This paper describes 1.0 V operation power performance of a double doped AlGaAs/InGaAs/AlGaAs heterojunction FET for personal digital cellular phones. The developed FET with a multilayer cap consisting of a highly Si-doped GaAs, an undoped GaAs and a highly Si-doped AlGaAs exhibited an on-resistance of 1.3 Ωmm and a maximum drain current of 620 mA/mm. A 28 mm gate-width device, operating with a drain bias voltage of 1.0 V, demonstrated an output power of 1.0 W, a power-added efficiency of 59% and an associated gain of 13.7 dB at an adjacent channel leakage power at 50 kHz off-center frequency of -48 dBc with a 950 MHz π/4-shifted quadrature phase shift keying signal.

We have discussed a ray tracing method to estimate the scattering characteristics from random rough surface. It has been shown from the traced rays that the diffracted rays dominate over the reflected rays. For the field evaluation, we have used the Fresnel function for the diffracted coefficient and the Fresnel's reflection coefficients. Numerical examples have been carried out for the scattering characteristics of an ocean wave-like rough surface and the delay spared characteristics of a building-like surface. In the present work we have demonstrated that the ray tracing method is effective to numerical analysis of a rough surface scattering.

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.

In this paper we propose a new timing and phase recovery algorithm to mitigate the inter-symbol interference (ISI) effect and to increase the permissible data rate. We use the mean excess delay of the channel as the timing instant for sampling no matter what symbol rates are transmitted and use the phase of the complex baseband impulse response sampled at the corresponding instant as the carrier phase for compensation. The mean excess delay of a channel is independent of the data transmission rates and can be estimated by the conventional timing recovery circuit by transmitting a low rate data sequence with symbol interval longer than the channel delay spread. We have numerically compared the transmission performances without and with applying our proposed algorithm in the timing and phase recovery. We also compare the transmission performance of the decision feedback equalizer (DFE) when the inputs to the DFE are sampled by the conventional method and by our proposed method. We found that the new scheme has a better performance. Compare with the conventional method, the normalized permissible data rate at a BER threshold of 10-5 and an outage probability of less than 2% can be increased by 5 times. While the new scheme is employed together with DFE, the performance can be further improved. Simulation results for both simulated and physical channels have verified the effectiveness of the new scheme.

This paper presents efficient time slot assignment algorithms applicable to the uplink of SDMA system. A frame consists of one control time slot and multiple communication time slots where terminals in different angular positions share the same time slot. In the proposed algorithms, a time slot is assigned to a new terminal considering not only the signal quality of the new terminal but also the signal quality of active terminals. Simple calculation method for estimated signal-to-interference plus noise ratio (SINR) is employed to decrease the computational complexity. The performance of the proposed algorithms is evaluated by computer simulation and compared with sectorized systems to show the validity of the proposed algorithms.

In order to ease the impact of the packet fragmentation problem and to avoid network congestion in TCP over UBR, packet discard schemes in ATM layer (such as PPD and EPD) have been proposed. These schemes drop packets before they reach their intended destinations if the network is congested and the packets are to be partially discarded. On the other hand, TCP also regulates data flow with its own flow control method. Due to restriction of data flow at the TCP layer, buffer space is not fully used in an ATM switch. In order to make use of more buffer resources, this paper generalizes the PPD and EDP schemes. From this generalization, an optimistic packet discard scheme named the "Probability-Based Delayed Packet Discard" (PDPD) scheme is proposed. Depending on a particular probability, this scheme sets a discard flag to delay actual discard operation. This paper presents the results of several simulated models to find out the potential of improvement of goodput by PDPD. The results of these simulations indicate that PDPD obtains higher goodput than ordinary schemes when the packet size is large and the input load is not light. This author concludes that a PDPD scheme should achieve effective goodput and link utilization while using more buffer resources effectively.

This paper provides a normalized Iterative Feedback Tuning (IFT) method that assures the boundedness of the gradient vector estimate (ρ) and the Hessian matrix estimate without the assumption that the internal signals are bounded. The proposed method uses the unbiased Gauss-Newton direction by the addition of the 4-th experiment. We also present blended control criteria and a PID-like controller as new design choices. In examples, the normalized IFT method results in a good convergence although the internal signal or the measurement noise variance is large.

The distribution for the envelope of the received signal over frequency-nonselective slow fading channels with additive white Gaussian noise (AWGN) is derived in this paper. System performances of noncoherent M-ary signals over slow and flat fading channels in the presence of AWGN can be evaluated from the new probability density function (PDF) of the envelope.

Voltage follower is one of the most useful building blocks in analog circuits. This paper proposes a voltage follower composed of a complementary pair of p-channel MOS(PMOS) and n-channel MOS (NMOS) differential amplifiers which operates under low power supply. The proposed circuit has a rail-to-rail dynamic range by combining complementary differential amplifiers.

The features of the negative resistance in common source and common gate FET configurations for wideband VCO are studied. They are also explained by the simplified three-capacitor model. A design procedure is then developed. The results are applied to a design of wide band oscillator at the several gigahertz region.

A timer-based scheme is proposed to manage information within terminal and service profiles for both incall registration/deregistration of UPT users and incall registration resets of terminal owners. In the timer-based scheme, information related to incall registration for a UPT user in a terminal profile is deleted due to a timer expiration without accessing the terminal profile. The performance of the timer-based scheme is compared with the previously proposed request-based scheme in terms of; 1) total cost and, 2) the number of terminal profile accesses per unit time for a terminal. Even though provision of the timer-based scheme requires the modification of incoming call delivery procedure, the timer-based scheme can reduce both the total cost and the number of terminal profile accesses compared to the previously proposed request-based scheme.

In this paper, we examine an optimal reliability assignment/redundant allocation problem formulated as a nonlinear mixed integer programming (nMIP) model which should simultaneously determine continuous and discrete decision variables. This problem is more difficult than the redundant allocation problem represented by a nonlinear integer problem (nIP). Recently, several researchers have obtained acceptable and satisfactory results by using genetic algorithms (GAs) to solve optimal reliability assignment/redundant allocation problems. For large-scale problems, however, the GA has to enumerate a vast number of feasible solutions due to the broad continuous search space. To overcome this difficulty, we propose a hybridized GA combined with a neural-network technique (NN-hGA) which is suitable for approximating optimal continuous solutions. Combining a GA with the NN technique makes it easier for the GA to solve an optimal reliability assignment/redundant allocation problem by bounding the broad continuous search space by the NN technique. In addition, the NN-hGA leads to optimal robustness and steadiness and does not affect the various initial conditions of the problems. Numerical experiments and comparisons with previous results demonstrate the efficiency of our proposed method.

The variabilities of device characteristics are usually regarded as a normal distribution. If we consider the variabilities over the whole wafer, however, they cannot be expressed as a normal distribution due to the existence of global systematic component. We propose a statistical model, characterizing the global systematic component according to the distance from the center of the wafer, which can express the variabilities over the whole wafer statistically.

The paper proposes a transmitter diversity scheme with a desired signal selection for the mobile communication systems in which the severe cochannel interference (CCI) is assumed to occur at the base station. The feature of the proposed scheme is that the criterion of the downlink branch selection is based on the desired signal power estimated by the correlation between the received signal and the unique word at the matched filter. Moreover, the unique word length control method according to the instantaneous SIR is applied to the proposed scheme, taking account of the uplink transmission efficiency. Computer simulation results show that the proposed scheme provides the better performance than the conventional transmitter diversity in the severe CCI environments, and that the unique word length control method applied to the proposed scheme decreases the unique word length without the degradation of the transmission quality, comparing with the fixed unique word length method.

Loss analysis in bent graded-index optical slab waveguides is given using the modal-matching method. The conformal mapping replaces curved structure by an equivalent straight waveguide with a modified index profile. For this planar waveguide structure, the normal modes are calculated using a multilayer approximation method. The wave incident on the bend is expanded initially into a finite set of normal modes of the equivalent straight structure, and the transverse fields are matched across the junction. The numerical results show the loss formation in the graded-index waveguides and its dependence of the effective index of the corresponding straight waveguide.

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 letter, we introduce new parameters for classifying digitally modulated unknown QAM and PSK signals. Our two parameters for the classification are the variance of magnitude ratios and the mean of mod 2π phase differences. The gain adjustments of amplitudes are not required for the classification. Five different types of QAM constellations and three different types of PSK constellations are tested and the characteristics of our classification parameters are investigated in various SNR environments. Simulation results demonstrate the effectiveness of our proposed technique.

A merged analog-digital circuit architecture is proposed for implementing intelligence in SoC systems. Pulse modulation signals are introduced for time-domain massively parallel analog signal processing, and also for interfacing analog and digital worlds naturally within the SoC VLSI chip. Principles and applications of pulse-domain linear arithmetic processing are explored, and the results are expanded to the nonlinear signal processing, including an arbitrary chaos generation and continuous-time dynamical systems with nonlinear oscillation. Silicon implementations of the circuits employing the proposed architecture are fully described.

The structural characteristics of clusters are investigated in the partitioning process. Two partition functions, which show opposite properties around the optimal cluster number, are found and a new cluster validity index is presented based on the combination of these functions. Some properties of the index function are discussed and numerical examples are presented.

Message Sequence Chart (MSC) standardized by International Telecommunication Union is a graphical and textual language for specification of concurrent systems. It has been used formally as well as informally to specify behavior of real-time systems, in particular telecommunication switching systems. Formal verification of a system specification is crucial to ensure that implementation of the system works correctly. In particular, verification methods based on finite states have been widely used in telecommunication systems design. The methods determine global system states and transitions between them (i. e. , build a global state transition graph (GSTG)), and verify the system's desired properties, such as safety and liveness, on the GSTG. In this paper, we focus on construction of GSTGs from MSC specifications. We propose action dependency graph as an intuitive description of semantics of MSC specifications and present an algorithm to translate MSC specifications to action dependency graphs as well as an algorithm to construct a global state transition graph from an action dependency graph.