In this paper, we describe design considerations for inverse dispersion fiber (IDF) whose chromatic dispersion is designed to compensate for that of conventional 1.3 µm zero-dispersion single-mode fiber (SMF). We clarify the appropriate structural parameters for W-type, triple-clad-type and ring-type refractive index profiles to realize a hybrid transmission line composed of SMF and IDF taking into consideration the bending sensitivity and the available wavelength bandwidth that achieves an average chromatic dispersion of below 1 ps/nm/km in the 1.55 µm region. We also show that, when the launched power is less than 0 dBm/ch, a hybrid transmission line composed of SMF and IDF provides better 40 Gbps 8 ch dense wavelength division multiplexing (DWDM) transmission performance than a conventional dispersion compensation scheme with a dispersion compensating fiber (DCF) module.

All-optical switching operating at 1.55 µm band in fabricated GaInAsP directional couplers loaded with grating are reported experimentally. These switching operations were realized in spatially separated output ports. The devices are suitable for optical integrated circuits and would operate as all-optical routing switches in practical power level by use of optical Kerr effect and Bragg grating. Using the optical bistability in the device, latching operation for output signal can be realized in spatially separated output ports and the outputs from each port are complementary. Two all-optical gate operations, which are optical inverting operation and optically controlled switching in spatially separated output ports, are also demonstrated, where the signal and control lights have different wavelength.

In this paper, we study loop pipeline scheduling problem under given resource assignment (operation to functional unit assignments and data to register assignments), which is one of the key tasks in data-path synthesis based on the assignment solution space exploration. We show an approach using a precedence constraint graph with parametric disjunctive arcs generated from the specified assignment information, and derive a scheduling method using branch-and-bound exploration of the parameter space. As an application of the proposed scheduling method, it is incorporated with Simulated-Annealing (SA) based exploration of assignment solution space, and it is demonstrated that data-paths of the fifth-order elliptic wave filter are successfully synthesized.

The Task-Coalition Assignment Problem (TCAP) is a formalization of the distributed computation problem. In TCAP, a set of agents and a set of tasks are given. A subset of the agents processes a task to produce benefit. The goal of TCAP is to find the combination of the tasks and the subsets of the agents that maximizes the sum of the benefit. In this paper, we define 1-TCAP, which is a practical subclass of TCAP. In 1-TCAP, tasks and agents are characterized by scalar values. We propose a polynomial-time approximation algorithm for 1-TCAP, and show that this algorithm achieves an approximation ratio 9/4. Here, an algorithm achieves an approximation ratio α for a maximization problem if, for every instance, it produces a solution of value at least OPT/α, where OPT is the value of the optimal solution.

We propose a set of Fabry-Perot etalons integrated in a planar lightwave circuit (PLC-FPE) designed for a unified system for broadcasting and communication. A PLC-FPE containing four etalons having different cavity lengths is fabricated and their loss and frequency characteristics are investigated. The total loss and the maximum finesse were found to be 8 dB and 34, respectively.

In this letter, a two-dimensional pilot-symbol aided (2-D PSA) channel estimation technique for coherent orthogonal frequency-division multiplexing (OFDM) systems with transmitter diversity is proposed. The 2-D PSA channel estimator and the corresponding orthogonality condition between the sets of pilot symbols are derived under minimum mean-square error (MMSE) criterion for OFDM systems with transmitter diversity. The proposed estimator is shown to be accurate and effective for tracking variations of channels between multiple transmitter antennas and receiver antennas.

In this paper, new integrated schemes of scheduling real-time traffic and cell loss control in high speed ATM networks are proposed for multiple priorities based on variable queue length thresholds for scheduling and the Partial Buffer Sharing policy for cell loss control. In our schemes, the queues for buffering arriving cells can be constructed in two ways: one individual queue for each user connection, or one physical queue for all user connections. The proposed schemes are considered to provide guaranteed QoS for each connection and cell sequence integrity for virtual channel/path characteristics. Moreover, these new schemes are quite flexible and can realize different scheduling algorithms. This paper also provides the Stochastic Petri Net models of these integrated schemes and an approximate analysis technique, which significantly reduces the complexity of the model solution and can be applied to real ATM switch models. From the numerical results, we can see that our schemes outperform those well-known schemes such as the head-of-line (HOL) priority control and the queue length threshold (QLT) policy.

Transmitter diversity is a powerful technique to improve the transmission quality of downlink in microcellular mobile communications systems. Under cochannel interference (CCI) at the base station (BS), the transmitter diversity is not necessarily effective, because the desired-plus-interference signal power used as a criterion of downlink branch selection is not always relative to the downlink propagation condition. This paper proposes the theoretical derivation of bit error rate (BER) performance in the transmitter diversity under CCI occurring at BS, as parameters of average SIR at BS, normalized Doppler frequency, and so on. It is confirmed from the correspondence of theoretical results with simulation results that the proposed theoretical approach is applicable to the CCI environments at BS.

As a new type of a linear decorrelating receiver, the Pseudo-Decorrelator was presented for asynchronous code division multiple access systems in [6]. In this paper, the concept of the Pseudo-Decorrelator is extended to derive a suboptimal receiver for WCDMA uplink systems in a Rayleigh fading environment. Starting with the analysis of the multiple access components of the decision statistics, a non-square cross-correlation matrix for each bit is obtained. This cross-correlation matrix is then inverted and the inverted matrix is applied to the decision statistics obtained from a conventional receiver. Simulation results are presented for K-user systems over a Rayleigh fading channel. The effects of the synchronization errors, such as time delays and carrier phase errors, are also examined through simulations in this paper.

A method for fast calibration of digital-beam-forming (DBF) receiving array antennas by means of digital signal processing is described. It uses plane wave arriving from a known direction that contains a known reference sequence. Non-uniformities of the amplitude and phase in the branches are detected and calibrated in real time by the complex correlation of a replica of the known reference sequence with the received signal obtained from the output signals of each element. No special circuit for calibration is required, and the non-uniformities can quickly be compensated for by digital signal processing even for an array antenna with many antenna elements. This method enables highly accurate calibration of large-scale array antennas operating at a high frequency even under a low signal-to-noise power ratio (SNR).

It is of considerable interest to study the vortex behavior of a multiply connected superconductor for potential applications of vortex devices. Our sample is made of a type-I superconductor Pb and a capillary plate. The nominal sizes are 1-µm in hole diameter and 1.8-µm in lattice pitch. The microholes form triangular lattice while a superconducting network consists of a honeycomb lattice. When each hole accommodates a single vortex 0, an applied magnetic field becomes a nominal matching field (7.83 G). We measure the magnetization curve of sample by means of a SQUID (superconducting quantum interference device) magnetometer in the accurate small fields on the order of Gauss. We find a sharp magnetization peak at 8.2 G at temperatures near the critical temperature Tc.

We fabricated ramp-edge junctions with barriers by modifying surface and integrating ground-planes. The fabricated junctions had current-voltage characteristics consistent with the resistive shunted-junction model. We also obtained a 1-sigma spread in the critical current of 7.9% for 100 junctions at 4.2 K. The ground-plane reduced the sheet inductance of a stripline by a factor of 3. The quality of the ground-plane was improved by using an anneal in oxygen atmosphere after fabrication. The sheet inductance of a counter-electrode with a ground-plane was 1.0 pH per square at 4.2 K.

Femtosecond optical pulses were irradiated into a YBa2Cu3O7-δ strip-line of 400 µm in width in order to investigate the relationship between the laser beam power profile and the distribution of the optically generated magnetic fluxes. To homogenize the current distribution in the strip-line, a half of the strip-line was patterned into the ordered array structure of holes of 2 µm in diameter at an interval of 4 µm, and several experimental conditions were examined by changing the focal size of the pulsed laser beam at the sample surface. As a result, it was found out that the generated optical magnetic fluxes strongly depend on the power profile of the femtosecond optical pulses, and showed a possibility for the application to a laser beam profiler and the other optical devices.

Independent component analysis (ICA) is a new method of extracting independent components from multivariate data. It can be applied to various fields such as vision and auditory signal analysis, communication systems, and biomedical and brain engineering. There have been proposed a number of algorithms. The present article shows that most of them use estimating functions from the statistical point of view, and give a unified theory, based on information geometry, to elucidate the efficiency and stability of the algorithms. This gives new efficient adaptive algorithms useful for various problems.

We have fabricated a novel type of intrinsic Josephson junctions with superconducting Bi2Sr2CaCu2O8+y (Bi-2212)/YBa2Cu3O7-x(YBCO) bilayer thin films deposited on MgO(100) substrates. We used the 4th harmonics of a Nd:YAG pulsed laser ablation. Furthermore, we studied the transport properties of a 25 µm 25 µm Bi-2212/YBCO mesa-type junction. The zero resistance temperature was around 50 K. The current-voltage characteristics showed flux-flow-like behavior and a supercurrent of about 2 mA at 4.2 K. Shapiro steps were observed when microwave was irradiated to the mesa junction. These Shapiro steps are attributed to the Josephson junction formed at the interface between the Bi-2212 and YBCO layers in the mesa structure and not to the intrinsic Josephson junctions in the Bi-2212 layer or the micro-grains within the films.

A new low-voltage, all-in-one ESD (electrostatic discharging) protection circuit was designed. One such ESD protection unit is enough to protect each I/O pad against ESD stresses of all modes, i.e., from I/O to power supply and ground positively and negatively. This novel ESD circuit features adjustable trigger-voltage, i.e., 5 V to 60 V, with low turn-on threshold down to 5 V, symmetric active discharging channels in all directions, fast response time of 0.1 to 0.3 ns, and high ESD performance/area ratio of greater than 80 V per micrometer width. It was implemented in commercial BiCMOS technologies and achieved 14 kV human body model (HBM) and 15 kV air-gap IEC ESD protection levels. This compact ESD structure can not only provide adequate ESD protection, but also minimize the ESD-induced parasitic effects, which makes it a suitable ESD protection solution for mixed-signal and RF ICs in very deep sub-micron regime.

This contribution discusses which information can be derived from estimated directions of arrival (DOAs) and directions of departure (DODs) from a multiple-input multiple-output (MIMO) radio system, and establishes two new parameters describing the multipath spread at both link ends. We find that the multipath component separation, MCS, combines delay, (double-) angular and Doppler dispersion, as appropriate. MCS provides a system-independent radio characterization of propagation environments and aids in selecting optimum positions for smart-antenna deployment. Evaluation of double-directional measurements (antenna arrays at both link ends) in indoor environments show the usefulness and the limits of the multipath component separation concept.

In the literature, the optimum discrete interpolation approximation is presented. However, this approximation is the optimum for the union of the set of band-limited signals and the set of the corresponding approximation errors. In this paper, under several assumptions, we present two optimum extended discrete interpolation approximations such that the set of the corresponding approximation errors is included in the set of signals if we ignore some negligible component of error. In this paper, we assume that the decimated sampling interval T satisfies T M, where M is the number of paths of the filter bank. The maximally distinct or under sampled filter banks treated in this paper have FIR analysis filters with or without a continuous pre-filter and FIR synthesis filters with a band-limited continuous D/A filter. The first discussion is useful for designing a kind of down-converter which transforms HDTV signal with wide band-width to SDTV signal with narrow band-width, for example. In this discussion, we assume that the SDTV signal is limited in |ω|π/T and the Fourier spectrum of the HDTV signal has wider band but is approximately included in the corresponding narrow band of the SDTV signal. In the well-known scalable coding of signals, if the spectrum of a signal with higher resolution is not included approximately in the spectrum of the corresponding signal with lower resolution, the quality of the quantized output signal with lower resolution will become quite low practically. As shown in [3], however, scalable coding has received much attention recently in the fields of HDTV/SDTV compatibility. Therefore, it will be natural to consider that the spectrum of HDTV signal with higher resolution is similar to and is included approximately in the corresponding spectrum of SDTV signal with lower resolution. The analysis filters are FIR filters with a continuous pre-filter approximately band-limited in |ω|π/T. To improve the quality of the SDTV signal, the whole spectrum component of the HDTV signal is used in the presented down-converter. Another discussion is a general theory of approximation for filter banks using the prescribed analysis filters. In this discussion, although some modification for the band-width is introduced in the process of analysis, the final band-width of the receiver is limited in |ω| π. The FIR analysis filters do not have pre-filter. The condition imposing on the set of signals is more general than the corresponding condition in the first optimum approximation theory. Finally, we present the optimum transmultiplexer TR. In general, under the condition that the receiver filters are prescribed, a transmultiplexer has approximation error between the original signal and the transferred signal. However, the presented TR minimizes approximately the supreme value of arbitrary positive measures of approximation error that can be defined, totally or separately, with respect to all the channels. Note that, in the presented discussion, we can prescribe the degree of FIR filters used in TR, strictly.

Existing code division multiple access (CDMA) cellular systems achieve capacity gains over conventional time division multiple access (TDMA) or frequency division multiple access (FDMA) systems, by assuming a large number of low data-rate and hence low power users uniformly distributed over a cell. In current CDMA proposals for providing higher data-rate packet services, however, burst high data-rate users do not satisfy this assumption and thus the capacity advantage is lost. In this letter, we quantify the capacity loss with focusing on location-dependent aspects of the degradation. This work contributes to a better understanding of the capacity problem encountered when introducing high data-rate packet services with the cellular band where existing low data-rate CDMA systems operate.

In this paper, the iterative decoding of BCH product codes also called Block Turbo Codes (BTC) is evaluated for the HIPERLAN/2 OFDM system. Simulations show that expurgated BCH codes should be chosen as constituent codes in order to outperform the specified convolutional code. We also show that the bit-by-bit frequency interleaver has a big impact on the behaviour of the turbo decoding process and that increasing its size together with time diversity lead to good performance when compared to the convolutional code.