Channel estimation is one of the key technologies in mobile communications. Channel estimation is critical in providing high data rate services and to overcome fast fading in very high-speed mobile communications. This paper presents a novel channel estimation based on hybrid spreading of I and Q signals (CEHS). Simulation results show that it can effectively mitigate the influence of fast fading and enable to provide high data rates for very high speed mobile systems.

Low-loss optical coupling structures between photonic crystal waveguides and channel waveguides were investigated. It was emphasized that impedance matching of guided modes of those waveguides, as well as field-profile matching, was essential to achieving the low-loss optical coupling. We developed an impedance matching theory for Bloch waves, and applied it to designing the low-loss optical coupling structures. It was demonstrated that the optical coupling loss between a photonic crystal waveguide and a Si-channel waveguide was reduced to as low as 0.7 dB by introducing an interface structure for impedance matching between the two waveguides.

We have fabricated several two-dimensional photonic-crystal (2DPC) slab waveguides by using fine electron beam lithography and dry etching. The 2DPC waveguides include straight, bend, Y-branch, directional coupler, and coupled-cavity waveguides on the GaAs/AlGaAs substrate as an application to the ultra-small and ultra-fast all-optical switching device. Transmission spectra and near field patterns were characterized in a wide wavelength range from 850 to 1600 nm with the sample finished to the air-bridge type 2DPC slab. These waveguides appear to be suitable for achieving the waveguide platform in the symmetrical-Mach-Zehnder device.

We have demonstrated low-threshold two-dimensional photonic crystal lasers with self-assembled InAs/GaAs quantum dots. Coupled cavity designs of whispering gallery modes are defined in square lattice photonic crystal slabs. Our lasers showed a small 120 µW input pumping power threshold. Actual absorption power is evaluated to be less than 20 µW. Our lasers show high spontaneous emission coupling (β) factors0.1. The mode volumes are expected to be 0.7-1.2 times cubed wavelength by our modelling. Based on threshold analysis, 80 QDs are the effective number of QDs defined as the number of QDs needed to make PC cavities transparent if they are on maximum optical field points. Using the same analysis we found that single quantum dot lasing is likely to occur both by proper alignment of the single quantum dot relative to geometries of photonic crystals and by using sharp QD emission lines in high-Q localized modes.

Artificial electromagnetic structures have significantly broadened the range of wave propagation phenomena available. In particular, it has been shown that metamaterials can be constructed for which the index-of-refraction is negative over a finite band of frequencies. In this paper, we present the design, fabrication and characterization of a metamaterial that exhibits negative refraction. The metamaterial design we explore is anisotropic in the plane of propagation. Based on our analysis and supporting simulations and measurements, we demonstrate that for the geometry considered, the anisotropic metamaterial has the identical negative refraction properties as would an isotropic negative index metamaterial.

We describe new architectures for micro-fabrication of large-scale PBG materials. A universal approach to embedding optical circuitry within a planar defect layer is illustrated for the square spiral and inverse opal PBG materials.

We theoretically investigated the resolution of the photonic crystal (PC) K-vector superprism, which utilized the wavelength-dependent refraction of light at an angled output end as a narrow band filter at 1.55 µm wavelength range. Similarly to the case of the conventional S-vector prism, we defined the equi-incident-angle curve against the dispersion surface, and calculated the beam collimation, wavelength sensitivity and resolution parameters for light propagation in the PC. We estimated that the resolution of the K-vector prism is the same as or higher than that of the S-vector prism and the PC can be significantly miniaturized. In addition, we clarified the relation of the S-vector prism phenomenon and the position of the output end in the K-vector prism, and different results for the reduced and repeated zone schemes, which are important for the detailed design. We also confirmed that the light propagation simulated by the FDTD method well agreed with the results of the dispersion surface analysis.

The design, fabrication, and measurement of photonic-band-gap (PBG) waveguides and resonators in two-dimensional photonic crystal slabs have been investigated. Although photonic crystal slabs have only partial gaps, efficient waveguides and resonators can be realized by appropriate design. As regards PBG waveguides, we show various designs for efficient single-mode waveguides in PhC slabs with SiO2 cladding, we report group dispersion measurements of PBG waveguides in PhC slabs, and describe the successful fabrication of PBG waveguides with adiabatic connectors that enable us to couple the light from single-mode fibers efficiently to PBG waveguides. As regards PBG resonators, we show how to realize very high-Q and small volume resonators in hexagonal PhC slabs, and report the fabrication of resonant tunneling filters that consist of PBG resonators coupled with PBG waveguides. We also describe the successful fabrication of resonant tunneling mode-gap filters with adiabatic mode connectors.

This paper proposes a new correction technique for a linear amplification with nonlinear components (LINC) transmitter. The technique, which is based on the minimum mean squared error (MMSE) criterion, estimates the gain and phase imbalance between the two amplifier branches. With information on the estimation, the imbalance is offset by controlling the amplitude and phase of the input signal that is fed into one of the two amplifiers. Computer simulations with a DS-CDMA system demonstrate that this method can compensate for the imbalance and sufficiently suppress the out-of-band distortion spectrum.

We have shown that a photonic sensor can be used as an electric-field probe for planar near-field measurements of X-band antennas. Because an antenna on the photonic sensor is small (about 0.1 λ) compared to the wavelength, the photonic sensor can directly measure the amplitude and the phase of the electric field close (about 0.3 λ) to the apertures of antennas without disturbing the electric field to be measured. Therefore we can obtain the antenna pattern by transforming the measured electric field without probe compensation. To verify the merits of the photonic sensor, we have evaluated the antenna patterns of a standard gain horn antenna and a microstrip array antenna at 9.41 GHz. Comparing the results obtained using the photonic sensor with those obtained using the conventional open-ended waveguide probe and other methods, we have shown that the antenna patterns agree with each other within 1 dB over wide ranges of directivity.

In this paper, we consider the problem of constructing a multicast tree in the star graph under the single-port communication model. Unlike previous studies for constructing space-efficient multicast trees, we adopt the completion time of each multicast as the objective function to be minimized. In particular, we study a special case of the problem in which all destination vertices are immediate neighbors of the source vertex, and propose a multicast scheme for the star graph of dimension n in 1.3125log2 n + O(log log n) time units. This running time is at most 1.3125 times of that of an optimal scheme.

In order to transport an ever-increasing amount of IP traffic effectively, Photonic IP networks that employ wavelength routing and Layer 3 cut-through are very important. This paper proposes a new network design algorithm that minimizes the network cost considering IP traffic growth for multi-layered photonic IP networks that comprise electrical label switched paths (LSPs) and optical LSPs. We evaluate the network cost obtained from the developed network design algorithm that considers IP traffic growth and compare it to the results obtained from a static zero-based algorithm. The static zero-based algorithm does not take into account the history of progressive past IP traffic changes/growth until that time. The results show that our proposed algorithm is very effective; the cost increase from the cost obtained using the zero-based algorithm is marginal. The algorithm developed herein enables effective multi-layered photonic IP network design that can be applied to practical networks where IP traffic changes/increases progressively and that can be used for long term network provisioning.

This paper presents a strictly time- and communication-optimal distributed sorting algorithm in a line network. A strictly time-optimal distributed sorting algorithm in a line network has already been designed. However, its communication complexity is not strictly optimal and it seems to be difficult to extend it to other problems, such as that related to multiple elements in a process, and also the dynamic sorting problem where the number of elements each process should have as its solution is not the same as that in the initial state. Therefore, the algorithm in this paper was designed by an alternative approach to make it strictly time- and communication-optimal. Moreover, an extension to the dynamic sorting problem is described.

A mechanical phase shifter is designed for beam scanning in co-phase fed single-layer slotted waveguide arrays. The multiple-way power divider in this array consists of a series of π-junctions with one guide wavelength spacing in a feed waveguide. The movable narrow walls placed between the π-junctions perturb the guide wavelength as well as the phase of output ports. Method of Moment (MoM) analysis for one unit consisting of one movable plate and two junctions is conducted to estimate the available phase shift as well as the degradation of reflection. A phase shift of 86 degrees is predicted between two π-junctions under the condition of reflection below -20 dB; experiments at 4 GHz confirmed the design. The beam scanning capability of the arrays is also surveyed and the beam-scanning of about 10 degrees is predicted.

We describe the first highly nonlinear dispersion-flattened polarization-maintaining photonic crystal fiber designed for nonlinear optics applications in the 1.55 µm region. The nonlinear coefficient of the fiber is 19 (W-1km-1), which is ten times that of dispersion shifted fiber. The chromatic dispersion and dispersion slope of the fiber at 1.55 µm are -0.23 ps/km/nm and 0.01 ps/km/nm2, respectively. We demonstrate the generation of a supercontinuum using the photonic crystal fiber. A symmetrical supercontinuum over 40 nm is obtained by injecting 1562 nm, 2.2 ps, and 40 GHz optical pulses into the 200 m-long photonic crystal fiber.

Linking schemes have been proposed assuming the model where the time-stamp issuer need not be trusted. However, in that environment, a fake chain attack and forward or backward dating attacks are still a residual risk in Time-Stamping services (TSS). In this paper, we propose a new time-stamping scheme that focuses on these problems. In our scheme, we use pseudonyms to prevent the time-stamp issuer from dating the time that the specific entity requests. Our scheme doesn't rely on only one trustworthy entity, and uses mutual communication between each entity. Two types of entities, server and clients without any trustworthy entities are configured in our system. The server provides an anonymous communication channel, but doesn't provide TSS, and the clients are not only time-stamp requesters but also issuers. So, when a client requests a time-stamp from the system, it is issued by one of the other clients.

A cache replacement policy which takes the transcoding time into account in making replacement decisions, for the emerging transcoding proxy servers is proposed. Simulation results show the proposed policy outperforms the conventional LRU in both the cache hit rate and the average object transcoding time.

In this paper, we describe the implementation and the test results of a Bluetooth baseband module we have developed. For small chip size, we eliminate FIFOs for data buffering between hardware functional units and data buffers for bit streaming among channel coding blocks. Furthermore, we carefully consider hardware and software partitioning. We implement complex control tasks of the Bluetooth baseband layer protocols in software running on an embedded microcontroller. Hardware-efficient functions, such as low-level bitstream link control; host controller interfaces (HCIs), such as universal asynchronous receiver transmitter (UART) and universal serial bus (USB) interfaces; and audio CODEC are performed by dedicated hardware blocks. In addition, the bitstream data path block of the link controller constructing the baseband module has been designed by considering low power. The design of the baseband module is done using fully synthesizable Verilog HDL to enhance the portability between process technologies. A field programmable gate array (FPGA) implementation of the module was tested for functional verification and real time operation of file and bitstream transfer between PCs. The module was also fabricated in a 0.25 µm CMOS technology, the core size of which is only 2.792.80 mm2.

This paper proposes a robust method for estimating the fundamental frequency (F0) in real environments. It is assumed that the spectral structure of real environmental noise varies momentarily and its energy does not distribute evenly in the time-frequency domain. Therefore, segmenting a spectrogram of speech mixed with environmental noise into narrow time-frequency regions will produce low-noise regions in which the signal-to-noise ratio is high. The proposed method estimates F0 from the periodic and harmonic features that are clearly observed in the low-noise regions. It first uses two kinds of spectrogram, one with high frequency resolution and another with high temporal resolution, to represent the periodic and harmonic features corresponding to F0. Next, the method segments these two kinds of feature plane into narrow time-frequency regions, and calculates the probability function of F0 for each region. It then utilizes the entropy of the probability function as weight to emphasize the probability function in the low-noise region and to enhance noise robustness. Finally, the probability functions are grouped in each time, and F0 is obtained as the frequency with the highest probability of the function. The experimental results showed that, in comparison with other approaches such as the cepstrum method and the autocorrelation method, the developed method can more robustly estimate F0s from speech in the presence of band-limited noise and car noise.

This paper describes the performance improvement of power amplifiers by defected ground structure (DGS). Due to the excellent capability of harmonic rejection and tuning, DGS plays a great role in improving the major nonlinear behaviors of power amplifier such as output power, harmonics, power added efficiency (PAE), and the ratio between the carrier and the third order intermodulation distortion (C/IMD3). In order to verify the improvement of performances by DGS, measured data for a power amplifier, which adopts a 30 Watts LDMOS device for the operation at 2.1-2.2 GHz, are illustrated under several operating bias currents for two cases, i.e., with and without DGS attached. The principle of the improvement is described by the simple Volterra nonlinear transfer functions with the consideration of different operating classes. The obtained improvement of the 30 Watts power amplifier, under 400 mA of IdsQ as an example, includes the reduction in the second and third harmonics by 17 dB and 20 dB, and the increase in output power, PAE, and C/IMD3 by 1.3 Watts, 3.4%, and 4.7 dB, respectively.