Power delay profile and noise variance estimation for OFDM (original) (raw)
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Autocorrelation Method for Cyclic Prefix OFDM Estimation
IJITEE (International Journal of Information Technology and Electrical Engineering), 2019
A radio system design providing various data service needs becomes one of the Software Defined Radio (SDR) system advantages. SDR technology applies software functions further to be run in hardware platforms. The need for services with greater data rates can be resolved by using multi-carrier transmission techniques, one of which is the Orthogonal Frequency Division Multiplexing (OFDM) technique. This paper discusses the detection of OFDM signals and their parameters. Multi-carrier transmission can prevent Inter-Symbol Interference (ISI) occurrence due to multi-path fading effect. The recognition can classify the correctly received signals, including the signal conditions mixed with AWGN noise. The autocorrelation method was used to estimate the OFDM parameters, namely the one symbol duration and the cyclic prefix duration. The detected cyclic prefix durations were 1/2, 1/4, 1/8, and 1/16. This method is very simple, because with the cyclic prefix presence, a different signal peak w...
Universal Journal of Communications and Network, 2015
A Cyclic Prefix (CP) is a significant feature of an OFDM waveform. It is used to completely eliminate both Inter-Symbol Interference (ISI) and Inter-Carrier Interference (ICI) as long as the CP length is greater than the channel delay spread. By eliminating both ISI and ICI, the CP compensates for the effect of the multipath dispersion; but it consumes a considerable amount of the scarce spectrum and the power. Conventional OFDM uses a fixed and large CP length to overcome the ISI caused by channel delay spread under wireless mobile environment. This approach may degrade the overall spectral efficiency as well as consumes relatively more transmitter energy. Therefore, there is a need to adopt the CP length according to instantaneous channel parameters. In this paper, we presented a method for investigating the effect of varying the CP length on OFDM system performance over different multipath channel models. We estimated the variable CP length based on the RMS delay spread of the channels' power delay profile (PDP). According to this method, the estimated CP length optimizes the system capacity and improves the overall system performance. We showed that this approach could lead to a mathematical formula presenting the relationship between the CP length and the RMS delay spread of the channels.
Efficient OFDM Symbol Timing Estimator Using Power Difference Measurements
IEEE Transactions on Vehicular Technology, 2012
This paper presents an efficient blind symbol timing estimation scheme for orthogonal frequency-division multiplexing (OFDM) systems with constant modulus constellation. The proposed technique is designed to estimate symbol timing offsets by minimizing the power difference between subcarriers with similar indices over two consecutive OFDM symbols based on the assumption that the channel slowly changes over time. The proposed power difference estimator (PDE) is totally blind because it requires no prior information about the channel or the transmitted data. Monte Carlo simulation is used to assess the PDE performance in terms of the probability of correct timing estimate Plock-in. Moreover, we propose a new performance metric denoted as the deviation from safe region (DSR). Simulation results have demonstrated that the PDE performs well in severe frequency-selective fading channels and outperforms the other considered estimators. The complexity of the PDE can be significantly reduced by incorporating a low-cost estimator to provide initial coarse timing information. The proposed PDE is realized using feedforward and early-late gate (ELG) configurations. The new PDE-ELG does not suffer from the self-noise problem inherent in other ELG estimators reported in the literature.
An improved timing estimation method for OFDM systems
IEEE Transactions on Consumer Electronics, 2000
In this paper, we propose an improved timing estimation method for orthogonal frequency division multiplexing (OFDM) systems. The proposed preamble-aided method is independent of the preamble structure and is based on taking advantage of the whole products available from a given preamble for its correlation. Capable of having an extended correlation length far beyond those used by the previous methods, the proposed scheme presents an estimator with a remarkable performance in severe noise conditions. Further, we introduce a reduced complexity estimator along with the complexity assessments. We finally evaluate the performance of the proposed method in terms of mean square error (MSE). The results indicate that the new method significantly improves the performance compared to the previously presented methods 1 .
The performance of MIMO-OFDM network gets affected due to problems in the channel estimation which is essential for designing receivers. The issues in MIMO are due to sizable inadequate Cyclic Prefix (CP) in admired Orthogonal frequency division multiplexing (OFDM), a massive amount of detection error and channel estimation problem occurs due to which performance delay turn out. This paper proposes a solution, its implementation and analysis of results. The article uses the BAT and Modified Flower Pollination (MFP) algorithm for optimizing the CP length. Minimum CP length gets considered to achieve better throughput for the same MFP algorithm. This algorithm has been proposed to optimize CP length to achieve minimum error rate of bit (BER) and PAPR-Peak to average power ratio, thereby maximizing the spectrum efficiency. For comparing the efficacy of optimized CP and unoptimized CP, the paper examines the results obtained on studying the performance in the spectrum. The performance of BAT and MFP algorithm are compared with each other to determine the better optimization methodology for the problem.
Estimation of the Channel Impulse Response Length and the Noise Variance for OFDM Systems
2005 IEEE 61st Vehicular Technology Conference
In this paper, a new method for the channel impulse response (CIR) length and the noise variance estimation for orthogonal frequency division multiplexing (OFDM) systems is proposed. To estimate the CIR length and the noise variance, the difference between the statistical characteristics of the additive noise and the mobile radio channel is exploited. This difference lies in the fact that the true CIR coefficients are located within the CIR length, whereas the additive noise of an estimated channel tap is uniformly distributed over the whole length of the estimated CIR. Moreover, the CIR length changes more slowly than its coefficients. An auxiliary function is established to describe these characteristics. The CIR length and the noise variance can be estimated by varying the parameters of the auxiliary function. The proposed method provides a reliable information on the estimated CIR length even at signal-to-noise ratios (SNRs) of 0 dB.
IJERT-Analysis of proposed power delay profile pdp for mimo ofdm systems IJERTV2IS
International Journal of Engineering Research and Technology (IJERT), 2013
https://www.ijert.org/analysis-of-proposed-power-delay-profile-pdp-for-mimo-ofdm-systems https://www.ijert.org/research/analysis-of-proposed-power-delay-profile-pdp-for-mimo-ofdm-systems-IJERTV2IS100731.pdf The aim of this paper is to investigate the OFDM scheme, and realize a fully functional system and analyzing how it is reducing the inter-symbol interference caused by the multipath fading channels and different effects and estimating, evaluating the performance of it. The paper proposes a power delay profile (PDP) estimation technique for linear minimum mean square error (LMMSE) channel estimator of multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. For practical applications, only the pilot symbols of all transmit antenna ports are used in estimating the PDP. The distortions caused by null subcarriers and an insufficient number of samples for PDP estimation is also considered. The proposed technique effectively reduces the distortions for accurate PDP estimation. Simulation results show that the performance of LMMSE channel estimation using the proposed PDP estimate approaches that of Wiener filtering due to the mitigation of distortion effects
Channel Estimation and ISI/ICI Cancellation for MIMO-OFDM Systems with Insufficient Cyclic Prefix
Lecture Notes of the Institute for Computer Sciences, Social Informatics and Telecommunications Engineering, 2009
In multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) systems, the multipath components whose delays exceed cyclic prefix (CP) cause inter-symbol interference (ISI) and inter-carrier interference (ICI), which may degrade system performance severely. In this paper, we propose a joint channel estimation and ISI/ICI cancellation scheme in which a limited CP is used in a trade-off against high-rate performance in MIMO-OFDM systems. A channel estimation scheme based on the criterion of Expectation-Maximization (EM) algorithm can be proposed through the use of a training symbol. The EM algorithm uses an iterative procedure to estimate channel parameters and can estimate channel impulse response (CIR) accurately enough to mitigate ISI/ICI influences. Through the accurate CIR estimation, an efficient method has been developed to counteract ISI/ICI influences in signal detection in the case where the inserted CP length is less than the CIR length. Simulation results show that the proposed method can significantly enhance the overall MIMO-OFDM system performance after only a few iterations.
Estimation of symbol time offset using cyclic prefix in OFDM system
arXiv (Cornell University), 2023
In this paper synchronization techniques using cyclic prefix (CP) are analyzed to remove the influence of symbol time offset (STO) for correct synchronization in Orthogonal Frequency Division Multiplex (OFDM) system. For correct detection of STO using CP two techniques are used. The first one is based on finding the maximum correlation between two blocks and the second one on finding the similarity between two blocks which is maximized when the difference between them is minimized. Two cases are observed. The first one uses only additive white Gaussian noise (AWGN), while the second also uses the channel impulse response (CIR) of Rayleigh channel. When channel effect is added both performances of estimation by correlation and difference deteriorate if sufficient level of signal to noise (SNR) and proper length of CP are not provided.