Browsing by Author "Chung, Wei-Ho"

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A closed-form phase-comparison ML DOA estimator for automotive radar with one single snapshot
(2013)
Huang, Chung-Jung
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Dai, Chia-Wei
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Tsai, Tsung-Yu
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Chung, Wei-Ho
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Lee, Ta-Sung
In automotive radar systems, only a small number of snapshots are available for direction-of-arrival (DOA) estimation in high mobility scenarios. We here propose a closed-form single-snapshot maximum likelihood (ML) DOA estimator based on the phase-comparison technique. The estimator can be effective in a wide field-of-view (FOV) scenario and is robust to gain-mismatch effects among antenna elements. Computer simulations are conducted to confirm the effectiveness of the proposed method.
A geometry based efficient decoder for underdetermined MIMO systems
(2015-06-01)
Huang, Chung-Jung
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Lee, Chang-Shen
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Chung, Wei-Ho
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Lee, Ta-Sung
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電機資訊學士班
In this paper, a geometry based decoder with low decoding complexity and exact maximum-likelihood (ML) performance is proposed for underdetermined multiple-input multiple-output (MIMO) systems. In the proposed decoder, an underdetermined MIMO system can be divided into a multiple-input single-output (MISO) sub-system and a regular MIMO sub-system in which numbers of transmit and receive antennas are equal. An efficient slab search algorithm (ESSA) is adopted to efficiently obtain valid candidate points in the MISO sub-system. By adopting ESSA in the MISO sub-system and sphere decoding algorithm (SDA) in the MIMO sub-system, ML solution of underdetermined MIMO system can be obtained with low computational complexity. To further reduce the computational complexity, a near-ML SDA is proposed to more efficiently find the candidate points in the MIMO sub-system. In addition, an optimal preprocessing technique is proposed from the geometrical perspective and the comprehensive analysis on the complexity reduction is also provided. Simulation results indicate that the proposed approach significantly reduces the complexity as compared to existing ML decoders, particularly for systems with large number of antennas and/or high-order constellations. (C) 2015 Elsevier Inc. All rights reserved.
A Low Complexity Antenna Selection Algorithm for Energy Efficiency in Massive MIMO Systems
(2015)
Tai, Tzu-Hao
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Chung, Wei-Ho
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Lee, Ta-Sung
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電信工程研究所
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Institute of Communications Engineering
Massive multi-input multi-output (MIMO) system adopting large amount of antennas is a promising technique to improve spectral efficiency and energy efficiency for next generation wireless communication systems. However, the power consumptions of the radio frequency (RF) chains can be huge, which poses great challenges. In this paper, we consider the problem of transmit RF chain configuration with the goal to maximize energy efficiency under total power constraint in massive MIMO systems. The RF chain configuration can be decided by applying antenna selection methods. Considering the trade-off between performance and complexity, we propose the norm-and-correlation-based selection algorithm with low complexity for energy efficiency maximization. Our selection metric considers the effect of the norm of each channel column and correlation between columns while attaining low computational complexity. Simulation results validate the advantages of the proposed algorithm.
A Low Complexity Configuration Selection Algorithm in IA-aided Uplink Coordinated Multipoint Systems
(2014-01-01)
Lee, Ming-Chun
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Huang, Chung-Jung
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Chung, Wei-Ho
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Lee, Ta-Sung
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電機資訊學士班
This work investigates the configuration selection in IA-aided UL CoMP systems which pursues the maximal achievable sum rate. The configuration is defined by the number of data streams transmitted in each user. Intuitively, the solution can be found by exhaustively calculating the achievable sum rate for all the possible configurations, and select the configuration leading to the maximal achievable sum rate. The exhaustive search method is infeasible due to its high complexity. Based on the characteristics of IA-aided UL CoMP systems, an algorithm is proposed to obtain the configuration with extremely low complexity, and the proposed approach achieves comparable performance as in exhaustive method.
A Survey on Deep Learning-Based Vehicular Communication Applications
(1970-01-01)
Lin, Chia-Hung
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Lin, Yu-Chien
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Wu, Yen-Jung
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Chung, Wei-Ho
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Lee, Ta-Sung
Besides the use of information transmission, vehicular communications also perform an essential role in intelligent transportation systems (ITS) for exchanging critical driving information among end users, vehicles, and infrastructures. Moreover, to enhance the understanding of the local environment, increasingly more data are collected by sensors, inducing an extensive use of deep learning (DL)-based algorithms in ITS. To further promote the development of DL-based algorithms in ITS, in this paper, we present a concise introduction of DL technologies. Then, we conduct an in-depth investigation on two popular DL-based applications used in ITS, traffic flow forecasting and trajectory prediction, focusing onwhenandhowthe authors employ different DL models and training schemes in these tasks. Finally, we raise two existing problems while employing DL-based algorithms in practical ITS and further discuss certain recent advances in DL-based research to tackle these challenges. To encourage more researchers to focus on the development of DL-based algorithms in ITS for a better world, we hope this paper can be treated as an informational material for prospective researchers, which contains the essential background knowledge of DL-based ITS applications; we also hope this paper will encourage experienced researchers to counter the open challenges and achieve a technical breakthrough to ITS.
BER Analysis for Spatial Modulation in Multicast MIMO Systems
(2016-07)
Lee, Ming-Chun
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Chung, Wei-Ho
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Lee, Ta-Sung
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電機學院
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College of Electrical and Computer Engineering
In this paper, we investigate the bit error rate (BER) for multicast multiple-input multiple-output (MIMO) systems, employing spatial modulation (SM) and its variants, called multicast SM-type MIMO systems, in Rayleigh fading channels. The system BER, here, is derived by first attaining the BER of the worst receiver of each channel realization set, and then averaging over all possible sets. We first consider the uncorrelated channels. By exploiting the system statistics, a tight BER upper bound is proposed and the diversity is discussed for the systems. We then perform the asymptotic analysis, and show that the BER of the multicast SM-type MIMO system can be alternatively analyzed by analyzing the simple point-to-point SM-type MIMO system with Weibull fading channels. Through this property, a closed-form asymptotic BER upper bound is provided and the impact of the receiver number on BER is analyzed. Subsequently, our investigation is extended to correlated channels where all the receivers share the same correlation statistics. The BER analysis is performed again through the framework similar to the uncorrelated case. In the analysis, the tight upper bound is derived and the effect of correlations is analyzed. Moreover, we provide an explicit expression for the SNR degradation caused by the receive correlation through the analysis. Finally, simulations are exploited to evaluate the BER of the multicast SM-type MIMO systems and validate the analyses.
Distributed Channel Access Schemes for Multi-Channel ALOHA Cognitive Radio Networks
(2015)
Lee, Chang-Shen
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Chung, Wei-Ho
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Lee, Ta-Sung
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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
In this paper, the distributed channel access schemes for ALOHA-based cognitive radio networks are considered. In the considered system, time is divided into frames, which are further divided into sensing phase and transmission phase. We derive channel sensing policy in the sensing phase, and channel access policy in the transmission phase for a secondary user (SU) to maximize its throughput. To mitigate high complexities of the above scheme, we propose a threshold-based channel access scheme. In this scheme, an appropriate threshold is set based on channel occupancy information and channel state information, and only channels providing potentially high throughput will be sensed and accessed. The proposed schemes are fully distributed, i.e., no extra information exchange is needed among SUs, which is a highly desired and beneficial property. Simulation results confirm that the proposed schemes outperform prior random access schemes.
Distributed channel assignment for network MIMO: game-theoretic formulation and stochastic learning
(2015-05-01)
Tseng, Li-Chuan
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Chien, Feng-Tsun
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Chang, Ronald Y.
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Chung, Wei-Ho
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Huang, ChingYao
The cooperative frequency reuse among base stations (BSs) can improve the system spectral efficiency by reducing the intercell interference through channel assignment and precoding. This paper presents a game-theoretic study of channel assignment for realizing network multiple-input multiple-output (MIMO) operation under time-varying wireless channel. We propose a new joint precoding scheme that carries enhanced interference mitigation and capacity improvement abilities for network MIMO systems. We formulate the channel assignment problem from a game-theoretic perspective with BSs as the players, and show that our game is an exact potential game given the proposed utility function. A distributed, stochastic learning-based algorithm is proposed where each BS progressively moves toward the Nash equilibrium (NE) strategy based on its own action-reward history only. The convergence properties of the proposed learning algorithm toward an NE point are theoretically and numerically verified for different network topologies. The proposed learning algorithm also demonstrates an improved capacity and fairness performance as compared to other schemes through extensive link-level simulations.
Distributed Spectrum Trading in Multiple-Seller Cognitive Radio Networks
(2014)
Tseng, Li-Chuan
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Chien, Feng-Tsun
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Chang, Ronald Y.
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Chung, Wei-Ho
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電子工程學系及電子研究所
This paper studies spectrum trading in cognitive radio networks in which multiple service providers (SPs) sell unused spectrum to multiple unlicensed secondary users (SUs). Motivated by the nature of the problem with new considerations, spectrum trading is modeled as a multi-leader multi-follower expected Stackelberg game with two levels of competition. The SPs as leaders compete in offering subscription prices (upper-level subgame) and the SUs as followers compete in selecting service from the SPs (lower-level subgame). The lower-level subgame incorporates the time-varying spectrum availability as the external state so that the proposed scheme does not require knowledge of dynamic spectrum availability. To achieve self-organized network operation, we propose decentralized, stochastic learning-based algorithms for the game. The convergence properties of the proposed algorithms toward the Nash equilibrium (NE) are theoretically and numerically studied. The proposed scheme demonstrates good utility performance for the SUs as compared to other service selection schemes.
Efficient Interference Alignment Aided Transceiver Design for LTE-A Uplink Coordinated Multipoint Systems
(2013-01-01)
Huang, Chung-Jung
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Chung, Gang-Han
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Chung, Wei-Ho
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Lee, Ta-Sung
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電子工程學系及電子研究所
An efficient interference alignment (IA) aided transceiver design algorithm for uplink (UL) coordinated multipoint (CoMP) systems is proposed to mitigate interference. We use the block QR decomposition (BQRD) to resolve the interdependency of precoders among user equipment (UE) through the successive interference cancellation (SIC) technique. To further improve the efficiency, an additional constraint is employed by a projection operation. Simulation results show that the proposed algorithm substantially reduces iterations and obtain comparable performance as in conventional approaches.
Energy Efficient Hybrid Precoding for Multi-User Massive MIMO Systems Using Low-Resolution ADCs
(2016)
Lin, Li-Feng
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Chung, Wei-Ho
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Chen, Hsin-Jung
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Lee, Ta-Sung
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電信工程研究所
Millimeter wave (mmWave) communication is an emerging technique to provide large bandwidth in cellular systems. However, mmWave signals experience more pathloss than the microwave signals adopted in current wireless communications. Therefore, a mmWave system tends to adopt a large number of antennas to combat pathloss with high beamforming gain. In conventional multi-antenna systems, both beamforming and precoding are done digitally in baseband. The high cost and power consumption of certain components in mmWave systems render conventional architecture infeasible. In this paper, we consider low complexity hybrid analog/digital precoding and low-resolution ADCs in downlink multiuser mmWave MIMO systems. We propose a new transmission scheme involving rationale of beamspace MIMO communications and beam selection. We also develop a low complexity beam selection algorithm and evaluate adaptive selection on the RF configuration for energy efficiency (EE) optimization. Our analysis and simulation results show that the proposed scheme can significantly reduce system complexity and achieve good performance on energy efficiency and detection.
Energy Efficient Multi-User Millimeter Wave MIMO Systems Using Tree Search Hybrid Precoding and Few-Bit ADCs
(2018-10-01)
Chen, Hsin-Jung
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Lin, Li-Feng
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Chung, Wei-Ho
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Lee, Ta-Sung
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電信工程研究所
Millimeter wave (mmWave) communication is an emerging technique to provide large bandwidth in cellular systems. However, mmWave signals experience more pathloss than the microwave signals adopted in current wireless communications. Therefore, a mmWave system tends to adopt a large number of antennas to combat pathloss with high beamforming gain. In conventional multi-antenna systems, both beamforming and precoding are done digitally in baseband. The high cost and power consumption of certain components in mmWave systems render conventional architecture infeasible. In this paper, we consider low complexity hybrid analog/digital precoding and low-resolution analog-digital converters (ADCs) (1-3 bits) in downlink multiuser mmWave MIMO systems. We propose a new transmission scheme involving rationale of beamspace MIMO communications and beam selection. We also develop a low complexity beam selection algorithm and evaluate adaptive selection on the RF configuration for energy efficiency (EE) optimization. Our analysis and simulation results show that the proposed scheme can significantly reduce system complexity and achieve good performance on energy efficiency and detection.
Energy Efficient Norm-and-Correlation-based Antenna Selection Algorithm in Spatially Correlated Massive Multi-User MIMO Systems
(2017-01-01)
Tai, Tzu-Hao
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Chen, Hsin-Jung
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Chung, Wei-Ho
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Lee, Ta-Sung
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電信工程研究所
Massive multiuser multi-input multi-output (MUMIMO) system adopting large amount of antennas is a promising technique to improve spectral efficiency and energy efficiency for next generation wireless communication systems. In practice, the channels composed of pairs of transmit and receive antennas are often correlated and computational complexity is one of the critical concern in implementation issue. Hence, antenna selection techniques can be adopted to improve system performance. In this paper, we propose a norm-and-correlation-based selection algorithm for energy efficiency maximization to decide transmit RF chain configuration under the total power constraint in massive MU-MIMO systems.
Exact Performance of NOMA with Full-Duplex Energy Harvesting Relaying in Nakagami-m Frequency-Selective Fading Channel
(2018-01-01)
Wang, Szu-Liang
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Wang, Chih-Yu
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Chung, Wei-Ho
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交大名義發表
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National Chiao Tung University
In this paper, the NOMA transmission with fullduplex energy harvesting relaying ( FDEHR) is investigated. Closed-form expressions for the outage probability of the near and far users are presented over Nakagami-m frequency-selective fading channel. Monte Carlo simulations are provided throughout to verify the accuracy of the derivations. Simulation and numerical results demonstrate that the near user without FDEHR possesses lower outage probability than the far user. While the outage performance of the far user could be improved and better than the near user with FDEHR.
Generalized Precoder Design Formulation and Iterative Algorithm for Spatial Modulation in MIMO Systems With CSIT
(2015-04-01)
Lee, Ming-Chun
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Chung, Wei-Ho
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Lee, Ta-Sung
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電機資訊學士班
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Undergraduate Honors Program of Electrical Engineering and Computer Science
In this paper, we propose two generalized precoder designs to enhance the bit error rates for the general category of spatial modulation (SM) in multiple-input multiple-output (MIMO) systems with channel state information at the transmitter (CSIT). We investigate typical SM-MIMO systems and propose two optimization formulations for designing precoders. Our design rationale for the first formulation is to maximize the minimum Euclidean distance among codewords; for the second formulation, it is to minimize the total signal power for the lower-bounded Euclidean distances among codewords. Since both formulations are non-convex and their optimal solutions are generally intractable, we propose an algorithm that acquires effective solutions by iteratively solving the alternative convex problem linearized and approximated from the original non-convex problem. Discussions on complexity analysis, performance comparisons, design challenges, and robustness in imperfect CSIT are then provided. By generalizing the design formulations, the proposed precoder designs can be extended to generalized SM, which completes the investigation for virtually all SM-type systems. Simulation results show that the proposed designs improve the performance of SM-/GSM-MIMO systems and outperform existing precoding methods with a potentially higher complexity cost.
Geometric Approach to Passive Ranging in Underwater Localization Systems
(2018-01-01)
Lin, Yu-Chien
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Chen, Hsin-Jung
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Chung, Wei-Ho
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Lee, Ta-Sung
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交大名義發表
The use of underwater surveillance systems is critical for effective command of maritime power. Ships or submarines equipped with active sonar systems emit sounds to obtain range or angle information. Unfortunately, security issues may occur in this situation. To meet the security considerations for obtaining location information, a passive tracking or localization technique, the bearings-only target motion analysis (BO-TMA), was developed along with a given direction of arrival (DOA) estimation. With limited resources, a passive ranging approach with only a single passive array is practical, and is considered in this paper. In this paper, we propose a new geometric approach and derive a closed-form solution, which can be implemented in BO-TMA algorithms for initiation and updating the range of targets with a single passive sensor. Finally, analysis and simulation results showed that the proposed scheme can achieve good performance and is effective for a short operation time, such that an observer can move with more flexibility in combat scenarios. The proposed algorithm can further be performed by trackers to generate the initiation information and hence reduce the estimation bias.
Limited Feedback Precoder Design for Spatial Modulation in MIMO Systems
(2015-11-01)
Lee, Ming-Chun
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Chung, Wei-Ho
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Lee, Ta-Sung
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電機資訊學士班
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Undergraduate Honors Program of Electrical Engineering and Computer Science
We investigate the limited feedback precoding for spatial modulation in multiple-input multiple-output systems via using the codebook. To enhance bit error rate, we propose a codebook design which iteratively trains the codebook by two criteria. The first criterion is to partition the training set by assigning the best codeword to each training symbol; the second criterion is to optimize the codewords according to the assigned training symbols. Simulation results show that the proposed codebook design can effectively improve the SM-MIMO systems with small overhead.
Linear transceiver design in uplink coordinated multipoint multiple-input multiple-output systems
(2014-11-27)
Lee, Ming-Chun
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Chung, Wei-Ho
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Huang, Chung-Jung
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Chung, Gang-Han
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Lee, Ta-Sung
The authors investigate linear transceiver design in uplink (UL) coordinated multipoint transmission and reception (CoMP) multiple-input multiple-output (MIMO) systems with joint detections. A two-stage design algorithm is proposed by exploiting the technique of interference alignment, optimising the structure of the effective channel and employing power loading, with the goal to achieve high throughput and convergence performance. In contrast to conventional CoMP transceiver design, which is investigated under a predefined number of data streams transmitted by each user, the authors further investigate the selection of the number of data streams, called the configuration selection, and propose a corresponding low-complexity algorithm. By combining the proposed linear transceiver algorithm and low-complexity configuration selection algorithm, this work presents a new practical framework for linear transceiver design in UL CoMP MIMO systems. The simulation results confirm that the proposed algorithms achieve higher sum-rate performance than prior linear transceivers used in UL CoMP MIMO systems. Furthermore, the proposed transceiver offers comparable performance to existing IA-aided transceivers with significantly faster convergence.
Local Cyber-Physical Attack for Masking Line Outage and Topology Attack in Smart Grid
(2019-07-01)
Chung, Hwei-Ming
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Li, Wen-Tai
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Yuen, Chau
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Chung, Wei-Ho
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Zhang, Yan
Malicious attacks in the power system can eventually result in a large-scale cascade failure if not rectified in a timely manner. These attacks, which are traditionally classified into physical and cyber attacks, can be avoided by using the latest advanced detection mechanisms. However, a new threat called cyber-physical attacks jointly targets both the physical and cyber layers of the system to interfere with the operations of the power grid is more malicious than traditional attacks. In this paper, we propose a new cyber-physical attack strategy where the transmission line is first physically disconnected, the line-outage event is masked to mislead the control center into detecting this as an obvious line outage at a different position in the local area of the power system. Therefore, the topology information in the control center is interfered with as a result of our attack. We also propose a novel procedure for selecting vulnerable lines and analyze the observability of our proposed framework. Our proposed method can effectively and continuously deceive the control center into detecting fake line-outage positions, and thereby increase the chance of cascade failure because the attention is given to the fake outage. The simulation results validate the efficiency of our proposed attack strategy.
Network Selection in Cognitive Heterogeneous Networks Using Stochastic Learning
(2013-12-01)
Tseng, Li-Chuan
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Chien, Feng-Tsun
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Zhang, Daqiang
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Chang, Ronald Y.
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Chung, Wei-Ho
Coexistence of multiple radio access technologies (RATs) is a promising paradigm to improve spectral efficiency. This letter presents a game-theoretic network selection scheme in a cognitive heterogeneous networking environment with time-varying channel availability. We formulate the network selection problem as a noncooperative game with secondary users (SUs) as the players, and show that the game is an ordinal potential game (OPG). A decentralized, stochastic learning-based algorithm is proposed where each SU's strategy progressively evolves toward the Nash equilibrium (NE) based on its own action-reward history, without the need to know actions in other SUs. The convergence properties of the proposed algorithm toward an NE point are theoretically and numerically verified. The proposed algorithm demonstrates good throughput and fairness performances in various network scenarios.