Browsing by Author "Chen, Yung-Han"

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A fast handoff protocol for cellular IEEE 802.11e WLAN systems
(2007-02-01)
Chen, Yung-Han
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Chang, Chung-Ju
;
電信工程研究所
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Institute of Communications Engineering
This letter proposes a fast handoff protocol (FHP) for cellular IEEE 802.11e wireless local area network (WLAN) systems. The FHP, which is standard compatible, provides a controlled contention period (CCP) designated for handoff requests (HO-REQs), arranges these HO-REQs to contend sequentially in CCP, and proposes a fuzzy adjustment method (FAM) to determine a proper length for CCR Simulation results reveal that the FHP can significantly decrease the forced termination rate of HO-REQs and still enhance the system throughput of contention period for cellular IEEE 802.11e WLAN systems.
A Multi-Factors Cell Selection Scheme for Heterogeneous Networks with Multimedia Traffic
(2013)
Chung, Wen-Ching
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Chang, Chung-Ju
;
Hsieh, Chih-Yuan
;
Chen, Yung-Han
;
電機資訊學士班
In this paper, we propose a multi-factors cell selection (MFCS) scheme for heterogeneous networks with multimedia traffic. In heterogeneous networks, it is an important issue to determine a suitable access network for call request to support seamless service and highspeed connectivity. The MFCS scheme first chooses candidate cells for call request to satisfy the received signal strength constraint, cell loading constraint, and dwell time constraint. It then determines a target cell from candidate cells based on the QoS factor, loading factor, and mobility factor. Simulation results show that, the MFCS scheme reduces the handoff occurring ratio by 25.5 % and improves the overall system throughput by 15.9 % as compared to the utility and game-theory based network selection (UGNS) scheme [6].
A Preference Value-Based Cell Selection Scheme in Heterogeneous Wireless Networks
(2010)
Chang, Chung-Ju
;
Hsieh, Chih-Yuan
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Chen, Yung-Han
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電信工程研究所
;
Institute of Communications Engineering
This paper proposes a preference value-based cell selection (PVCS) scheme to satisfy quality of service (QoS) requirements, maximize accommodated number of calls, and minimize handoff occurrence frequency in heterogeneous wireless networks. The PVCS scheme contains three stages including candidate cells selection, preference value calculation, and target cell determination. The candidate cells selection is used to sift the suitable cells for the call request. All suitable cells form a candidate cell set. The preference value calculation computes the preference value of each cell in the candidate cell set, which is optimized by considering QoS factor, loading factor, and mobility factor, for the purpose of maintaining QoS requirements of a call request, maximize accommodated number of calls, and minimizing handoff occurrence frequency. Eventually, the candidate cell, which has the maximum preference value, would be selected for the call request. Simulation results show that PVCS scheme achieves higher total throughput than UGT while satisfying the QoS requirements. It also has lower new call blocking rate and handoff call dropping rate than UGT, which means more accommodated calls than UGT. Besides, PVCS reduces the total handoff occurrence frequency by about 20% as compared to UGT.
A utility function-based access selection method for heterogeneous WCDMA and WLAN networks
(2007)
Chen, Yung-Han
;
Yang, Nuan-Yu
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Chang, Chung-Ju
;
Ren, Fang-Ching
;
電信工程研究所
WCDMA/WLAN interworking networks are considered to support high-data-rate multimedia services and high mobility. In this paper, we propose a utility function-based access selection method (UFAS) to determine which cell is most suitable for a mobile node's service request in heterogeneous WCDMA and WLAN networks. The UFAS method contains three parts, cells classification, utility function computation, and target cell determination. This utility function is composed of four evaluation functions, and is designed with a balancing index which can reduce the utility value of a cell if the cell is heavily loaded. Simulation results show that the UFAS method achieves larger system throughput than a policy-enabled (PE) handoff decision method [8]. Moreover, the UFAS method can reduce handoff occurrence rates and strike a balance between system utilization and cell loading while maintaining QoS requirements.
Fuzzy Q-Learning Admission Control for WCDMA/WLAN Heterogeneous Networks with Multimedia Traffic
(2009-11-01)
Chen, Yung-Han
;
Chang, Chung-Ju
;
Huang, Ching Yao
;
電子工程學系及電子研究所
;
電信工程研究所
In this paper, admission control by a fuzzy Q-learning technique is proposed for WCDMA/WLAN heterogeneous networks with multimedia traffic. The fuzzy Q-learning admission control (FQAC) system is composed of a neural-fuzzy inference system (NFIS) admissibility estimator, an NFIS dwelling estimator, and a decision maker. The NFIS admissibility estimator takes essential system measures into account to judge how each reachable subnetwork can support the admission request's required QoS and then output admissibility costs. The NFIS dwelling estimator considers the Doppler shift and the power strength of the requested user to assess his/her dwell time duration in each reachable subnetwork and then output dwelling costs. Also, in order to minimize the expected maximal cost of the user's admission request, a minimax theorem is applied in the decision maker to determine the most suitable subnetwork for the user request or to reject. Simulation results show that FQAC can always maintain the system QoS requirement up to a traffic intensity of 1.1 because it can appropriately admit or reject the users' admission requests. Also, the FQAC can achieve lower blocking probabilities than conventional JSAC proposed in [20] and can significantly reduce the handoff rate by 15-20 percent.