The combination of OFDM and multiple antennas in either the transmitter or receiver is attractive to increase a diversity gain. However, multiple antennas system requires an antenna separation of 5-10 λ to keep the correlation coefficient below 0.7 for the space diversity, so this may be difficult to implement in a mobile station with high mobility. Recently, the polarization transmit diversity is considered in a mobile station. However, polarization transmit diversity requires twice transmit powers to compare with the conventional transmit diversity, since only vertically polar antenna cannot receive the horizontal signal components. In this paper, we express the cross correlation of each polarization antenna and the cross polarization discrimination (XPD) of multiple polarization antennas with simple model, and we propose an wideband OFDM using Alamouti coded heterogeneous polarization antennas for reducing the previous problem. From the simulated results, the proposed system shows better BER performance than that of the conventional STBC/OFDM.

This letter presents an investigation of channel estimation scheme for a high rate WPAN system using multiple transmit antennas over indoor wireless channel. A simple algorithm utilizing the autocorrelation property of a CAZAC preamble is proposed for channel estimation. Simulation and analytical results show the performance of the proposed algorithm in terms of mean square error (MSE) of channel estimation. At the same time, the effect of imperfect channel estimation introduced by relatively large RMS delay spread is highlighted.

This letter develops a practical sectorized antenna array using center-fed half-wavelength dipole antennas that are parallel to and a distance in front of a large ground plane reflector. Each element in the array is designed to provide coverage to isolate each 120sector from adjacent sectors. We derive a closed-form expression for spatial correlation function that can be used as guides in evaluating the effects of array spatial correlation on diversity performance in sectorized cellular communications.

Location control of grains by µ-Czochralski process with excimer-laser is a powerful tool for realizing high performance single-crystalline Si TFTs (c-Si TFTs). This study reports the behavior of p-channel single-crystalline Si TFTs fabricated inside a location-controlled grain by µ-Czochralski method. Self-aligned p-channel single-crystalline Si TFTs is fabricated with a top gate structure having ECR-PECVD SiO2 as gate insulator. The field effect hole mobility of 250 cm2/Vs and subthreshold swing of 0.29 V/dec. are obtained successfully. Effects of active Si thickness and boron channel doping on the characteristics of the c-Si TFTs were studied.

In this paper, we propose an algorithm, named efficient utilization polling (EUP), to support asynchronous data traffic at MAC layer by using the characteristics of Bluetooth technology. The algorithm uses a single bit in the payload header to carry the knowledge of queues in slaves for dynamically adapting the polling intervals for achieving the goals of high channel utilization and power conserving. In addition, we propose a differentiation mechanism, named shift-polling window (SPW). Based on EUP, the SPW differentiates the throughput from various classes, and still keeps the link utilization high and almost the same as that of the best-effort services. Extensive simulations are experimented on the behavior of the EUP and SPW by tuning the related parameters, such as polling interval, buffer size, queue threshold level, etc., in order to verify the expectation of these methods.

We have investigated the pretilt angle of liquid crystal (LC) molecules induced by photo-alignment films of polyimide (Azo-PI) containing azobenzene in the backbone structure. To generate finite pretilt angles, the Azo-PI film with inclined alignment of the backbone structure was prepared by a double light-exposure method. In this method the corresponding polyamic acid (Azo-PAA) film was first exposed to linearly polarized ultraviolet/visible (UV/VIS) light (LP-light) at normal incidence, and then oblique angle irradiation of unpolarized UV/VIS light (UP-light) was performed in the plane of incidence perpendicular to the polarization direction of the LP-light. Repeated photo-isomerization reactions of azobenzene induce the alignment of the Azo-PAA backbone structure. By thermally imidizing the photo-treated film we obtained a thermally and optically stable Azo-PI film. The orientational distribution of the Azo-PI backbone structure was determined by measuring the polarized infrared absorption spectra as a function of the sample rotation angle and the angle of incidence. The pretilt angle of LC molecules was determined by a crystal rotation method. We found that the average inclination angle of the Azo-PI backbone structure increased with the UP-light exposure. The pretilt angle of LC molecules, measured from the surface plane, also increased with the UP-light exposure. We succeeded in generating a pretilt angle of 3. The relation between the LC pretilt angle and the average inclination angle of the Azo-PI backbone structure is discussed.

To improve the DS-CDMA signal transmission performance in a frequency-selective fading channel, the frequency-domain equalization (FDE) can be applied, in which simple one-tap equalization is carried out on each subcarrier component obtained by fast Fourier transform (FFT). Equalization weights for joint FDE and antenna diversity combining based on maximal ratio combining (MRC), zero-forcing (ZF), and minimum mean square error (MMSE) are derived. The conditional bit error rate (BER) is derived for the given set of channel gains in a frequency-selective multipath fading channel. The theoretical average BER performance is evaluated by Monte-Carlo numerical computation method using the derived conditional BER and is confirmed by computer simulation. Performance comparison between DS- and multi-carrier (MC)-CDMA both using FDE is also presented.

Recently, a cluster map based blind RBF equalizer (CM-BRE) has been proposed. By utilizing the underlying structure characteristics of RBF equalizer, the CM-BRE can be implemented by the combination of neural-gas algorithm (NGA) with several sorting operations. Although the CM-BRE is able to achieve almost identical performance with the optimal RBF equalizer, the high computational load mainly caused by NGA limits it's application. In this paper, we propose a downsizing method that employs the inter-relation among RBF centers and significantly reduces the NGA's computational load. Furthermore, a method to determine the feedback vector is derived, then CM-BRE is extended to a cluster map based blind RBF decision feedback equalizer (CM-BRDFE). The proposed CM-BRDFE also shows the close performance with the optimal RBF decision feedback equalizer in simulations.

In this paper, the previous definition of the Reverse Jacket matrix (RJM) is revised and generalized. In particular, it is shown that the inverse of the RJM can be obtained easily by a constructive approach similar to that used for the RJM itself. As new results, some useful properties of RJMs, such as commutativity and the Hamiltonian symmetry appearing in half the blocks of a RJM, are shown, and also 1-D fast Reverse Jacket transform (FRJT) is presented. The algorithm of the FRJT is remarkably efficient than that of the center-weighted Hadamard transform (CWHT). The FRJT is extended in terms of the Kronecker products of the Hadamard matrix. The 1-D FRJT is applied to the discrete Fourier transform (DFT) with order 4, and the N-point DFT can be expressed in terms of matrix decomposition by using 4 4 FRJT.

This paper presents a simple learning algorithm for network formation. The algorithm is based on self-organizing maps with growing cell structures and can adapt input data which correspond to nodes of the network. In basic numerical experiments, as a parameter is selected suitably, our algorithm can generate network having small-world-like structure. Such network structure appears in some natural networks and has advantages in practical systems.

In this paper, we consider a direct sequence spread spectrum (DS-SS) microphone system in 2.4 GHz ISM band under indoor environments. It can be modeled as the asynchronous DS-CDMA system in which multiple transmitters share a common channel to transmit information to a single receiver. However, this system has the two critical defects, one is that many burst errors are occurred because of the long-term deep fade in an indoor channel, and the other is that power control is impossible due to the unidirectional structure. Since the reliable performance of DS-CDMA systems can be guaranteed under a reliable bit error rate performance and perfect power control, the solution to these problems is imperative. Hence, in order to overcome these problems, we propose a zero forcing equalizer (ZFE) based multi-user detection (MUD) receiver for this system, since an MUD receiver doesn't require rigorous power control and is able to remove multiple access interference using linear equalization. We derive the modeling and the tap coefficients of the proposed ZFE, and also analyze the performance of the proposed receiver. Based on the performance comparison with the conventional receivers, such as single user detection and post-detection combining diversity receivers, it is shown that the proposed receiver can achieve a lower bit error rate performance.

This paper proposes and theoretically evaluates two different schemes of code acquisition for pulse-position modulation (PPM) and overlapping PPM (OPPM) fiber-optic code-division multiple-access (CDMA) systems, namely threshold-based and demodulator-based code acquisition. Single-dwell detector and serial-search algorithm are employed for both schemes. Theoretical analysis is carried out for shot-noise-limited photon-counting receiver. Discussions upon effects of various parameter settings on the performance of code acquisition for PPM/OPPM fiber-optic CDMA systems, such as index of overlap, PPM/OPPM multiplicity, average photon counts per information nat, and darkcurrents, are presented. It is shown that when the threshold is properly selected, the threshold-based code acquisition system offers better performance, in terms of mean number of training frames, than the demodulator-based one.

Energy consumption is one of the most critical constraints in the design of portable embedded systems. This paper describes an empirical study about the impacts of compiler optimizations on the energy consumption of the address bus between processor and instruction memory. Experiments using a number of real-world applications are presented, and the results show that transitions on the instruction address bus can be significantly reduced (by 85% on the average) by the compiler optimizations together with bus encoding.

In this study, a fourth-order cumulants based iterative algorithm for blind channel equalization is introduced, which is robust with respect to the existence of heavy Gaussian noise in a channel and does not require the minimum phase characteristic of the channel. The transmitted signals at the receiver are over-sampled to ensure the channel described by a full-column rank matrix. It changes a single-input/single-output (SISO) finite-impulse response (FIR) channel to a single-input/multi-output (SIMO) channel. Based on the properties of the fourth-order cumulants of the over-sampled channel inputs, the iterative algorithm is derived to estimate the deconvolution matrix which makes the overall transfer matrix transparent, i.e., it can be reduced to the identity matrix by simple reordering and scaling. In simulation studies, both a closed-form and a stochastic version of the proposed algorithm are tested with three-ray multi-path channels, and their performances are compared with the methods based on conventional second-order statistics and higher-order statistics (HOS) as well. Relatively good results with fast convergence speed are achieved, even when the transmitted symbols are significantly corrupted with Gaussian noise.

This letter presents a new probability expression for a multi-carrier (MC) DS/CDMA acquisition system with a reference matched filter (RMF). To evaluate the mean acquisition time (MAT) as a measure of the system performance, the probabilities of detection, miss, and false alarm are derived. From the results, it is shown that the MAT of the MC-CDMA hybrid system with RMF is comparable to the optimum mean acquisition time of the conventional MC-CDMA hybrid system, maintaining approximately the same degree of structuring complexity.

The operation of a polarization mode dispersion (PMD) compensator using a polarizer and a Faraday rotator-based polarization controller (FRPC) is analyzed in detail, and the compensation performance is experimentally evaluated in 40 Gbit/s operation. The evaluation results show that a wide range of differential group delay over a bit period can almost be completely compensated using the PMD compensator. The characteristics of electrical spectrum-based signal monitoring methods are investigated in detail, and the results shows advantages of a low frequency band monitoring method that produces about double the wider dynamic range than a fundamental repetition frequency monitoring method. The automated PMD compensator using a polarizer and a FRPC driven by the low frequency band monitoring method is experimentally investigated using a terrestrial 40 Gbit/s wavelength division multiplexing system involving 350-km installed single-mode fibers. The PMD compensator produces highly stable signal performance in the field environment for a long term and reduces the standard deviation of the Q-factor distribution.

This paper proposes the dynamic resource assignment (DRA) scheme in the multi-carrier mesh-topology millimeter-wave (MMW) broadband entrance networks. In the DRA scheme, the radio path allocation and the frequency channel assignment techniques are deployed to maximize the network throughput. In the radio path allocation technique, the traffic load is distributed into the appropriate paths. On the other hand, the frequency channel assignment is performed based on the linear programming (LP) method. As the results, the proposed DRA scheme yields higher throughput performance than the conventional scheme using the random frequency channel assignment. In addition, the proposed scheme can guarantee the throughput performance when the number of frequency channels is 36 and the input load is no more than 9 Gbps. Moreover, the proposed scheme can yield the satisfaction sub-optimum throughput with the small computational complexity.

The 70-GHz band propagation characteristics of two different hot-spot zones are measured and analyzed: (1) a transmitter fixed to a ceiling servicing the area beneath it (type A), and (2) a transmitter fixed to a wall servicing the area in front of it (type B). Measurements were made in two different settings, a lobby and a train. The results show that zone B produces a smaller delay spread in relation to distance. A comparison of the use of vertical and circular polarization shows that circular polarization produces a smaller delay spread in the type B zone. The results also indicated that the function of the delay spread value for the distance in a lobby and train in type B zone.

The bandwidth occupied by individual telecommunication devices in the field of mobile radio communication must be narrow in order to effectively exploit the limited frequency band. Therefore, it is necessary to implement low-bit-rate speech coding that is robust against background noise. We examine vector quantization using a neural network (NNVQ) as a robust LSP encoder. In this paper, we compare four types of binary patterns of a hidden layer, and clarify the dependency of quantization distortion on the bit pattern. By delayed decision (selection of low-distortion codes in decoding, i.e., EbD method) the spectral distortion (SD) can be decreased by 0.8 dB (20%). For noisy speech, the performance of the EbD method is better than that of the conventional VQ codebook mapping method. In addition, the SD can be decreased by 2.3 dB (40%) by using a method in which the neural networks for encoding and decoding are combined and re-trained. Finally, we examine the SD for speech having different signal-to-noise ratios (SNRs) from that used in training. The experimental results show that training using SNR between 30 and 40 dB is appropriate.

When we try to solve Multiobjective Optimization Problems (MOPs) using an evolutionary algorithm, the Pareto Genetic Algorithm (Pareto GA) introduced by Goldberg in 1989 has now become a sort of standard. After the first introduction, this approach was further developed and lead to many applications. All of these approaches are based on Pareto ranking and use the fitness sharing function to maintain diversity. On the other hand in the early 50's another scheme was presented by Nash. This approach introduced the notion of Nash Equilibrium and aimed at solving optimization problems having multiobjective functions that are originated from Game Theory and Economics. Since the concept of Nash Equilibrium as a solution of these problems was introduced, game theorists have attempted to formalize aspects of the equilibrium solution. The Nash Genetic Algorithm (Nash GA), which is introduced by Sefrioui, is the idea to bring together genetic algorithms and Nash strategy. The aim of this algorithm is to find the Nash Equilibrium of MOPs through the genetic process. Another central achievement of evolutionary game theory is the introduction of a method by which agents can play optimal strategies in the absence of rationality. Not the rationality but through the process of Darwinian selection, a population of agents can evolve to an Evolutionary Stable Strategy (ESS) introduced by Maynard Smith in 1982. In this paper, we propose Game theory based Co-Evolutionary Algorithm (GCEA) and try to find the ESS as a solution of MOPs. By applying newly designed co-evolutionary algorithm to several MOPs, the first we will confirm that evolutionary game can be embodied by co-evolutionary algorithm and this co-evolutionary algorithm can find ESSs as a solutions of MOPs. The second, we show optimization performance of GCEA by applying this model to several test MOPs and comparing with the solutions of previously introduced evolutionary optimization algorithms.