Research And Implementation On The Virtual Network Device And Vertical Handoff System Of Vehicle Gateway

In some developed countries, the cost the vehicle electronic application has occupied a high proportion in automobile manufacture. And with the rapid progress of modern science and technology, it still shows an upward tendency. Thus, the development and innovation of the new product in automotive field is closely connected with the development of vehicle electronic technology. At present, the development of vehicle electronic technology in China, which still remains at the stage of GPS and Information Enquiry, is relatively low compared with some developed countries.With the rapid development of vehicle gateway technology, the wireless communication plays a more and more important role. The wireless communication network includes the following parts: WLAN, WMAN, WWAN, satellite networks and AdHoc networks. These kinds of different isomeric access network, together, provide the users a larger access networks environment. The automobiles were supposed to access onto the Internet through a certain kind of wireless network to obtain the target information or communicate with another terminal. It should involve the network switching through which the vehicle terminal switches from one base station to another. Generally speaking, the switching between the homogeneous networks is called horizontal switching, while the switching between the isomeric networks is called vertical switching.The vertical switching technology in this article involves two kinds of wireless networks: CDMA and WLAN, each of which has its own advantages and disadvantages. CDMA belongs to WWAN. Its signal covers a widespread area, but with less bandwidth which can no longer fulfill our demands. The maximum transmitting rate of CDMA is 153Kbps and the steady effective rate is 70–80 Kbps. Relatively, WLAN has a larger bandwidth with the speed rate of 5.5Mbps. WLAN is much easier then CDMA and of stronger Anti-Interference Function, the range and mobility of which is weaker. CDMA and WLAN have complementary advantages. The vertical switching technology in this project is to make it possible that the two networks can make up with each other and switch seamlessly on the vehicle.Compared to the technology before, the core of the vehicle gateway described in this article uses an entirely new model technology based on Linux. The package- intercepting model, Socket virtual network devices and wireless virtual network devices in this article are all based on this model technology. The basic kernel technology under Linux ensures the high-tech of the project, the security of the database and the efficiency of the communication. Another difference of the vehicle gateway from the technology before is the separate zone technique which can separate the logical and communication layer related to the application, and then dealt by the application; separate the controlling logical and communication layer of the basic accessing, and then dealt by the application.In the whole project, the communication centre of the vehicle gateway plays a very important role. There are two main aspects of the communication: The first is that the remote serve sends the controlling and enquiry command to the CAN node of the vehicle gateway. According to the CAN network managing strategy after receiving the package, the gateway processes the command and send it the corresponding CAN node to execute the action. The second is that after the vehicle gateway receives the returning CAN nod status code or the GPS information, it will send it to the remote server after processing.The design and realize of the virtual network devices in the vehicle gateway is the most important and difficult part in the whole project. The Socket virtual network devices and wireless virtual network devices of the vehicle gateway are both designed and realized by model. Socket virtual network device, which is the centre of the communication in the vehicle gateway, is to deal with the communication details between the vehicle applications and the corresponding ECU node. The function and the importance are similar to the vehicle gateway in the whole project. The controlling and enquiry command received through the wireless network virtual interface from the remote server will be sent to the corresponding Socket virtual network interface, and then it will be sent to the vehicle service program corresponding to the vehicle gateway after processed. After the vehicle application restores and processes of the package, the Socket virtual network interface will deal with it and then send it again to the corresponding CAN node to execute the corresponding action. Similarly, the returning status code information and GPS information from the CAN node or GPS device to the remote server will also be sent firstly to the corresponding Socket virtual network interface by the driver program, and then sent upward. So the design and the realization of the Socket virtual network interface straightly influence the efficiency of the whole vehicle gateway.Meanwhile, the other important core model of the vehicle gateway, the wireless virtual network interface, is the only external interface, which means if you want to build a communication between the remote server and the vehicle gateway, the only path is the wireless virtual network device. Through this device, the command is handed over to the other model of the vehicle gateway. Similarly, the data from the vehicle gateway to the remote server is sent through this wireless virtual network interface.The wireless virtual network interface also has the role of tunnel, and could receive and analyze the packet from the counterpart. this project realize the vertical handoff technology on this virtual interface, to make sure that the vehicle could chose the CDMA or WLAN smartly to communication with the remote server. Normally, vertical handoff include three phrase: initiation phase, decision phase and execution phase. the execution phase in this thesis is based on the decision: prefer to chose WLAN. that's to say, if the WLAN is possible, the vehicle will chose WLAN to communication with the remote server, and if not, the vertical will chose back to the CDMA.Through the test, the virtual network device and the function of vertical handoff mentioned in this thesis works well and achieve the desired result.