Browsing by Author "Liu, Chia-Lung"

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A Local IP Access Mechanism for VoIP Service in LTE Home eNodeB Systems
(2013)
Chang, Chia-Hsuan
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Chao, Hsi-Lu
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Liu, Chia-Lung
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Huang, Kuei-Li
;
Lin, Yi-Bing
The need for multimedia communication through wireless media brings development of 4G cellular wireless networks. Long Term Evolution (LTE) is one of 4G standards and specified in 3GPP. In an LTE system, home base station (HeNB) is designed for indoor usage. Since packets are always routed back to the core network before to destination, if two user equipments (UEs) stay in the same HeNB, the routing path is detour and results in longer packet delivery delay, jitters and thus lower data throughput. As a result, the idea of local IP Access (LIPA) was drawn and two solutions have been proposed. However, the two solutions would suffer from poor voice quality in a VoIP application. We propose a novel solution which establishes an additional data radio bearer (DRB) between UE and HeNB to detect local packets. Once local packets are detected, the data radio bearer is then responsible for local packet delivery. Simulation results show that our method outperforms the other two solutions in terms of packet delivery delay and mean opinion score (MOS).
A Novel Channel-Aware Frequency-Domain Scheduling in LTE Uplink
(2013)
Chao, Hsi-Lu
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Chang, Chia-Kai
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Liu, Chia-Lung
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資訊工程學系
;
Department of Computer Science
Due to the power consumption issue of user equipment (UE), Single-Carrier FDMA (SC-FDMA) has been selected as the uplink multiple access scheme of 3GPP Long Term Evolution (LTE). Similar to OFDMA downlink, SC-FDMA enables multiple UEs to be served simultaneously in uplink as well. However, the single carrier characteristic requires that all the allocated subcarriers to a UE must be contiguous in frequency with each time slot. Moreover, a UE should adopt the same modulation and coding scheme at all allocated subcarriers. These two constraints do limit the scheduling flexibility. In this paper, we formulate the UL scheduling problem with taking two constraints into consideration. Since this optimization had been proven to be an NP-hard problem, we further develop a heuristic algorithm with low complexity. We demonstrate that competitive performance can be achieved in terms of system throughput, which is evaluated by using 3GPP LTE system model simulations.
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.
An Efficient Measurement Report Mechanism for Long Term Evolution Networks
(2011)
Chou, Shih-Fan
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Chao, Hsi-Lu
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Liu, Chia-Lung
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資訊工程學系
;
Department of Computer Science
LONG-TERM EVOLUTION (LTE) is expected to ensure 3GPP's competitive edge over other cellular technologies. The advantages of LTE include improving end-user throughputs, and reducing latency. LTE systems utilize a network-controlled and the user equipment (UE) assisted handover procedure for mobility in connected mode. In this paper, we first introduce the measurement report mechanism defined in the specification of LTE systems. We further explore possible problems and the impact on handover decision. Followed, we propose rules for timer adjustment, including timeToTrigger and reportInterval. Our mechanism aims at reducing incorrect handover decisions and maximizing the throughput performance. By conducting simulation, we evaluate the designed mechanism. The simulation results show that our proposed mechanism does achieve our design goals.
Multi-User MIMO Scheduling in LTE-Advanced Uplink Systems
(2013-01-01)
Hsu, Lung-Han
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Chao, Hsi-Lu
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Liu, Chia-Lung
;
Huang, Kuei-Li
;
資訊工程學系
Due to the facts of wireless data usage being increasing faster now than ever before and more multimedia content being generated by users and uploaded to the network, multi-user MIMO (MU-MIMO) technology would be crucial to improve the LTE-A uplink spectral efficiency for meeting the service demands. On the other side, adopting clustered SC-FDMA technology as the uplink multiple access scheme of LTE-A means that a User Equipment (UE) can be allocated more than one cluster which consists of contiguous RBs (this is the contiguity constraint). Moreover, all allocated RBs to a UE must use the same modulation and coding scheme (this is the robust rate constraint). The two constraints make MU-MIMO UL scheduling more complicated. In this paper, we formulate the MU-MIMO UL scheduling problem with taking two constraints into consideration. Since this optimization had been proven to be an NP-hard problem, we further develop two low-complexity heuristic algorithms. We demonstrate that competitive performance can be achieved in terms of system throughput and fairness index.
Performance Enhancement of Contention-Based Bandwidth Request Mechanism in IEEE 802.16 WiMAX Networks
(2010)
Chou, Shih-Fan
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Liu, Jen-Hsi
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Chao, Hsi-Lu
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Guo, Tzu-Chi
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Liu, Chia-Lung
The IEEE 802.16 standard is a promising technology for 4G mobile networks. Though supporting versatile service classes, best effort (BE) service class is expected to dominate WiMAX networks, due to operational simplicity. One of bandwidth request mechanisms that subscriber stations (SS) can utilize to issue bandwidth requests (BW-REQ) for BE connections is contention-based random access. An SS starts a timer T16 when transmitting a BW-REQ. If getting a grant before timer expiration, the SS transmits data packets at the allocated time slots; otherwise it performs truncated binary exponential backoff process for BW-REQ retransmission. The default value of T16 is one frame time. However, T16 impacts on contention and request collision significantly. In the paper, we develop an analytical model for T16 timer setting. Besides, we derive analytical expressions for the average number of tries per BW-REQ and the average packet delay. We compare the theoretical results of fixed and adjustable timers. The results show that adjusting timer reduces both the number of collision and the average packet delay.
Sum Throughput-Improved Resource Allocation for LTE Uplink Transmission
(2011)
Chang, Ching-Hsu
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Chao, Hsi-Lu
;
Liu, Chia-Lung
;
資訊工程學系
;
Department of Computer Science
Long Term Evolution (LTE) is a promising technology for 4G mobile networks. Due to utilize OFDMA in downlink and SC-FDMA in uplink, the LTE system is expected to provide significantly high throughput with 20 MHz spectrum allocation. To increase the cell throughput and multi-user diversity gain, channel dependent scheduling (CDS) is implemented for the OFDMA-based multi-user scenario to allocate resource blocks (RBs) to users experiencing better channel conditions. Nevertheless, CDS may not perform well in SC-FDMA due to its two inherent constraints - one is contiguous RB assignment and the other is robust modulation and coding mode. In this paper, the formulation of resource allocation for a SC-FDMA system upon considering two inherent constraints is proposed. Since the optimization problem of resource allocation in SC-FDMA is NP-hard, we further propose two heuristic algorithms to find feasible solutions. We evaluate the proposed formulation and heuristic algorithms by conducting simulation. The simulation results show that our methods achieve significant performance improvement not only in system sum throughput but also in transmission delay.
Window-Based Frequency-Domain Packet Scheduling With QoS Support in LTE Uplink
(2013-01-01)
Hsu, Lung-Han
;
Chao, Hsi-Lu
;
Liu, Chia-Lung
;
資訊工程學系
;
Department of Computer Science
Due to the power consumption issue of user equipment (UE), Single-Carrier FDMA (SC-FDMA) has been selected as the uplink multiple access scheme of 3GPP Long Term Evolution (LTE). Similar to OFDMA downlink, SC-FDMA enables multiple UEs to be served simultaneously in uplink as well. However, the single carrier characteristic requires that all the allocated subcarriers to a UE must be contiguous in frequency with each time slot. Moreover, a UE should adopt the same modulation and coding scheme at all allocated subcarriers. These two constraints do limit the scheduling flexibility. In this paper, we formulate the UL scheduling problem with proportional fairness support by taking two constraints into consideration. Since this optimization had been proven to be an NP-hard problem, we further develop one heuristic algorithm. We demonstrate that competitive performance can be achieved in terms of system throughput, which is evaluated by using 3GPP LTE system model simulations.