本文選題：編碼調(diào)制系統(tǒng) + 低信噪比�。� 參考：《西安電子科技大學(xué)》2014年碩士論文

【摘要】：對于BICM系統(tǒng)來說,它可以在距離Shannon限很近的信噪比(SNR)區(qū)域工作。但是這個結(jié)論的前提是BICM系統(tǒng)中能達到完全同步,即符號定時和載波同步能完美進行。但是在實際運用中,只有在信噪比較高的區(qū)域才能實現(xiàn)。在低信噪比區(qū),解調(diào)器傳給譯碼器的信息中包含一定數(shù)量的誤差,這就使得BICM系統(tǒng)的譯碼性能差。因此,當(dāng)BICM系統(tǒng)中采取解調(diào)和譯碼分離的方案時,整個系統(tǒng)只能在距離Shannon容量限較遠(yuǎn)的區(qū)域工作。作者結(jié)合中國電子科技集團公司第54研究所的合作項目,在理解BICM(比特交織編碼)系統(tǒng)的基礎(chǔ)上,深入研究了載波同步和符號定時同步的原理,通過解調(diào)器利用譯碼器的反饋信息改善定時和載波相位恢復(fù)的性能,構(gòu)造定時誤差和相位偏移的聯(lián)合解調(diào)譯碼方案,使迭代譯碼能很好地工作在距離Shannon限很近在低信噪比區(qū)域。本文作者主要完成的工作有以下幾個方面：1.構(gòu)造包含同步過程的BICM系統(tǒng)框架,在這基礎(chǔ)上得到了容量限的表達式,并得出仿真結(jié)果。通過與CM系統(tǒng)容量的對比,指出了在調(diào)制星座確定的情況下,格雷映射可以使BICM系統(tǒng)的容量最大化。2.介紹了載波相位同步方法：獨特字輔助下載波相位同步,利用軟信息的最大似然相位估計,利用軟信息計算相位搜索步長的相位迭代以及基于PLL(鎖相環(huán))的載波相位同步。通過仿真結(jié)果的比較,得出聯(lián)合譯碼反饋的最大似然相位估計方法的性能最佳。3.對符號定時同步框架以及各個結(jié)構(gòu)的功能和實現(xiàn)進行說明,然后對于迭代定時誤差檢測介紹了MM定時誤差檢測器,加窗迭代搜索算法；對于非迭代的定時誤差檢測,介紹了Gardner定時檢測器,并分別給出仿真性能圖。在這基礎(chǔ)上,提出通過解調(diào)器利用譯碼器的反饋信息改善定時和載波相位恢復(fù)的性能的聯(lián)合方案,仿真效果說明,低信噪比下,BICM系統(tǒng)中Turbo同步的效果性能很好。
[Abstract]:For the BICM system, it can work in the SNR region which is very close to the Shannon limit. But the premise of this conclusion is that the BICM system can achieve complete synchronization, that is, symbol timing and carrier synchronization can be carried out perfectly. But in practice, it can only be realized in the region with high signal-to-noise ratio (SNR). In the low signal-to-noise ratio region, the demodulator's information to the decoder contains a certain number of errors, which makes the decoding performance of the BICM system poor. Therefore, when the scheme of demodulation and decoding is used in BICM system, the whole system can only work in a region far from the Shannon capacity limit. On the basis of understanding the BICM (bit Interleaved coding) system, the author has studied the principle of carrier synchronization and symbol timing synchronization in combination with the cooperative project of the 54th Research Institute of China Electronic Science and Technology Corporation, and based on the understanding of BICM (bit Interleaved coding) system, By using the feedback information of the decoder to improve the performance of timing and carrier phase recovery, a joint demodulation and decoding scheme with timing error and phase offset is constructed, so that the iterative decoding can work well in the region of low signal-to-noise ratio (SNR) close to the Shannon limit. The main work accomplished by the writer is as follows: 1. The BICM system framework including synchronization process is constructed, and the expression of capacity limit is obtained on this basis, and the simulation results are obtained. By comparing with CM system capacity, it is pointed out that when the modulation constellation is determined, Gray map can maximize the capacity of BICM system. This paper introduces the carrier phase synchronization methods: unique word aided download wave phase synchronization, maximum likelihood phase estimation of soft information, phase iteration of phase search step size calculated by soft information and carrier phase synchronization based on PLL (PLL). By comparing the simulation results, it is concluded that the maximum likelihood phase estimation method with joint decoding feedback has the best performance. The symbol timing synchronization framework and the function and implementation of each structure are described. Then the MM timing error detector and windowed iterative search algorithm are introduced for iterative timing error detection, and for non-iterative timing error detection, non-iterative timing error detection is introduced. The Gardner timing detector is introduced, and the simulation performance diagram is given. On this basis, a joint scheme is proposed to improve the performance of timing and carrier phase recovery by using the feedback information of the decoder. The simulation results show that the performance of Turbo synchronization in low SNR system is very good.
【學(xué)位授予單位】：西安電子科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2014
【分類號】：TN911.3

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