In this paper, we propose a new preemptive scheme with release message in optical burst switching (OBS) networks. In the proposed scheme, when a low priority burst is preempted at some intermediate node, two RELEASE messages are sent immediately from the intermediate node to both source and destination nodes (two-way release message transmission), and the RELEASE messages release the corresponding wavelengths for the preempted burst. We consider six wavelength selection rules for the preemption and evaluate the performances of the selection rules by simulations. Numerical examples show that our scheme utilizes wavelengths effectively and, with the optimal selection rule, can decrease the burst loss probability in a large-scale DWDM network.

A total coloring of a graph G is a coloring of all elements of G, i.e. vertices and edges, such that no two adjacent or incident elements receive the same color. Let L(x) be a set of colors assigned to each element x of G. Then a list total coloring of G is a total coloring such that each element x receives a color contained in L(x). The list total coloring problem asks whether G has a list total coloring for given L. In this paper, we give a sufficient condition for a series-parallel graph to have a list total coloring, and we present a linear-time algorithm to find a list total coloring of a given series-parallel graph G if G and L satisfy the sufficient condition.

Buffer insertion plays a great role in modern global interconnect optimization. But too many buffers exhaust routing resources, and result in the rise of the power dissipation. Unfortunately, simplified delay models used by most of the present buffer insertion algorithms may introduce redundant buffers due to the delay estimation errors, whereas accurate delay models expand the solution space significantly, resulting in unacceptable runtime. Moreover, the power dissipation problem becomes a dominant factor in the state-of-the-art IC design. Not only transistor but also interconnect should be taken into consideration in the power calculation, which makes us have to use an accurate power model to calculate the total power dissipation. In this paper, we present two stochastic optimization methods, simulated annealing and solution space smoothing, which use accurate delay and power models to construct buffered routing trees with considerations of buffer/wire sizing, routing obstacles and delay and power optimization. Experimental results show our methods can save much of the buffer area and the power dissipation with better solutions, and for the cases with pins ≤ 15, the runtime of solution space smoothing is tens of times faster.

The design aspects of the bulk InGaAsP semiconductor optical amplifier integrated Mach-Zehnder interferometer (SOA-MZI) optimized for 40 Gbps-NRZ all optical wavelength conversion are described. The dimensions of the SOA active waveguide have been optimized for fast gain recovery by maximizing the gain and adjusting the wavelength-converted NRZ waveforms. Submicron-width buried heterostructure (BH) SOA waveguides were fabricated successfully and showed little leakage current. The experimental wavelength-converted optical waveform agreed well to the numerical simulations, and mask-compliant 40 G-NRZ wavelength-converted waveform was obtained by the optimized SOA-MZI. 40 G-NRZ full C-band operation and polarization-insensitive operation of SOA-MZI were also achieved.

This paper investigates fast Packet Classification techniques, where a large routing table is divided into many much smaller tables by an index key at first; the resulting small tables are much easier to search. A traditional way is to use the front bits as the index key, but we show it's not an effective way to divide a routing table. In this paper, we propose three bit selection methods for division. They can be implemented by CAM or hash structure. Simulations show that the bit selection methods decrease the delay of classification 50% compared to the traditional method. We also propose an optimized method which is adapted to the biased traffic pattern, which shows 70% improvement in our simulation.

Interactive audio-video applications over IP networks have subjective tradeoffs between fidelity and latency owing to packet buffering at the receiver. Increasing the buffering time improves the fidelity, whereas it degrades the latency. This paper makes the subjective tradeoff between fidelity and latency clear in a quantitative way. In addition, we examine the effect of tasks on the subjective tradeoff. In evaluating the effect of tasks, we use two tasks according to ITU-T Recommendation P.920. An experiment was conducted to measure user-level QoS of an interactive application with the psychometric methods. We then investigate the subjective tradeoff quantitatively by QoS mapping. The experimental results confirm that there exists the buffering time which makes user-level QoS the highest. The results also show that the optimum buffering time depends on the kind of task.

We investigate the issues involved in designing a packet scheduler for the proportional delay differentiation (PDD) model in differentiated services (DiffServ) networks. The PDD model controls the average waiting time of each class such that the average waiting time is proportional to its corresponding delay differentiation parameter. This paper proposes a novel packet scheduler for PDD referred to as the longest waiting time first (LWTF). By adding certain conditions, we found that the LWTF scheduler can be reduced to a known packet scheduler-priority queue with linear priorities (PQ-LP). The properties and behaviors of LWTF can be predicted from the analysis of PQ-LP. The simulation results in comparison with other PDD algorithms have also revealed that LWTF provides no worse level of service quality in long timescales and affords more accurate and robust control over the delay ratio in short timescales.

In this paper we modeled and analyzed the ridge type InGaAlAs/InP semiconductor laser with lateral current confinement structure, and optimized the design for the ridge wave guide with the current confinement. We proposed and fabricated the ridge type InGaAlAs/InP laser with a cost effective selective undercut etching method and demonstrated the improvement of the ridge laser performance. This paper provides a solution to solve the cost/yield issue for conventional BH (buried hetero-structure) type laser and performance issue for conventional ridge type laser.

Monolithically integrated four-channel distributed feedback (DFB) laser array has been fabricated by metal organic vapor phase epitaxy (MOVPE) selective area growth for 1.55 µm coarse-wavelength division multiplexing (CWDM) systems. Wide-stripe MOVPE selective area growth and electron-beam lithography are used to obtain wide CWDM channel spacing of 20 nm. Compared to hybrid integration of discrete lasers, monolithic integration of laser array on a single substrate greatly simplifies device alignment and packaging process.

Parallel downloading retrieves different pieces of a file from different servers simultaneously and so is expected to greatly shorten file fetch times. A key requirement is that the different servers must hold the same file. We have already proposed a proxy system that can ensure file freshness and concordance. In this paper, we combine parallel downloading with the proxy server technology in order to download a file quickly and ensure that it is the latest version. Our previous paper on parallel downloading took neither the downloading order of file fragments nor the buffer space requirements into account; this paper corrects those omissions. In order to provide the user with the required file in correct order as a byte stream, the proxy server must reorder the pieces fetched from multiple servers and shuffle in the delayed blocks as soon as possible. Thus, "substitution download" is newly introduced, which requests delayed blocks from other servers to complete downloading earlier. Experiments on substitution download across the Internet clarify the tradeoff between the buffering time and the redundant traffic generated by duplicate requests to multiple servers. As a result, the pseudo-optimum balance is discovered and our method is shown both not to increase downloading time and to limit the buffer space. This network software can be applied to download files smoothly absorbing the difference in performance characteristics among heterogeneous networks.

This paper presents two steganographic methods for JPEG2000 still images which approximately preserve histograms of discrete wavelet transform coefficients. Compared with a conventional JPEG2000 steganography, the two methods show better histogram preservation. The proposed methods are promising candidates for secure JPEG2000 steganography against histogram-based attack.

Existing standard speech coders can provide high quality speech communication. However, they tend to degrade the performance of automatic speech recognition (ASR) systems that use the reconstructed speech. The main cause of the degradation is in that the linear predictive coefficients (LPCs), which are typical spectral envelope parameters in speech coding, are optimized to speech quality rather than to the performance of speech recognition. In this paper, we propose a speech coder using mel-frequency cepstral coefficients (MFCCs) instead of LPCs to improve the performance of a server-based speech recognition system in network environments. To develop the proposed speech coder with a low-bit rate, we first explore the interframe correlation of MFCCs, which results in the predictive quantization of MFCC. Second, a safety-net scheme is proposed to make the MFCC-based speech coder robust to channel errors. As a result, we propose an 8.7 kbps MFCC-based CELP coder. It is shown that the proposed speech coder has a comparable speech quality to 8 kbps G.729 and the ASR system using the proposed speech coder gives the relative word error rate reduction by 6.8% as compared to the ASR system using G.729 on a large vocabulary task (AURORA4).

IEEE 802.11 DCF is an asynchronous and distributed MAC protocol which does not require the existence of a central controller for medium access coordination. This flexibility, which is due to DCF's contention-based nature, comes at the expense of the overhead associated with contention resolution. The overhead consists of frame collision time and channel idle time, which is particularly severe when channel is saturated. In this paper, we present an enhancement of DCF which aims at reducing its contention resolution overhead by equipping it with a distributed reservation mechanism. The proposed reservation mechanism enhances collision avoidance mechanism of DCF by enforcing a partially ordered medium access through an implicit agreement between neighboring nodes. Simulation results, using ns-2 network simulator, show that the added reservation scheme 1) effectively reduces DCF's overhead and improves channel utilization particularly when node density and traffic load is high, 2) significantly enhance DCF's fairness.

An improved signal-to-jamming and noise ratio (SJNR) method is proposed for the linear precoding of multiuser MIMO downlink systems. To well balance suppression of co-channel interference and suppression of noise, the proposed method modifies the noise variance term to argument of a piecewise linear function, and then enhances the suppression of noise. A dynamic power allocation scheme is also introduced to further decrease the overall average bit error rate of the system. Simulation results prove the effectiveness of the proposed scheme.

The propagation characteristics of the leaky TE mode in a two-dimensional photonic crystal waveguide is analyzed using the Fourier series expansion method combined with the Chew's perfectly matched layer (PML). The complex propagation constant and mode field profiles are numerically tested in detail. It is shown that the leakage phenomena can be well modeled by choosing the PML parameters in proper range.

Nowadays, MIMO systems are playing an important role in wireless communications. In this paper, we propose a spatial-temporal adaptive MIMO beamforming scheme for single carrier transmission in frequency-selective fading channels with the assumption of perfect channel state information (CSI) at both the transmitter and receiver. The transmit and receive weight vectors for detecting the preceding signal and the receive weight vectors for detecting the delayed signals of the preceding signal are designed by an iterative update algorithm. Based on minimum mean square error (MMSE) method, the delayed versions of the preceding signal are exploited to maximize the output signal to interference and noise ratio (SINR) instead of suppressing them at the receiver. The improvement of output SINR is useful for MIMO systems to enhance the high-quality communication in broadband wireless systems.

The electromagnetic disturbance that leaks from ICT (information and communications technology) equipment might contain important information. Our measurements show that the information hidden inside of the electromagnetic disturbance can be monitored. First, we measured the level of the electromagnetic disturbance that leaks from laser printers and collected the waveform in the time domain. Then, we reconstructed the printed image from the data. As a result of our measurements, we found that at points 200 cm away or beyond it is difficult to reconstruct the printed image, and therefore the threat to electromagnetic security is not significant.

In this letter, we propose a limited feedback precoding scheme based upon grassmannian beamforming and user selection for downlink multiuser MIMO systems. Conventional random beamforming scheme only enjoys significant performance gains with a large number of users, which limits its practical application. With proper codebook size the proposed scheme outperforms conventional random beamforming scheme when the number of users is small or moderate.

In nature an unbalanced clock tree exists in a SoC because the clock sinks of IPs have distinct input capacitive loads and internal delays. The construction of a bottom-up RLC clock tree with minimal clock delay and zero skew is crucial to ensure good SoC performance. This study proves that an RLC clock tree construction always has no zero skew owing to skew upward propagation. Specifically, this study proposes the insertion of two unit-size buffers associated with the binary search for a tapping point into each pair of subtrees to interrupt the non-zero skew upward propagation. This technique enables reliable construction of a buffered RLC clock tree with zero skew. The effectiveness of the proposed approach is demonstrated by assessing benchmarks.

The Multiple Access Interference (MAI) and the Multipath Fading (MPF) restrict the performance of Code-Division Multiple-Access (CDMA) systems. The Multiuser Detection (MUD) based on Particle Swarm Optimization algorithm (PSO) with Rake processing is proposed in this paper to overcome these obstacles, followed by full details of how to apply the Binary PSO MUD (BPSO-MUD) on a CDMA system. Simulations show that the BPSO-MUD has significantly better performance than the Conventional Detection (CD).