Research And Design On Vehicle Passive Keyless Entry System

Passive Keyless Entry System is a new vehicle entry security technology inrecent years. It is composed of the base-station and the key. When the base-station istriggered (car door, engine-start button, trunk), it will transmit LF command to thekey. After the key authenticates the signal, it will return corresponding value throughUHF signal. Especially, if the return signal is the value of received signal strength, thebase-station will estimate the position of the key and finish corresponding operationaccording to the base-station triggered signal. Because of the security of the mutualauthentication technology and the convenience of the entry without button pressed,the system gets perfect user experience in high-grade cars and will gradually be usedin low-grade cars.The article analyzes the communication characteristics of the LF125kHzsignal and the UHF433.92MHz signal used in the system and discusses thepositioning principle through3D coiling antenna in the key. For LF communicationmodule, the article analyzes the circuit principle of the antenna series resonance loopin the transmitter and the antenna parallel resonant circuit in the receiver. The articlealso selects the chips and matches the antenna loops. Through test, when the currentamplitude of the driver in the transmitter is200mA, the communication distance canreach2.2m. As far as UHF communication module is concerned, the article analyzesthe design process of the PCB loop antenna in the transmitter and the match processof the antenna. The article also selects the chips and designs the antennas. Throughtest, the communication distance of the UHF can reach30m.For algorithm, the article analyzes and makes the communication protocol of theLF communication and UHF communication and imports the AES-128algorithm toencrypt the key data to increase the security of data transmission. As far aspositioning algorithm is concerned, the article uses four LF antennas which are laid inthe main driver door, the vice driver door, the middle of the front and the trunk todetect the position of the key in the four corresponding detection area. Through test,the system can estimate the position correctly. The article also analyzes the power consumption in the base-station and the key and the system response time. Throughanalysis, the system designed can meet the requirements of the Passive Keyless EntrySystem.