Browsing by Author "Tseng, Chun-Kai"

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An Effective Antenna Allocation for CoMP Transmission in Dense Small Cell Networks
(2016-01-01)
Tseng, Chun-Kai
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Wu, Sau-Hsuan
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Chao, Hsi-Lu
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Liu, Chia-Lung
;
Gan, Chai-Hien
Despite that network capacity can increase with cell densification, interferences from adjacent cells may deteriorate the throughput of users close to cell edges. To alleviate this problem and to offer a service quality with no significant cell edge degradation, we propose a feasible coordinated multi-point (CoMP) transmission architecture from a new look on antenna allocation in dense small cell networks (DSN). The CoMP idea is based on a two-step mechanism; the first step partitions the entire service region into multiple areas, and the second step adjusts the number of active users for each area. We then develop an antenna allocation algorithm to enhance the cell-edge user throughput, making use of the spatial multiplexing (SM) gain, array gain and cooperative diversity gain. Simulation results show that applying SM to DSN plays a crucial role to enhance the user throughput. And one of our proposed cooperative schemes is shown to have a great potential to improve the throughput for a large portion of users or the cell service area.
Effective Cooperative ARQ Protocols with the Opportunistic Selective AF Relaying: The Perspectives of Outage versus Packet Error Probabilities
(2011)
Tseng, Chun-Kai
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Wu, Sau-Hsuan
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傳播研究所
;
Institute of Communication Studies
In contrast to the outage analysis, the packet error rates (PERs) of two types of cooperative automatic retransmission request (ARQ) protocols with opportunistic selective amplified-and-forward (OSAF) relaying are investigated from the perspective of the maximum likelihood sequence detection (MLSD). The results show that PERs with the threshold requirements derived from the outage analysis cannot benefit from the diversity via opportunistic retransmissions. Based on the PER analysis, effective threshold setting methods for the two types of ARQs are developed to avoid the diversity losses during ARQs, and verified via simulations using convolutional codes. In contrast to the ARQ protocols with the typical opportunistic AF relaying, the new threshold setting methods allow the OSAF ARQ protocols to provide for practical systems a spatial and temporal diversity comparable to what predicts with the outage analysis.
Effective Protocols and Channel Quality Control Mechanisms for Cooperative ARQ With Opportunistic AF Relaying
(2018-03-01)
Tseng, Chun-Kai
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Wu, Sau-Hsuan
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電信工程研究所
;
Institute of Communications Engineering
Incorporating relaying techniques into automatic repeat reQuest (ARQ) in general will provide diversity and throughput enhancements. However, when opportunistic amplify-and-forward (AF) relaying is applied to cooperative ARQ, the system design becomes much more involved. First, our capacity outage analysis shows that the temporal diversities of ARQs with a single AF relay cannot be exploited unless the channel quality to the relay exceeds a threshold. This notion of selective AF relaying is extended to systems with multiple relays in an attempt to jointly explore the temporal and spatial diversities with ARQ. Two types of selective and opportunistic AF relaying schemes are then developed for such kinds of relay-assisted ARQ. And our analysis further shows that the temporal and spatial diversities cannot be fully exploited without the use of overhearing among relays and a proper link quality control mechanism to prescreen the overheard signals. This quality control mechanism is implemented with a set of thresholds designed for each hop of the relaying path. Feasible threshold setting methods are also developed for the proposed ARQ protocols to achieve their potential diversities. In contrast to our designs, the ARQ scheme with the typical opportunistic AF relaying method suffers from severe diversity losses. Simulations also show that the proposed ARQ schemes are more effective in throughput enhancement, and can provide cell-edge users almost three times the throughput gain in comparison with ARQ with no relay-assisted forwarding.
Effective Service Architecture and Antenna Allocation Mechanism for CoMP Transmissions in Ultra Dense Networks
(2019-09-01)
Tseng, Chun-Kai
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Wu, Sau-Hsuan
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Chao, Hsi-Lu
;
Quek, Tony Q. S.
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Gan, Chai-Hien
A practical and effective service deployment method is proposed for coordinated multi-point (CoMP) transmissions in ultra-dense networks (UDN). Despite the potential of UDN for throughput enhancement, the throughput of edge users is still considerably deteriorated by interferences from adjacent cells. Applying the CoMP transmissions among cells appears to be a feasible solution to resolve this issue. However, the nature of the almost randomly deployed locations of small cell base stations (BSs) and their limited numbers of antennas make it difficult to design an effective resource coordination mechanism for the CoMP services in UDN. Reconsidering this problem from an antenna allocation viewpoint, we present a simple yet effective approach to improve the cell-edge throughput under a centralized radio access network architecture. The first step is to partition the entire service area into multiple subareas, and the second step is to allocate the antenna degrees of freedom to each subarea. To improve the scalability of this service method, a two-tier service deployment method is further introduced based on the BS clustering and service area partitioning of the entire network. The simulation results show that the proposed service architecture can provide a significant improvement on the cell-edge throughput while still maintaining a good average throughput in the UDN.
Robust Linear Beamformer Designs for CoMP AF Relaying in Downlink Multi-Cell Networks
(2012)
Kuo, Chun-, I
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Wu, Sau-Hsuan
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Tseng, Chun-Kai
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電信工程研究所
;
Institute of Communications Engineering
Robust beamforming methods are studied to support relay-assisted coordinated multi-point (CoMP) retransmissions in downlink multi-cell networks. Linear beamformers (BFers) for relay stations of different cells are jointly designed to maintain, in a CoMP amplify-and-forward (AF) relaying manner, the target signal to interference-plus-noise ratios (SINR) at the cellular boundaries of this type of networks. Considering the feasibility in realizations, BFer designs are only allowed to use the channel state information (CSI) feedbacks of the wireless links inside a network. This kind of designs turns out to be a challenging optimization problem when attempting to maintain the SINR under the estimation and quantization errors in CSI. A conservative criterion and solution method is proposed for this robust design problem. Despite the conservativeness, the proposed method appears to provide an effective BFer design for CoMP AF relaying, either from the perspective of power consumption or from the viewpoints of BFers\' complexity and feasibility in syntheses. Simulations also show that when applying the proposed CoMP AF relaying method in Automatic Retransmission reQuest (ARQ), data throughput can be efficiently increased for users close to the joint cellular boundaries inside a multi-cell network.
Robust Linear Beamformer Designs for Coordinated Multi-Point AF Relaying in Downlink Multi-Cell Networks
(2012-09-01)
Kuo, Chun-I
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Wu, Sau-Hsuan
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Tseng, Chun-Kai
;
電信工程研究所
;
Institute of Communications Engineering
Robust beamforming methods are studied to support relay-assisted coordinated multi-point (CoMP) retransmissions in downlink multi-cell networks. Linear beamformers (BFers) for relay stations of different cells are jointly designed to maintain, in a CoMP amplify-and-forward (AF) relaying manner, the target signal to interference-plus-noise ratios (SINR) at the cellular boundaries of this type of networks. Considering the feasibility in realizations and deployments, BFer designs are only allowed to use the channel state information (CSI) feedbacks of the wireless links inside a network. This kind of designs turns out to be a challenging optimization problem when attempting to maintain the SINR under the estimation and quantization errors in CSI. A conservative criterion and solution method is proposed for this robust design problem. Despite the conservativeness, the proposed method appears to provide an effective BFer design for CoMP AF relaying, either from the perspective of power consumption or from the viewpoints of BFers' complexity and feasibility in syntheses. Simulations also show that when applying the proposed CoMP AF relaying method in Automatic Retransmission reQuest (ARQ), data throughput can be efficiently increased for users close to the joint cellular boundaries inside a multi-cell network.
Selective and Opportunistic AF Relaying for Cooperative ARQ: An MLSD Perspective
(2019-01-01)
Tseng, Chun-Kai
;
Wu, Sau-Hsuan
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電信工程研究所
;
Institute of Communications Engineering
Selective and opportunistic amplified-and-forward (SOAF) relaying has been shown more effective than the typical opportunistic AF relaying for cooperative automatic repeat request (ARQ). The key to exploit the diversity potential of SOAF ARQ lies in a proper quality control mechanism for the relayed signals. Although quality control methods have been proposed from the viewpoint of capacity outage probability, the methods are shown herein not enough for SOAF ARQ to exploit the full diversity in packet error rates (PERs). Reinvestigating the quality control problem from the perspective of maximum likelihood sequence detection, our analysis shows that the PERs can attain the full spatial diversity offered by relays in every ARQ round only if the thresholds to control the received signal qualities of the forwarding relays increase with the signal-to-noise ratio (SNR). Sufficient conditions on the thresholds settings are proposed, which explicitly characterize the relationship among the threshold requirements, the SNR, and the minimum codeword distance of the employed channel code. An effective threshold searching algorithm is further developed for SOAF ARQ to exploit both the diversity and the SNR gains in PER. Simulations with trellis codes also verify our analysis and the effectiveness of the proposed quality control method.
Simple Cooperative ARQ Protocols with Selective Amplify-and-Forward Relaying
(2009)
Tseng, Chun-Kai
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Wu, Sau-Hsuan
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電信工程研究所
;
Institute of Communications Engineering
Simple cooperative automatic retransmission request (ARQ) protocols are presented based on the selective amplified-and-forward (SAF) relaying method. Analysis shows that the temporal diversity of ARQs can be exploited with AF relaying only if the channel quality to the relay exceeds a threshold that depends on the source data rate requirement. Based on this analysis, an effective ARQ protocol is first developed from the concept of selective relaying to attain the full temporal diversity. Moreover, the notion of SAF relaying is further extended to systems with multiple relays to exploit the spatial and temporal diversities, incorporating the mechanism of opportunistic relaying. Two types of opportunistic-selective AF (OSAF) relaying methods are thus proposed for cooperative ARQs. Analysis shows that both OSAF protocols can offer much higher diversities than ARQ schemes with the typical AF relaying method. And the throughput of ARQs with OSAF is more robust to the variations of channel qualities and is close to their decode-and-forward counterparts.