CN104794509A

CN104794509A - RFID (radio frequency identification) anti-collision method based on adaptive searching of information bit coding

Info

Publication number: CN104794509A
Application number: CN201510218262.XA
Authority: CN
Inventors: 张小红; 胡应梦; 钟小勇
Original assignee: Jiangxi University of Science and Technology
Current assignee: Jiangxi University of Science and Technology
Priority date: 2015-05-04
Filing date: 2015-05-04
Publication date: 2015-07-22
Anticipated expiration: 2035-05-04
Also published as: CN104794509B

Abstract

The invention provides an RFID (radio frequency identification) anti-collision method based on adaptive searching of information bit coding. A reader sufficiently utilizes collision bit information, tags need to return collision bit coding information, an effective inquiring prefix is generated adaptively, occupied timeslot recognition on the tags is performed so as to reduce inquiring frequency and improve the performance of an algorithm, and the problem that transmission information is redundant in communication between the reader and the tags is solved. Effectiveness of the algorithm is proved through theoretical analysis, and an error between a theoretical value and an experimental value of throughput rate does not exceed 5%. By the adaptive searching (AS) algorithm, the performance of a system is improved, and consumption of energy of the tags is reduced. Particularly, when the number of tags is 1000, the throughput rate of the algorithm can be about 61%. The efficiency of the system using the adaptive searching algorithm is higher than the efficiency of a system using a query tree algorithm by 72% or so and is higher than the efficiency of a system using an adaptive multi-way tree algorithm by 20.1% or so.

Description

RFID anti-collision method based on self-adaptive search of information bit codes

Technical Field

The invention belongs to a multi-label reading technology in the technical field of radio frequency identification, and relates to a multi-label anti-collision method.

Background

Radio Frequency Identification (RFID) technology is a non-contact automatic Identification technology that uses Radio Frequency communication to quickly acquire target object data, and is one of the key technologies of the internet of things sensing layer. Compared with the traditional identification technology, the RFID technology has the advantages of simple operation, strong anti-interference performance, capability of identifying objects moving at high speed, adaptability to severe environments and the like, and is widely applied to the fields of logistics, tracking, positioning, traffic control and management and the like. Therefore, it is classified as one of the most promising information technologies in the 21 st century.

Generally, an RFID system is generally composed of three major parts, namely, an electronic Tag (Tag), a Reader-writer (Reader) and a backend Database (Database). The electronic tags can be divided into active tags and passive tags, and due to the limitation of various factors such as cost, most of RFID systems adopt passive tags, namely passive tags, and the required energy is completely provided by electromagnetic waves sent by a reader-writer. When a plurality of tags respond to a command from a reader/writer at the same time, signals interfere with each other, so that the reader/writer cannot read data accurately, which is a tag collision. Therefore, how to effectively and quickly identify the tag is always a main research direction of the RFID technology and is also a research hotspot in the technical field of internet of things.

The RFID system must adopt a certain strategy or algorithm to avoid the occurrence of collision phenomenon, namely, the response time sequence of the control tags are communicated with the reader-writer one by one, and the identification of all the tags is completed within a certain time. For this reason, scholars at home and abroad have made a lot of research on the problem of collision between a multi-tag and a reader/writer. These collision avoidance algorithms fall into two main categories: one is an ALOHA algorithm based on time slot random allocation, also called uncertainty algorithm; such as a slotted ALOHA algorithm, a frame slotted ALOHA algorithm, a dynamic frame slotted ALOHA algorithm, a Q algorithm, etc., all of which adopt the basic idea of back-off retransmission upon collision, so the implementation process is relatively simple. However, as the number of tags increases, the performance thereof deteriorates sharply, and researchers have proposed an enhanced dynamic frame slot algorithm, a packet dynamic frame slot ALOH algorithm, and the like in succession. Although these algorithms improve the performance of the system, the algorithms have certain randomness, and there may be a problem that a single label or a plurality of labels cannot be successfully identified within a long period of time, that is, the labels are "starved".

Another is a Binary Search based deterministic algorithm, which represents algorithms such as Binary Search (BS) algorithm, Dynamic Binary Search (DBS) algorithm, and Jumping Dynamic Tree (JDS) algorithm, Query Tree (QT) algorithm, quadtree (4-ary Query, 4QT) algorithm, and Adaptive Multi-Tree anti-collision (AMS) algorithm. The BS algorithm continuously reduces the number of response tags through multiple comparisons until the unique tags are identified; the DBS algorithm can dynamically adjust the ID length of the reader-writer query command and the label feedback information; the JDS algorithm is an improvement based on the two algorithms, and the query is not restarted from the root node, but is continued to the node at the upper layer, namely the parent node, so that the time complexity of the algorithm is reduced. The QT algorithm has relatively simple requirements on the label, the label does not need to have any memory function, and the manufacturing cost of the label is reduced. The disadvantages are long recognition time and low throughput. The 4QT algorithm reduces the collision slots and increases the idle slots. The AMS algorithm is a combination of these two algorithms, and by introducing a collision factor, the reader/writer adjusts the number of splits to improve the performance of the system. However, these algorithms have relatively long recognition time, and the data communication amount between the reader and the tag is relatively large, and the throughput rate is only about 50%.

The invention provides an Adaptive search RFID anti-collision Algorithm (AS) based on information bit coding on the basis of summarizing many previous classical algorithms.

Disclosure of Invention

The invention provides an anti-collision (AS) algorithm of self-adaptive search based on information bit coding in order to reduce the time for identifying object labels. The reader-writer fully utilizes collision bit information to require the tag to return collision bit coding information, further adaptively generates an effective query prefix, and identifies the tag without idle time slots, so that the query times are reduced, and the performance of the algorithm is improved. In addition, the AS algorithm also solves the problems of transmission information redundancy and the like in the communication between the reader and the tag. The effectiveness of the algorithm is proved through theoretical analysis, wherein the error between a theoretical value and an experimental value of the throughput rate is not more than 5%, and the algorithm is further analyzed in detail from time complexity and communication complexity. Simulation results show that: the AS algorithm not only improves the performance of the system, but also reduces the consumption of tag energy. Particularly, when the number of the labels is 1000, the throughput rate of the algorithm is still kept about 61%, and the system efficiency is improved by about 72% and 20.1% compared with that of the query tree algorithm and the adaptive multi-way tree algorithm respectively.

1. The basic idea of the invention.

The basic idea of the Q algorithm, the quadtree search algorithm or the AMS algorithm is to generate prefixes according to a fixed pattern once the highest collision bit is detected, and then to sequentially transmit the prefixes to query the tag. Because the reader does not know the specific information of the tag collision bit, the reader can only continuously take out the query prefix from the stack and blindly query the tag, a large amount of idle time slots are inevitably generated, and the performance of the system is finally influenced.

In order for the reader to obtain the collision bit information, the tag needs to correspondingly encode the first 4-bit collision bit information, as shown in table 1. The reader/writer detects information of the collision bit by using the characteristic of Manchester (Manchester). If only 1bit collides, the collision position is respectively set to be 0 and 1, two new prefixes are generated and are pressed into a Stack of a reader-writer Stack; otherwise, the information before the highest collision position is sent to the label, and the label receives the information and compares the information with the ID of the label. If the data are the same, the subsequent 4 bits (starting from the highest collision bit) are coded, and the coded information is returned to the reader-writer. Otherwise, the tag does not respond. Because only 1bit in the 16 bits after coding is 1, and the others are 0, no matter which situation the collision happens, the reader-writer can accurately decode the original collision information, finally generate a corresponding prefix and press the prefix into a stack.

2. And (5) analyzing the performance of the AS algorithm.

The AS algorithm inherits the advantages of the QT and AMS algorithms, i.e., the tags do not need to store previous query cases, and are improved on the basis of the previous query cases. The AS algorithm only has two or four fixed branches, adaptively allocates the multi-branch tree along with the distribution condition of the label ID, generates an effective query prefix, and identifies the label without an idle time slot, thereby improving the performance of the algorithm.

TABLE 1AS information bit encoding rules

2.1 analysis of the number of slots of the multi-way tree.

Assuming that the number of labels is m, L indicates the number of layers in, and B is the treelet used by the multi-treelet (B ═ 2,4,8, …). For a full B-ary tree, there are k labels selecting the same node response at L level at the same time, and the probability obeys two-term distribution:

p (k / m, L) = C_{m}^{k} p^{k} {(1 - p)}^{m - k} - - - (1)

from this, the probability that m tags appear idle (k ═ 0) at the L-th layer is:

p (0 / m, L) = C_{m}^{0} p^{0} {(1 - p)}^{m} = {(1 - B^{- L})}^{m} - - - (2)

the probability of successful tag identification (k ═ 1) is:

p (1 / m, L) = C_{m}^{1} p {(1 - p)}^{m - 1} = {mB}^{- L} {(1 - B^{- L})}^{m - 1} - - - (3)

the probability of tag collision is:

p(k＞1/m,L)＝1-p(0/m,L)-p(1/m,L)＝1-(1-B^-L)^m-mB^-L(1-B^-L)^m-1 (4)

the values of the ID of each label are mutually independent and accord with binomial distribution, and the probability that any one of the two labels does not collide is as follows:

r_{1} = 2 C_{2}^{0} {(\frac{1}{2})}^{0} {(\frac{1}{2})}^{2} = \frac{1}{2} - - - (5)

the probability of collision of any one of the two tags is as follows:

r_{2} = 1 - r_{1} = \frac{1}{2} - - - (6)

assuming that the length of the tag ID is D, the probability that only 1bit of the two tags collide is as follows:

r_{3} = C_{D}^{1} r_{2} {(r_{1})}^{D - 1} = {D 2}^{- D} - - - (7)

let q be_L,i/mRepresenting the probability of the ith node being visited in the L-th level, q_0,i/mThis is because the algorithm starts the search from the root node each time. If a node is to be visited, except the root node, it is premised on the fact that the parent node of the node must generate a collision. For convenience of description, the variable xi is set_L,i/mIs the probability of collision at the ith node in the L-th level. Wherein,

ξ_L,i/m＝ξ_L/m＝p(k＞1/m,L) (8)

therefore, the total number of slots of the full B-ary tree should be the sum of all the visited nodes, and the equations (4), (8) and (9) are combined to obtain:

the number of collision slots is:

the number of idle time slots is:

i (m) = t (m) c (m) - m = (\frac{B - 1}{B}) t (m) - \frac{1}{B} - m - - - (12)

substituting B-16 into (10), (11), (12), increasing the number of tags from 0 to 1000, and simulating by Matlab software, as shown in fig. 1.

From fig. 1, t (m), c (m), i (m) and the number m of labels are linearly increased, and in order to calculate more accurately, the invention fits the curves into a quadratic function curve:

t(m)＝-0.001m²+6.9m-120 (13)

i(m)＝-0.00093m²+5.5m-110 (14)

c(m)＝-6.2×10^-5m²+0.43m-7.4 (15)

2.2 analysis of the number of slots of the AS algorithm.

Since the AS algorithm uses 4-bit coding, it can be considered AS an optimization on the 16-way tree algorithm. When the reader-writer detects that only 1bit collides, the reader-writer does not need the tag to return collision bit information, directly sets collision bits to be 0 and 1 respectively, and can directly identify the two tags in the next time slot. Let g (m) be the number of tags that have only 1bit collision during the identification process.

Although the AS algorithm avoids the generation of idle time slots, when collision bit n is greater than 4 and multiple bits collide, the reader needs to send a Call command to obtain specific information of the tag collision bit, thereby determining that an effective prefix exists in the tag. Let F (m) represent the number of times the reader/writer sends the Call command, then

When the reader-writer detects that the collision bit n is less than 4, four-bit encoding is not enough, in order to reduce the calculation complexity of the label, the protocol provides that the highest collision bit is respectively set to be 0 and 1, and two new query prefixes are generated. Let H (m) be the number of times when the collision position n < 4 is detected, since the condition of H (m) is complicated, the invention analyzes it from the experimental point of view, as shown in FIG. 2. It can be seen that h (m) changes very slowly with increasing number of tags, approximates a linear relationship and occupies a small proportion of time slots, and the present invention still fits it as a quadratic curve:

H(m)＝3.6×10^-5m²+0.0027m-0.17 (18)

therefore, the total number of time slots required for the AS algorithm to successfully identify m tags is:

T(m)＝t(m)-i(m)+F(m)+H(m) (19)

substituting B with 16, and expressions (13), (14), and (17) into expression (19) can yield:

so that the throughput rate is

S = \frac{m}{T (m)} - - - (21)

3. And (4) AS algorithm agreement.

To implement this algorithm, the following three commands are defined to describe the algorithm, assuming the parameter M as the query prefix and n as the highest collision bit detected.

(1) Request command request (m): taking out a query prefix M from a Stack of a reader-writer, sending the query prefix M to a tag in a broadcast mode, comparing the query prefix M with a self serial number after the tag receives the command, and returning response information if the query prefix M is the same as the self serial number; otherwise, no response is made.

(2) Return collision information command Call (M, n): the tag receives the command, compares the serial number ID of the tag with the information M sent by the reader-writer, and if the prefix part of the ID of the tag is consistent with the prefix part of the ID of the tag, encodes the information (from the nth bit to the (n-3) th bit) of the four bits before the collision bit and returns the encoded information to the reader-writer.

(3) Sleep command Sleep (): after receiving the instruction, the tag compares the self serial number ID with the received information, and if the self serial number ID is the same as the received information, the tag enters a dormant state and does not answer the request (M) instruction any more.

The invention specifically comprises the following steps:

(S01): and initializing, namely emptying the Stack of the reader-writer Stack, and pushing an empty character string NULL into the Stack to request that the tags in the action range are in a standby state.

(S02): the reader fetches the stack head element from the stack and sends it to the tag in a broadcast manner, the tag response matching the query prefix, and returns the part of the respective ID complementary to the query prefix. If the reader-writer queries for the first time, a request (NULL) command is sent, and the tag is required to return a complete ID of the tag; if the stack is empty, jumping to step (S07);

(S03): after receiving the information returned by the label, the reader-writer firstly positions the position of the highest collision position n by using the Manchester coding principle, and then judges n:

i) if n is less than 4, the nth position is respectively set to be 0 and 1, two new query prefixes are generated and pressed into the stack, and the step (S02) is returned;

ii) otherwise, go to step (S04).

(S04): the reader-writer carries out corresponding processing according to the number of the response tags;

1) if only one tag responds, the data of the tag is directly read out, and a Sleep () command is sent to enable the tag to enter a Sleep state and not participate in the following query;

2) if there are two or more tags, further judgment is needed:

if only 1bit collides, the corresponding collision positions are respectively set to be 0 and 1, two prefixes are generated and pressed into the stack, and the step (S02) is returned;

ii, if the collision bit is 2bit or more than 2bit, the reader sends Call (M, n) command in broadcast mode, the label with the requirement condition is returned to the collision bit information, and the step (S05) is carried out.

(S05): after receiving the message M, the tag compares the message M with the ID prefix of the tag, if the message M is consistent with the ID prefix, the information from the nth bit to the nth-3 bit is correspondingly coded and returned to the reader-writer; otherwise, the label does not respond and waits for the next query;

(S06): after the reader-writer receives the coded information, the specific information that the tag collides can be obtained through decoding, and then an effective query prefix is generated and is pressed into a stack;

(S07): judging whether the stack is empty, and if so, finishing the identification process; otherwise, returning to the step (S02), the stack head element is taken out, and the above process is repeated until all the labels are identified.

The AS algorithm can obtain information of collision bits of all labels by utilizing the characteristic of Manchester coding, and requires the labels to return the collision bit coding information, after the reader-writer receives the information, an effective query prefix is generated, the labels are directly queried, and the labels only need to send the parts, complementary to the prefixes, in the serial numbers. Therefore, collision time slots are reduced, idle time slots are reduced to zero, the communication traffic of the system is reduced, the consumption of tag energy is reduced, and the RFID system is more suitable for low-cost RFID systems. The specific algorithm flow is shown in fig. 3.

The invention is characterized in that:

(1) and (5) error analysis.

In section 2.2, the present invention has performed theoretical analysis on the situation of each time slot, and the analysis result is shown in fig. 4 through experimental simulation and theoretical calculation. It can be seen from the figure that the experimental value of the throughput rate is very close to the theoretical calculation value, and the curve is relatively smooth. The maximum error of the two is 0.043 < 5%, so the experimental result is consistent with the result of theoretical analysis in the error allowable range, and the theoretical correctness is also verified from the experimental point of view. The error is mainly caused by the following reasons:

1) the sequence numbers of the tags are randomly generated and not theoretically evenly distributed, and the throughput rate is closely related to the sequence numbers.

2) In the calculation process, there is an operation of rounding, i.e. there is a loss of a certain precision.

3) H (m) is obtained by experimental statistics and therefore has certain errors.

(2) Selection of the information bit encoding length.

The reader-writer needs the tag to return collision information in order to obtain a valid query prefix. If the collision information is not encoded, the reader-writer is difficult to judge the specific information returned by each label. The invention takes the information bit coding length V as 2,3,4 and 5 bits respectively to carry out experimental simulation, as shown in FIG. 5, although the longer V, the higher the throughput rate, the higher the cost will be. Considering the tag cost and elements of various aspects, the AS algorithm selects V-4 bit. As can be seen from the figure, when V is 2, the throughput is only about 0.46. When V is 3, the performance is improved, but it is still not desirable. This is because each time a tag has a multi-bit collision, the reader needs to send a Call command once in addition in order to obtain specific information of the collision bit. When V is 2,3 bits, the step size of each query is small, the collision is severe, and therefore, the total number of slots must be increased, which ultimately results in low throughput.

(3) And analyzing the communication complexity.

The communication complexity analysis is an important method for evaluating the performance of an algorithm and comprises two parts, namely reader-writer communication complexity analysis and tag communication complexity analysis. The invention respectively simulates the communication traffic of the tag and the reader-writer in the identification process of the AS algorithm, the AMS algorithm, the JDS algorithm and the QT algorithm, and the AS algorithm command and the parameter length used in the simulation are shown in Table 3.

TABLE 3 command and parameter Length involved in AS Algorithm

1) Communication complexity of the reader/writer.

The communication complexity of the reader-writer refers to the total number of bits transmitted by the reader-writer for identifying all the tags, namely the communication traffic of the reader-writer. It can be seen from fig. 6 that the communication volume of the reader/writer in each algorithm linearly increases with the increase of the number of tags, wherein the QT algorithm increases fastest, the AMS algorithm and the JDS algorithm increase at a similar rate, and the AS algorithm increases more slowly. This is because the AS algorithm can adaptively generate an effective query prefix, which greatly reduces the number of times that the reader sends the query instruction. When the number of the tags is 1000, the communication volume of the reader-writer in the QT algorithm is 79681 bits, the JDS algorithm and the AMS algorithm are 61978 bits and 61098 bits respectively, while the AS algorithm is only 52697 bits, which is about 33.9% lower than the communication volume of the reader-writer in the QT algorithm and about 15% lower than the communication volume of the JDS algorithm and 13.8% lower than the communication volume of the reader-writer in the QT algorithm respectively.

2) The communication complexity of the tag.

In the process of identification, the tags need to respond to different commands of the reader-writer correspondingly, and the sum of the bit numbers sent by all the tags is called the traffic of the tags. The traffic of the tag is closely related to power consumption, the power consumption of the tag is increased along with the larger traffic, and the power consumption is limited for the ordinary tag. In addition, the data volume returned by the label is reduced, the risk of information leakage is reduced, and the safety of the system is improved. Therefore, the tag traffic should be reduced as much as possible. The AS algorithm inherits the advantages of the QT algorithm, which not only simplifies the design of the label, but also reduces the communication traffic of the label. AS shown in fig. 7, the traffic of the tag in the AS algorithm grows the slowest among the four algorithms, which is significantly lower than the other three algorithms. When the number of tags is 1000, the number of bits of the tags in the QT algorithm is 120700 bits, the JDS and AMS algorithms are 104942 and 108213 bits, respectively, whereas the AS algorithm is only 59266 bits, which results in approximately a 51% drop in tag traffic over the QT algorithm and 43.5% and 45.2% drops over the JDS and AMS algorithms, respectively.

(4) And (5) analyzing time complexity.

The number of queries required for the reader to successfully identify all tags is the time complexity, i.e., the total number of time slots, which is an important parameter for measuring the performance of an algorithm. The AS algorithm is an anti-collision algorithm without idle time slots, can accurately identify collision labels, can also adaptively allocate effective query prefixes, reduces the depth of a tree, and is beneficial to reducing the total time slot number. AS shown in fig. 8, the total number of slots of the four algorithms increases with the number of tags, and the total number of slots increases linearly, where the total number of slots of the QT algorithm increases fastest and the AS algorithm increases slowest. With the increasing number of labels, the advantage of the AS algorithm is more obvious. When the number of tags is 1000, the total number of slots of the AS algorithm is 1630, which is reduced by about 1174 compared to the QT algorithm, by about 369 compared to the JDS algorithm, and by about 327 compared to the AMS algorithm, which reduces the time complexity by 41.87%, 18.46%, and 16.71%, respectively.

(5) And analyzing the throughput rate.

The throughput rate is also an important index for measuring the performance of an algorithm and is closely related to the total time slot number. The invention compares the three classic anti-collision algorithms of the QT algorithm, the JDS algorithm and the AMS algorithm, as shown in FIG. 9. The throughput rates of the four algorithms are kept relatively stable, with the increase of the number of the tags, the throughput rate of the QT algorithm is about 0.35, the JDS and AMS algorithms are respectively kept about 0.5 and 0.51, and the throughput rate of the AS algorithm is highest and is kept about 0.6. When the number of tags is 1000, the throughput of the AS algorithm is improved by 72%, 22.7% and 20.1% compared to the QT, JDS and AMS algorithms, respectively.

Drawings

Fig. 1 shows the distribution of slots in a 16-ary tree.

Fig. 2 is a comparison of the number of two time slots. H (m) is the number of times when the collision bit n < 4 is detected, and T (m) is the total time slot number.

FIG. 3 is a flowchart of the AS algorithm according to the present invention.

Fig. 4 is a comparison of theoretical and experimental values of throughput.

Fig. 5 shows the effect of the coding length of the information bits on the throughput.

Fig. 6 is a traffic comparison of the reader/writer.

Fig. 7 is a traffic comparison of tags.

Fig. 8 is a comparison of the total number of slots for the four algorithms.

Fig. 9 is a comparison of throughput rates for the four algorithms.

In the figure, AS: the algorithm of the invention, AMS: adaptive Multi-tree collision Avoidance (AMS) algorithm, JDS: jump and Dynamic Searching (JDS) algorithm, QT: query Tree (QT) algorithm.

Detailed Description

The invention will be further illustrated by the following examples.

The invention comprises three stages of a stack initialization stage, a query prefix generation stage and a label identification stage, and the specific process is as follows:

(1) a stack initialization phase.

The Stack of the reader-writer Stack is emptied, and an empty character string NULL is pushed into the Stack, so that the tags in the action range are required to be in a standby state.

(2) And a query prefix generation phase.

1) The reader fetches the stack head element from the stack and sends it to the tag in a broadcast manner, the tag response matching the query prefix, and returns the part of the respective ID complementary to the query prefix. If the reader-writer queries for the first time, a request (NULL) command is sent, and the tag is required to return a complete ID of the tag;

2) after receiving the information returned by the label, the reader-writer firstly positions the position of the highest collision position n by using the Manchester coding principle, and then judges n:

if n is less than 4, respectively setting the nth position to 0 and 1, generating two new query prefixes, pressing the two new query prefixes into a stack, and returning to the step 1);

ii, if not, proceeding to step 3).

3) The reader-writer performs the following processing according to the number of the response tags:

if only one tag responds, directly entering a tag identification stage;

ii if there are two or more tags, further determination is needed:

a, if only 1bit is collided, respectively setting the corresponding collision positions to be 0 and 1, generating two prefixes and pressing the prefixes into a stack, and returning to the step 1);

b, if the collision bit is 2bit or more than 2bit, the reader sends a Call (M, n) command in a broadcasting mode, the label meeting the requirement returns the collision bit information, and the step 4 is carried out;

4) after receiving the M message, the tag compares the M message with the ID prefix of the tag, if the M message is consistent with the ID prefix, the tag correspondingly encodes the information from the nth bit to the (n-3) th bit and returns the information to the reader-writer; otherwise, the label does not respond and waits for the next query;

5) after the reader-writer receives the coded information, the specific information that the tag collides can be obtained through decoding, and then an effective query prefix is generated and is pressed into a stack.

(3) And (5) a label identification stage.

The reader judges whether the stack is empty:

1) if the identification is empty, the identification process is ended;

2) otherwise, returning to step 1) in the prefix generation stage, and taking out the elements in the stack and sending the elements to the label.

If only one tag responds, the data of the tag is directly read out, and a Sleep () command is sent to enable the tag to enter a Sleep state and not participate in the following inquiry; otherwise, returning to the step 3) in the prefix generation stage, generating a new query prefix again, and repeating the process until all the tags are identified.

The invention provides an adaptive search RFID anti-collision (AS) algorithm based on information bit coding, and AS with a QT algorithm, a label does not need to memorize the previous query condition and only needs to be compared with a prefix sent by a reader. If the match is successful, only the sequence following the prefix needs to be sent to reduce the data transmission of the tag. Although the invention is experimental simulation and theoretical analysis of the AS algorithm within 1000, most of the conclusions above are still true when the number of labels is 1200,1500, except for slight increase of error. In addition, the algorithm is also analyzed in detail from the time complexity and the communication complexity. Simulation results show that AS the number of tags increases, the AS algorithm is the same AS QT, JDS and AMS algorithms, and the traffic volume of the tags and the reader and the total number of time slots almost keep increasing linearly. Among them, the AS algorithm grows most slowly, the total amount of traffic and time slots is minimum, and the throughput rate is highest and is maintained at about 60%. Therefore, the AS algorithm provided by the invention can effectively improve the working efficiency of the RFID system, reduce the identification time and reduce the energy consumption of the label. Aiming at the identification of a large number of labels, the AS algorithm has remarkable advantages and has wide application prospect in Internet of things engineering.

Claims

1. An adaptive search RFID anti-collision method based on information bit coding is characterized by comprising the following steps:

(S01): initializing, namely emptying a Stack of a reader-writer, pressing an empty character string NULL into the Stack, and requiring that a label in an action range is in a standby state;

(S02): the reader-writer takes out the stack head element from the stack, sends the stack head element to the label in a broadcasting mode, responds to the label matched with the query prefix and returns the part which is complementary with the query prefix in the ID of each reader-writer; if the reader-writer queries for the first time, a request (NULL) command is sent, and the tag is required to return a complete ID of the tag; if the stack is empty, jumping to step (S07);

(S03): after receiving the information returned by the label, the reader-writer firstly positions the position of the highest collision position n by using the Manchester principle, and then judges n:

1) if n is less than 4, the nth position is respectively set to be 0 and 1, two new query prefixes are generated and pressed into the stack, and the step (S02) is returned;

2) otherwise, go to step (S04);

2. The adaptive search RFID collision avoidance method based on information bit encoding as claimed in claim 1, wherein said (S04) comprises the steps of:

(1) if only one tag responds, the data of the tag is directly read out, and a Sleep () command is sent to enable the tag to enter a Sleep state and not participate in the following query;

(2) if there are two or more tags, further judgment is needed:

1) if only 1bit is collided, the corresponding collision positions are respectively set to be 0 and 1, two prefixes are generated and pressed into the stack, and the step (S02) is returned;

2) if the collision bit is 2bit or more than 2bit, the reader sends Call (M, n) command in broadcast mode, the label with the requirement condition is returned to the collision bit information, and the step is carried out (S05).