We present a numerical analysis of the optimal number of active mobile users for minimizing average data delivery delay in intelligent people-centric urban sensing, in which context-aware mobile devices act as sensor-data carriers and sensor nodes act as data accumulators within CDMA cellular networks. In the analysis, we compute the optimal number of mobile users for different environmental conditions and then investigate the minimum average data delivery delay for this optimal number of mobile users.

This paper proposes an approach to image segmentation using Iterated Graph Cuts based on local texture features of wavelet coefficients. Using Haar Wavelet based Multiresolution Analysis, the low-frequency range (smoothed image) is used for the n-link and the high-frequency range (local texture features) is used for the t-link along with the color histogram. The proposed method can segment an object region having not only noisy edges and colors similar to the background, but also heavy texture change. Experimental results illustrate the validity of our method.

We propose a user-defined on-demand matching strategy, called O-matching, in which users can control the order of matching arguments of each operation symbol. In ordinary matching schemes it is not important to set the order of matching, however, in on-demand matching schemes, it is very important since an input term may be changed while doing the on-demand matching process. O-matching is suitable to combine with the E-strategy, which is a user-defined reduction strategy in which users can control the order of reducing arguments. We show a sufficient condition under which the E-strategy with O-matching is correct for head normal forms, that is, any reduced term is a head normal form.

By modifying the private key and the public key setting in Boneh-Lynn-Shacham's short signature shcheme, a variation of BLS' short signature scheme is proposed. Based on this variation, we present a very efficient threshold signature scheme where the number of pairing computation for the signaure share verification reduces to half.

The performance of ultra-wideband (UWB) multiple input multiple output (MIMO) receiver based on the RAKE maximal ratio combiner (MRC) followed by a zero forcing (ZF) detector is analytically examined. For a UWB MIMO system with NT transmit antennas, NR receive antennas, and L resolvable multipath components, the proposed MIMO detection scheme is shown to have the diversity order of LNR-NT+1 and its analytical error rate expression is presented in a log-normal fading channel. We also compare the analytical BERs with the simulated results.

Kalman filters are effective channel estimators but they have the drawback of having heavy calculations when filtering needs to be done in each sample for a large number of subcarriers. In our paper we obtain the steady-state Kalman gain to estimate the channel state by utilizing the characteristics of pilot subcarriers in OFDM, and thus a larger portion of the calculation burden can be eliminated. Steady-state value is calculated by transforming the vector Kalman filtering in to scalar domain by exploiting the filter charactertics when pilot subcarriers are used for channel estimation. Kalman filters operate optimally in the steady-state condition. Therefore by avoiding the convergence period of the Kalman gain, the proposed scheme is able to perform better than the conventional method. Also, driving noise variance of the channel is difficult to obtain practical situations and accurate knowledge is important for the proper operation of the Kalman filter. Therefore, we extend our scheme to operate in the absence of the knowledge of driving noise variance by utilizing received Signal-to-Noise Ratio (SNR). Simulation results show considerable estimator performance gain can be obtained compared to the conventional Kalman filter.

We propose an optimized scanline filling algorithm for OpenVG two-dimensional vector graphics. For each scanline of a path, it adaptively selects a left or right scanning direction that minimizes the number of pixels visited during scanning. According to the experimental results, the proposed algorithm reduces the number of pixels visited by 6 to 37% relative to that with a constant scanning direction for all the scanlines.

In 2006, Chatterjee and Sarkar proposed a hierarchical identity-based encryption (HIBE) scheme which can support an unbounded number of identity levels. This property is particularly useful in providing forward secrecy by embedding time components within hierarchical identities. In this paper we show that their scheme does not provide the claimed property. Our analysis shows that if the number of identity levels becomes larger than the value of a fixed public parameter, an unintended receiver can reconstruct a new valid ciphertext and decrypt the ciphertext using his or her own private key. The analysis is similarly applied to a multi-receiver identity-based encryption scheme presented as an application of Chatterjee and Sarkar's HIBE scheme.

We present recent progress of high-speed Mach-Zehnder modulator technologies for advanced modulation formats. Multi-level quadrature amplitude modulation signal can be synthesized by using parallel Mach-Zehnder modulators. We can generate complicated multi-level optical signals from binary data streams, where binary modulated signals are vectorially summed in optical circuits. Frequency response of each Mach-Zehnder interferometer is also very important to achieve high-speed signals. We can enhance the bandwidth of the response, with thin substrate. 87 Gbaud modulation was demonstrated with a dual-parallel Mach-Zehnder modulator.

This paper proposes an indoor event detection system for homes and offices that is based on electric wave reception such as intrusion into home or office. The proposed system places antenna array on the receiver side and detects events such as intrusion using the eigenvector spanning signal subspace obtained by the antenna array. The eigenvector is based on not received signal strengths (RSS) but direction of arrival (DOA) of incident signals on the antenna array. Therefore, in a static state, the variance of the eigenvector over time is smaller than that of RSS. The eigenvector changes only when the indoor environment of interest changes intermittently and statically, or dynamically. The installation cost is low, because the detection range is wide owing to indoor reflections and diffraction of electric wave and only a pair of transmitter and receiver are used. Experimental results reveal that the proposed method can distinguish the state when no event occurs and that when an event occurs clearly. Since the proposed method has a low false detection rate, it offers higher detection rates than the systems based on RSS.

This paper describes the recent advances in semiconductor photodiodes for use in ultra-high-speed optical systems. We developed two types of waveguide photodiodes (WG-PD) -- an evanescently coupled waveguide photodiode (EC-WG-PD) and a separated-absorption-and-multiplication waveguide avalanche photodiode (WG-APD). The EC-WG-PD is very robust under high optical input operation because of its distribution of photo current density along the light propagation. The EC-WG-PD simultaneously exhibited a high external quantum efficiency of 70% for both 1310 and 1550 nm, and a wide bandwidth of more than 40 GHz. The WG-APD, on the other hand, has a wide bandwidth of 36.5 GHz and a gain-bandwidth product of 170 GHz as a result of its small waveguide mesa structure and a thin multiplication layer. Record high receiver sensitivity of -19.6 dBm at 40 Gbps was achieved. Additionally, a monolithically integrated dual EC-WG-PD for differential phase shift-keying (DPSK) systems was developed. Each PD has equivalent characteristics with 3-dB-down bandwidth of more than 40 GHz and external quantum efficiency of 70% at 1550 nm.

The Dst index is the most popular measure of a scale of magnetic storms, and it is widely used as a monitor of the conditions of the Earth's magnetosphere. Since the Dst index contains contributions from multiple magnetospheric phenomena, it is important to distinguish each of the contributions in order to obtain meaningful information about the conditions of the magnetosphere. There have been several efforts which modeled temporal evolution of the Dst index empirically, and these empirical models considers some contributions separately. However, they take only short-term varations into accout, and contributions from phenomena which show long-term variations are neglected. In the present study, we have developed a technique for estimating the component of long-term variations of the Dst index using solar wind data and a nonlinear empirical model. The newly-developed technique adopts an algorithm which is similar to the particle filter. This algorithm allows an on-line processing of a long sequence of Dst data, which would enable a real-time estimation of system variables in a nonlinear system model. The estimates of the long-term variations can be used for accurate estimation of other contributions to the Dst index, which would provide credible information about the conditions of the magnetosphere. The framework proposed in the present study could be applied for the purpose of continuous real-time monitoring of the environment of the magnetosphere.

We show that simultaneous perturbation can be used as an algorithm for on-line learning, and we report our theoretical investigation on generalization performance obtained with a statistical mechanical method. Asymptotic behavior of generalization error using this algorithm is on the order of t to the minus one-third power, where t is the learning time or the number of learning examples. This order is the same as that using well-known perceptron learning.

The ITU-T J.83 Annex B is a widely adopted standard in North America for digital video and audio transmission over coaxial cable. This paper proposes a new parallel processing architecture of the parity checksum generator and syndrome generator specified in the standard for packet synchronization and error detection. The proposed parallel processing architecture removes the performance bottleneck occurring in the conventional serial processing architecture, leading to significant decrease in processing time for generating a parity checksum in transmitter and a syndrome in receiver. Implementation results show that the proposed parallel processing architecture reduces the processing time by 92% for parity checksum generation and by 81% for syndrome generation over the conventional serial processing architecture.

We have developed a high-speed electroabsorption modulator integrated distributed feedback (EA/DFB) lasers. Transmission performance over 10 km was investigated under 25 Gbps and 43 Gbps modulation. In addition, the feasibility of wide temperature range operation was also investigated. An uncooled EA/DFB laser can contribute to the realization of low-power-consumption, small-footprint and cost-effective transceiver module. In this study, we used the temperature-tolerant InGaAlAs materials in an EA modulator. A wide temperature ranged 12 km transmission with over 9.6 dB dynamic extinction ratio was demonstrated under 25 Gbps modulation. A 43 Gbps 10 km transmission was also demonstrated. The laser achieved a clear, opened eye diagram with a dynamic extinction ratio over 7 dB from 25 to 85. The modulated output power was more than +2.9 dBm even at 85. These devices are suitable for next-generation, high-speed network systems, such as 40 Gbps and 100 Gbps Ethernet.

In this paper, we discuss software performability evaluation considering the real-time property; this is defined as the attribute that the system can complete the task within the stipulated response time limit. We assume that the software system has two operational states from the viewpoint of the end users: one is operating with the desirable performance level according to specification and the other is with degraded performance level. The dynamic software reliability growth process with performance degradation is described by the extended Markovian software reliability model with imperfect debugging. Assuming that the software system can process the multiple tasks simultaneously and that the arrival process of the tasks follows a nonhomogeneous Poisson process, we analyze the distribution of the number of tasks whose processes can be completed within the processing time limit with the infinite server queueing model. We derive several software performability measures considering the real-time property; these are given as the functions of time and the number of debugging activities. Finally, we illustrate several numerical examples of the measures to investigate the impact of consideration of the performance degradation on the system performability evaluation.

Some wireless OFDMA communication systems support the frequency reuse factor of 1. In order to reduce co-channel interference (CCI) caused by neighbor cells, the fractional frequency reuse (FFR) can be employed. A promising frequency partitioning policy and subcarrier allocation for FFR are essential. In this letter, we employ an efficient frequency partitioning mechanism with less interference and propose an efficient subcarrier allocation algorithm to maximize the sum of users capacity under FFR. We show that the proposed algorithm has higher spectral efficiency than the conventional method as well as significantly high system fairness.

In direct-conversion orthogonal frequency division multiplexing (OFDM) receivers, the impact of frequency-dependent I/Q mismatch (IQ-M) with carrier frequency offset (CFO) must be considered. A preamble-assisted estimation is developed to circumvent the frequency-dependent IQ-M with CFO. The results of a simulation and an experiment show that the proposed method could provide good estimation efficiency and enhance the system performance. Moreover, the proposed scheme is compatible with current wireless local area network standards.

Optical buffer memory for 10-Gb/s data signal is demonstrated experimentally using a polarization bistable vertical-cavity surface-emitting laser (VCSEL). The optical buffer memory is based on an optical AND gate function and the polarization bistability of the VCSEL. Fast AND gate operation responsive to 50-ps-width optical pulses is achieved experimentally by increasing the detuning frequency between an injection light into the VCSEL and a lasing light from the VCSEL. A specified bit is extracted from the 10-Gb/s data signal by the fast AND gate operation and is stored as the polarization state of the VCSEL by the polarization bistability. The corresponding numerical simulations are also performed using two-mode rate equations taking into account the detuning frequency. The simulation results confirm the fast AND gate operation by increasing the detuning frequency as well as the experimental results.

We present a novel high-speed transmitter consisting of a frequency modulated DBR laser and optical filters. The refractive index modulation in the phase control region of the DBR laser allows high-speed frequency modulation. The generated frequency modulated signal is converted to an intensity modulated signal using the edge of the optical filter pass band. We present theoretical simulations of high-speed modulation characteristics and extension of transmission reach. With the proposed transmitter, we review the experimental demonstration of 180-km transmission of a 10-Gb/s signal with a tuning range of 27 nm and 60-km transmission of a 20-Gb/s signal.