In 2006, Yeh and Tsai proposed a mobile commerce security mechanism. However, in 2008, Yum et al. pointed out that Yeh-Tsai security mechanism is not secure against malicious WAP gateways and then proposed a simple countermeasure against the attack is to use a cryptographic hash function instead of the addition operation. Nevertheless, this paper shows that both Yeh-Tsai's and Yum et al.'s security mechanisms still do not provide perfect forward secrecy and are susceptible to an off-line guessing attack and Denning-Sacco attack. In addition, we propose a new security mechanism to overcome the weaknesses of the previous related security mechanisms.

Recently there has been a surge of interest in construction of low correlation zone sequences. The purpose of this paper is to survey the known results in the area and to present an interleaved construction of binary low correlation zone sequences. The interleaved construction unifies many constructions currently available in the literature. These sequences are useful in quasi-synchronous code-division multiple access (QS-CDMA) communication systems.

Broadband wireless technology that enables a variety of gigabit-per-second class data services is a requirement in future wireless communication systems. Broadband wireless channels become extremely frequency-selective and cause severe inter-symbol interference (ISI). Furthermore, the average received signal power changes in a random manner because of the shadowing and distance-dependant path losses resulted from the movement of a mobile terminal (MT). Accordingly, the transmission performance severely degrades. To overcome the performance degradation, two most promising approaches are the frequency-domain equalization (FDE) and distributed antenna network (DAN). The former takes advantage of channel frequency-selectivity to obtain the frequency-diversity gain. In DAN, a group of distributed antennas serve each user to mitigate the negative impact of shadowing and path losses. This article will introduce the recent advances in FDE and DAN for the broadband single-carrier (SC) transmissions.

Through fractional sampling (FS) it is possible to separate multipath components and achieve path diversity. However, if no path component whose delay corresponds to the sampling point, FS cannot obtain diversity gain. In this paper, a novel scheme to improve the performance with FS over a sparse multipath channel is proposed. The proposed scheme uses multiple transmit antennas and sends multiple signals with fractional delays. The performance improvement with the proposed scheme is confirmed through computer simulation. It is shown that the proposed scheme increases the capacity of a MIMO-OFDM system by a factor of 1.5 to 2 and improves the BER performance on the sparse multipath channels.

Developing an adaptive 3-dimensional (3D) topology control algorithm is important because most wireless nodes are mobile and deployed in buildings. Moreover, in buildings, wireless link qualities and topologies change frequently due to various objects and the interference from other wireless devices. Previous topology control algorithms can suffer significant performance degradation because they only use the Euclidean distance for the topology construction. In this paper, we propose a novel adaptive 3D topology control algorithm for wireless ad-hoc sensor networks, especially in indoor environments. The proposed algorithm adjusts the minimum transmit power adaptively with considering the interference effect. To construct the local topology, each node divides the 3D space, a sphere centered at itself, into k equal cones by using Platonic solid (i.e., regular k-hedron) and selects the neighbor that requires the lowest transmit power in each cone. Since the minimum transmit power values depend on the effect of interferences, the proposed algorithm can adjust topology adaptively and preserve the network connectivity reliably. To evaluate the performance of algorithms, we conduct various experiments with simulator and real wireless platforms. The experimental results show that the proposed algorithm is superior to the previous algorithms in terms of the packet delivery ratio and the energy consumption with relatively low complexity.

In this letter, we apply recently proposed compressive projection principal component analysis (CPPCA) for MIMO channel feedback. A novel scheme with compressed feedback and efficient reconstruction is presented. Simulation results based on 3GPP spatial channel model (SCM) demonstrate the scheme is beneficial for large-scale MIMO systems.

Collecting environmental sound by utilizing high-end mobile phones provides us opportunities to capture rich contextual information in real world. The gathered information can be used for various purposes, ranging from academic research to livelihood support. Furthermore, mobility of mobile phones opens a door for easily forming a dynamic sensing infrastructure, in order to gather fine-grained, but still large-scale data from both spatial and temporal perspectives. However, collecting, analyzing, storing, and sharing of sound data usually involve large energy consumption than scalar data, and like any battery-operated device, mobile phones also face the reality of energy constraints. Because people's first priorities are naturally to use mobile phones for their own purposes, there are occasions when people will not be inclined to allow their mobile phones to be used as sensing devices fearing that they will run out of batteries. Therefore, our research focuses on energy-efficient sensing, to reduce average energy consumption and to extend overall system lifetime. In this paper, we propose a node scheduling scheme for mobile nodes. By applying this scheme, optimized sensing schedules (ACTIVE/SLEEP duty cycles) will be periodically generated at each node. Following the provided schedule during sensing, energy-efficiency can be realized while original Quality of Service (i.e. coverage rate) is retained. Unlike most previous works which were based on ideal binary disk coverage model, our proposal is designed under a probabilistic disk coverage model which takes the characteristic of sound propagation into consideration. Furthermore, this is the first scheme that is adaptable to large-scale mobile sensor networks where topology dynamically changes. An accurate energy consumption model is adopted for evaluating the proposed scheme. Simulation results show that our scheme can reduce up to 48% energy consumption in an ideal environment and up to 31% energy consumption in a realistic environment. The robustness of our scheme is also verified against different type of sensing terrains and communication environments.

Broadband antennas have various applications in digital terrestrial television (DTV) services. Compact broadband antennas are required for arranging in long and narrow space along the rim of a laptop display. A leaky-wave antenna using the composite right/left-handed transmission line (CRLH-TL) is one of the candidates for achieving the broadband antenna. However, there are not enough to design guideline of small leaky wave antennas using the CRLH-TL for UHF band. In this paper, a CRLH-TL comprising a ladder network is proposed for broadband and simple structure. The paper also discusses the design of a leaky-wave antenna with the CRLH-TL operating in the DTV band. The relation between the operating bandwidth and attenuation constant of the CRLH-TL is discussed. An antenna that can be accommodated in the limited and narrow space available in mobile terminals has to be designed. Hence, the effects of the number of cells and a finite ground plane are discussed with the purpose of achieving the miniaturization of the antenna. In this study, the transmission and radiation characteristics of the fabricated antennas are measured. The gain of the fabricated antenna is confirmed to remain almost constant even when the operating frequency is varied. The maximum gain and operating band achieved in this study are approximately -0.6 dBi and about 54%, respectively.

A method was developed for analyzing a system comprised of identical and indistinguishable elements with nonlinear dynamics. First, a moment vector equation (MVE) for the system was derived so as to avoid the curse of dimensionality by using the property that the elements are identical and indistinguishable. Next, an algorithm was developed to solve the MVE for deriving the moment vector in a steady state. It effectively uses eigen analysis on the basis of the property of the MVE. It can thus be used to clarify the structure of the solutions in the moment vector space and to derive multiple solutions by setting the initial value to the moment vector orthogonal to the solutions already obtained. Finally, the probability density function (pdf) for the state of the system was derived using the moment vectors in a steady state. Comparison of the pdfs thereby derived with those derived using numerical simulation showed that the method provided good approximations of the pdfs. Moreover, multiple solutions that are difficult to do using numerical simulation were derived.

Boolean matching is a fundamental problem in FPGA synthesis, but existing Boolean matchers are not scalable to complex PLBs (programmable logic blocks) and large circuits. This paper proposes a filter-based Boolean matching method, F-BM, which accelerates Boolean matching using lookup tables implemented by Bloom filters storing pre-calculated matching results. To show the effectiveness of the proposed F-BM, a post-mapping re-synthesis minimizing area which employs Boolean matching as the kernel has been implemented. Tested on a broad selection of benchmarks, the re-synthesizer using F-BM is 80X faster with 0.5% more area, compared with the one using a SAT-based Boolean matcher.

In a direct-sequence spread spectrum communication system, its multiple access interference, security and user number are mainly decided by correlation, linear span and family size of spreading sequences employed by such a system, respectively. In this letter, based on several families of the known sequences, a method for improving their linear span and family sizes is presented. It is worthy of mentioning that although the number of the proposed sequences with linear span not less than that of the known sequences is enormously increased, the former's correlation distribution is the same as the latter's one. In addition, the proposed sequences include No sequences and the known sequences mentioned above as special cases.

A new linearly tapered slot antenna (LTSA) with defected sides is proposed in this letter. Both sides are defected with half-dumbbell shape slots that may alter the surface current intensities on both sides. As the half-dumbbell size is increased, the 3-dB beamwidth of the proposed antenna is 4° and 6° lower in the E/H-plane, respectively, than these of the LTSA without defects. Accordingly, the measured gain is improved by up to 3.75 dB and the first side lobe level is lowered by about -10.8 dB and -5.8 dB in the E/H-planes, respectively.

We propose the Combined Symbol-based Closed-Loop Orthogonal Space-Time Block Code (CS-CL-OSTBC) for four transmit antennas. In the multiple antenna systems, the CS-CL-OSTBC not only achieves full rate and full diversity with linear maximum-likelihood detection but also obtains higher feedback gain than existing CL-OSTBCs due to more efficient utilization of channel feedback information. In the proposed scheme, all the complex-valued channel coefficients are rotated to positive real values with exact channel phase feedback information. As a result, the channel gain can be expressed as the square of the sum of all positive real values and can obtain the maximum value without any loss. Simulation results on bit error rate performance show that the CS-CL-OSTBC outperforms existing CL-OSTBCs for various modulation schemes.

We propose a time-frequency interleave (TFI) structure of single carrier (SC) frequency domain equalization (FDE) to combat spectral nulls of wireless channels. Permuted copies of block data are transmitted in the TFI-FDE, providing the same diversity order as maximal-ratio receiver combining. The spectral nulls are compensated by uncorrelated spectral components of the same channel. It shows 4 dB diversity gains at BER of 10-2 over an indoor channel. The TFI-FDE is computationally-efficient in combination with fast Fourier transform. This TFI-FDE fits SC systems with single antenna. It needs no channel state information at the transmitter.

The noise performances under AWGN channel of the IF-derivative and the quadrature differential FM discriminators, which are widely utilized in modern low power wireless radios, are analyzed and compared. The analysis relies upon the time-domain multi-sinusoidal representation of the noise that facilitates accurate and closed-form analytical SNR characteristics. Derivation of the SNR equations is detailed and discussion based on the analysis results is given to provide insights into the discriminators' performance limitation where it is demonstrated that the differential scheme is considerably more advantageous. Simulated SNR characteristics of practical continuous-phase frequency shift keying (CPFSK) systems using both the FM discriminators are presented as analysis verification.

A spiral array radial line slot antenna (SA-RLSA) is designed in 22 GHz band. A SA-RLSA excited with a coaxial feeder suffers from aperture illumination fluctuation in amplitude and phase in the circumferential (φ-) direction while in the radial direction, reasonably uniform distribution is observed. Rotational symmetry of radiation patterns is degraded and especially the sidelobe levels are unbalanced. This fluctuation is associated with the generation of the higher order modes in the φ-direction and is the unique defect of SA-RLSA which uses oversized waveguide. In this paper, a novel feeding structure with two pairs of parasitic pins around a coaxial feeder is proposed and designed so as to compensate the rotational asymmetry of aperture illumination. A measurement using the model antenna designed in 22 GHz band demonstrates the enhancement of the rotational symmetry; the circumferential fluctuation is reduced from 5.1 dB and 33 degrees to 1.8 dB and 12 degrees, while the fluctuation in the first sidelobe level suppressed from 10.7 dB to 1.2 dB.

In this paper, joint water filling and maximal ratio transmission (joint WF-MRT) downlink transmit diversity for a single-carrier distributed antenna network (SC DAN) is proposed. The joint WF-MRT transmit weight allocates the transmit power in both transmit antenna dimension and frequency dimension, i.e., the power allocation is done both across frequencies based on WF theorem and across transmit antennas based on MRT strategy. The cumulative distribution function (CDF) of the channel capacity achievable by joint WF-MRT transmit diversity is evaluated by Monte-Carlo numerical computation method. The channel capacities achievable with joint WF-MRT, MRT, and WF transmit weight (WF transmit weight is done across transmit antennas and frequencies based on WF theorem) are compared. It is shown that the joint WF-MRT transmit weight provides the highest channel capacity among three transmit weights.

In this paper, we present a hybrid speech emotion recognition system exploiting both spectral and prosodic features in speech. For capturing the emotional information in the spectral domain, we propose a new spectral feature extraction method by applying a novel non-uniform subband processing, instead of the mel-frequency subbands used in Mel-Frequency Cepstral Coefficients (MFCC). For prosodic features, a set of features that are closely correlated with speech emotional states are selected. In the proposed hybrid emotion recognition system, due to the inherently different characteristics of these two kinds of features (e.g., data size), the newly extracted spectral features are modeled by Gaussian Mixture Model (GMM) and the selected prosodic features are modeled by Support Vector Machine (SVM). The final result of the proposed emotion recognition system is obtained by combining the results from these two subsystems. Experimental results show that (1) the proposed non-uniform spectral features are more effective than the traditional MFCC features for emotion recognition; (2) the proposed hybrid emotion recognition system using both spectral and prosodic features yields the relative recognition error reduction rate of 17.0% over the traditional recognition systems using only the spectral features, and 62.3% over those using only the prosodic features.

We present an alternative approach to what we call the "standard optimization", which minimizes a cost function by searching a parameter space. Instead, our approach "projects" in the joint observation space onto the manifold defined by the "consistency constraint", which demands that any minimal subset of observations produce the same result. This approach avoids many difficulties encountered in the standard optimization. As typical examples, we apply it to line fitting and multiview triangulation. The latter produces a new algorithm far more efficient than existing methods. We also discuss the optimality of our approach.

Hydrogenated polymorphous Silicon allows to fabricate TFTs with very interesting characteristics including better threshold voltage stability than a-Si TFTs, lower leakage current than µc-Si:H TFTs and excellent uniformity. Investigation of threshold voltage shift mechanisms of pm-Si:H TFTs has shown a specific semiconductor material degradation with different activation energies compared to a-Si:H TFTs. TEM analysis has evidenced for the first time a significant structural difference between pm-Si:H and a-Si:H materials, in the TFT device configuration. Pm-Si:H appears to be very suitable for low cost and high performance AM-OLED fabrication.