Browsing by Author "Kuo, C. -C. Jay"

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A DATA-CENTRIC APPROACH TO UNSUPERVISED TEXTURE SEGMENTATION USING PRINCIPLE REPRESENTATIVE PATTERNS
(2019-01-01)
Zhang, Kaitai
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Chen, Hong-Shuo
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Zhang, Xinfeng
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Wang, Ye
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Kuo, C. -C. Jay
Features that capture textural patterns of a certain class of images are crucial for texture segmentation tasks. This paper introduces a data-centric approach to efficiently extract and represent textural information, which adapts to a wide variety of textures. Based on the strong self-similarities and quasi periodicity in texture images, the proposed method first constructs a representative texture pattern set for the given image by leveraging the patch clustering strategy. Then, pixel wise texture features are designed according to the similarities between local patches and the representative textural patterns. Moreover, the proposed feature is generic and flexible, and can perform segmentation task by integrating it into various segmentation approaches easily. Extensive experimental results on both textural and natural image segmentation show that the segmentation method using the proposed features achieves very competitive or even better performance compared with the stat-of-the-art methods.
Codeword Design for Ultra-Wideband (UWB) Precoding
(2010-01-01)
Chang, Yu-Hao
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Tsai, Shang-Ho
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Yu, Xiaoli
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Kuo, C. -C. Jay
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電機工程學系
A precoding technique applied to symbols transmitted in an ultra-wideband (UWB) system can concentrate the signal power at the receiver for a higher data detection rate. The codeword design problem for optimal UWB precoding is investigated in this work. After the problem formulation, we examine its solution in the full-rank and the reduced-rank subspaces to obtain different tradeoffs between the detection performance and the amount of feedback messages. Furthermore, we propose two subspace selection schemes, each of which corresponds to a code design method. The resultant optimal codewords improve the performance of previous work significantly at the expense of a slightly increased amount of feedback messages. Finally, the performance of a precoded UWB system with various codewords is compared via computer simulation.
Cross-layer QoS analysis of opportunistic OFDM-TDMA and OFDMA networks
(2007-05-01)
Chang, Yu-Jung
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Chien, Feng-Tsun
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Kuo, C. -C. Jay
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
Performance analysis of multiuser orthogonal frequency division multiplexing (OFDM-TDMA) and orthogonal frequency division multiple access (OFDMA) networks in support of multimedia transmission is conducted in this work. We take a cross-layer approach and analyze several quality-of-service (QoS) measures that include the bit rate and the bit error rate (BER) in the physical layer, and packet average throughput/delay and packet maximum delay in the link layer. We adopt a cross-layer QoS framework similar to that in IEEE 802.16, where service classification, flow control and opportunistic scheduling with different subcarrier/bit allocation schemes are implemented. In the analysis, the Rayleigh fading channel in the link layer is modeled by a finite-state Markov chain, and the channel state information (CSI) is assumed to be available at the base station. With the M/G/1 queueing model and flow control results, our analysis provides important insights into the performance difference of these two multiaccess systems. The derived analytical results are verified by extensive computer simulation. It is demonstrated by analysis and simulation that OFDMA outperforms OFDM-TDMA in QoS metrics of interest. Thus, OFDMA has higher potential than OFDM-TDMA in supporting multimedia services.
Delay Analysis and Comparison of OFDM-TDMA and OFDMA under IEEE 802.16 QoS Framework
(2006)
Chang, Yu-Jung
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Chien, Feng-Tsun
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Kuo, C. -C. Jay
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電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The delay analysis and comparison of OFDM-TDMA and OFDMA using a flow control scheme under the QoS framework of IEEE 802.16 are conducted in this work. We investigate the maximum packet delay performance by deriving delay bounds for several multiaccess modes with different subcarrier/time-slot assignment and bit allocation schemes. The analytical delay bounds provide insights into the performance difference among different multiaccess schemes, and demonstrate each scheme\'s capability of supporting real-time, delay-sensitive multimedia applications. The derived analytical results are verified by computer simulation.
Enhanced adaptive frequency hopping for wireless personal area networks in a coexistence environment
(2007)
Hsu, Alex Chia-Chun
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Wei, David S. L.
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Kuo, C. -C. Jay
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Shiratori, Norio
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Chang, Chung-Ju
In this paper, we present an enhanced adaptive frequency hopping (EAFH) mechanism for improving the performance of frequency hopping-based wireless personal area networks (WPANs) under frequency-static and frequency-dynamic interference. The proposed mechanism monitors the overall packet error rate (PER) of the system to determine the right number of channels to be excluded from the hopset. Then based on the PER of individual channel, it decides whether to exclude a certain channel or not. Finally, proper packet length is associated with those channels remaining in the hopset. These decisions, which pertain to hopset size and packet length, are made so as to optimize the performance of the hopping system in a coexistence environment. We developed an analytical model to justify the behavior and performance of the proposed mechanism. Simulations are conducted under an environment of some collocated Bluetooth (BT) piconets and a Wi-Fi network to validate the developed model and show the superiority of EAFH. Simulation results show that, compared with those existing mechanisms including orthogonal hopset-based mechanisms, EAFH could provide much higher throughput while still maintaining reasonably good channel occupancy.
Iterative joint channel estimation and multiuser detection for DS-CDMA in frequency-selective fading channels
(2008-07-01)
Wu, Sau-Hsuan
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Mitra, Urbashi
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Kuo, C. -C. Jay
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電信工程研究所
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Institute of Communications Engineering
An iterative joint channel estimation, symbol detection, phase recovery and interference cancellation structure is proposed for asynchronous code-division multiple-access systems over frequency-selective fading channels. Based on the expectation maximization (EM) algorithm, a recursive channel estimator is developed for blind channel tracking, using a novel stochastic signal processing technique. To perform symbol detection given the phase ambiguities of the resultant EM channel estimates, a noncoherent scheme is developed to compute the a posteriori probabilities (APPs) of data symbols. Moreover, by incorporating the APPs into the proposed recursive channel estimator, phase ambiguity due to the EM channel estimation can be resolved, which enables soft multiple access interference cancellation for multiuser detection. Based on these new signal processing schemes, an iterative structure is proposed for joint channel estimation and multiuser detection over fast fading channels.
MAI-free, MC-CDMA systems based on Hadamard-Walsh codes
(2006-08-01)
Tsai, Shang-Ho
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Lin, Yuan-Pei
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Kuo, C. -C. Jay
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電控工程研究所
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Institute of Electrical and Control Engineering
It is known that multicarrier code-division multiple-access (MC-CDMA) systems suffer from multiaccess interference. (MAI) when the channel is frequency-selective fading. In this paper, we propose a Hadamard-Walsh code-based MC-CDMA system that achieves zero MAI over a frequency-selective fading channel. In particular, we will use appropriately chosen subsets of Hadamard-Walsh code as codewords. For a multipath channel of length L, we partition a Hadamard-Walsh code of size N into G subsets, where G is a power of two with G >= L. We will show that the N/G codewords in any of the G subsets yields an MAI-free system. That is, the number of MAI-free users for each codeword subset is N/G. Furthermore, the system has the additional advantage that it is robust to carrier frequency offset (CFO) in a multipath environment. It is also shown that the MAI-free property allows us to estimate the channel of each user separately and the system can perform channel estimation much more easily. Owing to the MAI-free property, every user can enjoy a channel diversity gain of order L to improve the bit error performance. Finally, we discuss a code priority scheme for a heavily loaded system. Simulation results are given to demonstrate the advantages of the proposed code and code priority schemes.
On robustness of ultra-wideband (UWB) precoding against timing jitter
(2007)
Chang, Yu-Hao
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Tsai, Shang-Ho
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Yu, Xiaoli
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Kuo, C. -C. Jay
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電機學院
The channel phase precoding (CPP) technique was recently proposed For the ultra-wideband (UWB) communication system in I I I to save the feedback overhead and the computational complexity as compared with the time-reversal prefilter (TRP) technique [2]. Two ideal assumptions have been made in both systems;, namely, the availability of accurate channel information and perfect synchronization of transmitted pulses. In this work, we examine the impact of timing jitter on the performance of TRP and CPP and show that the CPP-UWB system is more robust against the timing jitter than the TRP-UWB system.
Opportunistic access with random subchannel backoff (OARSB) for OFDMA uplink
(2007)
Chan, Yu-Jung
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Chien, Feng-Tsun
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Kuo, C. -C. Jay
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
A distributed medium access control (MAC) algorithm for uplink OFDMA networks under the IEEE 802.16 framework is proposed and analyzed in this work. We present a simple yet efficient algorithm to enhance the system throughput by integrating opportunistic medium access and collision resolution through, random subchannel backoff. Consequently, the resulting algorithm is called the opportunistic access with random subchannel backoff (OARSB) scheme. OARSB not only achieves distributed coordination among users but also reduces the amount of information exchange between the base station and users. The throughput and delay performance analysis of OARSB is conducted using a Markov chain model. The superior performance of OARSB over an existing scheme is demonstrated by analysis as well as computer simulation.
Performance analysis and transceiver design for adaptive BIC-MIMO-OFDM systems
(2007)
Chiu, Fu-Hsuan
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Wu, Sau-Hsuan
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Kuo, C. -C. Jay
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交大名義發表
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National Chiao Tung University
The performance analysis and transceiver design of an adaptive bit-interleaved-coded multi-input multi-output orthogonal frequency division multiplexing (BIC-MIMO-OFDM) system without channel station information (CSI) in priori are investigated in this research. First, the noncoherent capacity of a MIMO-OFDM system with N subcarriers, n(t) transmit antennas and n(r) receive antennas is analyzed. It is shown that the lower bound of noncoherent capacity in the high signal-to-noise ratio (SNR) region is asymptotically equal to n* (1-n* L/N) log rho, where n* = min(n(t), n(r)), L is the number of channel taps and rho is the SNR value. Then, an adaptive BIC-MIMO-OFDM system based on transmitter beamforming and variable-rate-variable-power (VRVP) QAM is proposed. The throughput of adaptive scheme can achieve the noncoherent capacity, however, the gap to the coherent capacity cannot be totally compensated due to the overhead of training. The effect of imperfect channel state information (CSI) feedback is studied. It is demonstrated by numerical simulation that the proposed BIC-MIMO-OFDM scheme has better performance than adaptive trellis coded modulation (TCM) when outdated channel estimation is used.
Performance Comparison of OFDM-TDMA and OFDMA with Cross-Layer Consideration
(2006)
Chang, Yu-Jung
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Chien, Feng-Tsun
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Kuo, C. -C. Jay
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電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Performance comparison of multiuser OFDM-TDMA and OFDMA systems by considering physical and link cross-layer behavior is conducted in this work. We provide a new framework for performance evaluation that centers on "scheduling" with several different subcarrier/bit allocation schemes. The performance metrics include: the bit rate, the bit error rate (BER), packet throughput and delay. The instantaneous channel conditions of users are assumed to be available at the base station, which can be achieved by channel estimation at the mobile terminal (MT), and then fed back to the base station through a control channel. To perform the link layer comparison, we model the Rayleigh fading channel with a finite-state Markov chain, and adopt the M/G/1 queueing model as the analytical tool. Computer simulation is performed to verify conducted analytical results.
Performance Enhancement of Channel-Phase Precoded Ultra-Wideband (CPP-UWB) Systems by Rake Receivers
(2008)
Chang, Yu-Hao
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Tsai, Shang-Ho
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Yu, Xiaoli
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Kuo, C. -C. Jay
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電控工程研究所
We propose to use the Rake receiver to improve the system performance by collecting more signal power in an ultra-wideband (UWB) system precoded by the channel phase information, called the CPP-UWB system [1], in this work. The performance of the proposed system is determined by the selected channel taps and the corresponding combining schemes for those Rake fingers. Three combing schemes, i.e., the maximum ratio combining (MRC), the minimized mean square error (MMSE) and the zero-forcing (ZF), are proposed. When the MRC scheme is applied to the Rake receiver with M fingers, M channel taps can be easily found to maximize the averaged signal power at the receiver output by exploiting the property of the channel-phase-precoded channel. It is shown by simulation results that the proposed scheme significantly outperforms the precoding system using one matched filter as proposed in [1].
Receiver Design for Bit-interleaved MIMO-OFDM Systems over Time-varying Channels
(2006)
Chiu, Fu-Hsuan
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Wu, Sau-Hsuan
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Kuo, C. -C. Jay
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交大名義發表
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National Chiao Tung University
A complete solution to joint channel tracking and symbol detection for bit-interleaved MIMO-OFDM systems in a time-varying frequency-selective fading environment is proposed in this research. In the training mode, the Rao-Blackwellised particle filter (RBPF) is used to estimate the phase offset (PO) and the carrier frequency offset (CFO). In the data mode, based on a recursive EM procedure in conjunction with soft decoding, we develop an iterative algorithm that performs the minimum mean squared error (MMSE) channel estimation and the maximum a posterior (MAP) probability symbol detection jointly. The soft decoding module is composed of the list sphere decoder (LSD) and the soft-in-soft-out (SISO) channel decoder based on the BCJR algorithm. The performance of the proposed algorithm is evaluated via simulation. It is demonstrated that the new algorithm has robust performance in the presence of phase noise and the carrier frequency offset.
Simplified Multiaccess Interference Reduction for MC-CDMA With Carrier Frequency Offsets
(2010-06-01)
Tadjpour, Layla
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Tsai, Shang-Ho
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Kuo, C. -C. Jay
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電機工程學系
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Department of Electrical and Computer Engineering
Multicarrier code-division multiple-access (MC-CDMA) system performance can severely be degraded by multiaccess interference (MAI) due to the carrier frequency offset (CFO). We argue that MAI can more easily be reduced by employing complex carrier interferometry (CI) codes. We consider the scenario with spread gain N, multipath length L, and N users, i.e., a fully loaded system. It is proved that, when CI codes are used, each user only needs to combat 2(L - 1) (rather than N - 1) interferers, even in the presence of CFO. It is shown that this property of MC-CDMA with CI codes in a CFO channel can be exploited to simplify three multiuser detectors, namely, parallel interference cancellation (PIC), maximum-likelihood, and decorrelating multiuser detectors. The bit-error probability (BEP) for MC-CDMA with binary phase-shift keying (BPSK) modulation and single-stage PIC and an upper bound for the minimum error probability are derived. Finally, simulation results are given to corroborate theoretical results.
TEXTURE ANALYSIS VIA HIERARCHICAL SPATIAL-SPECTRAL CORRELATION (HSSC)
(2019-01-01)
Zhang, Kaitai
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Chen, Hong-Shuo
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Wang, Ye
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Ji, Xiangyang
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Kuo, C. -C. Jay
A hierarchical spatial-spectral correlation (HSSC) method is proposed for texture analysis in this work. The HSSC method first applies a multi-stage spatial-spectral transform to input texture patches, which is known as the Saak transform. Then, it conducts a correlation analysis on Saak transform coefficients to obtain texture features of high discriminant power. To demonstrate the effectiveness of the HSSC method, we conduct extensive experiments on texture classification and show that it offers very competitive results comparing with state-of-the-art methods.
Understanding and Removal of False Contour in HEVC Compressed Images
(2018-02-01)
Huang, Qin
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Kim, Hui Yong
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Tsai, Wen-Jiin
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Jeong, Se Yoon
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Choi, Jin Soo
A contour-like artifact called false contour is often observed in large smooth areas of decoded images and video. Without loss of generality, we focus on detection and removal of false contours resulting from the state-of-the-art High Efficiency Video Coding codec. First, we identify the cause of false contours by explaining the human perceptual experiences on them with specific experiments. Next, we propose a precise pixel-based false contour detection method based on the evolution of a false contour candidate (FCC) map. The number of points in the FCC map becomes fewer by imposing more constraints step by step. Special attention is paid to separating false contours from real contours such as edges and textures in the video source. Then, a decontour method is designed to remove false contours in the exact contour position while preserving edge/texture details. Extensive experimental results are provided to demonstrate the superior performance of the proposed false contour detection and removal method in both compressed images and videos.
Visual tempo analysis for MTV-style home video authoring
(2008)
Wang, Shen-Zheng
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Chen, Yung-Sheng
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Lee, Shih-Hung
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Kuo, C. -C. Jay
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資訊工程學系
Automatic visual tempo analysis and adaptive shot detection are studied for MTV-style home video authoring. Based upon the significant variation caused by object and background independently, spatial and temporal analysis are integrated for region of interest(ROI) detection in video sequences. To further detect homogeneous shots, visual tempos are proposed to describe the variation. Then, an adaptive segmentation method is presented to automatically detect homogeneous shots using visual tempo cues. A baby video is used as an illustrative example, and the experimental results are encouraged.