A novel 1470-nm-band (S+ band) wavelength-division multiplexing (WDM) transmission system is described. The first advantage of S+-band transmission is suppression of degradation caused by four-wave mixing (FWM), which has been the dominant impairment factor in WDM transmission systems on dispersion-shifted fibers (DSFs). FWM suppression by using the S+ band instead of the conventional 1550-nm-band (M band) is successfully demonstrated. The second advantage is expansion of the usable bandwidth by using the S+ band together with other wavelength bands. A triple-wavelength-band WDM repeaterless transmission experiment using the S+ band, the M band and the L band (1580-nm-band) is conducted over DSF, and it is shown that degradation due to inter-wavelength-band nonlinear interactions is negligible in the transmission. Moreover, the transmission performance of an S+-band linear repeating system is estimated by computer simulation, and compared with that of other wavelength-band systems. In the experiments, thulium-doped fiber amplifiers (TDFAs) are used for amplification of signals in the S+ band.

We analyze the dispersion-managed optical transmission system for the non-return-to-zero (NRZ) pulse format. First, we investigate the physical image of dispersion management by computing small-signal-based transfer functions, and summarize the dependence of transmission performance on system parameters. Next, the Q-map is computed numerically to design long-distance large-capacity dispersion-managed transmission systems for a single channel in a more detailed manner. It is shown that the third-order dispersion of fibers negatively influences transmission performance, and third-order dispersion compensation is proved to be an effective method for extending the transmission distance of high bit-rate systems. Utilizing these results, guidelines can be derived for the optimal design of long-distance large-capacity NRZ transmission systems.

Waveguide photodiodes (WGPDs) are key devices for high-speed optical receivers in trunk lines because of their potential ability to provide both high efficiency and a high-speed response. We have designed a waveguide photodiode for 40-Gb/s-range optical receivers. The optical coupling characteristics were simulated in detail to optimize the waveguide structure, and the electrodes of the photodiode were designed to form a coplanar transmission line to match the system impedance, which minimized frequency-response degradation. A highly beryllium-doped, low-temperature-grown InGaAs contact layer grown by gas source molecular beam epitaxy was used to reduce the series resistance, and approximately 40% reduction of series resistance was achieved. The fabricated device exhibited both a very high external quantum efficiency of 81% for 1.55-µm light and a sufficient bandwidth of more than 40 GHz. Though we used a simple conventional fabrication process, excellent characteristics were achieved due to the optimized optical design and well suppressed parasitic parameters.

An access attempt overload control method is proposed for CDMA cellular system to provide good communication quality to mobile stations under the traffic overload condition. Under the normal traffic condition, the effect of access attempts on the interference is negligible. But under the traffic overload condition, the interference due to access attempts could be large and deteriorate the communication quality (or reduce the capacity of a reverse link) if access attempts are not controlled properly. The numerical and simulation results show that our access attempt overload control method can maintain the interference caused by access attempts very low and the capacity of the reverse link is not reduced under the traffic overload condition.

This paper proposes a fast encoding algorithm for iterated function system (IFS) coding of gray-level homogeneous fractal images. In order to realize IFS coding of high order fractal images, it is necessary to solve a set of simultaneous equations with many unknowns. Solving the simultaneous equations using a multi-dimensional, numerical root-finding method is however very time consuming. As preprocessing of numerical computation, the proposed algorithm employs univariate polynomial manipulation, which requires less computation time than multivariate polynomial manipulation. Moreover, the symmetry of the simultaneous equations with respect to the displacement coefficients enables us to derive an equation with a single unknown from the simultaneous equations using univariate polynomial manipulation. An experimental result is presented to illustrate that the encoding time of the proposed algorithm is about 5 seconds on a personal computer with a 400 MHz Pentium II processor.

A clock recovery circuit is a key component in optical communication systems. In this paper, an optoelectronic clock recovery circuit is reported that monolithically integrates a resonant tunneling diode (RTD) and a uni-traveling-carrier photodiode (UTC-PD). The circuit is an injection-locked-type RTD oscillator that uses the photo-current generated by the UTC-PD. Fundamental and sub-harmonic clock extraction is confirmed for the first time with good clock recovery circuit characteristics. The IC extracts an electrical 11.55-GHz clock signal from 11.55-Gbit/s RZ optical data streams with the wide locking range of 450 MHz and low power dissipation of 1.3 mW. Furthermore, the extraction of a sub-harmonic clock from 23.1-Gbit/s and 46.2-Gbit/s input data streams is also confirmed in the wider locking range of 600 MHz. The RMS jitter as determined from a single sideband phase noise measurement is extremely low at less than 200 fs in both cases of clock and sub-harmonic clock extraction. To our knowledge, the product of the output power and operating frequency of the circuit is the highest ever reported for injection-locked-type RTD oscillators. These characteristics indicate the feasibility of the optoelectronic clock recovery circuit for use in future ultra-high-speed fully monolithic receivers.

Texture has been investigated as a cue for reconstructing 3-D structure. There are various textures in a natural scene. In this paper, the regularity of alignment of texture elements was manipulated to investigate its effect on human perception. The results show that the regularity affects human perception when only the texel density gradient is given as cue or the density cue is inconsistent with the compression cue. We introduce a model based on a MAP estimation to account for the result from a viewpoint of an integration of 3-D cues. The model simultaneously estimates texture properties and 3-D surface orientation by using prior knowledge about texture and 3-D surface. The performance of the model accounts for the experimental result well.

We have proposed and demonstrated a novel optical regenerator architecture employing electroabsorption modulators as wavelength converters. The employment of EA modulators is advantageous for high-speed operation and flexibility in the bit-rate for the pulse regeneration. In addition, the EA modulator-wavelength-converter acts also as a photo diode for clock extraction. Compensation of the optical SNR and Q-factor has been demonstrated, even in cascaded noise load. Furthermore, against dispersion loading, we have confirmed that waveform recovery and Q-factor improvement is obtained by midway insertion of the optical regenerator. The proposed architecture will offer a wide-band-electronics-free optical regenerator in multi-tens of gigabit per second WDM networks.

In this paper we propose an algorithm for generating maximum weight independent sets in a circle graph, that is, for putting out all maximum weight independent sets one by one without duplication. The time complexity is O(n3 + β ), where n is the number of vertices, β output size, i. e. , the sum of the cardinalities of the output sets. It is shown that the same approach can be applied for spider graphs and for circular-arc overlap graphs.

Technical advances in the development of portable computers and wireless communications enable users to take part in distributed computing even while moving. The resulting environment is subject to be constrained by the mobility of users and the nature of the cordless medium. In this paper we propose a commit protocol for providing low-powered mobile hosts with two phase commit service which is a powerful technique to implement atomic actions in distributed systems, with some important aspects such as low power consumption, efficient mobility management, subject oriented service binding and effective disconnection handling to well adapt to a mobile computing environment.

We have developed an experimental 4 K 2 K pixel progressive scan color camera system. This new camera system has a data rate of 297 MHz pixel/sec and 60 frame/sec and we are sure that horizontal and vertical limiting resolution of 1500 TVL (TV lines) can be achieved on a color monitor. Instead of the previous approach of improving resolution simply by increasing the pixel count in a imager, a novel four-sensor pickup method with 2/3 inch 2 million pixel CMD (Charge Modulation Device) imagers is used in this system. These sensors have 1920 (H) 1035 (V) pixels within a 16:9 wide aspect image area and are successfully driven at 148 M pixel/sec in the progressive scan mode. In the four-sensor pickup method, two sensors are used for green and the rest are for red and blue. A spatial offset imaging method in the diagonal direction was applied to the two green sensors to improve the horizontal and vertical resolution effectively. The horizontal and vertical resolution of the red and blue signals become half that of the green signal, because only one 2 M-pixel imager is used for each signal. The resolution of this system, however, is not degraded so much because the luminance signal is mainly composed of green signals.

Modern micro-architectures employ superscalar techniques to enhance system performance. Since the superscalar microprocessors must fetch at least one instruction cache line at a time to support high issue rate and large amount speculative executions. There are cases that multiple branches are often encountered in one cycle. And in practical implementation this would cause serious problem while there are variable number of instruction addresses that look up the Branch Target Buffer simultaneously. In this paper, we propose a Range Associative Branch Target Buffer (RABTB) that can recognize and predict multiple branches in the same instruction cache line for a wide-issue micro-architecture. Several configurations of the RABTB are simulated and compared using the SPECint95 benchmarks. We show that with a reasonable size of prediction scope, branch prediction can be improved by supporting multiple / up to 8 branch predictions in one cache line in one cycle. Our simulation results show that the optimal RABTB should be 2048 entry, 8-column range-associate and 8-entry modified ring buffer architecture using PAs prediction algorithm. It has an average 5.2 IPC_f and branch penalty per branch of 0.54 cycles. This is almost two times better than a mechanism that makes prediction only on the first encountered branch.

A novel 10-Gb/s fast acquisition bit-synchronization circuit for use in a Tb/s throughput optical packet switch has been developed. The circuit is a best-sampled-data-select type based on multiple phase-clocks, and it processes the asynchronous input packets into a synchronous data stream in a serial manner, which is advantageous in terms of circuit scale and consumption power compared with the parallel processing type. The circuit was developed using Si-bipolar ultrahigh-speed gate arrays and it was used to develop a 10-Gb/s optical asynchronous packet receiver module. The core logic of this circuit module required about 100 gates, consume 6 W, and the size of the module was reduced to only 170 mm (W)130 mm (D) 10 mm (H). Using the receiver module, a fast acquisition time of 9 bits and receiver sensitivity penalty of less than 1.5 dB due to re-synchronization were measured.

We propose a new bit timing recovery (BTR) scheme, called perturbed sampling BTR (PSBTR), that can operate near the symbol rate in high-bit-rate wireless systems. A peculiar sample clock, the duty factor of which is not 50%, is used in the PSBTR scheme. We call this type of clock a perturbed sample clock and use it for clock recovery. In PSBTR, there is no cycle slip of the sample clock, and the PSBTR circuit is mostly digital. We examine the performance of the PSBTR scheme under additive white Gaussian noise (AWGN) by computer simulation and experiment, and from these results, clarify the relationship between the performance and circuit parameters of the PSBTR circuit. The overall results indicate that the PSBTR scheme performs well and can be employed as a BTR scheme for high-bit-rate wireless systems.

A wavelength division multiplexing (WDM) optical path-based Internet protocol (IP) backbone network is proposed as a cost-effective way of realizing robust IP-over-photonic systems. The WDM optical path is based on WDM transmission and wavelength routing. Between end-to-end IP backbone routers, the WDM optical path, a fat and robust optical pipe, is defined across photonic transport systems (PTS's). Tera-bit class PTS's will be required for the future IP backbone network and this level of performance is achievable. Optical layer routing is done at intermediate nodes, so the electrical packet-by-packet routing required by existing systems is eliminated. An optical signal format that permits cost-effective IP packet transmission is presented. WDM optical paths directly accommodate the IP packets via layer-2 frames. The cost-effectiveness of the proposed system, especially for heavy traffic, is demonstrated from the viewpoint of the overall network traffic transport capability and network node cost. The proposed system is as robust as existing systems; e. g. fault/degradation localization mechanism and optical layer network protection one are implemented. Thus the proposed IP-over-photonic system will create cost-effective and robust IP backbone networks.

This paper proposes adaptive line enhancers with new coefficient update algorithms on the basis of least-square-error criteria. Adaptive algorithms by least-squares are known to converge faster than stochastic-gradient ones. However they have high computational complexity due to matrix inversion. To avoid matrix inversion the proposed algorithms adapt only one coefficient to detect one sinusoid. Both FIR and IIR types of adaptive algorithm are presented, and the techniques to reduce the influence of additive noise is described in this paper. The proposed adaptive line enhancers have simple structures and show excellent convergence characteristics. While the convergence of gradient-based algorithms largely depend on their stepsize parameters, the proposed ones are free from them.

WDM transmission experiments over cascaded sections of optical links including wavelength converting 2R-transponders have been carried out in a loop testbed. Using dispersion compensated links and simple direct modulated transponder lasers, up to 11 cascaded crossconnects and 1750 km trunk lines have been bridged with 2.5 Gbit/s NRZ signals. The limitations are given mainly due to the accumulated jitter as it is shown by numerical simulations. The results indicate, that 2R-transponders are a useful approach to a flexible WDM network design using bitrate-transparent wavelength conversion.

In this paper, we study a new hybrid speech coder which employs a modified version of the harmonic sinusoidal analysis to encode the periodic contents of speech waveform and to split the speech spectrum into two frequency regions of harmonic and random components. A reliable fundamental frequency is estimated for the harmonic region using both speech and its linear predictive (LP) residual spectrum. The peak envelope of speech spectrum is encoded in terms of the coefficients of an all-pole spectrum. A harmonic tracking algorithm appropriately interpolates the sinusoidal parameters to achieve a smooth transition between the parameter update points and to reconstruct an essential level of periodicity in the synthetic voiced speech. The random part of spectrum and unvoiced speech are coded using the conventional CELP algorithm. The individual components are then combined at the decoder to obtain the synthetic speech. The proposed hybrid coder which combines the powerful features of the sinusoidal and CELP coding algorithms yeilds a high quality synthetic speech at 4.05 kbps.

We have developed an InP-based monolithic optical frequency discriminator consisting of a temperature-insensitive optical filter and dual photodiodes. This integrated device detects the optical frequency deviation of the input light as differential photocurrent from the dual photodiodes, and the photocurrent is fedback to the light source for frequency stabilization through a differential amplifier. The FSR and extinction ratio of the filter are 50 GHz and 20 dB. The total opto-electronic conversion efficiency is 40%. In a frequency stabilization experiment using the developed discriminator, the frequency fluctuation of a DFB laser was reduced to less than 10 MHz.

In this paper, a new gradient-based adaptive algorithm for the estimation of discrete Fourier coefficients (DFC) of a noisy sinusoidal signal is proposed based on a summed least mean squared error criterion. This algorithm requires exactly the same number of multiplications as the conventional LMS algorithm, and presents much improved performance in both white and colored noise environments at the expense of some additional memories and additions only. We first analyze the performance of the conventional LMS algorithm in colored additive noise, and point out when its performance deteriorates. Then, a summed least mean squared error criterion is proposed, which leads to the above-mentioned new gradient-based adaptive algorithm. The performance of the proposed algorithm is also analyzed for a single frequency case. Simulation results are provided to support the analytical findings and the superiority of the new algorithm.