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ABSTRACT: Wireless multi-hop relaying has been attracting considerable attention as a promising technique for future communication systems. The multi-hop relaying technique has many benefits, but many problems must be overcome if it is to be used successfully. One of the biggest is a degradation of system reliability that is caused by data being transmitted through many wireless links. Many automatic repeat request (ARQ) mechanisms have been proposed to improve system reliability. We propose an analytical model of hop-by-hop ARQ mechanisms and analyze performances using a discrete-time Markov chain (DTMC) technique. The proposed analytical model considers Poisson packet arrival, packet error rate, and channel capacity in a two-hop chain topology. In addition, we propose a rate control algorithm to compensate the weak point of the hop-by-hop ARQ mechanism. We evaluate the performance of the proposed ARQ mechanism with the rate control algorithm by comparing numerical analysis with simulation results.
Vehicular Technology Conference (VTC 2010-Spring), 2010 IEEE 71st; 06/2010
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ABSTRACT: Visible-light communication provides many advantages over other forms of communications, such as visibility, high SNR (Signal to Noise Ratio), easy installation, freedom of interference from radio or electromagnetic waves, usage of license free frequency band, and high security. Furthermore, the exponentially increasing requirements and quality of LEDs (Light Emitting Diodes) have encouraged the development of visible-light communication that makes use of LEDs. In a visible-light communication system, an LOS (Line of Sight) link between two transceivers should be guaranteed due to the straightness of the visible-light signal. However, link failure caused by temporary blocking or poor orientation of a transmitter frequently occurs, causing burst frame errors. In this paper, we focus on how to let a user know about link failure as quickly as possible, in order that the link failure problem may be solved by realigning the transmission signal towards the receiver. This is furthermore a relatively straightforward matter, by the very nature of this system being a visible means of communication. It is also required that the visibility should be supported when a user attempts initial access procedure. Nevertheless, by supporting visibility, system performance can be degraded because some additional resources are required for the visibility to be enabled. In this paper, we propose three schemes for supporting visibility without reducing system performance in a visible-light local area network
IEEE Transactions on Consumer Electronics 06/2010; · 0.94 Impact Factor
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Proceedings of the 71st IEEE Vehicular Technology Conference, VTC Spring 2010, 16-19 May 2010, Taipei, Taiwan; 01/2010
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ABSTRACT: In multi-hop relaying systems that have many relay stations (RSs), a cognitive radio (CR) technique can improve system performance greatly, due to an efficient resource sharing between the RSs. In this letter, the performance of an ARQ mechanism for CR-based multi-hop relaying systems is studied, using Markov chain and matrix signal flow graph (MSFG) techniques. Also, a priority-based resource allocation scheme is proposed to prevent performance degradation caused by the usage of unstable resources acquired by the CR technique.
IEEE Communications Letters 08/2009; · 0.98 Impact Factor
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IEEE Communications Letters. 01/2009; 13:504-506.
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ABSTRACT: Indoor wireless communication systems have been developed to improve cell coverage and throughput with low cost in indoor environment. Among several indoor wireless communication systems such as mobile WiMAX (worldwide interoperability for microwave access) system, WPAN (wireless personal area network) and WLAN (wireless local area network), the mobile WiMAX is one of the promising next-generation wireless communication systems and considered for military use by the U.S. Army. In indoor environment, a band AMC mode which is one of subchannel allocation modes in the mobile WiMAX system is mainly used since it is appropriate to the fixed or low mobility environments. However, the conventional band AMC mode is optimized for the outdoor environment, so it will cause many problems in the indoor environment. In this paper, we propose a new band AMC operation suited for the indoor environment. The proposed band AMC operation allocates the resource flexibly in indoor environment and it is compatible with the existing mobile WiMAX standard. The numerical analysis and simulation results show that a channel utilization of the proposed band AMC mode is higher than that of the conventional band AMC mode.
Military Communications Conference, 2008. MILCOM 2008. IEEE; 12/2008
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Proceedings of the 67th IEEE Vehicular Technology Conference, VTC Spring 2008, 11-14 May 2008, Singapore; 01/2008
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Proceedings of the 66th IEEE Vehicular Technology Conference, VTC Fall 2007, 30 September - 3 October 2007, Baltimore, MD, USA; 01/2007
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ABSTRACT: In high speed downlink packet access (HSDPA), packet scheduler is a key element for high-speed and efficient transmissions. In this paper, we propose an enhanced packet scheduling algorithm which computes the priority according to the proportional fair algorithm. That is, for users to need hybrid ARQ retransmission in case of erroneous packets, the priority of the proportional fair algorithm is elegantly modified to reduce the transfer delay without degradation of system throughput.
Vehicular Technology Conference, 2006. VTC-2006 Fall. 2006 IEEE 64th; 10/2006
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ABSTRACT: HSDPA (high-speed downlink packet access) is an evolved UMTS packet scheme that delivers increased user peak data rates and supports quality of service. A key technique supporting HSDPA is adaptive modulation and coding (AMC), in which the modulation scheme and the coding rate are changed adaptively according to the downlink channel quality reported by the user equipment (UE). Therefore, the channel quality indication (CQI) reporting scheme is directly related to the accuracy of AMC and the performance of HSDPA. In the current specification of HSDPA, each UE must periodically report to Node B the CQI. Hence, UE must report the same CQI value repeatedly when the channel quality is unchanged. Obviously, this is the waste of the UE's battery power. To solve this problem, we propose channel adaptive CQI reporting schemes in which UEs report the CQI value intelligently using information about channel quality. With the proposed schemes, the battery capacity of UEs can be conserved and the uplink interference can be lowered by filtering off redundant CQI reports or the transmission error rate can be lowered by fast CQI reports.
Vehicular Technology Conference, 2006. VTC-2006 Fall. 2006 IEEE 64th; 10/2006
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ABSTRACT: HSDPA (high-speed downlink packet access) is an evolved UMTS packet scheme that delivers increased user peak data rates and quality of service. A key technique supporting HSDPA is adaptive modulation and coding (AMC), in which the modulation scheme and the coding rate are changed adaptively according to the downlink channel quality reported by the user equipment (UE). Therefore, the channel quality indication (CQI) reporting scheme is directly related to the accuracy of AMC and the performance of HSDPA. This letter proposes channel adaptive CQI reporting schemes in which UEs report the CQI value intelligently by using information about channel quality. With the proposed schemes, the battery capacity of UE can be conserved and the uplink interference can be lowered by filtering off redundant CQI reports or the transmission error rate can be lowered by fast CQI reports
IEEE Communications Letters 07/2006; · 0.98 Impact Factor
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Vehicular Technology Conference, 2005. VTC-2005-Fall. 2005 IEEE 62nd; 10/2005
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ABSTRACT: To conserve the battery capacity of mobile terminals and manage uplink bandwidth effectively, power-efficient cache management schemes that can be used in mobile environments are proposed. With the proposed schemes, the number of redundant data request messages for identical data decreases significantly compared with conventional cache management schemes.
IEEE Communications Letters 08/2005; · 0.98 Impact Factor
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ABSTRACT: A major evolution of UMTS standard is the high speed downlink packet access (HSDPA). One of key techniques supporting HSDPA is the adaptive modulation and coding (AMC) in which the modulation scheme and the coding rate are adaptively changed according to the downlink channel quality reported by the user equipment (UE). Therefore, the channel quality indication (CQI) reporting scheme is directly related to the accuracy of AMC and the performance of HSDPA. This letter proposes an enhanced CQI reporting scheme that can be used when a proportional fair scheduling algorithm (PFA) is used as a packet scheduling algorithm. The proposed scheme uses a dynamic threshold to filter off redundant CQI reports. With the proposed scheme, the battery capacity of UK can be conserved, maintaining the performance of traditional CQI reporting scheme.
IEEE Communications Letters 06/2005; · 0.98 Impact Factor
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ABSTRACT: In mobile environments, where data is broadcasted, the caching of frequently accessed data in the battery-powered mobile terminals is a very attractive technique in terms of the energy and bandwidth efficiency. The invalidation report (IR) based caching strategy is one of the popular caching strategies by its scalability. In the IR-based caching strategy, the data consistency is maintained by using the IR which has the information of updated data. In this paper, we approach the IR-based caching strategy in view of the energy efficiency and propose the energy-efficient caching strategy. With the proposed caching strategy, redundant data request messages for the identical data decrease significantly. Simulation results show that the proposed caching strategy has a great effect on the conservation of the battery capacity of mobile terminals and the uplink bandwidth compared with the conventional IR-based caching strategy.
Vehicular Technology Conference, 2005. VTC 2005-Spring. 2005 IEEE 61st;
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ABSTRACT: A major evolution of UMTS standard is the High Speed Downlink Packet Access (HSDPA). Several new technologies are applied to HSDPA system. One of key techniques supporting HSDPA is the adaptive modulation and coding (AMC) in which the modulation scheme and the coding rate are adaptively changed according to the downlink channel quality reported by the user equipment (UE). Therefore, the channel quality indication (CQI) feedback scheme is directly related to the accuracy of AMC and the performance of HSDPA. This paper proposes an enhanced CQI feedback scheme that can be used when a proportional fair scheduling algorithm (PFA) is used as a packet scheduling algorithm. The enhanced CQI feedback scheme uses a dynamic threshold to filter off redundant CQI feedbacks. With the proposed scheme, the battery capacity of UE can be conserved, maintaining the performance of traditional CQI feedback scheme.
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[show abstract]
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ABSTRACT: HSDPA (High-Speed Downlink Packet Access) is an evolved UMTS packet scheme that delivers increased user peak data rates and supports quality of service. A key technique supporting HSDPA is adaptive modulation and coding (AMC), in which the modulation scheme and the coding rate are changed adaptively according to the downlink channel quality reported by the user equipment (UE). Therefore, the channel quality indication (CQI) reporting scheme is directly related to the accuracy of AMC and the performance of HSDPA. In the current specification of HSDPA, each UE must periodically report to Node B the CQI. Hence, UE must report the same CQI value repeatedly when the channel quality is unchanged. Obviously, this is the waste of the UE’s battery power. To solve this problem, we propose channel adaptive CQI reporting schemes in which UEs report the CQI value intelligently using information about channel quality. With the proposed schemes, the battery capacity of UEs can be conserved and the uplink interference can be lowered by filtering off redundant CQI reports or the transmission error rate can be lowered by fast CQI reports. This research was supported in part by University IT Research Center Project.(ITRC)
