The Application of RFID Technology in the Management of Prison Personnel Location
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The use of intelligent tracking and positioning systems in prisons is a new subject. Prisons in western developed countries are trying first. In December 2005, AeroScout and Alanco announced the development of the industry’s first Wi-Fi wireless LAN-based RFID tag personnel tracking system, which was launched in Europe. Trial in a prison. At present, Chinese prisons have not yet developed a complete intelligent tracking and positioning system. However, it is often heard about the use of “electronic shackles” against offenders on parole and individual offenders who are subject to security sanctions in Western developed countries and Taiwan.
There are many ways to realize the tracking and positioning of personnel and mobile objects. GPS (Global Positioning System) is the most widely used and most common positioning method, which is especially suitable for the positioning of vehicles and inaccessible field workers; mobile phone positioning developed in the past two years The system uses the feature of uninterrupted communication between mobile phones and machine stations to realize the positioning and tracking of personnel. China Unicom has launched this business; wireless local area network (WLAN) positioning is a new type of positioning method that uses wireless access points ( Nodes) are densely distributed, through “received signal strength, angle, time, etc., as well as a typical triangle algorithm” to determine the location of the moving target. Currently, wireless local area network positioning systems based on IEEE802.11 series standards and IEEE802. 15.4 Standard Zig-Bee technology wireless smart sensor network (WSN—WirelessSensor-Networks) positioning method; radio frequency identification card (RFID) positioning is an economical and accurate positioning method, using radio frequency tags and reading heads (readers) ) Communication link to determine the target location, using local area network (LAN) or wireless local area network (WLAN) to achieve location instructions. The safety management system of coal mine personnel in our country has adopted RFID positioning method.
The personnel positioning and tracking system of the prison must be based on the needs and possibility of correction of criminals. First, the human and the machine must not be separated. Ensure that the equipped tracker is carried with you. Once separated from the body, it will immediately report to the police. Second, the positioning must be accurate and the security requirements of the prison. The positioning accuracy is very high. 1 meter outside the wall and 1 meter inside the wall are “two worlds”. Inaccurate positioning will lose the meaning of positioning; three functions are complete. The positioning of personnel and other moving targets is the basic function of the tracking and positioning system. The prison requires that the tracking and positioning system should also have a timely alarm function for correcting personnel (passive alarm), and an active alarm function for criminals in over-guard areas; fourth, low investment, low operating costs, and high investment and operating costs will hinder the tracking and positioning system. Promotion.
Based on the above requirements, GPS positioning and mobile phone positioning are obviously not suitable for prisons to locate the prisoners. First, it is inconvenient to carry, and it is difficult to achieve “man-machine inseparability”; second, the investment and operation costs are high, and the prison is unbearable; third The positioning accuracy is not high. Although mobile phone positioning is claimed to be within 5 meters, the actual error is 15 meters to 50 meters. Although the accuracy of GPS is within 2 meters, whether it is mobile phone positioning or GPS positioning, it is limited to Plane positioning cannot solve the precise positioning of people in three-dimensional buildings such as floors. Therefore, under the current technical conditions, it is more suitable for prisons to use WLAN or WSN positioning and RFID positioning for personal positioning of correction personnel and criminals.
1. RFID tracking and positioning system
(1) Introduction to the basic situation of RFID
RFID, the English abbreviation of Radio Frequency Identifi.cation, is a non-contact automatic identification technology, which uses radio frequency signals and spatial (electromagnetic or inductive) coupling transmission characteristics to realize the identification of objects Automatic Identification. It includes two parts: electronic tag (transponder, Tag) and reader (reader, Reader). The reader also includes a reading head and an antenna, and many readers integrate the antenna and the reading head module into one device unit. In actual use, the electronic tag is attached to the surface or inside of the recognized object. When the recognized object with the electronic tag passes through the readable range of the reader, the reader automatically removes the agreement in the electronic tag in a non-contact manner. The identification information is read out, so as to realize the function of automatically identifying items or automatically collecting item mark information. RFID has been widely used in commodity retail, warehouse management, production line control, animal identification, transportation, military material tracking and other fields. my country’s railway system fully uses the RFID system for train operation control and carriage scheduling.
RFID is divided into active system and passive system according to whether it is self-powered or not. The one with its own power supply is active, and the one without a power supply that is activated by the electromagnetic field emitted by the reader is a passive system; it is divided according to the data modulation method. Active, passive, and semi-active. The active radio frequency system uses its own energy to actively transmit data to the reader. The active system belongs to the active type. The passive type uses the reader’s carrier to modulate its own signal. The passive system It is passive. Semi-active means it has a battery and only serves to supply power to the internal circuit of the tag. The data transmission is still activated by the reader’s energy field and transmitted through backscatter modulation; it is divided into low frequency according to the working frequency of the tag. (30-300KHz), high-frequency (3-30MHz), ultra-high frequency (above 300MHz such as 433HZ) and microwave (above 2.4GHz) systems, the lower the frequency, the lower the cost, the shorter the reading and writing distance, and vice versa; According to the readability of the label, it can be divided into read-only label, read-write label and read-write label once and read multiple times; according to the storage capacity of the data memory in the label, it can be divided into identification label and portable data file. The user stores a large amount of data, which can be used for user programming.
(2) Working principle of RFID personnel positioning system
Readers are densely distributed in the positioning area, and all personnel who need to be positioned are equipped with RFID cards. When the cardholder enters the reading area, the RFID tag will automatically transmit data to the reader at regular intervals and confirm it. Each reader is connected to a local area network, and is processed by computer through application software, and uses electronic maps, statistical tables, and agreed text information displays to reflect the location and movement trajectory of personnel in real time.
(3) Hardware requirements of prison RFID positioning system
1. Equipped with RFID card. The RFID card should choose the UHF or microwave system with a long reading distance. Each label should be written with specified data in advance so that the computer can identify the identity of the corresponding card holder. All persons who need to locate must carry it with them. For prisons, compulsory means and appropriate measures must also be taken to ensure that the RFID card is inseparable from the criminal’s body, such as it can be embedded in a strap-type device and tied to the wrist or ankle.
2. Install a sufficient number of readers. The number of readers should be able to meet the needs of positioning calculations, and ensure that the radio frequency card equipped with personnel in the positioning area can be read by more than three readers. If there are too few readers, there will be blind spots in communication, resulting in inaccurate positioning. The antenna and transmission power of the reader should be as large as possible to ensure that the reader can successfully communicate with the radio frequency card at a long distance, so as to minimize the number of readers. The reader is installed as firm as possible, and its power supply and data transmission facilities are not easily damaged.
3. A network that meets communication needs. All readers can be directly connected to the nearest computer through a multi-serial port card, and then connected to the local area network after localization processing; or directly connected to the local area network (wired or wireless) after localization filtering processing through special data processing middleware. The communication data of the reader must be aggregated to the server for centralized processing using special software to realize the positioning of personnel and moving objects.
(4) Performance requirements of prison RFID wristband positioning system
The performance of the prison RFID wristband tracking and positioning system depends to a large extent on the program design in the application software. The software design must have the following requirements in advance:
1. Personnel query function. Realize real-time dynamic query and historical query of various situations. According to authorization, you can arbitrarily inquire who is and where, who is where and who is, when and where, who is when and where, etc. It can not only reflect whether the criminal walks and stays according to the prescribed path, and who has contact with, etc. Circumstances, in order to check the performance of the criminals’ completion of labor operations, compliance with regulations and integrity, etc.; also can check whether the police on duty perform inspections according to regulations, when to talk to or contact with other criminals, etc. Retrospective investigation after the occurrence of an emergency.
2. Electronic map display function. It can display the respective locations of all radio frequency cards on the electronic map. After clicking or delimiting a certain range, the identity of the personnel represented by each radio frequency card will be displayed immediately; the range of activities of restricted personnel will be displayed; Querying someone’s path in a certain period of time in the past can display the line track on the map; display the location of various alarm signals and the corresponding personnel.The map itself should also have functions such as zooming in, zooming out, center movement, ruler ranging, saving, and printing.
3. Alarm and reminder function. The system can set the range of the restricted area and ensure that the cardholders enter the police immediately; set the criminal activity range to ensure that the criminal immediately alarms once the criminals move beyond the scope; set the line for the police on duty to call and patrol at different time periods, once the police do not perform their duties Get reminded in time; set any cardholder to be inactive for a long time at a certain place or the activity range is significantly smaller than the expected range (except for rest time) to alarm to prevent the card from being discarded, sleeping illegally, and personal injury; setting The label does not work and alarms for timely replacement; set a reminder that the radio frequency signal sent by the non-designated label is read by the reader to identify the source of the signal. If the alarm signal can be linked with the monitoring system, live broadcast or intercom system, the effect will be better.
Since the use of RFID as a prison personal positioning system is generally a passive system (the coal mine underground positioning system uses an active system, which is installed on the helmet and connected to the miner’s lamp power supply), the operating distance is short, and a large number of readers or high-powered devices need to be installed Transmitting antennas increase investment costs; passive RFID has high requirements for directivity and poor signal receiving sensitivity, which affects communication and positioning effects. In view of this, a wireless smart sensor network (WSN) tracking and positioning system based on 433HZ frequency RFID technology came into being.
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