Min-Kuan Chang

Performance analysis of cooperative communication system with hierarchical modulation over rayleigh fading channel

Much attention had been devoted to study the bit error rate (BER) of hierarchical modulation on point-to-point transmissions in recent years. But few mention the error performance of hierarchical modulation on cooperative communication systems. Thus, in this paper, we derive the explicit closed-form expressions of the exact bit error rate computation for cooperative communication systems with hierarchical modulation over additive white Gaussian noise (AWGN) channels and Rayleigh fading channels. To obtain the theoretical formulas of error rate performance, an analyzing model is proposed to clearly express all possibilities of each transmission. For error rate performance, the expression for BER is a function of distance parameters. Based on this relationship, a criterion is proposed to choose the optimal distance parameters for minimizing the BER of the refinement bits while guaranteeing the BER requirement of the base bits. Simulation results validate the correctness of the derived BERs of the base bits and the refinement bits. Also from simulation results, the performance with optimal distance parameters is greatly improved compared to the non-optimal distance parameters.

A Passive-Blind Forgery Detection Scheme Based on Content-Adaptive Quantization Table Estimation

In this paper, we propose a passive-blind scheme for detecting forged images. The scheme leverages quantization table estimation to measure the inconsistency among images. To improve the accuracy of the estimation process, each AC DCT coefficient is first classified into a specific type; then the corresponding quantization step size is measured adaptively from its energy density spectrum (EDS) and the EDSs Fourier transform. The proposed content-adaptive quantization table estimation scheme is comprised of three phases: pre-screening, candidate region selection, and tampered region identification. In the pre-screening phase, we determine whether an input image has been JPEG compressed, and count the number of quantization steps whose size is equal to one. To select candidate regions for estimating the quantization table, we devise a candidate region selection algorithm based on seed region generation and region growing. First, the seed region generation operation finds a suitable region by removing suspect regions, after which the selected seed region is merged with other suitable regions to form a candidate region. To avoid merging suspect regions, a candidate region refinement operation is performed in the region growing step. After estimating the quantization table from the candidate region, an maximum-likelihood-ratio classifier exploits the inconsistency of the quantization table to identify tampered regions block by block. To evaluate the schemes performance in terms of tampering detection, three common forgery techniques, copy-paste tampering, inpainting, and composite tampering, are used. Experiment results demonstrate that the proposed scheme can estimate quantization tables and identify tampered regions effectively.

Distributed edge detection with composite hypothesis test in wireless sensor networks

A statistical approach to distributed edge sensor detection with wireless sensor networks is proposed in this research. The objective is to determine whether a target sensor is located in the edge area of a certain phenomenon or not, based on data from its neighboring sensors. Due to the nature of wireless sensor networks, it is desirable to have a distributed algorithm that has a low computational complexity and a low data communication cost among sensors. With some reasonable assumptions and the aid of composite hypothesis testing, we propose data fusion as well as decision fusion methods for edge sensor detection to fulfill the aforementioned constraints. Numerical experiments are used to demonstrate the efficiency of the proposed algorithm.

Contour line extraction with wireless sensor networks

An algorithm to extract contour lines using wireless sensor networks is proposed for environmental monitoring in this work. In contrast to previous work on edge detection that is primarily concerned with the region of a certain phenomenon, contour lines offer more detailed information about the underlying phenomenon such as signal amplitude, density and source location. A distributed algorithm to extract the contour line information from local measurements is developed so that the phenomenon can be monitored in the basestation without demanding excessive raw data transmission. Simulation results are provided to demonstrate the efficiency of the proposed algorithm.

A FEATURE-BASED SCHEME FOR DETECTING AND CLASSIFYING VIDEO-SHOT TRANSITIONS BASED ON SPATIO-TEMPORAL ANALYSIS AND FUZZY CLASSIFICATION

In this paper, we propose a feature-based scheme for detecting different genres of video shot transitions based on spatio-temporal analysis and model parameter estimation. In feature extraction, th...

Power control for packet-based wireless communication systems

A power control scheme for packet-based wireless communication systems is proposed in this paper. The proposed power control scheme aims at minimizing the total number of transmissions that a packet needs before it is received successfully over a Rayleigh fading channel subject to two constraints. One is that the transmission power should be greater than zero. The other is imposed by the constraint on the total transmission power at the base station. We use the augmented Lagrangian multiplier method to solve this problem and provide a theoretical solution. The simulation results show that, with the proposed power control scheme, the number of re-transmission can be reduced and the delay of a packet wasted in the channel can be decreased as well.

A distributed approach to contour line extraction using sensor networks

An algorithm to extract contour lines using wireless sensor networks is proposed in this work. In con- trast with previous work on edge detection that is primarily concerned with the region of a certain phenomenon, contour lines offer more detailed information about the underlying phenomenon such as signals amplitude, density and source location. A distributed algorithm to extract the contour lines information from local measurements is developed so that the phenomenon can be monitored in the basestation without demanding excessive raw data transmission. Sim- ulation results are provided to demonstrate the efficiency of the proposed algorithm. Furthermore, a thorough per- formance analysis is conducted to understand the effects of the sensor density and the background noise power on the performance of the system.

Spectrum sharing in multi-channel cooperative cognitive radio networks: a coalitional game approach

In this paper, we study a coalitional game approach to resource allocation in a multi-channel cooperative cognitive radio network with multiple primary users (PUs) and secondary users (SUs). We propose to form the grand coalition by grouping all PUs and SUs in a set, where each PU can lease its spectrum to all SUs in a time-division manner while the SUs in return assist PUs’ data transmission as relays. We use the solution concept of the core to analyze the stability of the grand coalition, and the solution concept of the Shapley value to fairly divide the payoffs among the users. Due to the convexity of the proposed game, the Shapley value is shown to be in the core. We derive the optimal strategy for the SU, i.e., transmitting its own data or serving as a relay, that maximizes the sum rate of all PUs and SUs. The payoff allocations according to the core and the Shapley value are illustrated by an example, which demonstrates the benefits of forming the grand coalition as compared with non-coalition and other coalition schemes.

An Effective Shot Boundary Detection Algorithm for Movies and Sports

The shot change is the first step of video segmentation. Therefore, designing an efficient and low-complexity shot change detection becomes a significant issue. In this paper, we propose a simple and effective approach to detect abrupt shot changes based on interframe difference algorithm. Our approach can decrease false/miss caused by fast object motion and abrupt screen ash effectively. In order to increase the accuracy of shot change detection and decrease the complexity of computation, a novel method are developed to deal with those problems. The experimental result shows the validity of our proposed methods which provide not only a higher detection rate but also a faster computation speed to the shot change scenario.

Power control, adaptive modulation and subchannel allocation for multiuser downlink OFDM

A scheme to control transmission power, allocate subcarriers, and choose modulation schemes for each mobile terminal (MT) in a multiuser downlink OFDM system is investigated in this work. This proposed scheme attempts to make OFDM systems more flexible and robust to channel variations. The problem is decomposed into two stages. In the first stage, the min-max criterion is used to control the transmission power among different MTs in different allocated subchannels. Then, in the second stage, we choose modulation schemes for allocated subchannels of each MT with an objective to maximize the total transmission rate while satisfying the performance requirement of each MT. Simulations are conducted to demonstrate the performance of the proposed scheme under a varying number of MTs and a range of symbol error rates (SERs).