【摘要】：面對(duì)深空探測(cè)復(fù)雜惡劣的通信環(huán)境,如何在低信噪比、大動(dòng)態(tài)的惡劣通信條件下實(shí)現(xiàn)信號(hào)同步是進(jìn)行深空通信必須面對(duì)的難題。低信噪比下易發(fā)的通信中斷情況導(dǎo)致每次通信鏈路重建都需重新進(jìn)行同步、多個(gè)未知解調(diào)參數(shù)估計(jì)等信號(hào)接收處理,但在低信噪比下很難實(shí)現(xiàn)快速解調(diào)處理。而大動(dòng)態(tài)的運(yùn)動(dòng)狀態(tài)又使得同步誤差參數(shù)在短時(shí)間內(nèi)變化劇烈,更難于估計(jì)。可以說這兩個(gè)通信條件對(duì)同步技術(shù)都有苛刻的要求,而二者兼具的通信環(huán)境、相悖的作用效果使得同步技術(shù)的實(shí)現(xiàn)更加困難。高效編碼方式的提出為改善同步系統(tǒng)在低信噪比環(huán)境中的工作性能提供了可能,基于譯碼輔助的同步技術(shù)是同步技術(shù)未來的發(fā)展方向。本文以深空探測(cè)為應(yīng)用背景,以深空通信中火星著陸過程為具體應(yīng)用實(shí)例,選擇譯碼輔助的同步技術(shù)作為基本實(shí)現(xiàn)方式,針對(duì)低信噪比大動(dòng)態(tài)下的接收信號(hào)同步過程進(jìn)行研究。論文通過分析低信噪比和大動(dòng)態(tài)應(yīng)用需求及其對(duì)接收信號(hào)的影響,將同步過程分為載波同步、定時(shí)同步、幀同步三個(gè)部分分別研究。在載波同步部分,為實(shí)現(xiàn)大動(dòng)態(tài)同步范圍,本文將載波同步分成了粗同步和細(xì)同步兩個(gè)部分。針對(duì)粗同步階段信噪比低、動(dòng)態(tài)范圍大的特點(diǎn),本文提出了一種改進(jìn)的頻域移位平均周期圖法,并設(shè)計(jì)了二次估計(jì)過程,實(shí)現(xiàn)了預(yù)設(shè)條件下的載波粗同步;在細(xì)同步階段,本文采用譯碼輔助的科斯塔斯環(huán)法,實(shí)現(xiàn)了低信噪比情況下的載波細(xì)同步。在定時(shí)同步部分,為實(shí)現(xiàn)全采樣周期的定時(shí)同步范圍,本文將分區(qū)搜索粗定時(shí)和迭代定時(shí)同步相結(jié)合的定時(shí)同步方案,首先利用分區(qū)搜索的思想將定時(shí)偏差縮小至半個(gè)符號(hào)周期范圍內(nèi),再利用譯碼輔助迭代定時(shí)同步算法對(duì)剩余定時(shí)偏差進(jìn)行細(xì)估計(jì)。在幀同步部分,本文列舉了兩種碼輔助幀同步算法,并通過仿真和計(jì)算對(duì)二者的同步性能進(jìn)行了對(duì)比,在兼顧算法性能和實(shí)現(xiàn)復(fù)雜度基礎(chǔ)上,最終選擇硬判決幀同步算法作為幀同步部分的實(shí)現(xiàn)算法。經(jīng)過仿真,各部分算法均能達(dá)到預(yù)期指標(biāo),實(shí)現(xiàn)在比特信噪比不低于2dB的情況下,系統(tǒng)誤碼率性能不高于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.
【學(xué)位授予單位】：中國科學(xué)院國家空間科學(xué)中心
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：TN919.34

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本文編號(hào)：2249028