Browsing by Author "Chang, MF"

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A batch-update strategy for the distributed HLRs architecture in PCS networks
(2003-05-01)
Hwang, HW
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Tseng, CC
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Chang, MF
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資訊工程學系
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Department of Computer Science
Owing to the increasing population of mobile subscribers, the rapidly expanding signaling traffic has become a challenge to the mobility management in PCS networks. Multiple database schemes to reduce signal traffic and to solve the bottleneck problem of the single home location register (HLR) architecture have been proposed by many researchers. However, in most of the multiple location databases or HLR systems, extra signaling is required for the multiple database updates. We propose a batch-update strategy, instead of the immediate update method, for the location-tracking schemes with replication to reduce the signaling overhead. In this paper, we first introduce a distributed HLRs architecture in which each HLR is associated with a localized set of VLRs and the location registrations and queries are processed locally. Then we propose our batch-update strategy and present two pointing schemes for inter-HLR call deliveries. The numerical result shows that our approach can effectively decrease the signaling cost of location registration and call delivery compared with the IS-41 standard. Copyright (C) 2002 John Wiley Sons, Ltd.
A direction-based location update scheme with a line-paging strategy for PCS networks
(2000-05-01)
Hwang, HW
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Chang, MF
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Tseng, CC
;
資訊工程學系
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Department of Computer Science
On the problem of location update and terminal paging, many schemes using ring-paging strategies have been proposed, However, sequentially paging the rings surrounding the mobile user's last updated location may cause large paging cost. In this letter, we propose a direction-based location update (DBLU) scheme using a line-paging strategy to reduce the paging cost. A moving direction identification mechanism using only simple computations detects the change of moving direction and updates the mobile's location. The numerical results show that our DBLU scheme achieves good performance when the paging cost is high.
A full code-patterns coverage high-speed embedded ROM using dynamic virtual guardian technique
(2006-02-01)
Chang, MF
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Chiou, LY
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Wen, KA
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
Crosstalk between bitlines induces read failure and limits the coverage of applicable code-patterns for high-speed contact/via-programming read-only memories (ROMs) in SoC. Owing to the variation in bitline loading across code-patterns, the amount of coupled noise on an accessed bitline is code-pattern-dependent. This crosstalk effect worsens, with larger coupling capacitance and smaller intrinsic loading, as the technology node shrinks. This study proposes dynamic virtual guardian (DVG) techniques for contact/via-programming ROM macros and compilers to eliminate the crosstalk-induced read failure and increase the code-patterns coverage. Compared with conventional ROMs, DVG techniques achieve higher speed, lower power consumption and better design for manufacturing (DFM) capability with full code-patterns coverage. Experiments on fabricated designs, a conventional ROM and two 256 Kb DVG ROMs, using 0.18 mu m 1P5M CMOS technology have demonstrated that DVG techniques achieve 100% code-pattern coverage under a small sensing margin.
Analysis of the direction-based location update schemes for wireless cellular networks
(2002)
Hwang, HW
;
Tseng, CC
;
Chang, MF
;
資訊工程學系
;
Department of Computer Science
In the paper, we first compare the performance of the direction-based location update (DBLL) schemes with that of the distance-based location update scheme under various mobility behaviors of the mobile hosts (MTs). The comparison results show that under the random walk model, the base DBLU scheme outperforms the distance-based location update scheme when the mobility to caff ratios (MCRs) of the MTs are low. However, it has been shown that the MTs are likely to possess forward-prone movement characteristics in micro-cellular architectures. If the MTs am indeed prone to make forward movements, the base DBLU scheme will he better than the distance-based location update scheme in all the MCRs according to our analysis. Therefore we further propose two enhanced DBLU schemes, namely the forward direction-based location update (FDBLU) and the restricted forward direction-based location update (RFDBLU) schemes, for the location tracking of the MTs m micro-cellular architectures. Analytical results also show that both FDBLU and RFDBLU schemes outperform the base DBLU scheme, and RFDBLU scheme is the best among the direction-based location update schemes.
Code-pattern insensitive embedded ROMs using dynamic bitline shielding technique
(2005-07-21)
Chang, MF
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Chiou, LY
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Wen, KA
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電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
A dynamic bitline shielding (DBS) technique is proposed for highspeed via-programming ROMs, to eliminate code-pattem-dependent crosstalk-induced read failure (CIRF) and increase code-pattem coverage. Fabricated 256 Kb conventional and DBS ROMs demonstrated that the DBS technique can eliminate the CIRF and operate with a small sensing margin.
Crosstalk-insensitive via-programming ROMs using content-aware design framework
(2006-06-01)
Chang, MF
;
Chiou, LY
;
Wen, KA
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Various code patterns of a via-programming read only memory (ROM) cause significant fluctuations in coupling noise between, bitlines (BLs). This crosstalk between BLs leads to read failure in high-speed via-programmable ROMs and limits the coverage of applicable code patterns. This work presents a content-aware design framework (CADF) for via-programming ROMs to overcome the crosstalk induced read failure. The CADF ROMs employ a content-aware structure and correspondent code-structure programming algorithm to reduce the amount of coupling noise source while maintaining nonminimal BL load for crosstalk reduction. A 256-Kb conventional ROM and a 256-Kb CADF ROM were fabricated using a 0.25-mu m logic CMOS process. The measured results ascertain that the read induced read failure is suppressed significantly by CADF. The CADF ROM also reduced 86.2% and 94.5% in power consumption and standby current compared to the conventional ROM, respectively.
Harvest rate of reconfigurable pipelines
(1996-10-01)
Shi, WP
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Chang, MF
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Fuchs, WK
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資訊工程學系
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Department of Computer Science
For a reconfigurable architecture, the harvest rate is the expected percentage of defect-free processors that can be connected into the desired topology. In this paper, we give an analytical estimation for the harvest rate of reconfigurable multipipelines based on the following model: There are n pipelines each with m stages, where each stage of a pipeline is defective with identical independent probability 0.5 and spare wires are provided for reconfiguration. By formulating the ''shifting'' reconfiguration as weighted chains in a partial ordered set, we prove when n = Theta(m), the harvest rate is between 34% and 72%.
Improving the fault tolerance of GSM networks
(1998-01-01)
Chang, MF
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Lin, YB
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Su, SC
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交大名義發表
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National Chiao Tung University
A PCS network constantly frocks the locations of the mobile stations so that incoming calls can be delivered to the target mobile stations. In general, a two-level database system is used to store location information of the mobile stations. When the location databases Fail, incoming calls may be lost. This article describes the standard GSM database failure restoration procedure which reduces the number of lost calls. Then we propose an efficient VLR identification algorithm for the HLR failure recovery procedure, which utilizes mobile station movement information to speed up the recovery procedure.
Load-balancing channel assignment for dual-band PCS networks
(2002-03-01)
Chang, MF
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Li, LS
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資訊工程學系
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Department of Computer Science
This paper investigates the channel assignment problem of dual-band PCS systems where single-band and dual-band handsets co-exist. Load-balancing channel assignment schemes are proposed to improve the system performance. To balance the loads of both bands, the BSC selects a band to serve a call request of a dual-band handset based on the loads of both bands. In addition, a channel re-assignment scheme is used to further improve the system capacity. Analytic models and computer simulations have been developed to evaluate the performance of the load-balancing schemes. The results indicate that both load-balancing and channel re-assignment techniques significantly increase the system capacity as the percentage of dual-band handsets increases. Furthermore, the load-balancing with channel re-assignment scheme that combines both techniques achieves the best system performance even when the percentage of dual-band handset is as low as 25%. In addition, we describe an approach to reduce the signal overhead of the load-balancing schemes. Copyright (C) 2002 John Wiley Sons, Ltd.
Mobile prepaid phone services
(2000-06-01)
Lin, YB
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Chang, MF
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Rao, HCH
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友訊交大聯合研發中心
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D Link NCTU Joint Res Ctr
During the past few years, the mobile prepaid service has been growing exponentially all over the world. Four approaches have been proposed to provide mobile prepaid service. We describe these approaches and compare their strengths and weaknesses. Our analysis indicates that the handset based approach is a low-cost, high-risk solution. The wireless intelligent network approach is a high-cost, low-risk solution. The service node approach is a quick solution, which allows fast deployment with limited capacity. The hot billing approach is an average solution that cannot provide real-time rating.
One-pass GPKS and IMS authentication procedure for UMTS
(2005-06-01)
Lin, YB
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Chang, MF
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Hsu, MT
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Wu, LY
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資訊工程學系
Universal Mobile Telecommunications System (UMTS) supports Internet protocol (IP) multimedia services through IP multimedia core network subsystem (IMS). Since the IMS information is delivered through the general packet radio service (GPRS) transport network, a UMTS mobile station (MS) must activate GPRS packet data protocol (PDP) context before it can register to the IMS network. In the Third-Generation Partnership Project (3GPP) specifications, authentication is performed at both the GPRS and the IMS networks before an MS can access the IMS services. We observe that many steps in this 3GPP "two-pass" authentication procedure are identical. Based on our observation, this paper proposes an one-pass authentication procedure that only needs to perform GPRS authentication. At the IMS level, authentication is implicitly performed in IMS registration. Our approach may save up to 50% of the IMS registration/authentication traffic, as compared with the 3GPP two-pass procedure. We formally prove that the one-pass procedure correctly authenticate the IMS users.
Performance evaluation of a push mechanism for WLAN and mobile network integration
(2006-01-01)
Chang, MF
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Wu, LY
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Lin, YB
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資訊工程學系
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Department of Computer Science
In this paper, we propose a universal mobile telecommunications system (UMTS) and a wireless LAN (WLAN) interworking solution called WLAN-based general packet radio service (GPRS) support node (WGSN), which allows a UMTS/WLAN dual mode mobile station (MS) to access heterogeneous wireless services. To reduce the power consumption of an MS, most WGSN applications are not activated at the MS, and MS-terminated services, such as incoming voice over IP (VoIP) calls, are not supported. To address this issue, a push mechanism called session initiation protocol (SIP)-based push center (SPC) was implemented in the WGSN node. For an incoming call to an MS, the SPC utilizes the UMTS short message service to activate the SIP User Agent of the MS. We study the performance of the SPC. An analytic model is proposed to derive the expected number of lost calls during the activation period. The analytic results are validated against the simulation experiments. Our study quantitatively indicates how the SPC performance is affected by the activation time and the timeout period, and we also suggest how to select appropriate values of these two factors to optimize the SPC performance.
Performance of hot billing mobile prepaid service
(2001-07-01)
Chang, MF
;
Lin, YB
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Yang, WZ
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資訊工程學系
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Department of Computer Science
Prepaid service has become an important mobile application with rapid growth for subscription rate in the recent years. Implementation of prepaid service may generate large network traffic that significantly affects the performance of a mobile network. This paper studies the hot billing solution for prepaid service. We investigate how the amount of prepaid credit and the Frequency of call detail record (CDR) transmissions affect network signaling and potential bad debt that a service provider may bear. Our study suggests that a prepaid service provider should encourage customers to buy large prepaid credits by giving them discounts. Furthermore. based on call traffic, an optimal CDR transmission frequency can be found by using our modeling technique. (C) 2001 Elsevier Science B.V. All rights reserved.
Performance of mobile prepaid and priority call services
(2002-02-01)
Chang, MF
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Yang, WZ
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資訊工程學系
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Department of Computer Science
In this letter, we conduct simulation experiments to study a mobile phone system that provides priority and prepaid call services using service nodes. An analytical model for the nonprepaid and prepaid services has been developed to verify the computer simulations. We observe that there exists a threshold point such that beyond this point, increasing the number of mobile switching center ports (service node ports or the radio channels) does not improve the system performance. Furthermore, our results show that priority assignment schemes may significantly affect the operator's revenue.
Performance of service-node-based mobile prepaid service
(2002-05-01)
Chang, MF
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Yang, WZ
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Lin, YB
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資訊工程學系
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Department of Computer Science
In the recent years, mobile prepaid service has become an important mobile application with rapid growth of subscription rate. The most widely deployed prepaid solution today is the service node approach that deducts and updates the prepaid credit during a phone call. Implementation of the service node approach may generate large number of credit checks that significantly degrades the performance of a service node. We investigate how the number of credit checks affects the workload of the service node and the bad debt that a service provider may bear. We propose an analytic model to derive the optimal credit checking/updating frequency for the service node approach. The analytic analysis is validated against simulation experiments. Our study indicates that the number of credit checks increases rapidly when the call pattern is irregular. We also observe that in order to reduce the checking cost of the service node, the prepaid service provider should encourage the customer to make long calls by giving them discounts.
Power and substrate noise tolerance of configurable embedded memories in SoC
(2005-08-01)
Chang, MF
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Wen, KA
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
When subject to various power and substrate noise, configurable embedded memories in multimedia SoCs are importantly affected with pattern-dependant soft failures. This work investigates the effects of such failures on memory cells, arrays and circuit design. The ground bounce reduces the memory cell current more than the supply voltage drop or the substrate bias dip. A noise track-and-filter (NTAF) architecture, which is a self-timed architecture with specific layout patterns, is presented to provide the required timing relaxation, while minimizing the speed degradation. This NTAF method provides greater noise tolerance and design for manufacturing (DFM) capability. Configurable embedded SRAM and ROM in 0.18 mu m CMOS process are studied.
Priority call service on PCS networks
(1999-09-01)
Yang, WZ
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Chang, MF
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Lin, YB
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資訊工程學系
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Department of Computer Science
This paper studies the "priority call service" for personal communication services such as GSM cellular networks. With this service, a priority call requires is buffered in a waiting queue if no free channel is available. The buffered request can be served as soon as free channels become available. We develop an analytic model to evaluate the performance for the priority call service. In addition, computer simulations are conducted to verify the analytic model. The results indicate that priority calls experience very low new call blocking probability, as well as low call incompletion probability at the cost of increasing the force-termination probability.
Supply and substrate noise tolerance using dynamic tracking clusters in configurable memory designs
(2004)
Chang, MF
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Wen, KA
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Kwai, DM
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電機學院
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College of Electrical and Computer Engineering
Pattern-sensitive soft errors, subject to varied supply and substrate noises, have become increasingly significant for configurable memories embedded in SoCs. In this paper, we study their effects on memory cell, array, and circuit design. It is found that the ground bounce reduces the cell current more severely than the supply voltage drop and substrate bias dip. This encourages the use of metal wires along the wordline or row direction. Bitline tracking by current ratio achieves better accuracy and design for manufacturing (DFM) capability than by capacitance ratio. It requires further enhancement to be resilient to the supply and substrate noises. The proposed dynamic tracking cluster technique provides necessary timing relaxation, while minimizing the speed degradation. Configurable embedded SRAM and ROM in 0.18mum CMOS process are studied.
vGPRS: A mechanism for voice over GPRS
(2003)
Chang, MF
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Lin, YB
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Pang, AC
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資訊科學與工程研究所
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Institute of Computer Science and Engineering
This paper proposes vGPRS, a voice over IP (VoIP) mechanism for general packet radio service (GPRS) network. In this approach, a new network element called VoIP mobile switching center (VMSC) is introduced to replace standard GSM MSC. Both standard GSM and GPRS mobile stations can be used to receive real-time VoIP service, which need not be equipped with the VoIP (i.e., H.323) terminal capabilities. The vGPRS approach is implemented using standard H.323, GPRS, and GSM protocols. Thus, existing GPRS and H.323 network elements are not modified. Furthermore, the message flows for vGPRS registration, call origination, call release and call termination procedures are described to show the feasibility of our vGPRS system.
vGPRS: A mechanism for voice over GPRS
(2001)
Lin, YB
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Pang, AC
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Chang, MF
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資訊工程學系
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Department of Computer Science
This paper proposes vGPRS, a voice over IP (VoIP) mechanism for general packet radio service (GPRS) network. In this approach, a new network element called VoIP mobile switching center (VMSC) is introduced to replace standard GSM MSG. The vGPRS approach is implemented using standard H.323, GPRS, and GSM protocols. Thus, existing GPRS and H.323 network elements are not modified. Furthermore, both standard GSM and GPRS mobile stations can be used to receive vGPRS service, which need not be equipped with the VoIP (i.e., H.323) terminal capabilities.