Browsing by Author "Yang, Wen-Hsin"

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A request control scheme for data recovery in DVB-IPDC systems with spatial and temporal packet loss
(2013-07-01)
Yang, Wen-Hsin
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Wang, You-Chiun
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Tseng, Yu-Chee
;
Lin, Bao-Shuh Paul
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資訊工程學系
Recently, digital video broadcasting-handheld (DVB-H) and IP datacast over DVB-H (DVB-IPDC) have been developed to support broadcasting services. DVB-H is designed to support digital video broadcast for handheld devices, whereas DVB-IPDC can integrate with an IP-relay network to complement the data loss problem in DVB-H. Assuming that WiMAX networks are adopted to support DVB-IPDC, this paper points out two critical problems: group packet loss (GPL) and broadcast data handover (BDH). GPL occurs when there is a burst of retransmission requests for the same pieces of data with high spatial or temporal correlation. BDH happens when some devices that made the above requests handover to new serving cells. To solve these problems, we propose lazy wait and group acknowledgement schemes to alleviate duplicate requests by exploiting their spatial and temporal correlations. This not only reduces the requests submitted by neighboring devices in both space and time domains but also avoids handovering devices from sending duplicate requests in new cells. Through mathematical analysis, we show how to adaptively adjust the timers of lazy wait and group acknowledgement based on channel quality. Simulation results prove that our schemes can efficiently reduce retransmission requests and retransmission packets, thus alleviating congestion in the IP-relay network. Copyright (c) 2011 John Wiley & Sons, Ltd.
Efficient Packet Recovery Using Prioritized Network Coding in DVB-IPDC Systems
(2012-03-01)
Yang, Wen-Hsin
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Wang, You-Chiun
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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
The DVB-H standard is proposed to disseminate videos to mobile devices. However, packet loss is inevitable due to the broadcasting nature. To deal with this issue, DVB-IPDC suggests incorporating another wireless network for data retransmission. This paper takes a WiMAX network as an example in DVB-IPDC and models its channel as repetitive frames. During each frame, mobile devices sends their recovery requests of lost packets to a WiMAX base station and the base station adopts network coding to broadcast these packets. This paper then formulates a prioritized network coding (PNC) problem that asks how the base station uses at most tau coded packets in each frame such that it can recover the maximum aggregate number of lost packets while minimize the aggregate number of packets discarded due to out of deadlines. We develop a solution using XOR coding, which constructs a weighted bipartite graph to calculate the benefit to broadcast each coded packet. Then, the solution tries to maximize the overall benefit by finding a maximum-weighted tau dominating set. The contribution of this paper is to propose a new PNC problem in DVB-IPDC systems and develop an efficient PNC solution.
Energy-efficient network selection with mobility pattern awareness in an integrated WiMAX and WiFi network
(2010-02-01)
Yang, Wen-Hsin
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Wang, You-Chiun
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Tseng, Yu-Chee
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Lin, Bao-Shuh P.
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資訊工程學系
To provide wireless Internet access, WiFi networks have been deployed in many regions such as buildings and campuses. However, WiFi networks are still insufficient to support ubiquitous wireless service due to their narrow coverage. One possibility to resolve this deficiency is to integrate WiFi networks with the wide-range WiMAX networks. Under such an integrated WiMAX and WiFi network, flow to conduct energy-efficient handovers is a critical issue. In this paper, we propose a handover scheme with geographic mobility awareness (HGMA), which considers the historical handover patterns of mobile devices. HGMA can conserve the energy of handovering devices from three aspects. First, it prevents mobile devices from triggering unnecessary handovers according to their received signal strength and moving speeds. Second, it contains a handover candidate selection method for mobile devices to intelligently select a subset of WiFi access points or WiMAX relay stations to be scanned. Therefore, mobile devices can reduce their network scanning and thus save their energy. Third, HGMA prefers mobile devices staying in their original WiMAX or WiFi networks. This can prevent mobile devices from consuming too much energy on interface switching. In addition, HGMA prefers the low-tier WiFi network over the WiMAX network and guarantees the bandwidth requirements of handovering devices. Simulation results show that HGMA can save about 59-80% of energy consumption of a handover operation, make mobile devices to associate with WiFi networks with 16-62% more probabilities, and increase about 20-61% of QoS satisfaction ratio to handovering devices. Copyright (C) 2009 John Wiley & Sons, Ltd.
Spatial and Temporal Packet Recovery Schemes for DVB-H Systems through IP-Relay Wireless Networks
(2009)
Yang, Wen-Hsin
;
Wang, You-Chiun
;
Tseng, Yu-Chee
;
Lin, Bao-Shuh P.
;
資訊工程學系
The DVB-H standard has been defined to provide digital video broadcast to mobile handheld devices. However, without a request channel, a handheld device may encounter data loss and thus it requires an additional recovery architecture to relieve this problem. In this paper, we follow the DVB-IPDC standard and propose combining a DVB-H system with an IP-relay wireless network. A handheld device losing DVB-H data can thus request the relay network for retransmission. Under this architecture, we identify two critical issues, group packet loss (GPL) and broadcast data handover (BDH). The GPL problem occurs when there are bursty requests for retransmissions of the same data with high spatial and temporal locality, causing network congestion. The BDH problem occurs when these requesting devices move out of their current serving cells. In this paper, we propose a bulk request recovery (BRR) scheme to solve these problems by exploiting spatial and temporal locality of recovery requests. Our scheme can efficiently reduce duplicate requests and schedule retransmissions of lost packets, so both GPL and BDH problems are relieved. Simulations results are also presented to verify the effectiveness of our result.