On Channel Estimation in OFDM Systems (original) (raw)
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Channel estimation for OFDM systems
2011
Orthogonal frequency division multiplexing (OFDM) has attracted a lot of attention because of its high data rate, high spectrum efficiency and robustness against frequency-selective fading channels This paper addresses channel estimation based on time-domain channel statistics. Here the statistical characteristics of AWGN channel is estimated using different methods like LS, MMSE and DFT-CE. The channel autocorrelation matrix and noise variance is obtained by using the noise suppressed channel impulse response. In this paper an efficient and improved channel estimation technique is presented using the MMSE channel estimation method.
Channel estimation for wireless OFDM systems
IEEE Communications Surveys and Tutorials, 2007
A channel estimation technique is developed for an OFDM system wit,li multiple transmit and multiple receive antenna,^. The approach exploits cha,iinel structure in t,he time domain and tlie frequency domain. The method is appropriate for OFDM systems operating in a time varying channel. A multi-inputmulti-output OFDM (MOFDM) sysleni model is defined, followed by a proposed excitation stra,tegy for sufficient ident,ification of tlie channel. The estiniat.ion strategy is shown to be opt.iuia1 within the class of linear MMSE est,imators. Experimental results of the algorit,hm are provided.
Time-Domain Channel Estimation Scheme for OFDM over Fast Fading Channels
Wireless Communications and Mobile Computing, 2022
In high-mobility scenarios, the time variation of mobile radio channels leads to a loss of orthogonality among subcarriers in orthogonal frequency division multiplexing (OFDM) systems, resulting in intercarrier interference (ICI) and performance deterioration. Conventional channel estimation schemes are usually based on pilot tones, which are distributed in each OFDM symbol to estimate the channel variation. Hence, the channel estimator itself suffers from ICI. In this study, a new estimation scheme, which does not suffer from ICI, is proposed to estimate the channel variation within OFDM symbols. The main idea is to zero-pad (ZP) the OFDM symbol in the time domain. Then, in the middle of the ZP interval, an impulse signal is inserted as a pilot sample, which is used to estimate the channel at the pilot signal in the OFDM symbol. Finally, a linear model is used to estimate the channel variation over an OFDM symbol. Additionally, we derive the mean squared error (MSE) of the proposed...
LS and MMSE Estimation with Different Fading Channels for OFDM System
In wireless communication system, the multipath channels introduce frequency selectivity and time varying properties in OFDM symbols which causes Inter-Carrier Interference (ICI) within symbols. For mitigation of such impairments caused by the fading channels, channel estimation is imperative. In present work, two main block-type pilot symbols assisted Least Square (LS) and Minimum Mean Square Error (MMSE) channel estimation techniques for two fading channel models, Rayleigh and Rician are implemented. The bit error rate characteristic performance for both estimators is compared for slow fading channel models with different symbol mapping techniques. The results show that the MMSE estimator has good performance for both Rayleigh and Rician channels as compared to LS estimator. However, MMSE estimator has higher complexity than that of LS.
International Journal of Engineering Research and Technology (IJERT), 2016
https://www.ijert.org/comparative-performance-study-of-ls-and-mmse-channel-estimation-over-time-varying-channel-in-ofdm-system https://www.ijert.org/research/comparative-performance-study-of-ls-and-mmse-channel-estimation-over-time-varying-channel-in-ofdm-system-IJERTV5IS031192.pdf Orthogonal Frequency Division Multiplexing (OFDM) has been recently applied widely in wireless communication systems, due to high data rate, transmission capability with high bandwidth efficiency and its robustness to multipath delay. Channel estimation is an essential problem at the receiver, where the wireless channel is usually frequency selective and time varying. The estimation of channel at pilot subcarriers is based on Least Square (LS), Minimum Mean Square Error (MMSE) while interpolation is done using linear interpolation. For performance evaluation of LS and MMSE channel estimators in OFDM system, the previous works use the block type pilot arrangement, where the pilot tones are transmitted into all subcarriers but at specific period which is suitable for frequency selective fading. In order to keep track of the time-varying channel characteristic, the pilot tones symbols must be placed as the coherence time which causes data reduction. Aiming at this disadvantage, we propose to use the comb-type pilot arrangement where the pilot tones are transmitted at each time to track the rapid variation of the channel. The Clarke' model is used to perform the time varying channel and 16-QAM as the modulation scheme. The performance of the algorithms is measured in terms of Mean Square Error (MSE) and Symbol Error Rate (SER). Simulation results reveal that MMSE estimator provides better performance to track the time-varying channel .
Channel Estimation Algorithms in OFDM, A Review
2013
Main objectives of this paper is to review the work already done related to channel estimation in OFDM (Orthogonal Frequency Division Multiplexing) using QAM (Quadrature Amplitude multiplexing) & PSK (Phase Shift Keying) modulation techniques used in OFDM for wireless communications. To estimate the channels three algorithms are used i.e. LS, LMMSE & Modified MMSE. These three algorithms have basically played key role in channel estimation.
Comparison And Analysis Of Channel Estimation Algorithms In OFDM Systems
International Journal of Scientific & Technology Research, 2013
: - The channel estimation can be performed for analyzing effect of channel on signal by either inserting pilot tones into all of the subcarriers of OFDM symbols with a specific period or inserting pilot tones into each OFDM symbol. The block type pilot channel estimation has been developed under the assumption of slow fading channel. When the data is transmitted at high bit rates, the channel impulse response can extend over many symbol periods, it leads to inter symbol interference. Orthogonal Frequency Division Multiplexing is one of the promising candidate to mitigate the ISI. This work improved various channel performance measures based on the comparison of various channel estimation algorithms and suggest a new technique which provides better performance. Keywords: - OFDM, Block Pilot symbols, Channel estimation, Linear minimum mean square error (LMMSE), Mean square error (MSE), Bit error rate (BER) ———————————————————— I. I NTRODUCTION Orthogonal Frequency Division Multiplex...
A REDUCED COMPLEXITY AND AN EFFICIENT CHANNEL ESTIMATION FOR OFDM
During the last few years, the progress in wireless communication is widely increasing to mitigate the ever increasing demand of higher data rates. OFDM (Orthogonal Frequency Division Multiplexing) techniques using more densely packed carriers, thus achieving higher data rates using similar channels.
Channel Estimation in OFDM Systems
2006
This application note gives an overview of the channel estimation strategies used in orthogonal frequency division multiplexing (OFDM) systems. Section 1 describes the protocols associated with OFDM systems and the problems posed by such systems. Section 2 through Section 5 describe the various types of channel estimation methods for use in such systems. The implementation complexity and system performance of the methods are studied and compared in Section 6, measuring performance in terms of symbol error rate (SER).
EURASIP Journal on Advances in Signal Processing, 2006
Focusing on transmit diversity orthogonal frequency-division multiplexing (OFDM) transmission through frequency-selective channels, this paper pursues a channel estimation approach in time domain for both space-frequency OFDM (SF-OFDM) and space-time OFDM (ST-OFDM) systems based on AR channel modelling. The paper proposes a computationally efficient, pilotaided linear minimum mean-square-error (MMSE) time-domain channel estimation algorithm for OFDM systems with transmitter diversity in unknown wireless fading channels. The proposed approach employs a convenient representation of the channel impulse responses based on the Karhunen-Loeve (KL) orthogonal expansion and finds MMSE estimates of the uncorrelated KL series expansion coefficients. Based on such an expansion, no matrix inversion is required in the proposed MMSE estimator. Subsequently, optimal rank reduction is applied to obtain significant taps resulting in a smaller computational load on the proposed estimation algorithm. The performance of the proposed approach is studied through the analytical results and computer simulations. In order to explore the performance, the closed-form expression for the average symbol error rate (SER) probability is derived for the maximum ratio receive combiner (MRRC). We then consider the stochastic Cramer-Rao lower bound(CRLB) and derive the closed-form expression for the random KL coefficients, and consequently exploit the performance of the MMSE channel estimator based on the evaluation of minimum Bayesian MSE. We also analyze the effect of a modelling mismatch on the estimator performance. Simulation results confirm our theoretical analysis and illustrate that the proposed algorithms are capable of tracking fast fading and improving overall performance.