A new system, in which a real-time VLBI (very-long-baseline interferometer) is utilized, for real-time monitoring of atmospheric disturbances on a very-long baseline has been developed. In this system, beacon waves from geo-stationary satellites are used for received signals and public communication lines are used for data transmission. Connecting the system to the 6-m Kagoshima and the 10-m Mizusawa radio telescopes enables atmospheric disturbances to be observed. The cross-correlation phase was calculated from the received signals, and the Allan standard deviation of the phase was obtained. It was found that the Allan standard deviation across almost the whole region of the time interval reflects atmospheric disturbances.

Call demand suddenly and greatly increases in the aftermath of a major disaster, because people want to check on their families and friends in the stricken area. Many call attempts in mobile cellular systems are blocked due to the limited radio frequency resources. In this paper, as a solution to this problem, limiting the holding time of calls is investigated and a dynamic holding time limit (DHTL) method, which varies the holding time limit dynamically based on the number of call attempts, is proposed. The effect of limiting the holding time is investigated first using a computer simulation with a constant and heavy traffic load model. This simulation shows that the average holding time of calls is decreased as the holding time limit is reduced. But it also shows limiting the holding time decreases the number of calls blocked and forced call terminations at handover considerably. Next, a simple estimation method for the holding time limit, which reduces the blocking rate to the normal rate for increasing call demand, is described. Finally, results are given of a simulation, which show that the DHTL method keeps good performance for a sudden and great traffic load fluctuation condition.

This paper discusses self-similarity in cell dwell time of a mobile terminal, the discovery of which was described in our previous paper, and its effects on teletraffic of mobile communication networks. We have evaluated various teletraffic statistics, such as cell dwell time and channel occupancy time, of a mobile terminal based on measurements of motion for various types of vehicles. Those results show that cell dwell time follows a long-tailed log-normal distribution rather than the exponential distribution that has been used for modeling. Here, we first elaborate on self-similarity in cell dwell time of various vehicles. We then evaluate self-similarity in channel occupancy time. For future mobile multimedia communication systems employing a micro-cell configuration, it is anticipated that data communication will be the main form of communication and that call holding time will be long. For such cases, we have shown that channel occupancy time will be greatly affected by the cell dwell time of the mobile terminal, and that self-similarity, a characteristic that is not seen in conventional systems, will consequently appear. We have also found that hand-off frequently fails as self-similarity in cell dwell time of a mobile terminal becomes stronger.

In evaluating the teletraffic of mobile communication networks, it is important to model the motion of terminals. In the previous migration model, mobility characteristics of terminals, such as cell dwell time, have been expressed by a single probability distribution. In this paper, we discuss the modeling of the cell dwell time of terminals in each cell. Using measured data we show that cell dwell time differs from cell to cell and follows log-normal distributions rather than conventional exponential distributions.

For wireless communication, a low-voltage monolithic LC-tank CMOS voltage-controlled-oscillator (VCO) is developed with 0.2-µm fully-depleted silicon-on-insulator (SOI) CMOS process technology. The VCO features a double-tuning technique to achieve a wide tuning range with lateral p-n junction varactors. The VCO has the following features at the supply voltage of 1.5 V: (1) Output frequency range from 1.07 GHz to 1.36 GHz, (2) Third-harmonic below -37 dBc, and (3) Phase noise of -120 dBc/Hz at 1 MHz offset frequency.

Wireless data transmission at 3.0 Gbit/s was achieved by using millimeter-wave photonic techniques, such as optical 120-GHz subcarrier generation, optical modulation, and high-power photonic millimeter-wave emission. We have successfully demonstrated the transmission of optical Gigabit Ethernet signals over this link.

STM/STS measurements have been carried out for TTF-TCNQ complex films evaporated on hydrogen-terminated silicon substrates, and the variation of tunneling spectra has been investigated on morphologically different crystal grains. Very thin semiconductive adsorbed layers were found to cover the as-deposited film surfaces. By removing the adsorbed layers, the intrinsic electronic structures of two different phases were revealed. A 'needle phase' which appears at the early stage of film growth has a semiconductive character and a 'granular phase' which grows later has a metallic character similar to bulk crystals. The electronic structure of the needle phase is considered to be affected by the substrate although the crystallographic structure is similar to the bulk crystal of TTF-TCNQ.

In this paper, we present a new approach to the construction of a set of binary sequences with a zero-correlation zone. The set consists of n pairs of binary sequences and the length of each binary sequence is n2(m+2) for some integers m and n. The Hadamard sequences with length n are used to construct the set. Any sequence in the set has 2(m+1) subsequences, each of length 2n. The author proves that any two subsequences are orthogonal if they belong to different pairs of binary sequences in the set.

Transmit beamforming is a promising way to increase the downlink capacity of wireless networks. Since all users are coupled via their radiation patterns, the beamforming vectors must be optimized along with power control. It is necessary to balance the signal-to-interference levels according to individual QoS requirements. This problem leads back to the minimization of the infinity-norm of a certain vector and has first been studied by Gerlach and Paulraj in [1]. It has been assumed that the optimum solution can be obtained by minimizing the 1-norm instead, thereby leading to a new problem, which is generally easier to handle. The analytical and numerical results in this paper, however, indicate that this conjecture is generally not valid. We characterize the case where the 1-norm solution also solves the infinity-norm problem. In particular, it is shown that for the special case of a 2-user scenario, both optimization problems are indeed equivalent and a closed-form solution can be given. The analytical results provide new insights into the problem of coupled downlink beamforming and offer a useful approach to the design of efficient and reliable algorithms.

We proposed the conduction mechanism of organic light-emitting diode (OLED) using a one-dimensional discontinuous model. We assumed that each emitting molecule corresponds to a hopping site according to the actual charge transfer between adjacent molecules. Both carrier mobility of Alq3 and barrier heights for each carrier were derived from experimental data. We calculate transient behavior of carrier, field, and exciton distribution. Both carrier injections assumed the Schottky injection. In the previous results, when we assumed that calculated current density fit the experimental one in the current density field curve, calculated light-emission intensity did not fit the experimental one in the light-emission field curve. Furthermore, the slope of the calculated light emission-field curve is too small to fit the experimental one. In the previous study, hopping distance was assumed to be 1 nm. In this study, it is assumed to be 1.7 nm. We consider that field dependence of electron injection is too weak to explain only the Schottky emission. When the electron injection is assumed to be both Schottky emission and Fowler-Nordheim emission calculated light-emission field as well as the current-density field curves were fit to the curve of each experimental characteristics.

We have developed the new energy storage system utilizing a radical redox reaction of poly (2,2,6,6-tetramethylpiperidinoxy methacrylate), PTMA. The coin-type cell with PTMA cathode demonstrates the charge capacity of is 72 Ah/kg, which corresponds to 65% of the theoretical capacity, and the coulombic efficiency was 90% in first charge-discharge cycle. The results indicate that the stable polyradical cathodes are promising materials due to their high charge utilization and the possibilities for the wide diversity of molecular design.

Organic light emitting diodes (OLEDs) containing nanostructured cathode buffer layers were fabricated, and their electrical and emitting properties were investigated. The OLEDs have an ITO anode/CuPc/TPD/Alq3/buffer layer/Al cathode structure with the buffer layers made from nanostructured alternating layers Alq3 and Al. The driving voltage and the efficiency of the devices were improved by insertion of the buffer layer. It was estimated that some modulations of the Schottky barrier at the Alq3 and the Al cathode interface were induced due to the insertion of the buffer layer and it caused an enhancement of electron injection from the Al cathode.

The optical pulses of 50 MHz has been obtained from an organic light emitting diode (OLED) based on the Alq3 emissive layer with the active area of 0.01 mm2. We demonstrate that the OLEDs can be applied to fields of optical communication as the electro-optical conversion device for transmitting the signals of moving picture.

The threshold voltage of Coulomb staircase using organic molecules was analyzed by extending our previous model with only consideration of the metal/organic film interfacial space charge to the generalized one. The generalized model is helpful to examine coupling capacitance in organic double barrier tunneling junction (DBTJ). The current-voltage (I-V) characteristic of metal/polyimide (PI)/rhodamine-dendrimer (Rh-G2)/PI/metal junction was analyzed using this generalized model. The calculation results were in good agreement with our experimental data.

Metal nanostructure of organic/metal interface showing photocurrent multiplication phenomenon more than 105-fold was investigated. Au films deposited on organic films were revealed to be a gathering of nanoparticles and the multiplication rate can be tuned by the particle size. Spatial gaps formed between Au sphere and organic surface, which provide the hole accumulation sites (structural trap), was concluded to be indispensable for the photocurrent multiplication.

Timed token protocols inadequately provide periodic communication service, although this is crucial for hard real time systems. We propose an algorithm to guaranteeing periodic communication service on a timed token protocol network. In this approach, we allocate bandwidth to each node so that the summation of bandwidth allocations is Target Token Rotation Time (TTRT). If a node cannot consume the allocated time, the residual time is made concession to other nodes for non-periodic service using a timer which contains the unused time value and is appended to the token. This algorithm can always guarantee transmission of real-time messages before their deadlines when the network utilization is less than 50%.

In 1998, Fan and Lei proposed a partially blind signature scheme that could reduce the computation load and the size of the database for electronic cash systems. In this Letter, we show that their scheme could not meet the untraceability property of a blind signature.

The circular decoding algorithm for tail-biting convolutional codes is executed using a fixed number of computations and is suitable for DSP/ASIC implementations. This letter presents the performance and complexity trade-off in the circular decoding algorithm using an analytic bound on the error probability. An incremental performance improvement is shown as the complexity increases from O(L) to O(L+10K) where L is the length of the decoding trellis and K is the constraint length. The decoding complexity required to produce the maximum-likelihood performance is presented, which is applicable to many codes of practical interest.

A novel delta-sigma modulator that utilizes a resonant-tunneling diode (RTD) quantizer is proposed and its operation is investigated by HSPICE simulations. In order to eliminate the signal-to-noise-and-distortion ratio (SINAD) degradation caused from the poor isolation of a single-stage quantizer (1SQ), a three-stage quantizer (3SQ), which consists of three cascoded RTD quantizers, is introduced. At a sample rate of 10 Gsps (samples per a second) and a signal bandwidth of 40 MHz (oversampling ratio of 128), the modulator demonstrates a SINAD of 56 dB, which corresponds to the effective number of bits of 9.3.

Multicast is an efficient way to send messages to a group of members. It is becoming the basis for a number of applications, such as teleconferencing, news groups, and on-line games. Security is one of the main issues in realizing multicast communications. A working group within IETF dedicated to multicast security has been formed and RFCs and working drafts concerning multicast security are proposed. This letter analyzes the security of a scheme proposed in [1] for securely establishing a shared, secret key in a large, dynamic group. We show that it fails to provide forward and backward security.