Research On Real-time Of Wireless Sensor Networks

Wireless sensor network, as one of the most hot technologies in the 21st century, can be used in real-time applications widely, such as military, medical care, urban management, earthquake monitoring, device monitoring, building structure monitoring etc.The subject derives from three projects which use the wireless sensor network to monitor fan health, earthquake and pipeline. Multi-wireless sensor nodes sample the vibration information, and then forwarded to the center base node by self-organized and wireless multi hop routing, finally transmitted to the sever to diagnosis the fault reason of the fan, seismic P-waves, and the pipeline fault locators. The sample which need nodes high precision time synchronization, and the vibration wave contained the faulty information which is fleeting, will not recurrent, so higher demand are proposed on the real-time of WSN.In order to improve the real-time of WSN, the researcher can analyze it from the aspects of the hardware platforms, operating system, the programming language, communication protocol and time synchronization algorithm. The paper mainly from the special real-time operating system for WSN to research, combine with the requirement of the fan, earthquake and pipeline monitoring.The thesis deeply analyzed the structure and related service of the operating system kernel, such as task management, synchronous and communication mechanism between the tasks, memory management, energy and time management, interrupt mechanism and scheduling schemes. Then design a real-time operating system model for the strong monitoring system.The small businesses operating system, for the wireless sensor network which developed by foreign are expensive and complicated, and the source code is not public, are not suit for the hard time monitoring system. As the open source code OS, Tinyos, t-kernel andμC/OS-Ⅱ, are not suit too. Tinyos is Single-task kernel, the task can't be preempted, it can't guarantee time.μC/OS-Ⅱ, t-kernel are preempted kernel, but the footprint occupy large memory. Therefore, we need introduce an operating system which is hard time and small memory overhead About the way of operating system architecture design, first analyzing many kinds of embedded operating system architectures, in order to achieve efficient, simple, flexible and safety, hierarchy hierarchical architecture is used in the used in the design of Operating system architecture. Then, combine with the modular design approach.To achieve the hard time, the paper focus on the scheduling mechanism and interrupt management. In the system, the tasks can be divided into hard time tasks and the soft tasks. As the hard task need scheduling in time, take into account fairness, this paper presents a hybrid scheduling, the soft time tasks with round robin scheduling algorithm and the hard time tasks are based on priority preemption scheduling. There are four priorities in the hard tasks of the three applications, The hard tasks in order from high to low:Energy state monitoring task, sensor sampling task, RT management task and the MAC task, and the hard time tasks has corresponding interrupt vector which can reduce the number of task switching, and the real-time of the system is improved.As the response to interrupts of the hard real-time monitoring system need faster and stability, maskable interrupts have a unified entry, semi-nested interrupt mechanisms and combined with the interruption fragmented mechanisms to solve the problem of ITC share.The paper also design the basic services of the operating system such as task management, task synchronization and communications, time management, memory management, energy management. Finally, through function testing and real-time testing, the result indicate that the operating system design is reasonable, and the hard real-time of the OS is good.