Recently, many application systems have been developed by using a large number of cameras. If 3D points are observed from synchronized cameras, the multiple view geometry of these cameras can be computed and the 3D reconstruction of the scene is available. Thus, the synchronization of multiple cameras is essential. In this paper, we propose a method for synchronizing multiple cameras and for computing the epipolar geometry from uncalibrated and unsynchronized cameras. In particular we using affine invariance to match the frame numbers of camera images for finding the synchronization. The proposed method is tested by using real image sequences taken from uncalibrated and unsynchronized cameras.

This paper proposes an image authentication method that detects tamper and localizes tampered areas efficiently. The efficiency of the proposed method is summarized as the following three points. 1) This method offers coarse-to-fine tamper localization by hierarchical data hiding so that further tamper detection is suppressed for blocks labeled as genuine in the uppper layer. 2) Since the image feature description in the top layer is hidden over an image, the proposed method enciphers the data in the top layer rather than enciphers all data in all layers. 3) The proposed method is based on the reversible data hiding scheme that does not use highly-costed compression technique. These three points makes the proposed method superior to the conventional methods using compression techniques and methods using multi-tiered data hiding that requires integrity verification in many blocks even the image is genuine. Simulation results show the effectiveness of the proposed method.

In this paper, an alternative transform based on the correlation of the residual block is proposed for the improvement of the H.264/AVC coding efficiency. A discrete sine transform is used alternately with a discrete cosine transform in order to greatly compact the energy of the signal when the correlation coefficients of the signal are in the range of -0.5 to 0.5. Therefore, the discrete sine transform is suggested to be used in conjunction with the discrete cosine transform in H.264/AVC. The alternative transform selecting the optimal transform between two transforms by using rate-distortion optimization shows a coding gain compared with H.264/AVC. The proposed method achieves a PSNR gain of up to 1.0 dB compared to JM 10.2 at relatively high bitrates.

In this paper, we design an adaptive mobility-supporting MAC (AM-MAC) protocol for mobile sensor networks. In our protocol, as in S-MAC [1], each virtual cluster that consists of a subset of sensor nodes has its own listen-sleep schedule. Hence, when a mobile sensor node moves into a new virtual cluster, it needs to adapt to the listen-sleep schedule of the corresponding virtual cluster in a timely and energy efficient manner. To this end, in our protocol, we utilize schedule information on border nodes between virtual clusters. This allows us to implement fast and energy efficient listen-sleep schedule adaptation for mobile nodes, which consists of two main functions: energy efficient secondary listen period and smart scheduling adaptation. Simulation results show that our protocol can provide fast schedule adaptation while achieving energy efficiency.

A simple and successful design of initial codebook of vector quantization (VQ) is presented. For existing initial codebook algorithms, such as random method, the initial codebook is strongly influenced by selection of initial codewords and difficult to match with the features of the training vectors. In the proposed method, training vectors are sorted according to the norm of training vectors. Then, the ordered vectors are partitioned into N groups where N is the size of codebook. The initial codewords are obtained from calculating the centroid of each group. This initializtion method has a robust performance and can be combined with the VQ algorithm to further improve the quality of codebook.

In this paper, a new fractional sample rate conversion (SRC) scheme based on a direct insertion/cancellation scheme is proposed. This scheme is suitable for signals that are sampled at a high sample rate and converted to a lower sample rate. The direct insertion/cancellation scheme may achieve low-complexity and lower power consumption as compared to the other SRC techniques. However, the direct insertion/cancellation technique suffers from large aliasing and distortion. The aliasing from an adjacent channel interferes the desired signal and degrades the performance. Therefore, a modified direct insertion/cancellation scheme is proposed in order to realize high performance resampling.

Wireless Sensor Networks (WSNs) have become a key technology for ubiquitous computing environments. In WSNs, battery recharge or replacement is impossible because sensors are left unattended after deployment. Therefore, WSNs need a networking protocol scheme to increase the life time of sensor nodes. The clustering technique is an efficient approach for reducing energy consumption in wireless sensor networks. In cluster topology, however, there is a problem which causes a large amount of energy consumption of cluster head. In addition, in the sparsely deployed sensor field, mesh topology can be more energy-efficient than cluster topology. In this paper, we propose a Hybrid Cluster Mesh (HCM) scheme, which recognizes the density of neighbor nodes and each node decides its topology itself, and HCM-RO (reorganization) scheme which reorganizes clusters. Simulation results show that the proposed hybrid topology control scheme is more energy-efficient than each topology of cluster or mesh.

Compared with previous standards, H.264/AVC adopts variable block size motion estimation (VBSME) and multiple reference frames (MRF) to improve the video quality. Full search motion estimation algorithm (FS), which calculates every search candidate in the search window for 7 block type with multiple reference frames, consumes massive computation power. Mathematical analysis reveals that the aliasing problem of subsampling algorithm comes from high frequency signal components. Moreover, high frequency signal components are also the main issues that make MRF algorithm essential. As we know, a picture being rich of texture must contain lots of high frequency signals. So based on these mathematical investigations, two fast VBSME algorithms are proposed in this paper, namely edge block detection based subsampling method and motion vector based MRF early termination algorithm. Experiments show that strong correlation exists among the motion vectors of those blocks belonging to the same macroblock. Through exploiting this feature, a dynamically adjustment of the search ranges of integer motion estimation is proposed in this paper. Combing our proposed algorithms with UMHS almost saves 96-98% Integer Motion Estimation (IME) time compared to the exhaustive search algorithm. The induced coding quality loss is less than 0.8% bitrate increase or 0.04 dB PSNR decline on average.

The spectral efficiency of cooperative relaying in interference-limited environments in which a given channel is spatially reused is investigated. Cooperative relaying is a promising technique that uses neighboring stations to forward the data toward the destination in order to achieve spatial diversity gain. It has been reported that by introducing cooperative relaying into communication between an isolated source-destination pair, the error rate or spectral efficiency is generally improved. However, it is not intuitively clear whether cooperative relaying can improve the performance in interference-limited environments because the simultaneous transmission of multiple stations increases the number of interference signals. Assuming the most fundamental cooperative relaying arrangement, which consists of only one relay station, numerical results reveal that cooperative relaying is not always superior to non-cooperative single-hop and two-hop transmissions in terms of spectral efficiency.

Jeong et al. recently have proposed a strong ID-based key distribution scheme in order to achieve security against long-term key reveal and session state reveal attacks. In this letter, we show that, unfortunately, the ID-based key distribution scheme is vulnerable to an impersonation attack such that anyone can manipulate public transcripts generated by a user to impersonate the original user.

In time-varying channels, the channel state information available at the transmitter (CSIT) is outdated due to inherent time delay between the uplink channel estimation and the downlink data transmission in TDD systems. In this letter, we propose an iterative precoding method and a linear decoding method which are both based on minimum mean-squared error (MMSE) criteria to mitigate the interference among data streams and users created by outdated CSIT for multiuser MIMO downlink systems. Analysis and simulation results show that the proposed method can effectively reduce the impairment of the outdated CSIT and improve the system capacity.

The manifold-ranking algorithm has been successfully adopted in content-based image retrieval (CBIR) in recent years. However, while the global low-level features are widely utilized in current systems, region-based features have received little attention. In this paper, a novel attention-driven transductive framework based on a hierarchical graph representation is proposed for region-based image retrieval (RBIR). This approach can be characterized by two key properties: (1) Since the issue about region significance is the key problem in region-based retrieval, a visual attention model is chosen here to measure the regions' significance. (2) A hierarchical graph representation which combines region-level with image-level similarities is utilized for the manifold-ranking method. A novel propagation energy function is defined which takes both low-level visual features and regional significance into consideration. Experimental results demonstrate that the proposed approach shows the satisfactory retrieval performance compared to the global-based and the block-based manifold-ranking methods.

The signalling protocol vulnerability opens DDoS problem in Mobile WiMAX networks. This letter proposes an authentication method that uses the unrevealed upper 64 bits of Cipher-based MAC as a solution. It runs for MSs in idle mode and reduces the calculation complexity by 59% under DDoS attack while incurring 1% overhead under normal condition.

This paper focuses on the numerical and experimental investigations of the influence of two polymers (PA6 and POM) on the arc behavior during arc motion process. The mathematical model of 3-dimentional air arc plasma considering the ablation of lateral walls is built based on magnetic hydro-dynamics (MHD). By adopting the commercial computational fluid dynamics (CFD) package based on control-volume method, the above MHD model is solved and the distribution of temperature field, concentration field, flow field and electrical potential field in the arc chamber are calculated. The simulation results indicate that the vapor concentration behind the arc column is higher than that in front of the arc column because of the existence of "double vortices" in the arc chamber. The use of polymers causes the maximal arc voltage increase 16.2% with POM and 18.9% with PA6 in this case and causes the average arc velocity increase 15.8% with POM and 21.1% with PA6 in this case. The experiments are also carried out to study the influence of polymers on arc voltage and arc root position in the arc chamber during arc motion. The experimental results prove the validity of the numerical investigation.

A blind image restoration for non-linear motion blurs with non-uniform point spread functions based on multiple blurred versions of a same scene is proposed. The restoration is separately considered as identification and deconvolution problems. In the proposed identification process, an identification difficulty is introduced to rank an order of blur identification. A blurred image with the lowest identification difficulty is initially identified by using a single-image-based scheme. Then, other images are identified based on a cross convolution relation between each pair of blurred images. In addition, an iterative feedback scheme is applied to improve the identification results. For the deconvolution process, a spatial adaptive scheme using regional optimal terminating points is modified from a conventional iterative deconvolution scheme. The images are decomposed into sub-regions based on smoothness. The regional optimal terminating points are independently assigned to suppress a noise in smooth regions and sharpen the image in edgy regions. The optimal terminating point for each region is decided by considering a discrepancy error. Restoration examples of simulated and real world blurred images are experimented to demonstrate the performance of the proposed method.

In this paper, a robust sound source localization approach is proposed. The approach retains good performance even when model errors exist. Compared with previous work in this field, the contributions of this paper are as follows. First, an improved broad-band and near-field array model is proposed. It takes array gain, phase perturbations into account and is based on the actual positions of the elements. It can be used in arbitrary planar geometry arrays. Second, a subspace model errors estimation algorithm and a Weighted 2-Dimension Multiple Signal Classification (W2D-MUSIC) algorithm are proposed. The subspace model errors estimation algorithm estimates unknown parameters of the array model, i.e., gain, phase perturbations, and positions of the elements, with high accuracy. The performance of this algorithm is improved with the increasing of SNR or number of snapshots. The W2D-MUSIC algorithm based on the improved array model is implemented to locate sound sources. These two algorithms compose the robust sound source approach. The more accurate steering vectors can be provided for further processing such as adaptive beamforming algorithm. Numerical examples confirm effectiveness of this proposed approach.

In this paper, we propose new joint transport and MAC protocols for ad hoc wireless networks based on an optimization framework. To overcome the practical and efficiency limitations of previous research, we develop a different framework based on independent sets and propose an implementable heuristic algorithm. We address the implementation issues of the proposed algorithm. Simulation results confirm the efficiency and fairness of our protocols.

Constructing ideal (t,n) threshold secret sharing schemes leads to some limitations on the maximum number of users, that are able to join the secret sharing scheme. We aim to remove these limitations by reducing the information rate of the constructed threshold secret sharing schemes. In this paper we propose recursive construction algorithms of (t,n) threshold secret sharing schemes, based on the generalized vector space construction. Using these algorithms we are able to construct a (t,n) threshold secret sharing scheme for any arbitrary n.

In this paper, we propose a new localization algorithm and improve the DV-Hop algorithm by using a differential error correction scheme that is designed to reduce the location error accumulated over multiple hops. This scheme needs no additional hardware support and can be implemented in a distributed way. The proposed method can improve location accuracy without increasing communication traffic and computing complexity. Simulation results show the performance of the proposed algorithm is superior to that of the DV-Hop algorithm.

In this paper, a new large spreading code set with a uniform low cross-correlation is proposed. The proposed code set is capable of (1) increasing the number of assigned user (capacity) in a multicarrier code division multiple access (MC-CDMA) system and (2) reducing the peak-to-average power ratio (PAPR) of an orthogonal frequency division multiplexing (OFDM) system. In this paper, we derive a new code set and present an example to demonstrate performance improvements of OFDM and MC-CDMA systems. Our proposed code set with code length of N has K=2N+1 number of codes for supporting up to (2N+1) users and exhibits lower cross correlation properties compared to the existing spreading code sets. Our results with subcarrier N=16 confirm that the proposed code set outperforms the current pseudo-orthogonal carrier interferometry (POCI) code set with gain of 5 dB at bit-error-rate (BER) level of 10-4 in the additive white Gaussian noise (AWGN) channel and gain of more than 3.6 dB in a multipath fading channel.