Enhancing WLAN/UMTS dual-mode services using a novel distributed multi-agent scheduling scheme Jiann-Liang Chen a, * , Ming-Chiao Chen b , Yan-Cheng Chang c a Department of Electrical Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan, ROC b Department of Computer Science and Information Engineering, National Taitung University, Taitung 95002, Taiwan, ROC c Department of Computer Science and Information Engineering, National Dong Hwa University, Hualien 97401, Taiwan, ROC article info Available online 28 February 2009 Keywords: Intelligent agent WLAN/UMTS dual-mode network Quality of Service Distributed multi-agent scheduling scheme abstract WLAN services are inexpensive and have a high bandwidth, while UMTS services provide wider coverage area and high mobility. Based on intelligent deduction, this study presents a novel service scheduling scheme for WLAN/UMTS dual-mode networks. The proposed system, Distributed Multi-Agent System (DMAS), consists of a set of problem-solving agents that autonomously process their own tasks and interoperate with one another by a shared database to reach a suitable schedule for dual-mode network services. A two-level control mechanism comprising local-control and meta-control is presented to achieve a high degree of goodness in service scheduling. Simulation results indicate that the Quality of Service (QoS) of the proposed discipline in terms of average delay and jitter is better than that of the pure UMTS network by 25% and 10%, respectively. The scheduling discipline can improve the service quality in multiple-mode networks. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction The ability of 3G (Universal Mobile Telecommunication System; UMTS) networks to operate seamlessly with existing WLAN (IEEE 802.11 Network) is critical for their widespread adoption [1]. Mobile nodes will adopt 3G networks to browse the Internet or communicate with one another [2]. Hence, multiple standards coexist in the same service environment, otherwise a combined multi-function system is generated for future wireless communications systems (see Fig. 1). There- fore, the interworking of systems must be optimized. Various systems have their own properties. High-tier systems like UMTS have a high mobility and low transmission bandwidth. Conversely, low-tier systems such as WLAN have low service costs and low mobility [3,4]. This study presents a novel discipline for service scheduling in WLAN/UMTS dual-mode net- works to achieve optimal service quality. A dual-mode node in a two-tier hierarchical architecture can choose either a WLAN or a UMTS as its access network. A dual-mode node can adopt WLAN as its access network, in which case the data traffic is sent through the wireless Access Point (AP) to the Internet. Mobile nodes have high data service rates and low service cost in this scenario. However, when the mobile user moves frequently between the WLAN APs or leaves indoor environment, the mobile node can adopt the UMTS signal to access the network service, and can thus avoid frequent handoff between different APs. Although possibly losing the high data rate and the low service cost, the mobile node obtains the highest mobility effect [5]. In the proposed two-tier hierarchical architecture, the UMTS network is called the high-tier network, and the WLAN is called the low-tier network. If a dual-mode device, the mobile node can choose the better network as its access network to connect with IP 0045-7906/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.compeleceng.2009.01.004 * Corresponding author. Tel.: +886 2 27376685x6743; fax: +886 2 27376699. E-mail addresses: Lchen@mail.ntust.edu.tw (J.-L. Chen), joechen@nttu.edu.tw (M.-C. Chen), yanchang@BenQ.com (Y.-C. Chang). Computers and Electrical Engineering 35 (2009) 609–621 Contents lists available at ScienceDirect Computers and Electrical Engineering journal homepage: www.elsevier.com/locate/compeleceng