In recent years, the space-time block coding (STBC) method has attracted attention to provide transmission diversity in mobile communication systems. Although the STBC method is very effective in slow fading environments, its performance in fast fading environments has yet to be clearly verified. In this paper we propose a railway radio communication system using space-time coding in cooperation with two base stations. Here, we considered the differential STBC (D-STBC) method in railway communication system to overcome difficulties caused by the fast fading environment. We have compared the performance of STBC and D-STBC method where there is frequency offset between two base stations. Moreover, we have presented the simulation result of overall performance of the system including frequency offset and transmission time delay when operating D-STBC method. The overall evaluation on this paper shows that the D-STBC method is suitable for realizing highly reliable railway communication systems.

Among spatial diversity schemes, orthogonal space-time block code (OSTBC) and cyclic delay diversity (CDD) have been widely studied for the cooperative wireless relaying system. However, conventional OSTBC and CDD cannot cope with change in the number of relays owing to low throughput or error performance. In this letter, we propose the space-time cyclic delay diversity (STCDD) scheme which provides good error performance and full rate. Simulation results show that bit error rate (BER) performance of the proposed STCDD is superior to that of OSTBC and CDD when sufficient quality of source-relay channels are guaranteed.

We analyze the carrier dynamics in MOSFETs under low-voltage operation. For this purpose the displacement (charging/discharging) current, induced during switching operations is studied experimentally and theoretically for a 90 nm CMOS technology. It is found that the experimental transient characteristics can only be well reproduced in the circuit simulation of low voltage applications by considering the carrier-transit delay in the compact MOSFET model. Long carrier transit delay under the low voltage switching-on operation results in long duration of the displacement current flow. On the other hand, the switching-off characteristics are independent of the bias condition.

This paper proposes joint maximum a posteriori (MAP) detection and spatial filtering for MIMO-OFDM mobile communications; it offers excellent receiver performance even over interference-limited channels. The proposed joint processor consists of a log likelihood generator and a MAP equalizer. The log likelihood generator suppresses cochannel interference by spatially filtering received signals and provides branch metrics of transmitted signal candidates. Using the branch metrics, the MAP equalizer generates log likelihood ratios of coded bits and performs channel decoding based on the MAP criterion. In the first stage, the log likelihood generator performs spatio-temporal filtering (STF) of the received signals prior to the fast Fourier transform (FFT) and is referred to as preFFT-type STF. Estimation of parameters including tap coefficients of the spatio-temporal filters and equivalent channel impulse responses of desired signals is based on the eigenvalue decomposition of an autocorrelation matrix of both the received and transmitted signals. For further improvement, in the second stage, the generator performs spatial filtering (SF) of the FFT output and is referred to as postFFT-type SF. Estimation of both tap coefficients of the spatial filters and channel impulse responses employs the recursive least squares (RLS) with smoothing. The reason for switching from preFFT-type STF into postFFT-type SF is that preFFT-type STF outperforms postFFT-type SF with a limited number of preamble symbols while postFFT-type SF outperforms preFFT-type STF when data symbols can be reliably detected and used for the parameter estimation. Note that there are two major differences between the proposed and conventional schemes: one is that the proposed scheme performs the two-stage processing of preFFT-type STF and postFFT-type SF, while the other is that the smoothing algorithm is applied to the parameter estimation of the proposed scheme. Computer simulations demonstrate that the proposed scheme can achieve excellent PER performance under interference-limited channel conditions and that it can outperform the conventional joint processing of preFFT-type STF and the MAP equalizer.

Microarray technology has been applied to various biological and medical research fields. A preliminary step to extract any information from a microarray data set is to identify differentially expressed genes between microarray data. The identification of the differentially expressed genes and their commonly associated GO terms allows us to find stimulation-dependent or disease-related genes and biological events, etc. However, the identification of these deregulated GO terms by general approaches including gene set enrichment analysis (GSEA) does not necessarily provide us with overrepresented GO terms in specific data among a microarray data set (i.e., data-specific GO terms). In this paper, we propose a statistical method to correctly identify the data-specific GO terms, and estimate its availability by simulation using an actual microarray data set.

We have evaluated the tunneling contact resistivity based on numerical calculation of tunneling current density across an AlGaN barrier layer in non-polar AlGaN/GaN heterostructures. In order to reduce the tunneling contact resistivity, we have introduced an n+-AlXGa1 - XN layer between an n +-GaN cap layer and an i-AlGaN barrier layer. The tunneling contact resistivity has been optimized by varying Al composition and donor concentration in n+-AlXGa1-XN. Simulation results show that the tunneling contact resistivity can be improved by as large as 4 orders of magnitude, compared to the standard AlGaN/GaN heterostructure.

Given a sparse linear system, A x = b, we can solve the equivalent system P A PT y = P b, x = PT y, where P is a permutation matrix. It has been known that, for example, when P is the RCMK (Reverse Cuthill-Mckee) ordering permutation, the convergence rate of the Krylov subspace method combined with the ILU-type preconditioner is often enhanced, especially if the matrix A is highly nonsymmetric. In this paper we offer a reordering heuristic for accelerating the solution of large sparse linear systems by the Krylov subspace methods with the ILUT preconditioner. It is the LRB (Line Red/Black) ordering based on the well-known 2-point Red-Black ordering. We show that for some model-like PDE (partial differential equation)s the LRB ordered FDM (Finite Difference Method)/FEM (Finite Element Method) discretization matrices require much less fill-ins in the ILUT factorizations than those of the Natural ordering and the RCMK ordering and hence, produces a more accurate preconditioner, if a high level of fill-in is used. It implies that the LRB ordering could outperform the other two orderings combined with the ILUT preconditioned Krylov subspace method if the level of fill-in is high enough. We compare the performance of our heuristic with that of the RCMK (Reverse Cuthill-McKee) ordering. Our test matrices are obtained from various standard discretizations of two-dimensional and three-dimensional model-like PDEs on structured grids by the FDM or the FEM. We claim that for the resulting matrices the performance of our reordering strategy for the Krylov subspace method combined with the ILUT preconditioner is superior to that of RCMK ordering, when the proper number of fill-in was used for the ILUT. Also, while the RCMK ordering is known to have little advantage over the Natural ordering in the case of symmetric matrices, the LRB ordering still can improve the convergence rate, even if the matrices are symmetric.

This paper proposes a new method to numerically obtain Floquet multipliers which characterize stability of periodic orbits of ordinary differential equations. For sufficiently smooth periodic orbits, we can compute Floquet multipliers using some standard numerical methods with enough accuracy. However, it has been reported that these methods may produce incorrect results under some conditions. In this work, we propose a new iterative method to compute Floquet multipliers using eigenvectors of matrix solutions of the variational equations. Numerical examples show effectiveness of the proposed method.

The paper demonstrates a novel two-peak negative differential resistance (NDR) circuit combining Si-based metal-oxide-semiconductor field-effect-transistor (MOS) and SiGe-based heterojunction bipolar transistor (HBT). Compared to the resonant-tunneling diode, MOS-HBT-NDR has two major advantages in our circuit design. One is that the fabrication of this MOS-HBT-NDR-based application can be fully implemented by the standard BiCMOS process. Another is that the peak current can be effectively adjusted by the controlled voltage. The peak-to-valley current ratio is about 4136 and 9.4 at the first and second peak respectively. It is very useful for circuit designers to consider the NDR-based applications.

Recently, various types of 3-D nonvolatile memory (NVM) devices have been researched to improve the integration density [1]-[3]. The NVM device of pillar structure can be considered as one of the candidates [4],[5]. When this is applied to a NAND flash memory array, bottom end of the device channel is connected to the bulk silicon. In this case, the current in vertical direction varies depending on the thickness of silicon channel. When the channel is thick, the difference of saturation current levels between on/off states of individual device is more obvious. On the other hand, when the channel is thin, the on/off current increases simultaneously whereas the saturation currents do not differ very much. The reason is that the channel potential barrier seen by drain electrons is lowered by read voltage on the opposite sidewall control gate. This phenomenon that can occur in 3-D structure devices due to proximity can be called gate-induced barrier lowering (GIBL). In this work, the dependence of GIBL on silicon channel thickness is investigated, which will be the criteria in the implementation of reliable ultra-small NVM devices.

This paper proposes an adaptive selection algorithm for the surviving symbol replica candidates (ASESS) based on the maximum reliability in maximum likelihood detection with QR decomposition and the M-algorithm (QRM-MLD) for Orthogonal Frequency Division Multiplexing (OFDM) multiple-input multiple-output (MIMO) multiplexing. In the proposed algorithm, symbol replica candidates newly-added at each stage are ranked for each surviving symbol replica from the previous stage using multiple quadrant detection. Then, branch metrics are calculated only for the minimum number of symbol replica candidates with a high level of reliability using an iterative loop based on symbol ranking results. Computer simulation results show that the computational complexity of the QRM-MLD employing the proposed ASESS algorithm is reduced to approximately 1/4 and 1/1200 compared to that of the original QRM-MLD and that of the conventional MLD with squared Euclidian distance calculations for all symbol replica candidates, respectively, assuming the identical achievable average packet error rate (PER) performance in 4-by-4 MIMO multiplexing with 16QAM data modulation. The results also show that 1-Gbps throughput is achieved at the average received signal energy per bit-to-noise power spectrum density ratio (Eb/N0) per receiver antenna of approximately 9 dB using the ASESS algorithm in QRM-MLD associated with 16QAM modulation and Turbo coding with the coding rate of 8/9 assuming a 100-MHz bandwidth for a 12-path Rayleigh fading channel (root mean square (r.m.s.) delay spread of 0.26 µs and maximum Doppler frequency of 20 Hz).

A PN junction current model for advanced MOSFETs is proposed and implemented into HiSIM2, a complete surface-potential-based MOSFET model. The model includes forward diode currents and reverse diode currents, and requires a total of 13 model parameters covering all bias conditions. Model simulation results reproduce measurements for different device geometries over a wide range of bias and temperature values.

The binary exponential back-off mechanism is one of the basic elements that constitute the IEEE 802.11 protocol. The models of the back-off mechanism have been developed with the assumption that collisions occur only due to nodes within the carrier sensing range and the collision probability is constant in steady-state. However, the transmission collisions can occur due to hidden nodes and these tend to occur consecutively, contrary to the collisions due to nodes within the carrier sensing range. Consecutive collisions increase the back-off time exponentially, resulting in less frequent transmission attempts. Ignoring this collision characteristic in modeling the back-off mechanism can produce large errors in the performance analysis of networks. In this paper, we model the back-off process as a Markov renewal process by taking into account such consecutive collisions due to hidden nodes, and then compare this result with NS2 simulation results. According to the simulation results, the proposed model reduces the relative error in the attempt probability by more than 90% in the grid topology. We also propose a new collision model for a simple network considering consecutive collisions due to hidden nodes, and analyze the network under saturated traffic condition using the proposed models. The attempt and collision probabilities are estimated with high accuracy.

The problem of analyzing transient in transmission line circuits is studied with emphasis on obtaining the transient voltage and current distributions. A new method for solving Telegrapher equation that characterizes the uniform transmission lines is presented. It not only gives the time domain solution of the line terminal voltage and current, but also their distributions within the lines. The method achieves its goal by treating the voltage and current distributions as distributed state variables and transforms the Telegrapher equation into an ordinary differential equation. This allows the coupled transmission lines to be treated as a single component that behaves like other lumped dynamic components, such as capacitors and inductors. Using Backward Differentiation Formulae for time discretization, the transmission line component is converted to its time domain companion model, from which its local truncation error for time step control can be derived. As the shapes of the voltage and current distributions get more complicated with time, they can be approximated by piecewise exponential functions with controllable accuracy. A segmentation algorithm is thus devised so that the line is dynamically bisected to guarantee that the total piecewise exponential approximation error is only a small fraction of the local truncation error. Using this approach, the user can see the line voltage and current at any point and time freely without explicitly segment the line before starting the simulation.

We introduce a novel power allocation scheme for decode-and-forward relaying system with partial channel state (CSI) information, i.e., the source knows full CSI of source-relay link but only statistical CSI of source-destination and relay-destination links. Our objective is to minimize the outage probability by jointly allocating the transmit power between the source and relays. To avoid exhaustive search, the MAOP scheme and the MMS scheme are proposed to approach the optimal allocation in the high and low signal-to-noise ratio regimes, respectively.

In this study, a performance isolation mechanism based on a fuzzy control technique is developed in such a way that ambiguous situations caused when estimating the workload of cluster-based web servers, client request rates, and dynamic request rates can be represented effectively. The proposed mechanism involving a fuzzy-based technique is compared with a non-fuzzy technique in terms of the response time in the 95th percentile. Experiments showed that the proposed technique improves the performance of web servers that provide differentiated services.

Image restoration based on Bayesian estimation in most previous studies has assumed that the noise accumulated in an image was independent for each pixel. However, when we take optical effects into account, it is reasonable to expect spatial correlation in the superimposed noise. In this paper, we discuss the restoration of images distorted by noise which is spatially correlated with translational symmetry in the realm of probabilistic processing. First, we assume that the original image can be produced by a Gaussian model based on only a nearest-neighbor effect and that the noise superimposed at each pixel is produced by a Gaussian model having spatial correlation characterized by translational symmetry. With this model, we can use Fourier transformation to calculate system characteristics such as the restoration error and also minimize the restoration error when the hyperparameters of the probabilistic model used in the restoration process coincides with those used in the formation process. We also discuss the characteristics of image restoration distorted by spatially correlated noise using a natural image. In addition, we estimate the hyperparameters using the maximum marginal likelihood and restore an image distorted by spatially correlated noise to evaluate this method of image restoration.

In this letter, we propose a multi-cell cooperation method for broadcast packet transmission in the OFDM-based cellular system with multiple transmit antennas. In the proposed method, to transmit two streams of spatially demultiplexed or transmit diversity coded symbols, we divide a coded packet into subparts to each of which different cell group and antenna pairs are assigned. It is shown that the proposed method reduces the outage probability with only negligible increase in channel estimation.

Boundary detection is one of the most studied problems in computer vision. It is the foundation of contour grouping, and initially affects the performance of grouping algorithms. In this paper we propose a novel boundary detection algorithm for contour grouping, which is a selective attention guided coarse-to-fine scale pyramid model. Our algorithm evaluates each edge instead of each pixel location, which is different from others and suitable for contour grouping. Selective attention focuses on the whole saliency objects instead of local details, and gives global spatial prior for boundary existence of objects. The evolving process of edges through the coarsest scale to the finest scale reflects the importance and energy of edges. The combination of these two cues produces the most saliency boundaries. We show applications for boundary detection on natural images. We also test our approach on the Berkeley dataset and use it for contour grouping. The results obtained are pretty good.

A sound field reproduction method is proposed that uses blind source separation and a head-related transfer function. In the proposed system, multichannel acoustic signals captured at distant microphones are decomposed to a set of location/signal pairs of virtual sound sources based on frequency-domain independent component analysis. After estimating the locations and the signals of the virtual sources by convolving the controlled acoustic transfer functions with each signal, the spatial sound is constructed at the selected point. In experiments, a sound field made by six sound sources is captured using 48 distant microphones and decomposed into sets of virtual sound sources. Since subjective evaluation shows no significant difference between natural and reconstructed sound when six virtual sources and are used, the effectiveness of the decomposing algorithm as well as the virtual source representation are confirmed.