We report tunable optical devices based on fiber Bragg gratings (FBGs), whose filtering characteristics are controlled by strain distributions. These devices include a widely wavelength tunable filter, a tunable group-velocity dispersion (GVD) compensator, a tunable dispersion slope (DS) compensator, and a variable-bandwidth optical add/drop multiplexer (OADM), which will play important roles for next-generation reconfigurable optical networks.

This paper describes a new multi-channel method of noisy speech recognition, which estimates the log spectrum of speech at a close-talking microphone based on the multiple regression of the log spectra (MRLS) of noisy signals captured by distributed microphones. The advantages of the proposed method are as follows: 1) The method does not require a sensitive geometric layout, calibration of the sensors nor additional pre-processing for tracking the speech source; 2) System works in very small computation amounts; and 3) Regression weights can be statistically optimized over the given training data. Once the optimal regression weights are obtained by regression learning, they can be utilized to generate the estimated log spectrum in the recognition phase, where the speech of close-talking is no longer required. The performance of the proposed method is illustrated by speech recognition of real in-car dialogue data. In comparison to the nearest distant microphone and multi-microphone adaptive beamformer, the proposed approach obtains relative word error rate (WER) reductions of 9.8% and 3.6%, respectively.

To avoid over-engineered and expensive systems, it is important that the design takes account of variations in optical fiber characteristics due to the presence of many fiber pieces and splices in optical fiber networks. We present a design method for optical fiber networks that employ distributed Raman amplification (DRA), that considers variations in both optical losses at signal and pump wavelengths, Raman gain characteristics and splice losses. Our method can be applied to the design of both newly developed systems and installed systems. We show design examples based on our method and reveal the practicability of our method.

This paper proposes a channel allocation principle that prevents TCP throughput degradation in multihop transmissions in a mesh network based on the carrier sense multiple access with collision avoidance (CSMA/CA) MAC protocol. We first address the relationship between the network topology of wireless nodes and the TCP throughput degradation based on computer simulations. The channel allocation principle is discussed in terms of resolution into a coloring problem based on throughput degradation. The number of required channels for the proposed channel allocation principle is evaluated and it is shown that two channels are sufficient for more than 96% simulated multihop patterns. The proposed channel allocation principle is extendable to generic mesh networks. We also clarify the number of required channels for mesh networks. The simulation results show that three channels are sufficient for more than 98% patterns in the generic mesh networks when the number of nodes is less than 10.

This paper presents a multiple constrained subspace based multiuser detector for synchronous long-code downlink multirate DS-CDMA systems. The novel receiver adapts its fractionally-spaced equaliser tap-weights based upon two modes, namely training and decision-directed modes. Switching between two modes is achieved by changing the code constraint in the associated subspace algorithm. Moreover, detection of the desired user requires the knowledge of the desired user's spreading code only. Simulation results show that the proposed receiver is capable of multiple access interference (MAI) suppression and multipath mitigation. Besides, the results reveal the improvement in terms of convergence speed and mean square error (MSE) of the proposed receiver over the existing receiver in both static and dynamic environments.

This paper describes recent progress in research on wavelength converters that employ quasi-phase-matched LiNbO3 (QPM-LN) waveguides. The basic structure and operating principle of these devices are presented. The conversion efficiency in difference frequency generation (DFG), second harmonic generation (SHG) and an SHG/DFG cascade scheme are explained. Device fabrication technologies such as periodic poling, and those used for annealed proton-exchanged (APE) waveguides, and direct bonded waveguides are introduced. An APE waveguide is used to demonstrate the wavelength conversion of broadband (> 1 Tbit/s) WDM signals. The low penalty conversion of high-speed (40 Gbit/s) based WDM signals is also reported. Excellent resistance to photorefractive damage in a direct bonded waveguide is presented. This high level of resistance enabled highly efficient wavelength conversion. A new design concept is introduced for a multiple QPM device based on the continuous phase modulation of a periodically poled structure. This multiple QPM device enables the variable wavelength conversion of WDM signals. High-speed wavelength switching between ITU-T grid wavelengths using a finely tuned multiple QPM device is also reported. QPM-LN based wavelength converters have several advantages, including the ability to convert high-speed signals of 1 THz or greater, no signal-to-noise (S/N) ratio degradation, no modulation format dependence, and they are capable of the simultaneous conversion of broadband WDM channels. They will therefore be key devices in future photonic networks.

We are developing a simple three-dimensional (3-D) display method that uses only two transparent images using luminance division displays without any extra equipment. This method can be applied to not only electronic displays but also the printed sheets. The method utilizes a 3-D visual illusion in which two ordinary images with many edges can be perceived as an apparent 3-D image with continuous depth between the two image planes, when two identical images are overlapped from the midpoint of the observer's eyes and their optical-density ratio is changed according to the desired image depths. We can use transparent printed sheets or transparent liquid crystal displays to display two overlapping transparent images using this 3-D display method. Subjective test results show that the perceived depths changed continuously as the optical-density ratio changed. Deviations of the perceived depths from the average for each observer were sufficiently small. The depths perceived by all six observers coincided well.

Live streaming media are delay sensitive and have limited allowable delays. Current conventional multicast protocols do not have a loss retransmission mechanism. Even though several reliable multicast protocols with retransmission mechanisms have been proposed, the long delay and high packet loss rate make them inefficient for live streaming. This paper proposes a multicast protocol focusing on the allowable delay called the QoS Multicast for Live Streaming (QMLS) protocol. QMLS routers are placed along the multicast tree to detect and retransmit lost packets. We propose a method that enables data recovery to be done immediately after lost packets are detected by the QMLS router and a method that reduces the unnecessary packets sent to end receivers. This paper discusses the mathematical analysis of the proposed protocol and compares it with other multicast protocols. The results reveal that our protocol is more effective in live streaming. Finally, we do a simulation to evaluate its performance and study the effect of consecutive losses. The simulation reveals that consecutive losses can slightly increase losses with our protocol.

The problem of estimating code timings in DS-CDMA systems with multiple antennas is considered in the presence of multipath time-varying fading channels and near-far environments. We present an efficient algorithm for an approximate maximum likelihood approach of jointly estimating the multipath timings of a desired user for DS-CDMA systems that consist of multiple antennas either uncorrelated or fully correlated in space. The procedures of the algorithm to estimate code-timings are developed in order to better exploit the time-varying characteristics of the fading process. In the multipath fading channels, the solution of the proposed algorithms is based on successively optimizing the criterion for increasing numbers of multipath delays. It is shown via simulation results that the modified approaches of the approximate maximum likelihood algorithm much more improve its acquisition performance in the time-varying fading channels. It is seen that the acquisition performance of multiple antennas based acquisition scheme is much better than that of a single antenna based timing estimator in the presence of multipath fading channels and the near-far problem. Furthermore, it is observed that the proposed algorithms outperform the correlator and MUSIC estimator in the multiuser environments with near-far situation on time-varying Rayleigh fading channels.

This paper describes the modeling of various emotional expressions and speaking styles in synthetic speech using HMM-based speech synthesis. We show two methods for modeling speaking styles and emotional expressions. In the first method called style-dependent modeling, each speaking style and emotional expression is modeled individually. In the second one called style-mixed modeling, each speaking style and emotional expression is treated as one of contexts as well as phonetic, prosodic, and linguistic features, and all speaking styles and emotional expressions are modeled simultaneously by using a single acoustic model. We chose four styles of read speech -- neutral, rough, joyful, and sad -- and compared the above two modeling methods using these styles. The results of subjective evaluation tests show that both modeling methods have almost the same accuracy, and that it is possible to synthesize speech with the speaking style and emotional expression similar to those of the target speech. In a test of classification of styles in synthesized speech, more than 80% of speech samples generated using both the models were judged to be similar to the target styles. We also show that the style-mixed modeling method gives fewer output and duration distributions than the style-dependent modeling method.

Optical regeneration technique using an electro-absorption modulator (EAM) is reviewed. Simple 3R optical regeneration using an EAM was proposed and verified at 20 Gbit/s. The optical nonlinearities including cross-absorption modulation (XAM) and cross-phase modulation (XPM) induced in an EAM were quantitatively characterized by experiment. High bit-rate 2R type all-optical regeneration (wavelength conversion) at 100 Gbit/s was demonstrated by an EAM in conjunction with a delayed interferometer (DI) with required optical pulse energy of 1.5 pJ. It was verified that the operable bandwidth of the EAM-DI wavelength converter at 40 Gbit/s covered almost full range of C-band without tuning operation conditions.

Recursive programs are often easier to read and write than iterative ones, but their execution frequently requires large numbers of procedure calls and stack operations. This causes problems in program optimization related to inline coding and the locality of data references. In addition to these problems, defining programs recursively sometimes leads to repetitive execution of similar computations, causing programs to have exponential time complexity. As a result, recursion removal methods, which transform a given recursive program to an iterative one without using the stack and increasing the amount of computation time, have been studied since the 1970s. In 1998, our group proposed a recursion removal method for a linear recursive program. In this paper, we extend the method to deal with non-linear recursive programs with one descent function (RPODs), which are programs of the form f(x) = if p(x) then b(x) else a(c(x),f(d(x)),f(d2(x)),...,f(dn(x))). First, we define the cumulative function for an RPOD. Next, based on the new cumulative function, several transformation techniques for RPODs are shown. These include a unified method of deriving logarithmic-order iterative programs or loop-free programs. Finally, the relationships between our method and various tupling strategies are discussed.

We propose a new diversity scheme for orthogonal frequency division multiplexing/multi-input multi-output (OFDM/MIMO) systems. The proposed scheme, named turbo layered space-frequency coded OFDM (TLSFC-OFDM), exploits the turbo principle with space hopping (SH). The TLSFC-OFDM system with SH provides a spatial coding so that we can obtain the transmit diversity. We also introduce a successive interference cancellation (SIC) algorithm that requires no ordering and fewer iterations to converge. As a result, this scheme reduces computational complexity. Computer simulation results show that the unordered SIC-based TLSFC-OFDM system outperforms the OFDM/H-BLAST system. It is also shown that the proposed system can operate even with fewer receive antennas than transmit antennas.

To enable the use of passive transmission lines (PTLs) for the interconnection of single-flux-quantum (SFQ) circuits, we have implemented a driver and a receiver and have developed a method for designing SFQ circuits with passive interconnections. Basic components and properties of passive interconnections, such as the frequency characteristics of the driver and receiver, the PTL delay, and the crosstalk between PTLs, have been experimentally verified. Our developed components and design method have been applied to actual SFQ circuits, such as a 44 switch having block-to-block passive interconnections and a 22 switch having gate-to-gate passive interconnections. We have also shown the advantages of PTLs over Josephson transmission lines (JTLs). We also discuss the prospects of SFQ circuits having passive interconnections.

Multi-Carrier CDMA (MC-CDMA) has been considered as a combination of the techniques of Code Division Multiple Access (CDMA) and Orthogonal Frequency Division Multiplex (OFDM). However, even until now, the efficient MC-CDMA scheme is still under study because of the inherent bugs in OFDM, such as the troubles caused by Multiple Access Interference (MAI) and Peak to Average Power Ratio (PAPR). In this paper, we present a novel two-dimensional spreading sequence named "Two Dimensional Combined Complementary Sequence" (TDC). If we take this kind of sequences as spreading codes, several prominent advantages can be achieved compared with traditional MC-CDMA. First, it can achieve MAI free in the multi-path transmission both in uplink and downlink. Second, it offers low PAPR value within 3 dB with a quite simple architecture. The last but not the least, the proposed MC-CDMA scheme turns out to be an efficient approach with high bandwidth efficiency, high spreading efficiency and flexible transmission rate enriched by a special shift-and-add modulation. Meanwhile, an algorithm that constructs TDC sequences is discussed in details. Based on above results, we can get the conclusion that the novel TDC sequences and corresponding MC-CDMA architecture have great potential for applications in next generation wireless mobile communications, which require high transmission rate in hostile and complicated channels.

In this letter, we evaluate the performance of Optical Cross Connect (OXC) architectures equipped with limited-range wavelength converters. Performance will be evaluated according to both an optimum and a random output wavelength assignment strategy. Analytical and simulation results show the possibility to reduce the conversion degree of the Wavelength Converters while keeping network performance high.

An audio signal level compressor is presented, which is based on the approximation algorithm using an interpolating polynomial. To implement a compression characteristic in a digital audio system, a power calculation with fractional numbers is required and it is difficult to be performed directly in digital circuits. We introduce a polynomial expression to approximate the power operation, then the gain calculation is easily performed with a number of additions, multiplications and a division. Newton's interpolation formula is used to calculate the compression characteristics in a very short time and the obtained compression characteristics are very close to the ideal ones.

In this paper we propose a new algorithm for computing the optimal configuration of the Multiple Fractional Guard Channel (MFGC) admission policy in multiservice mobile wireless networks. The optimal configuration maximizes the offered traffic that the system can handle while meeting certain QoS requirements. The proposed algorithm is shown to be more efficient than previous algorithms appeared in the literature.

Non-equal length, three section coupled transmission line couplers are proposed. The proposed structure offers increased design flexibility and the compact circuit design capability over the conventional quarterwave coupled lines. The detailed analysis results and design method are presented along with the numerical and the experimental verification.

Video telephone service (VTS) is considered one of promising services provided in wideband CDMA (WCDMA) networks. Without a designated call admission policy, VTS calls are expected to suffer from relatively high probability of blocking since they normally have more stringent signal quality requirement than ordinary voice calls. In this letter, we consider a prioritized call admission design in order to reduce the blocking probability of VTS calls, which may encourage the users to access the newly-provided VTS in a more comfortable way. The VTS calls are given a priority by reserving a number of channel-processing equipments. With the reservation, the blocking probability of prioritized VTS calls can be reduced evidently. That of ordinary calls, however, is increasing instead. This letter provides a system model that counts the blocking probabilities of VTS and ordinary calls simultaneously, and numerically examines an adequate level of the prioritization for VTS calls. The results show that the prioritization level should be selected depending on received interference as well as bandwidth required for VTS.