Journal of the Korea Institute of Information and Communication Engineering (한국정보통신학회논문지)

The Korea Institute of Information and Commucation Engineering (한국정보통신학회)
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Digital Predistortion for Closely Spaced Dual-Band Signals

근접한 이중대역 신호에 대한 디지털 전치왜곡 기법

  • Jeong, Eui-Rim (Department of Information and Communication Engineering, Hanbat National University) ;
  • Oh, Joo-Hyun (Research Center of Communication and Electronic Warfare, LIG Nex1) ;
  • Kim, Do-Kyoung (Research Center of Communication and Electronic Warfare, LIG Nex1)
  • Received : 2018.10.25
  • Accepted : 2018.11.05
  • Published : 2018.12.31
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Abstract

A new digital pre-distortion (DPD) technique for closely spaced dual-band signals is proposed. In the system under consideration, dual-band signals are amplified by a single broadband power amplifier (PA) at a transmitter. The PA output is distorted by cross-modulation between the two bands as well as their own inter-modulation distortion. Especially, if the two bands are placed in close proximity to each other, their spectral regrowths due to in-band intermodulation overlap with each other, which degrades DPD performance. To solve this problem, we propose a new DPD technique where the dual-band PA characteristics are estimated first, and then the DPD parameters are obtained from the estimated PA characteristics. By finding the DPD parameters through two steps, pre-distortion can perform well for the closely-spaced dual band signals. The proposed technique is verified through computer simulation. Simulation result shows that the proposed method performs better than the conventional method for closely-spaced dual band signals.

근접한 이중대역 신호에 대한 새로운 디지털 전치왜곡 기법을 제안한다. 본 논문에서 고려하는 시스템은 이중대역 신호를 한 개의 전력증폭기로 증폭하는 송신기이다. 이 경우 전력증폭기 출력신호는 두 대역 신호의 교차변조 및 상호변조에 의해 왜곡이 발생한다. 특히 두 대역이 가까울 때에는 각 대역에서 상호변조에 의해 발행한 스펙트럼이 서로 겹칠 수 있고 이는 전치왜곡 성능을 저하시킨다. 이러한 문제를 해결하기 위해서 제안하는 기법은 먼저 전력증폭기 특성을 추정하고 이렇게 추정한 전력증폭기 특성을 바탕으로 전치왜곡 계수를 추출한다. 이러한 두 단계를 통해 전치왜곡 계수를 구하면 근접한 이중대역 신호에 대해서도 서로 간섭 없이 전치왜곡이 동작할 수 있다. 제안하는 기법은 컴퓨터 모의실험을 통해 검증하는데, 모의실험 결과에 따르면 제안하는 기법이 기존의 이중대역 전치왜곡 방법보다 우수한 성능을 보인다.

Keywords

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Fig. 1 architecture of proposed DPD for closely spaced dual-band signals

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Fig. 2 DPD coefficient extraction from identified PA characteristics

HOJBC0_2018_v22n12_1684_f0003.png 이미지

Fig. 3 Memory PA model for simulation

HOJBC0_2018_v22n12_1684_f0004.png 이미지

Fig. 4 Spectrums of feedback signal and identified PA output for Band1(up) and Band2(down).

HOJBC0_2018_v22n12_1684_f0005.png 이미지

Fig. 5 PA output spectrum after applying DPD.

Table. 1 Summary of recursive least squares for PA identification

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Table. 2 Improvement of spectral regrowth

HOJBC0_2018_v22n12_1684_t0002.png 이미지

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