• Title/Summary/Keyword: adaptive schemes

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Incremental Redundancy Hybrid ARQ (IR-HARQ) Scheme Using Block LDPC Codes (블록 LDPC의 Incremental Redundancy Hybrid ARQ (IR-HARQ) 기법)

  • Kim, Dong Ho;Lee, Ye Hoon
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.38A no.8
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    • pp.662-668
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    • 2013
  • Mobile communication systems have been adopting link adaptive transmission schemes such as adaptive modulation and coding (AMC) and hybrid-ARQ (HARQ). Incremental redundancy (IR) HARQ scheme is known to be highly efficient in terms of throughput and power consumption and can be a good solution for mobile communication systems. In this paper, we propose an IR-HARQ scheme based on dual-diagonal parity-type block LDPC codes in which we define a transmission priority of coded bits and propose the sub-packet construction rule. We present the throughput performance of IR-HARQ with various modulation and coding and multi-antenna modes. Consequently, the proposed scheme provides the improvement of system throughput by elaborate link adaptation with CQI information.

Dynamic Right Sizing of Maximum-windows for Efficient Bandwidth Allocation on EPON (EPON에서 효율적 대역폭 할당을 위한 최대전송윈도우 크기의 동적변화기법)

  • Lee, Sang-Ho;Lee, Tae-Jin;Chung, Min-Young;Lee, You-Ho;Choo, Hyun-Seung
    • Journal of Internet Computing and Services
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    • v.8 no.4
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    • pp.41-49
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    • 2007
  • Ethernet passive optical network(EPON) is the next-generation technology for supporting services of high-quality at low-cost. In the EPON, all optical network units(ONUs) have to share a limited uplink channel for upstream data. In order to satisfy bandwidth demands of users on high-capacity local access networks(LANs), the optical line terminal(OLT) efficiently divides and allocates time slots of uplink channel to all ONUs. We discuss previous schemes for dynamic bandwidth allocation(DBA), such as interleaved polling with adaptive cycle time(IPACT) and sliding cycle time(SLICT). In this paper, dynamic right sizing of maximum-windows(DRSM), as a novel bandwidth allocation service, is proposed for more effective and efficient time slot allocation of the uplink channel. DRSM which is based on past information of bandwidth allocated by OLT calculates maximum available bandwidth and dynamically alters the maximum window size for the next ONU. This scheme does not only exert every effort to meet bandwidth demands of ONUs with the possible scope, it also seeks fairness of bandwidth allocation among ONUs.

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Design and Performance Evaluation of Receiver Feedback Closed Loop Pre-Distortion System (수신기 포함 폐루프 전치왜곡기 설계와 성능 평가)

  • Bok, Junyeong;Jo, Byung Gak;Baek, Gwang Hoon;Ryu, Heung-Gyoon
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.37A no.10
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    • pp.827-833
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    • 2012
  • The receiver performance is degraded by nonlinear memory problem in communication system. The pre-distorter techniques are an effective technique to compensate for the nonlinear distortion of the HPA without memory effects. However, memory effect of HPA can no longer be ignored when data signal is transmitted in high speed. Many adaptive pre-distorter schemes have been studied to compensate for memory effect problem of HPA in transmitter. The complexity and cost of satellite will increase when using adaptive pre-distorter in satellite communication system. In this paper, we propose receiver feedback closed loop pre-distortion technique in order to compensate for nonlinear problem of HPA with memory problem. The purpose of this paper is to reduce complexity and cost of satellite design by using only pre-distorter at terrestrial station.

Performance Enhancement of Slot-Count Selection Algorithm with Weight Differentiation in Gen-2 RFID Systems (Gen-2 RFID 시스템에서 가중치 차별화를 통한 슬롯 카운트 선택 알고리즘의 성능 향상)

  • Lim, In-Taek
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.15 no.3
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    • pp.561-566
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    • 2011
  • In EPCglobal Class-1 Gen-2 RFID system, a slot-count selection algorithm has been proposed to determine the slot-count size depending on the status of reply slot. In the slot-count selection algorithm of Gen-2, the slot-count value is increased or decreased by the weight C, which is identical and independent of the slot status. It has an advantage that the algorithm is simple, but it is difficult to maintain an optimal slot-count size. Therefore, in this paper, we propose an adaptive slot-count selection algorithm, which applies the parameter C differently based on the result of tag replies. Through simulations, it is demonstrated that the collision rate for the proposed scheme is about 42% and 65% lower than the schemes proposed by Wang and Gen-2. Therefore, the adaptive slot-count selection algorithm achieves faster tag identification time compared with the existing algorithms due to the low collision rate.

Performance Analysis of Adaptive Bandwidth and Subcarrier Allocation Scheme for a Multi-user OFDM System (다중 사용자 OFDM 시스템을 위한 적응적 대역폭 및 부반송파 할당 기법의 성능 분석)

  • Lim, Yeon-Ju;Park, Sang-Kyu
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.31 no.11A
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    • pp.1113-1119
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    • 2006
  • For a multi-user OFDM system in mobile channels which requires low-complexity in adaptive resource allocations, resource allocation algorithm using multi-threshold is proposed. The allocation scheme, which is performed by the multi-threshold values in descending order, considers only subcarriers over each threshold level. Moreover, some subcarriers with the lowest channel gain can be· removed in the present threshold level within the constraint of satisfaction of the required data rate, in order to allocate them to the other users when the allocation process of next threshold is executed. As a result, the proposed bandwidth and subcarrier algorithm has better system performances than the conventional allocation schemes in terms of required power and processing time, which is expected as a technique that improves the spectral efficiency of OFDM systems in a mobile environment.

A Study of Core-Stateless Mechanism for Fair Bandwidth Allocation (대역 공평성 보장을 위한 Core-Stateless 기법 연구)

  • Kim, Hwa-Suk;Kim, Sang-Ha;Kim, Young-Bu
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.28 no.4C
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    • pp.343-355
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    • 2003
  • Fair bandwidth allocations at routers protect adaptive flows from non-adaptive ones and may simplify end-to end congestion control. However, traditional fair bandwidth allocation mechanisms, like Weighted Fair Queueing and Flow Random Early Drop, maintain state, manage buffera and perform packet scheduling on a per-flow basis. These mechanisms are more complex and less scalable than simple FIFO queueing when they are used in the interi or of a high-speed network. Recently, to overcome the implementation complexity problem and address the scalability and robustness, several fair bandwidth allocation mechanisms without per-flow state in the interior routers are proposed. Core-Stateless Fair Queueing and Rainbow Fair Queuing are approximates fair queueing in the core-stateless networks. In this paper, we proposed simple Layered Fair Queueing (SLFQ), another core-stateless mechanism to approximate fair bandwidth allocation without per-flow state. SLFQ use simple layered scheme for packet labeling and has simpler packet dropping algorithm than other core-stateless fair bandwidth allocation mechanisms. We presente simulations and evaluated the performance of SLFQ in comparison to other schemes. We also discussed other are as to which SLFQ is applicable.

Symbol Based Rate Adaptation in Coded MIMO-OFDM Systems (심볼 기반의 적응 변조 기법을 이용한 채널 부호화된 MIMO-OFDM 시스템)

  • Sung, Chang-Kyung;Kim, Ji-Hoon;Lee, In-Kyu
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.33 no.1A
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    • pp.50-58
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    • 2008
  • The use of space-division multiple access(SDMA) in the downlink of multiuser multi-input/multi-output(MIMO) wireless transmission systems can provide substantial gains in system throughput. When the channel state information(CSI) is available at the transmitter, a considerable performance improvement can be attained by adapting the transmission rates to the reported CSI. In addition, to combat frequency selective fadings in wideband wireless channels, bit-interleaved coded OFDM(BIC-OFDM) modulation schemes are employed to provide reliable packet delivery by utilizing frequency diversity through channel coding. In this paper, we propose an adaptive modulation and coding(AMC) scheme combined with an opportunistic scheduling technique for the MIMO BIC-OFDM with bandwidth-limited feedback channels. The proposed scheme enhances the link performance by exploiting both the frequency diversity and the multiuser diversity. To reduce the feedback information, the proposed AMC scheme employs rate adaptation methods based on an OFDM symbol rather than on the whole subchannels. Simulation results show that the proposed scheme exhibits a substantial performance gain with a reasonable complexity over single antenna systems.

Channel State-Aware Joint Dynamic Cell Coordination Scheme using Adaptive Modulation and Variable Reuse Factor in OFDMA (OFDMA 하향링크에서 적응적 변조와 여러 개의 재사용 지수를 동시에 사용하고 채널 상태를 고려한 동적 셀 코디네이션)

  • Byun, Dae-Wook;Ki, Young-Min;Kim, Dong-Ku
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.32 no.1A
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    • pp.24-33
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    • 2007
  • In this paper, two different dynamic cell coordination strategies for frequency flat and selective fading are proposed for efficient subcarrier allocation in the joint consideration of adaptive modulation and variable frequency reuse in the channel-aware OFDMA downlink multicellular environment. Compared to a conventional OFDMA system without cell coordination, where system throughput may become degraded due to the persistent interference from other cells, the proposed system dynamically allows RNC to apply different reuse factors on each subchannel and scheduling in consideration of channel and interference conditions of individual users so as to increase the system throughput and guarantee QoS of each user. In a frequency flat fading, the dynamic scheme with the proposed scheduling achieves on average three times larger throughput than the conventional dynamic scheme [8]. In a selective fading channel, the proposed schemes showed 2.6 times as large throughput as that of a single reuse factor of one for all subchannels.

Outage Analysis and Optimal Power allocation for Network-coding-based Hybrid AF and DF (네트워크 코딩 기반의 협력통신에서 Hybrid AF and DF 방식의 아웃티지 성능 분석 및 최적 파워 할당 기법)

  • Bek, Joo-Ha;Lee, Dong-Hoon;Lee, Jae-Young;Heo, Jun
    • Journal of Broadcast Engineering
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    • v.17 no.1
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    • pp.95-107
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    • 2012
  • Network coding was proposed to increase the achievable throughput of multicast in a network. Recently, combining network coding into user cooperation has attracted research attention. For cooperative transmission schemes with network coding, users combine their own and their partners messages by network coding. In previous works, it was shown that adaptive DF with network coding can achieve diversity gain and additional throughput gain. In this paper, to improve performance of conventional protocols and maximize advantage of using network coding, we propose a new network coding based user cooperation scheme which uses adaptively amplify-and-forward and decode-and-forward according to interuser channel status. We derive outage probability bound of proposed scheme and prove that it has full diversity order in the high SNR regime. Moreover, based on the outage bound, we compute optimal power allocation for the proposed scheme.

Gateway Strategies for VoIP Traffic over Wireless Multihop Networks

  • Kim, Kyung-Tae;Niculescu, Dragos;Hong, Sang-Jin
    • KSII Transactions on Internet and Information Systems (TIIS)
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    • v.5 no.1
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    • pp.24-51
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    • 2011
  • When supporting both voice and TCP in a wireless multihop network, there are two conflicting goals: to protect the VoIP traffic, and to completely utilize the remaining capacity for TCP. We investigate the interaction between these two popular categories of traffic and find that conventional solution approaches, such as enhanced TCP variants, priority queues, bandwidth limitation, and traffic shaping do not always achieve the goals. TCP and VoIP traffic do not easily coexist because of TCP aggressiveness and data burstiness, and the (self-) interference nature of multihop traffic. We found that enhanced TCP variants fail to coexist with VoIP in the wireless multihop scenarios. Surprisingly, even priority schemes, including those built into the MAC such as RTS/CTS or 802.11e generally cannot protect voice, as they do not account for the interference outside communication range. We present VAGP (Voice Adaptive Gateway Pacer) - an adaptive bandwidth control algorithm at the access gateway that dynamically paces wired-to-wireless TCP data flows based on VoIP traffic status. VAGP continuously monitors the quality of VoIP flows at the gateway and controls the bandwidth used by TCP flows before entering the wireless multihop. To also maintain utilization and TCP performance, VAGP employs TCP specific mechanisms that suppress certain retransmissions across the wireless multihop. Compared to previous proposals for improving TCP over wireless multihop, we show that VAGP retains the end-to-end semantics of TCP, does not require modifications of endpoints, and works in a variety of conditions: different TCP variants, multiple flows, and internet delays, different patterns of interference, different multihop topologies, and different traffic patterns.