The Software Design And Imlementation Of Wireless Sensor Network Base Station

With the progress of computer technology, communication technology and sensor technology, the technology of wireless sensor network becomes more and more practicable. It has been used in more and more field, from military area to common area. Because sensor technology can sense the world, communication technology can connect the world and computer technology can analyze the world, the wireless sensor network technology becomes the most important technology in this century which can sense and connect the whole world. This article comes from an actual project which uses wireless sensor network project. This project uses the sensor technology to get data from the area which we want to watch, then uses the communication technology to send the data to a base station, then the base station send the data to a platform server through Ethernet, then the platform processes the data and responds. This article will introduce the design and architecture of the software of base station. The base station is a very important part in the system of this project. Firstly, it is the bridge between wireless sensor network and other network, and it is also the bridge between this system and other system. Secondly, it manages the network and the time synchronization. Therefore an efficient, steady base station is the guarantee of a powerful system.The base station as an embedded system, in order to develop it, we should customize its hardware platform. Considering base station will receive and process lots of data from wireless sensor network, and send it to platform server through Ethernet, we choose ARMS3C2410 as centre process unit which has a frequency of 203M, we choose CS8900A as controlling chip which has a 10Mbps transmission rate, and we choose CC2420 RF transceiver to communicate with nodes in WSN, which accords with 2.4 GHz IEEE 802.15.4 and has an effective data rate of 250 kpbs. All the customization has been tested and can meet our need.After customizing the hardware platform of base station, we should choose an embedded operation system for this hardware platform. We choose Windows CE at last. We have 2 reasons for this choice. Firstly, it supports multi-thread, multi-task, preemption and modularization. Secondly, Microsoft will provide lots of helpful document for us. This is very helpful for us.After choosing the operation system of base station, we should customize the operation system for the hardware platform of our base station. The main work is to develop the Board Support Package (BSP) for the target hardware platform. BSP is a layer of software between hardware and operation system. All the direct operation about hardware is implemented by BSP. BSP includes four parts: boot loader, OEM Adaptation Layer (OAL), device drivers and configuration files. Boot Loader is a small section of code running before the Windows CE kernel runs. Its function is to initiate the hardware and load operating systems kernel image into RAM. OAL is the layer of code between operation system kernel and the hardware. It abstracts operations involving hardware so that Windows CE can be independent of specific hardware platform. Configuration file contains configuration information which creating Windows CE platform needs. Driver is the more important part of BSP, which makes operation system recognize the device and provide the method of using the device to the application software.Because BSP lie between the hardware and the operation system, in order to develop it, we should be very familiar with the hardware and the Window CE operation system. If you want to develop the BSP totally by yourself, it is very difficult. But we can use the BSP of the similar platform instead. In this way, we can save a lot of time and spend more time on the design of the driver of our special device. In this project, we use the BSP of a similar platform, and only add the driver of CC2420. For the development of CC2420 driver, we develop a simple CC2420 driver with out interrupt. After it passes all the tests, we modify some function in OAL and add the interrupt function. After we add the interrupt successfully, we develop the interface for route module and time synchronization module. When we finish all the things above, a CC2420 and DSP which can meet out need is finished.When the software and hardware platforms have been established, we can develop the application software for this project. According to the practical need of this project, we divided this application into 4 modules: wireless communication module, Ethernet communication module, data process module and buffer pool module. The function of wireless communication module is to communicate with wireless sensor network, including receiving data and sending data. The function of Ethernet communication module is to communicate with platform server, including receiving data and sending data. The function of data process module is to process all the data received from wireless sensor network. It includes two very important sub-modules: time synchronization module and route module. The function of time synchronization module is to synchronize all the nodes in wireless sensor network with the clock of base station. The function of route module is to tell base station the next hop when base station wants to send data to a node. The buffer pool module has two functions. Firstly, when the Ethernet fails, it can save the data temporarily. When the Ethernet recovers, we can send the data to platform server, too. Secondly, when the thread to receive data in two threads which communicate with each other dies, the data sent by another thread can be saved and when the dead thread is restarted, the data can be received, too.