Hock n Chua

Design and development of a mobile peer-to-peer social networking application

The proliferation of wireless and mobile devices such as personal digital assistants and mobile phones has created a large demand for mobile software applications such as social networking software. In addition, the realization and widespread usage of peer-to-peer (P2P) networking have drastically increased the number of applications utilizing these technologies. The convergence of mobile and P2P networking have generated increasing interest in the mobile peer-to-peer (MP2P) community. In this paper, we describe the design and development of a mobile social software (MoSoSo) based on a P2P network architecture using Juxtapose (JXTA) and Juxtapose for Java MicroEdition (JXME). The MoSoSo application allows users to discover, communicate and share resources with one another. We present three facets of designing the MoSoSo: object-oriented software design, network infrastructure design, and user-interface design. The software has been fully implemented and tested on a variety of mobile devices for use in a campus setting. By studying the design and implementation of the MoSoSo, we hope to benefit the entire mobile application development community by providing common models and insights into developing MP2P software.

An investigation into the parameters affecting total harmonic distortion in low-voltage low-power Class-D amplifiers

We investigate the influence of two important practical design parameters on total harmonic distortion (THD) for the design of low-voltage (0.9-1.4 V) low-power analog Class-D amplifiers: the linearity of the carrier waveform and the impedance of the output stage. We show that the carrier nonlinearity results in THD and propose a novel mathematical analysis method to model the nonlinearity. We recommend a range of the parameter that describes the carrier nonlinearity and that results in a good compromise to the dynamic range of the pulsewidth modulator of the Class-D amplifier. We show that the impedance of the output stage has little effect on THD. We verify our analyses by means of MATLAB and HSPICE computer simulations, and on the basis of practical measurements.

A new collusion attack and its performance evaluation

In this paper, we propose a new blind watermarking scheme by embedding a digital image signature/watermark in the wavelet domain and using Independent Component Analysis (ICA) technique for blind watermark extraction. The watermark is inserted in the middle frequency sub-bands. A visual masking function is used to modify the digital signature to assure the perceptual quality of the watermarked image. Independent Component Analysis (ICA) method is employed for blind watermark extraction without requiring the original image. The presented technique has been successfully evaluated and compared with other wavelet-based blind watermarking techniques against the most prominent attacks, such as JPEG and JPEG2000 compression and quantization.

Grammatical Inference using an Adaptive Recurrent Neural Network

In this study, we proposed an adaptive recurrent neural network that is capable of inferring a regular grammar, and at the same time of extracting the underlying grammatical rules emulated by a finite-state automata. Our proposed network adapts from an initial analog phase, which has good training behavior, to a discrete phase for automatic rule extraction. A modified objective function is proposed to accomplish the discretisation process as well as logic learning. Comparison on learning Tomita grammars shows that our network has a significant advantage over other approaches.

BER formulation for the blind retrieval of MPEG video watermark

A multiple watermarks embedding scheme based on multi-stage vector quantisation (VQ) is proposed. A reference watermark is generated first by referring to all the fake watermarks and the real one. Then all the watermarks except the real one are embedded into each stage of the multistage VQ system. The generated keys can be assigned to the related users to share the hidden information. Combining all the extracted watermarks, the real watermark will appear. With the fake watermarks and the structure of the multistage vector quantisation, the proposed scheme has superior features than traditional VQ-based watermarking schemes not only in security, encoding time, and codebook storage space, but also in secret sharing ability.

A practical and efficient approach to the constrained via minimization problem

This paper presents an efficient and practical approach to the Constrained Via Minimization (CVM) problem, which assigns wire segments to the layers, using the minimum number of vias, given a feasible partial routing. The feasible partial routing is first represented by a directed bipartite graph to reflect the mutual constraints. An energy function is then proposed to turn the problem into a cost optimization problem. An efficient heuristic algorithm, combining hill-climbing and simulated annealing, is developed for the cost optimization. The algorithm has the capability to escape from the local minimums and eventually reaches a near-optimal or optimal solution. The proposed method is practical as it can handle many practical constraints such as a multi-way wire split from a single via, and pre-allocation of power nets and terminals. Experimental results show that our proposed method is efficient in handling complex grid-based routing.

Throughput adaptation for scalable video multicast in wireless networks

We present a novel method of cross-layer adaptation for scalable video coding (SVC) extension of H.264/AVC multicast in wireless network. Transmission strategy for the single-hop multicast adapts according to wireless channel condition and SVC layer. Efficient transmit power and unequal FEC bit budget allocations are proposed while existing adaptive technique for throughput optimization is applied. We formulated a convex optimization problem to obtain the optimal time-division scheduler for all multicasts such that the wireless network delivers all SVC layers in noisy wireless channels and severe network capacity constraints. The cross-layer adaptation technique is verified by simulation results.

Detection and Removal of Rainboweffect Artifacts

Due to the imperfect separation of luminance and chroma signals in receivers demodulation, composite video signals suffer from rainbow effect artifacts, which present themselves as interlaced color stripes in regions of high luminance frequency and high luminance intensity. In this paper, we derive the formulas governing the rainbow effects. Based on these formulas, we propose a novel method to detect and remove these annoying artifacts. Experimental results on both captured video frames and simulated frames show that our method can remove the rainbow-effect artifacts effectively and improve the image quality notably.

Improved bit rate control for real-time MPEG watermarking

The alteration of compressed video bitstream due to embedding of digital watermark tends to produce unpredictable video bit rate variations which may in turn lead to video playback buffer overflow/underflow or transmission bandwidth violation problems. This paper presents a novel bit rate control technique for real-time MPEG watermarking applications. The proposed bit rate control scheme evaluates the combined bit length of a set of multiple watermarked VLC codewords and successively replaces watermarked VLC codewords having the largest increase in bit length with their corresponding unmarked VLC codewords until a target bit length is achieved. The proposed method offers much flexibility and scalability compared to the pioneering scheme proposed by Hartung and Girod. Experimental results show that the proposed bit rate control scheme is effective in meeting the bit rate targets and capable of improving the watermark detection robustness for different video contents compressed at different bit rates.

Enhancement of blind watermark retrieval in drift-compensated MPEG video

The concept of drift compensation has been proposed to alleviate the propagation of visual distortions between successive video frames, which exists as a result of embedding watermarks in the compressed domain without re-performing motion prediction. By viewing the drift compensation data as watermark signals with inverse polarity, we propose to enhance the blind watermark retrieval of drift-compensated watermarked MPEG video by appropriately de-spreading the drift compensation data and adding the resultant correlation output to the usual watermark correlation sum. In our experiments, spread spectrum watermarks with additive and multiplicative embedding for MPEG video are used. The results show that the proposed technique is indeed capable of improving the reliability of the estimated watermark for different videos compressed at different bit rates. The proposed idea is expected to be applicable to any image and video compression formats with predictive coding, including MPEG-1, MPEG-2, MPEG-4, H.261, or H.263.