Research On Enhancement Technology And Optimization Design Of 5G SSB

The 3rd Generation Partnership Project(3GPP)requires that the 5th Generation(5G)networks can provide User Equipments(UE)access experience with ultra-high reliability,ultra-low network latency and seamless network switching anytime and anywhere.The initial cell accessing is a necessary process for UE to connect and communicate with gNB.Synchronization Signal Block(SSB)for initial cell accessing is introduced in 5G systems.The research on the enhancement technology and the optimization design of 5G SSB is of great significance to improve the success rate of cell search and Physical Broadcast Channel(PBCH)decoding,which can accelerate the initial cell accessing procedure.The configuration of the Sub-carrier Spacing(SCS)is flexible in 5G systems,which is different from Long Term Evolution Advanced(LTE-A)systems.During the initial cell accessing process,UE cannot know the specific SCS directly before obtaining time and frequency synchronization with the service cell like in LTE-A systems.Therefore,it is necessary to perform SCS detection.Based on the cyclostationary of Orthogonal Frequency Division Multiplexing(OFDM)signals,we propose a SCS detection algorithm with correlation calculation on OFDM signals.The proposed algorithm is theoretically analyzed and the theoretical expression for the detection error rate is derived by approximating and modeling the correlation errors.The algorithm is evaluated and analyzed through simulation in different scenarios.The analytical and simulation results show that the proposed algorithm is effective and the performance is roughly consistent with the theoretical analysis results.In 5G systems,the Demodulation Reference Signal(DMRS)is newly introduced in PBCH for channel estimation and demodulation.During the initial cell accessing procedure,UE cannot know the specific DMRS sequence received directly.It is necessary to utilize a blind detection on the DMRS sequence for PBCH decoding.We study how to combine multiple received DMRS in a transmission time interval of SSB to enhance the sequence detection performance.Two DMRS detection enhancement algorithms based on the combination of likelihood function and the combination of channel correlation matrix are proposed.The simulation results show that the proposed algorithms can enhance the detection performance of DMRS in multiple channel scenarios.In addition,we study the DMRS sequence design schemes to optimize the performance of DMRS detection.Theoretical analysis and simulation results show that the sequence design with maximum Euclidean distance among sequences can optimize the blind detection performance of DMRS under the additive white Gaussian noise channel and orthogonal sequence design can optimize the blind detection performance of DMRS in the single-path Rayleigh channels.The receiving performance of PBCH depends not only on the detection performance of DMRS,but also on the performance of channel decoding.5G systems use the Polar code as the channel coding scheme for all uplink and downlink public channels.In this thesis,the enhancement study of PBCH decoding is studied based on the Cycling Redundancy Check(CRC)aided serial cancellation list decoding algorithm which is widely used.There are two proposed enhancement methods.Firstly,cycling redundancy check is carried out during the decoding process and only retains the decoding path which can pass CRC to reduce the Block Error Rate(BLER)of channel decoding.Secondly,path metric threshold can be used to terminate the decoding process of the wrong decoding path in advance to reduce the complexity.Simulation results show that the channel decoding performance of PBCH is effectively enhanced based on the proposed enhancement technology.