This paper proposes an adaptive modulation/TDMA scheme to achieve high capacity personal multi-media communication systems. TDMA is employed to cope with various bit rate for multi-media services. The modulation scheme is selected from 1/4-rate QPSK, 1/2-rate QPSK, QPSK, 16QAM and 64QAM according to the received C/IC (power ratio of the desired signal to the co-channel interference) and the delay spread. The spectral efficiency is evaluated by using the simulated bit error rate (BER) performance as well as the cumulative distribution of the C/IC with parameters of cell configurations. The results show that the spectral efficiency of the proposed scheme is 3.5 times higher than that of the conventional QPSK systems at the outage probability of 10%, and the effect is more remarkable at lower outage probability. The results also show that the proposed adaptive modulation is effective in improving delay spread immunity.

To provide personal, intelligent, and multimedia services through a mobile communications network, a Mobile Service Control Point (M-SCP) was developed, which performs both the location register and service control functions. The M-SCP was constructed on a common platform to allow quick introduction of new services. Software techniques to reduce the frequency of process-switching, assign the highest priority to real-time tasks, and operate a multiple-CPU structure provide faster real-time processing. This is confirmed by computer simulation and research in the field.

Development of a large-scale mobile communications network (IMN: Intelligent Mobile communications Network), as an infrastructure integrating multimedia functions, is indispensable for the support of future mobile communication services aiming toward "personalization," "intelligence," and "multimedia services." This paper discusses the aims of mobile communications and the outline of network technology aspects of PDC (Personal Digital Cellular) network which is currently in service. In addition, the future prospect of mobile communication technologies is discussed with special focuses on the support of universal mobility, network architecture including mobile communications platform, and multimedia technologies in the transport and access systems.

ACk is the class of problems solvable by an alternating Turing machine in space O(log n) and alternation depth O(logk n) [S. A. Cook, A taxonomy of problems with fast parallel algorithms, Inform. Contr. vol. 64]. We consider a game played by two persons: each player alternately moves a marker along an edge of a given digraph, and the first palyer who cannot move loses the game. It is shown that the problem to determine whether the first player can win the game on a digraph with n nodes exactly after logk n moves is complete for ACk nuder NC1 reducibility.

A numerical method is introduced which is suitable for mode analysis in an optical resonator with complicated refractive-index variations such as vertical cavity surface emitting lasers (VCSELs). In this method, the optical field of a laser mode is expressed as a linear combination of component fields with their coefficents to be determined. After a hypothetical boundary is set surrounding the region to be analyzed, the component fields are obtained by numerically integrating the wave equation in the inside region using the conditions on part of the boundary as the initial values of the integration. The total field, which is a linear combination of these fields, satisfies the equation and the selected part of the boundary conditions regardless of the coefficients. The conditions imposed on the total field on the rest of the boundary lead to a matrix eigenvalue problem, from which the optical frequency and the coefficients are obtained. The matrix expresses only boundary conditions and, therefore, its size is much smaller than that of a matrix expressing bulk conditions, as appears in the finite element method or the finite difference method. At the same time, this method has the advantage of adaptability for graded-index problems in contrast to conventional boundary formalisms such as the boundary element method and the mode matching method, because in the present method the component fields (or base functions) are calculated for individual index distributions while in these methods an inflexible set of base functions is used. As an example of the application of the method, mode properties in gain-guided VCSELs are analyzed using this method based on a two-dimensional model. This is the first model that takes into account the effects of standing-wave formation in the resonator and of the incident angle- and polarization-dependence of reflectivity. The ability to treat these effects makes the present method suitable for VCSELs equipped with a thin active layer and with multi-layer reflectors. Basic properties including polarization, threshold gain, oscillation wavelegths, and deflection of far-field patterns have been predicted for various cavity sizes and for various gradients in gain distributions. The major results of the analysis are: TE modes have lower thresholds than TM modes; the laser beam can be steered by tailoring the gain distribution as with edge-emitting lasers.

Radar signals fluctuate because of the incoherent scattering of raindrops. Dual-polarization radar estimates rainfall rates from differential reflectivity (ZDR) and horizontal reflectivity (ZH). Here, ZDR and ZH are extracted from fluctuating radar signals by averaging. Therefore, instrumentally measured ZDR and ZH always have errors, so that estimated rainfall rates also have errors. This paper evaluates rainfall rate errors caused by signal fluctuation. Computer simulation based on a physical raindrop model is used to investigate the standard deviation of rainfall rate. The simulation considers acquisition time, and uses both simultaneous and alternate sampling of horizontal and vertical polarizations for square law and logarithmic estimators at various rainfall rates and elevation angles. When measuring rainfall rates that range from 1.0 to 10.0mm/h with the alternate sampling method, using a logarithmic estimator at a relatively large elevation angle, the estimated rainfall rates have significant errors. The simultaneous sampling method is effective in reducing these errors.

We studied the selective epitaxy of GaAs grown by a technique called pulsed-jet epitaxy. Pulsed-jet epitaxy is a kind of atomic layer epitaxy (ALE) based on low-pressure metalorganic vapor-phase epitaxy (MOVPE). We compared growth behavior and layers grown by ALE and MOVPE. During ALE we supplied trimethylgallium (TMGa) and arsine (AsH3) alternately; however, during MOVPE we supplied TMGa and AsH3 simultaneously. At a growth temperature of 500, we obtained a better growth selectivity using ALE than using MOVPE. The lateral thickness profile of the ALE-grown GaAs layer at the edge of SiO2 mask was uniform. In contrast, the MOVPE growth rate was enhanced near the mask edge. Using ALE, we selectively grew GaAs epilayers even at mask openings with submicron widths. Scanning electron microscopy revealed that the ALE selectively grown structures had an uniform thickness profile, though the facets surrounding the structures depended on the orientation of mask stripes. After MOVPE, however, the (001) surface of the deposited layer was not flat because of the additional lateral diffusion of the growth species from the gas phase and/or the mask surface and some crystal facets. The experimental results show that, using ALE, we can control the shape of selectively grown structures. Selective epitaxy by ALE is a promising technique for fabricating low-dimensional quantum effect devices.

This paper presents the M-LCELP (Multi-mode Learned Code Excited LPC) speech coder, which has been developed for the next generation half-rate digital cellular telephone systems. M-LCELP develops the following techniques to achieve high-quality synthetic speech at 4kb/s with practically reasonable computation and memory requirements: (1) Multi-mode and multi-codebook coding to improve coding efficiency, (2) Pitch lag differential coding with pitch tracking to reduce lag transmission rate, (3) A two-stage joint design regular-pulse codebook with common phase structure in voiced frames, to drastically reduce computation and memory requirements, (4) An efficient vector quantization for LSP parameters, (5) An adaptive MA type comb filter to suppress excitation signal inter-harmonic noise. The MOS subjective test results demonstrate that 4.075kb/s M-LCELP synthetic speech quality is mostly equivalent to that for a North American full-rate standard VSELP coder. M-LCELP codec requires 18 MOPS computation amount. The codec has been implemented using 2 floating-point dsp chips.

We report the development of high-performance small-scale AlGaAs/GaAs collector-up heterojunction bipolar transistors (C-up HBT) with a carbon (C)-doped base layer. Oxygen-ion (O+) implantation is used to define their intrinsic emitter/base junctions and zinc (Zn)-diffusion is used to lower the resistivity of their O+-implanted extrinsic base layers. The highly resistive O+-implanted AlGaAs layer in the extrinsic emitter region sufficiently suppresses electron injection even under high-forward-bias conditions, allowing high collector current densities. The use of a C-doped base is especially effective for small-scale C-up HBT's because it suppresses the undesirable turn-on voltage shift caused by base dopant diffusion in the intrinsic area around the collector-mesa perimeter that occurs during the high-temperature Zn-diffusion process after implantation. Even in a small-scale trasistor with a 2 µm2 µm collector, a current gain of 15 is obtained. A microwave transistor with a 2 µm10 µm collector has a cutoff frequency fT of 68 GHz and a maximum oscillation frequency fmax of 102 GHz. A small-scale C-up HBT with a 2 µm2 µm collector shows a higher fmax of 110 GHz due to reduced base/collector capacitance CBC and its fmax remains above 100 GHz, even at a low collector current of 1 mA. The CBC of this device is estimated to be as low as 2.2 fF. Current gain dependence on collector size is also investigated for C-up HBT's and it is found that the base recombination current around the collector-mesa perimeter reduces the current gain.

Linear lightwave networks (LLNs) are optical networks in which network nodes perform only linear operations on optical signals: power splitting, combining, and non-regenerative amplification. While previous efforts on LLNs assume only one fiber per link, we consider a multi-fiber linear lightwave network (M-LLN) architecture for telecommunications where switching exchanges are normally connected by multi-fiber cables. We propose a class of linear path (LP) allocation schemes for establishing optical paths in M-LLNs, and show that they have a better performance than those proposed for single-fiber LLNs. We show that M-LLNs can be implemented with commercially available components, and discuss the implementation issues in detail.

The techniques for imaging optically opaque region using an electromagnetic wave radar are being developed. One important application of these techniques is the detection of buried pipes and cables. The image quality of subsurface radar often becomes low because the electromagnetic waves are affected by the attenuation and inhomogeneity of soil. Hence, a method which improves the quality of the radar images has been required. The migration method is utilized in reflective seismic processing and is derived based on the solution of the wave equation represented in spatial frequency domain. It is classified into the F-K and the phase-shift (P-S) migration method. The former is derived on the assumption that propagation velocity of the wave is uniform in the soil while the latter is assumed that the propagation velocity is varying depending on the depth from the ground surface. The P-S method gives relatively good quality images but it requires very long computation time. In this paper, we propose the block migration method in which the F-K method is applied to the divided image blocks with local propagation velocity. In order to solve a problem concerning the connection between the contiguous blocks we present two approaches which are the processings using the overlapped regions and the Lapped Orthogonal Transform (LOT). Some experimental results point out that the block migration method has a good capability of improving the image quality and the processing time using LOT becomes one tenth in comparison with the P-S method.

The performance of multi-pulse pulse position modulation (MPPM) consisting of m slots and 2 pulses, denoted as (m, 2) MPPM, with imperfect slot synchronization is analyzed. The word error probability of (m, 2) MPPM in the presence of timing offset is analyzed, and the optimum symbol sets of (m, 2) MPPM minimizing the symbol error probability are assigned. When an unassigned symbol is detected, the receiver decodes the unassigned symbol as one of the assigned symbols having the highest probability of transition from the assigned symbol to the unassigned symbol. The bit error probability of (m, 2) MPPM in the presence of the timing offset is analyzed, and the bit error probability of (m, 2) MPPM is compared with that of PPM for the same transmission bandwidth and the same transmission rate. Moreover, the bit error probability of (m, 2) MPPM synchronized by a phase-locked loop (PLL) is also analyzed. It is shown that a word with two continuous pulses has better performance than a word with two separate pulses. It is also shown that when the timing offset occurs, and when the slot clock is synchronized by a PLL, (m, 2) MPPM performs better than PPM because (m, 2) MPPM has the optimum assigned symbols, and can decode detected words more correctly than PPM.

This paper presents new go-back-N ARQ protocols for point-to-multipoint communications over broadcast channels such as satellite or broadcast radio channels. In the conventional go-back-N ARQ protocols for multidestination communications, usually only error detection codes are used for error detection and m copies of a frame are transmitted at a time. In one of our protocols, a bit-by-bit majority-voting decoder based on all of the m copies of a frame is used to recover the transmitted frame. In another protocol, a hybrid-ARQ protocol, which is an error detection code concatenated with a rate repetition convolutional code with the Viterbi decoding, is used. In these protocols, a dynamic programming technique is used to select the optimal number of copies of a frame to be transmitted at a time. The optimal number is determined by round trip propagation delay of the channel, the error probability, and the number of receivers that have not yet received the message. Analytic expressions are derived for the throughput efficiency of the proposed protocols. The proposed point-to-multipoint protocols provide satisfactory throughput efficiency and perform considerably better than the conventional protocols under high error rate conditions, especially in environments with a large number of receivers and large link round trips. In this paper we analyze the performances of the proposed protocols upon the random error channel conditions.

This paper propeses a new motion compensation (MC) technique which reduces blurring called drift in moving pictures down-scaled with layered coding system. Encoder of the system compresses large amounts of digital video data in the same way of MPEG (Moving Picture Experts Group) algorithm. Decoder, on the other hand, expands a part of the compressed data and reconstructs down scaled pictures. The purpose of this paper is to reduce blurring which is observed in the reconstructed pictures. In this paper, cause of the blurring is analyzed and the method is introduced as a solution to the problem. The new method is implemented by a little modification of motion compensation (MC) of the decoder, namely increasing the number of tap of interpolation fillters of the MC. Compressing moving pictures, its effectiveness is also confirmed by means of not only subjective test but also signal to noise ratio.

Overlapping multi-pulse pulse position modulation (OMPPM) is a modulation scheme having higher capacity and cutoff rate than other conventional modulation schemes when both off-duration between pulses shorter than a laser pulsewidth and resolution better than a laser pulsewidth are realized [1],[2]. In Refs. [1],[2] erasure events of a few chips that can be decoded correctly is defined as an erasure event. This results in lower bounds on the performance of OMPPM in optical-direct-detection channel in quantum limited case. This paper analyzes more exact performance of OMPPM in optical direct-detection channel in quantum limited case when both off-duration between pulses shorter than a laser pulsewidth and resolution better than a laser pulsewidth are realized. First we derive the error probability of OMPPM with considering what chips are detected or erased. Then we derive the capacity and the cutoff rate of OMPPM using the error probability. It is shown that OMPPM outperforms on-off keying (OOK), pulse position modulation (PPM), multi-pulse PPM (MPPM), and overlapping PPM (OPPM) in terms of both capacity and cutoff rate for the same pulsewidth and the same duty cycle. Moreover, it is shown that OMPPM with fewer slots and more pulses per block has better cutoff rate performance when the average received power per slot is somewhat large.

A full CMOS cell technology for high density SRAMs has been developed. A 0.4 µm n+/p+ spacing has been achieved by a shallow trench isolation with a retrograde and a shallow well design. Dual gate 0.35 µm n- and p-channel MOSFETs were used for the high density full CMOS SRAM cell. The side-wall inversion problem to which MOSFETs are subject due to the trench isolation structure has been controlled by combining taper angled trench etching and a rounded trench edge shape. A dual gate 0.4 µm nMOS/pMOS spacing has also been accomplished with no lateral gate dopant diffusion by an enlarged grain size tungsten polycide gate structure. These techniques can resolve the bottleneck problem of full CMOS SRAM cell size reduction, and realize a competitive cell size against conventional polysilicon resistor load SRAM cell (E/R type cell) or thin-film-transistor load SRAM cell (TFT type cell) structures. A test chip of a 256 k bit full CMOS SRAM was fabricated to verify the process integration of the shallow trench isolation with the retrograde shallow well design and the dual gate CMOS structure. It has been recognized that the above techniques are possible solutions for deep sub-micron high density full CMOS SRAM cell structure.

This paper describes CMOS embedded RAMs we developed utilizing 1.3 µm and 0.8 µm process technologies. Our goal was to achieve high-performance switching for digital communication systems. Because such switching can best be obtained by using high-performance embedded RAMs, we used 0.8 µm process technology and developed a 4 kW9 b single-port embedded RAM with 5 ns access time and 100 mW power dissipation during32 MHz operation, and a 1 kW9 b dual-port embedded RAM with 3.7 ns access time and 100 mW power dissipation during 40 MHz operation. We implemented these RAMs on one chip in developing three time-switch VLSIs, one buffer memory VLSI for ATM switches, and two cross-connect switch VLSIs.

The progress of LSI technologies makes it possible to fabricate 256 MDRAM. However, it depends on the cost effectiveness of device fabrication that LSI memory can continue to be the technology driver or not. It is indispensable to make the device, process, and equipment as simple as possible for next generation LSI. For example, wavefront technologies in lithography, high energy ion implantation, and simple DRAM cell with SOI structure or high dielectric constant capacitor, are under development to satisfy both device performance improvement and process simplicity.

The data retention characteristics of a Flash memory cell with a self-aligned double poly-Si stacked structure have been drastically improved by applying a bi-polarity write and erase technology which uses uniform Fowler-Nordheim tunneling over the whole channel area both during write and erase. It is clarified experimentally that the detrapping of electrons from the gate oxide to the substrate results in an extended retention time. A bi-polarity write and erase technology also guarantees a wide cell threshold voltage window even after 106 write/erase cycles. This technology results in a highly reliable EEPROM with an extended data retention time.

High temperature superconductors are eminently suitable for use in high frequency devices because of their large energy gap. We fabricated weak link Josephson junctions connected in series. The junctions were constructed of EuBa2Cu3O7-x (EBCO) superconducting thin films on bicrystal MgO substrates. We measured their microwave broadband detection (video detection) characteristics. The responsivity (Sr) of the junctions depended on the bias current and their normal state resistance. The array junctions were effective in increasing normal state resistance. We obtained a maximum Sr of 22.6 [V/W].