JP2013097408A - Radio tag device, radio communication system and retransmission control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radio tag device for, when failing in communication with a radio reader device, setting appropriate priority in accordance with the number of following chances of retransmission, and for performing appropriate retransmission control on the basis of the priority.SOLUTION: A radio tag device 2 receives a reply request signal from a radio reader device 3, and measures the reception intensity, and determines the success/failure of communication with the radio reader device 3 in response to the reply request signal, and performs movement determination on the basis of the increase/decrease of the reception strength, and performs far-near determination by comparing the reception intensity with a threshold, and performs area determination on the basis of the determination result of the movement determination and the far-near determination. When failing in communication with the radio reader device 3, the radio tag device 2 controls a retransmission timing in accordance with priority (long range desorption: highest, short range desorption: high, short range approach: middle, long range approach: low) determined for each area on the basis of the determination result of the area determination.

Description

  The present invention relates to a wireless tag device having a function of performing retransmission control when communication with a wireless reader device fails.

  Conventionally, a sensor is installed on the side of an expressway, and sensor information (measurement data) measured by the sensor is recorded by a roadside unit installed in the vicinity of the sensor, and the vicinity is detected by an in-vehicle unit mounted on the vehicle. There has been proposed a system that collects sensor information from a roadside unit by wireless communication while traveling a vehicle while passing (see, for example, Patent Document 1). In this case, the in-vehicle unit corresponds to a wireless reader device, and the roadside unit corresponds to a wireless tag device.

  In such a system, a large number of sensors are installed along the highway. When a large number of wireless tag devices exist within the communicable area of the wireless reader device, response signals are transmitted from a plurality of wireless tag devices in response to response request signals (beacon signals) from the wireless reader device, and they collide ( Collision). When a collision occurs due to a response from the wireless tag device, one wireless tag device succeeds in communication with the wireless reader device, while another wireless tag device fails in communication with the wireless reader device. Become.

  When communication with the wireless reader device fails, generally, retransmission control is performed to retransmit the response signal (see, for example, Patent Document 2). For example, in a conventional retransmission control method, a wireless communication device (wireless reader device) randomly assigns a time slot corresponding to the number of transmission failures of a wireless terminal device (wireless tag device) and notifies the wireless tag device. In the wireless tag device, retransmission is performed in the time slot assigned by the wireless reader device.

JP 2010-117837 A JP 2009-218672 A

  However, in the conventional method, the main control of the retransmission control is performed on the wireless reader device side, and there is a problem that the processing on the wireless reader device side becomes heavy when the number of wireless tag devices increases.

  The speed of the vehicle traveling on the highway is high (for example, 80 km / h). When the wireless reader device moves at a high speed, the wireless tag device immediately goes out of the communicable area, so that the retransmittable period is short. However, when the retransmittable period is short, there is a problem that if the retransmission timing (time slot) is randomly assigned, the possibility of recollision increases.

  The fact that the wireless reader device moves at a high speed (the wireless tag device immediately goes out of the communicable area) can be said to have few opportunities for retransmission from the wireless tag device in the future. Nevertheless, there has been a problem that if re-collision occurs, it will result in missed opportunities.

  The present invention was made to solve the above-described conventional problems. When communication with the wireless reader device fails, an appropriate priority is set according to the number of future retransmission opportunities, and the priority is set. An object of the present invention is to provide a wireless tag device capable of performing appropriate retransmission control based on the degree.

  The wireless tag device according to the present invention transmits a response request signal transmitted from a wireless reader device, a reception intensity measurement unit that measures the reception intensity of the response request signal, and a response to the response request signal. A communication success / failure determination unit that determines whether or not a response signal is received by the wireless reader device and communication with the wireless reader device is successful, a reception strength of a previous response request signal, and a reception strength of a current response request signal Based on the movement determination unit for determining a movement when the reception strength is increasing, and determining a movement when the reception strength is decreasing, and a response determination signal for the current response Based on the received intensity, a perspective judgment is performed to determine a near distance when the received intensity is equal to or greater than a predetermined threshold, and to determine a far distance when the received intensity is less than the threshold. And area determination that determines whether the area belongs to a long-distance departure area, a short-distance departure area, a short-distance approach area, or a long-distance approach area based on the determination result of the movement determination and the perspective determination When it is determined that communication between the area determination unit and the wireless reader device has failed, the response signal is retransmitted according to the priority determined for each area based on the determination result of the area determination. A retransmission timing control unit for controlling a retransmission timing to be performed, wherein the priority of the long-distance departure area is the highest priority, and the priority of the short-distance departure area is lower than the first priority. The priority of the short-distance approach area is a third priority lower than the second priority, and the priority of the long-distance approach area is a fourth priority lower than the third priority. It has a configuration that.

  With this configuration, the movement determination and the perspective determination are performed based on the reception strength (for example, RSSI) of the response request signal from the wireless reader device, and the area to which the wireless tag device belongs is “long distance departure area”, “short distance departure area” It is determined whether it is “a short-distance approaching area” or “a long-distance approaching area”. If it is determined that communication with the wireless reader device has failed, the retransmission timing for retransmitting the response signal is controlled according to the priority determined for each area. For example, in the long-distance leaving area, the wireless reader device and the RFID tag device are at a long distance and are separated (distant) from each other, so there are few opportunities for future retransmission (coming soon out of the communicable area) Therefore, the highest priority (first priority) is set, and the response signal is retransmitted with the highest priority. In addition, the short-distance leaving area is considered to have the next few chances of retransmission next to the long-distance leaving area because the wireless reader device and the RFID tag device are located at a short distance but are separated from each other. Therefore, the second highest priority (second priority) is set. Furthermore, since the wireless reader device and the wireless tag device are close to each other and are close to each other in the short-distance approaching area, it is considered that there are more opportunities for retransmission than the short-distance leaving area. Set to priority (third priority). In the long-distance approach area, since the wireless reader device and the wireless tag device are at a long distance and are close to each other (approaching), there are most opportunities for future retransmissions (staying within the communicable area for a while) ), The lowest priority (fourth priority) is set. As described above, according to the present invention, an appropriate priority can be set on the wireless tag device side according to the number of future retransmission opportunities, and the retransmission timing is appropriately controlled based on the priority. be able to.

  In the wireless tag device of the present invention, the retransmission timing control unit has a configuration for controlling the retransmission timing of the response signal so that the higher the priority is, the larger the number of retransmissions per predetermined period is. .

  With this configuration, the retransmission timing of the response signal (retransmission control) is performed so that the higher the priority, the greater the number of retransmissions per predetermined period (for example, one frame). For example, when one frame is composed of two units (first unit and second unit) and one unit is composed of 45 subframes (first subframe to 45th subframe). Assume that communication with the wireless reader device has failed in the first unit. In that case, if it is a long distance departure area, the response signal is retransmitted in all 45 subframes (first subframe to 45th subframe) of the second unit, and if it is a short distance departure area, the second unit The response signal is retransmitted in 30 subframes (for example, the 16th subframe to the 45th subframe). If the area is a short-distance approach area, the response signal is retransmitted in 20 subframes (for example, the 26th to 45th subframes) of the second unit. The response signal is retransmitted in 10 subframes (for example, the 36th subframe to the 45th subframe). As described above, according to the present invention, it is possible to appropriately control the retransmission timing so that the number of retransmissions according to the number of retransmission opportunities in the future.

  In addition, the wireless tag device of the present invention is configured to transmit the response signal in advance at a timing before the retransmission timing determined by the retransmission timing control unit when it is determined that the distance is determined by the distance determination. It has the structure provided with the transmission control part.

  With this configuration, when it is determined that communication with the wireless reader device has failed, if it is determined that the distance is determined to be a long distance in the perspective determination, a response is received at a timing before the retransmission timing determined by the retransmission timing control unit. A signal is transmitted in advance. For example, when the wireless tag device passes so as to cover the edge (fringe) of the communicable area of the wireless reader device, there is the least chance of future retransmission (coming soon out of the communicable area). Conceivable. According to the present invention, in such a case, since the response signal is retransmitted in advance at a timing before the retransmission timing, the success rate of communication with the wireless reader device can be further increased.

  The retransmission control method of the present invention is a retransmission control method used in a wireless tag device, which receives a response request signal transmitted from a wireless reader device, measures the reception strength of the response request signal, and transmits the response request signal. A response signal transmitted as a response to the wireless reader device is received by the wireless reader device to determine whether or not the communication with the wireless reader device is successful, and the reception strength of the previous response request signal and the current response request signal Based on the above, when the reception strength is increased, it is determined as approaching, and when the reception strength is decreased, movement determination is performed to determine separation, and the reception strength of the current response request signal is determined. On the basis of this, when the reception strength is equal to or greater than a predetermined threshold, it is determined as a short distance, and when the reception strength is less than the threshold, a perspective determination is performed to determine a long distance. Based on the determination result of the perspective determination, an area determination is performed to determine which of the long-distance leaving area, the short-distance leaving area, the short-distance approaching area, and the long-distance approaching area, and communication with the wireless reader device If it is determined that the response signal has failed, the retransmission timing for retransmitting the response signal is controlled according to the priority determined for each area based on the determination result of the area determination. The priority of the distance leaving area is the highest first priority, the priority of the near distance leaving area is the second priority lower than the first priority, and the priority of the near distance approaching area is the first priority. The third priority is lower than the second priority, and the priority of the long-distance approaching area is the fourth priority lower than the third priority.

  Also in this method, as described above, an appropriate priority can be set on the wireless tag device side in accordance with the number of future retransmission opportunities, and the retransmission timing is appropriately controlled based on the priority. be able to.

  The wireless communication system of the present invention is a wireless communication system including a wireless tag device and a wireless reader device, wherein the wireless tag device receives a response request signal transmitted from the wireless reader device; A reception strength measurement unit that measures the reception strength of the response request signal, and a determination as to whether or not the response signal transmitted as a response to the response request signal is received by the wireless reader device and communication with the wireless reader device is successful Based on the communication success / failure determination unit and the reception strength of the previous response request signal and the reception strength of the current response request signal, if the reception strength is increased, it is determined as approaching and the reception strength decreases. If the reception strength is greater than or equal to a predetermined threshold based on the movement determination unit that performs a movement determination that determines that it is a detachment and the reception strength of the current response request signal A distance determination unit that determines a distance, and performs a distance determination to determine a long distance when the reception intensity is less than the threshold, and based on a determination result of the movement determination and the distance determination, a long distance departure area, When it is determined that communication between the area determination unit that performs area determination to determine which of the short-distance leaving area, the short-distance approaching area, and the long-distance approaching area and communication with the wireless reader device has failed, A retransmission timing control unit that controls a retransmission timing for retransmitting the response signal according to the priority determined for each area based on the determination result of the area determination, and the priority of the long-distance leaving area The priority is the highest first priority, the priority of the short distance departure area is the second priority lower than the first priority, and the priority of the short distance approach area is the second priority. A lower third priority, the priority of the far proximity area has a configuration which is lower fourth priority than the third priority.

  Also in this method, as described above, an appropriate priority can be set on the wireless tag device side in accordance with the number of future retransmission opportunities, and the retransmission timing is appropriately controlled based on the priority. be able to.

  The retransmission control method according to the present invention is a retransmission control method used in a wireless communication system, wherein a response request signal transmitted from a wireless reader device is received by a wireless tag device, and the response request signal of the wireless tag device is received by the wireless tag device. Measure the reception strength, determine whether or not the response signal transmitted as a response to the response request signal is accepted by the wireless reader device and the communication with the wireless reader device is successful, and the reception strength of the previous response request signal Based on the received strength of the response request signal and the current response request signal, when the received strength is increased, it is determined as approaching, and when the received strength is decreased, movement determination is performed to determine leaving. Based on the reception strength of the response request signal this time, when the reception strength is greater than or equal to a predetermined threshold, it is determined that the distance is short, and when the reception strength is less than the threshold, the long distance Based on the determination result of the movement determination and the perspective determination, it is determined whether it belongs to a long-distance departure area, a short-distance departure area, a short-distance approach area, or a long-distance approach area When the area determination is performed and it is determined that communication with the wireless reader device has failed, the response signal is determined according to the priority determined for each area based on the determination result of the area determination. Retransmission timing is controlled, and the priority of the long distance departure area is the highest first priority, and the priority of the short distance departure area is the second priority lower than the first priority. Yes, the priority of the short-distance approaching area is a third priority lower than the second priority, and the priority of the long-distance approaching area is a fourth priority lower than the third priority.

  Also in this method, as described above, an appropriate priority can be set on the wireless tag device side in accordance with the number of future retransmission opportunities, and the retransmission timing is appropriately controlled based on the priority. be able to.

  According to the present invention, when communication with the wireless reader device fails, an appropriate priority can be set according to the number of future retransmission opportunities, and appropriate retransmission control can be performed based on the priority. A wireless tag device having an effect can be provided.

The block diagram of the radio | wireless communications system in the 1st Embodiment of this invention Explanatory drawing of the radio | wireless communications system in the 1st Embodiment of this invention Explanatory drawing of four areas (long-distance approaching area, short-distance approaching area, short-distance leaving area, long-distance leaving area) and their priorities in the first embodiment of the present invention Explanatory drawing of a radio | wireless frame structure in the 1st Embodiment of this invention Sequence diagram for explaining retransmission control in the first embodiment of the present invention The block diagram of the radio | wireless communications system in the 2nd Embodiment of this invention Explanatory drawing of fringe passage in the second embodiment of the present invention Explanatory drawing of the radio | wireless frame structure in the 2nd Embodiment of this invention. The sequence diagram for demonstrating the prior transmission control in the 2nd Embodiment of this invention

  Hereinafter, a wireless tag device and a wireless communication system according to embodiments of the present invention will be described with reference to the drawings. In this embodiment, a case where the present invention is applied to a sensor network or the like for inspection and monitoring of a structure such as a highway is illustrated.

(First embodiment)
A configuration of the wireless tag device and the wireless communication system according to the first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of the wireless communication system of the present embodiment, and FIG. 2 is an explanatory diagram of the wireless communication system of the present embodiment. As shown in FIGS. 1 and 2, the wireless communication system 1 includes a wireless tag device 2 and a wireless reader device 3.

  The wireless tag device 2 is installed on the side of a highway or the like and connected to a sensor 4. Various sensors can be used as the sensor 4. As shown in FIG. 1, the wireless tag device 2 is provided with a sensor interface 5 (sensor I / F) to which measurement data is input from the sensor 4. The measurement data of the sensor 4 is stored in the storage unit 6 as untransmitted data until it is transmitted to the wireless reader device 3.

  The wireless tag device 2 includes a receiving unit 7 that receives a signal transmitted from the wireless reader device 3 and a transmitting unit 8 that transmits a signal to the wireless reader device 3. The reception unit 7 receives a response request signal (beacon signal) transmitted from the wireless reader device 3. From the transmission unit 8, a response signal (ACK signal) to the response request signal is transmitted. Data (received data) received by the receiving unit 7 is sent to the control unit 9.

  In addition, the wireless tag device 2 is provided with a reception strength measuring unit 10 that measures the received electric field strength (RSSI) when a beacon signal is received from the wireless reader device 3. The RSSI data measured by the reception intensity measurement unit 10 is sent to the control unit 9. Further, the RSSI data sent to the control unit 9 is sent to the storage unit 6 and stored therein.

  The control unit 9 is composed of, for example, a CPU and has a function of controlling the entire apparatus of the wireless tag device 2. The received data sent to the control unit 9 is sent to the communication success / failure determination unit 11. The communication success / failure determination unit 11 determines whether or not the ACK signal transmitted to the wireless reader device 3 as a response to the beacon signal has been received by the wireless reader device 3, that is, whether or not communication with the wireless reader device 3 has been successful. A function of determining based on received data is provided. When communication with the wireless reader device 3 is successful and transmission of untransmitted data stored in the storage unit 6 is completed, the untransmitted data is deleted from the storage unit 6.

  Further, the wireless tag device 2 includes a determination processing unit 12 that performs various determinations based on RSSI (movement determination, perspective determination, area determination). Here, these determinations will be described in detail with reference to FIG.

  As shown in FIG. 3, in the movement determination, when the RSSI is increased based on the RSSI (stored in the storage unit 6) of the beacon signal received previously and the RSSI of the beacon signal received this time, It determines with "approaching (approaching)", and when RSSI is decreasing, it determines with "leaving (distant)".

  In the perspective determination, the RSSI of the beacon signal received this time is compared with the threshold, and when the RSSI is equal to or greater than the threshold, it is determined as “near distance (near)”, and when the RSSI is less than the threshold, “ It is determined as “far (far)”.

  In the area determination, based on the determination result of the above movement determination and perspective determination, the tag device is any of “long distance departure area”, “short distance departure area”, “short distance approach area”, and “far distance approach area”. Determine if it belongs to the area. Priorities are set for these areas. In this case, “Long distance departure area: Highest (Immediately retransmit)” “Near distance departure area: High (Resend early)” “Near distance approach area: Middle (Slightly early retransmission)” “Long distance approach area: Low (slowly) "Resend") is set.

  Returning to FIG. 1, the description of the configuration of the wireless tag device 2 will be continued. The wireless tag device 2 includes a transmission timing control unit 13. The transmission timing control unit 13 has a function of determining a timing (in which time slot to transmit) an ACK signal for a beacon signal. The wireless tag device 2 includes a random number generator 14. The random number generator 14 generates a random number for performing random control. The transmission timing control is a random control in which a time slot for transmitting an ACK signal is randomly assigned based on the random number generated by the random number generation unit 14.

  Further, the transmission timing control unit 13 has a function of performing retransmission control for retransmitting an ACK signal according to the priority of the area based on the determination result of the area determination when the communication with the wireless reader device 3 fails. I have. In this case, the retransmission timing of the ACK signal is controlled so that the higher the priority is, the greater the number of retransmissions per frame period (retransmission frequency) is.

  Here, the control of the retransmission timing of the ACK signal will be described in detail with reference to FIG. FIG. 4 shows an example of a radio frame configuration. As shown in FIG. 4, for example, one frame is composed of two units (first unit and second unit), and one unit is composed of 45 subframes (first subframe to 45th subframe). It is assumed that n time slots are included in one frame.

  In this case, assuming that communication with the wireless reader device 3 has failed in the first unit, all 45 subframes (first subframe to 45th subframe) of the second unit are in the long-distance leaving area. The response signal is retransmitted, and if it is a short distance departure area, the response signal is retransmitted in 30 subframes (for example, the 16th subframe to the 45th subframe) of the second unit. If the area is a short-distance approach area, the response signal is retransmitted in 20 subframes (for example, the 26th to 45th subframes) of the second unit. The response signal is retransmitted in 10 subframes (for example, the 36th subframe to the 45th subframe).

  The wireless reader device 3 includes a transmission unit 15 that transmits a signal to the wireless tag device 2 and a reception unit 16 that receives a signal from the wireless tag device 2. A beacon signal or the like to the wireless tag device 2 is transmitted from the transmission unit 15. The receiving unit 16 receives an ACK signal transmitted from the wireless tag device 2. Data (received data) received by the receiving unit 16 is sent to the control unit 17. Further, the data sent to the control unit 17 is sent to the storage unit 18 and stored therein.

  The operation of the wireless communication system 1 configured as described above will be described with reference to the sequence diagram of FIG. Here, the retransmission control which is a characteristic operation of the present invention will be mainly described.

  As shown in FIG. 5, in the wireless communication system 1 of the present embodiment, first, a broadcast beacon is transmitted from the wireless reader device 3 to the wireless tag device 2 in the 0th time lot (TS0) of the first unit. In this case, it is assumed that two wireless tag devices 2 (tag A and tag B) exist in the communicable area of the wireless reader device 3. The broadcast beacon is received by the two wireless tag devices 2 (tag A and tag B), and the RSSI is measured by each of the wireless tag devices 2.

  Similarly, a broadcast beacon is transmitted from the wireless reader device 3 to the wireless tag device 2 also in the first time slot (TS1). This broadcast beacon is also received by each of the two wireless tag devices 2 (tag A and tag B), and RSSI is measured.

  In the second time slot (TS2), an ACK signal is transmitted as a response to the broadcast beacon from the two wireless tag devices 2 (tag A and tag B). In this case, since the ACK signal is transmitted from the two RFID tag apparatuses 2 at the same timing, a collision (collision) occurs when the ACK signal is received. The wireless reader device 3 receives only one ACK signal (ACK signal from tag A) and discards the other ACK signal (ACK signal from tag B).

  Then, in the third time slot (TS3), as a response to the ACK signal from the wireless tag device 2, a unicast beacon signal notifying that “communication with the tag A is successful” is transmitted from the wireless reader device 3. . Thereby, one wireless tag device 2 (tag A) recognizes that the communication with the wireless reader device 3 is successful, and the other wireless tag device 2 (tag B) communicates with the wireless reader device 3. Recognize the failure. The wireless tag device 2 (tag A) that has succeeded in communication with the wireless reader device 3 performs saving control to reduce power consumption.

  A broadcast beacon signal is transmitted from the wireless reader device 3 in the fifth time slot (TS5) and the seventh time slot (TS7). This beacon signal is received by the wireless tag device 2 (tag B) that is not subjected to saving control (communication with the wireless reader device 3 has failed), and RSSI is measured.

  Thereafter, the RFID tag device 2 (tag B) compares the RSSI of the broadcast beacon signal (the most recently received beacon signal) received at TS7 with a threshold value, and performs near / far determination, and also receives the broadcast beacon received at TS0. The movement determination based on the increase / decrease of RSSI is performed from the signal (beacon signal received first) and the broadcast beacon signal received by TS7 (beacon signal received most recently). Then, the area determination is performed based on the determination results of the perspective determination and the movement determination, and based on the determination result of the area determination, the retransmission timing according to the priority of the area (for example, the n-1th time of the second unit). Slot (TSn-1), etc.) is determined. Thereafter, the wireless tag device 2 (tag B) also performs saving control for suppressing power consumption.

  When the wireless tag device 2 (tag B) receives the broadcast beacon signal from the wireless reader device 3 in the n-2 time slot of the second unit, the wireless tag device 2 (tag B) uses the next n-1 time slot (TSn-1). The ACK signal is retransmitted to the wireless reader device 3. When the wireless reader device 3 receives the ACK signal from the wireless tag device 2 (tag B), the wireless reader device 3 transmits a unicast beacon signal notifying that “communication with the tag B was successful”. Thereby, the wireless tag device 2 (tag B) recognizes that the communication with the wireless reader device 3 is successful. The wireless tag device 2 (tag B) that has successfully communicated with the wireless reader device 3 performs a saving control for suppressing power consumption.

  According to the wireless tag device 2 of the first embodiment as described above, when communication with the wireless reader device 3 fails, an appropriate priority is set according to the number of future retransmission opportunities, Appropriate retransmission control can be performed based on the priority.

  That is, in the present embodiment, the movement determination and the distance determination are performed based on the RSSI of the beacon signal from the wireless reader device 3, and the area to which the wireless tag device 2 belongs is “long distance departure area” “short distance departure area”. It is determined whether it is a “short-distance approaching area” or a “far-distance approaching area”. If it is determined that the communication with the wireless reader device 3 has failed, the retransmission timing for retransmitting the ACK signal is controlled according to the priority determined for each area.

  For example, in the long-distance leaving area, the wireless reader device 3 and the wireless tag device 2 are “far away” and “separated” from each other (away from each other), so there are few opportunities for future retransmission (communication is possible soon) Therefore, the highest priority (first priority: highest) is set, and the response signal is retransmitted with the highest priority. In addition, since the wireless reader device 3 and the wireless tag device 2 are “near distance” in the short-distance leaving area, they are “separated” (distant) from each other. Since it is considered to be the next smallest, the next highest priority (second priority: high) is set. Further, in the short-distance approach area, the wireless reader device 3 and the wireless tag device 2 are “near-distance” and “close” to each other. Therefore, the next priority (third priority: medium) is set. In the long-distance approach area, the wireless reader device 3 and the wireless tag device 2 are “far” and are “close” to each other (approaching). Therefore, the lowest priority (fourth priority: low) is set.

  As described above, according to the wireless communication system 1 of the present embodiment, an appropriate priority can be set on the wireless tag device 2 side according to the number of future retransmission opportunities, and based on the priority. Thus, the retransmission timing can be appropriately controlled.

  Further, in this embodiment, control of retransmission timing of response signals (retransmission control) is performed such that the higher the priority, the greater the number of retransmissions per predetermined period (for example, one frame).

  For example, as shown in FIG. 4, one frame is composed of two units (first unit and second unit), and one unit includes 45 subframes (first subframe to 45th subframe). Suppose that communication with the wireless reader device 3 has failed in the first unit. In that case, if it is a long distance departure area, the response signal is retransmitted in all 45 subframes (first subframe to 45th subframe) of the second unit, and if it is a short distance departure area, the second unit The response signal is retransmitted in 30 subframes (for example, the 16th subframe to the 45th subframe). If the area is a short-distance approach area, the response signal is retransmitted in 20 subframes (for example, the 26th to 45th subframes) of the second unit. The response signal is retransmitted in 10 subframes (for example, the 36th subframe to the 45th subframe).

  As described above, according to the present embodiment, it is possible to appropriately control the retransmission timing so that the number of retransmissions (retransmission frequency) according to the number of retransmission opportunities in the future.

(Second Embodiment)
Next, the wireless tag device 2 according to the second embodiment of the present invention will be described. Here, the wireless tag device 2 according to the second embodiment will be described focusing on differences from the first embodiment. Unless otherwise specified, the configuration and operation of the present embodiment are the same as those of the first embodiment.

  FIG. 6 is a block diagram of the wireless communication system 1 according to the present embodiment. As shown in FIG. 6, a pre-transmission control unit 19 is added to the wireless tag device 2 of the present embodiment. The pre-transmission control unit 19 performs control to transmit an ACK signal to the wireless reader device 3 in advance at a timing before the retransmission timing determined by the retransmission control when it is determined as “far” in the perspective determination. A function for performing (pre-transmission control) is provided.

  This pre-transmission control is based on the assumption that the wireless tag device 2 passes so as to cover the edge (fringe) of the communicable area of the wireless reader device 3 as shown in FIG. That is, when the wireless tag device 2 passes so as to cover the edge (fringe) of the communicable area of the wireless reader device 3, there is the least chance of future retransmission (coming soon out of the communicable area). Therefore, the ACK signal is transmitted before the retransmission control transmission timing.

  FIG. 8 is a diagram illustrating an example of a radio frame configuration. As shown in FIG. 8, for example, one frame is composed of eight units (first unit to eighth unit), and the second half unit (fifth unit to eighth unit) is the same as in the first embodiment. Assume that similar retransmission control is performed. In this case, the pre-transmission control is performed by the first half units (for example, the second unit and the fourth unit).

  Here, the prior transmission control performed in the wireless communication system 1 of the present embodiment will be described in detail with reference to the sequence diagram of FIG.

  As shown in FIG. 9, in the wireless communication system 1 according to the present embodiment, first, the wireless reader device 3 to the wireless tag device 2 in the 0th time lot (TS0) and the first time slot (TS1) of the first unit. A broadcast beacon is transmitted. Also in this case, it is assumed that there are two wireless tag devices 2 (tag A and tag B) in the communicable area of the wireless reader device 3. The broadcast beacon is received by the two wireless tag devices 2 (tag A and tag B), and the RSSI is measured by each of the wireless tag devices 2.

  In the second time slot (TS2), an ACK signal is transmitted as a response to the broadcast beacon from the two wireless tag devices 2 (tag A and tag B). Also in this case, since the ACK signals are transmitted from the two RFID tag apparatuses 2 at the same timing, a collision (collision) occurs when the ACK signals are received. The wireless reader device 3 receives only one ACK signal (ACK signal from tag A) and discards the other ACK signal (ACK signal from tag B).

  Then, in the third time slot (TS3), as a response to the ACK signal from the wireless tag device 2, a unicast beacon signal notifying that “communication with the tag A is successful” is transmitted from the wireless reader device 3. . Thereby, one wireless tag device 2 (tag A) recognizes that the communication with the wireless reader device 3 is successful, and the other wireless tag device 2 (tag B) communicates with the wireless reader device 3. Recognize the failure. The wireless tag device 2 (tag A) that has succeeded in communication with the wireless reader device 3 performs saving control to reduce power consumption.

  When a broadcast beacon signal is transmitted from the wireless reader device 3 in the fifth time slot (TS5), this beacon signal is not subjected to saving control (communication with the wireless reader device 3 has failed). 2 (tag B), and RSSI is measured.

  In this case, the RFID tag device 2 (tag B) compares the RSSI of the broadcast beacon signal received in TS5 (the recently received beacon signal) with a threshold value, makes a perspective determination, and transmits transmission timing (prior transmission) For example, the (m-1) th time slot (TSm-1) of the second unit is determined. Thereafter, the wireless tag device 2 (tag B) also performs saving control for suppressing power consumption.

  When the wireless tag device 2 (tag B) receives the broadcast beacon signal from the wireless reader device 3 in the m-2 time slot of the second unit, the wireless tag device 2 (tag B) uses the next m-1 time slot (TSm-1). An ACK signal is transmitted to the wireless reader device 3 in advance. When the wireless reader device 3 receives the ACK signal from the wireless tag device 2 (tag B), the wireless reader device 3 transmits a unicast beacon signal notifying that “communication with the tag B was successful”. As a result, the wireless tag device 2 (tag B) recognizes that communication with the wireless reader device 3 has succeeded, and performs saving control to suppress power consumption.

  The wireless tag device 2 according to the second embodiment also has the same operational effects as the first embodiment.

  In addition, in the present embodiment, when it is determined that communication with the wireless reader device 3 has failed, if it is determined that the distance is determined to be a long distance by the distance determination, the time before the retransmission timing determined by the above retransmission control is determined. At the timing, an ACK signal is transmitted in advance. For example, when the wireless tag device 2 passes so as to cover the edge (fringe) of the communicable area of the wireless reader device 3, the chances of future retransmissions are fewest (soon to go out of the communicable area). However, according to the present embodiment, since the ACK signal is retransmitted in advance at a timing before the retransmission timing in such a case, the success rate of communication with the wireless reader device 3 is further increased. be able to.

  The embodiments of the present invention have been described above by way of example, but the scope of the present invention is not limited to these embodiments, and can be changed or modified according to the purpose within the scope of the claims. is there.

  For example, in the above description, the system in which the wireless reader device 3 moves and the wireless tag device 2 is fixed has been described. However, the scope of the present invention is not limited to this, and the wireless tag device 2 moves and wirelessly moves. It can also be used in a system in which the reader device 3 is fixed.

  As described above, when the communication with the wireless reader device fails, the wireless tag device according to the present invention sets an appropriate priority according to the number of future retransmission opportunities, and based on the priority. It has the effect of being able to perform appropriate retransmission control, and is useful when applied to a sensor network for inspection and monitoring of structures such as expressways.

DESCRIPTION OF SYMBOLS 1 Wireless communication system 2 Wireless tag apparatus 3 Wireless reader apparatus 4 Sensor 5 Sensor interface 6 Storage part 7 Reception part 8 Transmission part 9 Control part 10 Reception strength measurement part 11 Communication success / failure determination part 12 Judgment processing part 13 Transmission timing control part 14 Random number Generation unit 15 Transmission unit 16 Reception unit 17 Control unit 18 Storage unit 19 Pre-transmission control unit

Claims (6)

A receiving unit for receiving a response request signal transmitted from the wireless reader device;
A reception intensity measuring unit for measuring the reception intensity of the response request signal;
A communication success / failure determination unit that determines whether a response signal transmitted as a response to the response request signal is received by the wireless reader device and communication with the wireless reader device is successful;
Based on the reception strength of the previous response request signal and the reception strength of the current response request signal, when the reception strength is increased, it is determined as approaching, and when the reception strength is decreased, it is detached. A movement determination unit for performing movement determination to determine
Based on the reception strength of the response request signal this time, when the reception strength is equal to or greater than a predetermined threshold, it is determined as a short distance, and when the reception strength is less than the threshold, it is determined as a long distance A perspective determination unit for performing the determination;
An area determination unit that performs area determination to determine which of a long distance departure area, a short distance departure area, a short distance approach area, and a long distance approach area based on the determination result of the movement determination and the perspective determination When,
When it is determined that the communication with the wireless reader device has failed, the retransmission timing for retransmitting the response signal is controlled according to the priority determined for each area based on the determination result of the area determination A retransmission timing control unit,
With
The priority of the long-distance leaving area is the highest first priority, the priority of the short-distance leaving area is the second priority lower than the first priority, and the priority of the short-distance approaching area is The wireless tag device according to claim 1, wherein the third priority is lower than the second priority, and the priority of the long-distance approach area is a fourth priority lower than the third priority.   The wireless tag device according to claim 1, wherein the retransmission timing control unit controls the retransmission timing of the response signal such that the higher the priority is, the larger the number of retransmissions per predetermined period is.   A pre-transmission control unit that transmits the response signal in advance at a timing prior to the retransmission timing determined by the retransmission timing control unit when it is determined that the distance is determined by the distance determination; The wireless tag device according to claim 1 or 2. A retransmission control method used in a wireless tag device,
Receiving a response request signal transmitted from the wireless reader device;
Measure the reception strength of the response request signal,
A response signal transmitted as a response to the response request signal is received by the wireless reader device to determine whether communication with the wireless reader device is successful;
Based on the reception strength of the previous response request signal and the reception strength of the current response request signal, when the reception strength is increased, it is determined as approaching, and when the reception strength is decreased, it is detached. Move determination to determine,
Based on the reception strength of the response request signal this time, when the reception strength is equal to or greater than a predetermined threshold, it is determined as a short distance, and when the reception strength is less than the threshold, it is determined as a long distance Make a decision,
Based on the determination result of the movement determination and the perspective determination, an area determination is performed to determine which of the long-distance leaving area, the short-distance leaving area, the short-distance approaching area, and the long-distance approaching area,
When it is determined that the communication with the wireless reader device has failed, the retransmission timing for retransmitting the response signal is controlled according to the priority determined for each area based on the determination result of the area determination And
The priority of the long-distance leaving area is the highest first priority, the priority of the short-distance leaving area is the second priority lower than the first priority, and the priority of the short-distance approaching area is A retransmission control method, wherein the third priority is lower than the second priority, and the priority of the long-distance approach area is a fourth priority lower than the third priority. A wireless communication system comprising a wireless tag device and a wireless reader device,
The wireless tag device is:
A receiver for receiving a response request signal transmitted from the wireless reader device;
A reception intensity measuring unit for measuring the reception intensity of the response request signal;
A communication success / failure determination unit that determines whether a response signal transmitted as a response to the response request signal is received by the wireless reader device and communication with the wireless reader device is successful;
Based on the reception strength of the previous response request signal and the reception strength of the current response request signal, when the reception strength is increased, it is determined as approaching, and when the reception strength is decreased, it is detached. A movement determination unit for performing movement determination to determine
Based on the reception strength of the response request signal this time, when the reception strength is equal to or greater than a predetermined threshold, it is determined as a short distance, and when the reception strength is less than the threshold, it is determined as a long distance A perspective determination unit for performing the determination;
An area determination unit that performs area determination to determine which of a long distance departure area, a short distance departure area, a short distance approach area, and a long distance approach area based on the determination result of the movement determination and the perspective determination When,
When it is determined that the communication with the wireless reader device has failed, the retransmission timing for retransmitting the response signal is controlled according to the priority determined for each area based on the determination result of the area determination A retransmission timing control unit,
With
The priority of the long-distance leaving area is the highest first priority, the priority of the short-distance leaving area is the second priority lower than the first priority, and the priority of the short-distance approaching area is A wireless communication system, wherein the third priority is lower than the second priority, and the priority of the long-distance approach area is a fourth priority lower than the third priority. A retransmission control method used in a wireless communication system,
The response request signal transmitted from the wireless reader device is received by the wireless tag device,
In the wireless tag device,
Measure the reception strength of the response request signal,
A response signal transmitted as a response to the response request signal is received by the wireless reader device to determine whether communication with the wireless reader device is successful;
Based on the reception strength of the previous response request signal and the reception strength of the current response request signal, when the reception strength is increased, it is determined as approaching, and when the reception strength is decreased, it is detached. Move determination to determine,
Based on the reception strength of the response request signal this time, when the reception strength is equal to or greater than a predetermined threshold, it is determined as a short distance, and when the reception strength is less than the threshold, it is determined as a long distance Make a decision,
Based on the determination result of the movement determination and the perspective determination, an area determination is performed to determine which of the long-distance leaving area, the short-distance leaving area, the short-distance approaching area, and the long-distance approaching area,
When it is determined that the communication with the wireless reader device has failed, the retransmission timing for retransmitting the response signal is controlled according to the priority determined for each area based on the determination result of the area determination And
The priority of the long-distance leaving area is the highest first priority, the priority of the short-distance leaving area is the second priority lower than the first priority, and the priority of the short-distance approaching area is A retransmission control method, wherein the third priority is lower than the second priority, and the priority of the long-distance approach area is a fourth priority lower than the third priority.

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