Research On Synchronization Technologies In Future Cellular Mobile Communication Systems

As an indispensable infrastructure of modern information society,cellular mobile communication systems should have high performance to meet diversified demand.Synchronization performance guarantee is not only one of the key capabilities of the future cellular mobile communication systems,but also a necessary prerequisite for the normal operation.However,for the standalone long term evolution-unlicensed(SA LTE-U)which is introduced to increase the available spectrum for the future cellular mobile communications,it is difficult to achieve reliable synchronization due to the discontinuity of the channel which is shared with the other systems.Moreover,synchronization performance is interrelated with the other performance of the system.For the densely deployed small cell system which is introduced to increase spectrum reuse to the future cellular mobile communications,the synchronization of uplink and downlink switching time will affect the system's capability of the interference suppression and the flexibility of supporting asymmetric traffic,thereby affecting the other performance of the system.This thesis aims to study the synchronization schemes and performance as well as their impacts on the other performance in the future cellular mobile communication systems.For the SA LTE-U system,the influence of the channel access modes and the coexistence systems' parameters on the performance of the synchronization between the base station and user equipment are studied.Two kinds of synchronization of SA LTE-U are defined,namely,initial synchronization and maintaining synchronization.For the SA LTE-U that adopting Frame-Based-Equipment(FBE)channel access mode and Load-Based-Equipment(LBE)channel access mode,analysis frameworks of synchronization performance are respectively proposed.The success rates and the energy consumptions of the synchronization of FBE-and LBE-based SA LTE-U are derived,respectively.The applicability of FBE and LBE is investigated according to the success rates and the energy consumptions of the synchronization,which provides a basis for system design and parameter setting.In addition,the frame structure of SA LTE-U is designed for better syncrinization.The frame structure is not only compatible with long term evolution(LTE)systems,but also supports the uplink/downlink asymmetric traffic flexibly.Besides,it meets the requirements of the law in unlicensed frequency band on that both base stations and user equipments should sense the channel firstly and then access the channel.The design of special subframe can make synchronization and the other important processes start as soon as possible after accessing channel.Increasing the sending frequency of synchronization signals in downlink subframes can increase the success rate of synchronization.For the densely deployed small cell system with time-division duplex(TDD)technology,the impact of the intercell synchronization of uplink and downlink switching time on the capability of interference suppression and flexibility of supporting asymmetric traffic is studied.Based on cell clustering and intra-cluster synchronization scheme,an analysis framework is established.In this framework,the locations of small cell access points and user equipments are modeled as independent poisson point processes(PPPs),and the random arrival of packets is modeled as a discrete-time queuing system.The analysis framework not only portrays the spatial and temporal randomness,but also considers the non-saturated traffic,which has universal significance.System stability conditions and the mean packet throughput(MPT)of the densely deployed small cell system with non-saturated traffic are derived.Furthermore,the MPTs of two special cases are obtained.That is,the MPT in the densely deployed small cell system based on static time-division duplex(S-TDD)when cluster size equals 1 and that in dynamic time-division duplex(D-TDD)when cluster size is infinite,respectively.The influence of various network and service parameters on MPT is analyzed,and the guidance for cluster design and system configuration in densely deployed small cell systems are provided.