Harmonic balance (HB) method is well known principle for analyzing periodic oscillations on nonlinear networks and systems. Because the HB method has a truncation error, approximated solutions have been guaranteed by error bounds. However, its numerical computation is very time-consuming compared with solving the HB equation. This paper proposes an algebraic representation of the error bound using Grobner base. The algebraic representation enables to decrease the computational cost of the error bound considerably. Moreover, using singular points of the algebraic representation, we can obtain accurate break points of the error bound by collisions.

In this letter, we emphasize the performance associated problem of the TCP protocol in the wired-wireless networks. It is shown that the increase of TCP congestion window is strongly influenced by the wireless link. To accelerate the increase of TCP congestion window regardless of wireless link conditions we adopt a fast snoop agent that sends indirect acknowledgement to the sender. Simulation results show that the proposed scheme achieves higher throughput with small data size.

We study the synchronization of dynamical systems induced by common additional external colored noise. In particular, we consider the special case that the external input noise is generated by a linear second-order differential equation forced by Gaussian white noise. So the frequency spectrum of this noise is not constant. In the case that noise-free dynamics is chaotic, we find examples where the synchronization is enhanced when the peak of the input noise is close to the peak of the noise-free dynamics in frequency space. In the case that noise-free dynamics is non-chaotic, we do not observe this phenomenon.

In a codebook based precoding MIMO system, the precoding codebook significantly determines the system performance. Consequently, it is crucial to design the precoding codebook, which is related to the channel fading, antenna number, spatial correlation etc. So specific channel conditions correspond to respective optimum codebooks. In this paper, in order to obtain the optimum codebooks, a universal unitary space vector quantization (USVQ) codebook design criterion is provided, which can design the optimum codebooks for various fading and spatial correlated channels with arbitrary antenna configurations. Furthermore, the unitary space K-mean (USK) algorithm is also proposed to generate the USVQ codebook, which is iterative and convergent. Simulations show that the capacities of the precoding MIMO schemes using the USVQ codebooks are very close to those of the ideal precoding cases and outperform those of the schemes using the traditional Grassmannian codebooks and the 3GPP LTE DFT (discrete Fourier transform) codebooks.

We present a tight time-hierarchy theorem for nondeterministic cellular automata by using a recursive padding argument. It is shown that, if t2(n) is a time-constructible function and t2(n) grows faster than t1(n+1), then there exists a language which can be accepted by a t2(n)-time nondeterministic cellular automaton but not by any t1(n)-time nondeterministic cellular automaton.

In this letter, a cooperative Piconet Coordinator (PNC) relay scheme is proposed based on a MB-OFDM system. For time domain diversity, the MB-OFDM UWB system transmits the same symbol twice in different time slots over different bands. Devices (DEVs) that are close to the PNC use it as a relay in the second transmission time. Additionally, a symbol transmission schedule is proposed to provide a sufficient time interval for cooperation. During the first transmission of the symbol, the PNC listens in on the signal from the Source Device (SDEV) to the Destination Device (DDEV) and decodes and re-encodes it with the same data rate. The PNC then transmits the signal in the second transmission as well as the SDEV. Our simulation results demonstrate the proposed cooperative PNC relay scheme can significantly improve the bit error rate (BER) performance, which translates into a power savings capability.

We present on-chip oscillator arrays synchronized by random noises, aiming at skew-free clock distribution on synchronous digital systems. Nakao et al. recently reported that independent neural oscillators can be synchronized by applying temporal random impulses to the oscillators [1],[2]. We regard neural oscillators as independent clock sources on LSIs; i.e., clock sources are distributed on LSIs, and they are forced to synchronize through the use of random noises. We designed neuron-based clock generators operating at sub-RF region (< 1 GHz) by modifying the original neuron model to a new model that is suitable for CMOS implementation with 0.25-µm CMOS parameters. Through circuit simulations, we demonstrate that i) the clock generators are certainly synchronized by pseudo-random noises and ii) clock generators exhibited phase-locked oscillations even if they had small device mismatches.

The performances of a PCTH-based communication UWB system with diversiform modulation schemes are compared on the classic AWGN channel propagation and the realistic IEEE-UWB channel model. By employing different versions of modulation at the transmitters, the performances of an optimal receiver and a Rake receiver with various combining schemes are studied in this paper. The numerical results for several compared cases illustrate the tradeoff between transmitter diversity and receiver complexity. It is shown that the actual performance of the PAM-PCTH scheme can be better in both kinds of channel propagation. We also find that the PCTH-based UWB system with the Rake receiver has better performance than the conventional proposal for overcoming the multipath propagation effects in the UWB indoor environment.

We propose a CMOS image sensor that realizes wide dynamic range imaging and nonlinear representation of I/O characteristics. The proposed image sensor controls the integration time for each pixel based on the brightness distribution of objects. The histogram at the end of the integration is estimated from the early intermediate photodiode values that are read out to an external circuit. Using the estimated histogram, the imaging parameters, which control the integration time pixel-by-pixel, are optimized in the external circuit. According to the imaging parameters, the intermediate photodiode value is compared with the threshold and reset to the starting value depending on the comparison result. These processes repeat several times. At the end of the integration, the photodiode value is reconstructed by using the imaging parameters. Then, wide dynamic range images with adapted I/O characteristics are obtained. We have fabricated a prototype with a size of 6464 pixels using a 0.35-µm 2-poly 4-metal CMOS process. In this paper, we explain the principle of the proposed sensor and discuss the system architecture and its operation. The experimental results obtained using the prototype are also presented, and we verify its effectiveness.

Programmable Metallization Cell (PMC) Random Access Memory is based on the electrochemical growth and removal of nanoscale metallic pathways in thin films of solid electrolytes. In this study, we investigate the nature of thin films formed by the photo doping of Cu into chalcogenide materials for use in programmable metallization cell devices. These devices rely on metal ion transport in the film so produced to create electrically programmable resistance states. The results imply that a Cu-rich phase separates owing to the reaction of Cu with free atoms from chalcogenide materials.

This letter proposes a novel scheme of joint antenna combination and symbol detection in multi-input multi-output (MIMO) systems, which simultaneously determines the antenna combination coefficients to lower the RF chains and designs the minimum bit error rate (MBER) detector to mitigate the interference. The joint decision statistic, however, is highly nonlinear and the particle swarm optimization (PSO) algorithm is employed to reduce the computational overhead. Simulations show that the new approach yields satisfactory performance with reduced computational overhead compared with pervious works.

We propose and demonstrate a scheme enhancing the performance of optical access networks with Manchester coded downstream and re-modulated NRZ coded upstream. It is achieved by threshold level control of a limiting amplifier at a receiver, and the minimum sensitivity of upstream is significantly improved for the re-modulation scheme with 5 Gb/s Manchester coded downstream and 2.488 Gb/s NRZ upstream data rates.

The ηT pairing for supersingular elliptic curves over GF(3m) has been paid attention because of its computational efficiency. Since most computation parts of the ηT pairing are GF(3m) multiplications, it is important to improve the speed of the multiplication when implementing the ηT pairing. In this paper we investigate software implementation of GF(3m) multiplication and propose using irreducible trinomials xm+axk+b over GF(3) such that k is a multiple of w, where w is the bit length of the word of targeted CPU. We call the trinomials "reduction optimal trinomials (ROTs)." ROTs actually exist for several m's and for typical values of w = 16 and 32. We list them for extension degrees m = 97, 167, 193, 239, 317, and 487. These m's are derived from security considerations. Using ROTs, we are able to implement efficient modulo operations (reductions) for GF(3m) multiplication compared with cases in which other types of irreducible trinomials are used (e.g., trinomials with a minimum k for each m). The reason for this is that for cases using ROTs, the number of shift operations on multiple precision data is reduced to less than half compared with cases using other trinomials. Our implementation results show that programs of reduction specialized for ROTs are 20-30% faster on 32-bit CPU and approximately 40% faster on 16-bit CPU compared with programs using irreducible trinomials with general k.

Based on the expectation-maximization (EM) algorithm, an iterative time-domain channel estimation approach capable of using a priori information is proposed for orthogonal frequency division multiplexing (OFDM) systems in this letter: it outperforms its noniterative counterpart in terms of estimation accuracy as well as bit error rate (BER) performance. Numerical simulations demonstrate that an SNR gain of 1 dB at BER=10-4 with only one iteration and estimation mean square error (MSE) which nearly coincides with the Cramer-Rao bound (CRB) in the low SNR region can be obtained, thanks to the efficient use of a priori information.

In recent years, the images captured by AVHRR (Advanced Very High Resolution Radiometer) on the NOAA (National Oceanic and Atmospheric Administration) series of satellites have been used very widely for environment and land cover monitoring. In order to use NOAA images, they need to be accurately transformed from the image coordinate system into map coordinate system. This paper proposes a geometric correction method that corrects the errors caused by this transformation. In this method, the errors in NOAA image are corrected in the image coordinate system before transforming into the map coordinate system. First, the elevation values, which are read from GTOPO30 database, are verified to divide data into flat and rough blocks. Next, in order to increase the number of GCPs (Ground Control Points), besides the GCPs in the database, more GCPs are generated based on the feature of the coastline. After using reference images to correct the missing lines and noise pixels in the top and bottom parts of the image, the elevation errors of the GCP templates are corrected and GCP template matching is applied to find the residual errors for the blocks that match GCP templates. Based on these blocks, the residual errors of other flat and rough blocks are calculated by affine and Radial Basis Function transform respectively. According to the residual errors, all pixels in the image are moved to their correct positions. Finally, data is transformed from image into map by bilinear interpolation. With the proposed method, the average values of the error after correction are smaller than 0.2 pixels on both latitude and longitude directions. This result proved that the proposed method is a highly accurate geometric correction method.

In this paper we compare various parallel preconditioners such as Point-SSOR (Symmetric Successive OverRelaxation), ILU(0) (Incomplete LU) in the Wavefront ordering, ILU(0) in the Multi-color ordering, Multi-Color Block SOR (Successive OverRelaxation), SPAI (SParse Approximate Inverse) and pARMS (Parallel Algebraic Recursive Multilevel Solver) for solving large sparse linear systems arising from two-dimensional PDE (Partial Differential Equation)s on structured grids. Point-SSOR is well-known, and ILU(0) is one of the most popular preconditioner, but it is inherently serial. ILU(0) in the Wavefront ordering maximizes the parallelism in the natural order, but the lengths of the wavefronts are often nonuniform. ILU(0) in the Multi-color ordering is a simple way of achieving a parallelism of the order N, where N is the order of the matrix, but its convergence rate often deteriorates as compared to that of natural ordering. We have chosen the Multi-Color Block SOR preconditioner combined with direct sparse matrix solver, since for the Laplacian matrix the SOR method is known to have a nondeteriorating rate of convergence when used with the Multi-Color ordering. By using block version we expect to minimize the interprocessor communications. SPAI computes the sparse approximate inverse directly by least squares method. Finally, ARMS is a preconditioner recursively exploiting the concept of independent sets and pARMS is the parallel version of ARMS. Experiments were conducted for the Finite Difference and Finite Element discretizations of five two-dimensional PDEs with large meshsizes up to a million on an IBM p595 machine with distributed memory. Our matrices are real positive, i.e., their real parts of the eigenvalues are positive. We have used GMRES(m) as our outer iterative method, so that the convergence of GMRES(m) for our test matrices are mathematically guaranteed. Interprocessor communications were done using MPI (Message Passing Interface) primitives. The results show that in general ILU(0) in the Multi-Color ordering and ILU(0) in the Wavefront ordering outperform the other methods but for symmetric and nearly symmetric 5-point matrices Multi-Color Block SOR gives the best performance, except for a few cases with a small number of processors.

A Lyapunov-based recurrent neural networks unified power flow controller (UPFC) is developed for improving transient stability of power systems. First, a simple UPFC dynamical model, composed of a controllable shunt susceptance on the shunt side and an ideal complex transformer on the series side, is utilized to analyze UPFC dynamical characteristics. Secondly, we study the control configuration of the UPFC with two major blocks: the primary control, and the supplementary control. The primary control is implemented by standard PI techniques when the power system is operated in a normal condition. The supplementary control will be effective only when the power system is subjected by large disturbances. We propose a new Lyapunov-based UPFC controller of the classical single-machine-infinite-bus system for damping enhancement. In order to consider more complicated detailed generator models, we also propose a Lyapunov-based adaptive recurrent neural network controller to deal with such model uncertainties. This controller can be treated as neural network approximations of Lyapunov control actions. In addition, this controller also provides online learning ability to adjust the corresponding weights with the back propagation algorithm built in the hidden layer. The proposed control scheme has been tested on two simple power systems. Simulation results demonstrate that the proposed control strategy is very effective for suppressing power swing even under severe system conditions.

This paper describes the matrix order reduction method by the nodal analysis formulation and the application of relaxation-based simulation technique to interconnect and plane networks. First, the characteristics of the power/ground plane networks are considered. Next, the formulation of the plane network by nodal analysis (NA) method is suggested. Furthermore, application and estimation results of the relaxation-based numerical analyses are shown. Finally, it is confirmed that the relaxation-based methods improved by the suggested formulation are much more efficient than the conventional direct-based methods.

A fine-grain reconfigurable VLSI for various applications including arithmetic operations is developed. In the fine-grain architecture, it is important to define a cell function which leads to high utilization of a logic block and reduction of a switch block. From the point of view, a universal-literal-based multiple-valued cell suitable for bit-serial reconfigurable computation is proposed. A series-gating differential-pair circuit is effectively employed for implementing a full-adder circuit of Sum and a universal literal circuit. Therefore, a simple logic block can be constructed using the circuit technology. Moreover, interconnection complexity can be reduced by utilizing multiple-valued signaling, where superposition of serial data bits and a start signal which indicates heading of one-word is introduced. Differential-pair circuits are also effectively employed for current-output replication, which leads to high-speed signaling to adjacent cells The evaluation is done based on 90 nm CMOS design rule, and it is made clear that the area of the proposed cell can be reduced to 78% in comparison with that of the CMOS implementatiuon. Moreover, its area-time product becomes 92% while the delay time is increased by 18%.

This paper introduces multiple view geometry under projective projection from four-dimensional space to two-dimensional space which can represent multiple view geometry under the projection of space-time. We show the multifocal tensors defined under space-time projective projection can be derived from non-rigid object motions viewed from multiple cameras with arbitrary translational motions, and they are practical for generating images of non-rigid object motions viewed from cameras with arbitrary translational motions. The method is tested in real image sequences.