Research On Random Access In LTE Trunking Communication System

The trunking communication system is widely used in professional communication because of its scheduling function and the characteristics of fast call.But as people understand the importance of trunking system,and the development of the information times causes the needs of cluster multimedia business needs,the traditional trunking communication system has been unable to meet the needs of high bandwidth and high rate.Therefore,the development of LTE broadband trunking communication system has become a research hotspot.Because the cluster system provides different permissions for different application fields,different users for different levels of random access services,and the characteristics of the scheduling,which lead to the needs for bursty access,the traditional LTE random access cannot meet requirements of user priority and access latency for trunking communication.Developing an improved random access mechanism which meets the needs of cluster users and ensures the priority and satisfaction of the users in trunking system has become the focus of the research.So,on the basis of LTE random access,the thesis focuses on two aspects: preamble selection scheme and backoff algorithm,and carries out the study of the random access of LTE trunking system,which mainly includes:First of all,the processes and applications of random access are studied.The thesis analyzes the shortcomings of LTE fair access and the problems that trunking system users and ordinary users encounter at the same time when they join cluster communication.Based on the characteristics of trunking system,the thesis proposes an access priority scheduling strategy,which can provide different access services for different users and ensure the access of high priority users.Secondly,we study the LTE preamble sequence and the preamble management scheme,considering the access priority and the distinction of the preamble selection set.In this thesis,we proposes a reserved management scheme of preamble index based on priority dynamic reservation,which combines the advantages of static and dynamic management scheme.Through the mathematical derivation and simulations,we verify its advantage over the existing random access scheme,regarding their success rate and resource utilization.Finally,the collision avoidance algorithm of LTE random access is studied,considering the problem of access collision rate in LTE system,we propose and analyze the performance of uniform backoff algorithm and binary exponential backoff algorithm.The thesis presents a multiuser backoff algorithms based on exponential backoff algorithm,which takes the access priority scheduling strategy into account and provides the access collision strategy for different users according to the number of users' maximum retransmission times and exponential backoff algorithm.The algorithm is applied to the preamble management scheme based on dynamic priority reservation.We show the improved performance of the proposed algorithms regarding delay and access success rate,compared with traditional random access algorithm.