| Satellite communication can make up for the shortcomings of existing networks in application coverage,which is the main direction of future research.The integrated space-space network with lower latency,higher reliability and greater connection will become the main foundation of future networks.Compared with traditional terrestrial communication,satellite communication has more challenges.Different orbital heights correspond to different dynamic Doppler frequency shifts.LEO satellites have lower orbits,short overtopping times,and Doppler which changes fast.In addition,due to the wide coverage of each beam of the satellite system,users in the corresponding beam will have different round-trip time differences,which has become one of the main factors limiting the performance of satellite communication.The above two problems have a very serious impact on the synchronization process.The effect of the Doppler frequency offset has a serious impact on the detection of the synchronization sequence.At the same time,the users in the beam also have their own residual frequency offset,which may cause interference problems between the uplink synchronization data.The large round-trip time difference causes the access sequence of the terrestrial structure can not cover the satellite coverage.Therefore,it is necessary to redesign the access sequence structure and propose a concise and fast detection algorithm.In response to the above problems,the main work and innovations of this paper are as follows:1.Because of the particularity of the low-orbit satellite communication scene,this paper divides the Doppler frequency shift into a common offset and a differential offset between users.Combined with the Doppler geometric model and the classical laws of mathematical physics,the common Doppler frequency shift of low-orbit satellites is analyzed and discussed.Combined with the pre-compensation method to complete the differential frequency offset compensation of the user’s uplink synchronization,a frequency offset estimation method combined with fractional Fourier transform is proposed,which has low computational complexity and is suitable for limited functions satellite end point.2.Studying the uplink synchronization process of satellite communication and combining the channel characteristics of the satellite communication system,the existing preamble sequence structure is analyzed and discussed.A design scheme is given by analyzing and discussing the advantages and disadvantages of various methods.Finally,the conjugate characteristics and long sequence characteristics are used to complete the sequence design.In order to reduce the reception complexity,an uplink synchronization detection method based on fractional Fourier transform is proposed to ensure the synchronization performance of the system. |
PDF Full Text Request