IJERT-Analysis of proposed power delay profile pdp for mimo ofdm systems IJERTV2IS (original) (raw)
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A PDP Estimation Technique For The LMMSE Channel Estimator Of MIMO- OFDM Systems
2013
The combination of multiple-input multiple-output (MIMO) system with OFDM techniques is regarded as one of the promising solution for wireless communication systems, including the 3rd Generation Partnership Project Long Term Evolution (3GPP-LTE) and IEEE 802.16 (Wi-MAX). In this paper, we propose a power delay profile (PDP) estimation technique for linear minimum mean square error (LMMSE) channel estimator of MIMO-OFDM systems. For practical applications, the proposed technique uses only the pilot symbols of all the transmit antenna ports to estimate the PDP with low computational complexity. In addition, this technique also reduces the correlation mismatch in the frequency domain, the distortions caused by null subcarriers and an insufficient no. of samples for PDP estimation. Simulation results show that the performance of LMMSE channel estimation using the Proposed PDP estimate is much better than the ML PDP estimator and an approximated PDP estimator(uniform or exponential).
IJERT-A PDP Estimation Technique for The LMMSE Channel Estimator of MIMO- OFDM Systems
International Journal of Engineering Research and Technology (IJERT), 2013
https://www.ijert.org/a-pdp-estimation-technique-for-the-lmmse-channel-estimator-of-mimo-ofdm-systems https://www.ijert.org/research/a-pdp-estimation-technique-for-the-lmmse-channel-estimator-of-mimo-ofdm-systems-IJERTV2IS70703.pdf The combination of multiple-input multiple-output (MIMO) system with OFDM techniques is regarded as one of the promising solution for wireless communication systems, including the 3rd Generation Partnership Project Long Term Evolution (3GPP-LTE) and IEEE 802.16 (Wi-MAX). In this paper, we propose a power delay profile (PDP) estimation technique for linear minimum mean square error (LMMSE) channel estimator of MIMO-OFDM systems. For practical applications, the proposed technique uses only the pilot symbols of all the transmit antenna ports to estimate the PDP with low computational complexity. In addition, this technique also reduces the correlation mismatch in the frequency domain, the distortions caused by null subcarriers and an insufficient no. of samples for PDP estimation. Simulation results show that the performance of LMMSE channel estimation using the Proposed PDP estimate is much better than the ML PDP estimator and an approximated PDP estimator(uniform or exponential).
Power delay profile and noise variance estimation for OFDM
IEEE Communications Letters, 2006
In this letter, we present cyclic-prefix (CP) based noise-variance and power-delay-profile estimators for Orthogonal Frequency Division Multiplexing (OFDM) systems. Signal correlation due to the use of the CP is exploited without requiring additional pilot symbols. A heuristic estimator and a class of approximate maximum likelihood (ML) estimators are proposed. The proposed algorithms can be applied to both unitary and non-unitary constellations. These algorithms can be readily used for applications such as minimum mean-square error (MMSE) channel estimation.
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.
Orthogonal frequency-division multiplexing (OFDM) effectively mitigates intersymbol interference (ISI) caused by the delay spread of wireless channels. Therefore, it has been used in many wireless systems and adopted by various standards. In this paper, we present a comprehensive survey on OFDM for wireless communications. We address basic OFDM and related modulations, as well as techniques to improve the performance of OFDM for wireless communications, including channel estimation and signal detection, time- and frequency-offset estimation and correction, peak-to-average power ratio reduction PAPR, intercarrier interference (ICI) and multiple-input–multiple-output (MIMO) techniques. We also describe the applications of OFDM in current systems and standards.
OFDM and Its Wireless Applications: A Survey
Orthogonal frequency-division multiplexing (OFDM) effectively mitigates intersymbol interference (ISI) caused by the delay spread of wireless channels. Therefore, it has been used in many wireless systems and adopted by various standards. In this paper, we present a comprehensive survey on OFDM for wireless communications. We address basic OFDM and related modulations, as well as techniques to improve the performance of OFDM for wireless communications, including channel estimation and signal detection, time-and frequency-offset estimation and correction, peak-to-average power ratio reduction, and multiple-input-multiple-output (MIMO) techniques. We also describe the applications of OFDM in current systems and standards.
OFDM Channel Parameters Estimation used for ICI Reduction in time-varying Multipath Channels
In this paper, we present an improved channel matrix estimation algorithm for orthogonal- frequency-division-multiplexing downlink mobile communication systems using comb-type pilot. The channel matrix, which contains the channel frequency response and the coefficients of inter-sub-carrier-interference (ICI), is estimated using parametric multipath channel model. In the algorithm, we assume the delays are time-invariant over several symbols. With delays information, the multipath complex gains time average over the effective duration of each OFDM symbol are estimated using LS or LMMSE criteria. After that, the time-variation of the multipath complex gains within one OFDM symbol are obtained by using low-pass interpolation. Hence, the channel matrix can be calculated and the ICI can be reduced. The simulation results show that the proposed method, with less number of pilots and without suppression of interference, gives a good performance over LS and LMMSE estimators with low-pass in...
A Novel Design of Time Varying Analysis of Channel Estimation Methods in OFDM
ABSTRACT: OFDM can be seen as either a modulation technique or a multiplexing technique. One of the main reasons to use OFDM is to increase the robustness against frequency selective fading or narrowband interference. In a single carrier system, a single fade or interferer can cause the entire link to fail, but in a multicarrier system, only a small percentage of the subcarriers will be affected. Error correction coding can then be used to correct for the few erroneous subcarriers. In this paper, channel estimation for Spatial Multiplexing (SM) is investigated for MIMO-OFDM system. Due to the channel characteristic of the transmission system is always changed by the time and its importance in wireless transmission to reconstruct the transmitted signals, the channel needs to be known as well as possible. Pilot symbols are used to gather knowledge about the channel and try to estimate it. The channel estimation based on the pilot symbol is called pilot aided channel estimation. In this research, Least Square (LS) method was chosen for initial channel estimation. By using applicable proposed system design, channel state information is estimated through the use of channel information before in subcarriers with no pilot symbols. Zero forcing (ZF) algorithms is used to detect and separate the received signal. Keywords- MIMO, OFDM , pilot symbol, channel estimation, least square, minimum mean square ,zero forcing.
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.