| Satellite communication is an important part of the space-based information transmission system,and it is also an important method to realize global seamless coverage and build an integrated information network between heaven and ground.With the generation replacement of ground mobile communication system,the fusion of satellite network and ground mobile network is also developing continuously.Before the ground user terminal establishes a connection with the network,it needs to ensure that its own uplink transmission time is synchronized with the base station through the random access process,so that the uplink frame timing of the network is aligned with the user terminal sending frame timing.High efficiency and low latency uplink access is the premise for ensuring normal communication between terminals and the network.Therefore,the research on random access technology is particularly important in the satellite and 5G fusion system.This thesis focuses on the GEO satellite and terrestrial 5G network integration system,taking the GEO satellite's wide-area coverage leading to longer propagation delay system characteristics as an entry point,integrating terrestrial 5G protocol design ideas to achieve high-efficiency and low-latency uplink access.The goal is to carry out research on fast random access technology.The research of this thesis starts from three aspects:fast random access channel design,detection algorithm optimization,and simulation platform design.The main work of the thesis is shown as follows:(1)Aiming at the problem of low access efficiency and long access delay in traditional random access schemes due to multiple information exchanges,this thesis analyzes the processing procedure and timing of the fast random access scheme proposed by 3GPP for terrestrial scenarios model,and discussed the feasibility of applying the scheme to GEO satellite scenarios to achieve high-efficiency and low-latency access.(2)Considering that the fast random access signal contains two parts:the preamble and the payload,which leads to the problem that the traditional random access channel is not applicable.Combined with the large beam coverage and the single antenna port system characteristics,this thesis presents a design scheme of fast random access channel.The scheme can reduce the access times by combining the leading and data loads,save the cost of physical resources and guarantee the better access performance.(3)Aiming at the problem of error propagation existing in traditional multi-user detection algorithm,the multi-decision OSIC(MD-OSIC)algorithm is proposed in the thesis.Firstly,the algorithm calculates the SINR of all users to be detected through the equivalent channel coefficients and the MMSE matrix,and optimizes the user selection strategy by sorting.Secondly,the symbols located in the unreliable area after MMSE linear detection are judged multiple times to improve detection performance.(4)The msgA signal transmission and detection scheme suitable for this system is designed in this thesis,and the link-level simulation platform is built based on MATLAB to simulate and verify the fast random access performance.In addition,this thesis evaluates the missed detection and false alarm probability of msgA preamble and the bit error rate performance of msgA payload,the simulation results verify the feasibility of the fast random access channel design scheme proposed in this thesis in satellite scenarios.Finally,by comparing the simulation results of MMSE-SIC and MD-OSIC detection performance,it is verified that MD-OSIC algorithm can effectively reduce the impact of error propagation on the bit error rate performance of msgA payload. |
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