Ray tracing is an efficient method for analyzing transmission characteristic of indoor wireless systems. However for simulating the transmission characteristic, using a path profile obtained by ray tracing, calculation times become enormous and there is no good theoretical model which can link a path analysis result with digital transmission characteristics evaluation. To overcome such problems, in this paper, a simple calculation method on spatial distribution of error occurrence due to intersymbol interference (ISI) based on "the equivalent transmission-path (ETP) model" is proposed. The ETP model is a technique that can simply estimate statistics of errors due to ISI that arise in Rayleigh and Nakagami-Rice fading environments. If a simple calculation method proposed in this paper is used, calculation time of digital transmission characteristics evaluation become tremendously shorter and results of this method agree with those of exact simulations with sufficient accuracy.

In cryptography, we want a Boolean function which satisfies PC(l) of order k for many (l,k). Let PCn(l,k) be a set of Boolean functions with n input bits satisfying PC(l) of order k. From a view point of construction, it is desirable that there exists (l0,k0) such that PCn(l0, k0) PCn(li,ki) for many i 1. In this paper, we show a negative result for this problem. We prove that PCn(l1,k1) PCn(l2,k2) for a large class of l1, k1, l2 and k2.

This paper proposes a space division multiplexed - coded orthogonal frequency division multiplexing (SDM-COFDM) scheme for multi-input multi-output (MIMO) based broadband wireless LANs. The proposed scheme reduces inter-channel interference in SDM transmission with a simple feed-forward canceller which multiplies the received symbols by the estimated propagation inverse matrix for each OFDM subcarrier. This paper proposes a new preamble pattern in order to improve power efficiency in the estimation of the propagation matrix. Moreover, the proposed likelihood-weighting scheme, which is based on signal-to-noise power ratio (SNR) of each OFDM subcarrier, improves the error correction performance of soft decision Viterbi decoding. Computer simulation shows that the proposed SDM-COFDM scheme with two transmitting/receiving antennas doubles the transmission rate without increasing the channel bandwidth and achieves almost the same PER performance as the conventional single-channel transmission in frequency selective fading environments. In particular, it achieves more than 100 Mbit/s per 20 MHz by using 64QAM with the coding rate of 3/4.

Array antennas are employed at the receiver for a variety of purposes such as to combat fading or to reduce co-channel interference. To evaluate the performance of a wireless communications system using antenna arrays it becomes necessary to have spatial channel models that describe the Angle of Arrival (AOA), Time of Arrival (TOA) and the Angle Spread (AS) of the multipath components. Among the most widely used radio propagation models is the single bounce scattering geometric model, where propagation between the transmitting and receiving antennas is assumed to take place via single scattering from an intervening obstacle. Currently, several geometric models are available such as circular and elliptical scattering models, with each model being applicable to a specific environment type. This paper addresses the modeling, simulation and evaluation of the angle spread in smart antenna systems taking into account the Gaussian density model, and proves that the model finds use both in a micro cell as well as in a macro cell environment. Moreover, we show statistics for the angle and time of arrival.

This paper proposes a 2-dimensional linear propagation prediction (LPP) in maximal ratio combining (MRC) transmitter diversity for orthogonal frequency division multiplexing (OFDM) time division multiple access--time division duplex (TDMA/TDD) systems in order to overcome the degradation of the transmission performance due to the fast fading or the TDD duration. In the proposed scheme, the downlink channel condition of each sub-channel is predicted by interpolating the uplink fading fluctuation with both the amplitude and phase, and the predicted downlink channel condition is used for the weighting factor to employ MRC transmitter diversity. Numerical results obtained by the computer simulation show that the proposed 2-dimensional LPP with the second-order Lagrangeis interpolation predicts the downlink channel condition accurately under the fast fading or the long TDD duration. Moreover, in such a condition, the proposed LPP provides far better performance than the conventional 1-dimensional LPP.

Adaptive beamforming, using the Conjugate Gradient Normal Equation Residual problem, is applied to a base station array, in the UTRA-TDD up-link. A Wideband Directional Channel Model is used, characterising specific micro-cell, street-type scenarios. These differ in the number of mobile terminals, grouped and placed along the street axis, and on their distances to the base station. Time- and angle-of-arrival spreads, and on-the-air interference content are the main parameters inherently varied and analysed. The average beamforming gain and signal-to-noise ratio are evaluated, also varying the number of array elements. The high number of arriving correlated and closely correlated signals, together with the composed nature of the correlation matrix in the algorithm's cost function, result in that other than the MMSE solutions may lead to the best interference suppression, for the tested scenarios. Among the several weighted interfering power components, the most relevant is due to the delayed signals from all the other links. The combination of the number of arriving orthogonal codes, time-of-arrival and angle-of-arrival spreads condition beamforming performance: the number of array elements affect performance, depending on the mobile terminal distance to the base station, and on the number of active links; for short distances and large number of users, larger time-of-arrival spread degrades beamformer performance, over the opposing effect of angle-of-arrival spread; the number of active users affects beamforming gain especially in the case that delay spreads are larger, i.e., for shorter mobile terminal distances to the base station.

A hybrid location system for a mobile station consists of a wireless-assisted GPS and a kind of cellular signals. This letter presents a location estimator improving the performance of the hybrid mobile station location for all terrain environments including inside or between buildings. An estimation structure eliminating non-line-of-sight propagation-delay error effectively improves location accuracy of the hybrid location system.

A performance comparison is developed between a chaotic communication system and a spread spectrum system with similar features in terms of bandwidth and transceiver structure but based on more conventional Gold sequences. Comparison is made in the presence of noise and multipath contributions which degrade the channel quality. It is shown that, because of its more favourable correlation properties, the chaotic scheme exhibits lower error rates, at a parity of the bandwidth expansion factor. The same favourable correlation properties are also used to explain and show, through a numerical example, the benefits of chaotic segments in a multi-user environment.

One of the reasons of slow convergence in Backpropagation learning is the diminishing value of the derivative of the commonly used activation functions as the nodes approach extreme values, namely, 0 or 1. In this letter, we propose arctangent activation function to accelerate learning speed. Simulation results indicate considerable improvement in convergence performance.

We have measured the non line-of-sight (NLOS) propagation characteristics of microwave frequencies in an urban environment with a base station antenna situated well above the surrounding buildings. When these characteristics are compared with the results of measurements made in the same environment with a low base station antenna height, it can be seen that with a low base station antenna height the attenuation coefficient varies greatly between line-of-sight (LOS) and NLOS environments, whereas with a high base station antenna height there is no variation of this sort. This is because the waves arriving NLOS environments from a high base station antenna do so primarily as a result of rooftop diffraction, and the path loss does not vary much over regions of equal distance between the base station and mobile station. We have confirmed that the frequency characteristics of relative loss in NLOS environments with a high antenna height follow a relationship of 22.8 log f, which is more or less the same as the characteristic for the UHF band. By modifying the frequency terms of the Sakagami model (used for UHF band) based on this trend to allow it to handle microwave frequencies, a close correspondence is seen between the results of actual measurements and the values predicted by the extended model.

This letter presents the empirical error performance of combining method of a binary numerical code and a single error correcting code on Gaussian channel by belief propagation (BP) decoding algorithm. The numerical codes mentioned here are constructed with any symbol value and have the parity check matrices in reduced-echelon form whose elements are binary (0 and 1). The simulation results show that the method yields good decoding error performance for medium code lengths.

Precise interconnect analysis is strongly required for giga-scale integration the operation frequency of which is excess 10 GHz. In this study, detailed and accurate analyses of a coaxial interconnect and an actual rectangular interconnect have been performed by the direct evaluation of Maxwell's equations and the finite element method, respectively. It has been revealed that there are two propagation modes for LSI interconnects: skin depth limited propagation mode and interconnect induced slow wave mode. In a miniaturized interconnect, the propagation mode is the interconnect induced slow wave mode; therefore, we cannot obtain the light-speed propagation due to such an interconnect-induced effect. In order to overcome this speed limitation or to improve signal integrity, it is essential to introduce a short interconnect for a miniaturized structure, and a much larger interconnect than the skin depth. We propose a gas-isolated interconnect as a candidate for an ultimately low-k structure in order to increase the signal-propagation speed. By the introduction of such structures, the performance of miniaturized devices in the deep submicron region will be effectively enhanced.

Implementation of Multi-Input Multi-Output (MIMO) channel sounder is considered, taking hardware cost and realtime measurement into account. A remarkable difference between MIMO and conventional Single-Input Multi-Output (SIMO) channel sounding is that the MIMO sounder needs some kind of multiplexing to distinguish transmitting antennas. We compared three types of multiplexing TDM, FDM, and CDM for the sounding purpose, then we chose FDM based technique to achieve cost effectiveness and realtime measurement. In the framework of FDM, we have proposed an algorithm to estimate MIMO channel parameters. Furthermore the proposed algorithm was implemented into the hardware, and the validity of the proposed algorithm was evaluated through measurements in an anechoic chamber.

A method of learning for multi-layer artificial neural networks is proposed. The learning model is designed to provide an effective means of escape from the Backpropagation local minima. The system is shown to escape from the Backpropagation local minima and be of much faster convergence than simulated annealing techniques by simulations on the exclusive-or problem and the Arabic numerals recognition problem.

We review recent progresses in our studies on the fiber-optic soliton compression and related subjects with special emphasis on dispersion-flattened fibers (DFFs). As for the ultimately short pulse generation, it has been demonstrated to compress 5 ps laser diode pulses down to 20 fs with a 15.1 m-long single-stage step-like dispersion profiled fiber employed. The compression was brought about through a series of the higher order soliton processes in conjunction with a single and ordinary erbium-doped fiber preamplifier, and DFFs contained at its end played a major role. We have performed intensive investigations on the DFF compression mechanisms in the 100-20 fs range. A fairly reliable model was developed for the higher order soliton propagation along a DFF in the temporal range from 100 down to 30 fs by taking into consideration the higher order nonlinear and dispersion effects as well as incident pulse shape dependence. Through the simulation, parametric spectrum generation originating from the modulation instability gain was pointed out at frequencies apart from the pump wave frequency, which agrees with the experimental observation. Its possible application is also discussed.

This paper describes a design scheme of generalized minimum variance controllers (GMVC) using a group method of data handling (GMDH) network for nonlinear systems. Concretely, the predictive value of the output required in the GMVC is obtained by using the GMDH which is a kind of multilayered networks. Since the predictive value of the output in GMVC is calculated by a nonlinear model which is generated by the GMDH network, one can expect to obtain the better control performance than that by the conventional scheme. The behavior of the newly proposed control scheme is evaluated on numerical examples.

To generalize characteristics of a received signal level distribution from narrow- to wide-bands in a mobile radio channel, a new propagation parameter called equivalent received bandwidth (2ΔfΔLmax) has been proposed. The distributions are discussed mainly with computer simulation results. The simulation results shows the level distribution depends on 2ΔfΔLmax and power ratio a of direct to indirect waves, and the value of 2ΔfΔLmax classifies the radio channel as narrow- or wide-bands transmission. To confirm these simulated results, a field test was performed with a 3.35 GHz radio wave. This paper describes that the field test demonstrated the simulation results. It is concluded that the equation representing received signal level in the computer simulation is valid. And the fading depth depends directly on 2ΔfΔLmax, and the 2ΔfΔLmax is effective for generalizing the received signal level distribution. Furthermore, a method for calculating the power ratio was found to be better for a peak level model.

We have experimentally measured the propagation characteristics of 60-GHz-band millimeter wave between two vehicles to design of inter-vehicle communication (IVC) system in intelligent transport systems (ITS). Received power and bit error rates of 1-Mbps data transmission between a transmitter mounted on a leading vehicle and two receivers attached on a following vehicle were measured. A two-ray propagation model was devised to calculate the instantaneous propagation characteristics, and these estimations agree well with the measured characteristics. The feasibility of 1-Mbps data transmission between the running vehicles on an actual expressway was demonstrated. The cumulative distribution of received power between the two running vehicles when their height from the road surface fluctuated was also determined from the proposed two-ray propagation model and experimental measurements.

Interest in service offerings at Ka-band (20/30 GHz) and above has been increasing recently, driven mainly by the availability at higher frequencies of wider bandwidths, which are attractive for many multimedia applications, for example. A dominant concern in implementing systems to operate in such bands is the severe propagation environment that exists on many transmission paths, such as paths in rainy climates or at low path elevation angles. Adequate understanding of the propagation environment is imperative in the design of economically viable telecommunication systems at these frequencies. A propagation measurement campaign that addressed many of these concerns was conducted in North America with 20.2 and 27.5 GHz radio beacons on NASA's Advanced Communications Technology Satellite (ACTS). Data were collected at seven locations over a continuous 5-year period to supply statistics of propagation impairments for a variety of climate types and path geometry. The primary results of the ACTS campaign as reported to date are reviewed. Studies performed to address related issues, including fading dynamics, site diversity and mobile-satellite performance, are also described. Elements of this paper were presented at the 2000 International Symposium on Antennas and Propagation (ISAP 2000), Fukuoka, Japan, 21-25 August 2000.

In this paper we propose a learning algorithm to enhance the fault tolerance of feedforward neural networks (NNs for short) by manipulating the gradient of sigmoid activation function of the neuron. We assume stuck-at-0 and stuck-at-1 faults of the connection link. For the output layer, we employ the function with the relatively gentle gradient to enhance its fault tolerance. For enhancing the fault tolerance of hidden layer, we steepen the gradient of function after convergence. The experimental results for a character recognition problem show that our NN is superior in fault tolerance, learning cycles and learning time to other NNs trained with the algorithms employing fault injection, forcible weight limit and the calculation of relevance of each weight to the output error. Besides the gradient manipulation incorporated in our algorithm never spoils the generalization ability.