Research On Random Access Technology Of 5G Low Orbit Satellite Communication System

As satellite communication technology advances rapidly,satellite communication system has become an important part of the integrated network of heaven and earth.LEO communication satellite has been widely used because of its advantages of low transmission loss and short communication delay.Using terrestrial 5G technology to propel the integrated development of terrestrial 5G and satellite communications will greatly accelerate the establishment of an air-space-earth integrated network system.As the first step of establishing connection between user and satellite,random access is an important link of establishing uplink between user and satellite.Therefore,the research on random access technology of satellite ground integrated communication system is essential.Based on 5g LEO satellite communication system,this paper studies the 2-step random access technology,and designs and implements the scheme on FPGA.The work of this paper mainly includes the following aspects:(1)Aiming at the problem of uplink random access in the low-orbit satellite and terrestrial 5G fusion communication network,taking the large coverage of LEO satellite beams as the entry point,and aiming to achieve low-latency and high-efficiency uplink access,the existing 2-step random access The processing flow and timing model of the access are analyzed,and the feasibility of using the 2-step random access scheme for 5G loworbit satellites is discussed.(2)Based on the characteristics of 2-step random access signal structure and the beam coverage of low-orbit satellites,the design principle of MsgA PRACH random access pilot sequence,the allocation of MsgA PUSCH data load resources,the mapping relationship between MsgA PRACH pilot sequence and MSgA PUSCH data load are analyzed.A 2step random access scheme for 5G low-orbit satellites is proposed.(3)A system model of multi-user uplink access in 5G low-orbit satellite communication system is established,and the data transmission and detection scheme of this system is designed based on SCMA nonorthogonal multiple access technology.The uplink-level simulation platform of the 5G low-orbit satellite communication system is established by the simulation tool.The performance of the MsgA PRACH random access preamble signal and the MsgA PUSCH data payload is evaluated to verify the feasibility of the proposed scheme in the 5G low-orbit satellite communication system.(4)The 2-step random access scheme is designed and implemented on Vivado,which is the development platform of the field bus using Verilog language.The hardware implementation ideas and detailed design scheme of the main modules are given.Simulator is used to simulate the function and time sequence,which verifies the correctness of the function simulation implemented by the field bus.In addition,for the prolongation of SCMA receiver iteration processing,a design scheme of SCMA receiver with parallel node updates is presented,which can effectively reduce the processing delay.