Robust Digital Predistortion for LTE/5G Power Amplifiers Utilizing Negative Feedback Iteration

doi:10.12142/ZTECOM.202003008

ZTE Communications ›› 2020, Vol. 18 ›› Issue (3): 49-56.DOI: 10.12142/ZTECOM.202003008

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Robust Digital Predistortion for LTE/5G Power Amplifiers Utilizing Negative Feedback Iteration

LIU Xin¹, CHEN Wenhua¹(), WANG Dehan¹, NING Dongfang²

^1.Tsinghua University, Beijing 100084, China
^2.RHP System Department, ZTE Corporation, Xi’an 710114, China

Received:2019-12-12 Online:2020-09-25 Published:2020-11-03
About author:LIU Xin received the B.S. degree in electronic information science and technology from Xidian University, China in 2017. She is currently pursuing the Ph.D. degree at Department of Electronic Engineering, Tsinghua University, China. Her current research interests include the behavioral modeling and digital predistortion for RF power amplifiers.|CHEN Wenhua (chenwh@tsinghua.edu.cn) received the B.S. degree in microwave engineering from the University of Electronic Science and Technology of China (UESTC) in 2001, and the Ph.D. degree in electronic engineering from Tsinghua University, China in 2006. From 2010 to 2011, he was a postdoctoral fellow with the Intelligent RF Radio Laboratory (iRadio Lab), University of Calgary, Canada. He is currently a professor with the Department of Electronic Engineering, Tsinghua University. His main research interests include power-efficiency enhancement for wireless transmitters, PA predistortion, and smart antennas. He has authored or coauthored over 120 journal and conference papers. Dr. CHEN is as an associate editor for the IEEE Transaction on Microwave Theory and Techniques, and the International Journal of Microwave and Wireless Technology. He was the recipient of the 2015 Outstanding Youth Science Foundation of NSFC, the 2014 URSI Young Scientist Award and the Student Paper Award of the 2010 Asia–Pacific Microwave Conference (APMC).|WANG Dehan received the B.S. degree in integrated circuit design and integration system from the University of Electronic Science and Technology of China (UESTC) in 2016. He is currently pursuing the Ph.D. degree at the Department of Electronic Engineering, Tsinghua University, China. His current research interests include the design of RF power amplifiers and RF integrated circuits.|NING Dongfang received the Ph.D. degree in control theory and control engineering from Northwestern Polytechnical University， China in 2009. He has been a wireless communication system expert of ZTE Corporation with over 10 years’ experience in algorithm architecture and design. His research interest focuses on RF technology.
Supported by:
National Key R&D Program of China(2018YFB1801603);National Science and Technology Major Project(2017ZX03001024);NSFC(61801259);Beijing National Research Center for Information Science and Technology (BNRist)

Abstract

Abstract:

A robust digital predistortion (DPD) technique utilizing negative feedback iteration is introduced for linearizing power amplifiers (PAs) in long term evolution (LTE)/5G systems. Different from the conventional direct learning and indirect learning structure, the proposed DPD suggests a two-step method to identify the predistortion. Firstly, a negative feedback based iteration is used to estimate the optimal DPD signal. Then the corresponding DPD parameters are extracted by forward modeling with the input signal and optimal DPD signal. The iteration can be applied to both single-band and dual-band PAs, which will achieve superior linear performance than the conventional direct learning DPD while having a relatively low computational complexity. The measurement is carried out on a broadband Doherty PA (DPA) with a 200 MHz bandwidth LTE signal at 2.1 GHz, and on a 5G DPA with two 10 MHz LTE signals at 3.4/3.6 GHz for validation in dual-band scenarios.

Key words: 5G, digital predistortion, power amplifiers, negative feedback iteration

LIU Xin, CHEN Wenhua, WANG Dehan, NING Dongfang. Robust Digital Predistortion for LTE/5G Power Amplifiers Utilizing Negative Feedback Iteration[J]. ZTE Communications, 2020, 18(3): 49-56.

Figures/Tables 10

Figure 1 Indirect learning (IDL) and direct learning (DL) architectures.

Figure 2 Structure of the negative feedback iteration based DPD technique in single-band scenario.

Figure 3 Proposed negative feedback loop for iteration.

Figure 4 Structure of the negative feedback iteration based DPD technique in dual?band scenario.

Figure 5 Robust digital predistortion (DPD) test bench.

Figure 6 Measured AM/AM and AM/PM characteristics and PSDs.

Table 1 Measured performance in single band scenario

ACPR/dBc

(±100 MHz)

Figure 7 Iterative convergence trend.

Figure 8 Measured PSDs and AM/AM, AM/PM characteristics at power amplifier (PA)’s output with/without the proposed DPD.

Table 2 Measured performance in dual-band scenario

Scenario	Lower Band		Upper Band
Scenario	Without DPD	Proposed DPD	Without DPD	Proposed DPD
ACPR/dBc (±10 MHz)	-28.28/-28.81	-51.71/-51.45	-30.26/-29.43	-54.04/-53.33

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Robust Digital Predistortion for LTE/5G Power Amplifiers Utilizing Negative Feedback Iteration

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