OFDM 통신 시스템을 위한 경량 SNR 추정 알고리즘
A Low-complexity Time-domain SNR Estimation Algorithm for OFDM Communication Systems
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초록
직교 주파수 분할 멀티플렉싱 (Orthogonal frequency division multiplexing: OFDM)은 고속의 송신 신호를 다수의 직교하는 협대역 부 반송파로 변조시켜 다중화 하는 기술로, 개별 OFDM 심볼이 받는 주파수 선택적 페이딩에 강한 특성을 가지고 있어서 4G 및 5G 이동통신과 같은 광대역 디지털 통신 시스템과 무선 근거리 통신망 (WLAN) 등에서 필수적으로 사용되고 있다. 그러나 모든 채널 환경에 적합한 단일화 된 심볼검출기 및 채널추정 등은 실제 사용에 어려움이 있어서 통신 시스템의 각 블록에 SNR에 기반을 둔 알고리즘들이 사용되고 있다. 따라서 SNR 추정 정확도가 중요한 OFDM무선 통신 시스템의 주요한 성능요소가 되었다. 본 논문에서는 OFDM 통신 시스템 중 대표적인 IEEE802.11규격을 기준으로 시간영역 기반 SNR 추정을 간략화한 방법을 제안하였다. 제안된 방법은 시간 영역 SNR 추정을 기반으로 근사화 되었으며, 제곱연산이나 나눗셈 연산이 없이 간단히 구현 가능한 구조로 제시되고, 모사실험을 통해 그 성능을 보여주었다. 근사화가 없는 시간영역 SNR 추정과 비교하였을 때, AWGN과 채널모델 D의 주파수 페이딩 채널 환경에서 각각 약 0.5dB와 0.2dB의 낮고 일정한 오차를 보이고 있으며, 통신 시스템의 성능을 좌우하는 낮은 SNR 영역에서 기존의 근사화 방법 대비 제안한 방법이 효과적으로 사용될 수 있음을 보여주었다.
Abstract
Orthogonal Frequency Division Multiplexing technology is a multi-carrier modulation technique that uses multiple narrowband subcarriers for high speed data transmission, wherein each subcarrier carrying corresponding data bit, among which are orthogonal to each other. Because of its strong resistance to frequency selective fading, it is indispensable for broadband digital communication systems such as 4G and 5G, and wireless local area networks. However, since the unified symbol detector and channel estimation suitable for all channel environments are difficult in practical cases, algorithms using estimated SNR are used in each block of the communication system. Therefore, SNR estimation accuracy has become a major performance factor in an important OFDM wireless communication system. In this paper, we propose a simplified method of time-domain based SNR estimation based on the representative IEEE802.11 standard among OFDM communication systems. The proposed method is approximated based on time-domain SNR estimation, presented as a simple implementation without square or division, and its performance is shown by simulation. Compared with the time-domain SNR estimation without approximation, it shows low and constant errors of about 0.5 dB and 0.2 dB in the frequency fading channel environment of AWGN and channel model D, respectively. And, it is shown that the proposed method can be effectively used compared to the existing approximation method in the low SNR region that influences the performance of the communication system.
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