Browsing by Author "Tsai, Cheng-Jie"

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An I-D Two-State Dynamic Receive Window Adjustment Scheme for Solving Bufferbloat Problems
(2018-01-01)
Lee, Tsern-Huei
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Tsai, Cheng-Jie
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Yang, Yung-Chun
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電機工程學系
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Department of Electrical and Computer Engineering
Bufferbloat is a phenomenon caused by excessive buffering of packets that results in high latency, large jitter, as well as throughput degradation. It happens when a loss-based Transmission Control Protocol (TCP), such as New Reno or Cubic, is used for data transfer. A dynamic receive window adjustment (DRWA) scheme has recently been proposed to solve the bufferbloat problem. It was reported that, with the DRWA scheme, the bufferbloat problem can be effectively solved. However, we found that when there are multiple TCP connections sharing some bottleneck link, the ones with DRWA tend to lose their bandwidth share to those without DRWA. Moreover, when a user equipment establishes multiple TCP connections all implemented with DRWA and all connections pass through the same bottleneck link, the connection which is established last will dominate the bandwidth. In this paper, we present a simple scheme, called I-D (increasing-decreasing) two-state dynamic receive window adjustment, which according to simulation results can effectively solve the bufferbloat problem without the unfair bandwidth-dominating issues.
Optimum Multi-Subframe Scheduling for LTE Licensed-Assisted Access to Unlicensed Spectrum
(2017-01-01)
Tsai, Cheng-Jie
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Lee, Tsern-Huei
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電機工程學系
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Department of Electrical and Computer Engineering
Licensed-Assisted Access (LAA) is a new operation mode for the Long Term Evolution Advanced systems to transmit data via both licensed spectrum and unlicensed spectrum based on the framework of carrier aggregation. For LAA uplink (UL) transmission, there is a mismatch between resource allocation and actual data transmission due to the requirement of listen-before-talk (LBT). Such a mismatch may cause severe throughput degradation and, therefore, is an important issue to be addressed. In Release 14, two different ideas of multi-subframe scheduling (MSS) were proposed to improve UL throughput by allowing user equipments to either transmit data continuously for multiple subframes or have multiple opportunities to perform LBT. In this paper, we present a family of scheduling schemes which combines the two MSS ideas and evaluate its performance. The optimum one in the proposed family of schemes which maximizes throughput is determined.
Quality of Service Support under DRX Mechanism in LTE Advanced Wireless Networks
(2013)
Lee, Tsern-Huei
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Tsai, Cheng-Jie
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Wu, Tzu-Han
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電機資訊學士班
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Undergraduate Honors Program of Electrical Engineering and Computer Science
Energy saving and quality of service (QoS) support are two important issues of Long-Term Evolution Advanced (LTE-A) wireless networks. Unfortunately, achieving high energy saving efficiency often implies degradation of QoS support. In this paper, we address the issue of QoS support under Discontinuous Reception (DRX), the power saving mechanism of LTE-A. Different from previous studies which analyzed average packet delay under DRX mechanism, we adopt packet loss ratio due to violation of delay bound as QoS requirements of real-time applications. The problem of QoS support under DRX mechanism is defined as an optimization problem to maximize average power saving under the constraint that the packet loss ratio is no greater than a pre-determined threshold. We derive packet loss ratio and energy saving efficiency given DRX parameter values and propose an approach to select appropriate DRX parameter values. Simulations are conducted to verify our analysis. We found that the analytical results match well with simulations. Moreover, the energy saving efficiency achieved by the selected DRX parameter values is very close to that of the optimum solution.
Uplink performance enhancement for LTE licensed-assisted access to unlicensed spectrum
(2018-01-22)
Tsai, Cheng-Jie
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Lee, Tsern-Huei
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電機工程學系
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Department of Electrical and Computer Engineering
Licensed-assisted access (LAA) is a new operation mode of carrier aggregation for the Long Term Evolution Advanced systems to transmit data on both licensed and unlicensed spectrum. To deal with the issue of co-existence with WiFi systems, LAA is required to perform listen-before-talk, which can significantly impact its resource utilization. In this paper, the concept called multi-subframe scheduling (MSS) which can enhance the performance of uplink LAA data transmission is presented. MSS allows a user equipment to have multiple channel sensing opportunities and/or to transmit data continuously for multiple subframes. Both scheduling-based and random access schemes are evaluated and compared. The optimum configuration of MSS which maximizes resource utilization of LAA is also provided. Numerical results show that MSS improves resource utilization on the unlicensed spectrum significantly.