JP5199850B2 - Wireless tag and wireless communication method - Google Patents

Description

  The present invention relates to a wireless tag system and a wireless communication method for transmitting and receiving information between a wireless tag and a wireless reader.

  Conventionally, there is a wireless tag system as in Patent Document 1. In Patent Document 1, in order to detect the location of an article stored in logistics or a warehouse, an active wireless tag that can communicate at a relatively long distance is attached to the article, and in response to an inquiry signal from a wireless reader Information on the wireless tag is returned, or the wireless tag emits sound and light in response to the call, thereby facilitating discovery of the target article. In particular, the wireless tag disclosed in Patent Document 1 discloses a technique for turning on the battery power of the wireless tag using minute radio wave energy radiated from a portable wireless transmitter (wireless reader).

  Moreover, as shown in Patent Document 2, there is a fully automatic meter-reading system in which a slave unit reads the value of a meter such as water or gas provided in each house and wirelessly transmits it to the master unit. This automatic meter reading system is a handy terminal operated by a meter reader, and the handset provided in each house, and the radio wave reaching distance between the handset and the base unit is required to be about 100 m. This is a wireless tag system having an active wireless tag and a wireless reader driven by the mobile phone. In addition, the RFID tag system corrects the transmission signal error and reduces battery consumption so that it can accurately start the slave unit and realize wireless communication with the master unit without being affected by noise. To perform intermittent transmission and reception.

JP 2003-23385 A JP-A-10-198881

  In the wireless system of Patent Document 1, since the wireless tag uses radio waves emitted from the wireless reader, it is necessary to increase the transmission output of the wireless reader in order to operate stably, and the power consumption of the wireless reader is compared. Increase.

  In the wireless system of Patent Document 2, a CRC code for error detection, a BCH code for error detection / correction, and the like are added to the preamble frame in order to ensure the reliability of wireless communication. The reception must be continued until the actual data frame is received, and the reception period becomes longer as compared with the method not including the error code.

  In addition, in the wireless system of Patent Document 2, when the number of redundant bits increases, the reception time during intermittent reception increases, and in a device in which battery driving is indispensable, such as an active wireless tag, a factor that shortens the battery life. It was. In particular, in the case of a general active RFID system, there is almost no communication period in which nothing is transmitted by the wireless reader. Nevertheless, the wireless tag needs to perform intermittent reception, so how to receive it. The issue was how to shorten the time.

  SUMMARY An advantage of some aspects of the invention is that it provides a wireless communication system and a wireless communication method that suppress power consumption of a wireless tag.

The present invention is a wireless tag based on means for intermittently receiving a plurality of preamble frames, each including a cycle counter based on the order of transmission from a wireless reader, and a cycle counter included in the last received preamble frame. Means for obtaining a scheduled reception time of the actual data frame, means for stopping the reception operation of the wireless tag until the scheduled reception time after receiving a plurality of preamble frames, and the transmitted from the wireless reader Means for receiving an actual data frame at the scheduled reception time. In addition, the wireless tag according to the present invention is preferably, when each received preamble frame does not include a redundant bit, and the value for preamble frame recognition indicated by each of the plurality of received preamble frames is the same, Means for determining that a normal preamble frame has been received. The wireless tag system according to the embodiment of the present invention is a wireless tag system that transmits and receives information between a wireless tag and a wireless reader, and transmits an actual data frame after repeatedly transmitting a preamble frame a predetermined number of times. When the transmitting wireless reader and the preamble frame transmitted by the wireless reader are received by intermittent reception, the scheduled communication time of the actual data frame is obtained based on the cycle counter included in the preamble frame, and the actual data frame is transmitted and received at the scheduled communication time. The preamble frame transmitted by the wireless reader includes at least a bit synchronization signal, a frame synchronization signal, a cycle counter, and a wireless tag identification signal. The wireless tag is a wireless frame identification signal of the preamble frame. Received at least twice and the received preamble Le frames you determined that the communication has succeeded when the same.

In the wireless tag system according to an embodiment of the present invention, the preamble frame wireless reader transmits includes cycle counter that indicates the number of times of repeatedly transmitting a preamble frame, the wireless reader every time it sends repeatedly a preamble frame The wireless tag calculates the actual data frame communication scheduled time based on the received preamble frame cycle counter, stops communication until the scheduled communication time, and starts communication at the scheduled communication time. It intends line communication of the actual data frame to.

Further, the present invention provides a wireless communication method including a transmission step executed by a wireless reader and a reception step executed by a wireless tag, wherein the transmission step includes a plurality of preambles each including a cycle counter based on a transmission order. A step of transmitting a frame; and a step of transmitting an actual data frame after transmitting the plurality of preamble frames, wherein the receiving step intermittently receives two or more of the plurality of preamble frames; A step of obtaining a scheduled reception time of an actual data frame based on a cycle counter included in a last received preamble frame; and after the reception of the two or more preamble frames until the scheduled reception time, A step of stopping the tag receiving operation, and the actual data frame transmitted from the wireless reader. The characterized in that it comprises a a step of receiving the reception scheduled time. The radio communication method according to an embodiment of the present invention, between the wireless tag and the radio reader, a wireless communication method for transmitting and receiving information, the real data frame after repeat count transmitted is predetermined a preamble frame A wireless reader process for transmitting, and when receiving a preamble frame by intermittent reception, a wireless tag process for obtaining a scheduled communication time of the actual data frame based on a cycle counter included in the preamble frame and transmitting / receiving the actual data frame at the scheduled communication time The preamble frame transmitted by the wireless reader process includes at least a bit synchronization signal, a frame synchronization signal, a cycle counter, and a wireless tag identification signal. The wireless tag process includes a wireless tag identification signal of the preamble frame. Received at least twice and the received preamble frame There it determined that there is communication in the case of the same was successful.

In the wireless communication method according to an embodiment of the present invention, the preamble frame transmitted radio reader step comprises a cycle counter that indicates the number of times of repeatedly transmitting a preamble frame, the wireless reader process repeatedly a preamble frame transmission The wireless tag process calculates the scheduled communication time of the actual data frame based on the received preamble frame cycle counter, stops the communication until the scheduled communication time, and at the scheduled communication time. It intends line communication of the actual data frame to start the communication.

In the wireless communication method according to an embodiment of the present invention, the wireless tag process, when the actual data frame transmitted multiple times from a wireless reader process communication scheduled time is the same actual frame, the normal you determined that the actual data frame.

  According to the present invention, a preamble frame repeatedly transmitted by a wireless reader is not added with redundant bits such as error detection and correction, and a preamble frame having a minimum amount of information is repeatedly transmitted. There is an effect that the reception continuation time by can be made substantially equal to the transmission time of one preamble frame.

  In addition, when a preamble frame having at least the same value is received multiple times by the wireless tag, it is determined that it is a regular preamble frame, thereby preventing erroneous detection of the preamble frame and without impairing the reliability of wireless communication. The power consumption can be reduced by shortening the reception time.

  Hereinafter, the best mode for carrying out the present invention (hereinafter referred to as an embodiment) will be described with reference to the drawings.

  FIG. 1 shows a configuration of a wireless tag system 1 that implements article search and location management. The wireless tag system 1 includes, for example, a wireless tag (10, 21, 22) attached to a product packaging box, and a wireless reader 20 that performs wireless communication with a plurality of wireless tags 10 with weak wireless in the 300 MHz band. Have. The wireless tag 10 is driven by a transmission unit 17 and a reception unit 19 that communicate with the wireless reader 20, a timer 16 that measures communication timing, a memory 15 that stores information on the wireless tag 1 and product information, and a CPU 13. LED 11 and buzzer 12, CPU 13 for controlling wireless tag 10, and battery 14 for supplying power. The wireless reader 20 includes a transmission unit 41 and a reception unit 42 that communicate with the wireless tag 10, and a display unit 44 and an operation unit 45 for selecting the wireless tag 10 and reading / writing information.

  When an operator carrying the wireless reader 20 instructs the wireless tag 10 to turn on an LED or sound a buzzer, the presence or location of the wireless tag 10 can be determined with eyes or ears. In such a wireless tag system 1, the wireless tag 10 requires a quick response to the instruction even though there is almost no communication period during which the wireless reader 20 does not transmit the instruction. It is necessary to wait for instructions at an early cycle. Further, the wireless tag 10 is small and needs to be driven by a battery, and there is a problem of how to shorten the standby time in order to ensure the battery life. Thus, one of the characteristic features of the wireless tag system of the present invention is that, for example, when realizing a power-saving wireless tag that can be used continuously for about five years, the current consumption is increased by increasing the cumulative operation time due to intermittent operation. Therefore, the continuous use period is extended by shortening the reception processing time that causes battery consumption.

  FIG. 6 shows a conventional preamble frame and a preamble frame according to the present embodiment, which are helpful in understanding the present embodiment. In the configuration of the conventional preamble frame, in order for the wireless tag to detect the frame synchronization signal 2, the transmission of the wireless reader and the reception of the wireless tag are asynchronous, so at least the reception duration needs to be 12.29 ms or more. is there. On the other hand, in the configuration of the preamble frame of the present embodiment, at least the reception is continued in order for the wireless tag to detect the frame synchronization signal 1 by removing the CRC and using the frame synchronization signal 1 with the frame synchronization signal 2 shortened. The time can be set to 7.5 ms or more, and the reception time can be shortened as compared with the conventional configuration. Further, according to an experiment, when the intermittent reception period of the wireless tag is 5 seconds and the lifetime of the battery having a battery capacity of 2100 mAh is obtained at the period, the conventional system is about 5 years, and the present embodiment is about 6.6 years. The improvement effect of 1.6 years was obtained.

  FIG. 2 shows a timing chart of the wireless tag system 1. The wireless reader communicates with the wireless tag using the preamble frame 31 and the actual data frame 32. The preamble frame 31 transmitted by the wireless reader includes a bit synchronization signal, a frame synchronization signal 1 and a cycle counter, and the same preamble frame is repeatedly transmitted a plurality of times. The actual data frame 32 includes a bit synchronization signal, a frame synchronization signal 2, a tag ID, a control signal, and a CRC, and is repeatedly transmitted a plurality of times in the same manner. When the received control signal is an LED lighting instruction or a buzzer sounding instruction, the wireless tag performs LED lighting or a buzzer sounding.

  FIG. 5 shows a timing chart of writing to the wireless tag. By this processing, user data such as storage date / time required for a wireless tag used in an inventory management system or the like, and recording / updating of the number of inventory can be written. The basic operation is the same as in FIG. 2, but control information and write data, which are user data write instructions, are inserted into the actual data frame. When the wireless tag receives the data frame for the local station, the wireless tag writes user data to the memory according to the control information included in the data frame, and returns ACK to the wireless reader when the writing of the user data is completed normally. If the wireless reader receives ACK, it determines that the user data writing has been completed normally.

  FIG. 3 shows a configuration of a preamble frame and an actual data frame transmitted by the wireless reader. The bit synchronization signal of the preamble frame 31 in FIG. 3 is a signal for synchronizing the bit timing on the transmission side on the reception side, and is 24 bits of 0 and 1 of “0101, 0101, 0101, 0101, 0101, 0101”. It is a repetitive signal. The frame synchronization signal 1 and the frame synchronization signal 2 are signals for recognizing the data bit position on the receiving side such as a wireless tag, and the frame synchronization signal 1 of the present invention recognizes the data bit position on the receiving side. It is used as a signal for

  In the present embodiment, the power consumption is reduced by using “0001, 1011, 1010, 1000” which is the upper 16 bits of the 31-bit M-sequence code for the frame synchronization signal 1 of the preamble frame 31, and the actual data frame includes a frame The synchronization signal 2 uses a 31-bit M-sequence code of “0001, 1011, 1010, 1000, 0100, 1011, 0011, 111”, thereby shortening the preamble frame that is a signal for matching the timing.

  If the preamble frame is simply shortened, there is a method using a 15-bit M-sequence code. However, since it can be processed in units of 8 bits considering the ease of software processing, the upper 16 of the 31-bit M-sequence code is used. Adopted a bit. Also, from the experimental results, in the method using the upper 8 bits for the purpose of shortening the preamble frame, the frequency of erroneously recognizing noise as a frame synchronization signal increases, so the effect of shortening the total reception time cannot be obtained. . Therefore, since the frequency of erroneous recognition is reduced by using the upper 16 bits and it has become clear that the effect of shortening the reception time can be obtained by shortening the preamble frame, this method was adopted.

  In FIG. 2, the wireless reader repeatedly transmits a preamble frame (4.58 ms) during an interval of 5.2 seconds, and immediately thereafter transmits an actual data frame (16.25 ms) six times (97.5 ms). The cycle counter (CC) sets the preamble frame immediately before the actual data frame to 0 and transmits it so as to decrement at intervals of 0.5 seconds. In the present embodiment, the initial value of the cycle counter is set to 10 and the count down is performed from 10 to 9, 8, 7,. The wireless tag performs intermittent reception at a cycle of 5 seconds, and the reception duration is set to 7 ms so that the frame synchronization signal of the preamble frame 31 can be received at least once.

  When the wireless tag receives the frame synchronization signal, the reception duration is further extended by 20 ms from that point, and a preamble frame is received a plurality of times, and if a preamble frame showing at least the same value is received a plurality of times It is determined that the frame is a preamble frame. When no frame synchronization signal is received, reception is stopped until the next intermittent reception cycle.

When it is determined that the frame is a regular preamble frame, the waiting time until the actual data frame is received is calculated using Equation 1 using the cycle counter included in the preamble frame. “Wait time (seconds) = cycle counter value × 0.5 seconds” (Expression 1)
The wireless tag pauses the receiving operation until the waiting time elapses, and resumes the receiving operation after the waiting time elapses to receive the actual data frame. When it is determined that the wireless tag is an actual data frame for the local station based on the tag ID included in the received actual data frame, the wireless tag performs an operation according to the control information.

  FIG. 4 shows the processing flow of the wireless tag system, with the wireless reader on the left side and the wireless tag processing on the right side. The wireless reader sets “10” as an initial value in the cycle count CC, and after transmitting a preamble frame in step S10, the cycle count is decremented by 1 in step S12. If the cycle count is greater than 0 in step S14, the process returns to step S10. If the cycle count is less than 0, the wireless reader executes actual data transmission in step S16, and repeats actual data transmission six times by the determination process in step S18. When the above processing is completed, the process returns to the beginning.

  The wireless tag determines whether or not 5 seconds have elapsed in step S20 by a timer, and when 5 seconds have elapsed, executes the preamble reception in step S22. The wireless tag acquires the value of the cycle counter by receiving the preamble, and calculates the actual data reception time from the cycle counter in step S24. In step S26, the wireless tag waits until the scheduled time. When the scheduled time is reached, the actual data reception in step S28 is executed, and the contents of the actual data frame received in step S30 are the same. Will be confirmed. When the above processing is completed, the process returns to the beginning.

  As described above, in the wireless tag system according to this embodiment, the preamble frame repeatedly transmitted by the wireless reader is not added with redundant bits such as error detection and correction, and has the minimum necessary information. The wireless tag can make the reception continuation time due to intermittent reception substantially equal to the transmission time of one preamble frame.

  In addition, when a preamble frame having at least the same value is received multiple times by the wireless tag, it is determined that it is a regular preamble frame, thereby preventing erroneous detection of the preamble frame and without impairing the reliability of wireless communication. By shortening the reception time, power consumption can be reduced.

  The present invention relates to a wireless tag system, and can be used as a wireless tag system and a wireless communication method for transmitting and receiving information stored in a wireless tag between a wireless tag and a wireless reader.

1 is a configuration diagram showing a configuration of a wireless tag system including a wireless tag and a wireless reader according to an embodiment of the present invention. It is a timing chart figure of the radio | wireless tag system which concerns on embodiment of this invention. It is a block diagram which shows the structure of the preamble frame and real data frame which the radio | wireless reader of this embodiment transmits. It is a flowchart figure which shows the flow of a process of the wireless tag system of this embodiment. It is a timing chart figure of the RFID tag writing in this embodiment. It is explanatory drawing explaining the preamble frame of the conventional preamble frame and this embodiment used as a reference in understanding this embodiment.

Explanation of symbols

  1 wireless tag system, 10, 21, 22 wireless tag, 11 LED, 12 buzzer, 13 CPU, 14 battery, 15 memory, 16 timer, 17, 41 transmitter, 19, 42 receiver, 20 wireless reader, 31 preamble frame , 32 Actual data frame, 44 display section, 45 operation section.

Claims (3)

A wireless tag,
Means for intermittently receiving a plurality of preamble frames, each including a cycle counter based on the order of transmission from the wireless reader;
Means for obtaining the scheduled reception time of the actual data frame based on the cycle counter included in the last received preamble frame;
Means for stopping the reception operation of the wireless tag until the scheduled reception time after receiving a plurality of preamble frames;
Means for receiving the actual data frame transmitted from the wireless reader at the scheduled reception time;
A wireless tag comprising: The radio tag according to claim 1, wherein each received preamble frame does not include redundant bits.
Means for determining that a normal preamble frame has been received when the preamble frame recognition values indicated by each of the plurality of received preamble frames are the same;
A wireless tag comprising: A transmission step performed by the wireless reader;
A wireless communication method including a reception step executed by the wireless tag,
The transmission step includes
Transmitting a plurality of preamble frames each including a cycle counter based on a transmission order;
Transmitting an actual data frame after transmitting the plurality of preamble frames;
Including
The receiving step includes
Intermittently receiving two or more of the plurality of preamble frames;
Determining the scheduled reception time of the actual data frame based on the cycle counter included in the last received preamble frame;
After receiving the two or more preamble frames, until the scheduled reception time, stopping the reception operation of the wireless tag;
Receiving the actual data frame transmitted from the wireless reader at the scheduled reception time;
A wireless communication method comprising:

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