A clustering scheme for ad hoc networks is aimed at managing a number of mobile devices by utilizing hierarchical structure of the networks. In order to construct and maintain an effective hierarchical structure in ad hoc networks where mobile devices may move at high mobility, the following requirements must be satisfied. (1) The role of each mobile device for the hierarchical structure is adaptive to dynamic change of the topology of the ad hoc networks. The role of each mobile device should thus change autonomously based on local information in each mobile device. (2) The overhead for management of the hierarchical structure is small. The number of mobile devices in each cluster should thus be almost equivalent. This paper proposes an adaptive multihop clustering scheme for highly mobile ad hoc networks. The results obtained by extensive simulation experiments show that the proposed scheme does not depend on mobility and node degree of mobile devices in the network, which satisfy the above requirements.

In this paper, we present a new analog multiplier with wide input range which is achieved by utilizing the variable threshold voltage characteristics of FG-MOSFET's. The performance of the proposed multiplier is evaluated through HSPICE simulation with 2.0 µm CMOS process parameters. From HSPICE simulation, we can find that the proposed multiplier can be operated at the supply voltage of 3.0 V with 3.0 Vp-p input range. Namely, the input voltage range of the multiplier is equal to the supply voltage. The maximum power consumption of the multiplier is 8.8 mW. The THD is 1.36% under the condition that the amplitude of the input signal is 3.0 Vp-p and the frequency is 1 MHz. Under the same condition, the linearity error is less than 0.5%. The -3 dB bandwidth of the proposed multiplier is 23 MHz.

The use of concatenated codes in non-coherent synchronous optical fiber CDMA networks is proposed. The concatenated code sequences are generated using Walsh code sequences and balanced Walsh code sequences, which are selected from Walsh code sequences. The selection of balanced Walsh code sequences is presented and the design of fully programmable electro-optical transmitter and receiver is reported. In the proposed network, sequence-inversion keying of intensity modulated unipolar concatenated code sequences is employed at the transmitter and unipolar-bipolar correlation is implemented at the receiver. The analysis of the system BER performance is presented and it is proved that multiple-access interference is completely eliminated. It is also shown that the BER performance of the proposed system is better than that of non-coherent synchronous optical fiber CDMA system using optical orthogonal codes with double hard-limiters.

Evaluating the generalization performance of learning machines without using additional test samples is one of the most important issues in the machine learning community. The subspace information criterion (SIC) is one of the methods for this purpose, which is shown to be an unbiased estimator of the generalization error with finite samples. Although the mean of SIC agrees with the true generalization error even in small sample cases, the scatter of SIC can be large under some severe conditions. In this paper, we therefore investigate the causes of degrading the precision of SIC, and discuss how its precision could be improved.

In this paper, we investigate the problem how to construct integer codes capable of correcting any single error in the set {1,t,...,tk-1} and generalize our results to obtain (e1,e2,...,es) single error correctable codes where ei's are different elements in A. Moreover, we shall give the exact form of the check matrix in most of the classes considered in this paper.

Full-duplex transmission of 60.0 GHz and 59.6 GHz millimeter-wave (mm-wave) signals of 155.52-Mbit/s differential phase shift keying (DPSK) data, radio-on-fiber (ROF) signals over 25-km-long standard single-mode fibers (SMFs) is experimentally demonstrated for the first time using a single 2-RF-port electroabsorption transceiver (EAT). The simplification of base stations (BSs) is strongly required to realize cost-effective and high-reliability mm-wave wireless access. This single EAT detects a C-band ROF signal modulated by a mm-wave downlink signal and simultaneously modulates the L-band optical carrier by a mm-wave uplink signal. The BS mainly consists of the EAT, leading to a simple and low-cost BS. Optical pilot tones and optical bandpass filters are used for photonic downconversion and photonic upconversion, to convert frequencies between mm-wave signals and intermediate frequency (IF) signals in the optical domain. With the use of optical conversions, these signals have no significant fading problems. The simultaneous transmission of both up- and downlinks has been achieved with the BER of less than 10-9. Also the fading problems due to the fiber dispersion of photonic conversions are analyzed mathematically in this paper. The single-EAT BS will become a promising candidate for a ROF access system.

We have designed and fabricated air-bridged modulators with bandwidths exceeding 10 GHz, the highest yet realised to date for InGaAsP/InGaAsP multiple-quantum-well (MQW) asymmetric Fabry-Perot modulators (AFPMs). Microwave modulation, measurements of intermodulation between the photodetected downlink and modulated uplink signals, and bi-directional broadband data over fibre transmission experiments have been performed to verify the potential of the AFPM as a single electrical/optical transceiver. We also report the first direct integration of this AFPM with a microstrip patch antenna and present results of a preliminary microwave signal transmission experiment over a distance of 1.4 m in free-space at 5.2 GHz with the integrated AFPM as a photodetector.

A low power MPEG-4 video codec LSI with the capability for core profile decoding is presented. A 16-b DSP with a vector pipeline architecture and a 32-b arithmetic unit, eight dedicated hardware engines to accelerate MPEG-4 SP@L1 codec, CP@L1 decoding and post video processing, 20-Mb embedded DRAM, and three peripheral blocks are integrated together on a single chip. MPEG-4 SP@L1 codec, CP@L1 decoding and post video processing are realized with a hybrid architecture consisting of a programmable DSP and dedicated hardware engines at low operating frequency. In order to reduce the power consumption, clock gating technique is fully adopted in each hardware block and embedded DRAM is employed. The chip is implemented using 0.18-µm quad-metal CMOS technology, and its die area is 8.8 mm 8.6 mm. The power consumption is 90 mW at a SP@L1 codec and 110 mW at a CP@L1 decoding.

We demonstrate polarization-independent and highly-efficient optical fiber wavelength converters in a 10 Gb/s NRZ transmission system. They are based on synchronous phase or frequency modulations of the two orthogonally polarized pump lights, and can suppress not only the stimulated Brillouin scattering (SBS) but also the spread of the converted spectrum without modulating the signal light.

In 2002, Hwang and Yeh proposed some improved schemes to mend several security flaws in the Peyravian-Zunic password transmission scheme and password change scheme. However, this article will point out that there still exist some security flaws in the Hwang-Yeh schemes; at the same time, we shall also propose some improved versions of their schemes.

A decentralized estimation system usually contains a number of remotely located local sensors that can pre-process observed signal and convey the processed data to a fusion center that makes a final estimation. The local sensors are linked to the data fusion center by transmission channels. When the observation (or estimate of parameter) is quantized at the peripheral sensors and an assumption of conditionally independent sensor data is made, due to potential communication constraints on the channels, the problem of quantization design and bandwidth allocation among the channels linking local sensors to the fusion center is studied in this letter.

This paper proposes an automated 3D visualization method of embedded tubes applicable to the scanned result of pulse-radar Non-Destructive Testing (NDT). The proposed method consists of three stages. First, our method defines the processing region which includes a pattern generated by a tube. This region is determined by referring to the composition of a received wave. Second, after expert knowledge of a tube is translated into fuzzy inference rules, the positions of embedded tubes are identified by inferring them. Third, 3D links of the identified positions are formed to visualize the continuous shape of the tubes. Consequently, the tubes are extracted, and their 3D shapes are visualized. The experimental result on the specimens shows that our method was able to find all tubes that exist in the radiograph and the schematic. Our method could thus provide the internal information of concrete with sufficient accuracy required in the practical construction work.

In this paper, we propose a simple method to find the optimal rational function, with a fixed denominator, which minimizes an integral of polynomially weighted squared error to given analytic function. Firstly, we present a generalization of the Walsh's theorem. By using the knowledge on the zeros of the fixed denominator, this theorem characterizes the optimal rational function with a system of linear equations on the coefficients of its numerator polynomial. Moreover when the analytic function is specially given as a polynomial, we show that the optimal numerator can be derived without using any numerical integration or any root finding technique. Numerical examples demonstrate the practical applicability of the proposed method.

The CDMA/NC-PRMA protocol has been proposed to deal with multimedia traffic flexibly in mobile communications systems. The Load-Balancing (LB) method has been investigated for information slot assignment in CDMA/NC-PRMA systems. However, the LB method may be not effective in multi-cell environments due to inter-cell interference although this method is effective for single cell environments. In this paper, we propose new information slot assignment methods for multi-cell environments; a total reception power based assignment method and a signal to interference ratio (SIR) based assignment method. The former one assigns information slots based on the total reception power from both inside and outside the cell for each slot in the previous frame. The latter one predicts the SIR of receiving packets and assigns information slots to MSs only when predicted SIR exceeds the target SIR. The results of computer simulation show that the proposed schemes have superior transmission performance to the conventional scheme.

This paper focuses on a global ultrasonic system for self-localization of a mobile robot. The global ultrasonic system consists of some ultrasonic generators fixed at some arbitrary position in the global coordinates and two receivers in the moving coordinates of the mobile robot. This system is used to obtain the state vector of the mobile robot in the global coordinates from the distance measurement between the ultrasonic generator and the receiver. In order to avoid the cross-talk and to synchronize the ultrasonic sensors, the sequential cuing technique using small-sized radio frequency module is adopted. An extended Kalman filter algorithm is used to process the noisy ultrasonic signal and to estimate the state vector. Computer simulations and experiments are conducted to verify the effectiveness of the proposed global ultrasonic system.

The joint histogram of second order scale space differential invariants of natural images (including textures) is typically clustered about parabolic surface patches, whereas symmetrical elliptical patches (local convexities or concavities) are very rare and symmetrical hyperbolical patches also occur less frequently than parabolic patches. We trace the origin of this striking effect in the context of Gaussian random noise. For this case one may derive the joint histogram of curvedness and shape index analytically. The empirical observations are fully corroborated. In deriving these results we introduce a polar coordinate system in the space of second order scale space derivatives that turns out to be particularly useful in the study of the statistics of local curvature properties. The empirical observations apply also to non-Gaussian noise (e.g., Brownian noise) as well as to photographs of natural scenes. We discuss general arguments that help explain these observations.

Recently, layer-4 (L4) switches have been widely used as load balancing front-end routers for Web server clusters. The typical L4 switch attempts to balance load among the servers by estimating load using the load metrics measured in the front-end and/or the servers. However, insufficient load metrics, measurement overhead, and feedback delay often cause misestimate of server load. This may incur significant dynamic load imbalance among the servers particularly when the variation of requested content is high. In this paper, we propose a new content sniffer based load distribution strategy. By sniffing the requests being forwarded to the servers and by extracting load metrics from them, the L4 switch with our strategy more timely and accurately estimates server load without the help of back-end servers. Thus it can properly react to dynamic load imbalance among the servers under various workloads. Our experimental results demonstrate substantial performance improvements over other load balancing strategies used in the typical L4 switch.

To accommodate best-effort multimedia Internet protocol (IP) connections in mobile environments, we introduced new criteria for TCP-friendliness and developed a control algorithm for the transient response and stability in the packet transmission rate. We improved the maximum throughput and QoS guaranteed congestion control algorithm (MAQS) by using these two solutions, and solved the following problems that Reno and conventional congestion control algorithms have: (1) network congestion cannot be avoided when the round-trip time (RTT) is short and the holding time is long, (2) the packet transmission rate of a long-RTT connection is small when it is multiplexed with short-RTT connections, (3) the packet transmission rate cannot be adjusted quickly when the channel capacity changes according to hand-off.

Without transmit power control (TPC) and Rake combining, the uplink capacity of a direct sequence code division multiple access (DS-CDMA) packet mobile communication system significantly degrades due to the near-far problem and multipath fading. In this letter, assuming a single cell system with an interference-limited channel, the impact of the joint use of Rake combining and TPC on the uplink capacity is evaluated by computer simulation. Slow TPC is found to give a link capacity larger than fast TPC. This is because, with slow TPC, the received signal power variations due to fading remain intact and this results in a larger capture effect.

A new multilayer artificial neural network learning algorithm based on the pattern search method is proposed. The learning algorithm is designed to provide a very simple and effective means of searching the minima of an objective function directly without any knowledge of its derivatives. We test this algorithm on benchmark problems, such as exclusive-or (XOR), parity and alphabetic character learning problems. For all problems, the systems are shown to be trained efficiently by our algorithm. As a simple direct search algorithm, it can be applied to hardware implementations easily.