Recently, wearable devices which use the human body as a transmission channel have been developed. However, there has been a lack of information related the transmission mechanism of such devices in the physical layer. Electro-magnetic communication trials using human body as transmission media have more than a decade's history. However, most of the researches have been conducted by researchers who just want to utilize the fact and practically no physical mechanisms have been researched until recently. Hence, in previous study, the authors proposed calculation models of the wearable transmitter and the receiver attached to the arm using the FDTD method. Moreover, the authors compared the calculated received signal levels to the measured ones by using a biological tissue-equivalent phantom. However, there was little analysis on each component of the propagated signal. In this paper, the authors clarified the transmission mechanism of the wearable device using the human body as a transmission channel from the view point of the interaction between electromagnetic wave and the human body. First, the authors focused their attention on measuring the each component of the propagated signal using a shielded loop antenna. From these results, the favorable direction of electrodes of the transmitter was proposed to use the human body as a transmission channel. As a result, longitudinal direction is effective for sending the signal to the receiver, compared to the transversal direction. Next, the authors investigated the dominant signal transmission channel, because the question of whether the dominant signal channel is in or around the arm had remained unsettled. To clear this question, the authors proposed the calculation model of an arm wearing the transmitter and receiver placed into a hole of a conductor plate. The electric field distribution and received signal voltage was investigated as a function of the gap between the hole of the conductor plate and the surface of the arm. The result indicated that the dominant signal transmission channel is not inside but the surface of the arm because signal seems to be distributed as a surface wave.

Recent progress and achievements in creating single fundamental mode vertical cavity lasers with the technique of etching a 2-dimensional pattern of photonic crystal holes into the top distributed Bragg reflector are described. A simulation method for the design of single mode lasers is described, along with accuracy and limitations in predicting modal properties in these devices. Progress in improving output power, methods of lowering threshold currents, and small signal modulation of single mode lasers are discussed.

Propagation characteristics of acoustic waves in photonic crystal fibers (PCFs) have been theoretically investigated in details. In order to evaluate acoustic band structures and guided modes for out-of-plane propagation in PCFs, analysis methods based on the finite element method are newly formulated. It is shown through numerical results that complete acoustic band-gaps (ABGs) exist in the cladding region of PCFs and that acoustic guided modes could be localized in the defect region of PCFs by the ABG effect. Furthermore, it is shown that acoustic guided modes could also be localized in the defect region of PCFs by the total internal reflection. These confinement mechanisms of acoustic waves propagating along the fiber length are completely different to those of lightwaves.

Photonic crystal fiber (PCF) is a promising candidate for future transmission media due to its unobtainable features in a conventional single-mode fiber. We discuss some important problems to realize a PCF for transmission purpose. We also present recent progress on the PCF as a transmission media.

In this paper, we propose a global routing method for 2-layer BGA packages. In our routing model, the global routing for each net is uniquely determined by a via assignment of each net. Our global routing method starts from an initial monotonic via assignment and incrementally improves the via assignment to optimize the total wire length and the wire congestion. Experimental results show that our proposed method generates a better global routing efficiently.

Modulator output and fiber transmission characteristics of optical single sideband (SSB) modulations are analyzed under the assumption that SSB modulators are constructed using Mach-Zehnder (MZ) interferometers. The fiber input signal and the detected signal are derived theoretically for SSB modulation with and without an optical carrier. Optical SSB fiber transmission simulations show that the received signal waveform is degraded by harmonic components due to non-linear switching curve of MZ interferometer as a component of SSB modulators even if the Hilbert transformers is ideal for the definition. The optical SSB suppressed carrier is preferred to the SSB with an optical carrier from a viewpoint of waveform degradation.

Press-induced long-period fiber gratings exhibiting strong core-to-cladding mode coupling were formed in photonic crystal fiber. Only one resonance peak was observed over a 600 nm spectral range and the resonant wavelength was tuned over the whole range by tilting a groove plate before pressing the fiber. The resonant wavelength decreased with increasing periodicity of the grating, which was opposite to the trend of the step-index conventional optical fiber. Meanwhile, the resonant wavelength increased with increasing the ambient refractive index, which was also opposite to that of the conventional optical fiber.

We formally define the mobile agent allocation problem from a system-wide viewpoint and then prove that it is strongly NP-complete even if each agent communicates only with two agents. This is the first formal definition for scheduling mobile agents from the viewpoint of load balancing, which enables us to discuss its properties on a rigorous basis. The problem is recognized as preemptive scheduling with independent tasks that require mutual communication. The result implies that almost all subproblems of mobile agent allocation, which require mutual communication of agents, are strongly NP-complete.

In this paper, the previously introduced periodic Fourier transform concept is extended to a two-dimensional case. The relations between the periodic Fourier transform, harmonic series representation and Fourier integral representation are also discussed. As a simple application of the periodic Fourier transform, the scattering of a scalar wave from a finite periodic surface with weight is studied. It is shown that the scattered wave may have an extended Floquet form, which is physically considered as the sum of diffraction beams. By the small perturbation method, the first order solution is given explicitly and the scattering cross section is calculated.

We report the empirically obtained conditions for the fusion splicing with photonic crystal fibers (PCF) having large mode areas. By controlling the arc-power and the arc-time of a conventional electric-arc fusion splicer, the splicing loss between two PCFs could be lowered down to 0.2 dB in average. For the splicing PCF with a conventional single mode fiber (SMF), the loss was increased due to the modal field mismatch, but still below 0.45 dB in average. The tensile strength was weakened by the splicing from 2.83 GPa down to 1.04 GPa for the PCF-PCF case and 0.89 GPa for the PCF-SMF one.

In this paper, firstly, effects of third order dispersion (TOD) on coupled pulses are analyzed. Then, averaging method is modified and proved to be an effective way for obtaining non-radiative bi-soliton solution of the TOD perturbed nonlinear Schrodinger equation (NLSE), which models a dispersion managed (DM) optical transmission system. Finally, the obtained bi-soliton evolution behavior is studied, and compared with that of uni-soliton. With the increase of average TOD, pulse velocity of bi-soliton largely deviates from that of uni-soliton. Thus, even though TOD cannot be exactly vanished in fabrication, it is suggested to compensate average TOD as low as possible.

The history of forward error correction in optical communications is reviewed. The various types of FEC are classified as belonging to three generations. The first generation FEC represents the first to be successful in submarine systems, when the use of RS(255, 239) became widespread as ITU-T G.975, and also as G.709 for terrestrial systems. As WDM systems matured, a quest began for a stronger second generation FEC. Several types of concatenated code were proposed for this, and were installed in commercial systems. The advent of third-generation FEC opened up new vistas for the next generation of optical communication systems. Thanks to soft decision decoding and block turbo codes, a net coding gain of 10.1 dB has been demonstrated experimentally. That brought us a number of positive impacts on existing systems. Each new generation of FEC was compared in terms of the ultimate coding gain. The Shannon limit was discussed for hard or soft decision decoding. Several functionalities employing the FEC framing were introduced, such as overall wrapping by the FEC frame enabling the asynchronous multiplexing of different clients' data. Fast polarization scrambling with FEC was effective in mitigating polarization mode dispersion, and the error monitor function proved useful for the adaptive equalization of both chromatic dispersion and PMD.

When an application code is downloaded from an unknown server to the mobile device, it is important to authenticate the code. Usually, code execution is overlapped with downloading to reduce transfer/invocation delay. In this letter, we present an efficient code authentication scheme that permits overlapping of execution and downloading when the sequence of code execution is determined during the execution time. The proposed scheme is based on authentication trees. Compared with the tree chaining scheme, the proposed scheme has lower communication overhead and shorter average verification delay. Also, the computation cost of the proposed scheme on the receiver is much smaller than that of the tree chaining scheme.

The importance of informal communication on the Internet has been increasing in recent years. Several systems for informal communication have been developed. These systems, however, require a particular server and/or specialized 3D contents. In this paper, we propose a system, named InCom, for informal communication in a 3D virtual environment. Browsers which are component of InCom generate 3D virtual worlds from existing common 2D HTML documents. Browsers communicate in a peer-to-peer manner. Using avatars makes gaze awareness smooth. Our results show that users shared interests by gaze awareness.

We present and demonstrate a novel method of generating a π phase-alternated return-to-zero (RZ) signal together with pulse-amplitude equalization in a rational harmonic mode-locked fiber ring laser, by using a dual-drive Mach-Zehnder modulator. By adjusting the voltages applied to both arms of the modulator, amplitude-equalization and π phase shift can be achieved successfully at a 9.95 GHz repetition rate. The generated alternate-phase RZ signals show enhanced transmission performance in the single-mode fiber (SMF) links without dispersion compensation.

In this letter, a novel design of a branch-line coupler with considerable reduction in its size and suppressed harmonic passband is proposed. By embedding a defected ground structure (DGS) unit cell under a microstrip line, compact branch-line couplers are easily achieved. The electrical length is scaled appropriately according to the slow-wave effect. In this case, the experimental coupling (S21 or S31) is comparable to that of conventional branch-line couplers. Also, experimental results indicate that DGS section is quite effective for the suppression of higher order harmonics.

Although IP Multicast offers efficient data delivery for large group communications, the most critical issue delaying widespread deployment of IP Multicast is the scalability of multicast forwarding state as the number of multicast groups increases. Sender-Initiated Multicast (SIM) was proposed as an alternative multicast forwarding scheme for small group communications with incremental deployment capability. The key feature of SIM is in its Preset mode with the automatic SIM tunneling function, which maintaining forwarding information states only on the branching routers. To demonstrate how SIM increases scalability with respect to the number of groups, in this paper we evaluate the proposed protocol both through simulations and real experiments. As from the network operator's point of view, the bandwidth consumption, memory requirements on state-and-signaling per session in routers, and the processing overhead are considered as evaluation parameters. Finally, we investigated the strategies for incremental deployment.

This letter derives a new exact and general closed-form expression involving a two-dimensional joint Gaussian Q-function for the symbol error rate (SER) of M-ary Phase Shift Keying (MPSK) under an additive white Gaussian noise (AWGN) channel. By using two rotations of coordinates the correlation coefficient between two Gaussian random vectors is provided, then with the derived correlation coefficient that characterizes the two-dimensional joint Gaussian Q-function, a new expression for the SER of MPSK is presented. The derived new SER expression offers a convenient method to evaluate the performances of MPSK for various cases of practical interest.

For the power amplifier used in CDMA cellular phones, the supply voltage is switched between high and low at a transmission power several decibels higher than 10 dBm using a DC-DC converter to improve operational efficiency. The longer the operation time under low supply voltage, the lower the current consumption of the cellular phone. In order to increase the output power under low supply voltage, we applied the 2nd harmonic-injection technique, which is useful for distortion compensation. With 2nd harmonic-injection, there is an inflectional power point. The distortion increases rapidly when output power goes beyond the inflectional power point. It is important to make this inflectional power point high in order to compensate for distortion in the high output-power region. We report here that the inflectional power point can be increased by connecting a 2nd harmonic short circuit to the drain terminal of the FET to which the 2nd harmonic for distortion compensation is injected. A prototype of the final stage of the power amplifier under a supply voltage of Vdd=1.5 V is presented. We report that applying a CDMA uplink signal, 1.5 dB higher output power and 12% higher drain efficiency is achieved compared when only 2nd harmonic injection is employed.

A radio frequency identification tag LSI operating with the carrier frequency of 13.56 MHz as well as storing nonvolatile information in embedded ferroelectric random access memory (FeRAM) has been developed. A full wave rectifier composed of PMOS transistor diodes and NMOS transistor switches achieves RF-to-DC power conversion efficiency over 54%. The entire 16 kbits write and read transaction time can be reduced to 2.1 sec by the use of FeRAM, which corresponds to 2.2 times speed enhancement over conventional EEPROM based tag LSIs. The communication range of the FeRAM based tag LSI can be effectively improved by storing antitheft information in a ferroelectric nonvolatile flip-flop, which can reduce the power consumption of FeRAM from 27 µW to 5 µW. The communication range for the antitheft gate system becomes 70 cm.