Research on UHF RFID Reader Networking and Coordination Technology

As we all know, RFID system consists of electronic tags (tag), reader (reader) and data management system. There are three types of RFID electronic tags: active, passive and semi-active. Passive tags are characterized by low cost and are widely used. The scope of our research below is passive labeling. When passive tags are applied, proper planning is required for the deployment of readers. RFID deployment directly affects the coverage and identification effect of the UHF reader network. A reasonable and effective reader deployment solution can reduce network construction time and fully cover the target area; it can reduce interference between readers, adapt to network changes, and ensure the read rate of the entire network.

Reader networking has the following characteristics:

1. The structure of the RFID network system presents serious asymmetry. The performance of passive electronic tags is relatively weak, and the tags cannot communicate with each other. Passive tags cannot actively send communication signals, and can only communicate with the reader through backscattering. communication.

2. The wireless transmission environment in the RFID system is quite complicated. In most cases, the RFID system works in an indoor environment, and the multipath attenuation effect must be considered at this time. At the same time, the typical distance of reader-tag communication is less than 10m, which belongs to short-distance communication. Due to the essential characteristics of radio frequency signals, and in order to ensure coverage, the intersection between the identification areas of the reader is inevitable. Based on the existing wireless cellular network optimization model, according to the characteristics of the RFID system, a discrete model of reader network deployment r=(site, antenna, TIlt, Au) is proposed, where TIlt represents the antenna tilt angle, Au Indicates attenuation. In the case of coverage constraints, tag reflection signal constraints, minimum cost constraints, and minimum interference constraints, the genetic algorithm is used to find the optimal solution. These references do not consider the deployment of reader networks in the presence of handheld readers.

The purpose of reader-writer coordination is to ensure the communication requirements of the entire system, mainly to avoid reader-writer conflicts and control power. Interrogator conflict refers to the interference detected by one interrogator caused by another interrogator, including two cases: interrogator frequency conflict and tag conflict. Reader frequency conflict occurs when two or more readers use the same frequency to communicate with tags at the same time; tag conflict refers to the conflict that occurs when two or more readers communicate with a tag at the same time.

The characteristics of reader-writer conflict are as follows: the low-performance characteristics of passive tags make it unable to play an anti-collision role in the process of communicating with multiple readers; exacerbated. In the reader network including handheld readers, reader conflicts and changing topological structures are notable features, and they are also problems that must be solved when studying reader network deployment from a development perspective. Previous studies on reader network deployments have generally focused on stationary readers and, therefore, have not considered much to include mobile readers. Deployment of a reader network that includes handheld readers involves the number of mobile and fixed readers, the movement line and speed of the handheld readers, and the topology of the fixed readers caused by the movement of the handheld readers Structural changes, determination of periodic coverage of handheld readers, etc. Power control during coverage is also a research direction for reader network deployments that include handheld readers. Hand-held readers generally rely on batteries to provide power, which makes energy-saving issues very important, and power control can also reduce interference between readers.

Coordination among UHF readers

At present, there are two trends in the improvement of the reader network structure: one is that the learning algorithm is based on a multi-layer structure, which is not very practical. The function of the reader, the reader cannot communicate with each other, relying on the centralized controller (system) to coordinate. For this kind of network, the coordination between readers is similar to the frequency allocation and power control problems in wireless cellular systems. The future research direction is to comprehensively consider spectrum, time and space resources, and use combination optimization according to the communication requirements in practical applications. method to solve it.

The other is to enhance the function of the reader, relying on the reader itself to coordinate between the reader. This kind of network is similar to sensor network and ad hoc network, we can refer to the coordination technology in these communication networks, and according to the characteristics of RFID Reader network, study the use of distributed methods to solve the problem of reader coordination. For the tag conflict problem, due to the characteristics of passive tags, the solution can only be time-division multiple access, that is, only one reader with overlapping coverage can read and write tags within the overlapping coverage at the same time. must be taken into account in device coordination.