高效實現應用於無線通訊之高線性度發射機

Efficient Implementation of Highly Linear Transmitters for Wireless Communication Applications

林書辰(Shu-Chen Lin)

指導教授 ： 陳昭宏

國立臺灣大學/工學院/工程科學及海洋工程學研究所/博士(2021年)

https://doi.org/10.6342/NTU202104196

摘要

在無線傳輸系統中，效率一直是系統設計考量中最重要的因素之一，而在其中所佔功耗最大的功率放大器就成為了整個系統中最關鍵的原件。隨著高速傳輸的需求日益上升，新型的傳輸標準定義了更高的傳輸頻寬、更嚴峻的線性度要求及更高的峰均功率比，因而增加了無線傳輸機的設計難度。為了設計符合新型傳輸標準的傳輸機，本論文採用了擁有高效率與高線性度之特性的脈衝寬度調變之極座標架構。本論文的目標為針對數位前端以及射頻前端進行效率的優化，使提出的脈衝寬度調變之極座標架構能滿足第五代行動通訊之需求。
首先，本論文針對脈衝寬度調變之極座標架構的線性度設計了一寬頻功率放大器。藉由模擬以及量測，可成功驗證寬帶功率放大器可有效降低脈衝寬度調變之極座標系統在非線性放大時所遭受之失真。
接著，針對脈衝寬度調變的演算法，本論文進行了探討以及分析。舊有的脈衝寬度調變計算會使輸出訊號擁有抖動，此等抖動會增加切換功率放大器之非理想性，因而遭受更多的非線性放大。為了減緩此現象，本論文提出了新的脈衝寬度調變演算法，可有效的提升傅立葉級數在頻域的收斂性，從而抑制訊號在時域的抖動。利用新型的演算法，脈衝寬度調變極座標收發機可在沒有任何線性提升技術下通過嚴峻的20-MHz第五代行動通訊標準之基地台線性度要求。
接著，本論文針對內插法提出新的演算法。在新提出的演算法中，能在低複雜度的前提下擁有良好的頻率響應，並且能支援大多數無線通訊中所適用的頻寬。經由量測結果，它能適用於相當低的過取樣率，並在內插過程中有效抑制失真。不僅如此，本論文利用提出的內插法實作出了實時的脈衝寬度調變極座標系統，並能有效減少實作時硬體資源之使用，在數位前端達到高效之目標。
最後，本論文之研究將有助於開發實時脈衝寬度調變極座標架構的實現，並且能在提升效率的同時達到良好的線性度。

關鍵字

功率放大器 ； 極座標發射機 ； 數位預失真校正技術 ； 數位脈寬調變技術 ； 濾波器 ； 內插法

並列摘要

Efficiency has always been one of the most important design considerations when designing wireless communication systems. Hence, the power amplifier (PA) has always been the key factor since it is the most power consuming component in the whole system. With the ever-increasing need of higher data-rate transmission, wider bandwidth, higher linearity and higher peak-to-average power ratio are required for modern communication standards. Such requirements would increase the design complexity of the wireless transceiver. In order to implement a wireless transceiver for modern standards, the pulse-modulated polar transmitter (PMPT) architecture is adopted in this dissertation because of its high efficiency and good linearity. The objective of this dissertation is to improve the efficiency in both digital front-end (DFE) and radio front-end (RFE) so that the proposed PMPT can achieve the requirements of the 5G NR standard.
First, a wideband PA is designed for the linearity improvement of the PMPT. It is verified through simulation and measurement that the wideband design of PA can effectively reduce the distortion of PMPTs during non-linear amplification.
Second, detailed analysis and discussion are carried out in this dissertation. The conventional pulse-width modulation (PWM) scheme would generate aliasing of the desired output signal which increases the non-idealities when switching the non-linear PA. Accordingly, it would suffer from more distortion. In order to reduce the phenomenon, a new PWM method is proposed in this dissertation which can increase the frequency domain convergence of the Fourier series of pulse-modulated signals. As a result, the ripples in the time domain can be suppressed significantly. The proposed PMPT system using the new PWM scheme can achieve the strict 20-MHz linearity requirement of 5G base-stations.
Third, a new interpolation algorithm is proposed in this dissertation. The proposed method can be implemented efficiently and simultaneously achieve great frequency response. The measurement results show that the proposed method is applicable for low over-sampling ratio (OSR) and suppress the distortion during interpolation. Furthermore, a real-time PMPT system is demonstrated with the use of the proposed interpolation method. It is shown that the new method can effectively reduce the resource utilization and decrease the cost in the DFE.
Finally, this work will contribute to the development of real time PMPT systems, which can achieve high efficiency and good linearity concurrently.

並列關鍵字

power amplifiers ； polar transmitters ； digital pre-distortion correction ； digital pulse-width modulation (DPWM) ； filter ； interpolation

參考文獻

[1] Base Station (BS) radio transmission and reception, 3GPP TS 38.104, The 3rd Generation Partnership Project Tech. Specification Group, Valbonne, France, 2020.

[2] Z. Hasan, H. Boostanimehr and V. K. Bhargava, “Green cellular networks: a survey, some research issues and challenges,” IEEE Comm. Surveys Tuts., vol. 13, no. 4, pp. 524-540, Nov. 2011.

[3] W. H. Doherty, “A new high efficiency power amplifier for modulated waves,” Proc. IRE, vol. 24, no. 9, pp. 1163-1182, Nov. 1936.

[4] L. R. Kahn, “Single-sideband transmission by envelope elimination and restoration,” Porc. IRE, vol. 40, no. 7, pp. 803-806, July 1952.

[5] L. E. Barton, 1960, High-level modulated signal amplifier system, 2961615