CN100339860C - Method for increasing through put for radio frequency recognition system - Google Patents
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Abstract
The present invention relates to a method for enhancing the throughput of a radio frequency identification system, which can be used for the identification technique of novel individuality and non-contact type of a plurality of fields, such as production process management, supply chain management, physical distribution, transportation, retail sale, traffic transportation control, etc. In the method, each label is stored with two groups of data which are proper ID numbers and an orthogonal code which is written in random when the label is produced, and actual emitted signals of the label are the signals of the orthogonal code band spread. A reader-writer can obtain the real ID numbers of the label by relieving spread, the crash of a part of label can be avoided by the orthogonality of a spread spectrum code, and the throughput of the system can be enhanced. The method can dynamically enlarge the stable operating range of the system, and solves the problem that the system can not normally operate when a system load exceeds a time slot ALOHA stable condition.
Description
Technical field
The present invention is a kind of novel individuality, contactless recognition technology that is used for a plurality of fields such as production run management, supply chain management, logistics and transportation, distribution and retail, communications and transportation control, relate to ambits such as radio communication, Signal and Information Processing, Electromagnetic Field and Microwave Technology, relate in particular to a kind of method that improves existing radio-frequency recognition system handling capacity.
Background technology
REID (RFID:Radio Frequency Identification) is a kind of technology of utilizing wireless radio transmission to realize the contactless identification of object.It rose from the nineties in 20th century because its outstanding feature compares with traditional bar code, magnetic card and IC-card, intelligent label has that noncontact, reading rate are fast, wearing and tearing can be encrypted, do not had to data, not affected by environment, the life-span is grown, characteristics easy to use; Simultaneously, system with anticollision function also can handle a plurality of labels simultaneously, being considered to can these technology, be widely used in production run, logistic storage, retailing, commodity counterfeit prevention, security and traffic administration etc. at present to multi-field, realized the automatic collection of goods, personnel and animal information.
RFID is mainly by read write line (Interrogator/Transceiver) and intelligent label (Transponder/Tag, hereinafter to be referred as label) form, read write line sends the radiofrequency signal of certain frequency by emitting antenna, when entering the emitting antenna perform region, label produces induction current, label obtains energy and is activated, label sends information such as self coding by its built-in aerial, the read write line receiving antenna receives the carrier signal of sending from label, be sent to read write line through the antenna adjustments device, after read write line carries out the demodulation sign indicating number to received signal, data such as label coding are carried out exchanges data and can be carried out the order that application systems software is sent simultaneously by interface and upper control computer, realize different application functions.
But tending to occur to be carved with the label that surpasses when a certain in actual applications appears in the identified region of read write line simultaneously, they send its signal of data separately to read write line simultaneously, because all labels all use same frequency of operation, these signals aloft superpose and interfere with each other, and cause read write line can't accurately obtain the data that each label sends.This phenomenon is called label collision (Tag Collision).The quality of anticollision technical design has determined the rfid system performance to a great extent, and the label collision is the determinative that influences the rfid system handling capacity, and it is most important to the handling capacity that improves rfid system therefore to design more efficiently collision-proof method.
To be phase early 1970s be used to solve a kind of access technology at random that the user who disperses geographically uses the central computer resource jointly by what the University of Hawaii of the U.S. proposed first to ALOHA.Each user in the system all freely sends Frame when needed, and no matter this moment communication channel " busy/spare time " state, will inevitably data collision occur like this and cause the phenomenon of mistake, thereby must retransmit.But each user who bumps can not retransmit at once, thinks to do like this and just will inevitably continue to bump.The re-transmission policy that ALOHA system adopts is exactly to allow a user wait for that one period at random continues to retransmit again, and the little characteristics of possibility of utilizing each user to produce the identical stand-by period reduce the probability that bumps once more further.As bumping again, then wait for one section random time again, till retransmitting successfully.Result of theoretic analysis shows, obeys under the condition of Possion distribution in the arrival of Frame, and ALOHA system is under stable duty, and handling capacity S and system load S satisfy following relation:
S＝G·e
-2G
As can be seen, the maximum throughput of ALOHA system only is 1/2e=18.4%.In order to improve handling capacity, all users can be got up in time synchronously, and will be divided into a section isometric time slot (Slot) time, be designated as T equally
0And regulation and user can only could send Frame separately when each time slot begins, and such ALOHA system is referred to as time slot A LOHA or S-ALOHA.The S-ALOHA system is under stable duty, and handling capacity S and system load S satisfy following relation:
S＝G·e
-G
Obviously the throughput ratio ALOHA system of S-ALOHA system improves, and its maximum handling capacity can reach 1/e=36.8%.
Though the handling capacity of S-ALOHA system increases, it is the same with ALOHA system still to exist fatal defective, i.e. the restriction of steady operation condition, and the steady operation condition of ALOHA and S-ALOHA is respectively:
G＜0.5 and G＜1
But when the load of each system was regional above these, system played pendulum, and caused handling capacity to descend, and promptly showed the data frame number minimizing that successfully sends and the frame number increase that bumps.This situation causes more re-transmission, thereby offered load G is further increased.The result of vicious cycle makes handling capacity continue to descend till zero like this.At this moment, system load reaches very big numerical value, and Frame constantly sends, collides, retransmits ..., but there is no useful output.Total system can not have been worked fully.
Yet, for some applied environment, join goods center or checkout counter as the supermarket, exist read write line need handle numerous article that contain label simultaneously, can not be oversize and finish total time of article of handling these labels, otherwise can cause overstocking of article, influence the efficient of system handles, the load of system at this moment tends to surpass the stable condition of ALOHA or S-ALOHA system, can cause system's cisco unity malfunction, this situation be in actual applications exist but the existing insurmountable again problem of method.
Summary of the invention
Technical matters: the invention provides a kind of method that improves the radio-frequency recognition system handling capacity, can dynamically enlarge the stable operation range of system, solving when system load surpasses time slot A LOHA stable condition is the problem that causes system's cisco unity malfunction.
Technical scheme: a kind of method that improves the radio-frequency recognition system handling capacity of the present invention is in realizing the radio-frequency recognition system that time slot " ALOHA " inserts, as follows to the production process of label in the radio-frequency recognition system and card reader:
A. when carrying out label production, be used for storage tags ID number the data field except original, increase a data field in addition, be used for depositing an orthogonal code, and this orthogonal code is one that selects at random and write when producing in prior fixed spread spectrum code character; Simultaneously, increase corresponding spectrum spreading circuit in label, actual transmission is through the ID of this orthogonal code spread spectrum data when realizing that label sends self ID in entering the identified region of card reader;
B. for can successfully receive the ID data that each label is issued card reader, when carrying out the production of card reader, increase a data field and be used for storing pre-determined spread spectrum code character sequence and corresponding de-spreading circuit; Obtained under the synchronous condition in system (this condition by realize rfid system that the ALOHA mode inserts indispensability), card reader is when receiving the Frame that label sends, utilize each orthogonal code in the orthogonal code sets that the superposition of data that is received is carried out despreading successively, for selecting the different orthogonal sign indicating number separately for use and sending the label of Frame at same time slot, ID separately is because via different orthogonal code spread spectrums, and the orthogonality that card reader is utilized orthogonal code despreading respectively draws.
Principle of work of the present invention:
T
0The expression user sends the required time of single frames data, and handling capacity (Throughput) S is called throughput again, and it equals at T
0In the average frame number that sends of success, whether utilize it to weigh the utilization of channel abundant.Obviously, 0≤S≤1, and S=1 is a limiting case.When S=1, time frame sends one by one, frame and auspicious between do not have the space.Though this situation makes the utilization of channel the most abundant, be impossible realize under the situation of transmit frame at random numerous users.
It equals system load (Offered Load) G at T
0In the average frame number that sends altogether, comprise sending successful frame and not sending the frame that successfully retransmits because of colliding.Obviously, G 〉=S, and only when not bumping, G just equals S.G can be much larger than 1, and for example, G=10 is illustrated in T
0Interior network has sent 10 frame data altogether, and this can cause a lot of collisions certainly.
The principle of work and the system of the slotted ALOHA system that divides based on sign indicating number form as shown in Figure 1, main thought is summarized as follows: have two groups of data in each label: the ID of himself number and when producing a certain orthogonal code of random writing, the signal of the actual transmission of label is the signal through this orthogonal code spread spectrum, and read write line obtains the real ID of label number by despreading and utilizes the orthogonality of spreading code to stop the label collision of a part to improve the handling capacity of system.
Yet, because label ID number possible variation is much larger than the quantity of orthogonal code, thereby must have different labels in practice and selected identical orthogonal code for use, obtain on the synchronous basis at all labels, must also can bump when these labels send its ID simultaneously, at this moment still adopt random back in the Slotted-ALOHA system to reach the purpose of identification.Very simple when in label, realizing like this, only need increase by one group of quadrature and corresponding spectrum spreading circuit, change very little to the hardware circuit in the former label.In addition, the selected in advance and limited amount of all orthogonal code sets, and be stored in the read write line, this consideration both realized in label in order to be easy to, and also can be reduced in the complexity that realizes in the read write line.
In view of its good auto-correlation and cross correlation, can select the walsh code (Walsh sign indicating number) of different rank by the different demands of reality for use, after being carried out spread processing, ID number of label can be implemented in the identified region that the label of synchronization more than 2 enters read write line simultaneously with it, after they send separately ID number simultaneously, read write line also can intactly be isolated ID number of different labels when receiving these signals after space stack, broken through the restriction that time slot A LOHA algorithm can not have 2 above labels to arrive at synchronization.
Because ID number of all labels is inequality, only select different Walsh sign indicating numbers for use and in same time slot, send ID number just can successfully be obtained through despreading, and different at this moment labels still will cause the label collision after having selected identical Walsh sign indicating number for use by read write line when it.Obviously, when the number of tags that arrives in a certain time slot is k, when the Walsh code character exponent number that can Gong select for use was N, under the meaning of statistics, the average of the Walsh sign indicating number inequality that this k label is selected for use at random (was the average label that read write line at this moment can successful despreading in the crack
Number) can provide by following formula:
The average of system's number of tags of the successful despreading of energy in a certain time slot (is the handling capacity S of system under the condition that sign indicating number divides
C) be:
When the label of system arrives to Poisson process, under the system stability state, handling capacity S
CCan provide by following formula:
System load G and handling capacity S under the condition of different Walsh code character exponent number N
CRelation as shown in Figure 2.There is following formula to know, works as G=N, handling capacity S
CGet maximal value, i.e. max (S
C)=N/e, promptly Zui Da handling capacity be former slotted ALOHA system N doubly, promptly introduce sign indicating number and divide the handling capacity of mechanism back system to be improved, this has also obtained confirmation in the simulation result of back.In addition, when the exponent number of the Walsh sign indicating number of selecting for use is 16, the handling capacity maximum of the slotted ALOHA system that sign indicating number divides can reach 5.89, far above 0.368 of time slot A LOHA, and along with the raising of Walsh code character exponent number, the maximal value of handling capacity can also improve, but this is to be cost with the hardware complexity that increases read write line and label, thereby must make compromise selection in handling capacity and Walsh code character exponent number according to demand in actual use.
LOHA is the same with time slot A, when G＜N, and the handling capacity S of CS-ALOHA system
CIncrease along with the increase of system load G; After G＞N, handling capacity is on a declining curve, this is because after the number of labels that arrives in same time slot is increased to a certain degree, finiteness based on Walsh code character exponent number N, select for use identical Walsh sign indicating number will increase as the number of labels of spreading code, must cause the increase of colliding this moment, and system enters unsettled zone.Therefore, be shown below in the stable condition of slotted ALOHA system of dividing based on sign indicating number, the stable operation range of CS-ALOHA system is much larger than time slot A LOHA as can be seen, and can come the dynamically stable operation range of Adjustment System by the size that changes N.
G＜N
Certainly, because number of tags is much larger than the quantity of Walsh code character that can be selected in actual use, thereby have different labels unavoidably and selected identical Walsh sign indicating number randomly for use, when sending data simultaneously, such label still can cause collision, still adopt the random back mechanism in the slotted ALOHA system this moment, each label is delayed time separately and is sent data again after a period of time, utilizes the difference of the random back time that each label produces to reduce the probability of collision once more.In addition, during random delay long enough when retransmitting, can think when the label after keeping out of the way retransmits does not influence the characteristic that label arrives the Poisson process that is satisfied.
Beneficial effect:
(1) raising of handling capacity: the present invention can improve N doubly from 36.8% of time slot A LOHA with the maximum throughput of system, and wherein N is selected Walsh code character exponent number;
(2) lower implementation complexity: realize that in label the present invention only need increase by one group of orthogonal code and corresponding spectrum spreading circuit, changes very little to the hardware circuit in the former label; The selected in advance and limited amount of all orthogonal code sets, and be stored in the read write line, this consideration both realized in label in order to be easy to, and also can be reduced in the complexity that realizes in the read write line; All the other are all identical with the rfid system of realizing time slot A LOHA access.
(3) expansion of system stability working range: the present invention can bring up to G＜N from G＜1 with the stable operation range of former slotted ALOHA system, and can come the dynamically stable operation range of Adjustment System by the size that changes N.
Description of drawings
Fig. 1 is the slotted ALOHA system principle of work and the block diagram of system that divides based on sign indicating number of the present invention.
The throughput curve of Fig. 2 CS-ALOHA system.
The throughput ratio of Fig. 3 two systems.
Embodiment
A kind of method that improves the radio-frequency recognition system handling capacity of the present invention is in realizing the radio-frequency recognition system that time slot " ALOHA " inserts, as follows to the production process of label in the radio-frequency recognition system and card reader:
A. when carrying out label production, be used for storage tags ID number the data field except original, increase a data field in addition, be used for depositing an orthogonal code, and this orthogonal code is one that selects at random and write when producing in prior fixed spread spectrum code character; Simultaneously, increase corresponding spectrum spreading circuit in label, actual transmission is through the ID of this orthogonal code spread spectrum data when realizing that label sends self ID in entering the identified region of card reader;
B. for can successfully receive the ID data that each label is issued card reader, when carrying out the production of card reader, increase a data field and be used for storing pre-determined spread spectrum code character sequence and corresponding de-spreading circuit; Obtained under the synchronous condition in system (this condition by realize rfid system that the ALOHA mode inserts indispensability), card reader is when receiving the Frame that label sends, utilize each orthogonal code in the orthogonal code sets that the superposition of data that is received is carried out despreading successively, for selecting the different orthogonal sign indicating number separately for use and sending the label of Frame at same time slot, ID separately is because via different orthogonal code spread spectrums, and the orthogonality that card reader is utilized orthogonal code despreading respectively draws.
Because label ID number possible variation is much larger than the quantity of orthogonal code, thereby must have different labels in practice and selected identical orthogonal code for use, obtain on the synchronous basis at all labels, must also can bump when these labels send its ID simultaneously, at this moment still adopt random back in the Slotted-ALOHA system to reach the purpose of identification.In label, realize needing to increase by one group of orthogonal code and corresponding spectrum spreading circuit like this.
In addition, the selected in advance and limited amount of all orthogonal code sets, and be stored in the read write line, this consideration both realized in label in order to be easy to, and also can be reduced in the complexity that realizes in the read write line.
In view of its good auto-correlation and cross correlation, can select the walsh code (Walsh sign indicating number) of different rank by the different demands of reality for use, after being carried out spread processing, ID number of label can be implemented in the identified region that the label of synchronization more than 2 enters read write line simultaneously with it, after they send separately ID number simultaneously, read write line also can intactly be isolated ID number of different labels when receiving these signals after space stack, broken through the restriction that time slot A LOHA algorithm can not have 2 above labels to arrive at synchronization.
In order to verify the thinking of proposition, under the MATLAB environment, draw simulation result as Fig. 3.Wherein the exponent number N=4 with the Walsh code character is an example, and the handling capacity of the CS-ALOHA system that this paper is proposed and traditional slotted ALOHA system compares.Simulated conditions is that the arrival of label meets Poisson process, utilizes arrival rate to produce for the Poisson generator of G.From simulation result, under the condition of same arrival rate, the handling capacity of CS-ALOHA system is far above the S-ALOHA system, and increase along with arrival rate, the handling capacity of CS-ALOHA system also increases thereupon, and when G=4, reach maximum, and when G＞4, reducing along with the increase of arrival rate, this has just verified the performance of CS-ALOHA system and has reached its intended purposes.Gap as for simulation value and theoretical value mainly is to arrive sequence because only can choose the Poisson of certain-length in emulation, and can there be error in the sequence of these finite lengths with theoretical value on statistical significance, and this error can not reduce because of the increase of the sequence length that produces or eliminate, and similar situation also can exist when a certain label of emulation is selected the Walsh sign indicating number at random.
Claims (1)
1. method that improves the radio-frequency recognition system handling capacity is characterized in that: in realizing the radio-frequency recognition system that time slot " ALOHA " inserts, as follows to the production process of label in the radio-frequency recognition system and card reader:
A. when carrying out label production, be used for storage tags ID number the data field except original, increase a data field in addition, be used for depositing an orthogonal code, and this orthogonal code is one that selects at random and write when producing in prior fixed spread spectrum code character; Simultaneously, increase corresponding spectrum spreading circuit in label, actual transmission is through the ID of this orthogonal code spread spectrum data when realizing that label sends self ID in entering the identified region of card reader;
B. for can successfully receive the ID data that each label is issued card reader, when carrying out the production of card reader, increase a data field and be used for storing pre-determined spread spectrum code character sequence and corresponding de-spreading circuit; Obtained under the synchronous condition in system, card reader is when receiving the Frame that label sends, utilize each orthogonal code in the orthogonal code sets that the superposition of data that is received is carried out despreading successively, for selecting the different orthogonal sign indicating number separately for use and sending the label of Frame at same time slot, ID separately is because via different orthogonal code spread spectrums, and the orthogonality that card reader is utilized orthogonal code despreading respectively draws; Described obtained synchronous condition by realize rfid system that the ALOHA mode inserts indispensability.
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| CN100535922C (en) * | 2006-09-28 | 2009-09-02 | 中兴通讯股份有限公司 | Radio frequency identification multiple tag access method |
| CN101281587B (en) * | 2007-07-26 | 2010-06-09 | 北京航空航天大学 | Radio frequency recognition reading method and answering method |
| CN101499119B (en) * | 2008-01-31 | 2011-09-21 | 中兴通讯股份有限公司 | Label recognition method, system and apparatus based on radio frequency recognition |
| JP5266397B2 (en) * | 2008-12-12 | 2013-08-21 | ハンリム ポステック カンパニー リミテッド | Contactless power transmitter |
| CN103034825B (en) * | 2012-12-05 | 2015-11-04 | 无锡赛睿科技有限公司 | Based on the method for recognizing radio frequency label of walsh code |
| CN103117770A (en) * | 2013-01-24 | 2013-05-22 | 重庆邮电大学 | Multi-label anticollision method in RFID (radio frequency identification) system |
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| CN1496162A (en) * | 1998-02-21 | 2004-05-12 | ���ǵ�����ʽ���� | Transmitting method for mobile communication base station system |
| US20050058212A1 (en) * | 2003-09-15 | 2005-03-17 | Lei Shao | Multiple antenna systems and methods using high-throughput space-frequency block codes |
| CN1215657C (en) * | 2000-12-21 | 2005-08-17 | 三星电子株式会社 | Transmit antenna diversity appts. and method for base station in CDMA mobile communication system |
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| CN1496162A (en) * | 1998-02-21 | 2004-05-12 | ���ǵ�����ʽ���� | Transmitting method for mobile communication base station system |
| CN1215657C (en) * | 2000-12-21 | 2005-08-17 | 三星电子株式会社 | Transmit antenna diversity appts. and method for base station in CDMA mobile communication system |
| US20050058212A1 (en) * | 2003-09-15 | 2005-03-17 | Lei Shao | Multiple antenna systems and methods using high-throughput space-frequency block codes |
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