Research On Key Techniques Of VCM/ACM In Satellite Data Transmission Link

Variable coding modulation(VCM)and adaptive coding modulation(ACM)have become one of the key technologies for data transmission system to improve data transmission capacity effectively,which can support the satellite payload data transmission system to cope with the increasing mission requirements.For the data link scene of the transit ground station of the near-earth satellite,the traditional data transmission technology only adopts a fixed code modulation mode to ensure the communication at furthest satellite-earth distance.In the process of the satellite passing through the ground station,the distance between the satellite and the earth will gradually shorten and the link margin will also increase,resulting in a large waste of link resources.According to the link channel variation predicted,VCM can design the appropriate changing process of coding and modulation in advance to match the communication distance change during the satellite transit period,reduce the waste of link resource and improve the link data throughput effectively.ACM is actually a VCM with closed-loop control at both ends of the transceiver.Real-time link signal-to-noise ratio estimation is carried out at the receiving end,and the optimal coding and modulation mode is fed back to the sending end through the return channel.It can adapt to the random change of the channel,and is especially suitable for Ka band communication in rainfall environment,and can further improve link data throughput.Aiming at the application of VCM/ACM technology in the payload data transmission system of low-earth orbit satellites,a mode design method of variable coding modulation is proposed in this thesis by analyzing the bit error rate performance of various modes in DVB-S2 application specification and combining the channel time-varying characteristics of satellite-ground data link.In addition,the design of the rain-resistant adaptive coding modulation system is completed.Under the condition of maintaining the same channel bandwidth and transmitting power,the data throughput of data transmission link is improved than that of traditional data transmission technology.Then the key technologies of the integrated demodulator at the CCSDS-VCM receiver are broken through,and parts of the joint test at the CCSDS-VCM transmitter and receiver are realized.The specific research work completed is as follows:1.The system simulation of the transmitter end of CCSDS-VCM was carried out,and the overall structure of the transmission system and the FPGA design and test verification of the grouping module of the sending terminal principle prototype are completed,so as to realize the data transmission of four variable coding modulation modes and obtain accurate constellation map and signal spectrum.2.For low earth orbit satellite data transmission system,to maximize the data throughput in one satellite transit time as the goal,mode design method of variable coding modulation and rainfall attenuation adaptive coding modulation are presented respectively.According to the link budget and prediction of rainfall in rain environment,accurate data transmission link models are built,and the mode switch algorithms are presented.This mode design method can satisfy the application requirement of the link availability,reliability,and maximization of the data transmission throughput.3.In view of as low as-2 dB SNR condition at receiver input signal,a kind of frame synchronization method of optimal interval of correlation detection combined with double threshold peak detection and PLSC decoding controled by the state machine is presented.This method increases the correlation of the differential data of received signal,and can capture the next frame header quickly according the waiting time after solving the frame header information,as well as be suitable for the low SNR environment and variable coding modulation of data transmission system.4.Three synchronization algorithms of synthetical demodulation of CCSDS-VCM receiver are studied,including bit synchronization,framesynchronization and carrier synchronization.An integrated algorithm of bit synchronization,frame synchronization and carrier synchronization is presented.The architecture design,system simulation and hardware module design of each synchronization system at the receiver are completed.The research work of this thesis provides technical support for the application of variable coding modulation and adaptive coding modulation technology in the near-earth satellite data transmission system.VCM/ACM technology can further improve the throughput of link transmission in both x-band and ka-band.In particular,ACM technology can deal with the impact of link rain attenuation effectively.It can help broadband Ka band technology to realize high-speed data transmission for near-earth satellite.