A pilot contamination elimination (PCE) precoding was recently proposed for multi-cell massive MIMO systems with distributed antenna subarrays, where the number of subarrays is required to be not less than the number of users. In this paper, we consider practical scenario of insufficient number of subarrays, and propose a corresponding PCE precoding scheme. The key idea of the proposed scheme is to utilize multiple pilots in one cell rather than single pilot in the original scheme. It is shown that by separating users into multiple groups according to the associated pilots, multiple downsized equivalent MIMO channels can be obtained, which linearly reduces the required number of subarrays and therefore enable the PCE precoding. This linear relation based interpretation also introduces a new optimization problem of finding subarray power normalization factors to maximize signal-to-noise-plus-interference ratio, where an optimized solution is proposed. Finally, simulation results confirm the validity of the proposed PCE precoding scheme.

Spectrum sculpting (SS) is a precoding scheme for sidelobe suppression of orthogonal frequency division multiplexing (OFDM) signals and can shape a spectrum with deep notches at chosen frequencies. However, the SS method will degrade the error rate as the number of notched frequencies increases. Orthogonal precoding of the SS has both a notched spectrum and an ideal error rate, but the computational complexity of the precoder matrix is very large. This paper proposes a matrix decomposition of the precoder matrix of the orthogonal precoding to reduce the computational complexity. Numerical experiments show that the proposed method can drastically reduce the computational complexity.

In this paper, we study the impact of clock timing mismatch of analog-to-digital converter in a receiver that employs quadrature bandpass sampling of the radio frequency (RF) signal. It is shown that the clock timing mismatch introduces not only symbol timing offset but also image interference, that is, the interference between in-phase and quadrature signals. Then, a mismatch compensation scheme and a pilot-aided mismatch estimation method are proposed. We also propose a blind estimation method, where the clock timing mismatch can be estimated from the second order statistics of the sampled sequences. Numerical simulations confirm the validity of the proposed methods, even in the presence of unknown channel.

This paper proposes a mixed-reality shopping system for users who do not own a PC but do own a tablet. In this system, while viewing panoramic images photographed along the aisles of a real store, the user can move freely around the store. Products can be selected and freely viewed from any angle. Furthermore, by utilizing a Photo-based augmented reality (Photo AR) technology the product can be displayed as if it were in the hands of the user. The results of a user evaluation showed that even though the proposed system uses a tablet with a smaller screen it was preferred over a conventional e-commerce site using a larger monitor.

The cancellation of in-band self-interference caused by simultaneous transmission and reception is an essential issue to realize full-duplex wireless communication. In this paper, we investigate the impact of transmitter IQ imbalance on self-interference cancellation. From our results, it is shown that the residual self-interference in the presence of transmitter IQ imbalance has considerably large power. To cancel it, a baseband cancellation signal generated by widely linear (WL) filtering is proposed and the optimal WL filters are derived. For practical implementation, we also propose an adaptive algorithm based on the augmented complex least mean square method to directly obtain the WL filters. Simulation results demonstrate the validity of the proposed algorithm.

N-continuous orthogonal frequency division multiplexing (OFDM) is a modulation technique that has a lower sidelobe than the original OFDM as a result of the continuous connection with its higher-order derivatives between the OFDM symbols. However, N-continuous OFDM requires an iterative algorithm for removing correction symbols from received signals at the receiver. In this paper, a method called N-continuous symbol padding is proposed, which inserts N-continuous OFDM correction symbols only into the guard interval and seamlessly connects each OFDM symbol, thereby suppressing the sidelobes. It has been demonstrated by numerical experiments that the N-continuous symbol padding method provides power spectral density and SER characteristics equal to or better than those of the conventional method, without using an iterative algorithm. This method is particularly effective for a system with a small number of subcarriers.

The paper proposes a novel estimation of carrier frequency offset (CFO) and I/Q imbalance, based on the popular repeated preamble. By investigating the nonlinear least squares cost function of CFO estimation, we discover a general relation among three arbitrary pilot symbols and derive several useful linear equations. Then, we propose a corresponding linear least squares estimation of unsigned CFO with explicit closed-form solution. Using the tentative CFO estimate, the I/Q imbalance can be estimated with sign ambiguity. Notice that the taps of the FIR filter representing frequency-dependent imbalance in practical frond-ends are constrained, we also propose a novel computation-free detection method to solve the sign ambiguity.

This paper proposes a novel time domain blind compensation for frequency-independent and frequency-dependent I/Q imbalance in direct-conversion receivers. Analysis of a difference filter representing the frequency-dependent I/Q imbalance shows that the filter taps are tightly constrained by analog front-end image attenuation (IA). For practical front-ends with reasonable IA, it is proved that the difference filter is minimum phase. We also show that the magnitude response of the difference filter can be obtained from the branch signal autocorrelations. Then, the magnitude response can be used to determine the corresponding minimum phase response. Subsequently, from the cross-correlation of the branch signals, we can estimate the frequency-independent phase imbalance. Since the proposed method has an analytical solution, it can be easily implemented. Simulations of various scenarios confirm its validity and its superior compensation performance.

A novel blind frequency-dependent I/Q imbalance compensation for direct-conversion receivers is proposed. By analyzing the filter which represents branch mismatches, we prove its minimum phase response, for practical front-ends with reasonable image attenuation quality. We also reveal that the received branch signals will have the same autocorrelation in the absence of frequency-dependent imbalance. The proposed method is to obtain the difference filter's magnitude response from the branch signals autocorrelations, and uniquely determine the corresponding minimum phase response afterwards. Then, the frequency-independent imbalance can be estimated subsequently from the branch signals cross-correlation. The proposed method has an analytical solution therefore can be easily implemented. Simulations confirm its superior performance in various I/Q imbalance scenarios.

N-continuous orthogonal frequency division multiplexing (OFDM) is a modulation technique that produces smaller sidelobes than standard OFDM as a result of continuous connections with higher-order derivatives between OFDM symbols. In this method, the transmitter inserts symbols into the signal such that inter-symbol connections are continuous through Nth-order derivatives. On the receiving side, the inserted symbols are deleted using an iterative algorithm and data symbols are demodulated. The conventional method has required numerous iterations, which is a problem due to the calculation load on the receiver. This paper therefore proposes a method by which the power of high frequency insertion symbols is canceled, and cancellation tones are used to allow a reduction in the number of receiver iterations on the receiving side. Numerical experimentation shows that by increasing transmit power by 1%, the number of receiver iterations can be reduced from 8 to 2.

N-continuous OFDM is a modulation technique that produces a lower sidelobe than the original OFDM as a result of the continuous connection with its higher-order derivatives between the OFDM symbols. However, when there are low data channels, N-continuous OFDM has a high symbol error rate. In this paper, the authors propose a method for improving the symbol error rate of N-continuous OFDM using SLM and evaluate the effectiveness of this approach by means of numerical experiments. The experimental results showed that this method significantly improves the symbol error rate in systems with low data channels, and the authors confirmed the effectiveness of the method in systems with a scalable bandwidth, such as LTE.

The estimation of carrier frequency offset (CFO) and DC offset is a crucial issue in an OFDM direct-conversion receiver. Recently, a blind CFO estimator based on the correlation of the received OFDM samples has been proposed. In this paper, this symbol-wise CFO estimator is extended to consider the presence of DC offset. Assuming a constant DC offset during one OFDM symbol period, we can roughly estimate the DC offset by averaging the whole symbol, and then removing it to perform the CFO estimation. Also, by rewriting the signals in matrix forms, we propose a new cost function which can be used to estimate the CFO free of DC offset. The validity of the proposed estimators is confirmed by simulations.

In this paper, we propose a novel equalization method for OFDM systems without guard interval (GI). The performance of GI-free OFDM system is usually limited by inter-symbol interference (ISI) and inter-carrier interference (ICI). The proposed method is to firstly detect the tail part of transmitted OFDM symbol, then eliminate the ISI and ICI to recover the whole symbol. We find that the tail part can be obtained free of ISI and ICI, after frequency domain equalization of a proper channel, where proper means that the channel inverse is or can be approximated as FIR filter with suitable length. Since a minimum phase channel is usually proper, we also incorporate a time-domain equalizer to convert non-minimum phase channel into minimum-phase. The validity of the proposed method is confirmed by simulations.

We propose a novel pilot-aided compensation scheme for carrier frequency offset (CFO) and I/Q imbalance. The proposed scheme comprises a generalized periodic pilot and a low-complexity acquisition algorithm, where the CFO and the coefficients for I/Q imbalance compensation can be obtained in explicit closed-form.

In OFDM systems, since carrier frequency offset (CFO) destroys the orthogonality among subcarriers, whose estimation/compensation is a critical problem. However, the CFO estimation suffers from DC offset (DCO) generated in low-cost direct-conversion receivers (DCRs). More seriously, in general, DCO is time-varying due to the automatic gain control. In this paper, we propose a novel CFO estimator in the presence of time-varying DCO. It is shown the residual DCO after high-pass filtering varies in a linear fashion. Based on this observation and the periodicity of the training sequence, we derive a CFO estimator independent of DCO. Simulation results show the validity of the proposed estimation method.

We propose a novel subcarrier allocation (SCA) based approach for compensating carrier frequency offset (CFO) and I/Q imbalances in direct-conversion OFDM receivers. From the matrix representation of OFDM signals with CFO and I/Q imbalances, maximum likelihood CFO estimation and the associated SCA are given. Then, an SCA-based algorithm is proposed for the I/Q imbalances compensation. Moreover, the proposed approach is extended to a blind compensation scheme for OFDM signals with asymmetric SCA.

Recently, based on modified periodic pilot (MPP), a compensation scheme for carrier frequency offset (CFO) and I/Q imbalances in direct-conversion wireless receivers, has been proposed. However, it cannot be applied to IEEE 802.11 a WLAN directly, where only periodic pilot (PP) exists. In this paper, the impact of PP on the MPP-based scheme is studied. The results indicate that PP causes fatal degradation of performance, by inducing sign ambiguity in CFO estimation and invalidating the compensation of I/Q imbalances in the absence of CFO. Then, an efficient compensation scheme for the IEEE 802.11 a WLAN is proposed. In the proposed scheme, the CFO estimation is enhanced by a CFO sign detection and an autocorrelation-based estimator. Also, a novel I/Q imbalances compensation algorithm robust to the CFO value is proposed. Taking full advantage of the 802.11 a preamble, the proposed scheme is competent for various scenario of CFO and I/Q imbalances, which is confirmed by simulations.

In orthogonal frequency division multiplexing (OFDM) systems with direct-conversion transceivers, transmission performance is severely degraded by analog impairments, typically, carrier frequency offset, transmitter/receiver I/Q imbalance, and DC offset. The existing research considered only part of these impairments. In this paper, we analyze the OFDM signal corrupted by all these impairments. Then, a hybrid domain compensation scheme consisting of the time-domain and frequency-domain compensation is proposed. For the purpose of practical implementation, we also propose a comparable preamble, with which the compensation coefficients can be obtained by a low- complexity acquisition algorithm.

In direct-conversion orthogonal frequency division multiplexing receivers, the compensation of carrier frequency offset (CFO) and I/Q imbalance is critical. In the existing modified periodic pilot based scheme, I/Q imbalance compensation completely depends on CFO estimation, which however needs a computational expensive one-dimensional search and correct timing synchronization. In this paper, we propose a novel periodic pilot and an associated compensation method. Taking advantage of the pilot's periodicity, the proposed scheme simultaneously estimates the CFO and coefficients of I/Q imbalance compensation, in closed forms based on the linear least squares algorithm. The proposed scheme not only has significantly reduced complexity, but also is inherently robust to timing error. Simulations confirm the validity and superiority of the proposed scheme.

In this paper, a neural network (NN) for peak power reduction of orthogonal frequency-division multiplexing (OFDM) signals is improved in order to suppress its computational complexity. Numerical experiments show that the proposed NN has less computational complexity than the conventional one. The number of IFFT in NN can be reduced to half, and the computational time can be suppressed by 32.7%. From the HDL simulation for FPGA implementation, hardware resouces are approximately suppressed by about 30%.

In this letter, a blind joint carrier frequency offset and DC offset (DCO) estimator for OFDM systems is proposed. By exploiting the underlying subspace of the received OFDM signals after the time-domain-average based coarse DCO cancellation, the proposed estimator can achieve excellent performance, which is demonstrated by simulations.

Carrier frequency offset (CFO) and I/Q imbalances severely degrade the performance of direct-conversion OFDM receiver. In this paper, based on the subcarrier allocation (SCA) of OFDM signal, a novel approach for compensating CFO and I/Q imbalances is proposed. First, we derive a useful matrix representation of OFDM signal with CFO and I/Q imbalances. Then, maximum likelihood CFO estimation, as well as the associated SCA, are given. With the CFO estimate, a SCA-based algorithm which has a close-form solution, is proposed for the compensation of I/Q imbalances. Furthermore, due to the correspondence between the CFO estimate and the compensation of I/Q imbalances, the proposed approach can be extended to a blind compensation scheme, suitable for OFDM signals with asymmetric SCA. Finally, computer simulations demonstrate the validity of the proposed approach.

In an OFDM receiver with direct-conversion architecture, DC offset (DCO) and carrier frequency offset (CFO) cause a severe performance degradation. Recently, by investigating the subspace of OFDM signal after removing the coarse DCO estimate obtained via a time-domain average, we have proposed a null space based estimator (NSE), for blind CFO and DCO estimation. In this paper, we analyze the cost function of the NSE, and show that the full performance NSE is complexity reducible, which can indeed lead to a common null space based estimator (CNSE). Also, we develop a maximum-likelihood estimator (MLE), and prove that the CNSE is equivalent to the MLE. Furthermore, the Cramer-Rao bound of CFO estimation in the presence of DCO is given. Finally the analysis results are verified by simulations.

In wireless OFDM systems, the coexistence of direct current (DC) offset and carrier frequency offset (CFO) will severely degrade the transmission performance. This problem was only partially solved by pilot-aided approaches, at the expense of bandwidth. In this paper, we analyze the subspace structure of the received OFDM signal after coarse DC offset cancelation by time-domain average. Then, a novel blind estimator, which is able to estimate both CFO and DC offset in the absence of the pilot, is proposed. The validity of the proposed estimator is demonstrated by simulation results.

This article proposes a novel orthogonal frequency-division multiplexing (OFDM) system based on polynomial cancellation coded OFDM (PCC-OFDM). This proposed system can reduce peak-to-average power ratio (PAPR) by a neural phase rotator and it does not need any side information to transmit phase rotation factors. Moreover, this system can suppress intercarrier interference (ICI) by two techniques. One is a common phase error (CPE) compensation technique which allows estimating frequency offset at receiver. The other is a ICI suppression technique by using the replica method. We can generate a replica of the transmitted OFDM signal by using estimated frequency offset and suppress ICI at receiver. From numerical experiments, it is shown that our system can reduce PAPR and ICI at the same time and improve BER performance effectively.

Carrier frequency offset (CFO) in orthogonal frequency divisional multiplexing (OFDM) system severely degrades the transmission performance. This frequency offset can be divided into an integer part and a fractional part. The fractional part mainly introduces inter-carrier interference (ICI), while the integer part causes frequency ambiguity. In this paper, based on the underlying structure of the received OFDM symbols, a novel blind algorithm is proposed to estimate the integer part of CFO. Compared with the conventional M&M's blind integer CFO estimator, the proposed one has considerably reduced computational load. Furthermore, simulation results show that under the multipath fading channel, the proposed estimator has lower probability of failure than the M&M's estimator

This article proposes a novel OFDM system that is based on PCC-OFDM and can reduce ICI and PAPR at the same time by using neural phase rotator. The proposed system does not use side information to transmit phase rotation factors. It is clarified from numerical experiments that the system can reduce PAPR of PCC-OFDM, and BER performance is improved drastically

The aim of this paper is to reduce computational complexity of the neural network for PAPR reduction of OFDM signal, and to implement the neural network including 1,024 neurons by FPGA for practical OFDM transmitter of the terrestrial digital broadcast. A couple of IDFTs reduce computational complexity of the neuron updating from O(N/sup 2/) to O(N log N). This neural network is designed using VHDL for Xilinx FPGA device, XC2V6000, and 1,024-neuron system is implemented by less than 30% of resources of the device.

A novel method for the peak-to-average power ratio reduction on multicarrier modulation systems is proposed. The reduction problem is formulated as a combinatorial optimization, and is solved by using the chaotic neural network (CNN), which has easy structure and suitable for real time optimization. Experimental results show that CNN has better performance than conventional methods. Finally we consider relationship between a parameter of CNN and the chaotic behavior.

The correlation LMS (CLMS) algorithm and its extended version (ECLMS) have been proposed to solve the double-talk problem in the echo canceling for the teleconference system by authors previously. However, the computational load of the ECLMS is too large to be implemented. Here, we propose a new fast implementation of the ECLMS algorithm using frequency domain based on time lag of the correlation function. Also, we defined initialization and normalization methods. The performance has been verified by computer simulation using a speech signal. The computational complexity of the proposed algorithm is reduced to only 2.7% of the ECLMS algorithm.

The purpose of the paper is to derive a simplex genetic algorithm (GA) for blind equalization using RBF networks. In order to reduce the computation cost, this algorithm searches the center's elements instead of centers because of the inter-relation between the centers. Furthermore, by introducing the simplex operator into the GA, the proposed algorithm presents a fast convergence characteristic in simulation.

The design of a neural network-based estimation system for nonlinear economic time series, based on the Volterra model, is presented. We use ECLMS (extended correlation least mean squares) algorithms as the noise cancelling method for nonlinear time series. The validity of the proposed method is demonstrated by estimating a high-order Volterra model with ARCH (autoregressive conditional heteroscedasticity) errors. This algorithm has a good performance in solving nonlinear economic time-series estimation problems.

In this paper, a mixed sensitivity weighting strategy for H/sup /spl infin// controller design for an induction generator/infinity bus windmill power system is presented. The approach is based on a form of quasi-linearization which makes the windmill power system a linear function of the control input. The system controller is then synthesized by using H/sup /spl infin// standard controller design techniques. A combination of additive and multiplicative uncertainty representation is used to achieve the robust stability for a wide range of operating conditions. The capability of the proposed controller to damp out the oscillations of the power and angular velocity, and the robustness with respect to the system parameter variations and model errors are evaluated in the simulation study.

A method with 4th-order cumulant is proposed for nonlinear channel identification. Compared with the conventional method which uses 3rd-order cumulant, the proposed method does not need to use any constraints. Since the cost function with higher order statistics has local minima, we also propose to use a hybrid genetic algorithm (GA) to minimize the cost function. The applicability of the proposed method is demonstrated by computer simulations.

The radial basis function (RBF) network has been used in a digital channel's equalization for its identical structure to the optimal Bayesian Symbol-decision equalizer. The important problem in the equalization using RBF is to find the correct centers. A clustering algorithm has been proposed to find the desired centers. In fact, the problem can be changed to find the center's element set because of the inter-relation between the center's elements. A fast clustering algorithm using the inter-relation for RBF network equalization is proposed. The simulation results show its better convergency and less calculation than the traditional clustering algorithm.

The article describes the use of the complex adaptive line enhancer (CALE) for estimating a wind velocity in the presence of ground clutter. Experimental results from the real data are presented and the performance of the proposed method is compared with that of a conventional method. It is concluded that in the simulation, that resulting detection of the proposed method is shown, and we can see it is possible to detect the wind velocity in spite of the influence of the ground clutter on the wind profiler.

For handling human's subjective thought and judgment quantitatively, fuzzy theory has been utilized in various sphere of science, especially in the field of decision-making. Because the mode of human's thinking is an exceeding vague system, the fuzziness is regarded as the most effective way to reflect it. Therefore, it arrests many researcher's attention in recent years. In this paper, we utilize the fuzzy relation in the famous decision-making method of AHP (analytic hierarchy process) for solving the problem which is difficult to evaluate the alternatives by some vague criteria. We consider to establish the fuzzy relation between the vague criteria and some measurable items and make the decision through evaluating the alternatives by the measurable items.

The purpose of this paper is to construct a new two-dimensional (2-D) adaptive joint-process IIR filter with the generalized lattice structure. This filter is an IIR lattice filter with the restricted feedback structure, but the backward prediction error fields for every stage, like FIR lattice filter, are orthogonal which produce fast convergence. More importantly it can borrow both FIR and IIR features and simultaneously holds the well-known merits of lattice structure.