In Optical Burst Switched (OBS) networks, packets are assembled into bursts at ingress edge routers and disassembled at egress edge routers. This letter presents an analytical model to quantify the burstification latency in the OBS networks. To the authors' best knowledge, this letter is the first one to address the latency issue in OBS in a comprehensive manner analytically. The results allow us to quantitatively understand how OBS network parameters such as maximum burst length and maximum timeout affect the packet latency in the OBS networks. We show that the burstification latency in the OBS network is bounded and can be tuned by setting the system parameters under latency constraints.

Endothelial cell adhesion and growth were investigated on three types of surfaces with a plasma-polymerized coating (PPC): (1) the pristine surface of a hexamethyldisiloxane (HMDS) PPC (hydrophobic, electrically neutral surface); (2) an HMDS PPC surface with nitrogen-containing plasma treatment (hydrophilic, positively charged surface); and (3) an HMDS PPC surface treated with oxygen plasma (hydrophilic, negatively charged surface). Endothelial cells grew on surface (2) but not on surfaces (1) or (3). Next, endothelial cell adhesion and growth was investigated on a surface on which 80-µm squares were micro-patterned at 160-µm intervals in a mosaic composed of two different (cell-adhesive and non-cell-adhesive) regions. Cell growth on the patterned surfaces was different from that on non-patterned surfaces. PPC was shown to be a simple process for modulating cell adhesion to surfaces.

The reflection method is an accurate and simple method for measuring the radiation efficiency of a small antenna. However, it takes too long and has the disadvantage of underestimating the efficiency due to resonance in the cavity formed by the straight waveguide and two sliding shorts. To reduce the measurement time, one sliding short can be fixed while the other one is moved. To improve the accuracy of this technique, we can set the antenna to be measured at the center of the two sliding shorts or at a local anti-node of the standing wave in the waveguide. When one of the sliding shorts is fixed, the measured efficiency becomes negative at certain frequencies. We examine these reductions in efficiency using an equivalent transmission line model for the reflection method. We also derive analytical expressions for the overall efficiency in the above cases and verify new procedures that enable measurements to be performed without any drops in the measured efficiency.

This paper proposes a design method of a Doherty amplifier, which can determine the most efficient backed-off point of the amplifier by adjusting a load modulation parameter. The parameter is defined through the design of output transmission line of a carrier and a peak amplifier using a virtual open stub technique. This paper describes the design results using the technique to optimize efficiency of a Doherty amplifier for an orthogonal frequency division multiplexing (OFDM) signal, and parameter adjustment for a linearized Doherty amplifier using an adaptive digital predistortion (ADPD). Applying this method, the developed 250 W ADPD Doherty amplifier has achieved drain efficiency of 43.4% and intermodulation (IM) distortion of -48.3 dBc with output power of 44.1 dBm (10.1 dB output backed-off) at 563 MHz using an OFDM signal for integrated services digital broadcasting-terrestrial (ISDB-T).

Leaky wave radiation from evanescent-mode left-handed (LH) transmission lines is investigated that are composed of a cut-off parallel plate waveguide loaded with a one-dimensional (1-D) array of the disc type dielectric resonators. The apertures are placed on side walls of the parallel plate waveguide. First of all, the dispersion diagram is numerically obtained with the complex eigenmode solutions. The simulated and measured backward wave radiation characteristics validate the backward wave propagation along the 1-D waveguides. Based on the concept, the backfire leaky wave antenna was designed and demonstrated with the 15-cell structure. The beam scanning with the operational frequency was achieved by more than 30 degrees.

Application of microwave and millimeter-wave circuit technologies to InGaP-HBT ICs for 40-Gbps optical-transmission systems is demonstrated from two aspects. First, ICs for various important functions -- amplification of data signals, amplification, frequency doubling, and phase control of clock signals -- are successfully developed based on microwave and millimeter-wave circuit configurations mainly composed of distributed elements. A distributed amplifier exhibits ≥164-GHz gain-bandwidth product with low power consumption (PC) of 71.2 mW. A 20/40-GHz-band frequency doubler achieves wideband performance (40%) with low PC (26 mW) by integrating a high-pass filter and a buffer amplifier (as a low-pass filter). A compact 40-GHz analog phase shifter, 20- and 40-GHz-band clock amplifiers with low PC are also realized. Second, a familiar concept in microwave-circuit design is applied to a high-speed digital circuit. A new approach -- inserting impedance-transformer circuits -- to enable 'impedance matching' in digital ICs is successfully applied to a 40-Gbps decision circuit to prevent unwanted gain peaking and jitter increase caused by transmission lines without sacrificing chip size.

Though microwave emissions in association with hypervelocity impacts have been confirmed experimentally, the emission characteristics and the emission mechanism have not yet been made clear. For example, whether the emission is noise or a coherent signal is not known. In this paper, two kinds of analyses, output waveform analysis and spectral analysis, are discussed. Regarding output waveform analysis, microwave pulses are simulated on the basis of a microcrack model in consideration of discharge current, and are compared with experimental pulses in terms of the pulse shape and width. Regarding spectral analysis, the intensity and phase of waveforms are calculated in the frequency domain to examine the frequency characteristics. The spectral intensity is nearly flat and the phase has coherency. Accordingly, the microwave emission is not noise but a sequence of independent pulses.

In this paper, we propose a PON-based access network based on conventional TDM-PON architecture for the smooth, economical and effective transition to the future optical access network. We also propose a dynamic MAC protocol for wavelength channel and bandwidth allocation in the TDM-PON subscriber networks, which can provide enhanced network scalability and flexibility, and greater adaptability to the increasing number of subscribers in TDM-PON. In the proposed dynamic MAC protocol, several key functions are manifested, such as multiple wavelength channel utilization and dynamic allocation of multiple time-slots to a user depending on SLA between OLT and ONUs to meet QoS requirements. A dedicated control channel is used for delivering the request and status information between OLT and ONUs. We evaluate the performances of the proposed MAC protocol thru a statistical queuing analysis and numerical simulations. In addition, through simulations using various traffic models we verify the superior performance of the proposed approach by comparing it with conventional TDM-PONs.

In the 300 MHz to 3 GHz range, probes used to measure specific absorption rate (SAR) of mobile communication devices are usually calibrated using a rectangular waveguide filled with tissue-equivalent liquid. Above 3 GHz, however, this conventional calibration can be inaccurate because the diameter of the probe is comparable to the cross-sectional dimension of the waveguide. Therefore, an alternative method of SAR probe calibration based on another principle was needed and has been developed by the authors. In the proposed calibration method, the gain of the reference antenna in the liquid is first evaluated using the two-antenna method based on the Friis transmission formula in the conducting medium. Then the electric field intensity radiated by the reference antenna is related to the output voltage of the SAR probe at a given point in the liquid. However, the fields are significantly reduced in the liquid, and the gain is impossible to calibrate in the far-field region. To overcome this difficulty, the Friis transmission formula in the conducting medium must be extended to the near-field region. Here, we report results of simulations and experiments on estimated gain based on the extended Friis transmission formula, which holds in the near-field region, and test the validity of the new formula.

China has experienced fast growth in mobile communications. Now, China is the world largest mobile communication country with about 500 million users. Wide applications of mobile communications are giving strong pull to the research and development on the broadband wireless communication technology to meet the fast growing demand for high speed access into the information infrastructure. This makes the R&D on wireless technology play great role in the Chinese High-Tech program. This paper will review the key project--FuTURE (Future Technology for Universal Radio Environment)--development of the 863 program, which represents the Chinese efforts towards IMT-advance. Taking some works done in the Tsinghua National Laboratory for Information Science and Technology as examples, the paper will show what has been made in China on the broadband wireless technology, including the trial network in Shanghai.

This paper describes a technique for controlling the degree of expressivity of a desired emotional expression and/or speaking style of synthesized speech in an HMM-based speech synthesis framework. With this technique, multiple emotional expressions and speaking styles of speech are modeled in a single model by using a multiple-regression hidden semi-Markov model (MRHSMM). A set of control parameters, called the style vector, is defined, and each speech synthesis unit is modeled by using the MRHSMM, in which mean parameters of the state output and duration distributions are expressed by multiple-regression of the style vector. In the synthesis stage, the mean parameters of the synthesis units are modified by transforming an arbitrarily given style vector that corresponds to a point in a low-dimensional space, called style space, each of whose coordinates represents a certain specific speaking style or emotion of speech. The results of subjective evaluation tests show that style and its intensity can be controlled by changing the style vector.

DTW-based text-dependent speaker verification technology is an effective scheme for protecting personal information in personal electronic products from others. To enhance the performance of a DTW-based system, an impostor database covering all possible passwords is generally required for the matching scores normalization. However, it becomes impossible in our practical application scenario since users are not restricted in their choice of password. We propose a method to generate pseudo-impostor data by employing an acoustic codebook. Based on the pseudo-impostor data, two normalization algorithms are developed. Besides, a template compression approach based on the codebook is introduced. Some modifications to the conventional DTW global constraints are also made for the compressed template. Combining the normalization and template compression methods, we obtain more than 66% and 35% relative reduction in storage and EER, respectively. We expect that other DTW-based tasks may also benefit from our methods.

The error resilient entropy coding (EREC) provides efficient resynchronization method to the coded bitstream, which might be corrupted by transmission errors. The technique has been given more prominence, nowadays, because it achieves fast resynchronization without sizable overhead, and thereby provides graceful quality degradation according to the network conditions. This paper presents a novel framework to analyze the performance of EREC in terms of the error probability in decoding a basic resynchronization unit (RU) for various error prone networks. In order to show the feasibility of the proposed framework, this paper also proposes a novel EREC algorithm based on the slightly modified H.263 bitstream syntax. The proposed scheme minimizes the effect of errors on low frequency DCT coefficients and incorporates near optimal channel-matched searching pattern (SP), which guarantees the best possible quality of reproduced video. Given the number of bits generated for each RU, the near optimal SP is produced by the proposed iterative deterministic partial SP update method, which reduces the complexity of finding optimal solution, O((N-1)!), to O(m·N2). The proposed EREC algorithm significantly improves the decoded video quality, especially when the bit error rate is in the rage of 10-3-10-4. Up to 5 dB enhancement of the PSNR value was observed in a single video frame.

There is an increasing requirement for supporting complex multidimensional queries in Peer-to-Peer systems. In the centralized spatial database world, R-Trees and its variant structures are widely accepted due to their capabilities to manage complex multidimensional queries. In this paper, we propose a new multidimensional indexing structure for P2P systems, called Distributed Hilbert R-Trees (DHR-Trees), in which peers organize themselves into an overlay network, dynamically maintain routing tables with region information and collaboratively execute complex multidimensional queries, such as range query and k-nearest neighbors query, efficiently. DHR-Trees has similar topology to the P-Trees P2P system. The peers' routing tables are enhanced with spatial region information, which allow multidimensional query predicates to be adapted into P2P systems with minor modification. The structure design and two major multidimensional query algorithms are presented. Our experimental results demonstrate that it performs well on range queries and k-nearest neighbors queries with multidimensional data set.

In orthogonal frequency-division multiplex access (OFDMA) downlink systems, the carrier-frequency offset (CFO) between the multiple transceivers introduces inter-carrier interference (ICI). In this letter, we propose an iterative precoding scheme to suppress the ICI due to CFO. This scheme is applied at the transmitter, and can jointly cancel the ICI for all the receivers. Moreover, by the studies of the convergence behavior of the iterations, a sufficient condition for the convergence is presented. The theoretical analysis and simulation results both show that this iterative scheme is equivalent to the zero-forcing (ZF) scheme in function, but with much lower complexity.

We propose an effective subcarrier allocation scheme for multiuser orthogonal frequency division multiple access (OFDMA) system in the downlink transmission with low computational complexity. In the proposed scheme, by taking multiple attributes of a user's channel, such as carrier gain decrease rate and variation from the mean channel gain of the system, to determine a rank for the user, subcarriers are then allocated depending on the individual user's rank. Different channel characteristics are used to better understand a user's need for subcarriers and hence determine a priority for the user. We also adopt an attribute weighing scheme to enhance the performance of the proposed scheme. The scheme is computationally efficient, since it avoids using iterations for the algorithm convergence and also common water-filling calculations that become more complex with increasing system parameters. Low complexity is achieved by allocating subcarriers to users depending on their determined rank. Our proposed scheme is simulated in comparison with other mathematically efficient subcarrier allocation schemes as well as with a conventional greedy allocation scheme. It is shown that the proposed method demonstrates competitive results with the simulated schemes.

The article describes recent adaptive estimation algorithms over distributed networks. The algorithms rely on local collaborations and exploit the space-time structure of the data. Each node is allowed to communicate with its neighbors in order to exploit the spatial dimension, while it also evolves locally to account for the time dimension. Algorithms of the least-mean-squares and least-squares types are described. Both incremental and diffusion strategies are considered.

This paper presents a novel approach to single channel speech enhancement in noisy environments. Widely adopted noise reduction techniques based on the spectral subtraction are generally expressed as a spectral gain depending on the signal-to-noise ratio (SNR) [1]-[4]. As the estimation method of the SNR, the well-known decision-directed (DD) estimator of Ephraim and Malah efficiently is known to reduces musical noise in noise frames, but the a priori SNR, which is a crucial parameter of the spectral gain, follows the a posteriori SNR with a delay of one frame in speech frames [5]. Therefore, the noise suppression gain using the delayed a priori SNR, which is estimated by the DD algorithm matches the previous frame rather than the current one, so after noise suppression, this degrades the performance of a noise reduction during abrupt transient parts. To overcome this artifact, we propose a computationally simple but effective speech enhancement technique based on the sigmoid type function to adaptively determine the weighting factor of the DD algorithm. Actually, the proposed approach avoids the delay problem of the a priori SNR while maintaining the advantage of the DD algorithm. The performance of the proposed enhancement algorithm is evaluated by the objective and subjective test under various environments and yields better results compared with the conventional DD scheme based approach.

In this paper, we propose a blind method using hybrid signal extrapolation at the decoder to regenerate lost high-frequency components which are removed by encoders. At first, a decoded signal spectral resolution is enhanced by time domain linear predictive extrapolation and then the cut off frequency of each frame is estimated to avoid the spectrum gap between the end of original low frequency spectrum and the beginning of reconstructed high frequency spectrum. By utilizing a correlation between the high frequency spectrum and low frequency spectrum, the low frequency spectrum component is employed to reconstruct the high frequency spectrum component by frequency domain linear predictive extrapolation. Experimental results show an effective improvement of the proposed method in terms of SNR and human listening test results. The proposed method can be used to reconstruct the lost high frequency component to improve the perceptual quality of audio independent of the compression method.

This paper reports a novel design in Photonic Crystal Fibers (PCFs) with nearly zero ultra-flattened dispersion characteristics. We describe the chromatic dispersion controllability taking non-uniform air hole structures into consideration. Through optimizing non-uniform air hole structures, the ultra-flattened zero dispersion PCFs can be efficiently designed. We show numerically that the proposed non-uniform air cladding structures successfully archive flat dispersion characteristics as well as extremely low confinement losses. As an example, the proposed PCF with flattened dispersion of 0.27 ps/(nmkm) from 1.5 µm to 1.8 µm wavelength with confinement losses of less than 10-11 dB/m. Finally, we point out that full controllability of the chromatic dispersion and confinement losses, along with the fabrication technique, are the main advantages of the proposed PCF structure.