| Wireless sensor network is a distributed sensing network that utilizes sensor nodes for specific functions.In recent years,wireless sensor networks are widely used in defense science and technology,information collection and other fields,and its application scenarios turn out to be diversified.Therefore,the in-depth study of wireless sensor networks is of great significance.IEEE 802.15.4 standard is the most mature and stable standard for the wireless sensor networks which provides a unified specification for network infrastructure.The standard can support low rate services with low bandwidth,latency and power requirements.However,it is not able to guarantee the requirements of delay sensitive services.In order to meet the needs of the current business scenarios,IEEE 802.15.4 media access control layer mechanism needs to be deeply researched and analyzed to find an improved scheme suitable for complex application scenarios.The main contents of this thesis are divided into the following three parts: protocol introduction and simulation system design,performance testing and analysis,improvement of the proposed program and verification.Firstly,protocol introduction and the design part of the simulation system introduces IEEE 802.15.4 application scenarios and MAC layer-related mechanisms,and give a brief introduction to the principles of the basic simulation platform for the MAC layer and its functional modules.Secondly,IEEE 802.15.4 MAC layer simulation system is designed by using the simulation platform.Then,the implementation process of the super frame planning,channel access and data transmission part defined in the protocol is emphasized.The performance testing and analysis part mainly tests and analyzes the MAC layer mechanism of the protocol and assesses the throughput,delay,jitter and other performances of MAC layer mechanism in the different scenarios through the design a variety of test scenarios.According to the results,it is found that the MAC layer mechanism of IEEE 802.15.4 protocol can meet the needs of a single,low-rate business performance quite well,but it can't guarantee the quality of the high bandwidth,low delay service.The presentation of the schema improvement and the verification part specifically includes the following three points.Firstly,according to the problems that there are non-competitive access time,dense channel collision in the network,and the waste of time slot,the improvement of GTS request mechanism is put forward.That is,by carrying the GTS request in the data frame channel waste is reduced and therefore,the overall performance of the network is improved.Secondly,aiming to solve the problem that the high priority service quality can't be guaranteed,priority-based GTS assignment mechanism is put forward.The performance of high-priority service is improved by prioritizing the allocation of GTS for high-priority services.Aiming to solve the problem that the allocation of time slots is not timely in non-competitive access time,the super frames improvement mechanism is put forward.The performance of the GTS service is improved by placing the noncompetitive access time at the beginning of the super frame so that it can respond more quickly to the GTS request.Finally,the validity of the protocol improvement scheme is verified by theoretical analysis and simulation results.It shows that the improved MAC protocol can adapt to the more complicated application scenarios and provide the ideas for further research work. |
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