CN106682548A - Multichannel power random change control method for RFID (radio frequency identification) reader collision preventing - Google Patents

Abstract

The invention discloses a multi-channel power random change control method applied to RFID reader anti-collision, which includes: the reader randomly selects a channel; respectively measures the "reading" of the reader at different distances from the same tag and a single reader; Rate-output power" characteristic, select the average value of the range with the largest change from the characteristic curve, and then take the average of the range of change at different distances as the range of random change in the output power of the reader; every time the reader completes the reader ‑Tag communication, regardless of whether there is a tag response or not, the transmission power is adjusted by using the random variation range of the reader output power. The present invention can reduce reader-tag collision on the basis of avoiding reader-reader collision, thereby increasing the sum of recognition rates when multiple readers identify tags at the same time; it is suitable for multi-reader recognition occasions such as warehousing and logistics.

Description

A multi-channel power random change control method for RFID reader anti-collision

technical field

The invention relates to the application field of ultra-high frequency radio frequency identification (RFID), belongs to RFID anti-collision technology, in particular to a multi-channel power random change control method for RFID reader anti-collision.

Background technique

Radio Frequency Identification (RFID) uses radio frequency signals for non-contact two-way communication to identify specific targets and obtain corresponding data from them. This technology has the characteristics of long recognition distance, fast and convenient operation, good environmental adaptability, and high safety. Its appearance has provided a lot of help for the improvement of the efficiency of the industrialization process. From warehousing logistics to workshop management, RFID technology has a wide range of applications.

The RFID system is mainly composed of three parts: reader, electronic tag and computer host. When the system is working, the host computer controls the RFID reader to transmit electromagnetic waves to the electronic tag according to a certain communication protocol. When the electronic tag receives the electromagnetic wave signal sent by the reader, the tag obtains energy from the electromagnetic wave and sends the information it carries back to read. Then the reader processes the information returned by the tag to complete the read and write operations.

In applications such as warehousing and logistics, the recognition range of the reader is limited, so it is often necessary to deploy multiple readers to monitor the goods with electronic tags in a certain area. In order to ensure full coverage of the tags in the area, the identification between readers It is inevitable that the ranges will overlap, and at this time, the "collision" of electromagnetic waves occurs. "Collision" is one of the main factors affecting the recognition efficiency. Solving this problem is a key to improve the performance of RFID system.

Contents of the invention

The purpose of the present invention is to solve the problem of "collision" when multiple readers simultaneously read a single tag when a tag is located in the reading range of multiple readers (see Figure 1) in the RFID system, and proposes an ultra-high frequency radio frequency Identify the random power change control method in the system, set the change range of the reader output power through a series of measurement data, make the reader output power change randomly within their respective ranges, and use the output power between different readers when the power changes The capture effect caused by the difference improves the overall read efficiency in the multi-reader-single-tag case.

The purpose of the present invention is achieved like this:

A multi-channel power random change control method for RFID reader anti-collision, the method comprises the following specific steps:

Step 1: Reader sub-channel

The reader randomly selects the channel;

Step 2: Set the random power variation range

First, set the reader antenna and the tag on the same horizontal line, measure the "reading rate-output power" characteristics of the reader at different distances from the same tag and a single reader, and select the range with the largest change from the characteristic curve That is, the derivative of this section of the curve is greater than the average value of the derivative of the entire curve, and then average the variation ranges at different distances as the range of random variation of the output power of the reader; subsequently, determine the output power of other readers in the manner described Randomly varying range; Step 3: Reader reads tag

(1) The reader sends the Select command signal to select the tag group, and at the same time sets the initial frame length in the tag identification cycle, that is, the number of slots, and starts the tag identification cycle this time;

(2) Every time a reader-tag communication is completed, regardless of whether there is a tag response, the transmission power is adjusted by using the range of random changes in the output power of the reader;

(3) If the frame time slot is not 0, continue the identification cycle, and the reader continues to read the tag until the number of frame time slots is reduced to 0, and this identification cycle ends.

The weight of each power value in the range of random variation of the output power of the reader set by the present invention is the same, and the random variation of power adopts a uniform distribution mode, and random fluctuations are performed within the respective power variation ranges set; when multiple When the reader reads the same tag at the same time, the total recognition rate is improved.

The present invention is especially suitable for applications in places with large identification areas such as warehousing and logistics. In order to improve work efficiency, multiple readers can be deployed in the identification area to read tags at the same time. Applying the method of the present invention can avoid collisions between readers. It can also speed up the recognition rate of tags, and has great practical value for applications such as the Internet of Things.

Description of drawings

Figure 1 is a schematic diagram of the capture effect in RFID;

Fig. 2 is a flowchart of the present invention;

Fig. 3 is the characteristic curve of reading rate-output power of two readers;

FIG. 4 is a comparison graph of the sum of reading speeds of the present invention and the fixed power control method.

detailed description

Referring to Figure 1, the capture effect means that when multiple readers reflect signals to the tag at the same time, only the signal with stronger signal strength will be received by the tag normally. In the figure, R1 and R2 are two readers that are the same except for different transmission powers. The signal power transmitted by R1 is relatively high, and the signal power transmitted by R2 is small. The tag T1 is within the common reading range of R1 and R2. When the signals transmitted by readers R1 and R2 arrive at T1 at the same time, if the signal strength of R1 received by T1 is much greater than the signal strength of R2, only the signal of R1 is demodulated correctly by T1, that is, only the R1 reader can work normally at this time Read tags.

The present invention comprises the following specific steps:

(1) The reader is divided into channels

Before dealing with the collision problem of multiple readers preempting the same tag, first deal with the signal interference problem between readers:

Based on the EPC Class1 Gen2 protocol, the reader works in a fixed frequency band, assuming it is the USA frequency band, there are 50 data channels in this frequency band, and each reader will randomly occupy a data channel when it works. There will be no signal interference between the channels (the number of readers should not exceed the number of channels), thus avoiding the problem of signal collision between readers.

(2) Set the random power variation range

After avoiding interference between readers, in order to reduce the collision of multiple readers simultaneously grabbing the same tag. As shown in Figure 1, if the tag T1 is in the common reading range of R1 and R2, T1 may receive the signals of R1 and R2 at the same time, and the two signals are superimposed at T1, so that T1 cannot return the correct correspondence to R1 or R2 command, that is, neither R1 nor R2 can read T1 normally. When the signal strength difference between R1 and R2 is large, T1 only communicates normally with the reader with a stronger signal. Therefore, it is necessary to randomly change the output power of the reader within a certain range, so that each reader has a chance to read the tag normally. Experiments show that the reading rate of the reader varies with the output power, and only when the output power of each reader changes randomly within the range of reading rate-output power change, the reading The total reading rate of the reader will be larger, because at this time it is more likely that the output power of a certain reader in a certain time slot is much higher than that of other readers. Due to the existence of the capture effect, the reader in this time slot is faster It is easy to read the tag successfully, and reduce the situation that all readers cannot read the tag.

Therefore, first set the random variation range of output power for each reader:

First, place the reader antenna and the tag on the same horizontal line, measure the "reading rate-output power" characteristics of the reader at different distances from the same tag and a single reader, and select the range with the largest change from the characteristic curve (that is, the derivative of this section of the curve is greater than the average value of the derivative of the entire curve), and then the range of changes at different distances is averaged as the range of random changes in the output power of the reader. The range of random variations in the output power of the other readers is then determined as described.

Each power value within the set power change range has the same weight, so the random change of power adopts a uniform distribution method and fluctuates randomly within the respective set power change range. The power values are weighted the same so that each reader has almost the same chance of reading the tag, i.e. when reader R1 is at lower power and R2 is at higher power the probability should be the same as when R2 is at lower power and R1 is at higher power The probability of power is equal, so that the capture effect can be fully utilized to improve the sum of reader recognition rates.

After setting the random power variation range of the reader, the reader starts to read the tag. The reading process is as follows:

First, the reader sends the Select command signal to select the tag group, and at the same time sets the initial frame length (that is, the number of slots) in the tag identification cycle, and starts the tag identification cycle this time.

Secondly, every time the reader-tag communication is completed, no matter whether there is a tag response or not, the transmission power is adjusted by using the random variation range of the reader output power.

If the frame time slot is not 0, continue the identification cycle, and the reader continues to read the tag until the number of frame time slots is reduced to 0, and this identification cycle ends.

Finally, comparing the sum of the reading rates of the reader at different tag positions when the reader adopts the present invention and the reader has a fixed power value, it can be seen that the sum of the reading rates of the reader can be improved by adopting the present invention.

Example

Referring to Fig. 2, the present embodiment comprises the following specific steps:

Step 1. Based on the EPC Class1 Gen2 protocol; select the UHF RFID USA frequency band, namely 902.75-927.25MHz. There are 50 channels in this frequency band, and the channel interval is 500KHz. The reader randomly selects a channel N in the frequency band used, then the communication frequency of this channel is (902.75+N*0.5)MHz. In the application occasion where there are not many readers, this method of frequency division multiplexing can be used effectively. Avoid collisions between readers.

Step 2. Obtain the random power variation range through measurement.

Step 3. The reader sends a Select command signal to select the tag group, and at the same time sets the initial frame length (ie, the number of slots) in the tag identification cycle, and starts the current tag identification cycle.

Step 4. In the RFID system, each tag has a time slot counter inside. When the tag receives the QueryRep query command from the reader, the counter is decremented by 1. When the counter of a tag is reduced to 0, the tag returns data to the reader to complete a communication. Regardless of whether there is a tag response or not, the reader's random power variation range is used to adjust the transmit power.

Step 5. Step 3 is repeated until the number of frame time slots decreases to 0, and this identification period ends.

During the communication process between the reader and the tag, the reader adjusts the transmit power with a random power variation range. The power variation range of each reader is calibrated by the following method.

The output power of the radio frequency chip of the RFID reader used in this embodiment can be adjusted within the range of -19dB to 0dB, and the radio frequency chip is connected with a power amplifier and an antenna externally. The experiment uses two readers and one tag. The antennas and tags of the two readers are placed on the same horizontal line, where the A reader is located at 0cm, the B reader is located at 240cm, and the tag is located between the antennas of the two readers.

First, put the tag at 60cm, measure the "reading rate-output power" characteristic curve when the two readers A and B read the tag separately; then put the tag at 100cm, measure the A 1, B, the "reading rate-output power" characteristic curve when the two readers read the tag independently; then continue to change the position of the tag, carry out the above measurement, and the finally obtained curve is shown in Figure 3.

Select the range with the largest variation of the A curve from each sub-graph in Figure 3 (that is, the derivative of this section of the curve is greater than the average value of the derivative of the entire curve), and then average the maximum variation range of the A reader under different label positions, as A Range of random variation in reader output power. Then follow the above steps to determine the random variation range of the output power of the B reader. Finally, the output power variation interval of the A reader is set to [-11, -7] dB, and the output power variation interval of the B reader is [-19, -4] dB.

Fig. 4 shows the comparison of the sum of reading rates of the reader between the present invention and the fixed power. It can be seen from the figure that the reading rate of the reader is improved to a certain extent by adopting the present invention.

According to the experimental test, as shown in Figure 4, (x, y) in the figure means that the output power of reader A takes a fixed value x (dB) and the output power of reader B takes a fixed value y (dB), that is, the comparative reader uses this When the invention and the reader are at a fixed power value, the sum of the reading rates of the reader.

Among the figure, the dark curve is the sum of the reading rates of A and B two readers obtained by the present invention, and the light curve is the sum of the reading rates when the output power of the A and B readers is constant. It can be seen that the reading rate of the present invention is adopted The sum of the read rate of the device has been improved.

Claims (1)

1. a kind of multichannel power change at random control method for RFID reader anticollision, it is characterised in that the method bag Include step in detail below：

Step 1：Reader point channel

Reader randomly chooses channel；

Step 2：Random changed power scope is set

First, reader antenna and label are measured respectively same label and is existed with single reader on same level straight line Under different distance, " reading rate-output " characteristic of reader is chosen the maximum scope of change from characteristic curve and i.e. should The derivative of section curve is more than the meansigma methodss of whole curve derivative, then the excursion at different distance is averaged, and reads as this Read the scope of the change at random of device output；Subsequently, the change at random of other reader outputs is determined in described manner Scope；

Step 3：Reader reads label

（1）Reader sends Select command signals and selects population of tags, concurrently sets the initial frame length in the tag recognition cycle I.e. timeslot number, starts the recognition cycle of this secondary label；

（2）Often complete the communication of READER-TO-TAG, regardless of whether there is label to respond, using reader output with The scope adjustment transmission power of machine change；

（3）If frame slot is not 0, continue recognition cycle, reader continues to read label, until when frame slot number is kept to 0, this Recognition cycle terminates.