Browsing by Author "Chang, Tsung-Hui"

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Joint Power and Admission Control for Spectral and Energy Efficiency Maximization in Heterogeneous OFDMA Networks
(2016-05)
Lai, Wei-Sheng
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Chang, Tsung-Hui
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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
This paper studies the joint power and admission control (JPAC) problem for orthogonal frequency division multiplexing access (OFDMA) based heterogeneous networks. We consider a small-cell network coexisting with a macro-cell network. Small cells are not only subject to constraints imposed by interference with the macro-cell network but also by the minimum achievable rates of secondary user equipment (SUE). The goal is to admit as many SUE as possible to satisfy the minimum rate requirements while maximizing a certain network utility associated with the admitted SUE. To this end, we formulate two JPAC problems aimed at maximizing the network spectral efficiency (SE) and network energy efficiency (EE), respectively, where the latter has not been considered before. In light of the NP-hardness of the admission control and SE maximization problems, prior works have often treated the two problems separately without considering OFDMA constraints. In this paper, we propose a novel joint optimization framework that is capable of considering power control, admission control, and resource block assignment simultaneously. Via advanced convex approximation techniques and sequential SUE deflation procedures, we develop efficient algorithms that jointly maximize the SE/EE and the number of admitted SUE. Simulation results show that the proposed algorithms yield substantially higher SE/EE and admit more SUE than existing methods.
Lifetime Maximization for Uplink Transmission in UAV-Enabled Wireless Networks
(2019-01-01)
Chen, Kuo-Ming
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Chang, Tsung-Hui
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Lee, Ta-Sung
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交大名義發表
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電信工程研究所
The use of unmanned aerial vehicles (UAVs) as aerial wireless base stations has been recognized as an effective approach to on-demand deployment for providing services during a temporary event or emergency situation. High UAV mobility can be fully utilized to create line-of-sight connection and alleviate cross-link interference. While most of the prior works have studied UAV deployment, trajectory design and resource allocation strategies for improving the network throughput or energy efficiency, in this paper, we are interested in prolonging the lifetime of ground users for communications. The lifetime is defined as the communication time for the ground user before its battery is exhausted. We consider a frequency division multiplexing (FDM) uplink system where the ground users are served by multiple UAVs. We formulate a joint user association, power control, bandwidth allocation and UAV deployment problem for lifetime maximization, and propose an efficient approximation algorithm through judicious problem reformulation and successive convex approximation (SCA) techniques. For the scenario with only a single UAV, we show that the problem can be globally solved by simple bisection. Simulation results are presented to demonstrate that the proposed algorithms can achieve near-optimal performance and greatly outperform the heuristic methods.
Machine Learning Based Automatic Diagnosis in Mobile Communication Networks
(2019-10-01)
Chen, Kuo-Ming
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Chang, Tsung-Hui
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Wang, Kai-Cheng
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Lee, Ta-Sung
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交大名義發表
The self-healing function in self-organizing networks can not only detect the presence of fault conditions but also diagnose the root causes in a fully autonomous fashion. In this paper, we propose a machine learning based diagnosis algorithm that uses network condition indicators such as key performance indicators and performance management counters for network condition diagnosis. The proposed algorithm judiciously combines the classical supervised softmax neural network (SNN) and support vector machine (SVM), and therefore can be efficiently implemented by off-the-shelf tools while achieving promising diagnosis performance. In particular, the proposed algorithm combines the features extracted from SNN and SVM, and is able to robustly diagnose fault conditions with different levels of severity. Besides, the proposed algorithm can also handle complex scenarios where there is more than one fault condition present at the same time. Considering that data with labels of multiple faults are not available in general, we further propose a simple retraining procedure which allows the proposed algorithm to perform multi-fault diagnosis even when the training data are only single labeled. Simulation results demonstrate that the proposed algorithms provide desired diagnosis performance in both single-fault and multi-fault scenarios and outperform the traditional scoring based methods.
Robust Hybrid Beamforming with Phased Antenna Arrays for Downlink SDMA in Indoor 60 GHz Channels
(2013-09-01)
Wu, Sau-Hsuan
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Chiu, Lin-Kai
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Lin, Ko-Yen
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Chang, Tsung-Hui
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電信工程研究所
A hybrid architecture is presented for downlink beamforming (BF) with phased antenna arrays (PAA) in indoor 60 GHz spatial division multiple access (SDMA) channels. To manage the multiple access and inter-symbol interferences (MAI/ISI) encountered in SDMA with limited feedbacks, a cost-effective time-domain hybrid BF (HBF) method is presented to exploit the directivity provided by PAA in radio frequency (RF) beam patterns and the spatial diversity offered by multiple baseband processing modules. To maintain signal qualities under unpredictable MAI/ISI in wireless multimedia streaming to which indoor 60 GHz radio mainly applies, robust beamformers are designed to maintain the signal to interference-plus-noise ratio (SINR) for each user with minimum total transmit power. The percentages in which the target SINRs can be satisfied with the proposed HBF schemes are found sensitive to uncertainties in the phase shifters of PAA. Two kinds of robust formulations are thus proposed to jointly combat the MAI, ISI and phase uncertainties. Robust beamformers with semi closed-form expressions can be obtained with a nonlinear kind of them, whose SINR satisfaction ratio can attain 80% or more by extensive simulations in an indoor two-user 60 GHz environment if RF beam patterns of the users do not highly overlap in space.