Research And Simulation Of Deep Space Communication Modulation Technology

Deep space exploration will be an important way for the development and utilization of space resources, space science and technology innovation in 21 th Century.That has become one of the hot in the space activities of all space powers. In 2007,China’s lunar exploration program, moon’s success which it is the first step in the exploration of deep space, marked the beginning of deep space exploration, but also the inevitable requirement for further future deep space exploration. Our great success in2013, "Chang E No. 3" achieved, so that China has become the third country of independent implementation of the lunar soft landing in world, which indicates that China has entered the ranks of the world with a deep space exploration capability.However, with the development of the space exploration technology, deep space exploration mission has been more and more complex, which need to transport a large number of engineering data and image information real-time to ground receiving station.Therefore, it is required that the transmission rate of the satellite data transmission system becomes higher and higher, so that the RF spectrum becomes more and more crowded.In the deep space exploration, the communication system is responsible for the information connection between the ground station and the deep space station, also The normal operation of the communication system, communication link clear, and reliable information is the important guarantee for the normal operation of the whole deep space exploration mission. Characteristics of deep space communication contain long distance,long transmission delay, serious power loss, unstable link and complex environment.That must research deep space communication channel characteristics and modulation technique, channel coding, antenna technology and deep space communication network technologies which suit for deep space communication. Modulation technology is the key step in the digital band pass transmission system, which largely determines the quality of the signal transmission in the communication system. Appropriate and efficient modulation technology can improve the SNR and transmission error rate, also improve the bandwidth efficiency and reduce the interference of adjacent channels, inorder to fully protect the deep space mission. Therefore, it is of great practical significance to research the modulation technology in deep space communication to promote the development of deep space exploration.In deep-space communication system, the characteristic of deep space channel is power limited and bandwidth, also nonlinear, which requires large real-time engineering data and image information collected by the detector before through the channel, that modulation signal waveform keep(quasi) constant envelope characteristics, so that the information received by the ground receiving station is reliable and effective. Therefore,the(quasi) constant envelope characteristic(such as QPSK modulation, IJF-OQPSK modulation, SQORC modulation, FQPSK modulation and so on) is the key to ensure the signal transmission quality in deep space channel. Among them, FQPSK modulation patented by Feher professor as a constant envelope modulation way of high bandwidth efficiency and power efficient, which very suits for development requirements of future deep-space communications and has been CCSDS recommended.Firstly the paper introduces the development of digital modulation technology in deep space communication, and points out the advantage of the quasi constant envelope characteristic. Then it analyzes the complexity of the environment of deep space communication system and considers the effects of sun glint and solar noise on signal transmission, and Rician channel simulation model is established for deep space communication, and the channel model is simulated and verified. Another, the paper analyzes the origin of FQPSK and the characteristics of its modulation technology and have a deeply research on FQPSK modulation and demodulation schemes. Although FQPSK modulation technology have high the band utilization rate, it ensures that compared to QPSK modulation technique which have high power efficiency, FQPSK modulation sacrifice little power efficiency. The results of simulation show that FQPSK modulation is able to use smaller power efficiency to acquire higher bandwidth efficiency than QPSK modulation, and offer high bandwidth efficiency while the system reliability is guaranteed, which suits the development of current and future deep space communication. Finally, the paper introduces the data conversion between Matlab and Quartus II conversion, taking QPSK modulation as an example, introduced modern DSP technology to QPSK modulation system, then the Matlab code is converted into VHDL(Verilog HDL) code and embedded in the Quartus II development environment. What not only shorten the running cycle, but also greatly improves the flexibility and generality of software simulation and hardware design.