本文關(guān)鍵詞： 功率放大器 數(shù)字預(yù)失真 單比特 頻譜外推 歸一化增益 I/Q非平衡　出處：《中國科學技術(shù)大學》2017年博士論文　論文類型：學位論文

【摘要】：功率放大器(Power Amplifier,PA)是無線通信系統(tǒng)中主要的非線性器件。數(shù)字預(yù)失真(Digital PreDistortion,DPD)以其成本低、編程靈活等優(yōu)點成為目前射頻前端的主流線性化技術(shù)。未來DPD的發(fā)展趨勢主要集中在寬帶應(yīng)用場景下的低復雜度結(jié)構(gòu)及算法研究。模數(shù)轉(zhuǎn)換器(Analog-to-Digital Converter,ADC)是DPD系統(tǒng)反饋回路中功耗較大、成本較高的器件之一。本文圍繞降低ADC量化精度的要求與ADC的采樣速率展開研究,前者能降低系統(tǒng)功耗與成本,以應(yīng)對基站"小型化",后者則能在降低功耗的同時降低反饋信號帶寬,來應(yīng)對"大帶寬"的趨勢。除此之外,本文還會解決DPD系統(tǒng)中存在的諸多關(guān)鍵問題。傳統(tǒng)的DPD系統(tǒng)依賴于帶寬不低于原始信號5倍且量化精度足夠高的反饋信號,使得DPD在面向?qū)拵?yīng)用的時候受到很大限制。本文考慮降低ADC的量化精度降低到極端情況下的1比特,并對此時的DPD算法進行理論推導,證明單比特DPD系統(tǒng)的可行性。同時本文對單比特DPD系統(tǒng)中存在的問題逐一提出了解決方案,包括基于單比特采樣數(shù)據(jù)的頻域時間對齊算法,迭代步長的估計,系統(tǒng)復雜度的分析,并通過實驗測試驗證單比特DPD系統(tǒng)的線性化性能。此外本文在此基礎(chǔ)上提出一種改進的單比特DPD系統(tǒng),即前向建模輔助的單比特DPD參數(shù)提取方法,也被證明能夠有效對寬帶功放進行線性化。在寬帶場景下一方面DPD系統(tǒng)反饋帶寬受限,另一方面?zhèn)鹘y(tǒng)模型精度的提升也很困難。為此本文闡述一種采用頻譜外推思想的方法,在迭代的過程中不斷地用降低采樣速率的反饋數(shù)據(jù)來恢復出真實的功放輸出,從而能夠進一步得到精確的DPD參數(shù)。本文也對頻譜外推算法的數(shù)值穩(wěn)定性進行理論分析,并提出一種提高算法數(shù)值穩(wěn)定性的方法。同時考慮到硬件實現(xiàn)成本,本文為降低算法的計算復雜度設(shè)計出一種分段快速傅里葉變換方法來實現(xiàn)整個算法,極大地提升了計算效率。本文通過理論和仿真詳細分析在基于間接學習結(jié)構(gòu)的DPD系統(tǒng)中,不同歸一化增益對DPD性能的影響。隨后以DPD模塊不改變輸入信號的平均功率這一基本原則,推導出具有明確的物理意義的一步計算最優(yōu)歸一化增益的算法。另外,針對頻率相關(guān)I/Q非平衡對DPD線性化性能的影響,本文提出一種消除反饋回路I/Q非平衡的DPD參數(shù)提取算法,隨后將這種算法擴展到同時存在正交調(diào)制解調(diào)器兩種I/Q非平衡的場景,通過實驗驗證算法的有效性。
[Abstract]:Power Amplifier (PA) is the main nonlinear device in wireless communication system. The advantages of flexible programming have become the mainstream linearization technology of RF front-end at present. In the future, the development trend of DPD is mainly focused on the low complexity structure and algorithm research in wideband application scenarios. Analog-to-Digital conversion (ADC) is the feedback of DPD system. High power consumption in the loop, One of the most expensive devices. This paper focuses on the requirement of reducing the quantization accuracy of ADC and the sampling rate of ADC. The former can reduce the power consumption and cost of the system. To deal with the "miniaturization" of base stations, which can reduce power consumption while reducing the bandwidth of feedback signals to cope with the trend of "large bandwidth". In this paper, many key problems in DPD system will be solved. The traditional DPD system relies on feedback signals whose bandwidth is not less than 5 times of the original signal and the quantization accuracy is high enough. In this paper, the quantization accuracy of ADC is reduced to 1 bit in extreme cases, and the DPD algorithm is theoretically deduced. The feasibility of single bit DPD system is proved. At the same time, a solution to the problems in single bit DPD system is proposed one by one, including the frequency domain time alignment algorithm based on single bit sampling data and the estimation of iterative step size. The complexity of the system is analyzed, and the linearization performance of the single-bit DPD system is verified by experimental tests. On this basis, an improved single-bit DPD system is proposed, which is a single-bit DPD parameter extraction method assisted by forward modeling. It has also been proved that the wideband power amplifier can be linearized effectively. On the one hand, the feedback bandwidth of DPD system is limited, on the other hand, it is very difficult to improve the accuracy of the traditional model. In the process of iteration, feedback data with low sampling rate are used to restore the true output of power amplifier, thus the accurate DPD parameters can be obtained. The numerical stability of extrapolation method is also analyzed theoretically. A method to improve the numerical stability of the algorithm is proposed. Considering the cost of hardware implementation, a piecewise fast Fourier transform method is designed to reduce the computational complexity of the algorithm to realize the whole algorithm. In this paper, the DPD system based on indirect learning structure is analyzed in detail by theory and simulation. The effect of different normalized gain on the performance of DPD. Then, based on the basic principle that DPD module does not change the average power of input signal, an algorithm for calculating the optimal normalized gain in one step with clear physical meaning is derived. In view of the influence of frequency dependent I / Q nonequilibrium on the linearization performance of DPD, this paper proposes a DPD parameter extraction algorithm to eliminate the feedback loop I / Q nonequilibrium, and then extends the algorithm to the scenario where there are two kinds of I / Q nonequilibrium of orthogonal modems at the same time. The validity of the algorithm is verified by experiments.
【學位授予單位】：中國科學技術(shù)大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TN722.75

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