• ETRI Journal
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• 제41권5호
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• pp.648-657
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• 2019

A cluster topology was proposed with the assumption of zero noise to improve the performance of wireless body area networks (WBANs). However, in WBANs, the transmission power should be reduced as low as possible to avoid the effect of electromagnetic waves on the human body and to extend the lifetime of a battery. Therefore, in this work, we consider a bit error rate for a cluster-based WBAN and analyze the performance of the system while the transmission of sensors and cluster headers (CHs) is controlled. Moreover, a hierarchical topology is proposed for the cluster-based WBAN to further improve the throughput of the system; this proposed system is called as the hierarchical cluster WBAN. The hierarchical cluster WBAN is combined with a transmission control scheme, that is, complete control, spatial reuse superframe, to increase the throughput. The proposed system is analyzed and evaluated based on several factors of the system model, such as signal-to-noise ratio, number of clusters, and number of sensors. The calculation result indicates that the proposed hierarchical cluster WBAN outperforms the cluster-based WBAN in all analyzed scenarios.

• 한국방송∙미디어공학회:학술대회논문집
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• 한국방송공학회 1999년도 KOBA 방송기술 워크샵 KOBA Broadcasting Technology Workshop
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• pp.97.1-102
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• 1999

This paper porposes and efficient coding scheme for remote medical communication systems, or“telemedicine systems”. These systems require a technique which is able to transfer large volume of data such as X-ray images effectively. We have already developed a hierarchical image coding and transmission scheme (HITS), which achieves an efficient transmission of medical images simply[1]. In this paper, a new coding scheme for HITS is proposed, which used hierarchical context modeling for the purpose of improving the coding efficiency. The hierarchical context modeling divides wavelet coefficients into several sets by the value of a correspondent coefficient in their higher class, or“a parent”, optimizes a Golomb-Rice (GR) code parameter in each set, and then encodes the coefficients with the parameter. Computer simulation shows that the proposed scheme is effective with simple implementation. This is due to fact that a wavelet coefficient has dependence on its parent. As a result, high speed data transmission is achieved even if the telemedicine system consists of simple personal computers.

• 대한전자공학회논문지
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• 제26권8호
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• pp.1227-1237
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• 1989

In this paper, we propose a lossless progressive image transmission scheme using hierarchical pyramid structure and classified vector quantizer in DCT domain. By adopting DCT to the hierarchical pyramid signals, we can reduce the spatial redundance. Moreover, the DCT coefficients can be encoded efficiently by using classified vector quantizer in DCT domain. The classifier is simply based on the variance of a subblock. Also, the mirror set of training set of images can improve the robustness of codebooks. Progressive image transmission can be achieved through following processes: from top to bottom level of planes in a pyramid, and from high to low AC variance class in a plane. Some simulation results with real images show that the proposed coding scheme yields a good performance at below 0.3 bpp and an excellent result at 0.409 bpp. The proposed coding scheme is well suited for lossless progressive image transmission as well as image data compression.

• 한국항행학회논문지
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• 제16권6호
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• pp.975-981
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• 2012

서로 다른 품질을 요구하는 데이터들의 동시 전송 또는 효율적인 영상전송시스템에 응용될 수 있는 계층 16QAM (Quadrature Amplitude Modulation) 시스템에 대한 SNR 추정성능에 대해 분석한다. 계층 16QAM은 계층 변조파라미터를 제어하여 성좌점들의 형태를 변형시켜 사용자에게 고품질과 저품질 데이터서비스를 동시에 제공할 수 있는 변조 시스템이다. AWGN (Additive White Gaussian Noise) 채널환경에서 계층 16QAM 시스템에서 계층변조파라미터와 성좌점별 특성을 고려한 SNR (Signal to Noise power Ratio) 추정성능 특성을 분석하였다. 시뮬레이션 결과, 계층 16QAM의 여러성좌점들 중에 SNR 추정이 상대적으로 정확하게 이루어지는 성좌점이 존재함을 확인하였고, 계층변조파라미터 값에 따라 SNR 추정이 유리한 영역이 달라진다는 것을 알아내었다.

• 한국통신학회논문지
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• 제17권6호
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• pp.621-628
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• 1992

본 연구에서는 영상데이터 검색시스템에 적합한 계충적 확대축소법을 이용한 영상의 단계적 전송법을 제안한다. 종래의 단계적 전송방법은 계층간의 배율이 4(흑은 1 /4)로 고정되어 있어, 정보량의 증가가 급격히 일어나므로 해상도가 낮은 화면에서 갑자기 높은 화면으로 되지만, 본 방법은 계층간에 배율을 임의로 취할 구 있는 배율가변형 계층성을 단계적 전송에 도입함으로써, 계충간에 정보량을 서서히 증가시켜 전송하고 표시할 수 있으므로 화면의 해상도를 서서히 증가시킬 수 있다. 이 방법은 종래 제안된 LP법보다 압축율이 0.7bit/pel 개선된 상태에서 SNR이 5.7(dB)정도, PCS보다는 중간단계의 SNR이 약 1[dB]정도 개선되 고 있음을 보이고 있다

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권12호
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• pp.6017-6037
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• 2017

In a multi-resolution image encoding system, the image is encoded into a single file as a layer of bit streams, and then it is transmitted layer by layer progressively to reduce the transmission time across a low bandwidth connection. This encoding scheme is also suitable for multiple decoders, each with different capabilities ranging from a handheld device to a PC. In our previous work, we proposed an edge adaptive hierarchical interpolation algorithm for multi-resolution image coding system. In this paper, we enhanced its compression efficiency by adding three major components. First, its prediction accuracy is improved using context adaptive error modeling as a feedback. Second, the conditional probability of prediction errors is sharpened by removing the sign redundancy among local prediction errors by applying sign flipping. Third, the conditional probability is sharpened further by reducing the number of distinct error symbols using error remapping function. Experimental results on benchmark data sets reveal that the enhanced algorithm achieves a better compression bit rate than our previous algorithm and other algorithms. It is shown that compression bit rate is much better for images that are rich in directional edges and textures. The enhanced algorithm also shows better rate-distortion performance and visual quality at the intermediate stages of progressive image transmission.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제4권3호
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• pp.224-242
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• 2010

Data routing in wireless sensor networks must be energy-efficient because tiny sensor nodes have limited power. A cluster-based hierarchical routing is known to be more efficient than a flat routing because only cluster-heads communicate with a sink node. Existing hierarchical routings, however, assume unrealistically large radio transmission ranges for sensor nodes so they cannot be employed in real environments. In this paper, by considering the practical transmission ranges of the sensor nodes, we propose a clustering and routing method for hierarchical sensor networks: First, we provide the optimal ratio of cluster-heads for the clustering. Second, we propose a d-hop clustering scheme. It expands the range of clusters to d-hops calculated by the ratio of cluster-heads. Third, we present an intra-cluster routing in which sensor nodes reach their cluster-heads within d-hops. Finally, an inter-clustering routing is presented to route data from cluster-heads to a sink node using multiple hops because cluster-heads cannot communicate with a sink node directly. The efficiency of the proposed clustering and routing method is validated through extensive simulations.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제5권11호
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• pp.2068-2086
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• 2011

Based on the quincunx sub-sampling grid, the New Interleaved Hierarchical INTerpolation (NIHINT) method is recognized as a superior pyramid data structure for the lossless and progressive coding of natural images. In this paper, we propose a new image interpolation algorithm, Edge Adaptive Hierarchical INTerpolation (EAHINT), for a further reduction in the entropy of interpolation errors. We compute the local variance of the causal context to model the strength of a local edge around a target pixel and then apply three statistical decision rules to classify the local edge into a strong edge, a weak edge, or a medium edge. According to these local edge types, we apply an interpolation method to the target pixel using a one-directional interpolator for a strong edge, a multi-directional adaptive weighting interpolator for a medium edge, or a non-directional static weighting linear interpolator for a weak edge. Experimental results show that the proposed algorithm achieves a better compression bit rate than the NIHINT method for lossless image coding. It is shown that the compression bit rate is much better for images that are rich in directional edges and textures. Our algorithm also shows better rate-distortion performance and visual quality for progressive image transmission.

• 한국정보과학회논문지:정보통신
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• 제29권5호
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• pp.466-472
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• 2002

본 논문에서는 계층적 셀 구조에서 umbrella 셀과 overlaid 셀 사이의 부하 분배 문제를 연구한다. 부하 분배 정책을 제안하고 HSDPA에서 인터넷 트래픽을 전달하는 경우를 시뮬레이션하여 제안된 정책의 성능을 평가한다. 평가 결과, 마이크로 셀이 피코 셀의 부하를 잘 분담해주는 것으로 나타났으며, 특히 특정한 피코 셀 집단에 큰 부하가 가해졌을 경우에 그 효과가 크게 나타났다. 이 정책을 사용할 경우, 비정상적인 큰 부하에 대처하기 위해 필요한 용량을 확보할 필요가 없어지므로 시스템 설치비용을 줄일 수 있게 된다.

• 한국통신학회논문지
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• 제37A권9호
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• pp.728-737
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• 2012

본 논문은 계층변조(Hierarchical Modulation) 기법이 적용된 지상파 방송 전송 시스템의 지상파 방송권역 판단을 위한 해석적 기법을 제시한다. 계층 변조된 비균일 QAM 성상도에 대하여 AWGN 환경에서의 Q-함수 해석을 기반으로 비트오류율(BER, Bit Error Rate)을 유도한다. 도출된 비트오류율은 계층변조 지수(Hierarchical Modulation Factor, HMF, ${\alpha}$)와 연관성을 가지며, Log-distance 경로 손실 모델에 따라 전송 신호에 대한 링크 해석을 시행 하면 방송권역의 유효 반경으로 연결될 수 있다. 최종적으로 HMF에 따른 기본계층(High Priority, HP) 정보의 방송 권역과 향상계층(Low Priority, LP) 정보 방송 권역의 비율을 계산하며 이를 기반으로 하여 선택된 비율에 따른 HMF를 결정하게 된다.