Meng Hsun Tsai

A Rewarding Framework for Network Resource Sharing in Co-Channel Hybrid Access Femtocell Networks

With the explosive growth in mobile data traffic, femtocell technology is regarded as the most effective way to enhance the mobile service quality and system capacity of cellular networks. However, the major problem with femtocell deployment is finding an appropriate access control mode that mobile operators and users are willing to adopt. Among the various kinds of access control modes, the hybrid access mode is considered the most promising because it allows femtocells to give preferential access to femtocell owners, while other public users can only access femtocells with certain restrictions. Because all femtocell owners are selfish, how to provide sufficient incentives so that they will share their femtocell resources is a challenging issue. To address the problem, we propose an economic framework for mobile operator and femtocell users based on game theoretical analysis. We also exploit the concept of revenue sharing, which provides a positive cycle to sustain the femtocell service. In the framework, a femtocell game is formulated where the femtocell owners determine the proportion of femtocell resources they will share with public users, while the operator maximizes its benefit by setting the ratio of the revenue distributed to femtocell owners. We analyze the existence and uniqueness of the Nash Equilibrium of the game. The results of extensive simulations show that the proposed framework maximizes the operators benefit and satisfies the users service requirements.

Reducing Energy Consumption by Data Aggregation in M2M Networks

Machine-to-machine (M2M) communications have emerged as a new technology for next-generation communications. As the number of M2M devices and the amount of transmitted data increase, applying data aggregation is an efficient way to improve energy efficiency of M2M networks. In this paper, we devise an analytical model to compute the energy consumption and delivery delay in packet delivery by using data aggregation. Then we develop an extensive simulation to validate our proposed analytical model. Numerical results show that it is essential to smartly configure the parameters for data aggregation in M2M networks. Our study provides guidelines to determine the parameters in terms of the buffering time and the maximum number of buffered packets for data aggregation.

A client-side design and implementation for push to talk over cellular service

This paper proposes a client architecture for the push to talk over cellular (PoC) service based on the open mobile alliance (OMA) PoC specifications v1.0 release. We show that most standard VoIP modules can be reused for the PoC client, and the VoIP software can be easily extended to support PoC service. Then we present the detailed message flows between the PoC client and other network entities in the PoC system. A PoC client prototype has been implemented in the Industrial Technology Research Institute (ITRI) and National Chiao-Tung University (NCTU) Joint Research Center. Copyright

Bearer reservation with preemption for voice call continuity

Universal Mobile Telecommunications System (UMTS), the core network consists of two service domains: the circuit-switched (CS) and the packet-switched (PS) domains. A UMTS handset can initiate or receive a call in either the CS or the PS domain. During the call, the user may switch from one domain to another. The switching overhead is an important concern of domain transfer. In this paper, we propose the Bearer Reservation with Preemption (BRP) scheme to support fast domain transfer, and present both analytic model and simulation experiments to investigate the BRP performance. Our study indicates that when user behavior is irregular (i.e., either the variance of the domain residence times or the variance of the call holding times is large), the advantage of the BRP scheme becomes significant.

Talk burst control for push-to-talk over cellular

Push-to-talk over cellular (PoC) is a ldquowalkie- talkie-likerdquo service designed for mobile networks. In this service, the speak permission is arbitrated through the talk burst control (TBC) mechanism. This paper proposes an analytic model to study the performance of the TBC mechanism with queueing and without queueing. This analytic model is validated against simulation experiments. Through numerical examples, our study provides guidelines to set up the parameters for PoC service.

Eavesdropping Through Mobile Phone

Mobile telecommunication services have become very popular recently, and many people bring mobile phones with them wherever they go. However, we observe that mobile phones can be modified to become remote microphones for eavesdropping. The eavesdropping technique only requires modifications to the mobile phone to be spied on and does not require any network changes. This paper describes mobile-phone eavesdropping and analyzes how serious it can be. Based on our study, we provide suggestions to avoid being eavesdropped upon.

IMS emergency services: a preliminary study

Emergency call and walkie-talkie are two services utilized in emergency situations. During Typhoon Morakot in 2009, we experienced the deficiency of emergency call service that cannot continuously track callers in real time and walkie-talkie communications where a speaker may not be granted the permission to talk. These issues can be resolved by the emergency call and push-to-talk over cellular services in IP Multimedia Subsystem. This article conducts a preliminary study on how these two services can be effectively exercised in IMS.

Caching in I-CSCF of UMTS IP multimedia subsystem

Abstract-The IP multimedia core network subsystem (IMS) provides multimedia services for Universal Mobile Telecommunications System (UMTS). In IMS, any incoming call will first arrive at the interrogating call session control function (I-CSCF). The I-CSCF queries the home subscriber server (HSS) to identify the serving CSCF (S-CSCF) of the called mobile user. The S-CSCF then sets up the call to the called mobile user. This paper investigates the performance of the IMS incoming call setup. We also propose cache schemes with fault tolerance to speed up the incoming-call-setup process. Our study indicates that the I-CSCF cache can significantly reduce the incoming-call-setup delay, and checkpointing can effectively enhance the availability of I-CSCF.

Two-stage radio access for group-based machine type communication in LTE-A

In Long Term Evolution-Advanced (LTE-A) network, Machine Type Communication (MTC) provides random access-based communication for automation applications. In MTC, one of the most critical issues is the emergence of large number of MTC devices which may send requests to the base station at the same time, such that severe collision occurs. When collision occurs, the message delay accumulates, and the data delivery fails. In this paper, we propose a two-stage radio access scheme to alleviate collision for MTC. MTC devices are divided into several groups, where random access in each group (as the first stage) is controlled by a device called MTC gateway. Collision of random access to the base station (as the second stage) is then effectively alleviated. To observe the effect of numbers and sizes of groups, we propose analytical model and simulation model to investigate the performance in terms of utilization of random access slots, access success probability and average message delay. Simulation results show that, by sacrificing a little message delay, the proposed scheme significantly improves access success probability.

Active Location Reporting for Emergency Call in UMTS IP Multimedia Subsystem

The IP multimedia core network subsystem (IMS) provides multimedia services for Universal Mobile Telecommunications System (UMTS). In IMS, an emergency call is established by an Emergency-Call Session Control Function (ECSCF). The E-CSCF dispatches the call to the nearest public safety answering point (PSAP) according to the location of the caller. After emergency call setup, the caller s location is tracked by the PSAP through Location Polling. This paper investigates the performance of location tracking. Then we propose the active location reporting scheme to improve the performance of location tracking. Our study indicates that the active location reporting scheme may significantly outperform the location polling scheme.