DFT-based Channel Estimation Research Articles

Joint Channel Estimation Algorithm Based on DFT and DWT

Channel estimation is an important component of orthogonal frequency division multiplexing (OFDM) systems. The existence of virtual subcarriers leads to energy spreading in the time-domain when using Inverse Fast Fourier Transform (IFFT), resulting in poor noise reduction by the conventional Discrete Fourier Transform (DFT)-based channel estimation algorithm. To tackle this problem, this paper first proposes a segmental threshold-assisted DFT-based channel estimation algorithm. The key idea is that, by utilizing the distribution characteristics of the channel and the noise components of the channel impulse response in the time-domain, different thresholds for channel estimation under different SNR conditions are set. Compared with the traditional single-threshold DFT-based algorithm, the performance of the proposed algorithm is improved. However, it still has an estimation performance floor under high SNR. Motivated by the fact that the discrete wavelet transform (DWT)-based channel estimation algorithm can achieve better estimation performance under high SNR, we propose a joint channel estimation algorithm based on DFT and DWT, which can achieve dynamic optimal selection of the two estimation methods without any prior information. Simulation results of the Wi-Fi 6 system show that the mean square error (MSE) simulation performance of the joint channel estimation algorithm is close to its theoretical approximation. It achieves the optimal estimation of MSE and BER performance across the entire SNR range compared with the separated DFT-based or DWT-based channel estimation algorithms.

Improved DFT-based channel estimation for spatial modulated orthogonal frequency division multiplexing systems

Improved DFT-based channel estimation for spatial modulated orthogonal frequency division multiplexing systems

A Low-Complexity Channel Estimation Based on a Least-Squares Algorithm in OFDM Systems

As the channel frequency responses (CFRs) at virtual pilot subcarriers are assumed to be zero, the estimated CFRs will have a leakage effect for discrete Fourier transform (DFT)-based channel estimation in OFDM systems. The CFRs at odd pilot subcarriers and even pilot subcarriers are related if the number of maximum channel delay points is smaller than or equal to half the number of pilots (including virtual pilots). According to this correlation, we propose a low-complexity least-squares (LS) method to estimate the CFRs at virtual even and odd pilot subcarriers, respectively. This will solve the problem of the leakage effect in DFT-based channel estimation. The proposed method does not need to know the statistical properties of the channel or insert extra pilots as with some estimation methods. Furthermore, although this method has less computation than the LS method, both have almost the same channel estimation efficiency in simulation. The channel estimation efficiency of our proposed method is still similar to that of the LS method, even if the number of maximum channel delay points is greater than half the number of pilots. Therefore, the proposed low-complexity method is very suitable for equalizer hardware implementation.

DFT-Based Channel Estimation with Channel Response Mirroring for MIMO OFDM Systems

In this paper, DFT-Based channel estimation with channel response mirroring is proposed and analyzed. In General, pilot symbols for channel estimation in MIMO(Multi-Input Multi-Output) OFDM(Orthogonal Frequency-Division Multiplexing) Systems have a diamond shape in the time-frequency plane. An interpolation technique to estimate the channel response of sub-carriers between reference symbols is needed. Various interpolation techniques such as linear interpolation, low-pass filtering interpolation, cubic interpolation and DFT interpolation are employed to estimate the non-pilot sub-carriers. In this paper, we investigate the conventional DFT-based channel estimation for noise reduction and channel response interpolation. The conventional method has performance degradation by distortion called “edge effect” or “border effect”. In order to mitigate the distortion, we propose an improved DFT-based channel estimation with channel response mirroring. This technique can efficiently mitigate the distortion caused by the DFT of channel response discontinuity. Simulation results show that the proposed method has better performance than the conventional DFT-based channel estimation in terms of MSE.

Performance Evaluation of GFDM Channel Estimation Using DFT for Tactile Internet Application

In this work, discrete Fourier transform (DFT)-based channel estimation is proposed in generalized frequency division multiplexing (GFDM) system. In the GFDM system, the subcarriers are non-orthogonal; therefore, the pilot symbols cannot be easily observed due to the interference from data symbols and noise. The proposed method can improve the channel estimation of least square (LS) method by eliminating channel impulse response outside the number of actual impulse response. First, the received signal is demodulated using zero forcing demodulator. Then, it is divided with transmitted pilot symbols to obtain channel response. Interpolation in frequency and time domains is conducted to acquire channel response for all GFDM blocks. Finally, the channel estimation algorithm using DFT is performed. The parameters of the system are adjusted so that they are suitable for tactile internet application. The channel model used is NYUSIM, which utilizes mmWave. Three scenarios in NYUSIM such as urban microcell, urban macro cell and rural macro cell are used and power delay profiles generated from NYUSIM simulator are employed in this system. The results show that mean square error (MSE) from DFT-based channel estimation gives substantial improvement for all scenarios. In addition, symbol error rate (SER) of DFT-based channel estimation provides a slight improvement of ~1.5 dB than LS channel estimation.

Enhanced DFT-Based Channel Estimator for Leakage Effect Mitigation in OFDM Systems

The leakage effect occurs in a DFT-based channel estimator (CE) due to the presence of guard bands, where the energy of the channel impulse response (CIR) is dispersed to other estimated taps. Furthermore, some of the CIR energy leaks outside of the estimation range and fails to be captured in the channel estimation. This letter presents an enhanced DFT-based CE for orthogonal frequency-division multiplexing (OFDM) systems. The proposed method is composed of two techniques ( spectral extrapolation and circular shift ) to mitigate the leakage effect, followed by a denoising post-processing to enhance the estimation accuracy. Through performance analysis, it is demonstrated that the spectral extrapolation eliminates the leakage effect corresponding to the first CIR tap, and the circular shift improves estimation accuracy by incorporating the leaked CIR energy in the channel estimation. The simulation results show that the proposed method has superior performance compared with conventional CEs. In addition, the proposed method is feasible from a computational complexity perspective.

Channel estimation for 3D MIMO system based on LOS/NLOS identification

Channel estimation is one of the most important parts in three-dimensional multiple-input multiple-output (3D MIMO) systems. The characteristics of non-line-of-sight (NLOS) channel and line-of-sight (LOS) channel are different in 3D MIMO systems. If the same channel estimation scheme is used in LOS case as NLOS, the performance of estimation will be bad. In outdoor propagation environment, 3D MIMO channels between closely located antennas share the same delay support in temporal domain. With those prior knowledge, in this study, a new channel estimation scheme is proposed. The proposed scheme can be divided into two processes. First, it is needed to identify the received sounding reference signal whether is LOS or NLOS propagation. Then, different enhanced DFT-based channel estimation schemes are proposed separately according to the identification results. Simulation results verify the proposed algorithm outperforms traditional discrete Fourier transform (DFT)-based channel estimation. At signal-to-noise ratio of 20 dB, the proposed algorithm has 17.7 and 35.7% improvement in NLOS case and LOS case separately in terms of normalised mean squared error compared with traditional DFT-based channel estimation scheme, and is achieved with additional liner complexity.

DFT‐based channel estimation refinement by clustering in FBMC‐OQAM system

The conventional DFT-based channel estimation method can improve the performance of the least square (LS) or minimum mean square error (MMSE) channel estimation by removing the noise outside the maximum channel delay while the noise inside channel delay still remain. Here, a novel DFT-based pilot-aided channel estimation method for filter bank multicarrier with offset quadrature amplitude modulation (FBMC-OQAM) is proposed. Using clustering and discriminant analysis, this method can separate automatically the noise inside channel delay from channel impulse response (CIR) coefficient of the conventional DFT-based channel estimation. Theoretical analysis and simulation results show that the accuracy of channel estimation can be improved remarkably. Compared with conventional DFT-based channel estimation method and DFT-based channel estimation method with threshold, the proposed DFT-based channel estimation method with clustering has a better bit error ratio (BER) performance in additive white Gaussian noise (AWGN) channel and flat fading channel.

A Universal Channel Estimation Algorithm Based on DFT Smoothing Filtering

Channel estimation is a virtual component to ensure the performance in the orthogonal frequency division multiplexing (OFDM). Smoothing filter is often used to suppress noise to improve the estimation performance. However, the conventional smoothing filtering methods have paid little attention on the virtual subcarriers, which is required in practical system but will introduce interference. Therefore, in this paper, we proposed a universal channel estimation algorithm in which the discrete Fourier transform (DFT) smoothing filtering is used when the virtual subcarriers is considered. What is more, the proposed method is applicable to the OFDM system with either block-type or comb-type pilot, and it can be easily extended to multiple input multiple output (MIMO) system. The proposed method employs windowing, extraction and adaptive filter modules one or more based on conventional DFT-based channel estimation for different pilot patterns. The simulation results show that the proposed method has better performance than the conventional DFT-based channel estimation under the same complexity.

A Low-Complexity Hardware-Friendly DFT-Based Channel Estimator for the LTE Uplink Channel

In this work, a low-complexity hardware-friendly discrete Fourier transform (DFT)-based channel estimator with almost no inherent “edge effect” is designed for the long-term evolution (LTE) uplink channel. Specifically, we propose to perform the border symmetric extension (BSE) operation on the border subcarriers of the channel frequency response (CFR), such that the length of the extended CFR fulfills $$2^{\lceil {{\text {log}}_2N}\rceil }$$ , where N denotes the non-radix-2 length of the original CFR, and $$\lceil {x}\rceil$$ stands for the integer ceiling function. Based on the proposed BSE operation, the discontinuities at the CFR’s border subcarriers are significantly lessened and a better power concentration of the transform-domain channel impulse response is realized. As a result, the inherent “edge effect” caused by the virtual subcarriers in LTE systems can be substantially reduced. A further advantage of the proposed method is that the cumbersome application specific integrated circuit-based implementation of 34 different non-radix-2 length DFT/IDFT operations can be accomplished in a single structure by their fast Fourier transform and inverse fast Fourier transform counterparts. Numerical results illustrate that the proposed DFT-based channel estimator with BSE achieves significant performance gains over the conventional counterpart, despite imposing a reduced computational complexity.

DFT-Based Channel Estimation Scheme for Sidelink in D2D Communication

The 3rd Generation Partnership Project (3GPP) has recently developed device-to-device (D2D) communication to cope with the explosively increasing mobile data traffic. The D2D communication uses sidelink that is based on the single-carrier frequency-division multiple access scheme because of its low peak-to-average power ratio. In addition, the demodulation reference signal is designed to support multiple input multiple output. In this paper, we propose a DFT-based channel estimation scheme for sidelink in D2D communication. The proposed scheme uses the two-dimensional minimum mean square error interpolation scheme for a user moving at a high speed. We performed a system level simulation based on 20-MHz bandwidth of the 3GPP LTE-Advanced system. Simulation results show that the proposed channel estimation scheme has improved signal-to-interference-plus-noise ratio, throughput, and spectral efficiency as compared with a conventional scheme.

All-Digital Self-Interference Cancellation Technique for MIMO Full-Duplex Systems

In this paper, the MIMO full-duplex system is proposed to remove self-interference signal using modified DFT based channel estimation technique. In SISO full-duplex systems only single transceiver can transmit data on either side simultaneously whereas in MIMO full-duplex systems multiple transceivers can transmit data simultaneously from both sides. During MIMO full-duplex transmission selfinterference and circuit impairments may occur, to avoid such noises digital cancellation technique is used which is a lowest complexity self-interference cancellation technique in all fullduplex systems. In this technique receiver auxiliary chain and its copy circuit called ordinary receiver chain is used to cancel out the both self-interference and its circuit impairments. Noise added during wireless channel is suppressed by using passive suppression technique and Gaussian noise, phase noise and quantization noise is eliminated by the active cancellation technique. So, combination of active cancellation and passive suppression techniques are used to eliminate the circuit impairments. The proposed channel estimation technique is used to cancel out the self-interference produced at the output of both auxiliary and ordinary receiver chains. By using digital self-interference cancellation technique the amount of self-interference cancelled is 37dBm higher than the receiver noise floor. The achievable rate and throughput of MIMO full-duplex system is 28 bits/sec/Hz and 1049.04 Mbps respectively which is very large when compared to MIMO half-duplex , SISO full-duplex and SISO half-duplex systems. General Terms QAM, OFDM, Modified DFT based channel estimation, Digital cancellation.

Performance evaluation of DFT-based channel estimation in MIMO-OFDM system

Multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) is an emerging multiplexing technique used in modern mobile communication systems. A main challenge to MIMO-OFDM is retrieval of the channel state information (CSI) accurately and synchronisation between the transmitter and receiver. The CSI is retrieved with the help of channel estimation algorithms such as training-based, blind and semi-blind channel estimation by various researchers. The mean square error (MSE) of existing training-based least square (LS) and minimum mean square error (MMSE) estimation are usually high. In order to minimise MSE, discrete Fourier transform (DFT)-based channel estimation is proposed. This paper deals with MIMO-OFDM system and simulation of training-based LS and MMSE channel estimation, performance evaluation of DFT-based channel estimation. The simulation results clearly indicate the drastic minimisation of MSE by the implementation of DFT channel estimation with LS and MMSE estimation.

D2D 통신에서 사이드링크를 위한 DFT 기반 채널 추정 기법

Recently, 3rd Generation Partnership Project (3GPP) has developed device-to-device (D2D) communication to cope with the explosively increasing mobile data traffic. The D2D communication uses sidelink based on single carrier-frequency division multiple access (SC-FMDA) due to its low peak-to-average power ratio (PAPR). In addition, demodulation reference signal (DMRS) is designed to support multiple input multiple output (MIMO). In this paper, we propose the DFT-based channel estimation scheme for sidelink in D2D communication. The proposed scheme uses the 2-Dimensional Minimum Mean Square Error (2-D MMSE) interpolation scheme for the user moving at a high speed. We perform the system level simulation based on 20MHz bandwidth of 3GPP LTE-Advanced system. Simulation results show that the proposed channel estimation scheme can improve signal-to-interference-plus-noise ratio (SINR), throughput and spectral efficiency of conventional scheme.

Performance Evaluation of Channel Estimation Techniques in OFDM based Mobile Wireless System

In this modern wireless technology Multicarrier communication is one of the more suitable and reliable communication technique. Orthogonal Frequency Division Multiplexing (OFDM) is used as modulation technique in multicarrier communication. The present paper gives an overview of OFDM and the various Channel Estimation techniques used in OFDM. The results implemented in MATLAB gives the performance of LS and the MMSE channel estimators for an OFDM system based on the parameters of BER and MSE. Paper also describes the Delayed feedback MIMO OFDM channel estimation performance of LS and LMMSE and DFT based channel estimation technique for LS-linear and MMSE estimator. BPSK and 16-QAM modulation techniques are used.

LTE-A 시스템 상향링크를 위한 DFT 기반 채널추정 기법

In this letter, a DFT-based channel estimator is proposed for the uplink of LTE-A systems to solve the leakage and enhance the spectral efficiency. It is confirmed that the proposed estimator can significantly improve user and cell spectral efficiencies compared to conventional estimators.

Comparison of Downlink Channel Estimation Schemes for LTE-Based Smart Grid Communications

The long term evolution (LTE) based smart grid communication network is a promising candidate solution for the future power grid. In this paper, we discuss three channel estimation schemes for the LTE-based smart grids, including least square (LS), minimum mean square error (MMSE), and discrete Fourier transform (DFT) based channel estimators. In the simulations, we compare these three estimators, the results show that the DFT-based channel estimator can achieve the best tradeoff between the performance and the implementation complexity.

Analysis of the Effect of Coherence Bandwidth on Leakage Suppression Methods for OFDM Channel Estimation

In this paper, we analyze the effect of the coherence bandwidth of wireless channels on leakage suppression methods for discrete Fourier transform (DFT)-based channel estimation in orthogonal frequency division multiplexing (OFDM) systems. Virtual carriers in an OFDM symbol cause orthogonality loss in DFT-based channel estimation, which is referred to as the leakage problem. In order to solve the leakage problem, optimal and suboptimal methods have already been proposed. However, according to our analysis, the performance of these methods highly depends on the coherence bandwidth of wireless channels. If some of the estimated channel frequency responses are placed outside the coherence bandwidth, a channel estimation error occurs and the entire performance worsens in spite of a high signal-to-noise ratio.

Development of discrete Fourier transform‐based channel estimation algorithms for a coherent optical orthogonal frequency division multiplexing transmission system

In this study, the authors presented discrete Fourier transform (DFT)-based channel estimation algorithms for a coherent optical orthogonal frequency division multiplexing (CO-OFDM) transmission system. Influence of the proposed algorithms to the performance and computational complexity of the CO-OFDM system was analysed and compared with other published algorithms. Their simulation results demonstrated that the improved DFT-based channel estimation algorithms are significantly efficient in our experimental conditions. Those algorithms can be considered as efficiently compromised systems in balance out the outcome of performance and the requirement on computational complexity. Such relatively economic and practical approaches have provided an optimistic prospect in studies of transmission systems for future optical communications.

Chaotic-Sequence-Based Channel Estimation Algorithm for Secure Optical OFDM Systems

In this paper, in order to improve the security of optical OFDM system, we propose a new method to generate the pilot sequence of channel estimation using chaotic sequence. Firstly, we assign initial values to chaotic system, and calculate a chaotic sequence through an iteration method, then converting it into a binary sequence as the pilot of a DFT-based channel estimation algorithm. When the receiving end doesn’t know the chaotic-sequence-based pilot, the system will have very high BER, and can not restore the original data, which indicate that the new method provides a certain degree of security for optical OFDM systems without increasing the system complexity.