Parallel TCP is one possible approach to increasing throughput of data transfer in Long Fat Networks (LFNs). Using parallel TCP is something of black art. As high-speed transport-layer protocols appear, e.g. HSTCP, it is necessary to reinvestigate the performance of parallel TCP, because a choice has to be make among them for the system. In this paper, the performance of parallel TCP is evaluated by mathematical analysis based on a simple dumbbell topology. Packet drop rate and aggregate goodput are used as two metrics to characterize the performance of parallel TCP. Two cases, namely synchronization and non-synchronization, are analyzed in detail when DropTail is deployed on routers. The synchronization case is common in using parallel TCP, but the goodput deteriorates seriously. The non-synchronization case may benefit parallel TCP, but extra mechanisms are required, and it is not easy to implement in the real world. The problem also remains even if Random Early Detection (RED) queue management is employed on routers. The analysis results show the difficulty in using parallel TCP in practice.

Recently, we proposed space-time block coded-joint transmit/receive antenna diversity (STBC-JTRD) for narrow band transmission in a frequency-nonselective fading channel; it allows an arbitrary number of transmit antennas while limiting the number of receive antennas to 4. In this paper, we extend STBC-JTRD to the case of frequency-selective fading channels and propose frequency-domain STBC-JTRD for broadband direct sequence-spread spectrum (DSSS) signal transmission. A conditional bit error rate (BER) analysis is presented. The average BER performance in a frequency-selective Rayleigh fading is evaluated by Monte-Carlo numerical computation method using the derived conditional BER and is confirmed by computer simulation of the signal transmission. Performance comparison between frequency-domain STBC-JTRD transmission and joint space-time transmit diversity (STTD) and frequency-domain equalization (FDE) reception is also presented.

IEEE 802.11 DCF is an asynchronous and distributed MAC protocol which does not require the existence of a central controller for medium access coordination. This flexibility, which is due to DCF's contention-based nature, comes at the expense of the overhead associated with contention resolution. The overhead consists of frame collision time and channel idle time, which is particularly severe when channel is saturated. In this paper, we present an enhancement of DCF which aims at reducing its contention resolution overhead by equipping it with a distributed reservation mechanism. The proposed reservation mechanism enhances collision avoidance mechanism of DCF by enforcing a partially ordered medium access through an implicit agreement between neighboring nodes. Simulation results, using ns-2 network simulator, show that the added reservation scheme 1) effectively reduces DCF's overhead and improves channel utilization particularly when node density and traffic load is high, 2) significantly enhance DCF's fairness.

Time-frequency-selective, equivalently time-variant multipath, fading channels in orthogonal frequency division multiplexing (OFDM) systems introduce intercarrier interference (ICI), resulting in severe performance degradation. To suppress the effect of ICI, several symbol detection methods have been proposed, all of which are based on the observation that most of the ICI's power is distributed near the desired subcarrier. However, these methods usually ignore the channel variation in a OFDM symbol block by fixing the number of considered ICI terms. Therefore, we propose a novel frequency-domain symbol detection method with moderate complexity, which adaptively determines the number of ICI terms within each OFDM symbol block.

In this research, a sub-array preconditioner is applied to improve the convergence of conjugate gradient (CG) iterative solver in the fast multipole method and fast Fourier transform (FMM-FFT) implementation on a large-scale finite periodic array antenna with arbitrary geometry elements. The performance of the sub-array preconditioner is compared with the near-group preconditioner in the array antenna analysis. It is found that the near-group preconditioner achieves a little better convergence, while the sub-array preconditioner can be easily constructed and programmed with less CPU-time. The efficiency of the CG-FMM-FFT with high efficient preconditioner has been demonstrated in numerical analysis of a finite periodic array antenna.

Development of ultrafast optical interfaces that can operate in sub-terahertz region is important to apply superconducting electronic devices to the high-end systems. We have performed several fundamental researches to realize the ultrafast optical input interface for superconducting electronic devices. Firstly, we observed optical response of amorphous Ge thin films, and the results indicated that an amorphous Ge photoconductive switch could stably operate in a terahertz frequency range as an optical-to-electrical signal converter in the low-temperature region below Tc of YBCO. Next, we have fabricated optical-to-electrical signal conversion system with photomixing technique, and we have demonstrated the generation and the detection of high frequency signals over 50 GHz. Finally, we have observed optical responses of a Josephson vortex flow transistor under irradiation of femtosecond laser pulses, and the results suggeste that the device has high potential as an optical interface.

Nowadays, MIMO systems are playing an important role in wireless communications. In this paper, we propose a spatial-temporal adaptive MIMO beamforming scheme for single carrier transmission in frequency-selective fading channels with the assumption of perfect channel state information (CSI) at both the transmitter and receiver. The transmit and receive weight vectors for detecting the preceding signal and the receive weight vectors for detecting the delayed signals of the preceding signal are designed by an iterative update algorithm. Based on minimum mean square error (MMSE) method, the delayed versions of the preceding signal are exploited to maximize the output signal to interference and noise ratio (SINR) instead of suppressing them at the receiver. The improvement of output SINR is useful for MIMO systems to enhance the high-quality communication in broadband wireless systems.

Ultra-wideband pulse radars are promising candidates for 3-dimensional environment measurements by autonomous robots. Estimating 3-dimensional target shapes by scanning with an omni-directional antenna is an ill-posed inverse problem. Conventional algorithms such as the synthetic aperture method or parametric algorithms have a problem in terms of their calculation times. We have clarified the existence of a reversible transform between received data and target shapes for 3-dimensional systems. Calculation times are remarkably reduced by applying this transform because it directly estimates target shapes without iterations. We propose a new algorithm based on the transform and present an application example using numerical simulations. We confirm that the proposed algorithm has sufficient accuracy and a short calculation time.

This paper describes an 11-Gb/s CMOS demultiplexer (DEMUX) using redundant multi-valued logic (RMVL). The proposed circuit is received to serial binary data and is converted to parallel redundant multi-valued data. The converted data are reconverted to parallel binary data. By the redundant multi-valued data conversion, the RMVL makes it possible to achieve higher operating speeds than that of a conventional binary logic. The implemented DEMUX consists of eight integrators. The DEMUX is designed with 0.35 µm standard CMOS process. The validity and effectiveness are verified through HSPICE simulation. The DEMUX is achieved to the maximum data rate of 11-Gb/s and the average power consumption of 69.43 mW. This circuit is expected to operate at higher speed than 11-Gb/s in the deep-submicron process of the high operating frequency.

In this paper, we have derived the new solution for the medium-frequency and the high-frequency ground wave propagation in a surface duct over mixed-paths. We have shown newly that the solution for the ground wave propagation in a standard atmosphere can be obtained directly from the solution for the surface duct problem by applying the analytic continuation from the negative equivalent radius of curvature of the earth to the positive one. Through the theoretical and experimental studies, it is confirmed that the radio wave propagating over the sea in the land-to-sea mixed-paths is enhanced by the recovery effect. It is clarified that the ground wave is also enhanced in the surface duct in a long range propagation. It is shown that the unexpected attenuation and the anomalous variation with distance are appeared in the propagation in the urban area due to the emergence of the slow-wave type trapped surface wave.

In this paper, novel hardware sharing architectures are proposed for realizations of fast 44 and 88 forward/inverse integer transforms in H.264/AVC applications. Based on matrix factorizations, the cost-effective architectures for fast one-dimensional (1-D) 44 and 88 forward/inverse integer transforms can be derived through the Kronecker and direct sum operations. By applying the concept of hardware sharing, the proposed hardware schemes for fast integer transforms need a smaller number of shifters and adders than the direct realization architecture, where the direct architecture just implements the individual 44 and individual 88 integer transforms independently. With low hardware cost and regular modularity, the proposed hardware sharing architectures can process up to 125 MHz with the cost-effective area and are suitable for VLSI implementations to accomplish the H.264/AVC signal processing.

An electrooptic near-field mapping system based on a gain-switched distributed feedback (DFB) pulsed laser and a CdTe electrooptic crystal was used for characterizing stationary and transient near-field patterns of conventional and uniplanar compact photonic band gap (UC-PBG) patch antennas. Effect of the UC-PBG structure on reduction in surface waves in the UC-PBG patch antenna was experimentally verified by comparing stationary and transient near-field measurement of the conventional and UC-PBG patch antennas.

We study on the security proof of the improved efficient-Rabin (ERabin) scheme and the F-FDHS scheme. First, we show that the security theorem of the improved ERabin scheme is not correct, and then provide a correct theorem for it. Second, we show that the security theorem of the F-FDHS scheme lacks an assumption. Finally, we present a way to modify the improved ERabin scheme and the F-FDHS scheme.

In this paper we study the problem of how to identify multiple disjoint paths that have the minimum total cost OPT and satisfy a delay bound D in a graph G. This problem has lots of applications in networking such as fault-tolerant quality of service (QoS) routing and network-flow load balancing. Recently, several approximation algorithms have been developed for this problem. Here, we propose a new approximation algorithm for it by using the Lagrangian Relaxation method. We then present a simple approximation algorithm for finding multiple link-disjoint paths that satisfy the delay constraints at a reasonable total cost. If the optimal solution under delay-bound D has a cost OPT, then our algorithm can find a solution whose delay is bounded by (1+)D and the cost is no more than (1+k)OPT. The time complexity of our algorithm is much better than the previous algorithms.

When a cylindrically curved concave conducting surface is terminated abruptly at the edge, the whispering gallery (WG) mode propagating toward the edge direction is radiated into the free space from the aperture plane at the edge. In this paper, by applying the new analysis method, we shall derive a uniform geometrical theory of diffraction solution (UTD) for the electric-type WG mode radiation field applicable in the transition region near the geometrical boundaries produced by the incident modal ray on the edge of the curved surface. The UTD is represented by the summation of the solution for the geometrical ray converted from the modal ray of the WG mode and the solution for the uniform edge diffracted ray scattered at the cylindrically curved edge. By comparing with the reference solution obtained numerically from the integral representation of the radiation field, we will confirm the validity and the utility of the UTD proposed in this paper.

A novel procedure for an efficient and rigorous solution of electromagnetic scattering problems is presented. It is based on the use of universal bases that are obtained by applying the SVD procedure to PO-derived basis functions. These bases, constructed by totally bypassing any matrix-type approach, can be used for all angles of incidence and their use leads to a matrix with relatively small dimensions. The method enables us to solve 2D scattering problems in a computationally efficient and numerically rigorous manner.

Ultrahigh-speed fiber lasers operating at up to 40 GHz offer a clean longitudinal comb and a narrow linewidth. This makes them suitable for applications including optical comb generation, ultrahigh-speed optical pulse transmission including PSK, and as opto-microwave oscillators. In this paper, we describe recent progress on ultrafast fiber lasers and their applications to optical metrology.

In OFDM based mobile communication systems, channel variation during one symbol period introduces intercarrier interference (ICI). Conventional pilot-aided equalization mitigates the ICI at the price of band inefficiency. On the other hand, the blind or semi-blind equalization method, which utilizes the known statistic properties of the transmitted data, will raise system complexity. In this letter, without bandwidth-consuming pilots, a novel channel estimation and tracking method based on an iterative equalization technique (IET) is proposed. The proposed approach successfully achieves a good compromise between bandwidth efficiency and system complexity, and its validity is demonstrated by numerical simulations, especially for fast fading channel.

We propose a writing circuit scheme to screen intermittent failure cells for toggle MRAM. The scheme, comprising a current waveform circuitry that controls rise/fall time of writing current, drastically decreases the probability of intermittent failure. To apply the scheme to large-capacity MRAMs, a current booster containing discharging capacitors has also been developed. It adjusts the waveform of writing current to that designed by the current waveform circuitry even in presence of parasitic capacitors and resistors along the writing current path. Such a technique is essential for achieving stability in large-capacity MRAMs.

Guiding and nanofocusing of a two-dimensional (2D) optical beam in a negative-dielectric-gap waveguide is studied theoretically. An index-guiding method along the dielectric core embedded in the negative-dielectric-gap is proposed and the confinement properties of the 2D optical beam are studied by the effective-refractive-index method and FDTD simulations. We have shown that the lateral beam width of the 2D optical beam can be shrunk to zero beyond the diffraction limit. A tapered negative-dielectric-gap waveguide using adiabatic propagation achieves nano-focusing and can be applied to nano-optical couplers. This is a gateway from conventional dielectric waveguides to nano-optical integrated circuits.