In this paper, a new expression is derived for the bit error rate (BER) performance of Gray-encoded MDPSK for M=2 and 4 in orthogonal frequency division multiplexing (OFDM) systems over time-variant and frequency-selective Rayleigh fading channels. We assume that the guard time is sufficiently larger than the delay spread to solve the intersymbol interference (ISI) problem on the demodulated OFDM signal. In this case, the performance depends on the Doppler spread of fading channel. The closed form expression for the bit error probability of MDPSK/OFDM extended from the result in [5] shows that the BER performance of MDPSK is determined by (N + NG ) fD Ts where N is the number of subchannels, NG the length of the guard interval, fD the maximum Doppler frequency, and Ts the sampling period. The theoretical analysis results are confirmed by computer simulations for DPSK and QDPSK signals.

In this paper we propose a new simplified algorithm for cascaded second order adaptive notch filters implemented using an allpass filter, for elimination of multiple sinusoids. Each of the stages of the notch filter is implemented using direct form second order allpass filter. We also present an analysis which compares the proposed algorithm with the conventional simplified algorithm, and which indicates that the proposed algorithm has a reduced bias in the estimation of the multiple input sinusoids. Simulation results that have been provided confirm this analysis.

We evaluate the BER performance of the OFDM system with the one-tap equalizer bank under the two-ray multipath channel with the frequency offset by the simple Gaussian analysis method and by a proposed modified Gaussian analysis method. The proposed analysis method considers two adjacent inter-channel interferences, separately, and models the other inter-channel interferences as a Gaussian noise. It is shown that the proposed analysis method affords much closer results to the simulations than those by the simple Gaussian analysis method, when the frequency offset exists.

2.4-GHz-band mid-speed (1- to 2-Mbit/sec) wireless LAN systems are being widely used in offices and factories. Electromagnetic interference can occur between these systems because they use the same frequency range. In this paper, we investigate the characteristics of the interference between wireless LAN systems that use direct-sequence (DS) systems and frequency-hopping (FH) systems. The interference characteristics were measured for three DS systems and one FH system that meet the IEEE 802.11 and RCR standards and that use different modulation methods. Our results indicate that throughput depends on the system and the modulation method. We have also developed a model that can be used to calculate the interference characteristics between DS and FH systems by considering the bandwidth of their transmission signals, the dwell time of the FH system, and the time that the DS system needs to transmit a data frame. We used this model to calculate the bit error rate (BER) characteristics of the systems used in our experiment, and the results indicate that BER characteristics depend on the modulation method. The throughput characteristics of the systems used in our experiment were also calculated, and agreed with the experiment results within +/- 5 dB. The throughput characteristics of wireless LAN systems based on IEEE 802.11 were also calculated when the signal level was higher than the receiver noise level. The results show that FH systems require a D/U ratio about 7 or 8 dB higher than the ratio required in DS systems because the parameters in the standard differ between FH and DS systems.

Recently, in the modem, the spread spectrum communication system and the software radio, Digital Signal Processor type Squaring Loop (DSP-squaring-loop) is employed in the demodulation of Binary Phase Shift Keying (BPSK) signal. The DSP-squaring-loop extracts the carrier signal that is used for the coherent detection. However, in case the Signal to Noise Ratio (SNR) is low, the DSP-Phase Locked Loop (DSP-PLL) can not pull in the frequency offset and the phase offset. In this paper, we propose a DSP-squaring-loop that is robust against noise and which uses the adaptive notch filter type frequency estimator and the adaptive Band Pass Filter (BPF). The proposed method can extract the carrier signal in the low SNR environment. The effectiveness of the proposed method is confirmed by the computer simulation results.

We present a case of design and implementation of a high-speed burst QPSK (Quaternary Phase Shift Keying) receiver. Since the PSK modulation carries its information through the phase, the baseband digital receiver can recover transmitted symbol from the received phase. The implemented receiver estimates symbol time and frequency offset using sampled data over 32 symbols without transmitted symbol information, and embedded RAM is used for received phase delay over estimation time. The receiver is implemented using about 92,000 gates of Samsung KG75 SOG library which uses 0.65 µm CMOS technology. The fabricated chip test result shows that the receiver operates at 40 MHz clock rate on 5.6 V, which is equivalent to the 40 Mbps data rate.

This paper reviews analog-circuit researches in the 1990's especially from an academic-side point of view with the aim of pursuing what becomes important in the 21st century. To achieve this aim a large number of articles are surveyed and more than 200 are listed in References.

A passive branched optical network unified for broadcasting and communication utilizing a set of Fabry-Perot etalons with different cavity lengths is proposed and its basic operation including thermal stability of broadcasting channel is demonstrated. It is confirmed that a high transmission frequency in common for a pair of fiber Fabry-Perot etalons is always found however environmental temperature changes.

C-axis junction-arrays, with a-b plane sizes of sub-microns to 10 microns, were patterned on Bi2Sr2CaCu2O8+x single crystals with either a mesa or an overlap structure. We measured the current-voltage (I-V) characteristics with microwave irradiation at a few to 100 gigahertz. At a few gigahertz, often observed were chaotic properties. Under irradiation at 100 GHz, we successfully performed harmonic mixings between the 100 GHz signal and up to the 100th harmonic of a local oscillator at about 1 GHz. Given in this paper are discussions on the observation of individual Shapiro steps, and descriptions of the relevant results. Our experimental results show that intrinsic Josephson junctions in layered superconductors can be good candidates for high frequency applications.

This paper is, in half part, written in review nature, and presents recent theoretical results on linear-filtering and -prediction problems of nonstationary Gaussian processes. First, the basic concepts, signal and noise, are mathematically characterized, and information sources are defined by linear stochastic differential equations. Then, it is shown that the solution to a conventional problem of filtering or prediction of a nonstationary time series is, in principle, reducible to a problem, of which solution is given by Kalman-Bucy's theory, if one can solve a problem of finding the canonical representation of a Gaussian process such that it has the same covariance functions as those of the time series under consideration. However, the problem mentioned above is left open. Further, the problem of time-frequency analysis is discussed, and physical realizability of the evolutionary, i.e., the online, spectral analyzer is shown. Methods for dealing with differential operators are presented and their basic properties are clarified. Finally, some of related open problems are proposed.

A simple but effective fundamental frequency estimation method is proposed using parametric cubic convolution. The performance of the method is shown to be good not only for the stationary signals but also for the signal whose fundamental frequency is changing with time. In the simulation, comparisons with other high-accuracy methods are also shown. Due to its accuracy and simplicity, the proposed method is practically useful.

We analyze a scheme that provides frequency hopping pattern for DS/FH spread spectrum. The proposed scheme, based on the theory of finite projective planes, intends to make the number of transmitting terminals uniform across all channels and distribute the interference to all the participant terminals equally. Thus, when a terminal is in a state of power surge, the probability of having the worst case of interference for terminals sharing the same channel is reduced. In the performance evaluation, we demonstrate that the bit error rate is reduced by an order of magnitude through the use of the proposed hopping pattern for both internal and external interference.

A method for determination of the location, shape, and material properties of a 3D object from measurements of the scattered field, when the object is successively illuminated by a number of incident fields is presented. This work extends the method previously developed for reconstructions of 2D permittivity and conductivity from electromagnetic measurements to the more complicated full-vector 3D electromagnetic inversion. Furthermore, a frequency hopping strategy to improve the resolution of the unknown objects when the frequency is raised, is underlined. Results of numerical experiments are presented to illustrate both strengths and weaknesses of the method.

This paper presents a new design of spread spectrum signals with the minimally sufficient dimension from the view point of frequency diversity. Letting the signature signal duration and the bandwidth be denoted by T and B, respectively, we can nominally represent a signature signal of either Direct Sequence (DS) or MultiCarrier (MC) spread spectrum system as the sum of N=BT sinusoidal signal units with their frequencies separated by 1/T or its multiples. In our design,assuming the maximum expected channel delay spread σd « T as usual, one signature signal viewed in the frequency domain is made up of the minimum number K 2πσdB of sinusoidal signal units which are arranged so as there is placed at least one unit in coherence bandwidth 1/(2πσd) in which the fading channel transfer function has strong correlation. Although the signature signal does not make use of all the units in the given frequency domain as in the ordinary spread spectrum systems, but uses only skipped units, it can be shown that almost the same frequency diversity effect is attained. And it is also shown that the immunity to the external interfering signals is by no means inferior. If every L=N/K T/(2πσd) consecutive sinusoidal signal units are assigned to the K signal units of a signature signal, L different signature signals are simultaneously available mutually orthogonal when the synchronous demodulation is performed in the same T period. We call each of the orthogonal sinusoidal signal sets a Frequency Devision (FD) signal set. Now, CDMA can be independently realized on each of the L FD signal sets provided the operation is synchronous or quasi-synchronous with respect to the symbol demodulation (or signature) period. Partitioning the simultaneous users among the FD sets, it is possible to decrease the number of CDMA users to be processed, retaining the total number of simultaneous users. Owing to this effect, the multiple access performance for the FD/CDMA system is shown to be superior to that of the ordinary DS or MC/CDMA system, assuming matched filter reception based on the complete estimation of the channel characteristics for the both cases. The decrease of the number of CDMA users per FD set makes it practical for the receiver to employ multiple access interference cancellation and even the maximum likelihood detection. Curiously, any FD signal set can be represented in the time domain as L repetition of a sequence with its period equal to K in the number of 1/B duration time chips.

Blind channel estimation algorithm which is applicable to the time-variant channel under frequency-selective fading is proposed. The condition on the blind channel identifiability using temporally and spatially oversampled data is shown. The proposed algorithm consists of two stages. At the first stage, the channel equalization matrix is estimated by taking account of the time-variant characteristics of the channel. At the second stage, the signals and the channel matrix are alternately estimated by using the finite alphabet property of the transmitted symbols. Periodical return from the second stage to the first makes the blind estimation algorithm feasible for the time-variant channel with fast fading. The simulation results confirm the fast convergence property and the effectiveness of the proposed algorithm in coping with the frequency-selective fading.

In this work, a temperature stable voltage-to-frequency converter (VFC) in which the output frequency is proportional to the input voltage is proposed. The output frequency range is from 22 kHz to 60 kHz and the difference between simulated and calculated values is less than about 5% for this range of output frequency. The temperature variation of sample output frequencies is less than 0.5% in the temperature range -25C to 75C.

Voltage holding property of liquid crystal (LC) cell for long period was investigated and the experimantal results were analyzed using a microscopic model considered the movement of ions in LC layer. The time dependent voltage decay curve observed in the experiment, which is not driven by the analysis with the conventional equivalent circuit comprised of the capacitance and the resistance, can be well explained by the microscopic model.

A new method is introduced for sequential estimation of TDOA (time delay of arrival) and FDOA (frequency delay of arrival) in a two sensor array. The proposed scheme is basically a two step algorithm utilizing 1-dimensional slice functions of the third order cumulants between two signal measurements, and is capable of suppressing the effect of correlated Gaussian measurement noises. It is demonstrated that the proposed algorithm outperforms existing TDOA/FDOA estimation algorithms from the viewpoint of computational burden and in the sense of mean squared error as well.

MF (medium frequency) radars (MFR) are powerful tools for understanding the upper atmosphere, by measuring horizontal wind velocity and electron density. This article introduces three MFR systems, two in Japan, Yamagawa (31.20N, 130.62E) and Wakkanai (45.36N, 141.81E) radars, and one at Poker Flat, Alaska (65.1N, 147.5W). Experimental techniques, and their observed results are briefly shown. Horizontal wind velocity was observed by those MFRs, in height ranges of 60-100 km (day) and 80-100 km (night) at Yamagawa and Wakkanai, while the data coverage is unusually low, >54 km (day) and >68 km (night), at Poker Flat. Comparison of MFR winds with temperature observed by a collocated Rayleigh lidar at Poker Flat shows consistency of those two instrument results in terms of atmospheric wave theory, implying validity of MFR data at such low altitudes. Electron density results at Poker Flat agree reasonably with International Reference Ionosphere model values at 74-84 km, and agree well with variation of cosmic noise absorption by the Poker Flat imaging riometer, suggesting valid electron density estimation by MFR at least below 80-85 km.

An airborne X- and L-band synthetic aperture radar system was developed by the Communications Research Laboratory and the National Space Development Agency of Japan in their joint project from 1993 to 1996. It is installed in the airplane, Gulfstream II. In both the azimuth and range directions, the resolution is 1.5 m for the X-band and 3 m for the L-band. Both SARs can make fully polarimetric observations. The X-band SAR has a cross-track interferometric function. In this paper we describe the SAR system, its ground processing system, and its performance. We also discuss motion compensation and interferogram quality.