This study presents a fast adaptive algorithm for noise estimation in non-stationary environments. To make noise estimation adapt quickly to non-stationary noise environments, a robust entropy-based voice activity detection (VAD) is thus required. It is well-known that the entropy-based measure defined in spectral domain is very insensitive to the changing level of nose. To exploit the specific nature of straight lines existing on speech-only spectrogram, the proposed spectrum entropy measurement improved from spectrum entropy proposed by Shen et al. is further presented and is named band-splitting spectrum entropy (BSE). Consequently, the proposed recursive noise estimator including BSE-based VAD can update noise power spectrum accurately even if the noise-level quickly changes.

This paper investigates a modifying orthogonality factor for synchronous DS-CDMA uplink in dispersive Rician multipath fading channels, which reflects upon the effects of specular path power as well as decaying channel characteristics. Using this investigation, the orthogonal factors in indoor environments are evaluated and compared with the various parameters such as decaying factor, line-of-sight component, and the number of multipaths.

Power Spectral Density (PSD) computed by taking the Fourier transform of auto-correlation functions (Wiener-Khintchine Theorem) gives better result, in case of noisy data, as compared to the Periodogram approach in case the signal is Gaussian. However, the computational complexity of Wiener-Khintchine approach is more than that of the Periodogram approach. For the computation of short time Fourier transform (STFT), this problem becomes even more prominent where computation of PSD is required after every shift in the window under analysis. This paper presents a recursive form of PSD to reduce the complexity. If the signal is not Gaussian, the PSD approach is insufficient and we estimate the higher order spectra of the signal. Estimation of higher order spectra is even more time consuming. In this paper, recursive versions for computation of bispectrum has been presented as well. The computational complexity of PSD and bispectrum for a window size of N, are O(N) and O(N2) respectively.

As digital television transmission is becoming ubiquitous, a method that can remotely monitor the quality of the final and intermediate pictures is urgently needed. In particular, the case where standards conversion is included in the transmission chain is a serious issue as the input and output cannot simply be compared. This letter proposes a novel method to solve this issue. The combination of skipping fields/pixels and the previously proposed SSSWHT-RR method, using the information of correlation coefficients and variance of the picture, achieves accurate detection of picture failure.

In this paper, Information-Spectrum characterization is derived for the reliable transmission of general correlated sources over the general multiple-access channels. We consider the necessary and sufficient conditions for the transmission of general correlated sources over the general multiple-access channels by using Information-Spectrum methods which are introduced by Han and Verdu.

The RF environment in the future will consist of many mobile devices operating across a wide range of applications. Most radio developments assume a static operating environment. The physical layer, MAC layer, and network protocols are optimized for that specific environment. However, this new RF environment consisting of many mobile devices will be very dynamic. Radios will need the capacity to sense and adapt to changing environmental conditions. That characteristic is generally associated with cognitive radio. This paper will provide an introduction to new strategies for designing systems for this new, dynamic environment using cognitive radio technology.

This paper clarifies a necessary condition and a sufficient condition for transmissibility for a given set of general sources and a given general broadcast channel. The approach is based on the information-spectrum methods introduced by Han and Verdu. Moreover, we consider the capacity region of the general broadcast channel with arbitrarily fixed error probabilities if we send independent private and common messages over the channel. Furthermore, we treat the capacity region for mixed broadcast channel.

We study asynchronous SSMA communication systems using binary spreading sequences of Markov chains and prove the CLT (central limit theorem) for the empirical distribution of the normalized MAI (multiple-access interference). We also prove that the distribution of the normalized MAI for asynchronous systems can never be Gaussian if chains are irreducible and aperiodic. Based on these results, we propose novel theoretical evaluations of bit error probabilities in such systems based on the CLT and compare these and conventional theoretical estimations based on the SGA (standard Gaussian approximation) with experimental results. Consequently we confirm that the proposed theoretical evaluations based on the CLT agree with the experimental results better than the theoretical evaluations based on the SGA. Accordingly, using the theoretical evaluations based on the CLT, we give the optimum spreading sequences of Markov chains in terms of bit error probabilities.

The millimeter-wave (MMW) broadband mixers that are useful for measurement instruments to analyze MMW high data rate signals have been investigated. At first, we propose the specialized RF front-end for analyses of MMW high data rate signals. Next, the required specifications for the 1st mixers of the front-end are estimated, and the design, fabrication, and testing results of Q, V, and W-band monolithic broadband resistive mixers are described. The testing results are compared with performances of the diode mixer designed for V-band. It was found that the resistive mixers have very attractive performances of low conversion loss, good frequency flatness and high third order intercept point (IP3) with low Local (LO) oscillators power. The developed resistive mixers are suitable for the proposed MMW band measurement instruments.

This paper studies power spectrum density (PSD) of multi-user aggregate time hopping (TH) ultra wideband (UWB) signal with asynchronous transmission and synchronous transmission. TH codes under consideration are deterministic periodic code and random integer code. Based on the PSD, the in-band interference power for TD SCDMA is investigated as function of UWB system parameters. Two UWB modulations, TH pulse position modulation (PPM) and TH BPSK, are considered for calculating the in-band interference power. The numerical results indicate that asynchronous transmission is an effective way to decrease the peak in-band interference caused by multi-user aggregate TH-PPM UWB signal. Although increasing the maximum of time hopping code elements can smooth the PSD of TH UWB signal, it is not a good idea for reducing the peak in-band interference for TD SCDMA. For the random integer TH code, while only TH UWB continuous spectral exists in TD SCDMA band or multi-user signals of TH UWB are transmitted asynchronously, the in-band interference for TD SCDMA is in proportion to the number of the UWB users. For TD SCDMA in which band discrete spectral line exists the in-band interference caused by TH UWB with synchronous transmission is in proportion to the square of the number of the UWB users.

A method of evaluating the wavelength filter spectrum response is introduced. The increase of the crosstalk level due to the filtering and the relation between the total crosstalk and the spectral efficiency are derived in detail using the Gaussian filter. Since this method can be applied to various kinds of filter spectrum responses, the ultimate spectral efficiencies of filters are compared. In this comparison, the problem of the box-like filter, which has been considered to be desirable, is revealed, and this is improved by cascading the filter spectrum. The requirement on the rejection floor that inheres in the filter is also made clear.

We investigate the impact of symbol rate control, modulation level control, and the number of hops on the area spectral efficiency of interference-limited multihop radio networks. By controlling symbol rate and modulation level, data rate can be adapted according to received power. In addition, varying the number of hops can control received power. First, we evaluate the achievable end-to-end throughput of multihop transmission assuming symbol rate and modulation level control. Numerical results reveal that by controlling symbol rate or using multihop transmission, the end-to-end communication range can be extended at the cost of end-to-end throughput, and this may result in lower area spectral efficiency. Next, an expression for the area spectral efficiency of multihop radio networks is derived as a function of the number of hops and the end-to-end throughput. Numerical results also reveal that the resulting area spectral efficiency depends on the specific circumstances, which, however, can be increased only by using multihop transmission.

The present paper discusses a new construction of UWB pulses within the framework of soft-spectrum adaptation. The employed basis functions are B-splines having the following properties: (i) The B-splines are time-limited piecewise polynomials. (ii) The first-order B-splines are rectangular pulses and they converge band-limited functions at the limit that their order tends to infinity. (iii) There are an analog circuit and a fast digital filter for the generation of B-splines. Simple application of Gram-Schmidt orthonormalization process to the shifted B-splines results in a few basic pulses, which are well time-limited and have a broad band width, but do not comply with the FCC spectral mask. A constrained approximation technique is proposed for adaptively designing pulses so that they approximate target frequency characteristics. At the cost of using eleven shifted B-splines, an example set of four pulses comforting the FCC spectral mask is obtained.

A fast encoding technique is described for vector quantization (VQ) of line spectral frequency parameters. A reduction in VQ encoding complexity is achieved by using a preliminary test that reduces the necessary codebook search range. The test is performed based on two criteria. One criterion uses the distance between a specific single element of the input vector and the corresponding element of the codevectors in the codebook. The other criterion makes use of the ordering property of LSF parameters. The fast encoding technique is implemented in the enhanced variable rate codec (EVRC) encoding algorithm. Simulation results show that the average searching range of the codebook can be reduced by 44.50% for the EVRC without degradation of spectral distortion (SD).

The radiation properties of oscillating electric dipoles are studied theoretically for three and four layered systems including a single metallic slab based on angular spectrum representation of vector spherical waves. One of the remarkable results obtained is the transmission energy spectrum showing strong dependence on the thickness of a dielectric layer placed between oscillating electric dipole and metallic surface, which explains the experimental results of molecular fluorescence into surface plasmon modes. The theory based on angular spectrum representation and tunneling current provides us with a clear identification of plasmonic excitation transfer, transmission loss associated with plasmon transport in metallic layer, and energy dissipation or quenching of excitation due to surface plasmon excitation at the metallic surface in relation to the characteristic complex wave number of evanescent waves.

We observed the optically forbidden energy transfer between cubic CuCl quantum dots coupled via an optical near-field interaction using time-resolved near-field photoluminescence (PL) spectroscopy. The energy transfer time and exciton lifetime were estimated from the rise and decay times of the PL pump-probe signal, respectively. We found that the exciton lifetime increased as the energy transfer time fell. This result strongly supports the notion that near-field interaction between QD makes the anti-parallel dipole coupling. Namely, a quantum-dots pair coupled by an optical near field has a long exciton lifetime which indicates the anti-parallel coupling of QDs forming a weakly radiative quadrupole state.

Since WLAN (wireless LAN) systems share the 2.4-GHz frequency band with microwave ovens, interference caused by radiated oven noise is a serious problem in practical WLAN application. To mitigate the oven noise interference in DS-SS (direct-sequence spread spectrum) WLAN systems, the use of adaptive filters is proposed. This method is based on the fact that oven noise behaves like CW (continuous wave) interference within a short duration. In contrast to previous reduction techniques for oven noise, this method can be implemented without changing any specifications of current WLAN systems. The results of numerical and experimental analyses clearly demonstrate the effectiveness of adaptive filters for improving the bit error rates of WLAN links subject to oven noise interference.

Recently, DOAS (differential optical absorption spectroscopy) has been used for nondestructive air monitoring, in which the LS (least squares) method is used to calculate trace gas concentrations due to its computational simplicity. This paper applies the ICA (independent component analysis) method to the DOAS system of air monitoring, since the LS method is insufficient to recover the desired spectra perfectly due to sparsity characteristic. If the sparsity of reference spectra in the DOAS system imposes the assumption of independence, the ICA algorithm can be used. The proposed method is used to regress the observed spectrum on the estimates of the reference spectra. The ICA algorithm can be seen as a preprocessing method where the ICs of the references are used as the input in the regression. The performance of the proposed method is evaluated in simulation studies using synthetic data.

The measured values of electromagnetic disturbances should strongly correlate with degradation in the communication quality of digital wireless communication systems. The Amplitude Probability Distribution (APD) of a disturbance represents statistical information as applicable measurement readings that meet the above requirement. In this paper, correlations between APD measurements of disturbances and the bit error rate (BER) as a quality degradation index for victim systems are quantitatively investigated. Disturbance regulation by APD measurements is discussed from the viewpoint of protecting systems from disturbances. This investigation specifically considers the situation in which a repetition pulse disturbance impacts PHS and W-CDMA systems assumed as victims. The results confirm high correlations between the APD and BER not only experimentally but also theoretically under some conditions. A disturbance regulation criterion based on APD measurements is thus proposed for compliance testing of electronic appliances with the potential to act as disturbance noise sources.

The performance of integrated segmentation and recognition of handwritten numeral strings relies on the classification accuracy and the non-character resistance of the underlying character classifier, which is variable depending on the techniques of pattern normalization, feature extraction, and classifier structure. In this paper, we evaluate the effects of 12 normalization functions and four selected feature types on numeral string recognition. Slant correction (deslant) is combined with the normalization functions and features so as to create 96 feature vectors, which are classified using two classifier structures. In experiments on numeral string images of the NIST Special Database 19, the classifiers have yielded very high string recognition accuracies. We show the superiority of moment normalization with adaptive aspect ratio mapping and the gradient direction feature, and observed that slant correction is beneficial to string recognition when combined with good normalization methods.