I/Q 불균형이 있는 MIMO-OFDM 시스템의 BER 성능
BER Performance of MIMO-OFDM Systems with I/Q Imbalances
0
조회
0
다운로드
0
인용
0
참고문헌
키워드
초록
최근 무선통신 기술에서 급증하고 있는 데이터 트래픽 요구량에 대처하기 위해 다중 안테나 기술(Multiple-Input Multiple-Output : MIMO)과 Orthogonal Frequency Division Multiplexing(OFDM) 기술이 결합된 MIMO-OFDM 시스템이 널리 사용되고 있다. 하지만 무선통신 시스템에서 위상 잡음, 크기 감쇄, 전력 증폭기의 비선형성에 의해 국부 발진기(local oscillator)에서 In-phase 성분과 Quadrature 성분의 불균형이 발생한다. 이러한 불균형이 발생하게 되면 송신된 신호가 이상적인 성상도 위치에 수신되지 않아 비트 오류 확률(Bit Error Rate : BER)이 커지게 된다. 본 논문에서는 이러한 I/Q 불균형이 존재하는 상황에서 터보 부호를 적용한 MIMO-OFDM 시스템의 BER 성능을 모의실험 결과를 통해 분석한다. 이를 위해 현재 쓰이고 있는 LTE 환경에서 모의실험을 수행하였다. 또한, 채널 추정 단계에서 잡음 추정을 통해 얻어진 잡음 분산 값으로 MMSE 여파기의 사용 여부를 위한 임계값(threshold)을 결정한다.
Abstract
In next-generation wireless communication systems, high-rate data transmission is required with the multimedia contents. MIMO-OFDM(Multiple Input Multiple Output – Orthogonal Frequency Division Multiplexing) with multi-level modulation and iterative decoding schemes is used to cope with the data traffic problem. But the performance of the communication system is affected by I/Q(In-phase/Quadrature) imbalance with imperfect practical circuits in noisy environment. In order to overcome the I/Q, amplitude and phase, imbalance, estimating noise variance is one of the important methods to enhance the system performance especially with MMSE(Minimum Mean Square Error) scheme. In this paper, we analyzed BER(Bit Error Rate) performances of MIMO-OFDM system with I/Q imbalance where we considered iterative decoding and MMSE scheme. The estimated noise variance value is used to calculate weighting matrix for MMSE filter. For MMSE, according to the amount of I/Q imbalance, it impacts on noise variance estimating performance, and larger the amount of I/Q imbalance leads to worse SNR resulting in performance degradation. If a specific threshold value of noise variance, to decide whether MMSE function is operated or not, is used. we can get better performance with simultaneous operation of iterative decoding and MMSE than without MMSE scheme depending on the amount of I/Q imbalance. The simulation results validate the proposed technique in BER performance.
참고문헌 (15)
- G. L. Stuber., "Broadband MIMO-OFDM wireless communications", Proceeding of IEEE, 92(2), pp.271~294 (2004)
- A. Maltsev., "Comperative analysis of spatial covariance matrix estimation methods in OFDM communication systems", Proceeding of IEEE Symposium on Signal Processing and Information Technology, pp.551~555 (2006)
- 심병효, "MIMO 기술의 진화", 한국통신학회논문지, 38(8), pp.712~723 (2013), 한국통신학회
- J. Hou., "A novel channel estimation algorithm for 3GPP LTE downlink system using joint time-freqeuncy two-dimensional iterative wiener filter", Proceeding of IEEE International Conference on Communication Technology, 11, pp.289~292 (2010)
- A. Goldschmidt., "Capacity limits of MIMO channel", IEEE Journal on Selected Areas in Communications, 21(5), pp.684~702 (2003)
- A. Tarighat., "Compensation schemes and performance analysis of IQ imbalances in OFDM receivers", IEEE Transactions on Signal Processing, 53(8), pp.3257~3268 (2005)
- P. S. Bhanubhai., "Performance of turbo encoder and turbo decoder for LTE", International Journal of Engineering and Innovative Technology, 2(6), pp.125~128 (2012)
- C. Berrou., "Near shannon limit error-correcting coding and decoding : turbo-codes", IEEE Transactions on Communications, 44(10), pp.1261~1271 (1996)
- S. Benedtto., "Design Of parallel concatenated convolutional codes", IEEE Transactions on Communications, 44(5), pp.591~600 (1996)
- 방재권, "Channel Noise Estimation for MIMO-OFDM using Mask Function", 한국지식정보기술학회 논문지, 10(4), pp.485~492 (2015), 한국지식정보기술학회
- S-K. Park., "An alternative expression for the symbol error probability of MPSK in the presence of I", Q unbalance, 2004, pp.52(12), 2079~2081
- C. Liu, "Impacts of I", Q imbalance on QPSK-OFDM-QAM detection, 1998, pp.44(3), 984~989
- S. Boumard, "Novel noise variance and SNR estimation algorithm for wireless MIMO OFDM systems", Proceeding of IEEE Global Communications Conference Exhibition &Industry Forum, 3, pp.1330~1334 (2003)
- R. Fukane., "Role of noise estimation in enhancement of noisy speech signals for hearing aids", Proceeding of IEEE Computational Intelligence and Communication Networks, pp.648~652 (2011)
- V. Savaux., "A joint MMSE channel and noise variance estimation for OFDM", OQAM modulation, 2015, pp.63(11), 4254~4266