This paper focuses on the underdetermined blind source separation (BSS) of three speech signals mixed in a real environment from measurements provided by two sensors. To date, solutions to the underdetermined BSS problem have mainly been based on the assumption that the speech signals are sufficiently sparse. They involve designing binary masks that extract signals at time-frequency points where only one signal was assumed to exist. The major issue encountered in previous work relates to the occurrence of distortion, which affects a separated signal with loud musical noise. To overcome this problem, we propose combining sparseness with the use of an estimated mixing matrix. First, we use a geometrical approach to detect when only one source is active and to perform a preliminary separation with a time-frequency mask. This information is then used to estimate the mixing matrix, which allows us to improve our separation. Experimental results show that this combination of time-frequency mask and mixing matrix estimation provides separated signals of better quality (less distortion, less musical noise) than those extracted without using the estimated mixing matrix in reverberant conditions where the reverberant time (TR) was 130 ms and 200 ms. Furthermore, informal listening tests clearly show that musical noise is deeply lowered by the proposed method comparatively to the classical approaches.

A robust microphone array for speech enhancement and noise suppression is studied in this paper. To overcome target signal cancellation problem of conventional beamformer caused by array imperfections or reverberation effects of acoustic enclosure, the proposed microphone array adopts an arbitrary model of channel transfer function (TF) relating microphone and speech source. Since the estimation of channel TF itself is often intractable, herein, transfer function ratio (TFR) is estimated instead and used to form a suboptimal beamformer. A robust TFR estimation method is proposed based on signal subspace analysis technique against stationary or slowly varying noise. Experiments using simulated signal and actual signal recorded in a real room illustrate that the proposed method has high performance in adverse environment.

Today, pedestrian navigation systems for mobile phones use 2-dimensional maps as a navigation media in general. But 3-dimensional maps or scenery images are easier to understand for users than 2-dimensional maps. To use 3-dimensional maps or scenery guidance, the measuring accuracy of user position is essential to understand guidance images. In this paper, we will present a pedestrian navigation system using real scenery photographs as a navigation media, and based on experiments we will report the evaluation result of influence of positioning accuracy on the understandability of navigation. It is shown that 3 meters or less error of positioning is tolerable for pedestrian navigation systems using scenery images.

A scalable multicast session announcement system is a key component of a group communication framework over the Internet. It enables the announcement of session parameters (like the {source address; group address} pair) to a potentially large number of users, according to each site administrator's policy. This system should accommodate any flavor of group communication system, like the Any-Source Multicast (ASM) and Source-Specific Multicast (SSM) schemes. In this paper we first highlight the limitations of the current Session Announcement Protocol (SAP) and study several other information distribution protocols. This critical analysis leads us to formulate the requirements of an ideal multicast session announcement system. We then introduce a new session announcement system called "Channel Reflector". It appears as a hierarchical directory system and offers an effective policy and scope control technique. We finally mention some design aspects, like the protocol messages and configuration structures the Channel Reflector uses.

This paper proposes a simple timing synchronization method in order to design a timing synchronization circuit with low-complex and low-volume digital signal processing (DSP) for orthogonal frequency division multiplexing (OFDM) packet transmission systems. The proposed method utilizes the subtraction process for acquirement of a timing metric of fast Fourier transform (FFT) window, whereas the conventional methods utilize the multiplication process. This paper adopts the proposed method to a standardized OFDM format, IEEE 802.11a, and elucidates that the proposed one shows good transmission performance as well as the conventional one in fast time-variant multi-path Rayleigh fading channels by computer simulation.

Many reports have investigated TCP performance over wireless links, where a high and time-invariant frame error rate is assumed for cellular systems. However, the frame error rate is temporally and geographically changeable by fading and interference in cellular systems. On the other hand, SINR-based transmission power control, which is employed for the randomization of frame errors in DS-CDMA cellular systems, can not always work properly depending on the control parameters or the channel characteristics. In this paper, we investigate the TCP performance over the wireless links in a DS-CDMA cellular system by computer simulation. From the simulation results, it has been found that the assumption of random frame error is valid only for a part of the TCP performance even in the system with an SINR-based transmission power control scheme.

This paper presents a semi-automatic algorithm for video object segmentation. Our algorithm assumes the use of multiple key video frames in which a semantic object of interest is defined in advance with human assistance. For video frames between every two key frames, the specified video object is tracked and segmented automatically using Learning Vector Quantization (LVQ). Each pixel of a video frame is represented by a 5-dimensional feature vector integrating spatial and color information. We introduce a parameter K to adjust the balance of spatial and color information. Experimental results demonstrate that the algorithm can segment the video object consistently with less than 2% average error when the object is moving at a moderate speed.

This paper proposes a new family of space-time block codes whose transmission rate is 1 symbol per channel use. The proposed space-time codes can achieve full transmit diversity with larger coding gain for the constellation carved from the scaled complex integer ring κZ[i]. It is confirmed that the performances of the proposed space-time codes are superior to the existing space-time block codes by our simulation results.

A complete system for the implementation of digital logic in a Field-Programmable Gate Array (FPGA) platform is introduced. The novel power-efficient FPGA architecture was designed and simulated in STM 0.18 µm CMOS technology. The detailed design and circuit characteristics of the Configurable Logic Block, the interconnection network, the switch box and the connection box were determined and evaluated in terms of energy, delay and area. A number of circuit-level low-power techniques were employed because power consumption was the primary concern. Additionally, a complete tool framework for the implementation of digital logic circuits in FPGA platforms is introduced. Having as input VHDL description of an application, the framework derives the reconfiguration bitstream of FPGA. The framework consists of: i) non-modified academic tools, ii) modified academic tools and iii) new tools. Furthermore, the framework can support a variety of FPGA architectures. Qualitative and quantitative comparisons with existing academic and commercial architectures and tools are provided, yielding promising results.

An approach based on signal subspace analysis is proposed to blind estimation of the PN (Pseudo Noise) sequence from lower SNR (Signal to Noise Ratios) DS/SS (Direct Sequence Spread Spectrum) signals. The received signal is divided into vectors according to a temporal window, from which an autocorrelation matrix is computed and accumulated. The PN sequence can be reconstructed from principal eigenvectors of the matrix.

In this paper, we propose an OFDM scheme with pre-IDFT/DFT and the frequency domain equalization on frequency-selective Rayleigh fading channels. In this scheme, a two-dimensional block interleaving is used to randomize the correlated noise caused by the frequency domain linear equalizer. Then, the pre-DFT averages the interleaved noise enhancement and improves the error performance of the proposed scheme. Computer simulations confirm the bit error probability of the proposed scheme for multilevel modulations.

According to the proliferation of ubiquitous computing, various products which contain large-size embedded software have been developed. One of most typical features of embedded software is concurrency of software and hardware factors. That is, software has connected deeply into hardware devices. The existence of various hardware make quality assurance of embedded software more difficult. In order to assure quality of embedded software more effectively, this paper discusses features of embedded software and an effective method for quality assurance for embedded software. In this paper, we first analyze a failure distribution of embedded software and discuss the effects of hardware devices on quality of embedded software. Currently, in order to reduce hardware related faults, huge effort for testing with large number of test items is required. Thus, one of the most important issues for quality assurance of embedded software is how to reduce the cost and effort of software testing. Next, focusing on hardware constraints as well as software specifications in embedded software, we propose an evaluation metrics for determinating important functions for quality of embedded software. Furthermore, by referring to the metrics, undesirable behaviors of important functions are identified as root nodes of fault tree analysis. From the result of case study applying the proposed method to actual project data, we confirmed that test items considering the property of embedded software are constructed. We also confirmed that the constructed test items are appropriate to detect hardware related faults in embedded systems.

Due to the continuous growth of wireless communication technology and mobile equipment, the need for storing and processing data of moving objects arises in a wide range of location-based applications. In this paper, we propose a new spatio-temporal index structure for moving objects, namely the TPKDB-tree, which supports efficient retrieval of future positions and reduces the update cost.

An overview on the physics and circuit design oriented background of the advanced compact model HICUM is presented. Related topics such as the approach employed for geometry scaling and parameter extraction are briefly discussed. A model hierarchy is introduced, that addresses a variety of requirements encountered during the increasingly complicated task of designing analog and high-frequency circuits.

Investment planning for power plants involves making a long-term plan covering various facility investments, such as the construction of a new power plant or the replacement of an old plant with a new one, under uncertain environments. In this paper, we propose an optimization method for such a planning problem. Our method is based on decision tree analysis, in which uncertain environments are described as scenarios. The maintenance of existing plants is also taken into account by introducing the option of large-scale repair in addition to replacement. In order to avoid combinatorial explosion of failure event scenarios of plants, we introduce the concept of failure risk cost which contributes to simplification of the decision tree and reduction of the calculation time.

We have proposed a novel spatial filtering technique named "VIrtual Subcarrier Assignment (VISA)" for orthogonal frequency division multiplexing (OFDM) signals, which enables the transceiver equipped with an adaptive array antenna (AAA) to selectively receive or reject OFDM signals through coloring them with different virtual subcarrier positions in their frequency spectra. In this paper, we develop the VISA to use multiple virtual subcarrier assignment, which assigns a different combination of multiple virtual subcarrier positions in the frequency spectrum to each OFDM signal. Furthermore, we present two kinds of recursive least square (RLS)-based array weight control methods to support the VISA with multiple subcarrier puncturing in an IEEE802.11a-based system and evaluate the link-level performance in typical indoor wireless environments by computer simulations.

We present a simple bit allocation scheme based on adaptive coding for MIMO-OFDM (Multiple Input Multiple Output - Orthogonal Frequency Division Multiplexing) systems with V-BLAST (Vertical-Bell laboratories LAyered Space-Time) detector. The proposed scheme controls the code rate of the channel coding and assigns the same modulation and coding to the set of selected sub-channels, which greatly reduces the feedback burden while achieving good performance. Simulation results show that the proposed scheme with minimal feedback provides significant performance improvement over other systems.

We propose a rapid and reliable signal acquisition scheme for UWB (Ultra Wide Band) systems in indoor wireless environments. The proposed scheme is a two-step search with different thresholds and search windows, where each step utilizes the single-dwell search with the bit reversal. Simulation results show that the proposed scheme for the UWB signals can achieve significant reduction of the required mean acquisition time as compared to other schemes including general double-dwell search scheme for various threshold levels. Furthermore, it is also observed that the proposed scheme can achieve much faster and reliable signal acquisition as the first threshold is larger in noisy environments.

In VDSM era, crosstalk is becoming a more and more vital factor in high performance VLSI designs, making noise mitigation in early design stages necessary. In this paper, we propose an effective algorithm optimizing crosstalk under congestion constraint in the layer assignment stage. A new model for noise severity measurement is developed where wire length is used as a scale for the noise immunity, and both capacitive and inductive coupling between sensitive nets are considered. We also take shield insertion into account for further crosstalk mitigation. Experimental results show that our approach could efficiently reduce crosstalk noise without compromising congestion compared to the algorithm proposed in [1].

Recently, efficient algorithms have been proposed for finding all characteristic curves of one-port piecewise-linear resistive circuits. Using these algorithms, a middle scale one-port circuit can be represented by a piecewise-linear resistor that is neither voltage nor current controlled. In this letter, an efficient algorithm is proposed for finding all dc operating points of piecewise-linear circuits containing such neither voltage nor current controlled resistors.