Browsing by Author "Chen, Yu-Fan"

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A GA-Based Optimization for Frequency-Selective Scheduling in Downlink OFDMA Systems with Cyclic-Delay Diversity
(2012)
Chen, Yu-Fan
;
Sheen, Wern-Ho
;
傳播研究所
;
Institute of Communication Studies
CDD (cyclic-delay diversity) aided frequency-selective scheduling has been known as an effective technique to increase system capacity of the OFDMA (orthogonal frequency-division multiple access) systems. By increasing the channels' frequency selectivity with cyclic delays, the merit of multi-user diversity can be exploited more effectively in the system. In this paper, we aim to optimize the design of the CDD-aided frequency-selective scheduling for downlink OFDMA systems. A genetic algorithm (GA)-based optimization is devised to obtain the cyclic-delay values which provides a higher system sum-rate than the multi-degree adaptive cyclic-delay diversity method and has a lower computational complexity than the exhaustive method with only a slight degradation in system sum-rate. The effectiveness of the proposed method is verified by extensive computer simulations.
A Low-Complexity CDD-based Frequency Selective Scheduling with Efficient Feedback for Downlink OFDMA Systems
(2012)
Chen, Yu-Fan
;
Sheen, Wern-Ho
;
Wang, Li-Chun
;
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.
Control of matrix stiffness promotes endodermal lineage specification by regulating SMAD2/3 via lncRNA LINC00458
(2020-02-01)
Chen, Yu-Fan
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Li, Yi-Shuan J.
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Chou, Chih-Hung
;
Chiew, Men Yee
;
Huang, Hsien-Da
During endoderm formation, cell identity and tissue morphogenesis are tightly controlled by cell-intrinsic and cell-extrinsic factors such as biochemical and physical inputs. While the effects of biochemical factors are well studied, the physical cues that regulate cell division and differentiation are poorly understood. RNA sequencing analysis demonstrated increases of endoderm-specific gene expression in hPSCs cultured on soft substrate (Young's modulus, 3 +/- 0.45 kPa) in comparison with hard substrate (Young's modulus, 165 +/- 6.39 kPa). Further analyses revealed that multiple long noncoding RNAs (lncRNAs) were up-regulated on soft substrate; among them, LINC00458 was identified as a stiffness-dependent lncRNA specifically required for hPSC differentiation toward an early endodermal lineage. Gain- and loss-of-function experiments confirmed that LINC00458 is functionally required for hPSC endodermal lineage specification induced by soft substrates. Our study provides evidence that mechanical cues regulate the expression of LINC00458 and induce differentiation of hPSC into hepatic lineage progenitors.
Hybrid Protected Subframes Resource Allocation and Throughput Estimation in LTE-A HetNet
(2014)
Chen, Yu-Fan
;
Ding, Wei-Shiou
;
Wang, Li-Chun
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電機學院
;
電機工程學系
Hierarchical macrocell/small cells overlaying netowrks is regarded as a key role to the success of the next generation wireless systems. To increase the spectrum efficiency through cell splitting, Cell Range Expansion (CRE) in small cells is an effective way to help offloading macro user equipment (UE), but pose many challenges on managing the interference between the small cells and macrocells. To protect offloaded UEs from severe macrocell interference, a specific protected subframes is introduced in 3GPP Release 10 enhanced InterCell Interference Coordination (eICIC), known as Almost Blank Subframes (ABS). However, with a large CRE zone that induces more victim UEs, more ABS are required, which decrease the throughput of macro UE. An alternative to ABS is the Reduce Power Subframes (RPS), where reduced transmission power from macrocell is applied to mitigate the interference to small UEs. In this paper, a Hybrid Protected Subframes (HPS) resource allocation scheme is designed, which jointly considers ABS and RPS. We propose a two-stage configuration method which is based on the Proportional Fair (PF) metrics to determine the best allocation of HPS pattern. Comparing to previous work, simulation results show that the proposed scheme efficiently improves the small UE throughput, and maintain the macro UE throughput as the protected subframes is increased.
Joint User Scheduling and Interference Alignment Beamforming in Heterogeneous Wireless Networks
(2014)
Chen, Yu-Fan
;
Wang, Li-Chun
;
Sheen, Wern-Ho
;
電信工程研究所
;
Institute of Communications Engineering
Small cell networks are the key to the success of the next generation wireless systems because of the potential huge capacity gain, but pose many challenges on managing the inter-cell interference from huge number of small cells and that from macrocells. Recently, an interesting technique, called interference alignment (IA), was proposed to align the mutual inter-cell interference (ICI) in the same sub-space by designing the beamforming vector among the coordinated cells. Because of the reduced ICI, the system capacity of an IA system can be improved. Nevertheless, the methods of selecting a group of users for the IA system has been rarely seen in the literature, especially in the macrocell/small cells hierarchical overlaying networks. In this paper, we investigate the effects of pairing users and base stations in an IA-based hierarchical overlaying macrocell/small cells networks. Furthermore, we design an IA scheme that can not only reduce the inter-cell interference among small cells, but also avoid interfering with the overlaying macrocell. Comparing to the conventional IA scheme based on the random pairing for users and base stations, the sum rate of the proposed joint user scheduling and IA beamforming design is 30% and 64.5% improved for the cell edge users with the SNR-based and SINR-based pairing for the users and base stations.
Optimization of Cyclic-Delay Diversity Aided Frequency-Selective Scheduling in OFDMA Downlink Systems
(2014-05-01)
Chen, Yu-Fan
;
Sheen, Wern-Ho
;
Wang, Li-Chun
;
電機資訊學士班
;
電信工程研究所
Cyclic-delay diversity (CDD)-aided frequency-selective scheduling has been known as an effective technique for increasing the system capacity of orthogonal frequency-division multiple-access (OFDMA) systems. By increasing the channels\' frequency selectivity with different cyclic delays applied on transmit antennas, the merit of multiuser diversity can be more effectively exploited in the system. In this paper, we aim to optimize the design of the CDD-aided frequency-selective scheduling for OFDMA downlink systems. Optimization is done from two aspects: cyclic-delay search and scheduling-information feedback. In the optimization of cyclic-delay search, three new methods are proposed, including antenna-wise sequential search for frequency-nonselective (AWSS-FNS) channels, AWSS for frequency-selective (AWSS-FS) channels, and a genetic-algorithm-based search (GAS). AWSS-FNS achieves the optimal performance if a channel is frequency nonselective over a subchannel, whereas AWSS-FS and GAS provide good tradeoffs between system performance and complexity for channels that are frequency selective over a subchannel. In the optimization of scheduling-information feedback, a new channel-dependent feedback (CDF) method is proposed, where the feedback resource is allocated to users according to their frequency-selectivity rates and a principle of proportional fairness. The optimized scheduler is shown to provide significant improvement in both system sum rate and user fairness over previous methods under fixed feedback overhead.