The Design Of OBU Module In The ETC System Based On RFID

With the rapid development of China's economy, the existing highway capacity can't meet the increasing traffic demand, the ETC(Electronic Toll Collection) sysytem based on modern high-technology RFID(radio frequency identification technology) could do the charge efficiently,which ease various problems around the toll collection station such as the traffic pressure, traffic jam,noisy and environment pollution and so on.The ETC system consists of RSU(Road Side Unit) and OBU(On Board Unit).The paper dedicates on the hardware design and realization of the OBU module in the 5.8GHz ETC system based on RFID.First it introduces the current development status of the ETC system at home and abroad,and analyse the similarities and differences between European standards, the Japanese standards and our national standards on the DSRC (Dedicated Short-Range Communication)protocols,especially the specific standard indicators of physical layer,based on which it starts the design work of the OBU module.Antenna is the key part of the RFID, this paper use the 5.8GHz dual microstrip patch antenna array to complete wireless communication between OBU and RSU which has the small size and excellent performance. And it takes the STM32 embedded control system as the OBU's central control unit, combined with ML5830 launch chip from the RFMD company to lunch the uplink data.To the receive part, the paper choose a simple circuit is mainly composed of the diode ASK detector, the triode signal amplifier which can output the RF wake-up signal to active the power management module, and then drive all devices in the OBU system by the voltage. At the same time it change the system from low-power sleep mode to active mode to compelte the charge transaction so to save the energy,and also send the output data into the STM32 to do some associated processing. In addition, in order to improve the reliability of data transmission, uplink and downlink data use the FMO encoding, so it design the D flip-flop hardware FMO encoding circuit based on CPLD, and use the STM32's existing DMA and Timer capture function to achieve the FMO software decoding, while the high 72MHz working frequency of STM32 promise the real-time toll transaction for the ETC system.