Application of Intelligent Tracking and Positioning System in Criminal Correction
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The use of intelligent tracking and positioning systems in prisons is a new subject. Prisons in western developed countries have tried 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 operators; 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 the “received signal strength, angle, time, etc., as well as the typical triangle algorithm” to determine the location of the moving target. Currently, there are 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 readers ( The communication link of the reader) determines the target location, and the local area network (LAN) or wireless local area network (WLAN) is used to realize the location instruction. The safety management system of coal mine personnel in our country has adopted RFID positioning method.
The prison personnel positioning and tracking system must be based on the need and possibility of correction of criminals. One must be inseparable from man and machine, to ensure that the equipped tracker is carried with you, and once it is separated from the body, it will immediately report to the police; second, it 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 people 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. It 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 classified 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 belongs to the passive type. The semi-active type means that 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 the backscatter modulation method; according to the working frequency of the tag, it is divided into low frequency (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 tag, it is divided into read-only tags, read-write tags and read-only tags once written and read multiple times; according to the storage capacity of the data memory in the tags, it is divided into identification tags and portable data files. The former only serves as an identification. The latter stores large amounts of data by itself, 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 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, @ in order 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 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 now and where, when and where, who is when and where, etc. It can not only reflect whether the criminal walks and stays in accordance with the prescribed path and who is in contact with, etc. Circumstances, in order to check the criminal’s performance in completing labor operations, compliance and integrity, etc.; it can also 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, and display the identity of the personnel represented by each radio frequency card immediately after clicking or delimiting a certain range; display the range of activities of restricted personnel; display the restricted area that no personnel should be involved in; Querying someone’s path in a certain period of time in the past can display the track of the line 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 criminals will immediately report to the police once they move beyond the scope; set the line for the police on duty to call for patrol at different time periods, once the police do not perform their duties Be 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 the rest time) to alarm to prevent the card from being discarded, sleeping illegally, and personal injury; setting The label does not work and alarms so that it can be replaced in time; 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.
2. Prospects of wireless local area network positioning system
The use of wireless local area network to locate people or objects is practiced in the United States, Europe, and Japan. The wireless local area network based on the IEEE802.11 standard has the advantages of long communication distance, non-directional communication requirements, large data transmission capacity, and strong anti-interference ability, which makes up for the deficiencies of RFID technology. However, it has high power requirements, high power consumption, and all nodes must be connected to a network computer, which is not applicable to criminals who are extremely compulsory. Another new type of wireless local area network-wireless sensor network (WSN) based on the IEEE803.15.4 standard Zig-Bee technology, solves some of these problems.
ZigBee technology is a short-distance, low-speed (250KB/S), low-power, low-cost, self-organizing network, and low-complexity two-way wireless communication technology. It is mainly suitable for automatic control and remote control fields, and supports geographic positioning functions. . The low power consumption of ZigBee makes the configured power supply very small. Two AA batteries can be used for 6 months to 2 years, and the pocket rechargeable battery can be used indefinitely. ZigBee’s wireless data module (coordinator, equivalent to a machine station) has a high degree of integration and a small size, which is very easy to install; the wireless data module (equivalent to a handset) used in the child nodes is smaller in size and very easy to carry. Although ZigBee is a short-distance communication technology, theoretically the communication distance is 75 meters@, generally not more than 150 meters (depending on site conditions), but not only can the coordinator and child nodes communicate with each other, but also the coordinator and the child nodes can communicate with each other. Coordinators and sub-nodes can also communicate with each other, and the network can be established arbitrarily, making the network communication distance tens or even hundreds of times larger. ZigBee has unimaginable expansion capabilities. The modules can be networked anytime and anywhere, making the network very scalable. One WSN can accommodate 254 sub-node wireless data modules and one wireless data module as a coordinator. There can be 254 WSNs in the area at the same time, that is, up to 65,000 wireless data modules are allowed at the same time. ZigBee can be connected to a wired local area network (LAN) or a wide area network (WAN) anytime and anywhere to realize various remote control capabilities. The ZigBee input cost is relatively low. A wireless data module as a coordinator is less than 1,000 yuan, and a wireless data module as a child node is only about 450 yuan. The maintenance cost is very low. The use of 868MHz/915MHz and 2.4GHz is licensed worldwide. , Open frequency. The source of the name ZigBee is taken from the bees communicating through zigzag-shaped dances to share the location, distance, direction and other information of newly discovered food sources. Therefore, the original intention of zigBee design is to enable WSN to achieve ranging, direction finding, and positioning. This is not available in other wireless local area networks and RFID.
The prison WSN positioning system, in addition to fully having all the hardware requirements and functions of the RFID positioning system listed above, should also have the following requirements:
(1) Active reminder and automatic alarm function of the data module
Regardless of the data module worn by the criminal (hereinafter referred to as the communicator), the communicator carried by the police or the PDA (handheld computer) embedded with the data module, it should have an active reminder function, that is, the network control terminal can communicate with any one or multiple communications at any time The communicator is equipped with the sound device or light-emitting device of the voice module to remind the communicator holder to pay attention or perform certain behaviors according to the agreement, such as the holder entering the restricted area to alarm or violate the regulations for a long time Reminders for staying in a certain place, etc., to solve the defect that the RFID system cannot achieve two-way alarms. The communicator worn by the criminal can be inseparable from the criminal’s body by devices such as wristbands under normal circumstances. The inlaid circuit in the wristband is connected to the communicator. Once a short circuit occurs (the wristband is cut off) or the voltage exceeds the range (external circuit), it can be inseparable. The immediate alarm on the control terminal and the on-site alarm of the communicator (sound or light) prevent the saboteurs from continuing to perform sabotage.
(2) The network function of the police PDA
Utilizing the connection between WSN network and local area network, the PDA as a child node of the inlaid wireless data module is connected to the wired local area network as well as other wireless data modules, so as to check the operation status of any communicator or the holding of the communicator around the PDA at any time The situation of the person. In the case of being separated from the local area network, it can be networked with other communicators at any time. Such as taking criminals out of the supervision area to work, going out to see a doctor, escorting criminals, etc., know the position of the criminals holding the police relative to the PDA anytime and anywhere, and call the police if they leave the PDA receiving area or the distance set by the program. If the PDA is connected to the mobile network of the telecommunications department, the prison headquarters can also keep track of the movements of the outgoing personnel, and can be informed and deal with emergencies in time. The PDA should have an active alarm function when the police is in danger or need emergency support. Once a danger occurs, just press a specific button to send out an alarm signal. The central control room or other network terminals can all know the police in the first time. Name and location will be dealt with by the police immediately. The PDA should also have the real-time display function of the electronic map. The communicator around the PDA can display it completely. After clicking, it is very convenient to query the basic situation of the communicator holder. When the police talk to criminals, they can carry out targeted education. . The PDA can be configured with a call device, using the frequency of the WSN, to achieve intercom or group call between each other. Of course, using the mail system to send and receive short messages is a PDA’s own function. If the PDA is equipped with recording, photographing, and video functions, then the PDA can become a mobile intelligence station and command post.
Although the maintenance and operation cost of the WSN positioning system is very low, the initial investment is definitely unaffordable for most of the current prisons’ economic strength (assuming a high-security prison with about 3,000 people, the initial investment will require 3.5 million yuan above). As time goes by, the cost of WSN’s wireless data module will drop significantly; as the promotion of the prison WSN positioning system accelerates, the network development cost is shared, and the initial investment cost will also drop to a large extent. From the perspective of the development trend of prison management and correction technology, the WSN positioning system represents the development direction of prison correction technology, which is not only possible, but also necessary.
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