Pre-filtering Technique Research Articles

Gene selection using hybrid binary black hole algorithm and modified binary particle swarm optimization

In cancer classification, gene selection is an important data preprocessing technique, but it is a difficult task due to the large search space. Accordingly, the objective of this study is to develop a hybrid meta-heuristic Binary Black Hole Algorithm (BBHA) and Binary Particle Swarm Optimization (BPSO) (4-2) model that emphasizes gene selection. In this model, the BBHA is embedded in the BPSO (4-2) algorithm to make the BPSO (4-2) more effective and to facilitate the exploration and exploitation of the BPSO (4-2) algorithm to further improve the performance. This model has been associated with Random Forest Recursive Feature Elimination (RF-RFE) pre-filtering technique. The classifiers which are evaluated in the proposed framework are Sparse Partial Least Squares Discriminant Analysis (SPLSDA); k-nearest neighbor and Naive Bayes. The performance of the proposed method was evaluated on two benchmark and three clinical microarrays. The experimental results and statistical analysis confirm the better performance of the BPSO (4-2)-BBHA compared with the BBHA, the BPSO (4-2) and several state-of-the-art methods in terms of avoiding local minima, convergence rate, accuracy and number of selected genes. The results also show that the BPSO (4-2)-BBHA model can successfully identify known biologically and statistically significant genes from the clinical datasets.

Analytical methods for prefiltering of close approaches between space objects

In the history of space, for the first time an operational US communications satellite Iridium 33, in low-Earth orbit was struck and destroyed by the collision of a long defunct Russian communications satellite COSMOS 2251 on 10th February 2010. It is necessary to understand the circumstances of this collision for avoiding similar incidents in the future. In this direction a detailed conjunction analysis of all space objects is essential. Since a large number of objects are orbiting in space, it is very difficult to find out the close approach for all objects with simulations. Hence, a study related to the prefiltering of close approaches between space objects using analytical techniques is carried out in this paper. It is found that the presented methodology with prefiltering techniques is effective in reducing the number of objects for simulations.Keywords: Collision, orbit, prefiltering, debris, operational satellite

Cluster-head based feedback for simplified time reversal prefiltering in ultra-wideband systems

Time-reversal prefiltering (TRP) technique for impulse radio (IR) ultra wide-band (UWB) systems requires a large amount of feedback to transmit the channel impulse response from the receiver to the transmitter. In this paper, we propose a new feedback design based on vector quantization. We use a machine learning algorithm to cluster the estimated channels into several groups and to select the channel cluster heads (CCHs) for feedback. In particular, CCHs and their labels are recorded at both side of the UWB transceivers and the label of the most similar CCH to the estimated channel is fed back to the transmitter. Finally, the TRP is applied using the feedback CCH. The proposed digital feedback provides three main advantages: (1) it significantly reduces the dedicated bandwidth required for feedback; (2) it considerably improves the speed of transceivers; and, (3) it is robust to noise in the feedback channel since few bytes are required to send the codes that can be heavily error protected. Numerical results on standard UWB channel models are discussed, showing the advantage of the proposed solution.

A Statistically Robust Approach to Acoustic Impulse Response Shaping

Acoustic impulse response shaping is a prefiltering technique to reduce the perceptible effects of room reverberation. The room impulse responses to be shaped must first be measured, and these measurements can contain errors. Furthermore, room responses vary with changes in temperature and humidity and also with changes in measurement position. This letter presents a method for enhancing the robustness of the shaping procedure so that the effects of these errors and changes are minimized. The method uses a stochastic model of the channel variations to explicitly limit the probability of large deviations from the desired performance. The method is evaluated on realistic channel perturbations and the resulting shaped responses are shown to comply with the robustness specification.

The Prefiltering Techniques in Emotion Based Place Recommendation Derived by User Reviews

Context-aware recommendation systems attempt to address the challenge of identifying products or items that have the greatest chance of meeting user requirements by adapting to current contextual information. Many such systems have been developed in domains such as movies, books, and music, and emotion is a contextual parameter that has already been used in those fields. This paper focuses on the use of emotion as a contextual parameter in a tourist destination recommendation system. We developed a new corpus that incorporates the emotion parameter by employing semantic analysis techniques for destination recommendation. We review the effectiveness of incorporating emotion in a recommendation process using prefiltering techniques and show that the use of emotion as a contextual parameter for location recommendation in conjunction with collaborative filtering increases user satisfaction.

Two Efficient Techniques to Find Approximate Overlaps between Sequences.

The next-generation sequencing (NGS) technology outputs a huge number of sequences (reads) that require further processing. After applying prefiltering techniques in order to eliminate redundancy and to correct erroneous reads, an overlap-based assembler typically finds the longest exact suffix-prefix match between each ordered pair of the input reads. However, another trend has been evolving for the purpose of solving an approximate version of the overlap problem. The main benefit of this direction is the ability to skip time-consuming error-detecting techniques which are applied in the prefiltering stage. In this work, we present and compare two techniques to solve the approximate overlap problem. The first adapts a compact prefix tree to efficiently solve the approximate all-pairs suffix-prefix problem, while the other utilizes a well-known principle, namely, the pigeonhole principle, to identify a potential overlap match in order to ultimately solve the same problem. Our results show that our solution using the pigeonhole principle has better space and time consumption over an FM-based solution, while our solution based on prefix tree has the best space consumption between all three solutions. The number of mismatches (hamming distance) is used to define the approximate matching between strings in our work.

State Observer Design for Monitoring the Degree of Polymerization in a Series of Melt Polycondensation Reactors

A nonlinear reduced-order state observer is applied to estimate the degree of polymerization in a series of polycondensation reactors. The finishing stage of polyethylene terephthalate synthesis is considered in this work. This process has a special structure of lower block triangular form, which is properly utilized to facilitate the calculation of the state-dependent gain in the observer design. There are two possible on-line measurements in each reactor. One is continuous, and the other is slow-sampled with dead time. For the slow-sampled titration measurement, inter-sample behavior is estimated from an inter-sample output predictor, which is essential in providing continuous corrections on the observer. Dead time compensation is carried out in the same spirit as the Smith predictor to reduce the effect of delay in the measurement outputs. By integrating the continuous-time reduced-order observer, the inter-sample predictor and the dead time compensator together, the degree of polymerization is accurately estimated in all reactors. The observer performance is demonstrated by numerical simulations. In addition, a pre-filtering technique is used in the presence of sensor noise.

The Development of Terrain Pre-filtering Technique Based on Constraint Mode Tire Model

The Development of Terrain Pre-filtering Technique Based on Constraint Mode Tire Model

Zero-phase velocity tracking of vibratory systems

The focus of this paper is on the development of an input shaper/time-delay filter that permits the precise tracking of a ramp input, while eliminating residual vibrations. Zero phase error velocity tracking is often required in applications where moving parts have to be mated, such as manufacturing lines with high production output. A closed form solution to a pre-filtering technique is presented which achieves the desired characteristics. The performance of this technique is compared with other input shaper designs in current literature, and is shown to achieve smaller settling time and maintain zero steady state phase error without a priori knowledge of the initiation and termination of ramp profiles. The technique is then physically applied to a rotary pendulum to demonstrate the consistency of its ramp tracking and vibration reduction capabilities.

Output bandwidth enhancement of a pulsed ultrasound system using a flat envelope and compensated frequency-modulated input signal: Theory and experimental applications

A pre-filtering technique was used with an ultrasound transmit–receive system to increase the output signal bandwidth beyond that obtained with either conventional pulsing or linear frequency modulated (LFM) input signals. A compensated frequency modulated (CFM) excitation signal, with flat envelope and non-uniformly time-spaced amounts of spectral energy density, was applied to the system input. Two experiments were conducted to demonstrate practical applications of the proposed technique. Initially, in comparison to the bandwidth of the output signal generated by a LFM excitation, the system output signal bandwidth tripled with a pair of transducers. In a second experiment, the attenuation coefficient of a viscous fluid was measured and compared with the theoretical (assessed) value. Measured values for the attenuation coefficient were within ±0.03 relative of the theoretical values. The CFM input signal was shown to have enough energy to produce a larger −6dB bandwidth (three times more) compared to LFM signals.

Weak signal acquisition enhancement in software GPS receivers – Pre-filtering combined post-correlation detection approach

The Civilian Global Positioning System (GPS) receivers often encounter problems of interference and noise which degrade the receiver performance. The conventional methods of parallel code phase search acquisition with coherent, non-coherent and differential coherent detection for weak signal acquisition fail to enhance the signal for all conditions especially, when the Carrier to Noise ratio (C/N0) falls below 15dB-Hz. Hence, the GPS receiver has to employ sophisticated techniques to excise the noise and to improve the Signal-to-Noise Ratio (SNR) of the signal for further processing. In this paper, a pre-filtering technique of reduced rank Singular Spectral Analysis (SSA) is proposed for noise excision and is processed through coherent, non-coherent and differential detection postcorrelation methods to retrieve the signal embedded in noise. Monte Carlo simulations carried out to examine the acquisition sensitivity at various power levels with the different postcorrelation approaches indicate that the SSA combined with differential detection approach provides a significant performance improvement with lesser mean acquisition time. It has 96% probability of detection at a worst signal power level of −159dBm (i.e. C/N0 15dB-Hz), compared to other conventional methods.

One-bit time reversal using binary pulse sequence for indoor communications

Time reversal (TiR) is a pre-filtering technique that exploits the propagation channel state information in order to reduce the complexity of a user’s terminal in a communication system. TiR transfers the system complexity to the base station and has been proposed for ultra wideband (UWB) communications in highly dispersive multipath environments. In TiR-UWB two complex tasks must be carried out by the base station. The first is the estimation of the channel state information of the user’s terminal, and the second is the generation of the time reversed channel signal. In this paper, the use of a correlation receiver for the estimation of the multipath components (MPCs) of the propagation channel is proposed. Then, a novel binary time reversal (BTiR) method that makes use of the resolvable MPCs to simplify the transceiver tasks is introduced. When using BTiR the communication system can be regarded as a direct sequence spread spectrum (DSSS) scheme in which the spreading chips are provided by the propagation channel. The performance of the proposed BTiR scheme is assessed by using measurements of UWB spatial channels in a typical indoor environment.

Optimum controller design of an overhead crane: Monte Carlo versus pre-filter-based designs

In this paper, we consider an overhead crane model with some of its parameters known within given upper and lower bounds. It is shown that a controller with single valued gains based on the nominal values of the parameters could lead to unsatisfactory performance. Two design methodologies are applied to guarantee the desired performance of the considered overhead crane model and their results are compared. The first method utilizes the Monte Carlo approach to find optimum values of the controller gains based on minimizing a least-square error function representing the deviation of the swing angle from a desired trajectory. The second method uses a pre-filter to ensure that the closed-loop performance lies within two given desired responses. Simulation results are provided to compare the performance of the two methods where both show reasonable responses. The Monte Carlo-based approach, however, does not require additional hardware components, compared with the pre-filter technique.

Sub-carrier shaping for BOC modulated GNSS signals

One of the main challenges in Binary Offset Carrier (BOC) tracking is the presence of multiple peaks in the signal autocorrelation function. Thus, several tracking algorithms, including Bump-Jump, Double Estimator, Autocorrelation Side-Peak Cancellation Technique and pre-filtering have been developed to fully exploit the advantages brought by BOC signals and mitigate the problem of secondary peak lock. In this paper, the advantages of pre-filtering techniques are explored. Pre-filtering techniques based on the concepts of Zero-Forcing and Minimum Mean Square Error equalization are proposed. The BOC sub-carrier is modeled as a filter that introduces secondary peaks in the autocorrelation function. This filtering effect can be equalized leading to unambiguous tracking and allowing autocorrelation shaping. Monte Carlo simulations and real data analysis are used to characterize the proposed algorithms.

Transmitter pre-filtering for the downlink of a time-division-duplex/direct sequence-code division multiple access system over time-varying multipath fading channels

In this paper, we investigate an optimised transmitter pre-filtering technique for downlink time-division-duplex (TDD) code division multiple access (CDMA) communications, which employs the conventional matched filter (MF) detector at the mobile receivers. The proposed pre-filtering technique eliminates the multiple-access interference and intersymbol interference (MAI/ISI) effects by applying a very simple transmission scheme that combines a signal transformation with a cyclic prefix strategy under a power constraint condition. Two constrained pre-filtering transformations are suggested depending on the information required at the mobile unit. An open-loop transmitter pre-filtering is first formulated; however, this solution does not consider the properties of the noise at the mobile receiver. A second solution is then presented via a closed-loop transmitter pre-filtering that includes an optimum gain for a given transmit and noise power. Some associated issues such as system efficiency, computational complexity and channel estimation errors are also addressed. Simulation results show that the proposed transmitter pre-filtering scheme can be used to increase the system performance and capacity. In addition, its performance is compared with another similar transmit pre-processing scheme in order to evaluate the performance improvement by the proposed algorithm.

Transmission Strategies for MISO Downlink MC-CDMA Mobile Systems

This paper proposes two space-frequency schemes with a multi-user pre-filtering technique for downlink (DL) multicarrier code division multiple access (MC-CDMA) systems. We consider the use of antenna arrays at the base station (BS) and a single antenna at the mobile terminal (MT) and derive the proposed multi-user pre-filtering technique that modulates the transmitted signal to eliminate the effects of multiple access interference (MAI) and channel distortions at the mobile terminals, while maintaining low MT complexity. Two types of detectors are considered at the MT: simple despreading and single user equalizers. The performances of the proposed schemes are compared to those of other transmit signal design approaches that have been recently proposed for DL MC-CDMA, considering both typical indoor and pedestrian scenarios, and channel coding based on UMTS specifications.

Application of Hybrid c-Means Clustering Models in Inhomogeneity Compensation and MR Brain Image Segmentation

Intensity inhomogeneity or intensity non-uniformity (INU) is an undesired phenomenon that represents the main obstacle for MR image segmentation and registration methods. Various techniques have been proposed to eliminate or compensate the INU, most of which are embedded into clustering algorithms. This paper proposes a hybrid c-means clustering approach to replace the FCM algorithm found in several existing solutions. The novel clustering model is assisted by a pre-filtering technique for Gaussian and impulse noise elimination, and a smoothening filter that helps the c-means algorithm at the estimation of inhomogeneity as a slowly varying additive or multiplicative noise. The slow variance of the estimated INU is assured by a smoothening filter that performs a context dependent averaging, based on a morphological criterion. The experiments using 2-D synthetic phantoms and real MR images show that the proposed method provides more accurate and more efficient segmentation than the FCM based approach. The produced segmentation and fuzzy membership values can serve as excellent support for 3-D registration and segmentation techniques.

Increasing capacity of blind mobile system using pre-filtering technique

Increasing mobile system capacity is a hot topic in communication research. A new beamforming technique using a pre-filtering process that decreases noise and interference effects to improve capacity of cellular systems is proposed. Simulation results show significant improvement over the conventional beamforming techniques. The simulation is based on the constant modulus algorithm as a typical blind beamforming technique. This capacity enhancement is achieved with slight increase in computational cost.

Improved Intensity Inhomogeneity Correction Techniques in MR Brain Image Segmentation

Intensity inhomogeneity or intensity non-uniformity (INU) is an undesired phenomenon that represents the main obstacle for MR image segmentation and registration methods. Various techniques have been proposed to eliminate or compensate the INU, most of which are embedded into clustering algorithms. This paper proposes a pre-filtering technique for Gaussian and impulse noise elimination, and a smoothening filter that assists the fuzzy c-means (FCM) algorithm at the estimation of inhomogeneity as a slowly varying additive or multiplicative noise. The segmentation is produced by FCM algorithm together with the INU estimation. The slowly varying behaviour of the bias or gain field is assured by a smoothening filter that performs a context dependent averaging, based on a morphological criterion. The experiments using 2-D synthetic phantoms and real MR images show, that the proposed method provides accurate segmentation. The produced segmentation and fuzzy membership values can serve as excellent support for 3-D registration and segmentation techniques.

Non-Linear Pre-Coding for Multiple-Antenna Multi-User Downlink Transmissions with Different QoS Requirements

An efficient non-linear pre-filtering technique based on Tomlinson-Harashima pre-coding (THP) has recently been proposed by Liu and Krzymien in the context of multiple-antenna multi-user systems. The algorithm is based on the zero-forcing (ZF) criterion and is derived under the assumption that the number of users is equal to the number of transmit antennas. In contrast to other existing methods, it ensures the same signal-to-noise-ratio (SNR) at each mobile terminal so as to guarantee a fair treatment of all active users. In multimedia applications, however, several types of information with different quality-of-service (QoS) requirements must be sent simultaneously on different subchannels. Motivated by the above problem, in the present work we design a THP-based pre-filtering algorithm for multiple-antenna multi-user systems in which the base station allocates the transmit power according to the QoS requirement of each active user. Compared to existing alternatives, the proposed scheme is simpler to implement and suited for practical situations where the number of active users may be less than the number of transmit antennas