• 한국통신학회논문지
• /
• 제39A권4호
• /
• pp.209-211
• /
• 2014

본 논문에서는 HEVC 부호화의 연산 복잡도를 줄이기 위한 고속 움직임 탐색 방법을 제안한다. 고속움직임 탐색을 위한 종래의 방법은 현재 영상과 참조 영상 간의 거리에 따라 탐색 영역의 크기를 조절하는 반면, 제안 방법은 예측 단위 간의 움직임 벡터 차의 유사성을 이용하여 예측 단위에 따라 움직임 벡터 탐색 영역을 적응적으로 조절한다. 실험을 통해 제안 방법은 random access 실험 조건에서 움직임 예측의 연산 시간을 약 10.7% 감소시키는 반면, 약 0.1%의 낮은 부호화 성능 하락을 가지는 것을 확인하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제6권5호
• /
• pp.1286-1302
• /
• 2012

In this paper, the resource allocation problem with proportional fairness rate in cognitive OFDM-based wireless network is studied. It aims to maximize the total system throughput subject to constraints that include total transmit power for secondary users, maximum tolerable interferences of primary users, bit error rate, and proportional fairness rate among secondary users. It is a nonlinear optimization problem, for which obtaining the optimal solution is known to be NP-hard. An efficient bio-inspired suboptimal algorithm called immune clonal optimization is proposed to solve the resource allocation problem in two steps. That is, subcarriers are firstly allocated to secondary users assuming equal power assignment and then the power allocation is performed with an improved immune clonal algorithm. Suitable immune operators such as matrix encoding and adaptive mutation are designed for resource allocation problem. Simulation results show that the proposed algorithm achieves near-optimal throughput and more satisfying proportional fairness rate among secondary users with lower computational complexity.

• 한국통신학회논문지
• /
• 제36권6C호
• /
• pp.337-342
• /
• 2011

2009년 Arikan에 의해 처음 제안된 극 부호(polar codes)는 실용적인 부 복호화 복잡도로 채널 용량을 달성하는 것이 종영된 채널 부호이다. 채널 양극화(channel polarization) 현상을 이용하는 극 부호는 현재 보안 및 데이터 압축 등에 응용되어 활발히 연구되고 있다. 본 논문에서는 극 부호의 실제 통신 시스템 적용을 고려하여, 유한한 길이와 고정 부호율을 갖는 극 부호의 설계 방법을 제안한다. 그리고 모의실험을 통하여 경험적으로 찾아낸 가장 우수한 성능을 보이는 극 부호의 성능과 설계 방법을 제시한다.

• 한국컴퓨터정보학회논문지
• /
• 제7권2호
• /
• pp.95-100
• /
• 2002

피드백 채널을 이용한 디코더는 인코더로 전송에러에 의한 오염된 매크로 블록들의 주소를 알려준다. NACK 메시지의 수신으로 인코더는 전송에러가 발생된 프레임의 GOB와 MB를 기준으로 forward dependency를 적용으로 확산된 에러전파영역을 지닌 다음순서의 프레임을 만들어낸다. 이 프레임으로 현재 인코딩 하려는 프레임의 각 MB안에 4-corner에 존재하는 픽셀들에 대한 backward dependency를 적용함으로써 오염된 MB을 찾아낼 수가 있다. 이들 오염된 MB들에 대한 INTRA코딩을 적용함으로써 에러확산을 완전히 중단시킬 수 있다. 이와 같이 빠른 알고리즘의 적용으로 보다 적은 연산량과 보다 적은 양의 메모리 요구를 얻을 수 있다 또한 이러한 장점은 실시간 비디오 전송에 특히 적합하다.

• ETRI Journal
• /
• 제31권6호
• /
• pp.784-794
• /
• 2009

We present a full HD (1080p) H.264/AVC High Profile hardware encoder based on fast motion estimation (ME). Most processing cycles are occupied with ME and use external memory access to fetch samples, which degrades the performance of the encoder. A novel approach to fast ME which uses shared multibank memory can solve these problems. The proposed pixel subsampling ME algorithm is suitable for fast motion vector searches for high-quality resolution images. The proposed algorithm achieves an 87.5% reduction of computational complexity compared with the full search algorithm in the JM reference software, while sustaining the video quality without any conspicuous PSNR loss. The usage amount of shared multibank memory between the coarse ME and fine ME blocks is 93.6%, which saves external memory access cycles and speeds up ME. It is feasible to perform the algorithm at a 270 MHz clock speed for 30 frame/s real-time full HD encoding. Its total gate count is 872k, and internal SRAM size is 41.8 kB.

• 전자공학회논문지CI
• /
• 제46권2호
• /
• pp.1-9
• /
• 2009

본 논문에서는 H.264/AVC의 I-slice의 모든 블록들을 복원하지 않고 블록의 경계 부분만을 복원하여 intra prediction을 고속으로 수행하는 방법을 개발한다 이를 위하여 intra prediction의 참조 화소들로 구성될 수 있는 차이 블록의 경계를 고속으로 복원하는 고속 역 정수 DCT를 개발한다. 고속으로 복원된 차이 경계 화소들과 각 예측 모드에 알맞게 구한 예측 화소들을 더하여 경계 화소들을 update하며, intra prediction에 필요한 참조 화소들로 구성한다. 개발된 기법은 H.264/AVC의 정수 DCT와 호환성을 유지하고, 고화질 영상 부호화시 사용되는 대표적인 HD 시퀀스에 적용 가능함을 실험으로 검증하였다.

• 정보처리학회논문지C
• /
• 제13C권3호
• /
• pp.317-322
• /
• 2006

본 논문에서는 LEACH (Low-Energy Adaptive Hierarchy)를 사용한 무선센서네트워크에서 순환 부호를 사용하여 효율적인 사용자 협력 프로토콜을 제안한다. 제안한 시스템에서는 송수신단 간에 채널 상태 정보가 필요하지 않기 때문에 순환 부호를 부호화하는 것과 복호하는 것은 단순해지고 센서 노드의 처리 복잡도가 크게 줄어들 수 있다. 모의실험 결과를 통해서 순환 부호를 적용한 센서 네트워크는 단일 홉 전송의 비트오율 $10^{-4}$에서 네트워크 수명이 10dB까지 절약되는 것을 알 수 있었다.

• 한국통신학회논문지
• /
• 제25권10A호
• /
• pp.1473-1479
• /
• 2000

This paper presents the performance evaluation of an adaptive QAM scheme under flat and frequency selective fading channels for indoor wireless communication systems. The QAM modulation is combined with differential encoding and the demodulation process is carried out noncoherently. The adaptation is performed by varying the modulation level of QAM, depending upon received signal strength. The adaptation mechanism allows a 2- or 3-bit increase or decrease at a time, if the channel condition is considered to be significantly good or bad. Simulation results show that the average number of bits per symbol (ABPS) for each symbol block transmitted over a flat fading channel is higher than 5.0 and the BER performance is better than 10^-4 for a SNR value higher than 30 dB. For frequency selective fading channels, an oversampling technique in the receiver was employed. The BER performance obtained for frequency selective fading channels is better than 10^-4 with a SNR value of 40 dB and ABPS is found to be approximately 5.5. Therefore, this scheme is very useful in that it provides both very high bandwidth efficiency and acceptable performance with moderate SNR values over flat and frequency selective fading channels. In addition, this scheme provides reduced receiver complexity by way of noncoherent detection.

• Journal of Communications and Networks
• /
• 제15권2호
• /
• pp.217-221
• /
• 2013

Quantum low-density parity-check (LDPC) codes based on the Calderbank-Shor-Steane construction have low encoding and decoding complexity. The sum-product algorithm(SPA) can be used to decode quantum LDPC codes; however, the decoding performance may be significantly decreased by the many four-cycles required by this type of quantum codes. All four-cycles can be eliminated using the entanglement-assisted formalism with maximally entangled states (ebits). The proposed entanglement-assisted quantum error-correcting code based on Euclidean geometry outperform differently structured quantum codes. However, the large number of ebits required to construct the entanglement-assisted formalism is a substantial obstacle to practical application. In this paper, we propose a novel class of entanglement-assisted quantum LDPC codes constructed using classical Euclidean geometry LDPC codes. Notably, the new codes require one copy of the ebit. Furthermore, we propose a construction scheme for a corresponding zigzag matrix and show that the algebraic structure of the codes could easily be expanded. A large class of quantum codes with various code lengths and code rates can be constructed. Our methods significantly improve the possibility of practical implementation of quantum error-correcting codes. Simulation results show that the entanglement-assisted quantum LDPC codes described in this study perform very well over a depolarizing channel with iterative decoding based on the SPA and that these codes outperform other quantum codes based on Euclidean geometries.

• Journal of Communications and Networks
• /
• 제9권3호
• /
• pp.265-273
• /
• 2007

This paper expands an analytical performance model of 802.11 to accurately estimate throughput and energy demand of 802.11-based wireless sensor network (WSN) when sensor nodes employ Reed-Solomon (RS) codes, one of block forward error correction (FEC) techniques. This model evaluates these two metrics as a function of the channel bit error rate (BER) and the RS symbol size. Since the basic recovery unit of RS codes is a symbol not a bit, the symbol size affects the WSN performance even if each packet carries the same amount of FEC check bits. The larger size is more effective to recover long-lasting error bursts although it increases the computational complexity of encoding and decoding RS codes. For applying the extended model to WSNs, this paper collects traffic traces from a WSN consisting of two TIP50CM sensor nodes and measures its energy consumption for processing RS codes. Based on traces, it approximates WSN channels with Gilbert models. The computational analyses confirm that the adoption of RS codes in 802.11 significantly improves its throughput and energy efficiency of WSNs with a high BER. They also predict that the choice of an appropriate RS symbol size causes a lot of difference in throughput and power waste over short-term durations while the symbol size rarely affects the long-term average of these metrics.