Ming-Feng Chang

A direction-based location update scheme with a line-paging strategy for PCS networks

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 users last updated location may cause large paging cost. 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 mobiles location. The numerical results show that our DBLU scheme achieves good performance when the paging cost is high.

Performance of hot billing mobile prepaid service

Abstract 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.

Performance of service-node-based mobile prepaid service

The 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 a 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.

vGPRS: a mechanism for voice over GPRS

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.

Derivation of Cell Residence Times from the Counters of Mobile Telecommunications Switches

In mobile telecommunications, the residence times of users at a cell or a location area are an important input parameter for network planning and performance evaluation of a mobile network. However, measurement of cell residence times in a commercially operated mobile network is not trivial, which typically requires tracing the movement of individual users. In this paper, we show how to use the standard counter values (number of handovers and call traffic) measured in a mobile telecommunications network to derive the cell residence times. These counter values can be obtained directly from telecommunications switches. Therefore, we can provide a quick and simple solution to compute cell residence times.

Deriving the Vehicle Speeds from a Mobile Telecommunications Network

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.

Performance Modeling of Integrated Mobile Prepaid Services

Prepaid personal communication service users have outnumbered postpaid users. This paper studies the charging issues of an integrated Global System for Mobile Communications (GSM) and General Packet Radio Service (GPRS) prepaid service, where a single prepaid account provides a user both voice and data services. The call setup and charging procedures for GSM and GPRS are presented using the Customized Applications for Mobile network Enhanced Logic network architecture. To reduce the probability of terminating both ongoing voice and data calls, we suggest that no new call be admitted when the user credit is below a threshold. An analytic model has been developed to evaluate the performance of the approach. Computer simulations have also been used to verify the results. The numeric results indicate that the force-termination probability can be significantly reduced by choosing an appropriate threshold of the user credit

Performance evaluation of a push mechanism for WLAN and mobile network integration

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.

Analysis of the direction-based location update schemes for wireless cellular networks

We first compare the performance of the direction-based location update (DBLU) 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 call ratios (MCRs) of the MTs are low. However, it has been shown that the MTs are likely to possess forward-prone movement characteristics in microcellular architectures. If the MTs are indeed prone to make forward movements, the base DBLU scheme will be 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 in 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.

Performance of mobile prepaid and priority call services

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 operators revenue.