The Journal of Korean Institute of Electromagnetic Engineering and Science (한국전자파학회논문지)

The Korean Institute of Electromagnetic Engineering and Science (한국전자파학회)
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OFDM Communication System Based on the IMD Reduction Method

IMD 저감 방식을 기반으로 하는 OFDM 통신 시스템

  • Ryu, Heung-Gyoon (School of Electrical and Computer Engineering, Chungbuk National University)
  • 유흥균 (충북대학교 전기전자컴퓨터공학부)
  • Published : 2007.10.31
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Abstract

OFDM system has very good high spectral efficiency and the robustness to the frequency-selective fading. Because of the high PAPR, OFDM signals can be distorted in nonlinear HPA(High Power Amplifier). So, to overcome the nonlinear distortion, it is very important to reduce the IMD value. With respect to the BER performance, IMD reduction method is better than the PAPR reduction method. However, IMD reduction method has much more system complexity because of the additional FFT processor in transmitter. In this paper, we study the OFDM communication system based on the IMD reduction method using SPW method. A new IMD reduction method is proposed to reduce the computational complexity. SPW method is to divide the input OFDM data into several sub-blocks and to multiply phase weighting values with each sub-blocks for the reduction of PAPR or IMD. Unlike the conventional method, the system size and computational complexity can be reduced.

Orthogonal Frequency Division Multiplexing(OFDM) 시스템은 주파수 선택적 페이딩에 강하고 높은 대역 효율을 갖는 통신 시스템이다. OFDM 신호는 높은 PAPR로 인하여 비선형 증폭기에서 왜곡이 생긴다. 그래서 비선형 왜곡 성분인 IMD(Inter-Modulation Distortion)를 저감하는 것이 중요하다. IMD 저감 방식은 비선형 왜곡에 대하여 PAPR(Peak-To-Average Power Ratio) 저감 방식보다 BER 성능을 좋게할 수 있지만, 송신기에 FFT(Fast Fourier Transform)가 추가되어 시스템 복잡도를 증가시킨다. 본 논문에서는 IMD 저감 방식을 기반으로 하는 OFDM 통신 시스템의 BER 분석과 복잡도를 저감하기 위한 연구를 하였다. SPW(Sub-Block Phase Weighting)을 적용한 IMD 저감 방식에서 계산량 감소를 위한 새로운 방식을 제안하고 기존의 방식과 계산 복잡도를 비교한다. SPW 방식은 입력 데이터를 여러 개의 서브 블록으로 나누고 위상 회전 벡터를 곱해줌으로써 PAPR을 감소하거나 IMD를 저감한다. 제안된 방식은 BER 성능 면에서 기존 방식과 비슷하지만, PAPR처럼 시간 영역에서 IMD의 전력량을 계산하므로 시스템의 계산 복잡도와 시스템 크기를 줄일 수 있는 장점이 있다.

Keywords

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