Channel Noise Estimation for MIMO-OFDM using Mask Function

방재권,현광민 한국지식정보기술학회 2015 한국지식정보기술학회 논문지 Vol.10 No.4

In wireless communication systems, the estimated noise variance is a significant parameter for SNR (Signal to Noise Ratio) estimation, estimation of channel impulse response, and MMSE (Minimum Mean Square Error) calculation. More accurately estimated noise variance provides better signal detection performance of systems. However the conventional noise estimation methods result in degradation of performance for the estimation when the noise power becomes higher than threshold value, especially with MMSE filter. In this paper, for more accurate noise estimation, a new noise estimation scheme is proposed by using mask function for FFT (Fast Fourier Transform) block in frequency domain at receiver. The mask function can reduce magnitude of side-lobes of channel response in time domain then it can estimate more accurate reference symbols. Through estimated reference symbols for channel estimation step, more accurate noise component can be estimated so we can obtain better performance of noise variance estimation. The accurately estimated noise variance value is used to calculate weighting matrix for MMSE filter. To prove that the systems using a new noise estimation scheme have better BER performance, we could analyze under several channel variations and compare BER performances for MIMO-OFDM (Multiple Input Multiple Output – Orthogonal Frequency Division Multiplexing) systems. BER performances using the proposed scheme are better than those using conventional noise estimation scheme under all channel situations.

Modified MMSE Estimator based on Non-Linearly Spaced Pilots for OFDM Systems

Khan, Latif Ullah The Institute of Electronics and Information Engin 2014 IEIE Transactions on Smart Processing & Computing Vol.3 No.1

This paper proposes a Modified Minimum Mean Square Error (M-MMSE) estimator for an Orthogonal Frequency Division Multiplexing (OFDM) System over fast fading Rayleigh channel. The proposed M-MMSE estimator considered the effects of the efficient placement of pilots based on the channel energy distribution. The pilot symbols were placed in a non-linear manner according to the density of the channel energy. Comparative analysis of the MMSE estimator for a comb-type pilot arrangement and M-MMSE estimator for the proposed pilot insertion scheme revealed significant performance improvement of the M-MMSE estimator over the MMSE estimator.

고속 Binary CDMA 시스템에서 MMSE-DFE에 대한 SNR 추정 오차의 영향

강성진 ( Sung Jin Kang ) 한국항행학회 2011 韓國航行學會論文誌 Vol.15 No.5

본 논문에서는 고속 Binary CDMA 시스템에서 신호대잡음비의 추정 오차가 MMSE-DFE의 BER 성능에 미치는 영향을 분석하였다. MMSE 등화 알고리즘은 입력신호의 신호대잡음비 값이 필요하기 때문에, 프리엠블의 CAZAC시퀀스로부터 신호대잡음비를 추정해야한다. 그러나 잡음과 ISI가 존재하는 환경에서는 정확한 신호대잡음비 추정이 불가능하므로 추정 오차가 발생하고, 이로 인해 등화기의 성능이 열화된다. 본 논문의 실험 결과는 MMSE-DFE설계시에 SNR 추정 알고리즘의 선택 기준으로 활용될 수 있다. In this paper, we have analyzed the effect of SNR estimation error on the BER performace of MMSE-DFE in high-speed binary CDMA system. Since MMSE equalization algorithm requires the SNR value of input signal, it should be estimated using CAZAC sequence in preamble. However, when AWGN and ISI exist simultaneously, it is impossible to estimate the exact SNR value of input signal and thereby equalizer`s performance may be deteriorated. The simulation results can be used as a guideline for selection of SNR estimation algorithm for MMSE-DFE design.

Music/Voice Separation Based on Kernel Back-Fitting Using Weighted β-Order MMSE Estimation

김형국,김진영 한국전자통신연구원 2016 ETRI Journal Vol.38 No.3

Recent developments in the field of separation of mixed signals into music/voice components have attracted the attention of many researchers. Recently, iterative kernel back-fitting, also known as kernel additive modeling, was proposed to achieve good results for music/voice separation. To obtain minimum mean square error (MMSE) estimates of short-time Fourier transforms of sources, generalized spatial Wiener filtering (GW) is typically used. In this paper, we propose an advanced music/voice separation method that utilizes a generalized weighted β-order MMSE estimation (WbE) based on iterative kernel back-fitting (KBF). In the proposed method, WbE is used for the step of mixed music signal separation, while KBF permits kernel spectrogram model fitting at each iteration. Experimental results show that the proposed method achieves better separation performance than GW and existing Bayesian estimators.

Joint Channel Estimation and Equalization for MIMO-SCFDE Systems over Doubly Selective Channels

Zedong Xie,Xihong Chen,Xiaopeng Liu 한국통신학회 2017 Journal of communications and networks Vol.19 No.6

This paper considers a novel joint channel estimationand equalization (JCEE) algorithm for multiple-input-multipleoutputsingle-carrier frequency-domain-equalization (MIMOSCFDE)system over doubly selective channels for the first time. Given that the doubly selective channels can no longer support theassumption that the channel frequency-domain response remainsinvariant for the duration of one block, most of the channel estimationmethods cannot be applied directly in it. And the lack of theinformation interaction between channel estimation and channelequalization degrades the overall performance. We put forward anoise-eliminated minimum-mean-square-error channel estimation(MMSE-CE) algorithm for the initialization, which is then utilizedfor iterative processing using the ordered successive interferencecancellation (OSIC) technique. Analysis and simulation results validatethe improved performance of the proposed JCEE algorithmfor MIMO-SCFDE systems over doubly selective channels.

Inter-Sector Beamforming with MMSE Receiver in the Downlink of TDD Cellular Systems

Yeom, Jae-Heung,Lee, Yong-Hwan The Korea Institute of Information and Commucation 2008 Journal of communications and networks Vol.10 No.2

The use of beamforming is effective for users in limited power environments. However, when it is applied to the downlink of a cellular system with universal frequency reuse, users near the sector boundary may experience significant interference from more than one sector. The use of a minimum mean square error (MMSE)-type receiver may not sufficiently cancel out the interference unless a sufficient number of receive antennas are used. In this paper, we consider the use of inter-sector beamforming that cooperates with a neighboring sector in the same cell to mitigate this interference problem in time-division duplex (TDD) environments. The proposed scheme can avoid interference from an adjacent sector in the same cell, while enhancing the transmit array gain by using the TDD reciprocity. The performance of the proposed scheme is analyzed in terms of the output signal-to-interference-plus-noise power ratio (SINR) and the output capacity when applied to an MMSE-type receiver. The beamforming mode can be analytically switched between the inter-sector and the single-sector mode based on the long-term channel information. Finally, the effectiveness of the proposed scheme is verified by computer simulation.

Inter-Sector Beamforming with MMSE Receiver in the Downlink of TDD Cellular Systems

J.-H. Yeom,이용환 한국통신학회 2008 Journal of communications and networks Vol.10 No.2

The use of beamforming is effective for users in limited power environments. However, when it is applied to the downlink of a cellular system with universal frequency reuse, users near the sector boundary may experience significant interference from more than one sector. The use of a minimum mean square error (MMSE)-type receiver may not sufficiently cancel out the interference unless a sufficient number of receive antennas are used. In this paper, we consider the use of inter-sector beamforming that cooperates with a neighboring sector in the same cell to mitigate this interference problem in time-division duplex (TDD) environments. The proposed scheme can avoid interference from an adjacent sector in the same cell, while enhancing the transmit array gain by using the TDD reciprocity. The performance of the proposed scheme is analyzed in terms of the output signal-to-interference-plus-noise power ratio (SINR) and the output capacity when applied to an MMSE-type receiver. The beamforming mode can be analytically switched between the inter-sector and the single-sector mode based on the long-term channel information. Finally, the effectiveness of the proposed scheme is verified by computer simulation.

Linear versus Non-linear Interference Cancellation

Buehrer, R.Michael,Nicoloso, Steven P.,Gollamudi, Sridhar The Korean Institute of Communications and Informa 1999 Journal of communications and networks Vol.1 No.2

In this paper we compare linear and non-linear inter-ference cancellation for systems employing code division multi-ple access (CDMA) techniques. Specifically, we examine linear and non-linear parallel interference cancellation(also called multi-stage cancellation) in relationship to other multiuser detection al-gorithms. We show the explicit relationship between parallel inter-ference cancellation and the decorrelator (or direct matrix inver-sion). This comparison gives insight into the performance of paral-lel interference cancellation (PIC) and leads to vetter approaches. We also show that non-linear PIC approaches with explicit chan-nel setimation can provide performance improvement over linear PIC, especially when using soft non-linear symbol estimates. The application of interference cancellation to non-linear modulation techniques is also presented along with a discussion on minimum mean-squared error(MMSE) symbol estimation techniques. These are shown to further improve the performance of parallel cancella-tion.

Hybrid SNR‐Adaptive Multiuser Detectors for SDMA‐OFDM Systems

Uğur Yeşilyurt,Özgür Ertuğ 한국전자통신연구원 2018 ETRI Journal Vol.40 No.2

Multiuser detection (MUD) and channel estimation techniques in space‐division multiple‐access aided orthogonal frequency‐division multiplexing systems recently has received intensive interest in receiver design technologies. The maximum likelihood (ML) MUD that provides optimal performance has the cost of a dramatically increased computational complexity. The minimum mean‐squared error (MMSE) MUD exhibits poor performance, although it achieves lower computational complexity. With almost the same complexity, an MMSE with successive interference cancellation (SIC) scheme achieves a better bit error rate performance than a linear MMSE multiuser detector. In this paper, hybrid ML‐MMSE with SIC adaptive multiuser detection based on the joint channel estimation method is suggested for signal detection. The simulation results show that the proposed method achieves good performance close to the optimal ML performance at low SNR values and a low computational complexity at high SNR values.

빗 형태 패턴을 가지는 OFDM 시스템을 위한 파일럿 심볼 기반 채널 주파수 응답의 추정

김영웅(Youngwoong Kim),김남훈(Namhoon Kim),윤은철(Eunchul Yoon) 한국통신학회 2014 韓國通信學會論文誌 Vol.39 No.6(통신이론)

본 논문은 OFDM 블록에 파일럿 심볼들이 빗 형태의 패턴에 따라 배치된 경우, 가상 부반송파를 가지는 OFDM 시스템의 channel frequency response (CFR)를 추정하는 여러 방식들을 서로 비교한다. 채널 임펄스 응답을 먼저 예측하는 것이 목적인 minimum mean square error (MMSE) 기반의 채널추정 방식과 누설현상의 억제가 목적인 MMSE 기반의 채널추정 방식이 지금까지 비교되지 않았기 때문에, 본 논문에서는 후자 방식과 전자 방식의 mean square error (MSE) 값들의 차이가 양수가 됨을 유도함으로써 전자 방식의 우수성을 논리적으로 증명한다. 아울러 본 논문에서는 파일럿 수의 변화가 MMSE 기반 채널추정 방식과 least-square (LS) 기반채널 추정 방식의 성능에 미치는 영향을 조사한다. 컴퓨터 시뮬레이션을 통해 채널추정 방식들의 성능을 정량적으로 확인한다. The pilot assisted channel frequency response (CFR) estimation schemes for an OFDM-based system with virtual subcarriers are analyzed under the assumption that pilot symbols are located according to a comb-type pattern in the OFDM block. In particular, as the minimum mean square error (MMSE) based scheme aiming to directly predict the channel impulse response and the MMSE based scheme aiming to suppress the leakage have not been clearly compared, by proving that the mean square errors (MSEs) of the latter scheme is always larger than that of the former scheme, this paper shows that the former scheme is superior to the latter scheme. Moreover, the impact of the number of pilots on the performances of the MMSE and least-square based channel estimation schemes are investigated. The performance analyses of the presented schemes are confirmed by computer simulation.