Browsing by Author "Chang, Hsien-Wen"

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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
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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 New SDN-Based Architecture and Authentication Method for Taiwan High-Speed Rail
(2017-01-01)
Lin, Yi-Hao
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Ho, Ping-Fan
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Chen, Jyh-Cheng
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Yang, Jen-Shun
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Chang, Hsien-Wen
The urgency of improving user experience has reached a critical point in the high-speed rail environment. However, there is little literature considering authentication failure problems in the high-speed rail environment. In this paper, we present a new authentication architecture for Taiwan High-Speed Rail (THSR). This new authentication architecture applies Software-Defined Network (SDN)-based principles to an outbound LTE gateway platform. We propose a post-authentication method suitable for the high-speed mobile environment, such as THSR. The proposed architecture and method can improve user experience regarding successful authentication ratio, authentication latency, and network access latency compared to the existing system.
Achieving Arbitrary Multiplexing Rates for MIMO-OFDM Systems by Hybrid Cyclic Delay Diversity
(2013-03-01)
Chang, Hsien-Wen
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Wang, Li-Chun
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電機資訊學士班
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Undergraduate Honors Program of Electrical Engineering and Computer Science
This paper proposes a new hybrid cyclic delay diversity (HCDD) scheme for multiple input multiple output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. Unlike the existing double space time transmit diversity (DSTTD) and stacked cyclic delay diversity (SCDD) schemes that are suitable for integer multiplexing rates, the proposed HCDD scheme can achieve arbitrary non-integer multiplexing rates. Our results demonstrate that the HCDD scheme can provide flexibility in selecting the required number of transmitting antennas and in adjusting diversity and multiplexing gains to match various users requirements. The advantages of the proposed HCDD, including the flexible rate assignment and less complex receivers, are presented in applications of scalable video broadcasting (SVB).
Adaptive Handoff Initiation Method for Improving Throughput in Data-Oriented Communications Networks
(2011-01-01)
Chang, Hsien-Wen
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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
Handoff is the process to transfer an ongoing call for a mobile station from the serving base station to another base station. Most conventional handoff initiation methods are based on a fixed hysteresis to decide when the handoff process is initiated. A suitable hysteresis for handoff initiation can simultaneously reduce handoff rate and dropping probability. However, conventional handoff initiation method is not suitable for emerging data-oriented communication systems. In this paper, a novel handoff initiation method is proposed in an attempt to increase data rates. The proposed handoff initiation method is not only based on signal quality measurement, but also handoff interruption time. According to our simulation results, the proposed method can yield higher data rates and has more robust performances than other handoff initiation methods.
Multi-operator Fairness in Transparent RAN Sharing
(2018-01-01)
Lin, Ying-Dar
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Chien, Hsu-Tung
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Chang, Hsien-Wen
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Lai, Chia-Lin
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資訊工程學系
Radio access network (RAN) sharing attracts much attention from telecom operators. However, current mechanisms applied to RAN sharing do not consider fairness among operators such that the RAN is not fairly shared, and either under-or over-utilized. Fairness cannot be guaranteed among operators because resources are distributed on a first-come-first-serve basis. "Soft-partition with Blocking and Dropping" (SBD)" is proposed to offer inter-operator fairness based on a "soft-partition" concept. Subscribers to an operator may overuse the predefined service-level-agreement (SLA) when the shared RAN is under-utilized, but become blocked or even dropped when over-utilized. According to our simulation results, SBD maintains inter-operator fairness at 0.997, even better than hard-partition at 0.98 and much better than no-partition at 0.6. Meanwhile, it retains high utilization of shared RAN at 98%. SBD reduces blocking rate from 35% of hard partition to almost 0%, while controlling dropping rate at 5%.
Multi-Operator Fairness in Transparent RAN Sharing by Soft-Partition With Blocking and Dropping Mechanism
(2018-12-01)
Chien, Hsu-Tung
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Lin, Ying-Dar
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Chang, Hsien-Wen
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Lai, Chia-Lin
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資訊工程學系
Radio access network (RAN) sharing has attracted significant attention from telecom operators as a means of accommodating data surges. However, current mechanisms for RAN sharing ignore the fairness issue among operators, and hence the RAN may be under- or over-utilized. Furthermore, the fairness among different operators cannot be guaranteed, since the RAN resources are distributed on a first come, first served basis. Accordingly, the present study proposes a "soft-partition with blocking and dropping" (SBD) mechanism that offers inter-operator fairness using a "soft-partition" approach. In particular, the operator subscribers are permitted to overuse the resources specified in the predefined service-level-agreement when the shared RAN is under-utilized, but are blocked (or even dropped) when the RAN is over-utilized. The simulation results show that SBD achieves an inter-operator fairness of 0.997, which is higher than that of both a hard-partition approach (0.98) and a no-partition approach (0.6) while maintaining a shared RAN utilization rate of 98%. Furthermore, SBD reduces the blocking rate from 35% (hard partition approach) to almost 0%, whereas controlling the dropping rate at 5%. Notably, the dropping rate can be reduced to almost 0% using a newly proposed bandwidth scale down procedure.
On the Performance of Hybrid Stacked Cyclic Delay Diversity Schemes in MIMO-OFDM
(2010)
Ballesteros, Diego
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Chang, Hsien-Wen
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Wang, Li-Chun
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傳播研究所
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Institute of Communication Studies
In this paper, a new hybrid stacked cyclic delay diversity (HSCDD) scheme is proposed for the multiple input multiple output (MIMO) orthogonal frequency division multiplexing (OFDM) systems to flexibly maximize the tradeoff between multiplexing and diversity gains. Unlike the existing double space time transmit diversity (DSTTD) and the stacked cyclic delay diversity (SCDD) schemes which are suitable for the integer multiplexing rate, the proposed HSCDD scheme can achieve arbitrary number of multiplexing rate. Another advantage of the proposed HSCDD scheme over the DSTTD and the stacked CDD schemes is the flexibility in selecting the required number of transmit antennas. With this provided flexibility, the HSCDD can optimize the tradeoff between diversity and multiplexing gains to match the user's requirements.
Signal Measurement and Prediction of WiMAX Basestations on Taiwan High Speed Rail
(2016)
Wu, Dan-Chen
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Ho, Ping-Fan
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Chen, Jyh-Cheng
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Yang, Jen-Shun
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Chang, Hsien-Wen
When communicating at high-speed environment such as high-speed rail, the signals may encounter fast fading due to the terrain changes. In such communication environment, signal prediction can help improve the system throughput and reduce packet loss. In this paper, we propose a prediction mechanism called Window Weight Moving Average (WWMA) to predict the signal strength. We also analyze the real WiMAX signal data collected from Taiwan High Speed Rail (THSR). The analytical results will facilitate the migration from WiMAX to LTE.
TRANSPARENT RAN SHARING OF 5G SMALL CELLS AND MACROCELLS
(2017-12-01)
Lin, Ying-Dar
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Chien, Hsu-Tung
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Chang, Hsien-Wen
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Lai, Chia-Lin
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Lin, Kun-Yi
To cope with the growth of mobile data traffic in 5G systems, telecom operators have to set up more small cells and macrocells in the same area. However, because of space limitations, it is difficult for each operator to do so, and RAN sharing would thus become mandatory for 5G systems. In this work, RANP is proposed, which will achieve transparent RAN sharing by setting up RANP between a base station to be shared and multiple core networks. Over and above the general one-level proxy architecture, an extended two-level architecture is proposed that will share both small cells and macrocells. According to our emulation results, additional packet processing time of a RANP is about 2 ms, 3.8 percent of the total end-to-end latency. Its impact on throughput is about 3 percent and can be regarded as irrelevant.