Signal Detection Performance of Overlapped FFT Scheme with Additional Frames Consisting of Non-continuous Samples in Indoor Environment

Overlapped FFT has been proposed as a signal detection scheme in dynamic spectrum access to reduce the variance of the noise and improve the detection probability. However, the improvement of the detection probability in the conventional overlapped FFT is bounded with the upper limit of the overlap ratio. This paper proposes a new overlapped FFT scheme using additional frames. In the proposed scheme, in addition to the original FFT frames, new frames that consist of multiple subframes with non-continuous samples are constructed and included. It can realize the increase of the number of the FFT frames and the improvement of the detection probability compared with the conventional scheme. Numerical results through computer simulation show that the proposed scheme improves the detection probability by up to 0.07. On indoor channel models the proposed scheme also improves the detection probability. In addition, it is clarified that as the delay spread increases the detection probability reduces due to the correlation between the frames.     

A compact thin-film-based all-pass device for the compensation of the in-band dispersion in FBG filters

Fiber Bragg grating (FBG)-based bandpass filters, while possessing close to ideal sharp rolloff characteristics, can suffer from a significant amount of in-band dispersion. Results concerning the compensation of the in-band dispersion of a typical 100-GHz FBG using two thin-film all-pass filters, each composed of two coupled-cavities packaged in a compact configuration, are presented. The total peak insertion loss of the compensation package is less than 2.5 dB.     

All-optical discrimination based on nonlinear transmittance of MQWsemiconductor optical gates

This paper proposes an all-optical regenerator utilizing a novel all-optical discriminator. The impacts of nonlinearity of optical gates on discrimination performance are estimated. The evaluation of discrimination performance shows that amplified spontaneous emission noise and wave form distortion in optical signals can be effectively suppressed. We experimentally demonstrate the suppression using a low-temperature-grown optical switch up to 10 Gb/s     

Characteristics of transients among periodic attractors controlledby high-frequency injection in a chaotic laser diode

We numerically studied statistics of the transient response time when switching between periodic attractors obtained through chaos control with a high-frequency injection method in a laser diode that is subject to optical feedback. Each transient response time significantly depends on its position in the starting attractor, whereas the statistical distributions of the response times for many transients are determined almost entirely by the final attractor. The average transient response time is 40 times larger than the round time in the controlled periodic attractors. The transient response time is also strongly affected by the external cavity length. The shortest average transient response time is obtained at a minimum external cavity length and a zero phase difference between the laser field and the feedback light field     

Structural advantages of rectangular-like channel cross-section on electrical characteristics of silicon nanowire field-effect transistors

We have experimentally demonstrated structural advantages due to rounded corners of rectangular-like cross-section of silicon nanowire (SiNW) field-effect transistors (FETs) on on-current (I_ON), inversion charge density normalized by a peripheral length of channel cross-section (Q_inv) and effective carrier mobility (μ_eff). The I_ON was evaluated at the overdrive voltage (V_OV) of 1.0 V, which is the difference between gate voltage (V_g) and the threshold voltage (V_th), and at the drain voltage of 1.0 V. The SiNW nFETs have revealed high I_ON of 1600 μA/μm of the channel width (w_NW) of 19 nm and height (h_NW) of 12 nm with the gate length (L_g) of 65 nm. We have separated the amount of on-current per wire at V_OV = 1.0 V to a corner component and a flat surface component, and the contribution of the corners was nearly 60% of the total I_ON of the SiNW nFET with L_g of 65 nm. Higher Q_inv at V_OV = 1.0 V evaluated by advanced split-CV method was obtained with narrower SiNW FET, and it has been revealed the amount of inversion charge near corners occupied 50% of all the amount of inversion charge of the SiNW FET (w_NW = 19 nm and h_NW = 12 nm). We also obtained high μ_eff of the SiNW FETs compared with that of SOI planar nFETs. The μ_eff at the corners of SiNW FET has been calculated with the separated amount of inversion charge and drain conductance. Higher μ_eff around corners is obtained than the original μ_eff of the SiNW nFETs. The higher μ_eff and the large fractions of I_ON and Q_inv around the corners indicate that the rounded corners of rectangular-like cross-sections play important roles on the enhancement of the electrical performance of the SiNW nFETs.     

Penetration and stainability of modified Sato's lead staining solution.

The penetration and stainability of modified Sato's lead staining solution containing calcined lead citrate were studied. Modified Sato's lead solution was preserved for 1 week and for 2 years, each at room temperature and at 4 degrees C. Specimens were stained with these solutions to measure the stainability. After 2-min staining, specimens were stained to the depth of 1.0-1.2 microns even when there had been 2-year preservation of the staining solution. This modified solution could be preserved for a long time and good penetration and stainability could still be obtained. This solution is also suitable for the observation of semithin sections.     

Organic field-effect transistors based on J-aggregate thin films of a bisazomethine dye

We report on the fabrication and the characterization of p-type organic field-effect transistors based on vapor-deposited J-aggregate bisazomethine dye thin films. The absorption spectra of this non-ionic organic semiconductor in the solid state show a strong influence of the film thickness on the J-aggregate formation. However, the electrical characteristics of the devices demonstrate that the hole transport properties do not vary significantly in films thicker than 100 nm. This is due to the fact that the J-aggregates are formed in this material at the surface of the crystalline grains and do not influence the semiconductor/gate dielectric interface and the charge transport properties of the devices. Hole field-effect mobilities as high as 2.4 × 10^?4 cm² V^?1 s^?1 were obtained and could be slightly improved by a solvent vapor treatment due to changes in the film crystallinity. Overall, this study demonstrates that J-aggregate bisazomethine dye thin films are good candidates for the realization of organic electronic devices.     

Two-dimensional theory of distributed feedback semiconductor lasers

A theory which takes account of the two dimensional waveguide structure of the distributed-feedback (DFB) laser is presented. Laser threshold conditions in the case of no external reflections are calculated for a three-layer model in which one cladding layer has a periodically changing dielectric constant. In contrast with the coupled-wave theory the threshold conditions are found to be asymmetric with respect to the Bragg frequency. The longitudinal mode which lies below and nearest the Bragg frequency has the lowest threshold gain. The difference between the threshold gains of the two adjacent longitudinal modes straddling the Bragg frequency has a maximum as a function of the coupled strength of the grating     

Performance of handoff algorithm based on distance and RSSI measurements

The performance of a proposed handoff algorithm based on both the distance of a mobile station to neighboring base stations and the relative signal strength measurements is evaluated. The algorithm performs handoff when the measured distance from the serving base station exceeds that from the candidate base station by a given threshold and if the measured signal strength of the adjacent base station exceeds that of the serving base station by a given hysteresis level. The average handoff delay and average number of handoffs are used as criteria for performance. Numerical results are presented to demonstrate the feasibility of the distance-based handoff algorithm, including results for an additional criterion based on relative signal strength. The proposed algorithm is compared with an algorithm based on absolute and relative signal strength measurements and with a solely distance-based algorithm. It is found that the proposed handoff algorithm performs well in a log-normal fading environment when the distance estimate error is modeled by wide-sense stationary additive white Gaussian noise.     

A 5-GByte/s data-transfer scheme with bit-to-bit skew control forsynchronous DRAM

This paper describes a 5-GByte/s data-transfer scheme suitable for synchronous DRAM memory. To achieve a higher data-transfer frequency, the properties were improved based on the frequency analysis of the memory system. Then, a bit-to-bit skew compensation technique that eliminates incongruent skew between the signals is described with a new, multioutput controlled delay circuit to accomplish bit-to-bit skew compensation by controlling transmission timing of every data bit. Simulated maximum data-transfer rate of the proposed memory system resulted in 5.1/5.8 GByte/s (321/365 MHz, ×64 bit, double data rate) for data write/read operation, respectively