Design Of OQPSK Adaptive Transmission System Based On CCSDS Proximity-1

Deep-space channels are complex and changeable,so fixed-rate transmission is difficult to meet the requirements.The adaptive transmission technology effectively addresses the changing characteristics of deep-space channels.By changing the data transmission rate,it is possible to meet the requirements of the bit error rate with little overhead,furthermore,it improves the throughput of the adaptive system and ensure the effectiveness and reliability of the communication system.In order to promote cooperation in deep space exploration of various countries,the CCSDS Proximity-1 standard was proposed by Consultative Committee for Space Data Systems,which meets the short-time,medium-intensity,and short-range proximity space link data transmission.Based on the CCSDS Proximity-1 protocol,this paper uses adaptive transmission technology and combines the characteristics of deep space channels to design an OQPSK adaptive transmission system that meets the requirements of the protocol.The main contributions of the thesis are as follows:This thesis first introduces the CCSDS Proximity-1 protocol,the protocol data transmission unit and the link layered protocol model,later,gives the performance indicators of the designed adaptive transmission system according to the protocol requirements,moreover,designs the corresponding adaptive transmission system according to the requirements of the indicators.The simulation design of the OQPSK modulation and demodulation module is used.Secondly,according to the characteristics of deep space channel attenuation and fast change,corresponding gain detection and automatic gain control modules are designed.The gain detection module realizes multi-threshold detection,which meets different detection requirements of deep space communication interstellar space segment,planet near-field segment,and planetary surface segment.The automatic gain control module uses a high-level detection method to select an appropriate weighting factor,which effectively improves the loop stability and reduces the clock cycle required for stabilization.Then according to the protocol requirements,the adaptive technology module of the transmission system is designed,which mainly includes four key technologies such as channel modeling,signal-to-noise ratio estimation,code rate switching,and automatic retransmission.Deep space channel modeling simulates various attenuation factors of the deep space channel to obtain the attenuated IF signal.The signal-to-noise ratio is estimated using feedback SNV＿DF estimation and current channel quality is evaluated.The code rate switching is estimated based on the signal-to-noise ratio.Value and the current system’s required bit error rate,the system data rate can be adaptively adjusted by stepwise hopping;automatic retransmission is used to correct the bit damage caused by the burst condition by using a back-off N frame method.Finally,a hardware closed-loop test platform is built,and the integrity of the system is verified by using a combination of software and hardware.It is verified that the designed system meets the aforementioned adaptive system performance indicators.The designed OQPSK adaptive transmission system can successfully evaluate the channel quality,and adaptively adjust the data transmission rate according to the channel quality and bit error rate requirements,verifying the effectiveness and reliability of the designed system.