Communication method for onboard units and byroad units of ETC system based on WLAN

Abstract

The invention discloses a communication method of an ETC system vehicle unit based on WLAN and a roadside unit. The prior communication linkage between the ETC system based vehicle unit and the roadside unit is short in distance, and needs long time to be established, and is instable, and is not applicable for the linkage between a vehicle moving at high speed and a fixed toll collection system. In order to solve the above problems, the communication linkage between the vehicle unit and the roadside unit is established in the following steps. Firstly, the vehicle unit sends a probe request frame to the roadside unit to monitor an information frame. Secondly, the vehicle unit gets the information fame, and sends an authentication request frame to the roadside unit to monitor the authentication response frame returned from the roadside unit. Thirdly, the vehicle unit gets the authentication response frame, and sends financial transaction information to the roadside unit. By adopting the invention, more stable communications linkage can be established between the vehicle unit and the roadside unit more quickly.

Description

technical field [0001] The invention relates to a communication method between an on-board unit (OBU) and a roadside unit (RSU) of an ETC (Electronic Toll Collection) system applied to expressways or urban roads, in particular to a communication method based on wireless local area network (WLAN) technology. A communication method between an on-board unit and a roadside unit of an electronic toll collection system. The invention belongs to the technical field of intelligent transportation (abbreviated as ITS). Background technique [0002] With the rapid development of our country's economy, the contradiction between the ever-increasing car ownership and the limited road area has become increasingly prominent. In order to solve this contradiction, in addition to vigorously building roads, improving the utilization efficiency of existing roads is also an important part. In this context, intelligent transportation system has increasingly become a hot spot of research and deve...

AI Technical Summary

Problems solved by technology

However, the vehicle speed supported by the WLAN-based ETC system on-board unit and roadside unit is very high, usually in the range of 120km / h~180km / h, and the working distance of the RSU is only 50m~100m, which inevitably makes the connection enter the wireless The time requirements of the local area network are very strict (in milliseconds), and the established connection must be very stable, otherwise, due to the very fast traffic speed of the vehicle, there will be continuous or no time to successfully establish the connection or the established connection The phenomenon of disconnection, that is, the OBU and RSU are either not connected, or they are disconnected immediately after being connected, so that the entire ETC system cannot realize the function of non-stop charging

In addition, since the OBU is powered by a dry battery, an ordinary 1200mAh dry battery is required to power the OBU for 3 months. Therefore, from the perspective of power consumption, it is not allowed to have a long time to establish a connection between the OBU and the RSU

[0014] To sum up, it can be seen that the traditional IEEE802.11MAC layer protocol standard mainly aimed at stationary or low-speed mobile (below 5km / h) terminal applications must not be suitable for the communication between the vehicle-mounted unit and the roadside unit of the WLAN-based ETC system Connection, specifically in the following aspects: first, the traditional IEEE802.11MAC layer protocol standard is not sensitive to the mobile terminal’s moving speed, and the specification of this protocol does not take the situation of high-speed mobile as the main application mode; second, establish a connection The time required for a few seconds is too long for the communication application of the WLAN-based ETC system on-board unit and the roadside unit, and the power consumption at the OBU end and the function realization of the entire ETC system are intolerable; third, the RSU The beacon is sent in 100ms and a three-way handshake is required when establishing a connection. It is too complicated for the communication application of the vehicle-mounted unit and the roadside unit of the WLAN-based ETC system, which wastes a lot of time overhead, making it time for the OBU and the RSU to establish a communication connection. If it is too long, the power consumption of the OBU will be wasted in vain, and the life of the OBU will be greatly reduced; Fourth, the traditional IEEE802.11MAC layer protocol standard, which prioritizes communication effectiveness over reliability, is not suitable for WLAN-based For the communication application between the ETC system vehicle unit and the roadside unit, since the communication between the ETC system vehicle unit and the roadside unit based on WLAN requires only 300 bytes of data to be exchanged, the amount of information is extremely small, so it does not require a high information transmission rate ( 54Mbps), the minimum rate of 6Mbps specified on the RSU side is sufficient, therefore, it is entirely possible to exchange for the optimal connection that is more important for the communication application of the WLAN-based ETC system vehicle unit and roadside unit at the expense of the information transmission rate Stable and reliable; Fifth, in the process of establishing a communication connection, it is required that all kinds of communication between the OBU and the RSU must correspond to each other. This feature also greatly limits the flexibility of establishing a communication connection between the OBU and the RSU. resulting in a dramatic increase in connection establishment time

[0015] Moreover, all other existing MAC layer protocol standards are not suitable for the communication between the vehicle-mounted unit and the roadside unit of the WLAN-based ETC system due to the huge difference between the supported physical layer technology and the physical layer technology of WLAN. connect

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