Browsing by Author "Liou, Ren-Huang"

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A dynamic paging scheme for long-term evolution mobility management
(2015-03-01)
Lin, Yi-Bing
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Liou, Ren-Huang
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Chang, Chun-Ting
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資訊工程學系
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Department of Computer Science
In long-term evolution, the service area is partitioned into several tracking areas (TAs), which comprise one or more cells (the radio coverages of base stations). The TAs are grouped into TA list (TAL). When an incoming call arrives, the network attempts to connect to the user equipment (UE) by paging the cells in the UE's TAL, which may incur large paging traffic that significantly consumes the limited radio resources. To resolve this issue, this paper proposes a dynamic paging scheme that determines the paging sequence of cells in real time according to the UE movement and call behavior. We compare the performance of the dynamic paging with that of the previously proposed Cell-TA-TAL (CTT) paging. Our study indicates that the dynamic paging outperforms the CTT paging when movement pattern is regular and the UE moves frequently. Copyright (c) 2013 John Wiley & Sons, Ltd.
A Handset-Based Solution for Reducing International Roaming Costs
(2011-05-01)
Lin, Yi-Bing
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Liou, Ren-Huang
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Chen, Yuan-Kai
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Gan, Chai-Hien
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資訊工程學系
Today's mobile service providers allow their users to receive telecom services when they roam to other countries. However, international roaming is very expensive. In the standard mobile call setup procedure, a call from the visited country to a roaming user in that country results in two international calls. This phenomenon is referred to as the tromboning effect. Several third-party solutions have been proposed to resolve the tromboning problem by replacing two international calls with two local calls. These solutions require one or more gateways for call re-routing. This paper proposes a handset-based solution that does not need to add/modify network nodes in the existing mobile telecom systems. Analytic modeling and simulation experiments indicate that our solution is effective in international trunk elimination and call setup signaling.
A Weakly Consistent Scheme for IMS Presence Service
(2009-07-01)
Chen, Whai-En
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Lin, Yi-Bing
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Liou, Ren-Huang
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資訊工程學系
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Department of Computer Science
IP Multimedia Core Network Subsystem (IMS) provides presence service for Universal Mobile Telecommunications System (UNITS). In IMS, the presence server is responsible for notifying an authorized watcher of the updated presence information. If the updates occur more frequently than the accesses of the watcher, the presence server will generate many notifications. This paper uses a weakly consistent scheme (called delayed update) to reduce the notification traffic. In this scheme, a delayed timer is defined to control the notification rate. We propose an analytic model and simulation experiments to investigate the performance of delayed update. The study indicates that delayed update can effectively reduce the notification traffic without significantly degrading the valid access probability.
An Investigation on LTE Mobility Management
(2013-01-01)
Liou, Ren-Huang
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Lin, Yi-Bing
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Tsai, Shang-Chih
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資訊工程學系
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Department of Computer Science
Mobility management in Long Term Evolution (LTE) is different from that in the third generation mobile telecom networks. In LTE, the Mobility Management Entity (MME) is responsible for the mobility management function. The MME is connected to a large number of evolved Node Bs (cells) that are grouped into the Tracking Areas (TAs). The TAs are further grouped into TA Lists (TALs). When a User Equipment (UE) moves out of the current TAL, it reports its new location to the MME. If the LTE network attempts to connect to the UE, the MME asks the cells in the TAL to page the UE. In LTE paging, the MME may sequentially page a cell, the TA of the cell, and/or the TAL of the cell. This paper investigates the performance of LTE paging, and provides the guidelines for the best paging sequence of cells.
Automatic event-triggered call-forwarding mechanism for mobile phones
(2013-08-25)
Lin, Yi-Bing
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Liou, Ren-Huang
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Chen, Yuan-Kai
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Wu, Zheng-Han
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資訊工程學系
Call forwarding is a traditional telecom service that allows a user to forward incoming calls to another telephone number. call-forwarding algorithm (CFA) for mobile phones. By installing a software in a smartphone, call forwarding is automatically triggered (e.g., when the phone is plugged in a charger or is turned off) or disabled (e.g., when the phone is unplugged from the charger or is turned on). We investigate the performance of the CFA through analytic analysis, simulation, and measurement. Our study indicates that CFA is very feasible for commercial usage. Copyright (c) 2011 John Wiley & Sons, Ltd.
Deriving the Vehicle Speeds from a Mobile Telecommunications Network
(2013-09-01)
Liou, Ren-Huang
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Lin, Yi-Bing
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Chang, Yu-Long
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Hung, Hui-Nien
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Peng, Nan-Fu
Vehicle speeds are often measured by intelligent transportation systems (ITSs) by utilizing sensors or software solutions. Our previous work proposed the Lin-Chang-Huangfu (LCH) scheme to compute the cell residence times by the standard counter values in mobile telecommunications switches. In this paper, we use mathematical and statistical developments to investigate the accuracy of the LCH scheme by deriving the bias of the cell residence times computed in this scheme. Then, we extend the LCH scheme with some filtering and compensation techniques for vehicle speed estimation and validate our approach with vehicle detector (VD) measurements at National Highway 3, Longtan Township, Taoyuan County, Taiwan. Our study indicates that the LCH scheme is an effective approach to vehicle speed estimation.
Deriving the Vehicle Speeds from Mobile Telecommunications Network
(2012-01-01)
Liou, Ren-Huang
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Lin, Yi-Bing
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Chang, Yu-Long
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Chang, Ming-Feng
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資訊工程學系
Vehicle speeds of roads are measured by the Intelligent Transportation Systems (ITS) through some sensors or software solutions. Our previous work proposed the Lin-Chang-Huangfu (LCH) scheme to compute the cell residence times by the standard counter values in the mobile telecommunications switches without any modification to the telecommunications network. In this paper, we extend the LCH scheme and some filtering techniques to estimate the vehicle speeds, and validate our approach with the vehicle detector measurements at National Highway 3, Longtan Township, Taoyuan County, Taiwan. Our study indicates that the LCH scheme can provide accurate vehicle speeds.
Mobility management with the central-based location area policy
(2013-03-13)
Liou, Ren-Huang
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Lin, Yi-Bing
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資訊工程學系
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Department of Computer Science
In Long Term Evolution (LTE), the cells (the radio coverages of base stations) are grouped into the Tracking Areas (TAs), and the TAs are further grouped into the TA List (TAL). The location of the User Equipment (UE) is tracked at the TAL level. To better capture the "movement locality" of the UE, when the UE leaves the current TAL, the UE is assigned a new TAL whose central TA is the TA where the UE currently resides. This paper investigates the performance of the central-based LTE mobility management scheme, and compares this scheme with the previously proposed central-based mobility management schemes: the movement-based and the distance-based schemes. Our study indicates that under some traffic/mobility patterns, the LTE scheme yields the best performance. (C) 2012 Elsevier B.V. All rights reserved.
NCTU-VT: a freeware for wireless VoIP performance measurement
(2012-03-01)
Sung, Ya-Chin
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Lin, Yi-Bing
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Liou, Ren-Huang
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Shieh, Lon-Fon
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資訊工程學系
Voice over IP (VoIP) is a promising low-cost voice communication over the wireless IP network. To provide satisfactory VoIP services, the Quality of Service (QoS) of the wireless network should be guaranteed. This paper proposes a VoIP performance measurement freeware called NCTU VoIP Testing Tool (NCTU-VT). We compare NCTU-VT with two commercial tools SmartVoIPQoS and IxChariot in terms of packet loss, latency, and Mean Opinion Score (MOS) of the VoIP sessions in Wi-Fi network. Our study indicates that these three tools can accurately measure VoIP performance in Wi-Fi environment. Copyright (c) 2010 John Wiley & Sons, Ltd.
Performance Evaluation of LTE eSRVCC with Limited Access Transfers
(2014-05-01)
Lin, Yi-Bing
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Liou, Ren-Huang
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Sung, Yingrong Coral
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Cheng, Pai-Chun
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資訊工程學系
Long Term Evolution (LTE) evolved from Universal Mobile Telecommunications System (UMTS), which utilizes IP Multimedia Core Network Subsystem (IMS) to provide voice service. In most existing commercial operations, the LTE networks provide zonal coverage as compared with UMTS networks which provide full service coverage. A User Equipment (UE) can initiate or receive an IMS call in either LTE or UMTS. The UE uses LTE whenever it is available. If LTE is out of service, then the UE is transferred to UMTS. To support access transfer between LTE and UMTS during an IMS call, 3rd Generation Partnership Project (3GPP) proposed Enhanced Single Radio Voice Call Continuity (eSRVCC). If the UE frequently moves back and forth between LTE and UMTS during an IMS call, it may incur large access transfer traffic. To resolve this issue, we propose the limited access transfer algorithm that limits the number of access transfers in an eSRVCC call (referred to as the transfer limit) to reduce the transfer traffic. An analytic model is proposed to investigate the performance of the limited access transfer algorithm. Our study indicates that the selection of the transfer limit is not a trivial issue, and an appropriate transfer limit effectively reduces the access transfer traffic to enhance the LTE call control performance.
Performance of CS Fallback for Long Term Evolution Mobile Network
(2014-10-01)
Liou, Ren-Huang
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Lin, Yi-Bing
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Sung, Yingrong Coral
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Liu, Pang-Cheng
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Wietfeld, Christian
When a mobile operator migrates its network from the third generation (3G) system to Long Term Evolution (LTE), both 3G and LTE will coexist for a period of time. Since the 3G circuit-switched (CS) voice mechanism is more mature and available than that for the LTE Voice over Internet Protocol (VoIP), the operator may consider CS fallback (CSFB) as a solution for providing reliable voice calls. According to the 3G Partnership Project (3GPP) CSFB procedure, when a mobile user in the LTE network has an incoming or an outgoing call, the user equipment (UE) falls back from LTE to Universal Mobile Telecommunications System (UMTS). When the call is complete and released, the UE immediately returns to LTE. If the next activity for the UE is another voice call, immediately switching from UMTS to LTE may not be efficient. In this case, the UE has to perform another CSFB. To resolve this issue, we suggest delaying the returns to avoid unnecessary CSFBs, which is called delayed return (DR). Based on the measurements from the real UMTS and LTE networks, we develop an analytic model for investigating the performance of the CSFB with DR. This paper indicates that the DR scheme can effectively reduce the CSFB costs by up to 60%.
QoE-Aware LTE Radio Link Control Parameters for Voice over IP in Vehicular Environments
(2014-01-01)
Liou, Ren-Huang
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Ide, Christoph
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Dusza, Bjoern
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Wietfeld, Christian
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Lin, Yi-Bing
In Long Term Evolution (LTE), Voice over Internet Protocol (VoIP) is used for the delivery of the voice data. One of the major challenges for VoIP over LTE is to guarantee the Quality of Experience (QoE) of the VoIP calls. This paper uses an LTE base station emulator and a radio channel emulator to evaluate the impacts of different User Equipment (UE) velocities and Radio Link Control (RLC) parameter values on the QoE of the calls in the vehicular environment. Our study shows that LTE can provide acceptable VoIP quality in the high-speed scenarios (e.g., high-speed train). This paper provides the guidelines for the telecommunications operators to select the appropriate parameter values when deploying their VoIP services in LTE.
Reducing International Call Costs for Roamer to Roamer Calls
(2010-10-01)
Chen, Yuan-Kai
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Lin, Yi-Bing
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Liou, Ren-Huang
;
資訊工程學系
;
Department of Computer Science
Existing mobile telecom operators allow subscribers to receive mobile phone services when they roam in other countries. However, call setup to an international roaming subscriber is indirectly routed through the home network of the subscriber, which results in the usage of two expensive international telephone trunks. In this paper, we propose a plug-in roaming gateway to avoid the international trunk connections. Our solution is especially attractive when both call parties are roamers.
Reducing International Call Costs for Roamer to Roamer Calls
(2010-10-01)
Chen, Yuan-Kai
;
Lin, Yi-Bing
;
Liou, Ren-Huang
;
資訊工程學系
;
Department of Computer Science
Existing mobile telecom operators allow subscribers to receive mobile phone services when they roam in other countries. However, call setup to an international roaming subscriber is indirectly routed through the home network of the subscriber, which results in the usage of two expensive international telephone trunks. In this paper, we propose a plug-in roaming gateway to avoid the international trunk connections. Our solution is especially attractive when both call parties are roamers.