LS Channel Research Articles

Deep Residual Learning with Attention Mechanism for OFDM Channel Estimation

In this paper, we apply deep learning to the channel estimation problem of OFDM. Precisely speaking, to reduce the influence of noise on LS channel estimation, we design a channel estimation model based on attention mechanism and residual network. AttRNet-Conv and AttRNet-FC use attentional mechanism to change the weight of the feature to suppress noise. Compared with other channel estimation algorithms based on deep learning, AttRNet-Conv and AttRNet-FC avoid damaging channel information. The simulation results show that AttRNet-Conv and AttRNet-FC are superior to existing channel estimation algorithms based on deep learning in both high and low pilot frequency conditions. Even at low SNR, the estimation accuracy is higher than that of LMMSE. Experimental results show thatAttRNet-Conv and AttRNet-FC has strong robustness. In addition, we find that AttRNet-Conv is more suitable for channel estimation at low SNR in EPA, and the AttRNet-FC model is used in other cases.

Numerical Evaluation of the MU-MIMO Beamforming Performance with Channel Estimation

This paper presents the numerical evaluation of the ZF beamforming algorithm and DFT precoding using the LS channel estimation in the multiuser multiantenna (MU-MIMO) downlink system. The sum rate performance depending on a number of users are presented. The arising inter user correlation degrades the sum rate (spectral efficiency) performance of multiuser MIMO system especially in scenarios where the number of users is larger than the number of antennas at the BS. For MIMO channel simulation the QuaDRiGa channel model reflecting the real propagation conditions is used. The obtained performance of MU-MIMO ZF precoding in spatially correlated channel are compared with DFT precoding based on the empirical cumulative density function of the sum rate of multiple users. Numerical results show that the ZF precoder outperforms the DFT precoder in channel with less spatial correlation. The DFT precoder in spatially more correlated channel has advantage over ZF precoder.

Innovative Approach of Spectral Efficiency Optimization over Various Pilot Reuse Factors

The Massive MIMO with TDD is breakthrough technology for spectral efficiency gains. The CSI is essential for spectral efficiency gains and CSI can be obtained by channel estimation methods. The channel estimation methods employ known pilot s sequences to estimate the channel before actual data transmission. However, the channel coherence is time and frequency limited, which reflects the trade-off between the resources available for pilots and those available for data in coherent block for transmission. The pilot sequences reuse in other cells can reduce pilot overhead, called pilot reuse. However potential interference is introduced, by pilot reuse, in the channel estimation phase, called pilot contamination. The aim is to determine optimum pilot reuse factor for better SE using low computational complexity estimation method. The sum averaged SE has been obtained for pilot reuse factor 1, 2, 4, 8 and 16 using MMSE, EW-MMSE and LS channel estimation methods. The obtained results reveals that the difference between values of SEs for f=1 to f=2 to f=4 is very low and performance difference between estimators decreases as pilot reuse factor increases, which allows to use LS estimator to get performance almost equal to MMSE with less computational complexity. Also, the pilot reuse factor f=4 found optimum among all for given constraint.

Deep learning based channel estimation method for mine OFDM system

In this paper, we present a channel estimation approach based on deep learning to solve the problem that the orthogonal frequency division multiplexing (OFDM) system channel estimation algorithm cannot accurately obtain the channel state information in the complex environment of the mine, resulting in system performance degradation. First, LS channel estimation matrix is considered as a low-resolution image and the actual channel state information is considered as a high-resolution image. Then the optimization of the LS channel estimation matrix is achieved by the FSRCNN image super-resolution algorithm. We validate the effectiveness of the proposed algorithm by conducting experiments in different channel environments, different number of pilots, and mismatched signal-to-noise ratio scenarios. The simulation results show that the proposed scheme is much better than the traditional LS channel estimation method and the DFT-LS channel estimation method, and the accuracy of the proposed scheme approaches that of the MMSE channel estimation method when the number of pilots is low.

Strategic cooperation of live‐stream platform in e‐commerce

AbstractMany live‐stream platforms (LSPs) have sought cooperation with e‐tailers or/and manufacturers. Considering the existing cooperation modes, we propose models to examine the optimal cooperation mode. Our study shows that the LSP benefits from cooperating with both firms. Moreover, the manufacturer profits from the LSP only cooperating with itself, while the e‐tailer may profit from the LSP only cooperating with itself or the manufacturer. The consumers benefit from the LSP only cooperates with one firm. We further consider the case where the manufacturer's LS channel is not inferior to the e‐tailer's channels and examine the equilibrium strategies for players and consumers.

Turbo-Coded MIMO-OFDM Channel Estimation Using the Chaotic Grey Wolf Optimizer and Genetic Algorithm

Turbo-Coded multiple-input multiple-output orthogonal frequency division multiplexing Channel Estimation, using Chaotic Grey Wolf Optimizer and the Genetic Algorithm (TC-MIMO-OFDM-Hybrid-CGWO-GA), is proposed in this manuscript. To enhance the performance of the bit error rate (BER), the proposed turbo code lessens the maximal correlation of the channel in the frequency domain. Initially, the channel is estimated using LS-MMSE individually using Chaotic Grey Wolf Optimizer (CGWO) and the LS-MMSE is combined with a genetic algorithm to scale the best channel for reducing the error. The encoding and decoding methods are done with the help of Turbo-codes for LS channel estimation. Then, the performance of the proposed method is analyzed with different performance metrics, such as the bit error rate, mean square error, channel estimation, computational cost, overhead, and symbol error rate. From the analysis, the proposed method attains lower computational costs of 99.67%, 98.38%, 92.34% and 97.45%, lower bit error rates of 98.33%, 89.34%, 83.12% and 88.96% and lower mean square errors of 93.15%, 91.25%, 79.90% and 92.88% analyzed to the existing methods, such as TSO-CE-TC-MIMO-OFDM, MFPA-CE-MIMO-OFDM, OSBS-CEA-MIMO-OFDM, and IAMO-CE-MIMO-OFDM.

Efficient Image Transmission Over OFDM Channel with Energy Conservation and LS Channel Estimation with Various Modulation Schemes

To send data like text, images, music, and videos, packetization procedures are commonly used in communication apps. Just a portion of carriers in OFDM systems may be suitable for transmitting images due to channel fading. To reduce high channel errors at the receiver, the transmitter can proactively map descriptions onto good subcarriers and delete remaining descriptions if it has access to channel status information. In this study, discrete wavelet processing as an energy-saving approach for transmitting compressed image frames via OFDM channels. By utilizing one-bit channel status information at the transmitter, the descriptions are sorted and allocated to high-quality channels in a descending order of importance. To conserve energy, faulty sub-channel descriptions are removed at the transmitter. In this project, image transmission across OFDM channels is packetized to enable efficient data transfer while minimizing energy consumption. We also use the LS Channel estimation method to get a more accurate channel estimate with different modulation schemes and SNR. We obtained energy savings of up to 38% and improved channel estimation with various modulation schemes by utilizing MATLAB simulations to test on a variety of modulation schemes and channel SNR ratios.

A Pilot-Based Integration Method of Ranging and LS Channel Estimation for OFDM Systems

In the design of unmanned aerial vehicle (UAV) communication systems, orthogonal frequency division multiplexing (OFDM) is a commonly used communication technology. An efficient channel estimation and equalization algorithm is required to recover the amplitude, phase, and frequency of the signal in OFDM systems. At present, the more precise channel estimation method is based on the pilot. However, its spectrum utilization is relatively low. Therefore, this paper presents the design of a new pilot based on the LS channel estimation, which extends the role of the traditional pilot and improves the utilization of the spectrum. In addition to the channel estimation and equalization, the new pilot can also be utilized for ranging. Simulation results show that the proposed scheme can achieve both channel estimation and communication ranging functions by using the new pilot, and it outperforms the conventional method in channel estimation performance. The proposed method can complete ranging when the bit error rate (BER) is above 0 dB. Moreover, compared with the traditional channel estimation, it reduces the requirement for SNR by about 1 dB under the same BER.

The research on channel estimation and signal‐noise ratio estimation based on minimum error entropy kalman filter for single carrier frequency domain equalization system

SummaryIn this paper, the channel estimation and signal‐to‐noise ratio (SNR) estimation technique of single‐carrier frequency domain equalization (SC‐FDE) system under low SNR in aeronautical multipath channel are studied, a SNR estimation algorithm which is easy to implement in engineering and an improved LS channel estimation algorithm based on Kalman filter using minimum error entropy (MEE‐KF) are proposed. This paper first introduces the SC‐FDE system and introduces the principle of MEE‐KF, and then, the channel estimation flow based on MEE‐KF is obtained by combining it with the traditional LS channel estimation algorithm, which makes the estimation results perform better. Simulation results show that after getting more accurate noise variance, the channel estimation results can better follow the changes of the channel after MEE‐KF processing, so as to resist the doppler frequency offset effect and make the channel estimation results more accurate, that is the channel response results of the data part can be closer to the real situation, so that the communication performance of SC‐FDE system has also been greatly improved.

Performance Analysis of Compressive Sensing based LS and MMSE Channel Estimation Algorithm

In this paper, the optimality of Compressive Sensing based Least Square (LS-CS) and Compressive Sensing based Minimum Mean Square (MMSE-CS) channel estimation algorithms in Multi Input Multi Output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) system is investigated for a sparse communication channel. The performance of LS, MMSE, LS-CS and MMSE-CS channel estimation algorithms in terms of sparsity of the channel, compressive sensing and mathematical complexity is investigated and analyzed so that optimum ranges can be recommended.

Properties of exotic nuclei and their linkage to the nucleonic interaction

The structure of exotic nuclei sheds new light on the linkage of the nuclear structure to the nucleonic interaction. The self-consistent mean-field (SCMF) theories are useful to investigate this linkage, which are applicable to many nuclei covering almost the whole range of the nuclear chart without artificial truncation of model space. For this purpose, it is desired to develop effective interaction for the SCMF calculations well connected to the bare nucleonic interaction. Focusing on ground-state properties, I show the results of SCMF calculations primarily with the Michigan-three-range-Yukawa (M3Y)-type semi-realistic interaction, M3Y-P6 and M3Y-P6a to be precise, and discuss in detail how the nucleonic interaction affects the structure of nuclei including those far off the [Formula: see text]-stability. The central channels of the effective interaction are examined by the properties of the infinite nuclear matter up to the spin dependence and the isospin dependence. While experimental information of the infinite matter is obtained by extrapolating systematic data on finite nuclei in principle, it is not easy to constrain the spin dependence and the isospin dependence without connection to the bare nucleonic interaction. The noncentral channels play important roles in the shell structure of the finite nuclei. The tensor force is demonstrated to affect [Formula: see text]- or [Formula: see text]-dependence of the shell structure and the magic numbers, on which the spin–isospin channel in the central force often acts cooperatively. By using the M3Y-P6 interaction, the prediction of magic numbers is given in a wide range of the nuclear chart, which is consistent with almost all the available data. In relation to the erosion of magic numbers in unstable nuclei, effects of the tensor force on the nuclear deformation are also argued, being opposite between nuclei at the [Formula: see text]- and the [Formula: see text]-closed magicities. Qualitatively consistent with the [Formula: see text]-force effect on the [Formula: see text]-splitting suggested from the chiral effective field theory, the density-dependent LS channel, which is newly introduced in M3Y-P6a, reproduces the observed kinks in the differential charge radii at the [Formula: see text]-closed magic numbers and predicts anti-kinks at the [Formula: see text]-closed magic numbers. The pairing correlation has significant effects on the halos near the neutron drip line. A new mechanism called “unpaired-particle haloing” is disclosed.

Performance of MIMO-OFDM Systems

Orthogonal frequency division multiplexing (OFDM) is one of the new modulation techniques which is used to combat the frequency-selectivity of the transmission channel models achieving high data rate without inter-symbol interference. OFDM may be combined with antenna arrays at the transmitter and receiver to increase the system capacity on time-variant and frequency-selective channel models resulting in a multiple-input multiple-output (MIMO) configuration. In this paper, SISO, SIMO, MISO and MIMO-OFDM configurations of OFDM systems are proposed. LS channel estimator is used to calculate the channel coefficients. The four different OFDM systems are analysed and simulated. The simulation consists of four parameters namely bit error rate, mean square error, symbol error rate and capacity of the channel for MIMO-OFDM systems. The error rate values are minimised in 2×2 MIMO-OFDM systems compared to other 1×1, 1×2, 2×1 OFDM systems. Similarly channel capacity is maximised in 2×2 MIMO-OFDM systems, compared to the other OFDM systems. These performances are implemented using MATLAB software.

Channel Estimation and Data Transmission in Massive MIMO TDD Systems

This paper mainly elaborates the studies of channel estimation and downlink data transmission in Massive MIMO. As there are different types of interference in single-cell and multi-cell systems, this paper establishes different models for them separately. In terms of uplink training, for getting channel state information, we introduce LS and MMSE channel estimation algorithms and make a comparison between them. At the same time, the problem of pilot contamination is solved by cell classification and pilot identification. Next, this paper defines mathematical models for downlink data transmission. We use pre-coding methods (including Zero-forcing and Maximal Ratio Combining schemes) and optimize power distribution to improve channel capacity and transmission rate. Furthermore, this paper provides numerical results to show the simulation performance in both single-cell and multi-cell systems and extends to prospects in the future.

Improvement in Time Varying Multipath Channel Estimation

In this work, we propose a new algorithm that modifies the LS channel estimation technique by using a feedback LS channel estimator to improve upon its estimation capabilities and still retaining its simplicity. To examine its usefulness especially for wireless mobile applications, performance in terms of the symbol error rate is analyzed with varying Doppler frequency and delay parameters, which is found to be quite optimistic in comparison to LMMSE and LRMMSE algorithms.

LS Channel Estimation in Multicell Multiuser MIMO OFDM with Zadoff Chu Sequence as Pilots

High spectral efficiency and the ability to combat multipath fading are the key requirements of future wireless communication systems. Multiple-input multiple-output (MIMO) combined with orthogonal frequency- division multiplexing (OFDM) has been widely considered to be a promising candidate. Moreover Multi user MIMO OFDM can provide good spatial multiplexing with single antenna for each user. In the case of multicell multiuser MIMO OFDM system main challenge is to acquire the channel state information. In order to get the channel state information, channel estimation is to be done. Here pilot aided LS channel estimation is used to obtain the estimates. For multi cell multi user MIMO OFDM, channel estimation using pilot subcarriers causes pilot contamination. This is due to the reuse of pilot subcarriers in different cells. In order to reduce the impact of pilot contamination, pilot sequences must select properly. Here Zadoff Chu sequences are used for the design of pilots in different cells.

LS Channel Estimation and Signal Separation for UHF RFID Tag Collision Recovery on the Physical Layer.

In a passive ultra-high frequency (UHF) radio-frequency identification (RFID) system, tag collision is generally resolved on a medium access control (MAC) layer. However, some of collided tag signals could be recovered on a physical (PHY) layer and, thus, enhance the identification efficiency of the RFID system. For the recovery on the PHY layer, channel estimation is a critical issue. Good channel estimation will help to recover the collided signals. Existing channel estimates work well for two collided tags. When the number of collided tags is beyond two, however, the existing estimates have more estimation errors. In this paper, we propose a novel channel estimate for the UHF RFID system. It adopts an orthogonal matrix based on the information of preambles which is known for a reader and applies a minimum-mean-square-error (MMSE) criterion to estimate channels. From the estimated channel, we could accurately separate the collided signals and recover them. By means of numerical results, we show that the proposed estimate has lower estimation errors and higher separation efficiency than the existing estimates.

Performance analysis of OFDM receiver with modified PTS technique

Modified partial transmit sequence PTS technique with adjacent partitioning and four phase factors is implemented to enhance the PAPR performance of OFDM system and its PAPR reduction performance is evaluated in terms of the complementary cumulative distribution function CCDF. A multipath fading environment is considered and the performance of the OFDM receiver is evaluated using least square LS and minimum mean square error MMSE channel estimation methods. The performance of the receiver is evaluated in terms of mean square error MSE and bit error rate BER. The performance of the OFDM receiver is enhanced with PAPR reduction.

Further evidence for three-nucleon spin-orbit interaction in isotope shifts of nuclei with magic proton numbers

It was pointed out [Phys. Rev. C \textbf{91}, 021302(R)] that the isotope shifts of the Pb nuclei, the kink at $N=126$ in particular, can be well described by the Hartree-Fock-Bogolyubov calculations if a density-dependent LS interaction derived from the $3N$ interaction is incorporated. Effects of the density-dependence in the LS channel on the isotope shifts are extensively investigated for the Ca, Ni and Sn isotopes, using the semi-realistic M3Y-P6 interaction and its LS modified variant M3Y-P6a, as in the Pb case. It is found that almost equal charge radii between $^{40}$Ca and $^{48}$Ca are reproduced, as well as the isotope shifts in a long chain of the Sn nuclei, owing to the density-dependence in the LS channel. A kink is predicted at $N=82$ for the isotope shifts of the Sn nuclei, in clear contrast to the interactions without the density-dependence.

Effects of three-nucleon spin-orbit interaction on isotope shifts of Pb nuclei

We investigate effects of the $3N$ interaction, which effectively adds a density-dependent term to the LS channel, on the isotopes shifts of the Pb nuclei. With the strength so as to keep the $\ell s$ splitting of the single-nucleon orbits, the density-dependence in the LS channel tends to shrink the wave functions of the $j=\ell+1/2$ orbits while makes the $j=\ell-1/2$ functions distribute more broadly. Thereby the kink in the isotope shifts of the Pb nuclei at $N=126$ becomes stronger, owing to the attraction from neutrons occupying $0i_{11/2}$ in $N>126$. The density-dependence in the LS channel enables us to reproduce the data of the isotope shifts by the Hartree-Fock-Bogolyubov calculations in a long chain of neutron numbers, even without degeneracy between the $n1g_{9/2}$ and $n0i_{11/2}$ levels. We exemplify it by the semi-realistic M3Y-P6 interaction.

Channel Estimation and Equalization of DVB-T in Fast Fading Multipath Channels

Early Terrestrial Digital Video Broadcasting Systems (DVB-T) were planned to work in Line-of-Sight (LOS) environments where a significantly high Signal to Noise Ratio (SNR) is guaranteed for all times. However, the recent DVB standards are sought to work in non-LOS conditions where the SNR is relatively low. Hence, in such environments, there is a need for a successful channel estimation and detection technique to take care of the fast channel fluctuations. This article is dealing with LS channel estimation and detection method for DVB-T signals over various multipath fading channel. The proposed method has been proven successful for up to 16 Quadrature Amplitude Modulation (QAM) constellations even when there is no LOS. However, the performance is found to be insufficient for an acceptable user experience for higher number of constellations. 