CN116011478B - Unknown label identification method based on large-scale RFID system - Google Patents

Unknown label identification method based on large-scale RFID system Download PDF

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CN116011478B
CN116011478B CN202310152344.3A CN202310152344A CN116011478B CN 116011478 B CN116011478 B CN 116011478B CN 202310152344 A CN202310152344 A CN 202310152344A CN 116011478 B CN116011478 B CN 116011478B
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tag
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CN116011478A (en
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刘昊宙
陈鸿龙
林凯
闫娜
薛焕昇
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China University of Petroleum East China
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Abstract

The invention relates to an unknown label identification method based on a large-scale RFID system, which belongs to the technical field of radio frequency identification and the Internet of things, and comprises the following steps: firstly, a reader constructs an expected frame vector through EPC of a tag, and on the basis of the expected frame vector, the sizes of all '0' fragments are screened out, and the lengths of all '0' fragments are used for constructing an indication vector. The unknown label and the inactivated known label are marked simultaneously through the indication vector, so that the inactivation efficiency of the unknown label is greatly improved. When all known tags in the system are deactivated, the reader decodes all received unknown tag responses by Manchester encoding and constructs another indicator vector by screening out all "0" fragments. The reader causes the unknown tags to reply to their EPCs in a particular time slot via the indication vector. The indication vector can reduce the broadcasting cost of the reader, can effectively skip empty time slots and improves the identification efficiency of unknown tags.

Description

Unknown label identification method based on large-scale RFID system
Technical Field
The invention relates to the technical field of radio frequency identification and the Internet of things, in particular to an unknown tag identification method based on a large-scale RFID system.
Background
In general, a radio frequency identification (English: radio Frequency Identification, RFID) system consists of a back-end server with a database, a reader with one or more antennas, and a large number of RFID tags. Because the backend server has powerful computing power and memory power, it is possible to efficiently process the data stored in the database and the information returned by the reader, and provide instructions to the reader in real time to adjust, synchronize and manage the RFID tags. The reader is connected with the back-end server through a wired high-speed link, and sends radio frequency signals to the tags in the communication range through the antenna and receives information sent back by the tags. Each tag has a unique 96-bit electronic product code (english: electronic Product Code; EPC for short) for marking the identity of the target.
Through the quick checking of the tags in the system, the reader can realize the effective management of the tag targets in the RFID system. For example, in a large-scale warehouse, RFID-tagged product information is stored in a database of a back-end server. The reader can perform corresponding commercial operations on the marked products by counting tags, and unknown tags that enter the RFID system but are not registered will severely interfere with normal tag management. These unknown tags may choose the same time slot as the known tags to reply to the reader, resulting in collisions of tags that do not effectively monitor the known tags. Particularly in some important applications, identifying unknown tags in the system in time and eliminating their effect can avoid considerable economic profit losses and even safety accidents.
In the last decade, the problem of identification of unknown tags has been well studied in the academia. In the existing work, the main idea is to aim at improving the slot utilization based on the frame slot Aloha (english: framed Slotted Aloha, abbreviated: FSA) protocol. The FSA protocol is widely used for communication procedures between readers and tags, which allows each tag to randomly select a time slot to reply in a time frame. In view of this, since the time slots of the replies of the tags are random, empty time slots and conflicting time slots will be unavoidable, which will result in a relatively low efficiency when the reader collects the tags EPC.
To solve this troublesome problem in the FSA protocol, many researchers have conducted intensive studies and proposed many constructive methods. For example, chu et al propose an EUTI protocol that identifies unknown tags, in which an indicative vector is introduced to direct the known and unknown tags to respond in a particular time slot. In the first stage, the reader first builds a desired frame vector for labeling unknown tags, and then deactivates the known tags by a vector based on the desired non-gaps. However, a low proportion of the expected gaps may result in inefficient marking of unknown labels in one time frame. Furthermore, although collision slots are used to accelerate the deactivation process of known tags, the broadcasting of the indication vector introduces additional overhead. In the second stage, the EUTI protocol adopts a time frame with a larger frame length to reduce the proportion of conflict time slots, and constructs an indication vector to skip the expected empty time slots, so that the identification efficiency of unknown tags is improved. Compared with the prior work, the identification efficiency of the EUTI protocol can be greatly improved. However, a large number of "0" bits are included in the indication vector, so that the broadcasting overhead increases. Therefore, reducing broadcast overhead and improving the utilization of each slot are critical to improving recognition efficiency.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides an unknown label identification method based on a large-scale RFID system, which is reasonable in design, overcomes the defects in the prior art and has good effect.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
an unknown label identification method based on a large-scale RFID system, wherein the large-scale RFID system comprises a back-end server, an RFID reader,
Figure SMS_1
Personal known tag->
Figure SMS_2
An unknown tag, each tag having a unique 96-bit electronic code, designated EPC, said unknown tag identification method comprising the steps of:
s1, firstly entering a known tag deactivation stage, and carrying out hash operation on EPCs of all known tags by a reader to construct an expected frame vector consisting of 0 and 1
Figure SMS_3
The method comprises the steps of carrying out a first treatment on the surface of the The reader screens out all "0" fragments between the two "1" bits from the vector, wherein the maximum value of the length is +.>
Figure SMS_4
Indicating all->
Figure SMS_5
Binary character strings of bit length together form a vector +.>
Figure SMS_6
；
S2, broadcasting parameter requests to all tags by a reader, and storing an index vector in the memory of each RFID tag
Figure SMS_7
Each tag is based on hash result +.>
Figure SMS_8
And updated index vector->
Figure SMS_9
To determine if it is an unknown tag;
s3, marking the label which is not marked in S2 as a known label, and inactivating all the known labels by an RFID reader;
s4, entering an unknown label identification stage, and obtaining a hash result by each unknown label through hash operation
Figure SMS_10
And construct a length of +.>
Figure SMS_11
The bit vector is then sent to the reader;
s5, after receiving information sent back by all unknown tags, the reader decodes all the unknown tag information by Manchester decoding and reconstructs a compact indication vector
Figure SMS_12
；
S6, the reader reads the vector
Figure SMS_13
Broadcasting to all unknown tags in the system, wherein each unknown tag memory stores an index vector +.>
Figure SMS_14
If the hash result of each unknown tag +.>
Figure SMS_15
And if the value of the index vector is equal to that of the updated index vector, the unknown label sends the EPC to the reader in the corresponding time slot, so that the reader can identify the unknown label.
Further, the step S1 specifically includes: RFID reader is treated by random seed
Figure SMS_16
Hash the electronic codes of all known tags, map all known tags to a length +.>
Figure SMS_17
In the array of bits, a desired frame vector consisting of "0" and "1" is thus constructed>
Figure SMS_18
Wherein "1" represents a desired non-empty slot, including a desired single slot and a desired collision slot, and "0" represents a desired empty slot; the reader screens out all the "0" fragments between the two "1" bits from the vector and obtains the lengths of these "0" fragments, wherein the maximum value of the lengths is +.>
Figure SMS_19
A representation; the size of each "0" fragment is +.>
Figure SMS_20
Is represented by a binary string of (2), then all +.>
Figure SMS_21
Binary character strings of bit length together form a vector +.>
Figure SMS_22
。
Further, the step S2 specifically includes: the readers respectively broadcast parameters
Figure SMS_24
Sum vector->
Figure SMS_25
Feed systemAll tags in the system, each tag being based on a hash function +.>
Figure SMS_27
Obtaining hash result and obtaining final value after taking remainder of frame length>
Figure SMS_28
The method comprises the steps of carrying out a first treatment on the surface of the Each RFID tag memory stores an index vector, which is marked as +.>
Figure SMS_30
And initialized to "0"; each tag is added by +.>
Figure SMS_31
Each of +.>
Figure SMS_32
Bit fragment size to update +.>
Figure SMS_23
The method comprises the steps of carrying out a first treatment on the surface of the If updated->
Figure SMS_26
Is not equal to +.>
Figure SMS_29
The tag is marked as an unknown tag and will remain silent during the known tag deactivation phase until the unknown tag identification phase begins.
Further, the step S3 specifically includes: if a tag is not marked as an unknown tag, the tag will pass
Figure SMS_33
And
Figure SMS_34
determining whether to send a response message to the reader; if->
Figure SMS_35
Is equal to->
Figure SMS_36
The tag will send a short response to the reader in the corresponding slot, the index value of the response slot being used for updating +.>
Figure SMS_37
The index value of the "0" segment in all the "0" segments; if a tag replies in a single slot, the reader sends an "ACK" command to deactivate the tag; if the reader receives the responses of multiple tags simultaneously in a time slot, the reader sends an "NCK" command to keep the tags active and participate in the next round of known tag deactivation phase, i.e., loops steps S1 through S3, until all known tags are deactivated.
Further, step S4 specifically includes: when all the known tags are deactivated, the reader starts an unknown tag identification stage; mapping all unknown RFID tags to a long form
Figure SMS_38
In the array of bits, first the reader sends a parameter request command +.>
Figure SMS_39
Wherein->
Figure SMS_40
Is a random seed; when receiving the request command, each unknown tag is added by hash operation>
Figure SMS_41
Obtaining hash result and taking the remainder of frame length to obtain result +.>
Figure SMS_42
Then each tag constructs a length +.>
Figure SMS_43
Wherein the index value is +.>
Figure SMS_44
The value of the bit of (2)Is "1" and the remaining bits are "0".
Further, step S5 specifically includes: all unknown labels send the constructed vectors to a reader at the same time, the reader decodes all vectors by Manchester decoding, when the values of the same bit in all vectors are all 0, the reader decodes the corresponding bit into 0, and if at least one of the values of the same bit in all vectors is 1, the reader decodes the corresponding bit into X, namely, the X represents a conflict bit; the decoded tag information is recorded as a vector
Figure SMS_46
The reader will +.>
Figure SMS_47
Reconstructing a compact indicator vector +.>
Figure SMS_48
The method comprises the steps of carrying out a first treatment on the surface of the Reader screens out->
Figure SMS_49
The "0" fragments between all "X" of the sequence, and finding the maximum value of the lengths in all fragments, denoted +.>
Figure SMS_50
The method comprises the steps of carrying out a first treatment on the surface of the All "0" fragments are treated with one +.>
Figure SMS_51
The bit-long string indicates its length, all representing a length of "0" fragments +.>
Figure SMS_52
The strings of bits together form a vector +.>
Figure SMS_45
。
Further, the step S6 specifically includes: the reader will vector
Figure SMS_54
Broadcasting to all unknown tags in the system, wherein each tag is stored with another one in the memoryIndex vector->
Figure SMS_56
And initialized to "0", when +.>
Figure SMS_57
After that, each unknown tag is tagged by adding +.>
Figure SMS_58
Each of->
Figure SMS_59
Bit element to update +.>
Figure SMS_60
The method comprises the steps of carrying out a first treatment on the surface of the If updated->
Figure SMS_61
Is equal to->
Figure SMS_53
The unknown tag sends its EPC to the reader in the corresponding time slot, and the index value of the corresponding time slot is used for updating +.>
Figure SMS_55
Index values of "0" fragments in all "0" fragments; when an unknown tag sends EPC to the reader in a single time slot, the reader can correctly identify the unknown tag; if a plurality of unknown tags actually select a conflict time slot to send EPC, the reader cannot accurately identify all tags replied in the conflict time slot, and the unknown tags will participate in the next unknown tag identification phase, i.e. steps S4 to S6 are repeated until all the unknown tags are identified.
Further, at the first
Figure SMS_62
The number of known tags which are not inactivated during the sub-loop steps S1 to S3 is +.>
Figure SMS_63
UnlabeledKnowing the number of tags +.>
Figure SMS_64
Probability of one time slot being an expected empty time slot +.>
Figure SMS_65
The method comprises the following steps:
Figure SMS_66
； (1)
probability of one time slot being a desired single time slot
Figure SMS_67
The method comprises the following steps:
Figure SMS_68
； (2)
then at vector
Figure SMS_69
In (1) expect->
Figure SMS_70
0 segments, all 0 segments having an average length of
Figure SMS_71
The length of each fragment is +.>
Figure SMS_72
The binary number of bits represents a binary number of bits.
Further, in the step S2, the probability that an unknown label is marked is
Figure SMS_73
The expected value of the number of unknown tags marked in the current cycle is +.>
Figure SMS_74
。
Further, in the step S3, the expected value of the number of unlabeled unknown labels is
Figure SMS_75
The method comprises the steps of carrying out a first treatment on the surface of the Probability of a desired single time limit being selected by at least one unknown tag +.>
Figure SMS_76
The method comprises the following steps: />
Figure SMS_77
；(3)
Probability of successful deactivation of a known tag
Figure SMS_78
The method comprises the following steps:
Figure SMS_79
；(4)
the expected value of the known number of tags that are deactivated in this cycle is:
Figure SMS_80
；(5)
Figure SMS_81
in the +.>
Figure SMS_82
+1 cycles of steps S1 to S3, the number of known tags that have not been deactivated;
then the first
Figure SMS_83
Total execution time of sub-loop steps S1 to S3 +.>
Figure SMS_84
The method comprises the following steps:
Figure SMS_85
；(6)
wherein, the liquid crystal display device comprises a liquid crystal display device,
Figure SMS_86
time of broadcasting parameter request for reader, +.>
Figure SMS_87
Time taken for a single time slot for transmitting 1 bit of information, < > and->
Figure SMS_88
For the duration of the collision time slot, +.>
Figure SMS_89
The expected value of the time taken for a reader to send 1 bit of information to a tag to deactivate a known tag is:
Figure SMS_90
；(7)
Figure SMS_91
an expected value of time spent for deactivating a known tag during the ith cycle;
as is known from formula (7), when
Figure SMS_92
Optimal +.>
Figure SMS_93
Is a value of (2).
Further, at the first
Figure SMS_94
During the sub-loop steps S4 to S6, and (2)>
Figure SMS_95
Representing the number of unknown tags that were not identified before the current cycle was performed, the probability that a slot was not selected by any unknown tag +.>
Figure SMS_96
The method comprises the following steps:
Figure SMS_97
；(8)
probability that a time slot is selected by only one unknown tag
Figure SMS_98
The method comprises the following steps:
Figure SMS_99
；(9)
then at the first
Figure SMS_100
The number of unknown tags identified during the sub-loop steps S4 to S6 is +.>
Figure SMS_101
；
First, the
Figure SMS_102
Time spent in the process of sub-looping steps S4 to S6 +.>
Figure SMS_103
The method comprises the following steps:
Figure SMS_104
；(10)
wherein, the liquid crystal display device comprises a liquid crystal display device,
Figure SMS_105
time cost of single slot for tag transmission of 96-bit EPC, < >>
Figure SMS_106
Time taken for the tag to transmit 1 bit of information to the reader, < > for the tag>
Figure SMS_107
To be in vector->
Figure SMS_108
The number of "0" fragments in a sequence, the average length of all "0" fragmentsDegree is->
Figure SMS_109
The length of each fragment is +.>
Figure SMS_110
The binary number of bits represents;
the expected value of the time taken to identify an unknown tag is:
Figure SMS_111
；(11)
as is known from formula (11), when
Figure SMS_112
Finding optimal +.>
Figure SMS_113
Is a value of (2).
The invention has the beneficial technical effects.
(1) The invention introduces a compact index vector which is composed of the length of the 0 segment, shortens the broadcasting cost of the reader, and effectively improves the efficiency of unknown label marking and known label deactivation.
(2) The invention designs a compact index vector based on label reply, and collects EPCs of unknown labels by allocating a designated slot to each unknown label, thereby not only reducing broadcast overhead, but also eliminating useless empty time slots.
(3) The invention carries out extensive theoretical analysis and simulation, and proves the feasibility and effectiveness of the method.
Drawings
FIG. 1 is a schematic diagram of a process of the known tag deactivation phase of the present invention.
Fig. 2 is a schematic diagram of the manchester encoding process of the present invention.
FIG. 3 is a schematic diagram of the process of the unknown tag identification phase of the present invention.
Fig. 4 is a graph showing the results of simulation comparison experiments in which the deactivation time of the known tags varies with the number of known tags when u=10000 in the present invention.
Fig. 5 is a graph of simulation versus experimental results of the change of the deactivation time of the known tags with the number of unknown tags when n=10000 in the present invention.
Fig. 6 is a graph of simulation comparison experiment results of the change of the identification time of the unknown label with the number of the known labels when u=10000 in the present invention.
Fig. 7 is a graph of simulation comparison experiment results of the change of the identification time of the unknown label with the number of the unknown labels when n=10000 in the present invention.
Fig. 8 is a graph of simulation versus experiment results of the total execution time as a function of the number of known tags for u=10000 in the present invention.
Fig. 9 is a graph of simulated comparison experiment in which the total execution time varies with the number of unknown tags when n=10000 in the present invention.
Detailed Description
The following is a further description of embodiments of the invention, in conjunction with the specific examples:
an unknown label identification method based on a large-scale RFID system comprises a back-end server, an RFID reader and a plurality of RFID labels. The system comprises a set of known tags
Figure SMS_114
The set of unknown tags is +.>
Figure SMS_115
The number of tags is known as +.>
Figure SMS_116
The electronic codes EPC of all known tags are stored in the database of the back-end server, the number of unknown tags is +.>
Figure SMS_117
，/>
Figure SMS_118
The electronic code EPC of the size and unknown tag of (a) is notAs is known.
The invention provides an unknown tag identification method aiming at the RFID system to effectively collect EPCs of the unknown tags, which comprises two stages, namely (1) a known tag deactivation stage and (2) an unknown tag identification stage.
The known tag deactivation phase comprises two operations, namely unknown tag label and known tag deactivation, and mainly comprises the following steps:
s1, the RFID reader firstly uses random seeds as
Figure SMS_119
Hash the electronic code of 4 known tags, map 4 known tags to a length +.>
Figure SMS_120
In the array of =10, a desired frame vector consisting of "0" and "1" is thus constructed +.>
Figure SMS_121
= "0001010010", where "1" indicates a desired non-empty slot, including a desired single slot and a desired collision slot, and "0" indicates a desired empty slot; the reader screens out all "0" fragments between two "1" bits from the vector: "000", "0", "00", and gives the length of the longest "0" fragment +.>
Figure SMS_122
=3; the size of each "0" segment is represented by a 2-bit binary string, namely "00", "01" and "10". These 2-bit long binary strings are combined into a compact index vector +.>
Figure SMS_123
= "110110", the length of this vector is much smaller than +.>
Figure SMS_124
。
S2, the reader transmits the vector
Figure SMS_126
And->
Figure SMS_127
Equal parameters are broadcast to all tags in the system when the tags receive the vector + ->
Figure SMS_129
After that, each tag is according to the hash function +.>
Figure SMS_131
Obtaining hash result and obtaining final value after taking remainder of frame length>
Figure SMS_133
The method comprises the steps of carrying out a first treatment on the surface of the Each tag memory stores an index vector, which is marked as + ->
Figure SMS_135
And initialized to "0"; each tag is added by +.>
Figure SMS_137
Each of +.>
Figure SMS_125
Bit fragment size to update +.>
Figure SMS_128
The method comprises the steps of carrying out a first treatment on the surface of the As shown in FIG. 1, unknown tag +.>
Figure SMS_130
、/>
Figure SMS_132
、/>
Figure SMS_134
Updated +.>
Figure SMS_136
The values of (2) are 0, 9 and 7, respectively, and they are in +.>
Figure SMS_138
The value of the corresponding bit in (a)Are all "0", not equal to->
Figure SMS_139
These tags mark themselves as unknown tags and remain silent in the next process until the start of the unknown tag identification phase.
The unknown tag marked in S3 and S2 passes
Figure SMS_142
And->
Figure SMS_144
Is to decide whether or not to send a response message to the reader, as shown in fig. 1, because +_ updated by the first "0" fragment size>
Figure SMS_147
And their hash results->
Figure SMS_148
Equal, known tag->
Figure SMS_153
、
Figure SMS_154
And unknown tag->
Figure SMS_155
The reader will reply in the first time slot; because of the hash result->
Figure SMS_141
The second fragment size was added and was equal to +.>
Figure SMS_143
Known tag->
Figure SMS_145
The reader will reply in the second time slot; known tag->
Figure SMS_146
At the third time slotA reply reader; due to the known tag->
Figure SMS_149
And->
Figure SMS_150
Reply in a single slot, then the reader will send two "ACK" commands to deactivate them, respectively, whereas the tag +.>
Figure SMS_151
、/>
Figure SMS_152
And unknown tag->
Figure SMS_140
Will remain active and participate in the next round of known tag deactivation phase, i.e. loop steps S1 to S4, until all known tags are deactivated.
Suppose at the first
Figure SMS_156
The number of known tags which are not inactivated during the sub-loop steps S1 to S3 is +.>
Figure SMS_157
The number of unlabeled unknown tags is +.>
Figure SMS_158
Probability of one time slot being an expected empty time slot +.>
Figure SMS_159
The method comprises the following steps:
Figure SMS_160
； (1)
probability of one time slot being a desired single time slot
Figure SMS_161
The method comprises the following steps:
Figure SMS_162
； (2)
then at vector
Figure SMS_163
In (1) expect->
Figure SMS_164
The average length of all "0" fragments is +.>
Figure SMS_165
The length of each fragment is +.>
Figure SMS_166
The binary number of bits represents a binary number of bits. />
The probability of an unknown label being marked is
Figure SMS_167
The expected value of the number of unknown tags marked in the current cycle is +.>
Figure SMS_168
. The expected value of the number of unlabeled unknown tags is +.>
Figure SMS_169
The method comprises the steps of carrying out a first treatment on the surface of the Probability of a desired single time limit being selected by at least one unknown tag +.>
Figure SMS_170
The method comprises the following steps:
Figure SMS_171
；(3)
probability of successful deactivation of a known tag
Figure SMS_172
The method comprises the following steps:
Figure SMS_173
；(4)
the expected value of the known number of tags that are deactivated in this cycle is:
Figure SMS_174
；(5)
Figure SMS_175
in the +.>
Figure SMS_176
+1 cycles of steps S1 to S3, the number of known tags that have not been deactivated;
then the first
Figure SMS_177
Total execution time of sub-loop steps S1 to S3 +.>
Figure SMS_178
The method comprises the following steps:
Figure SMS_179
；(6)
wherein, the liquid crystal display device comprises a liquid crystal display device,
Figure SMS_180
time of broadcasting parameter request for reader, +.>
Figure SMS_181
Time taken for a single time slot for transmitting 1 bit of information, < > and->
Figure SMS_182
For the duration of the collision time slot, +.>
Figure SMS_183
The expected value of the time taken for a reader to send 1 bit of information to a tag to deactivate a known tag is:
Figure SMS_184
；(7)
Figure SMS_185
an expected value of time spent for deactivating a known tag during the ith cycle;
as is known from formula (7), when
Figure SMS_186
Optimal +.>
Figure SMS_187
Is a value of (2).
The unknown label identification stage is entered, and mainly comprises the following steps:
s4, after all the known RFID tags are deactivated, starting an unknown tag identification stage by the reader; mapping all unknown tags to one length
Figure SMS_188
In an array of 8 bits, the reader first sends a parameter request command to all unknown tags
Figure SMS_189
Wherein->
Figure SMS_190
Is a random seed; when receiving the request command, each unknown label is according to the hash function
Figure SMS_191
Obtaining hash result and taking the remainder of frame length to obtain result +.>
Figure SMS_192
Each unknown tag constructs an 8-bit binary character string, and transmits the 8-bit binary character string to a reader, wherein each binary character string comprises one bit of '1', the rest bits are '0', and the index value of the '1' bit is the result of tag hash operation->
Figure SMS_193
；
S5, all unknown labels simultaneously send the constructed vectors to a reader, and the reader decodes the vectors into a decoding vector through Manchester decoding
Figure SMS_194
= "0X00X 0", then the reader filters out all "0" fragments, i.e. "0", "00" and "0", the size of the longest fragment being 2, then each fragment is converted into a 2-bit binary string to indicate its size, and then the 2-bit strings are combined to construct->
Figure SMS_195
I.e. +.>
Figure SMS_196
=“011001”。
Specifically, as shown in fig. 2, manchester decoding is a synchronous clock decoding technique supported by the Gen2 standard, and is used in the physical layer to decode the clock and data of the synchronous bit stream. In manchester decoding, each bit is represented by a voltage transition. Specifically, "0" represents a single transition of the voltage from high to low, and "1" represents a single transition of the voltage from low to high. If the bits transmitted to the reader at the same time are not identical (i.e., "0" and "1"), the reader decodes the bits into a collision bit "X". If multiple bits simultaneously transmitted to the reader are identical (i.e., "0" or "1"), the reader can successfully decode the bits into the corresponding values (i.e., "0" or "1"). As shown in fig. 2, if the manchester decoded signal 1 is "010110", and the manchester decoded signal 2 is "110010", the superimposed signal will be decoded by the reader as "X10".
S6, the reader reads the vector
Figure SMS_202
Broadcasting to all unknown tags in the system, wherein each tag memory stores another index character string +.>
Figure SMS_203
And initialized to "0"; as shown in FIG. 3, when +.>
Figure SMS_204
After that, each unknown tag is labeled with (>
Figure SMS_205
+01=1) to update the index string +.>
Figure SMS_206
The method comprises the steps of carrying out a first treatment on the surface of the If unknown tag->
Figure SMS_207
Is->
Figure SMS_208
Is equal to->
Figure SMS_197
The tag will reply its EPC to the reader in the first time slot, unknown tag +.>
Figure SMS_200
、/>
Figure SMS_209
And->
Figure SMS_210
Will continue to pass (+)>
Figure SMS_211
+10+1=100) updates its index string +.>
Figure SMS_212
. Because of the hash result->
Figure SMS_213
Equal to->
Figure SMS_214
Unknown tag->
Figure SMS_198
Will be at the secondReplying to the reader in each time slot; unknown tag->
Figure SMS_199
And->
Figure SMS_201
In the third time slot reply, resulting in the generation of conflicting time slots, they will remain active and participate in the next round of unknown tag identification phase, i.e. the loop steps S4 to S6 are repeated until all unknown tags are identified.
In the first place
Figure SMS_215
During the sub-loop steps S4 to S6, and (2)>
Figure SMS_216
Representing the number of unknown tags that were not identified before the current cycle was performed, the probability that a slot was not selected by any unknown tag +.>
Figure SMS_217
The method comprises the following steps:
Figure SMS_218
；(8)
probability that a time slot is selected by only one unknown tag
Figure SMS_219
The method comprises the following steps:
Figure SMS_220
；(9)
then at the first
Figure SMS_221
The number of unknown tags identified during the sub-loop steps S4 to S6 is +.>
Figure SMS_222
；
First, the
Figure SMS_223
Time spent in the process of sub-looping steps S4 to S6 +.>
Figure SMS_224
The method comprises the following steps:
Figure SMS_225
；(10)
wherein, the liquid crystal display device comprises a liquid crystal display device,
Figure SMS_226
time cost of single slot for tag transmission of 96-bit EPC, < >>
Figure SMS_227
Time taken for the tag to transmit 1 bit of information to the reader, < > for the tag>
Figure SMS_228
To be in vector->
Figure SMS_229
The number of "0" fragments in (a) and the average length of all "0" fragments is +.>
Figure SMS_230
The length of each fragment is +.>
Figure SMS_231
The binary number of bits represents;
the expected value of the time taken to identify an unknown tag is:
Figure SMS_232
；(11)
as is known from formula (11), when
Figure SMS_233
Finding optimal +.>
Figure SMS_234
Is a value of (2). />
To further illustrate the advantages of the method of the present invention, the invention is further described in connection with experiments.
The invention compares with EUTI protocol, and carries out extensive simulation to evaluate the performance of the method (CUT for short) provided by the invention; the main evaluation index of unknown tag identification is the total execution time, which consists of two parts: (1) The deactivation time of a known tag and (2) the EPC collection time of an unknown tag;
first, the number of known tags was studied
Figure SMS_235
And the number of unknown tags->
Figure SMS_236
Impact on the deactivation time of CUT and EUTI protocols. In general, the greater the number of known tags and unknown tags, the longer it takes to deactivate the known tags. As shown in fig. 4, when the number of unknown tags is fixed to 10000, the influence of the number of known tags appears. As the number of known tags increases, the deactivation time of both CUT and eutr protocols increases. In addition, the CUT method reduces the overhead of broadcasting by avoiding broadcasting of desired frame vectors and employing a "0" segment design, thereby making recognition efficiency superior to the EUTI. FIG. 5 illustrates the effect of the number of unknown tags on the deactivation time, which is still better for the CUT method than for EUTI, and decreases with increasing number of unknown tags. The main reason is that the benefits of the "0" segment design are more pronounced when the number of unknown tags is large.
During the EPC collection phase, all known tags are deactivated and their effects are correspondingly eliminated. Thus, when the number of tags is known
Figure SMS_237
When changed, the EPC collection time of the unknown tag remains unchanged, as shown in fig. 6. Furthermore, when the number of unknown tags is +.>
Figure SMS_238
When=10000, the CUT method protocol saves about 2 seconds over the EUTI protocol in the EPC collection phase. FIG. 7 depicts the number of unknown tags when the number of known tags is fixed to 10000 +.>
Figure SMS_239
Unknown tag EPC collection time when changing from 1000 to 10000. The CUT method protocol proposed by the present invention still has some advantages in terms of collection time.
FIG. 8 illustrates when the number of unknown tags is
Figure SMS_240
=10000, known number of tags +.>
Figure SMS_241
From 1000 to 10000, the total execution time of the CUT method and the eutri protocol. The total execution time of both protocols increases gradually with the number of known tags, and the CUT method performs better than the EUTI protocol. When the number of unknown tags ∈ ->
Figure SMS_242
As it becomes larger, the gap between the time used by the CUT method and the EUTI protocol increases. Fig. 9 illustrates the effect of the number of unknown tags when the number of known tags is 10000. It is apparent that the CUT method is still superior to the EUTI protocol. This is because the design of the "0" segment will greatly reduce the broadcast overhead.
It should be understood that the above description is not intended to limit the invention to the particular embodiments disclosed, but to limit the invention to the particular embodiments disclosed, and that the invention is not limited to the particular embodiments disclosed, but is intended to cover modifications, adaptations, additions and alternatives falling within the spirit and scope of the invention.

Claims (8)

1. An unknown tag identification method based on a large-scale RFID system, wherein the large-scale RFID system includes a back-end server, an RFID reader, n known tags, and u unknown tags, each tag having a unique 96-bit electronic code denoted EPC, the unknown tag identification method comprising the steps of:
s1, firstly, entering a known label deactivation stage, wherein an RFID reader is R through a random seed 1 Carrying out hash operation on the electronic codes of all the known tags, mapping all the known tags into an array with a length of f bits, thereby constructing a desired frame vector V consisting of 0 and 1, wherein 1 represents a desired non-empty time slot, comprising a desired single time slot and a desired conflict time slot, and 0 represents a desired empty time slot; the reader screens out all '0' fragments between two '1' bits from the vector and obtains the lengths of the '0' fragments, wherein the maximum value of the lengths is denoted by l; the size of each '0' segment is represented by a binary string with a length of l, and then all binary strings with a length of l bits jointly form a vector I;
s2, the readers respectively broadcast parameters<f,R 1 >And vector I to all tags in the system, each tag receiving the request command according to a hash function H (EPC, R 1 ) Obtaining a hash result and obtaining a final value d after taking the remainder of the frame length; each RFID tag memory stores an index vector, which is marked as z and initialized as 0; each tag updates z by increasing the fragment size of each l bits in I in turn; if the updated z is not equal to d, the tag is marked as an unknown tag and will remain silent during the known tag deactivation phase until the unknown tag identification phase begins;
s3, marking the label which is not marked in S2 as a known label, and inactivating all the known labels by an RFID reader;
s4, entering an unknown label identification stage, obtaining a hash result b by each unknown label through hash operation, constructing a vector with h bits, and sending the vector to a reader;
s5, all unknown labels send the constructed vectors to a reader at the same time, the reader decodes all vectors by Manchester decoding, when the values of the same bit in all vectors are all 0, the reader decodes the corresponding bit into 0, and if at least one of the values of the same bit in all vectors is 1, the reader decodes the corresponding bit into X, namely, the X represents a conflict bit; the decoded label information is marked as a vector W, and the reader reconstructs the W into a compact indication vector L; the reader screens out the 0 segments among all the X segments in W, finds out the maximum value of the length in all the segments, and marks the maximum value as m; all the '0' fragments are represented by a character string with the length of m bits, and all the character strings with the length of m bits representing the '0' fragments jointly form a vector L;
and S6, broadcasting the vector L to all unknown tags in the system by the reader, wherein an index vector y is stored in each unknown tag memory, and if the hash result b of each unknown tag is equal to the value of the updated index vector, the unknown tag sends an EPC (electronic product code) to the reader in a corresponding time slot so that the reader can identify the unknown tag.
2. The method for identifying unknown tags based on a large-scale RFID system according to claim 1, wherein step S3 specifically comprises: if a tag is not marked as an unknown tag, the tag determines whether to send a response message to the reader through the values of d and z; if the value of z is equal to the value of d, the tag will send a short response to the reader in the corresponding time slot, and the index value of the response time slot is the index value of the "0" segment used for updating z in all the "0" segments; if a tag replies in a single slot, the reader sends an "ACK" command to deactivate the tag; if the reader receives the responses of multiple tags simultaneously in a time slot, the reader sends an "NCK" command to keep the tags active and participate in the next round of known tag deactivation phase, i.e., loops steps S1 through S3, until all known tags are deactivated.
3. The method for identifying unknown tags based on a large-scale RFID system according to claim 2, wherein step S4 specifically comprises: when all the known tags are deactivated, the reader starts an unknown tag identification stage; mapping all unknown RFID tags into an array with h bits, and firstly, a reader sends a parameter request command to all unknown tags<h,R 2 >Wherein R is 2 Is a random seed; upon receipt of the request command, each unknown tag is hashed by H (EPC, R 2 ) After the hash result is obtained and the frame length is left to obtain a result b, then each tag constructs a vector with length h, wherein the value of the bit with index value b is 1, and the rest bits are 0.
4. The method for identifying unknown tags based on a large-scale RFID system according to claim 3, wherein step S6 specifically comprises: the reader broadcasts a vector L to all unknown tags in the system, wherein the memory of each tag stores another index vector y and is initialized to 0, and after receiving L, each unknown tag updates y by adding each m-bit element in L; if the updated value of y is equal to b, the unknown tag sends its EPC to the reader in the corresponding time slot, and the index value of the corresponding time slot is the index value of the "0" segment used for updating y in all the "0" segments; when an unknown tag sends EPC to the reader in a single time slot, the reader can correctly identify the unknown tag; if a plurality of unknown tags actually select a conflict time slot to send EPC, the reader cannot accurately identify all tags replied in the conflict time slot, and the unknown tags will participate in the next unknown tag identification phase, i.e. steps S4 to S6 are repeated until all the unknown tags are identified.
5. The method for identifying unknown tags based on a large-scale RFID system as defined in claim 4, wherein the number of known tags that are not deactivated during the ith cycle steps S1 through S3 is N i The number of unlabeled unknown labels is U i Probability P that a slot is a desired empty slot ei The method comprises the following steps:
Figure FDA0004214032680000031
probability P that one slot is a desired single slot si The method comprises the following steps:
Figure FDA0004214032680000032
then in vector V, f (1-P is expected ei ) 0 segments, all 0 segments having an average length of
Figure FDA0004214032680000033
The length of each fragment is +.>
Figure FDA0004214032680000034
The binary number of bits represents a binary number of bits.
6. The method for identifying unknown tags based on a large-scale RFID system as recited in claim 5, wherein in said S2, a probability that an unknown tag is tagged is P ei The expected value of the number of marked unknown labels in the current cycle is U i P ei 。
7. The method for identifying unknown tags based on a large-scale RFID system as recited in claim 6, wherein in said S3, the expected value of the number of unlabeled unknown tags is U i ·(1-P ei ) The method comprises the steps of carrying out a first treatment on the surface of the Probability P of a desired single time limit being selected by at least one unknown tag ui The method comprises the following steps:
Figure FDA0004214032680000035
probability P of successful deactivation of a known tag i The method comprises the following steps:
Figure FDA0004214032680000036
the expected value of the known number of tags that are deactivated in this cycle is:
Figure FDA0004214032680000037
N i+1 is the number of known tags that have not been deactivated during the i+1th cycle steps S1 through S3;
the total execution time T of the ith loop steps S1 to S3 i The method comprises the following steps:
Figure FDA0004214032680000038
wherein T is query Time for broadcasting parameter request for reader, T s1 Time, T, for transmitting 1-bit information in a single slot c For the duration of the conflicting time slots, t rt The expected value of the time taken for a reader to send 1 bit of information to a tag to deactivate a known tag is:
Figure FDA0004214032680000041
E i an expected value of time spent for deactivating a known tag during the ith cycle;
as is known from formula (7), when E i The optimal value of f can be obtained at the minimum.
8. The method for identifying unknown tags based on a large-scale RFID system as defined in claim 7, wherein U 'is used during the j-th cycle steps S4 to S6' j Representing the number of unknown tags that were not identified before the current cycle was performed, the probability P that a slot was not selected by any unknown tag n The method comprises the following steps:
Figure FDA0004214032680000042
one or more ofProbability P that a slot is selected by only one unknown tag d The method comprises the following steps:
Figure FDA0004214032680000043
the number of unknown tags identified during the j-th loop steps S4 to S6 is h·p d ；
Time T 'spent in the j-th cycle of steps S4 to S6' j The method comprises the following steps:
Figure FDA0004214032680000044
wherein T is sEPC Time cost, t, of a single slot used for tag transmission of 96-bit EPC tr Time, h (1-P) n ) For the number of "0" segments in vector W, the average length of all "0" segments is
Figure FDA0004214032680000045
The length of each fragment is +.>
Figure FDA0004214032680000046
The binary number of bits represents;
the expected value of the time taken to identify an unknown tag is:
Figure FDA0004214032680000047
as is known from formula (11), when E' j And obtaining the optimal h value at the minimum.
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