The research of the application of the binary search algorithm of RFID system in the supermarket shopping information identification

Nowadays, going shopping in supermarkets has become one of the main channels for people’s daily consumption. A large number of daily necessities and household goods almost can be bought in the supermarket [1]. But now, the low efficiency of checkout in the large-scale supermarket leads to the high labor cost. On the other hand, for customers, the low efficiency of checkout and waiting too long will make them dissatisfied with the supermarket business model, especially in the peak of shopping. For example, on December 12, 2015, a large number of customers were waiting to check out, which reduced the amount of potential goods customers would buy and restricted the footfall of supermarkets [2, 3]. To solve the problem, large-scale supermarket had no other choice but to increase the number of checkout stands. But it was still unable to meet the needs of customers.

Radio frequency identification (RFID) is an automatic identification technology, which combines wireless communication technology with LSI. The technology of bar code has been applied into the field of scanning widely and it is continuing to mature, but the finiteness of storage spaces that determines the bar code only can be applied into the identification of the type of products [4]. Compared with bar code technology, RFID technology has some advantages of large storage space, reusability, and environmental adaptability. Even if the cost of RFID tag is higher than the bar code, as the RFID technology is becoming more and more perfect, the RFID tag will take the place of bar code and will be widely used in the commercial chain. Therefore, RFID is proposed to be used in supermarket shopping system and will take the place of bar code scanning system, but in practice, a large number of electronic tags should be identified at the same time, which there would be the problem of collisions [5–7]. Currently, the method to solve the problem is time division multiple access (TDMA) [8]. In many radio technology methods to solve the problem of collisions, TDMA is widely used in the field of digital mobile radio systems. TDMA allocates all available channels to multiple users on the basis of time. The most common way to achieve anti-collision mechanism of RFI system is TDMA, which is determined by the complexity, cost control, communications, and power consumption of the RFID system. The two basic types of TDMA are reader anti-collision control method and control RF card anti-collision method. However, due to the special nature of supermarket shopping system, the efficiency of the algorithm is too low, which cannot meet the requirements [9].

This paper analyzed the application of RFID technology into supermarket shopping system and used the anti-collision algorithm to identify on the basis of the unique sequence code. The RFID technology identifies the customer consumption goods and sort the consultation as a list and display it on the checkout stand. The application of this mode can provide great convenience for the customer as well as a supermarket. On this basis, in order to better resolve conflicts, this paper will use the binary search algorithm.

Binary search algorithm refers to a unique sequence code (UID) based on the identification tag, a set of predetermined sequences of instructions given between reader and a plurality of label, after a specific label selected for both data exchange between. The reader sends a request command to choose a set of labels; there will be data collision tag sequence code accurately transferred to the reader label channel transmission, using reader to verify the collision. If the reader test out the collision, it is necessary to do the next search in a smaller range [13–16].

3.1 Manchester coding

Whether the signal encoding used in the reader determines the exact location of the collision bit, which plays a decisive role in the implementation process of the binary search algorithm [17], Manchester encoding has this advantage, as they have been from the transponder to the reader uplink baseband data encoding. Manchester encoding is a certain value level rising or falling edge of a bit window (t_BIT) represented. The increase is stood by a logic “0” code, and the fall is stood by a logic “1” code (as shown in Fig. 6).

The transmission of Manchester encoding is often identified as an error, and it is not allowed to have a “no change” state. If multiple transponders simultaneously transmit different values, the result will be offset by rising and falling edges of the received. The reasons for this have not yet been specified, so it is seen as a way to query bit backtracking conflicts.

3.3 Binary search algorithm is to achieve the anti-conflict

Assuming Electronic Product Code (EPC) is ten digits, the range of the reader includes four microelectronic labels (see Table 1). The process of algorithm reader for electronic identification tag is as follows:

1. 1.

   Sending REQUEST from reader, that is, the command of “≤1111111111.” When the serial number is 1100101011, the transponders of the code sequence within the reader less than 1100101011 will be controlled. Reader decoding result is 110X1X10X1, so in the process of acceptance sequence code, the conflict will be recognized. There may be many transponders within the reader, the order received is 110X1X10X1, so the received code sequences have ten possibilities (as shown in Table 2).

    

Transponder 1	1111001100
Transponder 2	1100011011
Transponder 3	1111001001
Transponder 4	1100101011

Serial number 0	10-9-8	7	6	5	4-3	2	1	0
The data received by reader	1-1-0	X	1	X	1-0	0	X	1
The possible sequence code A	1-1-0	0	1	1	1-0	0	0	0
The possible sequence code B	1-1-0	0	1	0	1-0	0	0	1
The possible sequence code C	1-1-0	1	1	0	1-0	0	1	0
The possible sequence code D	1-1-0	1	1	1	1-0	0	1	1
The possible sequence code E	1-1-0	0	1	0	1-0	0	0	0
The possible sequence code F	1-1-0	0	1	1	1-0	0	0	1
The possible sequence code G	1-1-0	1	1	1	1-0	0	1	0
The possible sequence code H	1-1-0	1	1	0	1-0	0	1	1

The highest value of iteration (Section 4) is the first conflict that appeared in this position, which is in the range of SNR ≤ 1100101011. There is at least one transponder.

1. 2.

   The reader again sends the command of “≤ 1100101011,” which led to a change in parameters. There is the same serial number before the collision and after receiving, assuming the highest position of the collision is 0, and another serial number after the collision is 1. Reader search is the range of “≤ 1100101011.” In such a repeated operation, the no. 4 transponder is ultimately selected.

    
2. 3.

   The reader sends SELECT, the command of “1100101011.” Then, the transponder 4 serial code their own attributes transmitted to the reader, and the rest of the transponder and inactive. At this point, the reader can communicate through “READ-DATA” and the transponder 4. After the end of the program, “read/write,” the reader sends “UNSELECT” and the transponder 4, which makes the transponder 4 to re-enter the inactive state, thus achieving a complete between the reader and the transponder exchange of information. At this point take the binary arithmetic back policy, the reader resends “1111111111” command, namely, the search for the next round. This is the crux of the binary search algorithm to solve a collision problem.

    

In order to more clearly know the advantages of the binary search algorithm, the advantages of the binary search algorithm and the identification amount of the general anti-collision algorithm were compared in Fig. 7.

In Fig. 7, the binary search algorithm can significantly reduce the number of tag searching to reduce the time of computation. We can also evidently see that, with the increasing number of tags, the binary search algorithm has a very obvious effect of high-speed computing to meet the needs of the size of the supermarket.

In accordance with the requirements of the paper, to build a supermarket shopping system model-based RFID system binary search algorithm, Qt software design and experimental testing are used. The purpose of the experiment is the supermarket checkout efficiency, the reliability of security, and the impact of other factors.

4.1 The efficiency of checkout

In the experiment of the efficiency of checkout, a large number of electronic tags affixed to products that have been designated area RFID, RFID system, and the recognition time for all items traditional supermarket bar code scanning time are compared; the result is shown in Fig. 8. As can be seen in Fig. 8, for the checkout efficiency, the RFID system is far superior to the traditional bar code scanning.

4.2 The test of product recognition rate

In the test of product recognition rate, the products attached to the label were brought through the specific checkout area, which all contain membership cards. At this time, the merchandise identification rate of the test result is shown in Fig. 9. In Fig. 9, we can see that the same product recognition rate reached 100%, while the rate of recognition and membership card recognition rate of goods within a certain range of types of goods, which were up to 100%, but with the types of goods continuing to increase, this time, two both would go down to a certain extent.

4.3 The result of security testing

In security testing, the goods which were not paid were taken away from the supermarket. This paper used the initial condition, which was two items were not paid. They were taken away from the supermarket with other goods containing electronic tag. The result is shown in Fig. 10. The figure shows when the number of simultaneous detection of large commodity electronic tag, there will be a lower error rate.

We can see from the test result binary search algorithm has good accuracy in RFID systems in supermarkets. It also verifies the rationality of RFID-based supermarket system to meet the daily needs of supermarkets.

Through experiments, the binary search algorithm has good accuracy in RFID system in supermarkets. And it also verifies the article being constructed based on the rationality of things supermarket RFID system, to meet the basic needs of supermarket. In the test identification and anti-theft features exposed goods there with a binary search algorithm to identify the number of goods increases, the accuracy of the test has not been able to reach 100%. For the improvement of the binary search algorithm, achieving the precision will be the future research focus.