Shiao-Li Tsao

Design and evaluation of UMTS-WLAN interworking strategies

High tier wireless systems such as GPRS and UMTS provide users with high mobility but less bandwidth. On the other hand, low tier wireless systems such as wireless LAN offer high bandwidth with less mobility. The support of seamless roaming between heterogeneous wireless networks is regarded as one of the key issues in future mobile communication systems. The paper presents the design and evaluation of three possible UMTS-WLAN interworking strategies, i.e. Mobile IP approach, gateway approach, and emulator approach based on the current UMTS, WLAN and Mobile IP specifications. Recommendations to UMTS-WLAN interworking strategies according to different deployment scenarios are also discussed.

Proportional delay differentiation service based on weighted fair queuing

Differentiation service (Diffserv) is regarded as one of the practical architectures to realize quality of service (QoS) on the Internet. Relative differentiated service, which achieves relative QoS differentiation between traffic classes, is a simple and easily-deployed service model. Based on the concept of relative differentiated service, Dovrolis et al. (ACM SIGMETRICS Performance Evaluation Review vol.27, no.1, pp.204-5, 1999; IEEE Network, September 1999; ACM SIGCOMM-99, September 1999) proposed a proportional differentiation service model which guarantees the ratios of service differences between classes. They claimed that weighted fair queuing (WFQ) is not suitable for implementing relative differentiation service and employed priority-based scheduling algorithms in their model. In this paper, we extend WFQ and apply it to proportional delay differentiation service. The extended WFQ algorithm adjusts the weighting of each class dynamically so that the delay differences between classes can be well controlled. Simulations show that the proposed methods can realize proportional delay differentiation service effectively and efficiently.

Performance Analysis of Group Paging for Machine-Type Communications in LTE Networks

Machine-type communication (MTC) is a crucial service for next-generation cellular networks. Mass access to the network by MTC devices may result in the overload of radio access networks (RANs) and degrade the service quality of human-to-human communication. Group paging is one of the mechanisms proposed to alleviate the RAN-overload problem. This paper presents an analytical model based on a recursive contending-users estimation (RCE) method proposed in the literature to derive the performance metrics of collision probability, access success probability, average access delay, statistics of preamble transmissions, statistics of access delay, and utilization of random-access opportunities (RAOs) for group paging with various combinations of group sizes and reserved radio resources in a paging access interval. The optimal group size and required RAOs are subsequently derived based on the given target access success probability. Numerical results demonstrate that the proposed model can accurately estimate the performance of group paging.

RACH Collision Probability for Machine-Type Communications

This paper summarizes the two definitions of the collision probability from the perspective of an MTC device and an RAO were presented in 3GPP TR 37.868. We use the results presented in TR 37.868 to show the inconsistency between the two definitions. It worth to note that the researcher needs to clearly specify the definition they used in presenting the results of their proposed radio access network overload control schemes. This paper further presents an analytical model to derive the collision probability, the success probability, and the idle probability based on the two definitions.

VGSN: a gateway approach to interconnect UMTS/WLAN networks

High tier wireless systems such as GPRS and UMTS provide users high mobility but low bandwidth. On the other hand, low tier wireless systems such as wireless LAN offer higher bandwidth with less mobility. To support seamless roaming between. heterogeneous wireless networks is regarded as one of the key issues in the future mobile communication system. The paper presents method and system for seamless roaming between WLAN and UMTS networks. The two networks are assumed to be constructed and to operate independently, but wish to offer roaming services to their customers. A new logical node, called virtual GPRS support node (VGSN), is designed for this purpose to connect UMTS and WLAN core networks. VGSN is a normal GPRS support node (GSN) in a UMTS system and also acts as an access route in a WLAN network. The node converts control signals and routes data packets between two networks for roaming users. With the presented approach, Mobile IP is not required and users can have seamless roaming between networks based on one IP address.

Modeling and Estimation of One-Shot Random Access for Finite-User Multichannel Slotted ALOHA Systems

This paper presents a combinatorial model and approximation formulas to estimate the average number of successful and collided users for a one-shot random access in finite-user multichannel slotted ALOHA systems. The proposed model and approximation can be used to evaluate the performance of group paging for machine-type communication (MTC) in 3GPP LTE. Numerical results demonstrate the applicable range of the approximation formulas and the accuracy of the derived performance metrics.

Energy-Efficient Sleep-Mode Operations for Broadband Wireless Access Systems

Broadband wireless access systems usually provide flexible sleep-mode operations for mobile stations to conserve energy during idle or active modes. For example, the IEEE 802.16e offers several sleep-mode classes that can be applied to mobile subscriber stations (MSSs) to reduce their power consumptions for different applications. Unfortunately, previous studies did not fully utilize sleep-mode features, and the power consumption of an MSS with multiple network connections is not optimized. In this work, two scheduling algorithms for sleep-mode operations based on the IEEE 802.16e are proposed. These schemes guarantee the quality of services (QoSs) of the network connections for an MSS and also minimize the power consumption of the MSS. Simulation results demonstrate that the proposed schemes outperform the traditional approaches.

Extending earliest-due-date scheduling algorithms for wireless networks with location-dependent errors

Generalized processor sharing (GPS) and earliest-due-date (EDD) algorithms are two work conserving service disciplines to provide bounded delay and fair queuing for packet data network. Unfortunately, these algorithms can not apply to a wireless network directly due to the location-dependent errors in mobile environment. A number of studies enhanced GPS-like algorithms to facilitate the wireless environment, but the studies of EDD scheduling algorithms on a wireless network are almost ignored. Unlike GPS-like algorithms which guarantee a delay bound based on the weight that is tightly coupled to a reserved service rate, EDD and its extensions such as delay-EDD and jitter-EDD policies allow the separation of delay, delay-jitters and throughput guarantees for a particular data flow. In this paper, we explore EDD and delay-EDD policies, and present their extensions. Simulation results show that our proposed algorithms can achieve short term, long term fairness, and QoS guarantees on wireless networks.

Design and evaluation of a two-tier peer-to-peer traffic information system

Decentralized traffic information systems realize real-time traffic information services without the need for a server infrastructure. However, existing systems rely on either the vehicular ad hoc network or application-layer peer-to-peer protocols over a broadband wireless network suffering from low lookup success rate, high lookup latency, and maintenance overhead of the P2P network. This article proposes a two-tier VANET/P2P architecture that exploits both VANET and P2P technology. In the low tier, vehicles form a VANET via intervehicle communication to exchange traffic information. On top of the VANET, a portion of the vehicles further establish a P2P overlay through a broadband wireless infrastructure to mitigate the disconnectivity problems of the VANET. Simulation results demonstrate that the two-tier architecture can significantly improve the lookup success rate compared to the single-tier VANET systems while reducing lookup latency and maintenance overhead compared to the single-tier P2P systems.

Rank-Based Network Coding for Content Distribution in Vehicular Networks

We propose a rank-based network coding scheme for distributing content in vehicular ad-hoc networks, in which vehicles adaptively broadcast packets based on the content reception status of their neighbors. In contrast to the previous work, CodeOn, vehicles in the proposed method only exchange content reception information in the service channel. The packet injection probability in the proposed method is proportional to the estimated innovation that a vehicle can provide to its neighbors. We also give an analytical model to analyze the system throughput when vehicles apply rank-based network coding to broadcast data. Simulation results demonstrate that the proposed method improves the throughput by more than 32% while maintaining lower end-to-end delay and protocol overhead than the previous work.