低信噪比大动态下的同步技术研究

发布时间：2018-09-18 20:31

【摘要】：面对深空探测复杂恶劣的通信环境,如何在低信噪比、大动态的恶劣通信条件下实现信号同步是进行深空通信必须面对的难题。低信噪比下易发的通信中断情况导致每次通信链路重建都需重新进行同步、多个未知解调参数估计等信号接收处理,但在低信噪比下很难实现快速解调处理。而大动态的运动状态又使得同步误差参数在短时间内变化剧烈,更难于估计。可以说这两个通信条件对同步技术都有苛刻的要求,而二者兼具的通信环境、相悖的作用效果使得同步技术的实现更加困难。高效编码方式的提出为改善同步系统在低信噪比环境中的工作性能提供了可能,基于译码辅助的同步技术是同步技术未来的发展方向。本文以深空探测为应用背景,以深空通信中火星着陆过程为具体应用实例,选择译码辅助的同步技术作为基本实现方式,针对低信噪比大动态下的接收信号同步过程进行研究。论文通过分析低信噪比和大动态应用需求及其对接收信号的影响,将同步过程分为载波同步、定时同步、帧同步三个部分分别研究。在载波同步部分,为实现大动态同步范围,本文将载波同步分成了粗同步和细同步两个部分。针对粗同步阶段信噪比低、动态范围大的特点,本文提出了一种改进的频域移位平均周期图法,并设计了二次估计过程,实现了预设条件下的载波粗同步;在细同步阶段,本文采用译码辅助的科斯塔斯环法,实现了低信噪比情况下的载波细同步。在定时同步部分,为实现全采样周期的定时同步范围,本文将分区搜索粗定时和迭代定时同步相结合的定时同步方案,首先利用分区搜索的思想将定时偏差缩小至半个符号周期范围内,再利用译码辅助迭代定时同步算法对剩余定时偏差进行细估计。在帧同步部分,本文列举了两种码辅助帧同步算法,并通过仿真和计算对二者的同步性能进行了对比,在兼顾算法性能和实现复杂度基础上,最终选择硬判决帧同步算法作为帧同步部分的实现算法。经过仿真,各部分算法均能达到预期指标,实现在比特信噪比不低于2dB的情况下,系统误码率性能不高于103?。
[Abstract]:In the face of the complex communication environment of deep space exploration, how to realize signal synchronization under the bad communication conditions of low signal-to-noise ratio and large dynamic is a difficult problem for deep space communication. Under the condition of low signal-to-noise ratio (SNR), it is difficult to realize fast demodulation processing because of the need to resynchronize each communication link reconstruction, and to estimate several unknown demodulation parameters, but it is difficult to realize fast demodulation processing under low SNR. However, the large dynamic state of motion makes the synchronization error parameters change sharply in a short time, and it is more difficult to estimate. It can be said that these two communication conditions have harsh requirements for synchronization technology, and the contradictory effect of both communication environments makes the implementation of synchronization technology more difficult. It is possible to improve the performance of synchronization system in low SNR environment by using efficient coding method. The synchronization technology based on decoding is the development direction of synchronization technology in the future. In this paper, taking deep space exploration as the application background, taking the Mars landing process in deep space communication as the concrete application example, choosing the decoding assisted synchronization technology as the basic realization mode, the synchronization process of the received signal under the low SNR and large dynamic condition is studied. By analyzing the requirements of low signal-to-noise ratio (SNR), large dynamic applications and their influence on received signals, the synchronization process is divided into three parts: carrier synchronization, timing synchronization and frame synchronization. In the carrier synchronization part, in order to realize the large dynamic synchronization range, the carrier synchronization is divided into two parts: coarse synchronization and fine synchronization. Aiming at the characteristics of low SNR and large dynamic range in coarse synchronization stage, an improved shift average period diagram method in frequency domain is proposed, and a quadratic estimation process is designed to realize carrier coarse synchronization under preset conditions. In this paper, the carrier fine synchronization with low signal-to-noise ratio (SNR) is realized by using the decode-assisted Kostas loop method. In the part of timing synchronization, in order to realize the range of timing synchronization in the whole sampling period, this paper combines the coarse and iterative timing synchronization scheme. First, the timing deviation is reduced to half a symbol period by using the idea of partition search, and then the residual timing deviation is carefully estimated by decoding assisted iterative timing synchronization algorithm. In the part of frame synchronization, this paper enumerates two kinds of code-aided frame synchronization algorithms, and compares their synchronization performance by simulation and calculation. Finally, the hard decision frame synchronization algorithm is chosen as the realization algorithm of frame synchronization. The simulation results show that each part of the algorithm can reach the expected target, and the BER performance of the system is not higher than 103U when the bit SNR is not lower than 2dB.
【学位授予单位】：中国科学院国家空间科学中心
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN919.34

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