This paper describes a system architecture along with signal processing technique which allows a reduction in the complexity of a 3.1-10.6 GHz Ultra-Wideband radio. The proposed system transmits passband pulses using a pulser and antenna, and the receiver front-end down-converts the signal frequency by subsampling, thus, requiring substantially less hardware than a traditional narrowband approach. However, the simplified receiver front end shows a high sensitivity to timing offset. By proposing an analytic signal processing technique, the vulnerability of timing offset is mitigated; furthermore, a time resolution finer than the sampling period is achieved, which is useful for locationing or ranging applications. Analysis and simulations of system specifications are also provided in this paper.

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.

By deploying hundreds or thousands of microsensors and organizing a network of them, one can monitor and obtain information of environments or objects for use by users, applications, or systems. Since sensor nodes are usually powered by batteries, an energy-efficient data gathering scheme is needed to prolong the lifetime of the sensor network. In this paper, we propose a novel scheme for data gathering where sensor information periodically propagates from the edge of a sensor network to a base station as the propagation forms a concentric circle. Since it is unrealistic to assume any type of centralized control in a sensor network whose nodes are deployed in an uncontrolled way, a sensor node independently determines the cycle and the timing at which it emits sensor information in synchrony by observing the radio signals emitted by sensor nodes in its vicinity. For this purpose, we adopt a pulse-coupled oscillator model based on biological mutual synchronization such as that used by flashing fireflies, chirping crickets, and pacemaker cells. We conducted simulation experiments, and verified that our scheme could gather sensor information in a fully-distributed, self-organizing, robust, adaptive, scalable, and energy-efficient manner.

This letter presents a method to simulate a phase-included UWB channel impulse responses for a given indoor channel. In this method we decompose a UWB pulse into a finite number of spectral components. This enables the received signal to be determined by the sum of the convolutions between each spectral component and a corresponding frequency-dependent UWB channel impulse response. The ray-tracing algorithm is applied to calculate the amplitude and the phase of each frequency-dependent channel impulse response. Based on the calculated results, we finally show the simulation of the UWB channel impulse response.

Asynchronous optical packet switching (OPS) is a promising solution to support the continuous growth of transmission capacity demand. It has been, however, quite difficult to implement key functions needed at the node of such networks with all-optical approaches. We have proposed a new optoelectronic system composed of a packet-by-packet optical clock-pulse generator (OCG), an all-optical serial-to-parallel converter (SPC), a photonic parallel-to-serial converter (PSC), and CMOS circuitry. The system makes it possible to carry out various required functions such as buffering (random access memory), optical packet compression/decompression, and optical label swapping for high-speed asynchronous optical packets.

Carbon fiber composites are increasingly used as structural materials because of their unique and advantageous characteristics. Carbon fiber reinforced carbon matrix composite (C/C) has the characteristics of high fatigue resistance, fracture toughness and heat resistance up to 3000 K, and is an important component of refractory tiles and nozzles in space shuttles. Useful nondestructive testing methods for C/C are now required. We have developed a SQUID-NDT system based on a non-magnetic coaxial pulse tube cryocooler (PTC), a HTS-SQUID gradiometer and a field generator with ferrite cores that induces high currents in specimens with low electric conductivity. The cryostat with the PTC is compact, at 50 mm in diameter and 400 mm in height. It weighs a total of 4 kg. The system noise is 80 µ0/Hz1/2 corresponding to 1.3 nT/m/Hz1/2 at 100 Hz. We used the system to investigate the usefulness of the SQUID-NDT in detecting flaws in C/C composites. Hidden cracks in C/C multi-layered specimens were detected up to depth of 15 mm. Hidden cracks in C/C-Al stacked sample was also clearly detected. In addition, we magnetically detected the mechanical breaking process of a C/C specimen under tensile load using the current injection method. For this study, a technique for visualizing current detouring defects was developed for detection of deteriorating areas in the specimen. The deteriorating area, identified from the current map, expands during breaking process and agrees with the results obtained by the microscopic observation of the breaking process. The interrupted current Iint, estimated by summing the detour current, clearly changed depending on the stage of the breaking process, suggesting that Iint may be applicable as good index for distinguishing each stage in the breaking process. It is concluded that a SQUID-NDT is applicable to C/C composites and advanced complex materials with low electric conductivity in addition to metallic materials.

A new theoretical approach for the evaluation of the in-band nonlinear distortion effects on the performance of DS-CDMA systems is presented. Rather than widely used models of treating the effects of nonlinear distortion as additive Gaussian noise, the new approach is based on the asymptotic clipping and shot noise theories, which offer important insights into true nature of clipping process and can be further extended to many communications systems with high PAPR and peak-limited nonlinearities.

This paper presents pulse-coupled two bifurcating neurons. The single neuron is represented by a spike position map and the coupled neurons can be represented by a composition of the spike position maps. Using the composite map, we can analyze basic bifurcation phenomena and can find some interesting phenomena that are caused by the pulse-coupling and are impossible in the single neuron. Presenting a simple test circuit, typical phenomena are confirmed experimentally.

Recently Azou et al. proposed a method of model reduction for discrete systems based on a new impulse response Gramian. The reduced model was derived by first approximating the low-order impulse response Gramian, and then matching some Markov parameters and time-moments of an original model. In this note a modified method is presented so that the reduced model exactly preserves the low-order impulse response Gramian together with a slightly different set of Markov parameters and time-moments of the original model.

The use of metal-coated plastics is increasing as shielding materials of electronic and information products due to their lightweight. In this paper, a finite-difference time-domain (FDTD) algorithm, based on the derivation of a time-domain representation of the surface impedance of an equivalent resistive film, was developed to analyze the electromagnetic penetration of pulsed electromagnetic fields through metal-coated plastics. The validity of the proposed algorithm, in both the far-field and near-field cases, was verified by comparing the calculated penetrated electromagnetic fields or shielding effectiveness with theoretical and measured ones. Good agreement between them demonstrated the usefulness of the FDTD algorithm.

Imaging techniques for robots are important and meaningful in the near future. Pulse radar systems have a great potential for shape estimation and locationing of targets. They have an advantage that they can be used even in critical situations where optical techniques cannot be used. It is thus required to develop high-resolution imaging algorithms for pulse radar systems. High-resolution imaging algorithms utilize the carrier phase of received signals. However, their estimation accuracy suffers degradation due to phase rotation of the received signal because the phase depends on the shape of the target. In this paper, we propose a phase compensation algorithm for high-resolution pulse radar systems. The proposed algorithm works well with SEABED algorithm, which is a non-parametric algorithm of estimating target shapes based on a reversible transform. The theory is presented first and numerical simulation results follow. We show the estimation accuracy is remarkably improved without sacrificing the resolution using the proposed algorithm.

This paper presents circuit techniques using pulse-width and pulse-phase modulation (PWM/PPM) approaches for VLSI implementation of nonlinear dynamical systems. The proposed circuits implement discrete-time continuous-state dynamics by means of analog processing in a time domain, and also approximately implement continuous-time dynamics. Arbitrary nonlinear transformation functions are generated by the process in which a PPM signal samples a voltage or current source whose waveform in the time domain has the same shape as the desired transformation function. Because a shared arbitrary nonlinear voltage or current waveform generator can be constructed by digital circuits and D/A converters, high flexibility and real-time controllability are achieved. By using one of these new techniques, we have designed and fabricated a CMOS chaos circuit with arbitrary 1-D maps using a 0.6 µm CMOS process, and demonstrate from the experimental results that the new chaos circuit successfully generated various chaos with 7.5-7.8 bit precision by using logistic, tent and chaotic-neuron maps.

In this paper, a novel UWB system called pulse position controlled UWB is proposed. One of the problems in UWB systems is the restriction of data rates due to multipath. The proposed UWB system shorten the pulse interval adaptively depending on channel characteristics. It has been shown that the proposed UWB system can increase the data rate with about 30% and improve the BER at the same time.

This paper theoretically evaluates the performance of overlapping pulse-position modulation (OPPM) fiber-optic code-division multiple-access (FO-CDMA) systems in the presence of code synchronization errors. The analysis is carried out with a constraint on throughput-pulsewidth product. Discussions on effects of various system parameters, such as timing offset, index of overlap, number of users, are presented. The results show that the OPPM FO-CDMA systems with high index of overlaps have better resistance against imperfect synchronization. In fact, the acceptable performance could be maintained even with timing offsets of up to 30% of chip pulsewidth. On the other hand, strict code synchronization is necessarily required, preferably within a half code chip pulsewidth.

In this paper, Pre-Rake scheme for pulse based Ultra Wideband impulse radio (UWB-IR) communications system is proposed considering a standardized UWB channel model from IEEE 802.15 SG3a, which is based on an extensive set of short-range indoor channel measurements. Two kinds of pulse waveforms are taken in account here, namely, Gaussian mono-pulse and newly designed Prolate Spheroidal Wave Functions (PSWF) pulses corresponding to FCC Spectrum Mask. The Pre-Rake scheme is shown to contribute to the low-power, cost-efficient UWB system designing as well as Rake combining gain. Instead of building a Rake receiver at the receiving side (e.g. portable unit), the transmitter (e.g. access point) can pre-combine the UWB signal before transmission in the forward link by estimating the channel impulse response from the reverse link. While the Pre-Raked signal is convolved with the estimated channel impulse response, the function of Rake combination at the receiver is automatically performed. Meanwhile, in order to defeat inter-pulse-interferences (IPI) caused by severe multipath fading conditions, adaptive guard-time scheme for consecutive pulses is proposed as well. Monte-Carlo simulations are carried out to compare the Pre-Rake with Rake results and show that Pre-Rake scheme is as good as Rake combining for both types of pulse waveforms. Then the mobile or portable unit with a conventional receiver can still achieve the diversity gain of Rake combination. Moreover, the effects of placing guard-time between pulses are also verified.

We present mutually pulse-coupled two relaxation oscillators having refractoriness. The system can be implemented by a simple electrical circuit, and various periodic synchronization phenomena can be observed experimentally. The phenomena are characterized by a ratio of phase locking. Using a return map having a trapping window, the ratio can be analyzed in a parameter subspace rigorously. We then clarify effects of the refractoriness on the pulse coding ability of the system.

Superluminal group velocity in dispersive media has long been controversial. A partial source of confusion seems to be the absence of high precision numerical results concerning the waveform of the transmitted signal. This paper gives the precise waveforms of a causal half-sine-modulated pulse and a triangle-modulated pulse propagating in the Lorentz medium. Thus, the effects of analyticity of signal are clarified, which the analysis using Gaussian pulse cannot. Further, to deepen understanding of the mechanism of superluminal group velocity, we give a network theoretic consideration.

A cryogenic Whispering Gallery sapphire resonator oscillator has been investigated using a 4 K pulse-tube cryocooler. The turnover temperature of the chosen mode in the sapphire crystal was 9.17 K with an unloaded Q-factor of 7108. The prototype sapphire-loaded cavity oscillator was designed to oscillate at 9.195 GHz. A fractional frequency stability of 210-13 was measured at integration times of 10 s.

The AMR wideband speech codec was recently developed for high-quality wideband speech communications. Although it has an excellent performance due to expanded bandwidth of speech signal, it requires a huge amount of computation especially in codebook search. To solve this problem, this paper proposes an efficient codebook search method for AMR wideband codec. Starting from a poorly performing initial codevector, the proposed method enhances the performance of the codevector iteratively by exchanging the worst pulse in the codevector with a better one after evaluating the role of each pulse. Simulations show that the AMR wideband codec adopting the proposed codebook search method provides better performance with much less computational load than that using the standard method.

We have developed the tunable dispersion compensator based on two twin linearly chirped fiber Bragg gratings with various temperature gradients. Controlling the temperature gradient over one of the twin fiber Bragg gratings by Peltier elements, the dispersion and the dispersion slope were changed independently and continuously. The dispersion and dispersion slope compensator has a large bandwidth of 8 nm and low group-delay ripple of < 4 ps in its chirped fiber Bragg gratings. We experimentally demonstrated a precise controllability of the dispersion and the dispersion slope using linear and parabolic temperature gradient. The dispersion and the dispersion slope changes were achieved continuously with -0.67 ps/nm/ and -0.14 ps/nm2/. The transmission characteristics of the dispersion slope compensation were examined using ultra short pulses in the fiber link. When the total dispersion was zero, the distorted pulse was restored back and the tail was significantly suppressed. 160 Gbit/s signals were also demonstrated over 140 km within 1 dB power penalty by using the dispersion slope compensator.