Research On The Initial Access Process Of 5G NR

With the rapid development of wireless communication technology,the fifth generation(5G)mobile communication networks have entered the commercial phase.5G wireless networks have three major application scenarios: enhanced mobile broadband business,massive machine type communication business,ultra reliable & low latency communication business,and five features: large bandwidth,high mobility,ultra high reliability,ultra low latency,and large-scale connections.5G New Radio(NR)systems using frequency bands below6 GHz are currently in commercial use.For NR systems using millimeter wave bands,there are still many issues to be further researched.This dissertation takes the initial access process of the NR systems in the millimeter wave bands as the subject,and focuses on the initial beam search process and the downlink synchronization process.First of all,this dissertation introduces the basic physical layer information of the NR systems,focusing on the resource information of the Synchronization Signal Block(SSB)and Physical Random Access Channel(PRACH).At the same time,the specific steps of the initial access process of the NR systems are explained,leading to the importance of initial beam search and its relevance to the cell search and random access process.The above content is the basis for the following research.Subsequently,this dissertation researches the initial beam search scheme and proposes three newly designed beam search schemes: reverse iteration search,single layering search and dynamic layering search.Each scheme analyzes specific steps through an example,and evaluates performance through formula derivation,and analyzes its advantages and disadvantages.Then,this dissertation focuses on the sequence selection,detection and frequency offset estimation method of the primary synchronization signal(PSS).The main research is the correlation characteristics of the time-domain m-sequence used by the PSS in the NR systems,and the reasons why the NR systems do not follow the Zadoff-Chu(ZC)sequence adopted by the LTE systems.At the same time,cross-correlation detection,time-frequency joint correlation detection,cross-auto correlation detection and their frequency offset estimation methods are discussed.It is worth mentioning that this dissertation improves the frequency offset estimation method for cross-correlation detection.Finally,this dissertation performs a simplified downlink budget analysis of the NR systems using the millimeter wave bands,and simulates the PSS detection and frequency offset estimation methods studied above.Based on the simulation results,the choice of the initial beam search scheme is discusses.