is located at a distance A = a located near the center of both. This is the position where the RSSI received at (1) and the RSSI received at the antenna (2) are reversed. This is larger than the RSSI received by the antennas (3) and (4) at the same time. Accordingly, the control unit 13 of the wireless communication apparatus selects the antenna (1) by controlling the antenna switching unit 6 when the condition of A <a is satisfied. The boundary value may be set to either one.

  What is received by the antenna (2) is that when the RSSI received by the antenna (2) is compared with the RSSI received by the antenna (3), the antenna (2) has a larger RSSI than the antenna (3). Up to A = b shown. Note that this should be stronger than the RSSI received at the antenna (4) at the same time. Therefore, when the condition of a <A <b is satisfied, the control unit 13 controls the antenna switching unit 6 to select the antenna (2).

  Similarly, what is received by the antenna (3) is that when the RSSI received by the antenna (3) is compared with the received radio wave intensity received by the antenna (4), the antenna (3) is better than the antenna (4). Up to A = c where RSSI becomes stronger. Accordingly, when the condition b <A <c is satisfied, the control unit 13 controls the antenna switching unit 6 to select the antenna (3).

  Finally, the antenna (4) receives from the distance A = c at which the antenna (4) has a stronger received radio wave intensity than the antenna (3) to the distance A = d indicating the position of the antenna (4). . Therefore, when the condition of c <A <d is satisfied, the control unit 13 controls the antenna switching unit 6 to select the antenna (4).

  In this way, the wireless communication apparatus detects the reading object such as a person with the sensor 14 and measures the distance to the object. Further, based on the distance information, the above condition is determined, and the control unit 13 selects the antenna 7 that is related to the position that should be closest to the reading target. Since the distance detected from the antenna 7 is known, the transmission signal is transmitted to the wireless tag with the minimum power corresponding to the distance. Further, when a response signal is returned from the wireless tag, the RSSI detection unit 11 detects RSSI. If the response signal is low, the power amplifier 4 is controlled to increase the transmission power gain of the transmission signal, and the automatic gain control unit 10 receives the signal. Increase the gain. Conversely, if the RSSI is high, each is lowered. Thereafter, when the person advances and the sensor information changes, the wireless communication apparatus switches the antenna based on the sensor information acquired by another sensor 14.

  Next, based on FIG. 5B, a description will be given of a case where a plurality of antennas are arranged side by side on the upper side surface of the reading target and only two sensors are arranged opposite to each other to perform distance detection. Antennas (1) and (4) are provided on the side of a person, and antennas (2) and (3) are arranged side by side on the ceiling. The antenna (2) is disposed near the antenna (1), and the antenna (3) is disposed near the antenna (4). The sensor (1) is arranged near the antenna (1) on the person's side so that it can detect the distance between the person along the floor and the ceiling, and the sensor (2) is near the antenna (4) on the person's side. The sensor (1) is disposed so as to be able to detect the distance between the person along the floor and the ceiling.

  In this case, the antenna (1), (2), (3), (4) is selected based on the difference between the distance A from the sensor (1) to the person and the distance B from the sensor (2). I do. When the distance A is larger than the distance B as shown in the upper side of FIG. 5B, AB> 0, and it is a problem whether to transmit / receive with the antenna (1) or the antenna (2). Since the antennas (1) and (2) have directivity and the like, respectively, when A−B <a, the control unit 13 controls the antenna switching unit 6 to select the antenna (1). Similarly, when a <A−B <b is satisfied, the control unit 13 causes the antenna (2) to be selected.

  When the distance A is smaller than the distance B as in the lower side of FIG. 5B, A−B <0, and it is a problem whether to transmit / receive with the antenna (3) or the antenna (4). However, since the antennas (3) and (4) also have directivity, etc., when d <A−B <c, the control unit 13 controls the antenna switching unit 6 to select the antenna (3). . c is a neighborhood value of 0. Similarly, when A−B <d is satisfied, the control unit 13 selects the antenna (4). Note that the specific positions of the antennas (1), (2), (3), and (4) shown in FIG. 5 (b) are merely examples, and in short, the distance information A for each sensor. When -B is acquired, distance information to be selected for each antenna is determined and is associated with one to one.

  As described above, even when the two sensors are arranged so as to face each other and the distance is detected, the wireless communication device detects a reading target such as a person with the sensor 14 and measures the distance to the target. Further, based on the distance information, the above condition is determined, and the control unit 13 selects the antenna 7 that is closest to the reading target. Then, the transmission signal is transmitted to the wireless tag with the minimum power corresponding to the distance detected from the antenna 7. Further, when a response signal is returned from the wireless tag, the RSSI detection unit 11 detects RSSI, and if the level is low, the power amplifier 4 is controlled to increase the transmission power gain of the transmission signal, and the automatic gain control unit 10 Increase the receiving gain. If the RSSI level is high, each is lowered. Thereafter, when the person advances and the sensor information changes, the wireless communication apparatus switches another antenna based on the sensor information acquired by the other two sensors 14.

  Next, based on FIG. 6, a description will be given of a case where distance detection is performed by arranging a plurality of antennas in a line on the upper surface of the reading target and arranging two sensors on the side surfaces to face each other. In this case, only the antennas (1) and (4) described in FIG. 5B are arranged in a line on the ceiling, and the same as described above. When the distance information A-B is acquired by each sensor, distance information to be selected is determined for each antenna and is associated with one to one.

  Further, based on FIG. 7, a description will be given of a case where a plurality of antennas are arranged on the upper and lower surfaces of the reading target and two sensors are arranged opposite to each other on the upper and lower surfaces to perform distance detection. In this case, the direction information is acquired in addition to the distance, which is vector information. Therefore, the sensors (1) and (2) also acquire direction information. The description in this case is the same as that described with reference to FIG. 5B, but whether the reading target is detected on the left half surface across the sensors (1) and (2), or is this detected on the right half surface? , And then whether to select the antennas (1) and (2) or the antennas (3) and (4) according to the distance information.

  As described above, according to the wireless communication apparatus of Embodiment 1 of the present invention, power consumption can be reduced as much as possible without impairing responsiveness. When the reading target is detected, the transmission signal can be transmitted with the planned minimum power consumption corresponding to this distance. When the reading target is detected and the response signal cannot be received, the transmission power is increased. A transmission signal can be transmitted with limited power consumption. In addition, leakage electromagnetic waves radiated from the wireless communication device can be minimized, conditions for determining an antenna to be selected by the user can be set, and an antenna associated with this condition is set as a default antenna. be able to.

  The present invention can be applied to a wireless communication device such as a reader / writer device that wirelessly communicates with a wireless tag or the like.

1 is an overall configuration diagram of a wireless communication apparatus according to Embodiment 1 of the present invention. Format explanatory diagram of a response signal from a wireless tag for the wireless communication device according to the first embodiment of the present invention (A) Explanatory drawing when there is no response to the read request from the wireless communication apparatus in Embodiment 1 of the present invention, (b) Explanatory drawing when there is a response to the read request of (a), (C) Explanatory drawing when a low level response and a high level response are mixed with respect to the read request in (b) Flowchart of communication between wireless communication apparatus and wireless tag in Embodiment 1 of the present invention (A) Explanatory drawing when a plurality of antennas of the wireless communication apparatus according to Embodiment 1 of the present invention are arranged on the upper surface of the reading object and one sensor is provided for distance detection, (b) Implementation of the present invention Explanatory drawing when performing the distance detection by arranging a plurality of antennas of the wireless communication device in the form 1 on the upper side surface of the reading target and arranging two sensors facing the side surface. Explanatory drawing when distance detection is carried out by arranging a plurality of antennas of the wireless communication apparatus according to the first embodiment of the present invention in a line on the upper surface of the reading object and arranging two sensors facing each other on the side surface. Explanatory drawing when performing the distance detection by arranging a plurality of antennas of the wireless communication apparatus according to the first embodiment of the present invention on the upper and lower surfaces of the reading object and arranging two sensors on the upper and lower surfaces facing each other.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transmission signal generation part 2 Modulation part 3 Carrier wave generation part 4 Power amplifier 5 Transmission / reception sharing part 6 Antenna switching part 7 Antenna 8 Low noise amplification part 9 Demodulation part 10 Automatic gain control part 11 RSSI detection part 12 Signal decoding part 13 Control part 14 Sensor 15 Distance detection unit 16 Memory unit 16a Antenna information unit 17 Setting unit 21 Preamble 22 Data unit 23 CRC code

Claims (7)

A wireless communication device that transmits a transmission signal to a wireless tag that can move with a reading target, receives a response signal from the wireless tag, and reads information stored in the wireless tag in the response signal,
A plurality of antennas for communicating with the wireless tag;
An antenna selection unit for selecting and switching one antenna from the plurality of antennas;
A sensor for detecting the reading object and detecting a distance from the reading object;
An antenna information unit for associating any one of the plurality of antennas as a predetermined antenna corresponding to the distance according to the distance detected by the sensor;
A wireless communication apparatus comprising: a control unit configured to switch an antenna by the antenna selection unit with reference to the antenna information unit based on a distance detected by the sensor and to communicate with the wireless tag. The wireless communication apparatus according to claim 1, wherein when the sensor detects the reading target and detects a distance from the reading target, the control unit transmits with transmission power corresponding to the distance. 2. The control unit increases transmission power when the sensor detects the reading target and detects a distance from the reading target, when a response signal cannot be received from the wireless tag. Or the radio | wireless communication apparatus of 2. An electric field level detection unit that detects a reception electric field strength of the response signal, wherein the control unit adjusts reception gain and transmission power based on the reception electric field strength detected by the electric field level detection unit. Item 4. The wireless communication device according to any one of Items 1 to 3. When the response error rate of the wireless tag is less than or equal to a threshold, the control unit repeatedly transmits a transmission signal until one round of transmission ends, and when the response error rate exceeds the threshold, When the control unit increases the transmission power and repeats transmission until one round of transmission is completed, and there is no response signal of the wireless tag, the control unit detects the reading target and the reading target by the sensor. The wireless communication apparatus according to claim 4, wherein the distance is detected. 3. The wireless device according to claim 1, wherein the control unit stops a transmission signal transmitted to the wireless tag when a response signal cannot be received from the wireless tag even if the reading target is detected by the sensor. Communication device. The wireless communication apparatus according to claim 1, further comprising: a setting unit configured to set any one of the plurality of antennas as a predetermined antenna corresponding to a distance detected by the sensor.

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