Study On Real-time Communication Algorithms For IEEE 802.15.4

With the rapid development of wireless communication technology and low power consumption microprocessor, there are appearing more and more wireless sensor network applications: human health and physiological parameters monitoring, sports fitness, and medical monitoring etc. industrial control, hydrological and pipeline monitoring etc. in the industrial environment, infrastructure monitoring such as bridges, building automation and other quality. Thus it promotes the wide application of low-power real-time communication technology in wireless sensor networks. In this thesis, the CSMA/CA mechanism and GTS scheduling algorithms for IEEE 802.15.4 standard are studied in detail, and an algorithm to support the real-time and high speed communication for multiple sensor nodes in different periods are proposed. In addition, combined with context aware technology, this thesis studies on the improvement of the standard beacon-enabled CSMA/CA algorithm, which can be applied in scenarios with different traffic loads, and verificates the performance of algorithm in real-time applications. The explicit work includes the following:(1) This thesis discusses the GTS scheduling schemes for IEEE 802.15.4 in detail, analyzed the limitations when used for high speed real time data transmission applications. According to the bandwidth utilization, delay constraints, and energy efficiency etc. These algorithms for real time communication are classified, compared and analyzed, which will help for their deployment.(2) In the high-speed real-time heterogeneous data transmission applications, there are still some limitations of GTS allocating algorithms in IEEE 802.15.4 protocol. For example, it does not support real-time services in a superframe with more than seven devices; the delay constraints should be less than the superframe length and it is difficult to support the applications with different periods heterogeneous data transmissions. To overcome these limitations, this thesis proposes a new heterogeneous data communication-supported IEEE 802.15.4 real-time bandwidth allocation algorithm. It adjusts the sending time according to the transmision information of task with different periods. Performance analysis results show that this algorithm can strictly guarantee the delay constraints, satisfy the requirements of the heterogeneous data communication, and improve the bandwidth utilization significantly.(3) The classical CSMA/CA mechanism is lack of adaptability, which can not satisfy the requirements of the complex application. To combat this problem, this thesis proposes a priority based adaptive algorithm. It provides priority differentiated services for different streams and reduces the collision probability. Then it improves the throughput and reduces the packet loss, delay and energy consumption. And it can satisfies the service quality requirements of wireless sensor networks with different priority data streams in real time transmission environment.(4) In Tiny OS operating system environment, EGSA algorithm is implemented on the Imote2 platform. The system clock delay and real-time transmission performance of EGSA algorithm are discussed in detail in heterogeneous data transmission. In addition, the proposed CSMA/CA algorithm is implemented on the wearable sensor platform—Shimmer. The packet loss rate, the average network delay, the network throughput and the energy consumption are studied explicitly on the hardware platform.The research work in this thesis is important for IEEE 802.15.4 real-time commuications, and might have a promising future in the field of medical treatment, industry, society and etc.