Car Security and Anti-theft Keyless System

The initial electronicization of automobile security and anti-theft began in 1994 with Engine Anti-Theft (IMMO). As the first semiconductor company, NXP Semiconductors (then Philips Semiconductors) successfully applied RFID electronic tag technology to automotive electronic engine locks: The 125kHz wireless communication between the car and the key realizes electronic identification to judge the start of the car engine. This technology greatly improves the safety of cars, and is soon widely used in Europe and North America. In just a few years, the rate of car theft in Europe has been greatly reduced by 90%, so it has become a car in Europe. The standard configuration. The emergence of remote control key (RKE) has brought people a very good user experience and satisfied people's requirements for convenience and comfort, but due to the technical limitations of its radio frequency one-way communication, it has its own shortcomings in security . The integrated solution (Combi) launched by NXP Semiconductors (hereinafter referred to as NXP) in a timely manner combines the engine anti-theft and remote control keys into one, which is realized by one chip, which not only improves the security of the system, but also reduces the cost of the entire key. Gradually replacing independent remote control keys has become the mainstream solution in the European, American and Japanese markets. Of course, it still retains one-way communication on radio frequency communication, and the security has not been substantially improved.

Figure 1

In 2003, NXP launched a keyless system (PKE or PEPS), which completely changed the development prospects of automotive security applications and brought users a new comfortable and convenient experience: car owners do not need to use keys during the entire driving process. , Just need to carry it with you. When the owner enters the effective range near the car, the car will automatically detect the key and identify the identity, if successful, the door or trunk will be opened accordingly; when the owner enters the car, only need to press the engine start button, the car will automatically detect the key Position, determine whether the key is in the car, whether it is in the main driving position, if successful, start the engine. Don't underestimate this seemingly insignificant change, it plays a major role in simplifying your life. The keyless system not only brings comfort and convenience, but also has an essential improvement in security. Through two-way communication of low frequency and radio frequency, complex two-way identity authentication can be completed between the car and the key. In terms of security Similar to engine anti-theft, it is much better than traditional remote control keys. Since the successful mass production of keyless systems for a small number of high-end models in 2003, the global market has spent two to three years promoting the popularization of this technology. At present, almost every mainstream car manufacturer in the world has NXP keyless products, covering mid- to high-end Models, even low-end models. Next, let's take a look at how this technology is implemented:

As shown in Figure 2, the keyless system needs to detect and judge three types of areas: a gray exterior area, a pale pink interior area, and an off-white main driving position. The gray shaded area includes three parts, which represent the effective area of ​​the door control of the main driver, the co-driver, and the trunk. When the owner enters this position with the key, effective communication can be established between the car and the key, through the low-frequency signal In the field strength detection, the car can determine the corresponding position of the key, thereby deciding to open the corresponding door. The light pink interior area is the difficulty of the entire PKE system design. It is necessary to accurately determine whether the key is in the vehicle to determine the door status and whether the engine can be started. In the design of some high-end models, it will also detect the off-white main driving area, whether the key is valid, and whether there is a person in the main driving position, to avoid engine startup caused by children ’s misoperation, and may also include the detection of the area in the trunk to prevent the key It was accidentally locked into the trunk. In summary, we can find that in the keyless system, area detection is a very important technology that is different from various automotive security products in the past, so the accuracy of area detection has become an important parameter to measure the quality of a keyless system. At present, there are two main technologies on the market. One is to adjust the sensitivity of the low-frequency signal to make a fuzzy judgment based on whether the communication is stable. Its accuracy is limited but it is convenient to implement. The second is to judge based on the strength detection of the received low-frequency signal, namely RSSI (Received Signal Strength IndicaTIon), calculates the relative distance between the key and the low-frequency antenna in the car according to the size of the low-frequency signal, and accurately locates the specific position of the key through the cross-coverage of multiple low-frequency antennas. NXP products all use the second technology. In order to achieve the ideal performance parameters, NXP provides a minimum 2.5 mV three-dimensional low-frequency reception signal sensitivity of the front end, and the typical sensitivity value can reach 1mV. Different from the successive approximation (Successive ApproximaTIon) ADC of other solutions, NXP adopts 12-bit Sigma-Delta (Σ-Δ) ADC, which eliminates noise interference through multi-point sampling averaging. The detection accuracy outside the car is up to 2cm. At present, the detection accuracy usually required by the car manufacturer is 5 to 10 cm.

Figure II

The block diagram of the keyless system is shown in Figure 3. The left side is the car end, including the main controller (Body Control Unit), the door handle and trunk handle trigger module, the engine one-key start module, and the engine anti-theft base station module (IMMO BasestaTIon ), Low-frequency transmitter module and radio frequency receiver module. Three of the green modules are mainly used to trigger the entire system. When the owner pulls the door or presses a key to start the button, the corresponding module will send an interrupt signal to wake up the main control MCU and start the entire communication process. Common keyless system working modes are divided into two categories: trigger mode and scanning mode (polling), where the trigger mode is divided into mechanical trigger and electronic induction trigger, here need to comprehensively consider the system cost and system performance, such as the response time of the entire system. The engine anti-theft base station module is a low-frequency communication module (125KHz), which is used to achieve short-range communication with the key and start the engine. This function is a backup solution, also known as "no power mode", only when the key battery is exhausted or there is unexpected interference It is only used when the keyless system can not work normally. In this case, the user only needs to hold the key in a fixed position (such as a groove), and the key can establish communication with the base station and perform identity authentication to start the engine. A key feature of NXP's keyless systems PCF7952 and PCF7953 is that the chip itself integrates the engine anti-theft function and is fully compatible with all NXP Transponder products, including PCF7936. This greatly improves the reliability of the system without additional cost, specific details will be mentioned later.

Figure three

The low-frequency transmitting module and the RF receiving module are the basic communication links of the keyless system. The low-frequency transmitting uses 125KHz, which is the uplink (up-link), which is sent from the car end to the key end; the RF receiving uses 315MHz or 434MHz, which is the downlink Road (down-link), sent from the key end to the car end. The reason why 125KHz is used is on the one hand to be compatible with engine anti-theft technology, and more importantly, the 125KHz signal is sensitive to distance, which can realize accurate distance detection and play a key positioning role. The radio frequency uses the traditional RKE frequency band. On the one hand, it is compatible with the basic functions of the remote control key, and it also takes advantage of its fast communication speed. What needs to be emphasized here is that the so-called communication speed refers to the data used for authentication and encryption between the key and the car. Transmission, in order to ensure that the keyless door opening or ignition process is completed in a shorter time, a higher baud rate (generally 8 to 20 kbps) is required, and it is generally not recommended to use a low-end SAW transmitter module (about 1 kbps), and Adopt the launch chip based on phase-locked loop technology to realize, for example NXP's PCF7900, its maximum baud rate in FSK mode can reach 20kbps. Also for this purpose, the radio frequency band also tends to use higher frequency 868MHz or 915MHz. As shown in the figure, the low-frequency transmission module includes multiple low-frequency antennas, which are installed in the door handle of the vehicle to realize keyless entry (Keyless Entry), and installed inside the vehicle body to achieve keyless entry (one-key start Keyless Start).

The specific block diagram of the key end is shown in Figure 4. The main chip is NXP's PCF7952 or PCF7953, the radio frequency transmitting chip is NXP's PCF7900, and the corresponding radio frequency receiving chip at the car end is NXP's PQJ7910. PCF7952 / 53 has a low-frequency analog front end (LF Front End) for connecting peripheral 3D antennas. In the keyless system, the key end needs an external 3D low-frequency antenna, which can receive and detect the 3D energy field strength of the external space, respectively X, Y, and Z axes. By superimposing the energy in 3 directions, the key can be guaranteed at any angle Can detect the same field strength. The one-axis antenna is also multiplexed into the function of IMMO, enabling the engine to start in the no-electric mode. Through the uplink and downlink, the key can establish two-way communication with the car for complex identity authentication. The latest generation of authentication technology is called Mutual-AuthenTIcation. It not only requires the car to authenticate the key, but also needs the key to determine whether the car is legal. Any error will lead to the end of the entire communication to ensure the security of the system . The communication distance is determined by the low-frequency uplink 125KHz. The normal effective working distance of the PKE system is about 2.5m, and the actual effective door opening and closing distance is 1.5m ~ 2m. In addition to the detection accuracy inside and outside the car, the power consumption of the key end is also an important indicator to measure the quality of a keyless system. The power management module included in the PCF7952 can minimize the power consumption of the entire system. A mature keyless system solution, key In the case of a 2032 3V lithium battery, the battery life can be up to three years.

Figure 4

After the keyless system, where will car security and anti-theft products go? As a leader in the industry, NXP has given the exact answer: Keylink, the next generation of car keys. Its biggest breakthrough lies in linking the car key to peripheral smart terminals, so that the key can be connected to devices such as mobile phones, PDAs and other devices at close range (link), with the help of the display functions and powerful processing of smart terminals such as mobile phones Ability, a very vast application space is before us:

-Check the status of the vehicle, the status of the doors and windows, the amount of fuel in the fuel tank, the temperature in the car at any time ... the display on the mobile phone screen is everything

-Find a car, through the cooperation of the key and the mobile phone, the GPS navigation of the mobile phone helps you easily find the parking place

-Easily formulate travel routes, save the selected travel route in the key in front of the computer. When entering the car, the car navigation will automatically import travel information

-Vehicle maintenance, vehicle factory records, and maintenance records are all stored in the key for easy maintenance.

There are many more applications similar to the above. The following news is another new application of Keylink, which allows us to understand this technology more closely, and also ends this article:

October 22, 2008-BMW Technology R & D Department and NXP Semiconductors (NXP Semiconductors, an independent semiconductor company founded by Philips) launched the world's first prototype multi-function car key. This product prototype has contactless payment function, personal access control and advanced public transportation electronic ticket function to achieve a stronger mobility experience. Equipped with NXP's SmartMX security chip, this product prototype for the first time enables drivers to make fast, safe and convenient electronic payments through car keys, creating an exciting new application environment for future consumers.

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