The Software Design And Implementation Of Wireless Sensor Network Based Station Based On Embedded Linux

Wireless sensor network (WSN) is a new generation of sensor network, it is an emerging hot research spot which is concerned at home and abroad currently and consisted by many subjects which are intersectant highly. WSN integrates sensor technology, embedded computing technology, modern network, wireless communication technology and distributed information processing technology and so on. It can monitor, sense and collect various informations of environment or monitoring objects by various types of integrated micro-sensor cooperating. It can process informations by embedded system, and send the sensing informations to user terminals by random self-organizing wireless communication networks with multi-hop repeaters, there is able to realize the concept of "ubiquitous computing" really and truly. So wireless sensor network is considered as a technology which has tremendous effect in 21st century.This article researches on using the sensor technology to get data from the area which we want to watch, then using the communication technology to send the data to a base station. Then the base station sends the data to a platform server through Ethernet. The data which is get from the area which we want to watch is processed on the platform finally, and the platform also responds. This article will introduce the design of the software of base station. The base station is a very important part in the system of WSN. It is the bridge between wireless sensor network and external network, it is a junction to WSN, and manages the whole network. Therefore a functional base station is the base of a steady WSN.The base station is developed on embedded system. According to the general process of development of embedded system, we must choose a hardware platform for base station system. Because WSN is being applying in more and more areas, and the data processed by WSN increases rapidly, we choose ARM S3C2410 as central processing unit. The capability of communication is very important for base station. When the base station is working, it needs to communicate with external network and WSN nodes. In this article, the external network is Ethernet, so we need an Ethernet interface. We use CS8900A as an Ethernet interface. CS8900A has a 10Mbps transmission rate. The base station uses CC2420 RF transceiver to communicate with nodes in WSN. CC2420 is produced by TI Corporation. It is a true single-chip 2.4GHz IEEE802.15.4 compliant RF transceiver designed for low-power and low-voltage wireless applications. Its effective data rate is 250kpbs.After creating hardware platform, the next step is to choose an embedded operating system for base station. Finally, we use Linux as operating system of base station. The reasons of this choice are: First, Linux can be used for a variety of hardware platforms, Linux has been transplanted to a variety of hardware platforms, which is very attractive to research and developing projects which are affected by spending and time-limit. Prototype can be developed on a standard platform, and then migrate to specific hardware platform, the development of software and hardware has been accelerated. Second, Linux can be configured without any licence or business co-operation, source code can be obtained for free, this can save substantive development costs. Third, Linux has excellent network support. Micro-kernel supports network directly, not like other operating systems having to link TCP/IP protocol packets, because Linux develops from network.After having selected operating system, we need to build embedded Linux development environment. In the process of embedded Linux software development, we use cross-development whose meaning is developing at the host, running in the target board. Embedded Linux operating system is running in the target board, and its installing process is as follows: first of all, we need to cut the Linux kernel out, and then we install the Boot Loader which is used for loading and starting up the embedded operating system to development board. After this, the kernel image can be downloaded to the development board, but the kernel can only start normally with mounting the root file system. In cross-development environment, we usually use NFS file system. We mount the sharing root file system between the host and development board. This approach will greatly facilitate the host and target board in data sharing, so the final task is to install and configure network file system (Network File System, NFS).After building embedded development environment, we will proceed to achieve CC2420 device driver. The main function of base station is managing wireless sensor network and collecting the data which is from wireless sensor network. The basis of these features is the wireless communication between wireless sensor network and base station. CC2420 wireless transceiver module ensure the wireless communication between nodes and base station in wireless sensor network, it is a very important part to the whole system. Therefore the performance of the driver of CC2420 communication module is related to the base station's overall performance directly. CC2420 device driver can be implemented in two ways: non-interrupt and interrupt. The method of implementing non-interrupt driver is querying. It is correspondingly easy, but it will consume extra CPU resources. The driver with interrupt is rather complicated, but it will not take up extra CPU resources. We achieve a CC2420 RF chip driver which is efficient and stable with interrupt.When hardware and software platforms are built well and CC2420 RF transceiver chip can receive and send wireless data, we will be able to design applications for base station. Base station applications include wireless communication module, TCP/IP module and data-processing module. Wireless communication module is responsible for communication between base station and nodes, and then receive data from nodes and send data to nodes by calling the driver interface function; TCP/IP module is responsible for communications between base station and platform, base station receives commands and time synchronization packets which are from platform through ethernet network, while the base station also upload the whole network topology and the application data received from nodes to the platform; Data-processing module is mainly responsible for analysing and dealing with the data which is sent to base station from nodes.In this article, we achieve CC2420 device driver which is very important to the whole base station system in embedded Linux, and make a design of applications of base station. After several rounds of testing, the wireless transceiver is working to achieve the design objectives.