• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 하계종합학술대회 논문집(4)
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• pp.29-32
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• 2002

In typical block-based video coding, the objective of RC(Rate Control) is to select the quantization parameters so that the encoder produces bits at the rate of the channel and the overall distortion is minimized. To reduce the huge amount of computations required for offline RC, there have been significant efforts to speed up the process of video encoders. Those efforts have been mainly focused on the modes for bit rate and distortion in types of coders, in terms of the quantization parameters. Because previous works related to model based online RC are based on statistics of previous frame, it occurs the problem such that allocates bits unequally without regard to current frame statistics. In this thesis, an equal bit allocation scheme using current frame statistics is proposed.

• Journal of Information Processing Systems
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• 제10권2호
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• pp.163-175
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• 2014

This paper will focus on improving the performance of orthogonal frequency division multiplexing (OFDM) in Rayleigh fading environments. The proposed technique will use a previously published method that has been shown to improve OFDM performance in independent fading, based on ordered sub-carrier selection. Then, a simple non-iterative method for finding the optimal bit-loading allocation was proposed. It was also based on ordered sub-carrier selection. We compared both of these algorithms to an optimal bit-loading solution to determine their effectiveness in a correlated fading environment. The correlated fading was simulated using the JTC channel models. Our intent was not to create an optimal solution, but to create a low complexity solution that can be used in a wireless environment in which the channel conditions change rapidly and that require a simple algorithm for fast bit loading.

• 한국통신학회논문지
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• 제38A권9호
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• pp.750-758
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• 2013

본 논문은 type I 혼합-자동 반복 요구 (hybrid automatic repeat request: H-ARQ) 시스템에서 저밀도 패리티검사 (low-density parity-check: LDPC)로 부호화된 직교 주파수 분할 다중화 (orthogonal frequency division multiplexing: OFDM) 서브프레임의 전송 순서를 균등 결합 전력이 할당되도록 조정한 재전송 방법을 기초로 성능 개선을 채널 용량을 사용하여 분석하고, 계층 복호 방법을 적용하여 H-ARQ 재전송 기법의 수렴 속도 개선을 확인한다. 구체적으로 임의의 서브프레임 재전송 패턴에 대하여 채널 용량이 클수록 비트오류율 (bit error rate: BER) 성능도 우수하다는 사실을 검증한다. 그러므로 각 서브프레임에 대하여 균등 결합 전력 할당을 보장하는 서브프레임 재전송 패턴은 채널 용량을 최대로 하며, 임의의 다른 서브프레임 전송 순서 조정을 통한 재전송 패턴보다 성능이 우수하다. 결국 균등 결합 전력 할당을 만족하도록 서브프레임 순서를 조정하는 재전송 방법은 기존 체이스 결합 (Chase combining)보다 복호 복잡도를 증가시키지 않으면서도 주목할 만한 성능 개선을 보인다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권12호
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• pp.3018-3036
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• 2013

In this paper, we investigate power allocation scheme and outage performance for a physical-layer network coding (PNC) relay based secondary user (SU) communication in cognitive multi-antenna relay networks (CMRNs), in which two secondary transceivers exchange their information via a multi-antenna relay using PNC protocol. We propose an optimal energy-efficient power allocation (OE-PA) scheme to minimize total energy consumption per bit under the sum rate constraint and interference power threshold (IPT) constraints. A closed-form solution for optimal allocation of transmit power among the SU nodes, as well as the outage probability of the cognitive relay system, are then derived analytically and confirmed by numerical results. Numerical simulations demonstrate the PNC protocol has superiority in energy efficiency performance over conventional direct transmission protocol and Four-Time-Slot (4TS) Decode-and-Forward (DF) relay protocol, and the proposed system has the optimal outage performance when the relay is located at the center of two secondary transceivers.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제4권5호
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• pp.691-708
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• 2010

An important issue of supporting multi-users with diverse quality-of-service (QoS) requirements over wireless networks is how to optimize the systematic scheduling by intelligently utilizing the available network resource while, at the same time, to meet each communication service QoS requirement. In this work, we study the problem of a variety of communication services over multi-media heterogeneous cognitive OFDM system. We first divide the communication services into two parts. Multimedia applications such as broadband voice transmission and real-time video streaming are very delay-sensitive (DS) and need guaranteed throughput. On the other side, services like file transmission and email service are relatively delay tolerant (DT) so varying-rate transmission is acceptable. Then, we formulate the scheduling as a convex optimization problem, and propose low complexity distributed solutions by jointly considering channel assignment, bit allocation, and power allocation. Unlike prior works that do not care computational complexity. Furthermore, we propose the FAASA (Fairness Assured Adaptive Sub-carrier Allocation) algorithm for both DS and DT users, which is a dynamic sub-carrier allocation algorithm in order to maximize throughput while taking into account fairness. We provide extensive simulation results which demonstrate the effectiveness of our proposed schemes.

• ETRI Journal
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• 제37권3호
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• pp.471-479
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• 2015

Traditional designs of cognitive radio (CR) focus on maximizing system throughput. In this paper, we study the joint overlay and underlay power allocation problem for orthogonal frequency-division multiple access-based CR. Instead of maximizing system throughput, we aim to maximize system energy efficiency (EE), measured by a "bit per Joule" metric, while maintaining the minimal rate requirement of a given CR system, under the total power constraint of a secondary user and interference constraints of primary users. The formulated energy-efficient power allocation (EEPA) problem is nonconvex; to make it solvable, we first transform the original problem into a convex optimization problem via fractional programming, and then the Lagrange dual decomposition method is used to solve the equivalent convex optimization problem. Finally, an optimal EEPA allocation scheme is proposed. Numerical results show that the proposed method can achieve better EE performance.

• 한국음향학회지
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• 제15권6호
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• pp.59-65
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• 1996

본 논문에서는 기존의 4.8 kbps VSELP에 상응하는 음질을 갖는 4 kbps PSI-VSELP(Pitch Synchrononus Innovation-Vector Sum Excited Linear Prediction) 음성 부호화기를 제안한다. 'Half-rate'는 4kbps 내외에서 지역에 따라 다소 차이가 있으므로 기존의 half-rate 부호화기를 사용하기 위해서는 비트율을 감소시킬 필요가 생긴다. 이때, 비트율 감소에 따른 성능저하를 최소화하기 위해서는 전송 변수가 부호화기의 성능에 미치는 영향을 고려하여 비트 할당을 결정하는 것이 바람직하다. 본 논문에서는 이러한 접근 방식으로 비트율 감소 연구를 수행한 후, 제안된 부호화기에 대한 4 kbps 비트 할당을 결정한다. VSELP 부호화기의 음질 향상을 위해서, 성능에 가장 중요한 영향을 미치는 기저 벡터는 반복 폐회로 훈련 과정을 통해 최적화하며, PSI 기법을 VSELP 부호화기에 도입한다. 제안된 음성 부호화기의 성능을 평가하기 위해 배경 잡음과 채널 에러가 없는 환경에서 실험을 하였다. 실험 결과, 제안된 4 kbps PSI-VSELP는 4.8 kbps VSELP에 비해 객관적 음질은 낮았지만, 주과적 음질은 더 높게 나타났다.

• 한국통신학회논문지
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• 제38A권7호
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• pp.580-591
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• 2013

Orthogonal Frequency Division Multiple Access(OFDMA)는 4세대 무선 통신을 위해 고려되는 변조와 다중 접속 기술이다. 본 논문에서는, OFDMA 시스템에서 더 나은 proportional rate의 자원할당 기법을 위해 전체 전력, 비트 오류율, 유저 간의 rate proportionality에 대한 제한 조건을 만족시키면서, 유저의 전송률을 최대화 시키는 전략 할당 알고리즘에 대해 기술하였다. 그리고 subcarrier 할당의 비율과 유저의 정규화된 proportionality 조건에 기반을 둔 전력 할당 방식을 제안하였다. 유저에게 subcarrier 할당을 위한 방법으로는 greedy 알고리즘과 waterfilling 기술이 적용되었다. 제안된 알고리즘에 대한 평가는 시뮬레이션을 통해서 이루어졌으며, 시뮬레이션을 통해서 제안된 알고리즘이 유저 간의 rate proportionality를 유지하면서 더 높은 시스템 채널 용량과 적은 소요 시간을 보인다는 것을 확인할 수 있었다.

• ETRI Journal
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• 제36권3호
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• pp.374-384
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• 2014

To achieve high-speed (giga-bit) connectivity for short-range wireless multimedia applications, the millimeter-wave (mmWave) wireless personal area networks with directional antennas are gaining increased interest. Due to the use of directional antennas and mmWave communications, the probability of non-interfering transmissions increases in a localized region. Network throughput can be increased immensely by the concurrent time allocation of non-interfering transmissions. The problem of finding optimum time allocation for concurrent transmissions is an NP-hard problem. In this paper, we propose two enhanced versions of previously proposed multi-hop concurrent transmission (MHCT) schemes. To increase network capacity, the proposed schemes efficiently make use of the free holes in the time-allocation map of the MHCT scheme; thus, making it more compact.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제2권4호
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• pp.209-221
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• 2008

In this paper, we propose a subcarrier allocation method and a composite linear minimum mean square error (LMMSE) channel estimator to increase spectrum efficiency in orthogonal frequency division multiplexing (OFDM) transmit diversity. The pilot symbols for OFDM transmit (Alamouti) diversity are exclusively allocated in two OFDM symbols in different antennas, which causes serious degradation of spectrum efficiency. To reduce the number of pilot symbols, our subcarrier allocation method uses repetition-coded data symbols, and the proposed channel estimator maintains good bit error rate (BER) performance.