Performance Evaluation And Scheduling Optimization In TDMA/CSMA Hybrid Network

With the development of new control areas such as the Internet of things,there are more and more data of different quality requirements in the network.The traditional single channel access mechanism cannot meet the business requirements.The combination of TDMA and CSMA/CA mechanism can make full use of the high transmission rate of WLAN and the high real-time performance of TDMA mechanism,which is the research hotspot of current control network.However,different access mechanism running at the same time will inevitably cause mutual interference,and the time-slot scheduling of TDMA also directly affects the performance of real-time business and throughput of non-real-time business.Therefore,how to evaluate the hybrid network performance and optimize the scheduling is the key to effective use of TDMA/CSMA hybrid network.Firstly,a CSMA/CA saturation throughput evaluation model in hybrid network is established to analyze the effect of TDMA periodic real-time business on CSMA/CA non-real-time business.By analyzing the working principle and channel access mechanisms,TDMA business is equivalent to periodic strong interference of CSMA/CA,and a hybrid network analysis model is established.Based on the calculation of collision probability,the analysis model of DCF two-dimensional markov chain is improved,and the formula of the standard saturation throughput of CSMA/CA in hybrid network is derived.Simulation experiments are carried out by setting different parameters such as packet size and transmission rate.The change of packet loss rate and throughput is analyzed,and the accuracy of the model is verified.Secondly,scheduling and optimization method of time slot distribution is designed.The characteristic of different TDMA time slot distributions is analyzed and the average delay and throughput are calculated.It is proved that the time delay and jitter are smaller when distributed evenly,while the continuous distribution can provide more throughput for non-real-time business by merging the competition time slot.Based on the minimum channel demand time of CSMA/CA data and the throughput evaluation model proposed above,the switching strategy of distribution mode is designed to give consideration to both real-time and non-real-time business.Finally,the optimization algorithms for period selection and task scheduling of real-time tasks are designed.A harmonic period selection algorithm is proposed to reduce the jitter and network utilization of real-time tasks.The experiments prove that the algorithm in this paper has a shorter operation time,and it can provide more bandwidth for non-real-time business.For jitter problem of real-time tasks in mobile scenarios,a time slot reserved method based on minimum period is put forward.It can reduce the switching delay and jitter of response time by assigning higher priority to mobile tasks and scheduling beforehand.