OBS is a realistic solution to the mismatch of the capacity of optical fiber and electrical switching in backbone photonic networks. One of the critical issues in OBS networks is to avoid burst contention at transit nodes. This problem induces the rapid growth of burst-transmission delay time under heavy traffic loads. In this paper, we propose a low-delay burst transmission scheme using burst segmentation at source node to suppress the growth in burst-transmission delay. In our scheme, a burst is divided and burst-transfer time is determined by the multiple information about reservation of other bursts at all transit nodes. We analyzed capabilities of the proposed scheme and found that it more efficiently suppresses the growth of the burst-transmission delay time in heavy traffic loads compared with some conventional signaling schemes.

In D.O.A. estimation, identification of the signal and the noise subspaces plays an essential role. This identification process was traditionally achieved by the eigenvalue decomposition (EVD) of the spatial correlation matrix of observations or the generalized eigenvalue decomposition (GEVD) of the spatial correlation matrix of observations with respect to that of an observation noise. The framework based on the GEVD is not always an extension of that based on the EVD, since the GEVD is not applicable to the noise-free case which can be resolved by the framework based on the EVD. Moreover, they are not applicable to the case in which the spatial correlation matrix of the noise is singular. Recently, a quotient-singular-value-decomposition-based framework, that can be applied to problems with singular noise correlation matrices, is introduced for noise reduction. However, this framework also can not treat the noise-free case. Thus, we do not have a unified framework of the identification of these subspaces. In this paper, we show that a unified framework of the identification of these subspaces is realized by the concept of proper and improper eigenspaces of the spatial correlation matrix of the noise with respect to that of observations.

This paper examines a system which is inspected at equally spaced points in time. We express the observed states of the system as a discrete time Markov chain with an absorbing state. It is assumed that the true state is certainly identified through inspection. After each inspection, one of three actions can be taken: Operation, repair, or replacement. We assume that the result of repair is uncertain. If repair is taken, we decide whether to inspect the system or not. When inspection is performed after completion of repair, we select an optimal action. After replacement, the system becomes new. We study the optimal maintenance policy which minimizes the expected total discounted cost for unbounded horizon. It is shown that, under reasonable conditions on the system's deterioration and repair laws and the cost structures, a control limit policy is optimal. We derive several valid properties for finding the optimal maintenance policy numerically. Furthermore, numerical analysis is conducted to show our theoretical results could hold under weaker conditions.

This paper presents a fast transient simulation method for power distribution networks (PDNs) of the PCB/Package. Because these PDNs are modeled as large-scale linear circuits consisting of a large number of RLC elements, it takes large costs to solve by conventional circuit simulators, such as SPICE. Our simulation method is based on the leapfrog algorithm, and can solve RLC circuits of PDNs faster than SPICE. Actual PDNs have frequency-dependent dispersions such as the skin-effect of conductors and the dielectric loss. To model these dispersions, more number of RLC elements are required, and circuit structures of these dispersion models are hard to solve by using the leapfrog algorithm. This paper shows that the circuit structures of dispersion models can be converted to suitable structures for the leapfrog algorithm. Further, in order to reduce the simulation time, our proposed method exploits parallel computation techniques. Numerical results show that our proposed method using single processing element (PE) enables a speedup of 20-100 times and 10 times compared to HSPICE and INDUCTWISE with the same level of accuracy, respectively. In a large-scale example with frequency-dependent dispersions, our method achieves over 94% parallel efficiency with 5PEs.

Iterative receivers, which perform MMSE detection and decoding iteratively, can provide significant performance improvement compared with noniterative method. However, due to the high computational cost and numerical instability, conventional MMSE detection using a priori information can not be implemented in hardware. In this letter, we propose a newly-built iterative receiver which is division-free and numerically stable, and then we analyze the results of a fixed-point simulation and present the hardware implementation architecture.

Free-space optical communication systems can provide high-speed, improved capacity, cost effective and easy to deploy wireless networks. Experimental investigation on the next generation free-space optical (FSO) communication system utilizing seamless connection of free-space and optical fiber links is presented. A compact antenna which utilizes a miniature fine positioning mirror (FPM) for high-speed beam control and steering is described. The effect of atmospheric turbulence on the beam angle-of-arrival (AOA) fluctuations is shown. The FPM is able to mitigate the power fluctuations at the fiber coupling port caused by this beam angle-of-arrival fluctuations. Experimental results of the FSO system capable of offering stable performance in terms of measured bit-error-rate (BER) showing error free transmission at 2.5 Gbps over extended period of time and improved fiber received power are presented. Also presented are performance results showing stable operation when increasing the FSO communication system data rate from 2.5 Gbps to 10 Gbps as well as WDM experiments.

Substrate-coupling equivalent circuits can be derived for arbitrary isolation structures by F-matrix computation. The derived netlist represents a unified impedance network among multiple sites on a chip surface as well as internal nodes of isolation structures and can be applied with SPICE simulation to evaluate isolation strengths. Geometry dependency of isolation attributes to layout parameters such as area, width, and location distance. On the other hand, structural dependency arises from vertical impurity concentration specific to p+/n+ diffusion and deep n-well. Simulation-based prototyping of isolation structures can include all these dependences and strongly helps establish an isolation strategy against high-frequency substrate coupling in a given technology. The analysis of isolation strength provided by p+/n+ guard ring, deep n-well guard ring as well as deep n-well pocket well explains S21 measurements performed on high-frequency test structures targeting 5 GHz bandwidth, that was formed in a 0.25-µm CMOS high frequency.

JPEG2000 compression standard considers a block of wavelet coefficients, called codeblock, as the smallest coding unit that being independently entropy-coded. In this paper, we propose a codeblock-based concealment technique for JPEG2000 images to mitigate missing codeblock due to packet loss in network transmission. The proposed method creates a single JPEG2000 codestream from an image that composed of several subsampled versions of the original image and transmit the codestream over a single channel.The technique then substitutes the affected codeblock in a subsampled image with a copy of the corresponding codeblock obtained from other subsampled images. Thus, it does not require an iterative processing, which is time consuming, to construct an estimated version of the lost data. Moreover, it is applicable for a large codeblock size and can be implemented either in wavelet or codestream domain. Simulation results confirm the effectiveness of the proposed method.

Decoding performance of LDPC (Low-Density Parity-Check) codes is highly dependent on the degree distributions of the Tanner graphs which define the LDPC codes. We compare two LDPC code ensembles, one has a uniform degree distribution and the other a non-uniform one over a BEC (Binary Erasure Channel) and a BSC (Binary Symmetric Channel) thorough DE (Density Evolution). We then derive sufficient conditions on the erasure probability of a BEC and the error probability of a BSC, under which the LDPC code ensembles with uniform degree distributions outperform those with non-uniform degree distributions.

Lightwave switching is discussed with a cascaded connection of optical couplers with light intensity control elements. By employing wavelength-selective amplifiers such as a waveguide-type Raman amplifier, all-optical wavelength-selective switching can be realized. We discuss analytically using coupled-mode theory that the lightwave switching is feasible by controlling the intensity of propagating lightwave. The switching operation is verified numerically using finite-difference beam-propagation method. As a result, the expected operation is realized and some characteristics involved with dependencies of wavelength and phase are also investigated. A preliminary experiment using attenuators, beam splitters and mirrors is also described to verify the switching operation with only light-intensity control in interferometers.

A highly accurate measurement method of parameters of MZ-type LN optical intensity modulators is presented. In this method, a CW optical signal is input to an optical terminal and small CW RF signal is applied to an electrode of the modulator. Then sideband levels of an output optical signal at different bias points are measured by using optical spectrum analyzer. By using 1st order sideband levels which are measured at two different bias conditions, and using a compensation method to measured levels, we can obtain accurate chirp parameter even when very small power of RF signal is applied to the modulator. In this method, the chirp parameter can be obtained in good accuracy when the input RF voltage is only 3% of the halfwave voltage.

Optically controlled beam forming techniques are effective for phased-array antenna control. We have developed the Fourier transform optical beamformer (FT-OBF). The antenna radiation pattern inputted into an amplitude spatial light modulator (A-SLM) is optically Fourier transformed to a specific phase-front light beam equivalent to an antenna excitation in the FT-OBF. Optical signal processing, used the Fourier transform optics, is effective to large-scale, two-dimensional, and high-speed signal processing. To implement a flexible and finer antenna beam pattern control, we use an A-SLM as input image formation of the FT optics. And, to realize a small-size FT-OBF, we use symmetric triplet lenses with convex, concave and convex lens. The total optical system becomes below 1/5 length compared with the length using single lens. Finally, we evaluated the developed FT-OBF with the generated amplitude and phase distributions, which excitation signal of an array antenna. We measured an antenna radiation beam pattern, beam steering and beam width control, in the C-band. Measurement results agreed with theoretical calculated results. These results show the feasibility of the spatial light modulator based FT-OBF.

We propose a simple technique to form miniature optical circuits using microfibers embedded into a low refractive index matrix. As an example we demonstrate a silica microfiber knot resonator embedded in a fluoroacrylate polymer. Fabrication issues and initial experimental results are reported. We also present simulations aimed at understanding the current limitations to the Q-factor and the role of the embedding polymer refractive index on the Q-factor of future resonators. It is anticipated that using commercially available polymers high Q-factor resonators with radii as small as 100 micrometers can be made by this technique.

Using an electro-absorption duplexer (EAD) we presented a transceiver (TRx) module for dual function of both electrical-to-optical (E/O) and optical-to-electrical (E/O) conversion at 60 GHz band. The EAD chip was fabricated by monolithically integrating both a waveguide photodiode (PD) and an electro-absorption modulator (EAM) in association with traveling wave electrodes. We also investigated the issues of RF packaging in which the optoelectronic and electronic amplifier devices were co-packaged in a single housing. The RF impedance matching was accomplished in assistance with a microstrip bandpass filter.

This paper reports on a fiber-optic system for in-building wireless communication/broadcast systems developed in Samsung Electronics. Our system delivers the third generation mobile system, satellite-digital multimedia broadcast, and wireless local access network services over a single strand of single-mode fiber or multi-mode fiber. We present the design issue and experimental results of the radio-over-fiber link.

Optical processing with efficient coding is expected in photonic label routing network. We consider optical codes encoded in the time and spectral domains. Wavelength-selective devices are useful for effective processing of such optical codes. In this study, collinear acoustooptic (AO) switches are investigated as a constituent elements of a wavelength selective correlator for optical BPSK codes. It is theoretically shown that the number of optical codes that can be distinguished is 2Nt-1, where Nt is the bit number of optical pulses. The device can also be used for recognition of codes encoded in time and spectral domains. Crosstalk in code recognition is discussed with numerical analysis considering AO filtering characteristics for optical processing with collinear AO devices.

This paper starts by describing the advantages of cascaded modulation, i.e., using multiple concatenated external modulators to modulate CW (Continuous Wave) light. Next, the paper examines computer simulations of the resulting modulated light waveform shapes and intermodulation distortion values to elucidate the basic modulation characteristics of a cascaded modulation scheme. Examples of applying cascaded modulation to a multi-channel optical signal transmission system are shown, and the characteristics are clarified by optical transmission experiments. For example, the dependency of the signal quality on the modulation depth values of each external modulator is clarified. Moreover, experiments show that cascaded modulation permits the remote insertion of local broadcast programs into wide area broadcast programs. Last, the paper shows that cascaded modulation offers better modulation properties than the conventional single modulation approach.

This paper proposes an iterative maximum a posteriori probability (MAP) receiver for multiple-input-multiple-output (MIMO) and orthogonal frequency-division multiplexing (OFDM) mobile communications. For exploiting the space, time, and frequency diversity, the low-density parity-check code (LDPC) is used as a channel coding with a built-in interleaver. The receiver employs the expectation maximization (EM) algorithm so as to perform the MAP symbol detection with reasonable computational complexity. The minimum mean square error (MMSE), recursive least squares (RLS), and least mean square (LMS) algorithms are theoretically derived for the channel estimation within this framework. Furthermore, the proposed receiver performs a new scheme called backward symbol detection (BSD), in which the signal detection uses the channel impulse response that is estimated one OFDM symbol later. The advantage of BSD, which is explained from the viewpoint of the message passing algorithm, is that BSD can exploit information on the both precedent and subsequent OFDM symbols, similarly to RLS with smoothing and removing (SR-RLS) [25]. In comparison with SR-RLS, BSD reduces the complexity at the cost of packet error rate (PER) performance. Computer simulations show that the receiver employing RLS for the channel estimation outperforms the ones employing MMSE or LMS, and that BSD can improve the PER performance of the ones employing RLS or LMS.

An improved methodology, based on the genetic algorithm, is developed to design thermal-via structures and circuit parameters of advanced InGaP and InGaAs collector-up heterojunction bipolar transistors (C-up HBTs), which are promising miniature high-power amplifiers (HPAs) in cellular communication systems. Excellent simulated and measured results demonstrate the usefulness of this technique.

This paper describes a CMOS voltage reference circuit which occupies small die area and has less than 1.25 V of output voltage. The reference voltage is determined by a resistor ratio, and it is possible to set the reference voltage from zero to near the supply voltage with the same temperature independence as those of Widlar's and Brokaw's bandgap voltage references. The temperature-independent reference voltage is formed by adding two voltages: the amplified fractional VBE (base-to-emitter voltage) of a bipolar transistor with a negative TC (temperature coefficient) and the amplified VT (thermal voltage) with a positive TC. When a reference voltage smaller than 1.25 V is required, the voltage gain of the amplifier for VBE becomes less than one, and the voltage gain of the amplifier for VT becomes small. This enables the size of bipolar transistors for VT generation to be small. The proposed voltage reference circuit was implemented in a standard 0.35-µm CMOS technology. A temperature-independent current source was also obtained from the same circuit. The results were a TC (temperature coefficient) of 46 ppm/ over 130 change, a line regulation of 2.2 mV/V for the 0.5 V reference voltage with 8.7 µA of current consumption in the voltage reference part, and a 6% change over 130 change for the 13 µA current source.