Tag anti-collision method based on missed read warning in single reader mobile RFID system

Abstract

The present invention relates to a tag anti-collision method based on missed reading warning in a single-reader mobile RFID system, and belongs to the field of wireless radio frequency identification technology. The present invention adopts bit time slot ALOHA to improve reading efficiency, utilizes the mobility of the reader to obtain tag information, estimates the number of unrecognized tags, and judges whether missed reading will occur based on the number of unrecognized tags, and reduces missed reading by prompting the user to stop moving. The present invention first uses a mobile reader to collect data from a scene to estimate the number of unrecognized tags within the reader's recognition range, thereby obtaining the number of unrecognized tags within the reader's recognition range, and then compares the number of unrecognized tags in the previous recognition cycle to judge whether there is a risk of missed reading of tags. If there is a risk of missed reading of tags, the user is prompted to stop moving the reader to reduce missed reading of tags. The present invention can reduce the time wasted due to missed reading of tags in small and medium-sized warehouses, thereby improving recognition efficiency.

Description

Technical Field

[0001] The invention relates to a tag anti-collision method based on missed reading warning in a single-reader mobile RFID system, belonging to the technical field of radio frequency identification technology (RFID). Background Art

[0002] Currently, there are two main ways to identify RFID tags in small and medium-sized warehouses: one is to use multiple readers for joint identification, but the reader cost is too high and collisions between readers are very likely to occur; the other is to use a single reader mobile identification in the warehouse, which is simple, feasible and low-cost.

[0003] Through searching existing patents and papers, it was found that in existing small and medium-sized warehouse environments, due to the movement of a single reader, the tag leaves the reader signal area before being identified, that is, the tag is missed. Because in small and medium-sized warehouse environments, the movement direction of the reader is unidirectional, the missed tag requires the reader to move one circle back to the position of the missed tag before it can identify the missed tag in the previous circle, which results in a lot of time. Summary of the invention

[0004] The present invention provides a tag anti-collision method based on missed reading warning in a single-reader mobile RFID system, which is used to solve the following problems existing in single-reader RFID identification in small and medium-sized warehouses: 1) tags are missed and a lot of time is wasted; 2) the RFID system is not efficient; 3) the reader consumes too much energy, etc.

[0005] The technical solution of the present invention is: a tag anti-collision method based on missed reading warning in a single reader mobile RFID system, and the specific steps are as follows:

[0006] Step 1: RFID tags are randomly distributed in the environment. The user holds a single reader and moves along a fixed path, using the mobility of the reader to obtain tag information. The reader keeps reading tags during the movement.

[0007] Step 2: Hold the same reader and move along the same path. The reader sends a start command to start a new identification cycle. The tags in the reader signal area send a bit sequence of L bits, representing L bit slots. Each tag will randomly set the i-th bit in the bit sequence it sends to 1 and set the rest to 0. The tag records the bit slot it chooses.

[0008] Step 3: The reader receives the bit sequence sent by the tag. If a collision occurs in a certain bit position, it means that at least one tag selects the bit position. The reader records all the collision bit time slot numbers, and then queries the collision bit time slots from the tags in the reader signal area.

[0009] Step 4: Query the collided bit slots. The response received by the reader may appear in three situations:

[0010] (1) Idle time slot: There is no tag communicating with the reader in the signal area, the reader cannot read any information, and queries the next collision bit slot;

[0011] (2) Collision time slot: Multiple tags in the signal area communicate with the reader, and the reader cannot read any information, so it queries the next collision bit slot;

[0012] (3) Successful time slot: Only one tag in the signal area selects this time slot to communicate with the reader. The reader can successfully read the tag information. The reader silences the tag and queries the next colliding bit slot.

[0013] Step 5, after querying all collision bit slots, the reader estimates the number of unidentified tags in the reader signal area;

[0014] Step 6. The reader compares the number of unrecognized tags in the signal area of ​​the previous identification cycle with the number of unrecognized tags in the current signal area, and records the number of unrecognized tags in the current signal area. The reader determines whether there is a risk of missing tags. If there is a risk, the reader prompts the user that a tag is about to be missed, stops moving, and identifies all tags in the signal area at the original location before moving again. If there is no risk, it directly enters Step 7.

[0015] Step 7: Repeat Step 2-Step 6 for multiple rounds along a fixed path until all tags are identified.

[0016] Furthermore, when the reader determines that there is a risk of missing a tag, the reader prompts the user to stop moving.

[0017] Furthermore, after one recognition cycle, the reader estimates the number of unrecognized tags in the reader signal area. The specific method for the reader to estimate the number of tags is as follows:

[0018] Step 1: The reader selects a ca according to the number of collision bit slots in the identification cycle, where ca is the number of tags in each collision slot, specifically through formula (1):

[0019] ca=a*e (b*coll_bit) +c*e (d*coll_bit) (1)

[0020] coll_bit is the number of bit time slots with collisions during the current recognition cycle. a, b, c, d, and e are all fixed constants. Specifically, a = 1.9, b = 0.002957, c = 2.571×10^(-7), d = 0.1236, and e = 2.7182.

[0021] Step 2: Estimate the number of unrecognized tags in the reader signal area through Formula (2) as follows:

[0022] n = ca * coll_slot (2)

[0023] n is the number of unrecognized tags in the reader signal area, and coll_slot is the number of time slots with collisions during the current recognition cycle.

[0024] Furthermore, the reader uses the bit - time - slot ALOHA algorithm to identify tags in the warehouse, and the length of the bit time slot L = 128.

[0025] Furthermore, to reduce the tag missed - reading rate, when the reader determines that there is a risk of tag missed - reading, the reader prompts the user to stop moving.

[0026] Furthermore, the method for the reader to determine whether there will be a tag missed - reading phenomenon is as follows:

[0027] Step6.1: Compare the number of unrecognized tags n in the reader signal area with n_last, where n_last is the number of unrecognized tags in the previous recognition cycle. There are two cases:

[0028] (1) When n is greater than or equal to n_last, it indicates that during the current recognition cycle, the recognition rate is lower than the rate at which tags enter the signal area, and there is a risk of tag missed - reading. Update G according to Formula (3):

[0029] G = G_last + g (3)

[0030] G is the continuous increase in the number of unrecognized tags, used to determine whether the number of unrecognized tags in the reader signal area has been continuously increasing in the recent several recognition cycles; G_last is the number of unrecognized tags in the previous recognition cycle; g is the increase coefficient, and the value range of g is 0 < g < 0.5. The larger g is, the more sensitive the reader is to the continuous increase in the number of unrecognized tags, and the smaller g is, the more insensitive the reader is to the continuous increase in the number of unrecognized tags.

[0031] (2) When n is less than n_last, it indicates that during the current recognition cycle, the recognition rate is higher than the rate at which tags enter the signal area, and the risk of tag missed - reading is relatively low. Update G according to Formula (4):

[0032]

[0033] Step 6.2, determine whether G is less than 0, if G is less than 0, set G to 0;

[0034] Step 6.3, update n_last, make n_last = n, update G_last, make G_last = G;

[0035] Step 6.4, determine whether G is greater than 1, there are two cases:

[0036] (1) G is greater than or equal to 1. G is set to 0, which means that the reader's recognition rate is lower than the rate at which the tag enters the signal area during several recognition cycles. The reader determines that there is a risk of missing the tag. The reader prompts the user that there is a risk of missing the tag, and asks the user to stop moving and enter Step 6.5.

[0037] (2) If G is less than 1, it means that the risk of missing tags is low, and the process goes directly to Step 7.

[0038] Step 6.5, the reader stops moving and identifies the unidentified tags in the current signal area. In each identification cycle, after querying all collision bit time slots, the reader detects whether the coll_bit of the current identification cycle is 0. There are two cases:

[0039] (1) coll_bit is equal to 0, indicating that all tags in the current signal area have been identified. The reader prompts the user to continue moving and enters Step 7;

[0040] (2) If coll_bit is not equal to 0, it means that all tags in the current signal area have not been identified. The reader prompts the user to remain in the stopped state and repeat Step 6.5.

[0041] The beneficial effects of the present invention are:

[0042] 1. The present invention predicts the phenomenon of missed label reading and reduces the time cost wasted due to missed label reading;

[0043] 2. The present invention uses a reader to remind the user of the risk of missing tags, so that the reader stops moving, thereby reducing the number of missed tags;

[0044] 3. The present invention solves the problems of serious time waste and low system throughput in RFID tag recognition in small and medium-sized warehouses, and improves recognition efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a scene diagram of a small or medium-sized warehouse;

[0046] Figure 2It is a flow chart of the tag anti-collision method based on missed reading warning;

[0047] Figure 3 This is a performance comparison chart of the tag loss rate between the tag anti-collision method based on missed read warning and the original method. DETAILED DESCRIPTION

[0048] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0049] Example 1: Figure 1-3 As shown in Figure 1, a tag anti-collision method based on missed reading warning in a single reader mobile RFID system, a scene diagram of a single reader identifying RFID tags in small and medium-sized warehouses, as shown in Figure 1. Figure 1 shown.

[0050] RFID tags are randomly distributed in the tag distribution area P, the reader signal area radius is R_cov, and the reader moving area is area A. The reader moves unidirectionally in area A according to the movement direction marked in the figure.

[0051] The specific steps of the method are as follows Figure 2 As shown:

[0052] Step 1: RFID tags are randomly distributed in the environment. The user holds a single reader and moves along a fixed path, using the mobility of the reader to obtain tag information. The reader keeps reading tags during the movement.

[0053] Step 2: Hold the same reader and move along the same path. The reader sends a start command to start a new identification cycle. The tags in the reader signal area send a bit sequence of L bits, representing L bit slots. Each tag will randomly set the i-th bit in the bit sequence it sends to 1 and set the rest to 0. The tag records the bit slot it chooses.

[0054] Step 3: The reader receives the bit sequence sent by the tag. If a collision occurs in a bit slot, it means that at least one tag selects the bit position. The reader records all the collision bit slot numbers and then queries the collision bit slots from the tags in the reader signal area.

[0055] Step 4: Query the collided bit slots. The response received by the reader may appear in three situations:

[0056] (1) Idle time slot: There is no tag communicating with the reader in the signal area, the reader cannot read any information, and queries the next collision bit slot;

[0057] (2) Collision time slot: Multiple tags in the signal area communicate with the reader, and the reader cannot read any information, so it queries the next collision bit slot;

[0058] (3) Successful time slot: Only one tag in the signal area selects this time slot to communicate with the reader. The reader can successfully read the tag information. The reader silences the tag and queries the next colliding bit slot.

[0059] Step 5, after querying all collision bit slots, the reader estimates the number of unidentified tags in the reader signal area;

[0060] Step 6. The reader compares the number of unrecognized tags in the signal area of ​​the previous identification cycle with the number of unrecognized tags in the current signal area, and records the number of unrecognized tags in the current signal area. The reader determines whether there is a risk of missing tags. If there is a risk, the reader prompts the user that a tag is about to be missed, stops moving, and identifies all tags in the signal area at the original location before moving again. If there is no risk, it directly enters Step 7.

[0061] Step 7: Repeat Step 2-Step 6 for multiple rounds along a fixed path until all tags are identified.

[0062] Furthermore, after one recognition cycle, the reader estimates the number of unrecognized tags in the reader signal area. The specific method for the reader to estimate the number of tags is as follows:

[0063] Step 1: The reader selects a ca according to the number of collision bit slots in the identification cycle, where ca is the number of tags in each collision slot, specifically through formula (1):

[0064] ca=a*e (b*coll_bit) +c*e (d*coll_bit) (1)

[0065] coll_bit is the number of bit slots that collide in this identification cycle. a, b, c, d, and e are all fixed constants. Specifically, a=1.9, b=0.002957, c=2.571*10^(-7), d=0.1236, and e=2.7182.

[0066] Step 2: Estimate the number of unidentified tags in the reader signal area using formula (2). Formula (2) is as follows:

[0067] n=ca*coll_slot (2)

[0068] n is the number of unidentified tags in the reader signal area, and coll_slot is the number of time slots that collide in this identification cycle.

[0069] Furthermore, the method for the reader to determine whether there will be missed tag readings is as follows:

[0070] Step6.1. Compare the number of unrecognized tags n in the reader's signal area with n_last, where n_last is the number of unrecognized tags in the previous recognition cycle. There are two cases:

[0071] (1). If n is greater than or equal to n_last, it means that in this recognition cycle, the recognition rate is lower than the rate at which tags enter the signal area, and there is a risk of missed tag readings. Update G according to formula (3);

[0072] G = G_last + g (3)

[0073] G is the continuous increase in the number of unrecognized tags, used to determine whether the number of unrecognized tags in the reader's signal area has been continuously increasing in the recent several recognition cycles; G_last is the number of unrecognized tags in the previous recognition cycle; g is the increase coefficient, and the value range of g is 0 < g < 0.5. The larger g is, the more sensitive the reader is to the continuous increase in the number of unrecognized tags, and the smaller g is, the more insensitive the reader is to the continuous increase in the number of unrecognized tags.

[0074] (2). If n is less than n_last, it means that in this recognition cycle, the recognition rate is higher than the rate at which tags enter the signal area, and the risk of missed tag readings is relatively low. Update G according to formula (4);

[0075]

[0076] Step6.2. Determine whether G is less than 0. If G is less than 0, set G to 0;

[0077] Step6.3. Update n_last so that n_last = n, and update G_last so that G_last = G;

[0078] Step6.4. Determine whether G is greater than 1. There are two cases:

[0079] (1). If G is greater than or equal to 1, set G to 0, which means that in several recognition cycles, the recognition rate of the reader is lower than the rate at which tags enter the signal area. The reader determines that there is a risk of missed tag readings and prompts the user that there is a risk of missed tag readings, asking the user to stop moving and enter Step6.5;

[0080] (2). If G is less than 1, it means that the risk of missed tag readings is relatively low, and directly enter Step7;

[0081] Step 6.5, the reader stops moving and identifies the unidentified tags in the current signal area. In each identification cycle, after querying all collision bit time slots, the reader detects whether the coll_bit of the current identification cycle is 0. There are two cases:

[0082] (1) coll_bit is equal to 0, indicating that all tags in the current signal area have been identified. The reader prompts the user to continue moving and enters Step 7;

[0083] (2) If coll_bit is not equal to 0, it means that all tags in the current signal area have not been identified. The reader prompts the user to remain in the stopped state and repeat Step 6.5.

[0084] In this embodiment 1, MATLAB is used to perform simulation experiments. The scene diagram of the warehouse is as follows: Figure 1 , set the number of tags to be tested in the warehouse to 4000, the radius of the reader signal area to R_cov, the length of the tag distribution area to 5 times of R_cov, the width to 2.5 times of R_cov, the length of the bit time slot L to 128, g equals 0.4, in order to compare the performance of the improved tag anti-collision method with missed reading warning and the tag anti-collision method without missed reading warning of the present invention, the same performance indicator will be used: tag loss rate.

[0085] Simulation experiments have proved that the tag anti-collision method based on missed read warning only needs 15,000 time slots to identify 96.5% of the tags, and can be fully identified within 16,000 time slots, while the tag anti-collision method without missed read warning takes 15,000 time slots to identify only 13% of the tags; this shows that when there is a risk of missed read, the tag anti-collision method based on missed read warning can timely warn of the occurrence of missed read; the tag anti-collision method without missed read warning has a large number of unidentified tags that directly leave the reader signal area, resulting in a high tag loss rate; in general, the tag anti-collision method based on missed read warning can greatly reduce the tag loss rate and improve the system efficiency.

[0086] The present invention is applicable to the recognition scenario of RFID tags by a single reader in small and medium-sized warehouses, and can reduce the time wasted due to missed reading of tags in small and medium-sized warehouses, thereby improving the recognition efficiency.

[0087] The specific implementation modes of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above implementation modes, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A tag anti-collision method based on missed reading warning in a single reader mobile RFID system, characterized by: The specific steps are as follows: Step 1: RFID tags are randomly distributed in the environment. The user holds a single reader and moves along a fixed path, using the mobility of the reader to obtain tag information. The reader keeps reading tags during the movement. Step 2: Hold the same reader and move along the same path. The reader sends a start command to start a new identification cycle. The tags in the reader signal area send a bit sequence of L bits, representing L bit slots. Each tag will randomly set the i-th bit position in the bit sequence it sends to 1, and set the rest of the positions to 0. The tag records the bit slot it chooses. Step 3: The reader receives the bit sequence sent by the tag. If a bit slot collides, it means that at least one tag selects the bit position. The reader records all the colliding bit slot numbers and then queries the colliding bit slots from the tags in the reader signal area. Step 4: Query the collided bit slots. The response received by the reader may appear in three situations: (1) Idle time slot: There is no tag communicating with the reader in the signal area, the reader cannot read any information, and queries the next collision bit slot; (2) Collision time slot: Multiple tags in the signal area communicate with the reader, and the reader cannot read any information, so it queries the next collision bit slot; (3) Successful time slot: Only one tag in the signal area selects this time slot to communicate with the reader. The reader can successfully read the tag information. The reader silences the tag and queries the next colliding bit slot. Step 5, after querying all collision bit slots, the reader estimates the number of unidentified tags in the reader signal area; Step 6. The reader compares the number of unrecognized tags in the signal area of ​​the previous identification cycle with the number of unrecognized tags in the current signal area, and records the number of unrecognized tags in the current signal area. The reader determines whether there is a risk of missing tags. If there is a risk, the reader prompts the user that a tag is about to be missed, stops moving, and identifies all tags in the signal area at the original location before moving again. If there is no risk, it directly enters Step 7. Step 7: Repeat Step 2-Step 6 for multiple rounds along the fixed path until all tags are identified; In the tag estimation method in Step 5, the method for the reader to estimate the number of tags is as follows: Step 1: The reader calculates ca according to the number of collision bit slots in the identification cycle, where ca is the number of tags in each collision slot, specifically through formula (1): like=a*e (b*coll_bit) +c*e (d*coll_bit) (1) coll_bit is the number of bit slots that collide in this identification cycle. a, b, c, d, and e are all fixed constants. Specifically, a=1.9, b=0.002957, c=2.571*10^(-7), d=0.1236, and e=2.7182. Step 2: Estimate the number of unidentified tags in the reader signal area using formula (2). Formula (2) is as follows: n=ca*coll_slot (2) n is the number of unrecognized tags in the reader signal area, and coll_slot is the number of collision time slots in the current recognition cycle.

2. The tag anti-collision method based on missed reading warning in a single reader mobile RFID system according to claim 1, characterized in that: In Step 2, the tags are recognized using bit-slot ALOHA, and the length L of the bit slot is 128.

3. The tag anti-collision method based on missed reading warning in a single reader mobile RFID system according to claim 1 is characterized in that: In Step 6, to reduce the tag missed-reading rate, when the reader determines that there is a risk of missed reading, the reader prompts the user to stop moving.

4. The tag anti-collision method based on missed reading warning in a single reader mobile RFID system according to claim 1, characterized in that: The method for determining whether there will be a missed reading phenomenon in Step 6 is as follows: Step 6.1: Compare the number of unrecognized tags n in the reader signal area with n_last, where n_last is the number of unrecognized tags in the previous recognition cycle. There are two cases: (1) If n is greater than or equal to n_last, it means that in the current recognition cycle, the recognition rate is lower than the rate at which tags enter the signal area, and there is a risk of tag missed reading. Update G according to formula (3); G = G_last + g (3) G is the continuous increase in the number of unrecognized tags, used to determine whether the number of unrecognized tags in the reader signal area has been continuously increasing in the recent several recognition cycles; G_last is the number of unrecognized tags in the previous recognition cycle; g is the increase coefficient, and the value range of g is 0 < g < 0.

5. The larger g is, the more sensitive the reader is to the continuous increase in the number of unrecognized tags, and the smaller g is, the more insensitive the reader is to the continuous increase in the number of unrecognized tags; (2) If n is less than n_last, it means that in the current recognition cycle, the recognition rate is higher than the rate at which tags enter the signal area, and the risk of tag missed reading is relatively low. Update G according to formula (4); Step 6.2: Determine whether G is less than 0. If G is less than 0, set G to 0; Step 6.3: Update n_last so that n_last = n, and update G_last so that G_last = G; Step 6.4: Determine whether G is greater than 1. There are two cases: (1) If G is greater than or equal to 1, set G to 0, which means that in several recognition cycles, the recognition rate of the reader is lower than the rate at which tags enter the signal area. The reader determines that there is a risk of tag missed reading, and the reader prompts the user that there is a risk of tag missed reading and asks the user to stop moving and enter Step 6.5; (2) If G is less than 1, it means that the risk of tag missed reading is relatively low, and directly enter Step 7; Step 6.5: The reader stops moving and recognizes the unrecognized tags in the current signal area. In each recognition cycle, after querying all the collision bit slots, the reader checks whether coll_bit in the current recognition cycle is 0. There are two cases: (1) If coll_bit is equal to 0, it means that all the tags in the current signal area have been recognized, and the reader prompts the user to continue moving and enter Step 7; (2) If coll_bit is not equal to 0, it means that not all the tags in the current signal area have been recognized, and the reader prompts the user to stay stopped and repeat Step 6.5.

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