Application of RFID in path identification of electronic toll collection system

1 Introduction

With the continuous increase in the number of vehicles in my country, the semi-automatic toll collection (MTC) method currently used on highways has caused serious traffic congestion, especially during peak traffic hours. The fundamental way to solve the problem is to use electronic toll collection. However, due to the implementation of networked toll collection on my country's highways, a large number of road network connections have caused a multi-path problem, that is, there are often multiple optional paths for vehicles to travel from point A to point B in the road network, which leads to the problem of ambiguous path identification. In the networked toll collection environment of highways, the use of electronic toll collection must first solve the problem of ambiguous path driving, that is, according to which driving route standard the vehicle is charged tolls.

There are two ways to solve the problem of ambiguous path identification: one is to accurately identify the actual path of the vehicle in the road network through certain technical means, so as to solve the problem of charging and splitting; the other is to ignore the actual walking path when charging, and determine the path judgment in a certain way according to the shortest path standard as the basis for splitting the vehicle toll, and use fuzzy approximation of the probability of the truth to deduce the route. At present, provinces in China that have piloted electronic toll collection basically use the second method to deal with the problem of ambiguous paths in networked toll collection. This is mainly because the precise identification method is limited by the existing technical conditions, the highway toll operation system and the actual situation, and its operability is not strong, the comprehensive cost is high, and the benefit is low. With the increasing complexity of the road network structure, the difficulty of using fuzzy approximation of the truth is increasing, which seriously affects the function of networked toll collection and settlement of highways. Therefore, the study of ambiguous path identification is the core of the effective promotion of electronic toll collection, and it is also an urgent need to fundamentally solve the congestion of highway access and improve operational efficiency. Combined with the current domestic highway network toll collection practice and technical conditions, a design scheme combining RFID electronic tags with contactless IC cards for ambiguous path identification is proposed. This solution is compatible with the current technical conditions and actual environment of semi-automatic toll collection (MTC), and effectively solves the path identification problem in electronic toll collection. Simulation data proves that it has high practicality and operability.

2 Application Status of RFID Technology in Electronic Toll Collection System

2.1 RFID technology

Radio Frequency Identification (RFID) is most successfully used in the field of intelligent transportation. The RFID system of highways generally consists of three parts:

(1) Electronic tags (Tags) consist of coupling elements and other devices. Each tag has a unique electronic code and is installed on the vehicle to identify the vehicle information. It contains electronic data in a specified format. When exposed to radio frequency signals, it reflects back radio frequency signals carrying alphanumeric coded information for the reader to process and identify. Its operating frequency is generally above 915 MHz and is divided into active and passive.

(2) The reader is used to generate and transmit radio frequency signals and receive radio frequency signals reflected by the electronic tag. It can read and identify the vehicle data information stored in the electronic tag without contact. This can achieve the purpose of automatic vehicle identification. It can also write information to the tag, and further realize the management functions such as vehicle information collection, processing and remote transmission through computers and computer networks. Broadcast transmission radio frequency identification and reflection modulation radio frequency identification are used.

(3) Micro-antenna, also known as road test identification, is used to transmit radio frequency signals between electronic tags and readers. It is installed at the entrances and exits of highways and at intersections that generate ambiguous paths.

2.2 Problems in the application of RFID in highway electronic toll collection systems

The application of RFID in highways is reflected in electronic toll collection. The reader antenna is set up above the road about 50~100 m away from the toll gate. When a vehicle passes by the antenna, the antenna wakes up the electronic tag on the vehicle and transmits the vehicle ID information: issuing bank number, license plate number, vehicle type parameters, electronic tag number, etc. After the reader receives the vehicle ID information, it transmits it to the lane controller (backend computer). The legality of the electronic tag of the vehicle entering the toll lane is verified. The relevant information of the vehicle is analyzed, and the toll calculation and automatic deduction can be realized without stopping. This will minimize the traffic congestion caused by low toll collection efficiency at the toll station exit, improve the traffic capacity of the toll lane, reduce unnecessary fuel consumption by vehicles waiting at the toll gate, reduce noise and exhaust emissions at the toll gate, and reduce the pollution of vehicles to the environment, thereby achieving the purpose of saving energy and protecting the environment.

Although foreign RFID technology has been successfully used in electronic toll collection, some technical features and operation methods are not suitable for use on my country's expressways. Taking lanes as an example, there are dedicated lanes and mixed lanes; toll collectors on duty and unmanned management modes; low-speed and high-speed traffic modes. At present, a few provinces in China have implemented electronic toll collection, while most provinces have not yet implemented it. In addition to the lack of awareness of road users and the imperfect banking system, the main reason is that the compatibility problem between RFID technology and the existing semi-automatic toll collection (MTC) system has not been solved. Electronic toll collection will inevitably form multiple pass cards and multiple lanes, increasing the use cost of road users and the investment cost of operating units, thus affecting the implementation of electronic toll collection.

3 Design of combined RFID electronic toll collection system

Based on the above analysis, combined with the current highway MTC toll collection environment, a combined RFID electronic toll collection system design is proposed, the core of which includes frequency selection, two-piece electronic tag design and dual roadside identification design. The functional structure of the system is shown in Figure 1.

3.1 Selection of short-range communication standards

Article 13 of the Interim Technical Requirements for Networked Toll Collection on Expressways clearly states: "The recommended dedicated short-range communication frequency for the automatic vehicle identification system in the electronic toll collection technology is 5.8 GHz, and the electronic tag should be a readable and writable 'single-chip' (readable and writable smart electronic tag) or 'two-chip' (electronic tag with IC card interface). The 'two-chip' electronic toll collection system should be compatible with the manual semi-automatic toll collection system." Therefore, the 5.8 GHz short-range communication standard is selected as the dedicated short-range communication DSRC (Dedicated Short Range Communication) standard, with an output power of 300 mW; the modulation methods are ASK and BPSK; and the communication distance is 10 m.

There are three advantages to choosing 5.8 GHz as the central frequency band for microwave short-range communications: (1) The 5.8 GHz frequency band has low background noise and good anti-interference performance. (2) There are many equipment suppliers in the 5.8 GHz frequency band, which is conducive to the introduction of equipment for my country's ETC system and helps reduce system costs. (3) It is conducive to the development of other services of the intelligent transportation system in this frequency band in the future.

3.2 Design of a combined two-piece electronic tag

In view of my country's specific national conditions and taking into account that most toll stations adopt IC card transactions, the system uses a combined two-piece electronic tag as a carrier of vehicle identity, driving route records and toll payment information. The design structure is shown in Figure 2.

The combined two-piece tag combines the advantages of RFID and IC card technology. It consists of a "two-piece electronic tag + dual-interface CPU card". It can not only accurately record the vehicle's driving path within the road network, but also has the charging function of ordinary IC road networks. It uses a standard IC card interface (usually a contact IC card interface of ISO7816 specification or a contactless IC card interface of ISO14443 specification) and forms a complete set of combined two-piece vehicle-mounted equipment together with the IC card. To ensure sufficient signal strength, an active tag is used. This design has the following advantages: (1) The system uses IC cards as the charging medium and is fully compatible with the capabilities of semi-automatic toll collection (MTC) and electronic toll collection (ETC); (2) It is suitable for my country's basic national conditions, suitable for the established toll collection system and MTC toll collection system, and meets the functional requirements of electronic toll collection. Its installation is shown in Figure 3.

3.3 Design of dual roadside signs

The dual roadside identification design means that the system and tag information reading and writing use lane detection identification and multi-path identification respectively. Lane detection identification uses reflective modulation reading and writing, and is installed at the entrance and exit of the lane. Its function is to communicate with the electronic tag to complete ETC vehicle detection, identify vehicle driving paths and toll transactions. It consists of the following parts

(1) The roadside equipment controller is a computer device that is usually connected to the antenna and its controller, the capture system and other equipment. For a single-lane ETC system with a toll island, it is also connected to peripherals such as traffic lights and electric barriers. The roadside equipment controller performs various control, communication and processing functions for the connected equipment.

(2) The antenna and its controller realize communication with the on-board OBU.

(3) The photo-taking system is an electronic record system for vehicles that violate traffic rules and vehicles without electronic tags. It is used to collect tolls and impose penalties on these vehicles afterwards.

The lane antenna receives the data signal transmitted by the antenna controller, which is radiated by the antenna after modulation and power amplification. When an ETC user drives through the ETC lane, the lane antenna signal activates the electronic tag to enter the working state, and the electronic tag sends the corresponding response data back to the lane antenna according to the received command. The lane antenna is usually composed of a power supply unit, an RS485/422 communication interface, an oscillator, a transmitting unit, a receiving unit, a data processing unit, an external signal indicator, a horn antenna or a microstrip antenna.

The antenna controller receives communication requests from the lane control computer system, forms data frames that comply with the DSRC standard communication protocol, sends the data frames to the electronic tags on the lanes through the lane antennas, receives and parses the data returned from the electronic tags, and then uploads it to the lane control computer system. It has multiple control modules built in, each of which controls a lane antenna. The antenna control module is usually composed of a PC communication interface unit, a dual-port memory (DPRAM), a communication protocol processing unit, and an RS485/RS422 antenna interface unit. The PC communication interface unit is responsible for data communication between the antenna control module and the lane control computer, using an RS232 interface.

The multi-path road test sign adopts the broadcast transmission type and is installed at the road test of the multi-path intersection. The vehicle's driving path record is written into the electronic tag according to the direction of the vehicle. The specific parameters are consistent with the lane road test sign unit. Figure 4 shows the dual road side sign system diagram.

4. Result Verification

To verify the effectiveness of the design scheme, the Shaanxi Provincial Expressway Network is taken as an example. There are 206 toll stations and 134 ambiguous paths in the Shaanxi Provincial Expressway Network. 60 entrances and exits and 50 ambiguous paths are randomly selected from the 206 toll stations for simulation calculation. Table 1 gives the parameters required for the design scheme. Table 2 gives some verification results.

5 Conclusion

Aiming at the main problems of current highway network toll collection, this paper proposes a design scheme of electronic toll collection system based on RFID technology, which can better solve the problem of ambiguous path identification on highways. The design scheme has low cost, mature technology, good compatibility with existing systems, and simple later maintenance. Simulation experiments show that the system's recognition rate and recognition time of vehicles meet the performance index requirements. Compared with traditional toll collection methods, the lane capacity of this scheme is increased by more than 10 times, so it has strong practicality and operability.