Browsing by Author "Wang, Li-Chun"

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3-Cell Network MIMO Architectures with Sectorization and Fractional Frequency Reuse
(2011-06-01)
Wang, Li-Chun
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Yeh, Chu-Jung
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傳播研究所
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電機工程學系
;
Institute of Communication Studies
In this paper, we present a 3-cell network multiple-input multiple-output (MIMO) architecture with fractional frequency frequency (FFR) and a novel tri-sector frequency partition scheme. One fundamental question to apply the network MIMO technique in such a high interference environment is: how many base stations should be coordinated together to provide sufficient performance? We will demonstrate that the FFR-based 3-cell network MIMO architecture with the proposed tri-sector frequency partition can not only effectively overcome the inter-group interference, but can avoid executing the complex multibase-station joint processing for a huge number of cluster of cells at all locations. It will be shown that the proposed 3-cell network MIMO with the rearranged tri-sector frequency partition strategy can outperform the 7-cell network MIMO with omni-directional antennas. Various sector antenna architectures and the method for determining the inner region of the FFR cell planning are also discussed and analyzed on top of the network MIMO system. We hope that this study can provide important insights into the design of the network MIMO systems from the perspectives of architecture and deployment.
A Cellular Neural Network and Utility-Based Radio Resource Scheduler for Multimedia CDMA Communication Systems
(2009-11-01)
Shen, Scott
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Chang, Chung-Ju
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Wang, Li-Chun
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電機工程學系
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Department of Electrical and Computer Engineering
The paper proposes a cellular neural network and utility (CNNU)-based radio resource scheduler for multimedia CDMA communication systems supporting differentiated quality-of-service (QoS). Here, we define a relevant utility function for each connection, which is its radio resource function weighted by a QoS requirement deviation function and a fairness compensation function. We also propose cellular neural networks (CNN) to design the utility-based radio resource scheduler according to the Lyapunov method to solve the constrained optimization problem. The CNN is powerful for complicated optimization problems and has been proved that it can rapidly converge to a desired equilibrium; the utility-based scheduling algorithm can efficiently utilize the radio resource for system, keep the QoS requirements of connections guaranteed, and provide the weighted fairness for connections. Therefore, the CNNU-based scheduler, which determines a radio resource assignment vector for all connections by maximizing an overall system utility, can achieve high system throughput and keep the performance measures of all connections to meet their QoS requirements. Simulation results show that the CNNU-based scheduler attains the average system throughput greater than the EXP [9] and the HOLPRO [5] scheduling schemes by an amount of 23% and 33%, respectively, in the QoS guaranteed region.
A closed-form approximation for capacity of multiuser MIMO broadcast systems: A virtual user approach
(2008)
Wang, Li-Chun
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Yeh, Chu-Jung
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Li, Chi-Fang
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交大名義發表
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National Chiao Tung University
Besides delivering high data rates in a point-to-point scenario, multi-input multi-output (MIMO) antenna techniques can broadcast personalized data to multiple users in the point-to-multipoint scenario. Zero-forcing beamforming (ZFB) is a suboptimal but simple MIMO broadcast technique, which basically decouple the MIMO channel into many parallel single-input single-output (SISO) channels. In this article, we first derive the closed-form expression for the sum rate of the ZFB MIMO broadcast system with random user selection. Secondly, under the condition with finite users, we develop a virtual user approach approximation method for estimating the sum rate of the ZFB MIMO broadcast system with exhaustive user selection. Our results indicate that the proposed analysis method can accurately estimate the optimal sum-rate throughput of ZFB.
A Cloud-Assisted Network Coded Packet Retransmission Approach for Wireless Multicasting
(2014)
Chen, Yu-Jia
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Ho, Wan-Ling
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Wang, Li-Chun
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Wang, Kuo-Chen
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交大名義發表
In this paper, we propose a cloud-assisted network coded packet retransmission approach to reduce the number of packet retransmission in wireless multicasting. It is shown that the efficiency of packet retransmission can be significantly improved if we include network topology information (e.g., network connectivity) during the encoding process of network coding. We leverages the capability of software-defined networking (SDN) to dynamically monitor and control the entire network and design a network topology based network coded packet retransmission (NTNCPR) mechanism. The proposed NTNCPR mechanism can easily calculate the good packet combination based on network topology information.
A concurrent transmission MAC protocol for enhancing throughout and avoiding spectrum sensing in cognitive radio
(2007)
Wang, Li-Chun
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Wang, Chung-Wei
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Lu, Yin-Chih
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Liu, Chuan-Ming
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交大名義發表
For the cognitive radio (CR) network, a fundamental issue is how to identify the spectrum opportunities. First, each CR node determines whether there exists transmission opportunities on unlicensed bands. If not, this node will find other opportunity on licensed bands. Thus, increasing the opportunities of concurrent transmissions in unlicensed bands can reduce the overhead of wide-band sensing. In this paper, based on the carrier sensing multiple access protocol, we propose a novel concurrent transmissions MAC (CT-MAC) protocol to identify the possibility of establishing the second link in the presence of the first link in the unlicensed band. In addition to reducing the overhead of wide-band sensing, the proposed CT-MAC scheme can enhance overall throughput and is backward compatible with the IEEE 802.11 standard.
A Cooperative Multi-Group Priority MAC Protocol for Multi-Packet Reception Channels
(2009-11-01)
Yang, Wen-Fang
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Wu, Jwo-Yuh
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Wang, Li-Chun
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Lee, Ta-Sung
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電子工程學系及電子研究所
Medium access control (MAC) protocol design for cooperative networks over multi-packet reception (MPR) channels is a challenging topic, but has not been addressed in the literature yet. In this paper, we propose a cooperative multi-group priority (CMGP) based MAC protocol to exploit the cooperation diversity for throughput enhancement over MPR channels. The proposed approach can bypass the computationally-intensive active user identification process. Moreover, our method can efficiently utilize the idle periods for packet relaying, and can thus effectively limit the throughput loss resulting from the relay phase. By means of a Markov chain model, the worst-case throughput analysis is conducted. The results allow us to investigate the throughput performance of the proposed CMGP protocol directly in terms of the MPR channel coefficients. Simulation results confirm the system-wide throughput advantage achieved by the proposed scheme, and also validate the analytic results.
A cross-layer investigation for the throughput performance of CSMA/CA-Based WLANs with directional antennas and capture effect
(2007-09-01)
Wang, Li-Chun
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Chen, Anderson
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Huang, Shi-Yen
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電信工程研究所
;
Institute of Communications Engineering
In this paper, we develop a physical/medium-access-control (PHY/MAC) cross-layer analytical model to investigate the throughput performance of the wireless local-area network (WLAN) in a lossy wireless environment. From the PHY-layer perspective, the developed model incorporates the effects of capture and directional antennas, while from the MAC-layer perspective, our approach takes into account the carrier-sense multiple access with collision-avoidance (CSMA/CA) MAC protocol and the effect of the backoff process in the IEEE 802.11 WLAN. We derive explicit analytical expressions for the frame outage and capture probabilities of a directional antenna system in the presence of shadowing and Rayleigh fading. Applying this analysis, we can model the interaction between the PHY and MAC layers more accurately for the infrastructure-based WLAN. The numerical results show that our analytical model can approach that attained by simulations. The proposed cross-layer analytical model not only provides insights into the PHY layer impacts on the throughput of the CSMA/CA MAC protocol but also indicates to how directional antennas can improve the CSMA/CA-based WLAN in terms of antenna beamwidth and the number of radio transceivers.
A Dynamic Security Traversal Mechanism for Providing Deterministic Delay Guarantee in SDN
(2014-01-01)
Chen, Yu-Jia
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Lin, Feng-Yi
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Wang, Li-Chun
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Lin, Bao-Shuh
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電機資訊學士班
For security concerns, a security traversal service can route data flows through a sequences of security devices (middleboxes). In this paper, we identify the problem of delay guarantee in security traversal and propose a scheme to dynamically change the security traversal path. To provide deterministic delay guarantee with minimum virtual machine (VM) and transmission cost, we model this security traversal path determination as a constrained shortest path problem (CSP) and propose an optimal security traversal with middlebox addition (OSTMA) mechanism. Besides, we implement the proposed OSTMA mechanism in an Open Flow network by designing a centralized security traversal controller to dynamically monitor the network condition information and reconfigure the security traversal path. Our experimental results show that the proposed dynamic security traversal scheme can still achieve delay requirements for network topology changes and burst traffic.
A Flexible Analysis and Prediction Framework on Resource Usage in Public Clouds
(2012)
Lin, Chia-Yu
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Chen, Yan-Ann
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Tseng, Yu-Chee
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Wang, Li-Chun
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資訊工程學系
In cloud computing environments, users can rent virtual machines (VMs) from cloud providers to execute their programs or provide network services. While using this kind of cloud services, one of the biggest problems for the users is to determine the proper number of VMs to complete the jobs considering both budget and time. In this paper, we propose a resource prediction framework (RPF), which can help users choose the minimum number of virtual machines to complete their jobs within a user specified time constraint. In order to verify the feasibility of RPF, we have done three case studies, namely parallel frequent pattern growth (FP-Growth), parallel K-means, and Particle Swarm Optimization (PSO). FP-growth, K-means and PSO are data intensive algorithms. These algorithms are typically executed repeatedly with different execution parameters to find the optimal results. When evaluating RPF by these algorithms in cloud environments, we have to modify them to parallel versions. The evaluation results indicate that RPF can successfully obtain the minimum number of VMs with acceptable errors. According to our case studies, the proposed RPF can be adopted by data intensive jobs by providing flexibility to both end users and cloud system providers.
A Fully Integrated Nose-on-a-Chip for Rapid Diagnosis of Ventilator-Associated Pneumonia
(2014-12-01)
Chiu, Shih-Wen
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Wang, Jen-Huo
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Chang, Kwuang-Han
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Chang, Ting-Hau
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Wang, Chia-Min
Ventilator-associated pneumonia (VAP) still lacks a rapid diagnostic strategy. This study proposes installing a nose-on-a-chip at the proximal end of an expiratory circuit of a ventilator to monitor and to detect metabolite of pneumonia in the early stage. The nose-on-a-chip was designed and fabricated in a 90-nm 1P9M CMOS technology in order to downsize the gas detection system. The chip has eight on-chip sensors, an adaptive interface, a successive approximation analog-to-digital converter (SAR ADC), a learning kernel of continuous restricted Boltzmann machine (CRBM), and a RISC-core with low-voltage SRAM. The functionality of VAP identification was verified using clinical data. In total, 76 samples infected with pneumonia (19 Klebsiella, 25 Pseudomonas aeruginosa, 16 Staphylococcus aureus, and 16 Candida) and 41 uninfected samples were collected as the experimental group and the control group, respectively. The results revealed a very high VAP identification rate at 94.06% for identifying healthy and infected patients. A 100% accuracy to identify the microorganisms of Klebsiella, Pseudomonas aeruginosa, Staphylococcus aureus, and Candida from VAP infected patients was achieved. This chip only consumes 1.27 mW at a 0.5 V supply voltage. This work provides a promising solution for the long-term unresolved rapid VAP diagnostic problem.
A joint power and rate assignment algorithm for multirate soft handoffs in mixed-size WCDMA cellular systems
(2007-05-01)
Liao, Ching-Yu
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Chang, Chung-Ju
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Wang, Li-Chun
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Chen, Yih-Shen
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交大名義發表
This paper proposes a joint power and rate assignment (JPRA) algorithm to deal with multirate soft handoffs (SHOs) in mixed-size wideband code division multiple access cellular systems. This JPRA algorithm contains a link proportional power allocation scheme and an evolutionary computing rate assignment method to determine an appropriate allocation of transmission power and service rate for multirate SHOs. It can achieve power balancing among cells better than the conventional site-selection diversity transmission scheme with best effort rate allocation. Simulation results show that the JPRA algorithm can achieve better cell's service coverage! and higher system capacity with and without the measurement errors during the active set selection.
A Joint Subcarrier Power Allocation and Interference Avoidance Code Assignment Strategy for Multi-Rate MC-DS-CDMA with TF-Domain Spreading
(2006)
Chang, Chih-Wen
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Wang, Li-Chun
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電信工程研究所
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Institute of Communications Engineering
In the multi-rate multi-carrier direct sequence code division multiple access (MC-DS-CDMA) system, how to allocate subcarrier power to improve the received signal quality, control the multiple access interference (MAI) at an acceptable level, and simultaneously maintain high call admission is an interesting and challenging issue. In this paper, we propose a joint subcarrier power allocation and code assignment scheme for the synchronous multi-rate MC-DS-CDMA system with time-and frequency-domain spreading. The proposed scheme consists of a subcarrier power allocation method to optimize the received signal power as well as an interference avoidance code assignment strategy to eliminate MAI. For this purpose, we define a performance metric called the MAI coefficient to quantitatively predict the incurred MAI before assigning a spreading code. The simulation results show that the proposed joint subcarrier power allocation and code assignment strategy not only can reach a better received signal quality but also achieve high call admission rate.
A low-complexity beamforming-based scheduling to downlink OFDMA/SDMA systems with multimedia traffic
(2011-04-01)
Chung, Wen-Ching
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Wang, Li-Chun
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Chang, Chung-Ju
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電機工程學系
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Department of Electrical and Computer Engineering
In this paper, we propose a low-complexity beamforming-based scheduling scheme utilizing a semi-orthogonal user selection (SUS) algorithm in downlink orthogonal frequency division multiple access (OFDMA)/space division multiple access (SDMA) systems to support multimedia traffic. One of the challenges in the multidimensional (space, time, and frequency) radio resource allocation problem for OFDMA/SDMA systems is its high complexity, especially to simultaneously satisfy the quality of services (QoS) requirements for various traffic classes. In the literature, the SUS algorithm is usually applied to the single-class traffic environment, but extending the SUS algorithm to the multimedia environment is not straightforward because of the need to prioritize the real-time (RT) users and the non-real-time (NRT) users. To solve this problem, we propose the concept of urgency value to guarantee the fairness of the NRT as well as the best effort (BE) users while satisfying the delay requirement for the RT users. Simulation results show that, when traffic load is greater than 0.5, the proposed scheduling algorithm can improve the fairness performance by more than 100% over the most recently proposed algorithms.
A Low-Complexity CDD-based Frequency Selective Scheduling with Efficient Feedback for Downlink OFDMA Systems
(2012)
Chen, Yu-Fan
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Sheen, Wern-Ho
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Wang, Li-Chun
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傳播研究所
;
Institute of Communication Studies
Cyclic-delay diversity (CDD) based frequency-selective scheduling is an effective technique to increase system capacity with low complexity. By increasing the channels' frequency selectivity with cyclic delays, the merit of multi-user diversity can be exploited more effectively in the system. This paper aims to optimize the design of the CDD-aided frequency-selective scheduling for downlink OFDMA systems. First, a low-complexity search of CD-values is proposed that results in a higher system capacity than the existing methods. Second, a new feedback method is proposed based on the principle of proportional-fair, where users who currently enjoy more downlink source are allotted less uplink resource for feedback. The method is shown to provide a better tradeoff between system capacity and fairness than the traditional methods, under a fixed feedback overhead. The effectiveness of the proposed method is verified by extensive computer simulations.
A Low-Complexity Uplink Multiuser Scheduling for Virtual MIMO Systems
(2016-01)
Chang, Hsien-Wen
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Wang, Li-Chun
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電機學院
;
College of Electrical and Computer Engineering
Multiple-input-multiple-output (MIMO) antenna systems can provide the spatial multiplexing gain to enhance spectrum efficiency, but they are hampered by the fact that the number of antennas in a hand-held mobile device is smaller than that of a base station. To overcome this issue, the virtual MIMO techniques arrange a group of single-antenna mobile users to become a virtual multiple-antenna entity. However, existing virtual MIMO techniques are either applicable only to a small group or computationally too complex. We propose a low-complexity user scheduling for virtual MIMO with a flexible group size. In comparison with existing approaches, our results show that the proposed user scheduling for virtual MIMO can reduce the floating operations by 96% in the case of a 6 x 6 virtual MIMO system while maintaining the same throughput and fairness performance.
A Multi-Group Priority Based Cooperative MAC Protocol for Multi-Packet Reception Channels
(2009)
Yang, Wen-Fang
;
Wu, Jwo-Yuh
;
Wang, Li-Chun
;
Lee, Ta-Sung
;
電信工程研究所
Medium access control (MAC) protocol design for cooperative networks over multi-packet reception (MPR) channels is a challenging topic, but has not been addressed in the literature yet. In this paper, we propose a MAC protocol to exploit the cooperation diversity for throughput enhancement over MPR channels. The proposed approach can efficiently utilize the idle periods for packet relaying, and can thus effectively limit the throughput loss resulting from the relay phase. By means of a Markov chain model, the worst-case throughput analysis is conducted. Specifically, we derive (i) a closed-form upper bound for the throughput penalty of the direct link that is caused by the interference of concurrent packet relay transmission; (ii) a closed-form lower bound for the throughput gain that a user with packet transmission failure can benefit thanks to cooperative packet relaying. The results allow us to investigate the throughput performance of the proposed protocol directly in terms of the MPR channel coefficients. Simulation results confirm the system-wide throughput advantage achieved by the proposed scheme, and also validate the analytic results.
A multigroup priority queueing MAC protocol for wireless networks with multipacket reception
(2008)
Yang, Wen-Fang
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Wu, Jwo-Yuh
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Wang, Li-Chun
;
Lee, Ta-Sung
;
電信工程研究所
Relying on a simple flag-assisted mechanism, a multigroup priority queueing (MGPQ) medium access control (MAC) protocol is proposed for the wireless networks with multipacket reception ( MPR). The proposed MGPQ scheme is capable of overcoming two major performance bottlenecks inherent in the existing MPR MAC protocols. First, the proposed solution can automatically produce the list of active users by observing the network traffic conditions, remove the need of active user estimation algorithm, and thus can largely reduce the algorithm complexity. Second, the packet blocking constraint imposed on the active users for keeping compliant with prediction is relaxed. As a result, the proposed MGPQ is not only applicable to both homogeneous and heterogeneous cases, but also outperforms the existing MPRMAC protocols. Simulation results show that the network throughput can be improved by 40% maximum and 14% average as compared with the well- known dynamic queue (DQ) MAC protocol.
A PATCH-BASED CONTRACTION PROCESS FOR THE IMPROVEMENT OF IMAGE MATTING
(2017-01-01)
Syu, Jia-Hao
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Wang, Sheng-Jyh
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Wang, Li-Chun
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電子工程學系及電子研究所
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電信工程研究所
In this paper, we propose a patch-based contraction process for the improvement of image matting. Given an input image and a trimap, the proposed contraction process quickly refines the trimap by reclassifying the alpha values of the undetermined pixels into "foreground", "background", or "undetermined", based on the feature similarity of the undetermined pixels with respect to the foreground/background regions. The refinement of trimap causes the shrinkage of undetermined regions and may reveal more foreground/background information across isolated regions. Based on the refined trimap, the image matting algorithm can better estimate the alpha values of the image. Experimental results show that the proposed patch based process provides an effective and efficient way to obtain a refined trimap and the use of the trimap refinement improves the performance of image matting.
A Personal Emergency Communication Service for Smartphones using FM transmitters
(2013-01-01)
Chen, Yu-Jia
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Lin, Chia-Yu
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Wang, Li-Chun
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交大名義發表
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National Chiao Tung University
Communication networks such as cellular phone networks are quite likely to be severely damaged during a large-scale of disaster, making SOS message dissemination to rescue authorities extremely difficult. In this paper, we first propose a FM radio-based emergency communication service through the integration of FM transmitters into smartphones. FM radio provides a number of advantages such as longer propagation length and less susceptible to obstacles, making it suitable for broadcasting SOS messages. Besides, we design Morse code-based SOS message dissemination using FM transmitters (MCSOS-FM) and its corresponding communication procedure for the emergency communication service in order to improve communication range, victim localization and evacuation route planning. The combination of FM radio and Morse code is completely compatible with the current radio system equipped by rescue workers, and thus increases the possibilities of successful receiving and recognizing SOS messages. Our experiment result based on smartphone implementation shows that the proposed emergency communication service is cost effective and energy efficient with relatively large communication range.
A Privacy-Preserved Joint Group Time Scheduling Mechanism for Mobile Social Applications
(2013)
Chen, Yu-Jia
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Lin, Chia-Yu
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Wang, Li-Chun
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交大名義發表
;
National Chiao Tung University
In this paper, we develop a privacy preserving mechanism for a scheduling service for a group of users, which can compute the joint available time based on users' calendar information. We also propose a weighted voting game with partially homomorphic encryption (WVGPHE) scheme to protect the privacy of users' calendar information as well as users' weight. Even with the privacy protection, our experimental results show that the proposed scheme is still very computational and bandwidth efficient enough to provide immediate group meeting in mobile communications environments.