In this paper, we propose a speech enhancement algorithm by using MAP estimation with variable speech spectral amplitude probability density function (speech PDF). The variable speech PDF has two adaptive shape parameters which affect the quality of enhanced speech. Noise can be efficiently suppressed when these parameters are properly applied so that the variable speech PDF shape fits to the real-speech PDF one. We derive adaptive shape parameters from real-speech PDF in various narrow SNR intervals. The proposed speech enhancement algorithm with adaptive shape parameters is examined and compared to conventional algorithms. The simulation results show that the proposed method improved SegSNR around 6 and 9 dB when the input speech signal was corrupted by white and tunnel noises at 0 dB, respectively.

We have developed a portable NIRS-based optical BCI system that features a non-invasive, facile probe attachment and does not require muscle movement to control the target devices. The system consists of a 2-channel probe, a signal-processing unit, and an infrared-emission device, which measures the blood volume change in the participant's prefrontal cortex in a real time. We use the threshold logic as a switching technology, which transmits a control signal to a target device when the electrical waveforms exceed the pre-defined threshold. Eight healthy volunteers participated in the experiments and they could change the television channel or control the movement of a toy robot with average switching times of 11.5 ± 5.3 s and the hit rate was 83.3%. These trials suggest that this system provides a novel communication aid for people with motor disabilities.

This paper presents an elastic optical path network architecture as a novel networking framework to address the looming capacity crunch problem in internet protocol (IP) and optical networks. The basic idea is to introduce elasticity and adaptation into the optical domain to yield spectrally-efficient optical path accommodation, heightened network scalability through IP traffic offloading to the elastic optical layer, and enhanced survivability for serious disasters.

Spectrum sensing, a key technical challenge in cognitive radios (CR) technology, is a technique that enables the spectrum of licensed systems to be accessed without causing undue interference. It is well known that cyclostationarity detectors have great advantages over energy detectors in terms of the robustness to noise uncertainty that significantly degrades the performance as well as the capability to distinguish the signal of interest from the other interferences and noise. The generalized likelihood ratio test (GLRT) is a recognized sensing technique that utilizes the inherent cyclostationarity of the signal and has been intensively studied. However, no comprehensive evaluation on its performance enhancement has been published to date. Moreover high computational complexity is still a significant problem for its realization. This paper proposes a maximum ratio combining multi-cyclic detector which uses multiple cyclic frequencies for performance enhancement with reduced computational complexity. An orthogonal frequency-division multiplexing (OFDM) signal based on the ISDB-T (integrated services digital broadcasting terrestrial), a Japanese digital television broadcasting standard, was used in the evaluation assuming this as a primary system in WRAN (wireless regional area network) applications like IEEE 802.22.

This paper proposes Direct Spectrum Division Transmission with spectrum editing technique. The transmitter divides the single carrier modulated signal into multiple “sub-spectra” in the frequency domain and arranges each sub-spectrum so as to more fully utilize the unused frequency resources. In the receiver, the divided sub-spectra are combined in the frequency domain and demodulated. By editing the divided spectrum in the frequency domain, the total bandwidth occupied by the multiple “sub-spectra” is less than that of the modulated signal. The proposed technique allows the unused frequency resources scattered across the bands to be better utilized. Simulations show that the proposed technique makes the bit error rate negligible.

Phase structure of nonlinear dynamical system is governed by the vector field and decides the trajectories. Accordingly, the power spectra of trajectories include the structural field effect on the phase space. In this paper, we develop a method for analyzing phase structure using power spectra of trajectories and reconstitute a potential function in the system.

This paper suggests an outphasing scheme to reduce adjacent channel spectral regrowth triggered by the gain and phase mismatch between two signal paths in linear amplification with nonlinear component (LINC) systems. The error vector magnitude and power spectral density of the output signal considering path mismatch are described analytically using path mismatch factor. An outphasing scheme is proposed to reduce the spectral regrowth. The proposed outphasing scheme reshapes the phases of the separated signals in LINC systems to reduce the changes of the phases. Its performance is verified by performing simulations with multi-tone signals. The result shows that the scheme can reduce the spectral regrowth of the multi-tone signals significantly compared to the conventional outphasing scheme for LINC systems with path imbalance.

Railway inspection is important in railway maintenance. There are several tasks in railway inspection, e.g., defect detection and bolt detection. For those inspection tasks, the detection of rail surface is a fundamental and key issue. In order to detect rail defects and missing bolts, one must know the exact location of the rail surface. To deal with this problem, we propose an efficient Rail Surface Detection (RSD) algorithm that combines boundary and region information in a uniform formulation. Moreover, we reevaluate the rail location by introducing the top down information–bolt location prior. The experimental results show that the proposed algorithm can detect the rail surface efficiently.

In this letter, we propose an adaptive sensing/transmission scheduling policy in which the secondary user senses the spectrum when its channel condition is poor for transmission. The adaptive sensing/transmission scheduling is modeled as a Markov process and a near-optimal algorithm is proposed to determine the sensing/transmission policy. Simulation results verify our analysis and demonstrate the superiority of the proposed algorithm.

The range-dependence of clutter spectrum for forward-looking airborne radar strongly affects the accuracy of the estimation of clutter covariance matrix at the range under test, which results in poor clutter suppression performance if the conventional space-time adaptive processing (STAP) algorithms were applied, especially in the short range cells. Therefore, a new STAP algorithm with clutter spectrum compensation by utilizing knowledge-aided subspace projection is proposed to suppress clutter for forward-looking airborne radar in this paper. In the proposed method, the clutter covariance matrix of the range under test is firstly constructed based on the prior knowledge of antenna array configuration, and then by decomposing the corresponding space-time covariance matrix to calculate the clutter subspace projection matrix which is applied to transform the secondary range samples so that the compensation of clutter spectrum for forward-looking airborne radar is accomplished. After that the conventional STAP algorithm can be applied to suppress clutter in the range under test. The proposed method is compared with the sample matrix inversion (SMI) and the Doppler Warping (DW) methods. The simulation results show that the proposed STAP method can effectively compensate the clutter spectrum and mitigate the range-dependence significantly.

The probe used in the conventional SAR measurement is usually calibrated in a well filled with tissue-equivalent liquid surrounded by a rectangular waveguide and a matching dielectric window in the frequency range from 800 MHz to 3 GHz. However, below 800 MHz, the waveguides are too large to be used for the calibration. Therefore, we have developed another technique of calibrating the SAR-probe, that is, relating the output voltage of the probe to the field intensity produced by a reference antenna in the tissue-equivalent liquid by using two-antenna method. In this paper, the calibration system using the reference dipole antennas in the liquid at 450 MHz, 900 MHz and 2450 MHz is presented and far-field gain of the reference antenna and calibration factor of the SAR-probe are measured and compared with those obtained by using the conventional waveguide system.

To opportunistically use the licensed band, spectrum sensing has a vital role as the core component in cognitive radio systems. However, the accurate detection of the primary signal is always accompanied by significant overhead, reducing the secondary throughput. In this letter, we suggest remedying this problem by adopting multiple-stage spectrum sensing (MSS) technique. Furthermore, we investigate how our proposed MSS can be incorporated into the collaborative spectrum sensing. Our results are encouraging in that the proposed MSS with collaboration significantly reduces the sensing time compared to the conventional sensing scheme.

Cognitive radio (CR) in spectrum sharing mode allows secondary user (SU) to share the same spectrum simultaneously with primary user (PU), as long as the former guarantees no harmful interference is caused to the latter. This letter proposes a new type of constraint to protect the PU systems that are carrying delay-sensitive applications, namely the PU effective capacity loss constraint, which sets an upper bound on the maximum effective capacity loss of the PU due to the SU transmission. In addition, the PU effective capacity loss constraint is approximately transformed to the interference temperature (power) constraint, to make it easier to be implemented. As an example, we obtain a closed form expression of the SU effective capacity under the approximated peak interference power constraint and the results of simulations validate the proposed PU protection criterion.

As the fundamental component of dynamic spectrum access, implementing spectrum sensing is one of the most important goals in cognitive radio networks due to its key functions of protecting licensed primary users from harmful interference and identifying spectrum holes for the improvement of spectrum utilization. However, its performance is generally compromised by the interference from adjacent primary channels. To cope with such interference and improve detection performance, this paper proposes a non-coherent power decomposition-based energy detection method for cooperative spectrum sensing. Due to its use of power decomposition, interference cancellation can be applied in energy detection. The proposed power decomposition does not require any prior knowledge of the primary signals. The power detection with its interference cancellation can be implemented indirectly by solving a non-homogeneous linear equation set with a coefficient matrix that involves only the distances between primary transmitters and cognitive secondary users (SUs). The optimal number of SUs for sensing a single channel and the number of channels that can be sensed simultaneously are also derived. The simulation results show that the proposed method is able to cope with the expected interference variation and achieve higher probability of detection and lower probability of false alarm than the conventional method in both hard combining and soft combining scenarios.

This letter proposes a spread spectrum audio watermarking robust against playback speed modification (PSM) attack which introduces both time-scale modification and pitch shifting. Two important improvements are exploited to achieve this robustness. The first one is selecting an embedding region according to the stable characteristic of the audio energy. The second one is stretching the pseudo-random noise sequence to match the length of the embedding region before embedding and detection. Experimental results show that our method is highly robust to common audio signal processing attacks and synchronization attacks including PSM, cropping, trimming and jittering.

A Wavelength division multiplexing passive optical network (WDM-PON) system that uses spectrum-sliced broadband incoherent light is attractive because it avoids the cost of operating/administering wavelengths in optical network units (ONU) at customer premises. However, it is difficult to enhance the spectrum efficiency to ensure a sufficient signal to noise ratio because it would demand broad channel width. To overcome this problem, we proposed a spectrum-interleaved duplex technique. It enables upstream and downstream communications to share one channel by using a cyclic filter. This sharing of one channel eliminates the need for a guard interval between signal lights duplexed in the channel. One residual issue regarding single band transmission is its robustness to reflection in the transmission medium. To increase the reflection robustness of the spectrum-interleaved duplex scheme, we propose a reflection remover based on an optical code division multiplexing technique. We also evaluate the extent to which capacity of the spectrum efficiency of the spectrum-interleaved duplex WDM-PON system that uses spectrum-sliced broadband incoherent light can be increased.

The specific absorption rate (SAR) measurement procedure for wireless communication devices used in close proximity to the human body other than the ear was standardized by the International Electrotechnical Commission (IEC). This procedure is applicable to SAR measurement of data communication terminals that are used with host devices. Laptop PCs are assumed as host devices in this study. First, numerical modeling of laptop PCs and the validity of computations are verified with corresponding measurements. Next, mass averaged SARs are calculated dependent on the dimensions of the laptop PCs and the position of the terminals. The results show that the ratio of the maximum to minimum SARs is at most 2.0 for USB dongle and card-type terminals at 1950 MHz and 835 MHz.

There are two major challenges in wide-band spectrum sensing in a heterogenous spectrum environment. One is the spectrum acquisition in the wide-band scenario due to limited sampling capability; the other is how to collaborate in a heterogenous spectrum environment. Compressed spectrum sensing is a promising technology for wide-band signal acquisition but it requires effective collaboration to combat noise. However, most collaboration methods assume that all the secondary users share the same occupancy of primary users, which is invalid in a heterogenous spectrum environment where secondary users at different locations may be affected by different primary users. In this paper, we propose an automatic clustering collaborative compressed spectrum sensing (ACCSS) algorithm. A hierarchy probabilistic model is proposed to represent the compressed reconstruction procedure, and Dirichlet process mixed model is introduced to cluster the compressed measurements. Cluster membership estimation and compressed spectrum reconstruction are jointly implemented in the fusion center. Based on the probabilistic model, the compressed measurements from the same cluster can be effectively fused and used to jointly reconstruct the corresponding primary user's spectrum signal. Consequently, the spectrum occupancy status of each primary user can be attained. Numerical simulation results demonstrate that the proposed ACCSS algorithm can effectively estimate the cluster membership of each secondary user and improve compressed spectrum sensing performance under low signal-to-noise ratio.

With advances in communication technologies, network services provided via the Internet have become widely diversified, and people can use these services not only via wired networks but also via wireless networks. There are several wireless systems in practical use such as cellular, WiMAX and WiFi. Although these wireless network systems have developed independently of each other, they should be integrated for seamless access by users. However, each system uses an individual spectrum prescribed by law to avoid radio interference. To overcome such a situation, dynamic spectrum access technology is receiving much attention. We propose a dynamic spectrum assignment method in which a WiFi system temporarily uses a spectrum band of the WiMAX system in WiFi/WiMAX integrated networks to reduce call blocking probability of multimedia communication services. We confirm the effectiveness of the proposed method by simulation experiments.

In spectrum sensing, if the primary user (PU) signal and the channel noise both follow Gaussian distribution and neither of their probability distribution functions (PDFs) are known, the traditional approaches based on entropy or Likelihood Ratio Test (LRT) etc., become infeasible. To address this problem, we propose a spectrum sensing method that exploits the similarity of PDFs of two time-adjacent detected data sets with cross entropy, while accounting for achieving the detection performance of LRT which is Neyman-Pearson optimal in detecting the primary user. We show that the detection performance of the proposed method asymptotically approximates that of LRT in detecting the PU. The simulation results confirm our analysis.