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Now showing 1 - 9 of 9

Mini-slot scheduling for IEEE 802.16d chain and grid mesh networks
(2010-11-15)
Liang, Jia-Ming
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Wu, Ho-Cheng
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Chen, Jen-Jee
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Tseng, Yu-Chee
;
資訊工程學系
This work considers the mini-slot scheduling problem in IEEE 802.16d wireless mesh networks (WMNs) An efficient mini-slot scheduling needs to take into account the transmission overhead, the scheduling complexity, and the signaling overhead to broadcast the scheduling results We are interested in chain and grid WMNs, which are the basic topologies of many applications We propose scheduling schemes that are featured by low complexity and low signaling overhead. Compared to existing works, this work contributes in developing low-cost schemes to find periodical and regular schedules that achieve near-optimal transmission latencies by balancing between transmission overhead and pipeline efficiency and that are more practical and easier to implement To minimize the transmission latency, we model the transmission latency as a function of the transmission size and the subscriber stations' traffic demands, and take the first-order derivative of the transmission size to find the minimum latency Simulation results show that our schemes significantly improve over existing works in computational complexity while maintain similar or better transmission latencies (C) 2010 Elsevier B.V All rights reserved.
Integrating SIP and IEEE 802.11e to support handoff and multi-grade QoS for VoIP-over-WLAN applications
(2011-06-01)
Chen, Jen-Jee
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Lee, Ling
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Tseng, Yu-Chee
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資訊工程學系
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Department of Computer Science
With the increasing popularity of WLANs and the growing demand for VoIP services, there is a need to guarantee QoS for VoIP calls while support as many calls as possible. Prior efforts focus on call admission control (CAC), but did not address the important handoff and physical rate adaptation issues caused by mobility and wireless channel variation. Assuming that VoIP calls can be supported by multi-grade QoS levels and that handoff and rate adaptation are possible, we show how to conduct CAC and resource management by integrating SIP and the QoS mechanisms of IEEE 802.11e together. When wireless resource is stringent, our resource management can dynamically adjust the resource distribution among existing calls by controlling their supporting codecs and packetization intervals. This not only takes care of calls in bad channel conditions, but also can accept more calls. Thus multi-grade QoS is achieved with decreased blocking rate for new calls and less dropping rate for handoff calls. In addition, we also show how to achieve early resumption of resources for handoff calls. Both analytical and simulation results are presented to evaluate the performance of the proposed schemes. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.
Managing Power Saving Classes in IEEE 802.16 Wireless MANs: A Fold-and-Demultiplex Method
(2011-09-01)
Tseng, Yu-Chee
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Chen, Jen-Jee
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Yang, Yen-Chih
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資訊工程學系
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Department of Computer Science
In IEEE 802.16, power management at the Mobile Subscriber Station (MSS) side is always an important issue. The standard defines three types of power saving classes (PSCs). A PSC can bind one or multiple traffic flows. However, given multiple flows in an MSS, the standard does not define how to form PSCs, how to organize the cooperation of multiple PSCs to obtain better energy efficiency, and how to guarantee QoS of these flows. Given a set of flows and their QoS parameters, the objective of this paper is to define multiple PSCs and their listen-and-sleep-related parameters and packet-scheduling policy such that the unavailability intervals of the MSS can be maximized and the QoS of each flow can be guaranteed. To achieve this, we propose a novel fold-and-demultiplex method for an IEEE 802.16 network with PSCs of types I and II together with an earliest-next-bandwidth-first packet scheduler. Given a set of traffic flows in an MSS, the fold-and-demultiplex method first gives each flow a tentative PSC satisfying its bandwidth requirement. Then we fold them together into one long series so as to calculate the total bandwidth requirement. Finally, we demultiplex the series into multiple PSCs, each supporting one or multiple flows. It ends up with high energy efficiency of MSSs while meets flows' bandwidth requirements. Furthermore, our packet scheduler ensures that real-time flows' delay constraints can be met. To the best of our knowledge, this is the first result offering bounded packet delays under MSS's sleep-and-listen behaviors.
On Tile-and-Energy Allocation in OFDMA Broadband Wireless Networks
(2011-12-01)
Liang, Jia-Ming
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Chen, Jen-Jee
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Liu, Cheng-Wen
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Tseng, Yu-Chee
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Lin, Bao-Shuh Paul
The Orthogonal Frequency Division Multiple Access (OFDMA) technique has been widely applied in broadband wireless networks, such as IEEE 802.16 (WiMAX) and 3GPP Long Term Evolution (LTE). Existing studies have targeted at improving network throughput by increasing the transmission rates of mobile stations (MSs). Nevertheless, this is at the cost of higher energy consumption of MSs. In the letter, we consider the tile-and-energy joint allocation problem for uplink transmissions in an OFDMA wireless network. We formulate this problem as a mixed integer programming, where the objective is to minimize MSs' energy consumption subject to satisfying their traffic demands. We show this to be NP-hard and develop a heuristic taking advantage of the water-filling technique. Simulation results show that the performance of our heuristic is close to the optimum, especially when the network is under non-saturated condition.
Energy-efficient uplink resource allocation for IEEE 802.16j transparent-relay networks
(2011-11-10)
Liang, Jia-Ming
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Wang, You-Chiun
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Chen, Jen-Jee
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Liu, Jui-Hsiang
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Tseng, Yu-Chee
The IEEE 802.16j standard is defined to enhance WiMAX networks with relay capacity. Under the transparent mode, existing studies only target improving network throughput by increasing the transmission rates of mobile stations (MSs) and maximizing concurrent transmissions. However, using a higher transmission rate or allowing more concurrent transmissions could harm MSs in terms of their energy consumption, especially when they are battery-powered. In this paper, we consider the energy-conserved resource allocation problem in the uplink direction of an IEEE 802.16j network under the transparent mode. This problem asks how to arrange the frame usage with satisfying MSs' demands as the constraint and minimizing their total energy consumption as the objective. We prove this problem to be NP-complete and develop two energy-efficient heuristics, called demand-first allocation (DFA) and energy-first allocation (EFA) schemes. These heuristics employ a gradient-like search method to approximate the optimal solution. Specifically, DFA tries to satisfy MSs' demands first by using as less frame space as possible. Then, with the remaining frame space. DFA tries to save MSs' energy by lowering their transmission rates or adjusting their transmission paths. Viewed from a different perspective. EFA first allocates the frame space to MSs to consume the least energy. Since the total allocation may exceed the frame space. EFA then exploits spatial reuse and rate adjustment to pack all demands into one frame. simulation results show that our heuristics can approximate the ideal performance bounds and save up to 90% of MSs' energy as compared to existing results. (C) 2011 Elsevier B.V. All rights reserved.
Per-flow sleep scheduling for power management in IEEE 802.16 wireless networks
(2011-11-10)
Chen, Jen-Jee
;
Wu, Shih-Lin
;
Wang, Shiou-Wen
;
Tseng, Yu-Chee
;
資訊工程學系
Power management is a critical issue in IEEE 802.16 wireless networks. In the standard, a power saving class (PSC) of type II is defined to support real-time traffic flows. It allows a flow to switch periodically between active and sleep states to save energy. However, previous studies either consider adjusting start frames of PSCs by assuming that the PSCs are already given or assume one single PSC to accommodate all flows in a mobile station, thus leading to higher energy cost. This paper proposes two "per-flow" sleep scheduling schemes, which assign one PSC to each real-time flow according to its QoS parameters. This leads to less energy consumption, more efficient use of bandwidth, and more compact listening windows. We also prove that deciding whether a given scheduling problem is solvable can be reduced to a maximum matching problem, which is computationally tractable. Simulation results show that such a per-flow scheduling does perform much closer to the active ratio lower bound and achieve higher resource utilization than previous schemes. (C) 2011 Elsevier B.V. All rights reserved.
A seamless handoff mechanism for DHCP-based IEEE 802.11 WLANs
(2007-08-01)
Chen, Jen-Jee
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Tseng, Yu-Chee
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Lee, Hung-Wei
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資訊工程學系
;
Department of Computer Science
IEEE 802.11 wireless networks have gained great popularity. However, handoff is always a critical issue in this area. In this paper, we propose a novel seamless handoff mechanism for IEEE 802.11 wireless networks which support IEEE 802.11i security standard. Our approach consists of a Dynamic Tunnel Establishing procedure and a seamless handoff mechanism. Both intra- and inter-subnet handoff cases are considered in our seamless handoff approach. Our work focuses on handoffs in DHCP-based IP networks rather than Mobile IP-supported networks, but the proposed scheme can be easily tailored to Mobile IP-supported networks.
Design and implementation of a SIP-based mobile and vehicular wireless network with push mechanism
(2007-11-01)
Tseng, Yu-Chee
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Chen, Jen-Jee
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Cheng, Yu-Li
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資訊工程學系
;
Department of Computer Science
As portable devices are gaining more popularity, maintaining Internet connectivity anytime and anywhere becomes critical, particularly for mobile and vehicular networks. Network mobility (NEMO) and Internet Protocol mobility are gaining more and more importance. In this paper, we develop a Session Initiation Protocol (SIP)-based mobile network architecture to support NEMO for vehicular applications. We propose to form a mobile ad hoc network (MANET) by the mobile hosts (MHs) inside a vehicle or a cluster of vehicles. The MANET is connected to the outside world via a SIP-based Mobile Network Gateway (SIP-MNG), which is equipped with one or multiple external wireless interfaces and some internal IEEE 802.11 interfaces. The external interfaces of the SIP-MNG support Internet connectivity by aggregating user traffic to and from the Internet. In addition, exploiting the session information carried by SIP signaling, the SIP-MNG supports resource management and call admission control for the MHs. However, wireless access incurs charges, power consumption, and overhead of mobility management. So, it is desirable to allow the SIP-MNG to disconnect its external interfaces when necessary. To guarantee that users inside the mobile network will not lose any incoming request, we propose a push mechanism through short message service to wake up these wireless interfaces in an on-demand manner. We show the detailed signaling to support such a mechanism. The proposed system is fully compatible with existing SIP standards. Our real prototyping experience and some experimental results are also reported.
A Cross-Layer Framework for Overhead Reduction, Traffic Scheduling, and Burst Allocation in IEEE 802.16 OFDMA Networks
(2011-05-01)
Liang, Jia-Ming
;
Chen, Jen-Jee
;
Wang, You-Chiun
;
Tseng, Yu-Chee
;
資訊工程學系
IEEE 802.16 orthogonal frequency-division multiple access (OFDMA) downlink subframes have a special 2-D channel-time structure. Allocation resources from such a 2-D structure incur extra control overheads that hurt network performance. Existing solutions try to improve network performance by designing either the scheduler in the medium access control layer or the burst allocator in the physical layer, but the efficiency of overhead reduction is limited. In this paper, we point out the necessity of "codesigning" both the scheduler and the burst allocator to efficiently reduce overheads and improve network performance. Under the partial-usage-of-subcarriers model, we propose a cross-layer framework that covers overhead reduction, real-time and non-real-time traffic scheduling, and burst allocation. The framework includes a two-tier priority-based scheduler and a bucket-based burst allocator, which is more complete and efficient than prior studies. Both the scheduler and the burst allocator are tightly coupled together to solve the problem of arranging resources to data traffic. Given available space and bucket design from the burst allocator, the scheduler can well utilize the frame resource, reduce real-time traffic delays, and maintain fairness. On the other hand, with priority knowledge and resource assignment from the scheduler, the burst allocator can efficiently arrange downlink bursts to satisfy traffic requirements with low complexity. Through analysis, the cross-layer framework is validated to give an upper bound to overheads and achieve high network performance. Extensive simulation results verify that the cross-layer framework significantly increases network throughput, maintains long-term fairness, alleviates real-time traffic delays, and enhances frame utilization.

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