We present transmission- and reflection-type measurement methods for the differential mode delay (DMD) of a multimode optical fiber (MMF) optimized for high-speed local area networks (LANs) for the 850-nm band. Compared with a previously reported transmission-type measurement method for the 1550-nm wavelength band, we demonstrate here high-resolution DMD measurement methods for MMFs in the 850-nm band. As the method is based on a Fourier-domain intermodal interference technique, the measurement sensitivity is ∼60-dB, and it requires a fiber only a few meters in length. The shorter wavelength also allows a threefold improvement in the measurement resolution. The reflection-type measurement technique is a more practical than the transmission-type measurement technique for the field testing of short MMFs already installed in networks. We believe that this method will be a practical tool not only for field testing of short-length MMFs already installed in networks but also for the development of new plastic optical fibers (POFs).
In the statistic en-route filtering, each report generation node must collect a certain number of endorsements from its neighboring nodes. However, at some point, a node may fail to collect an insufficient number of endorsements since some of its neighboring nodes may have dead batteries. This letter presents a report generation method that can enhance the generation process of sensing reports under such a situation. Simulation results show the effectiveness of the proposed method.
Md. TARIQUZZAMAN Jin Young KIM Seung You NA Hyoung-Gook KIM Dongsoo HAR
In this paper, a novel visual signal reliability (VSR) measure is proposed to consider video degradation at the signal level in audio-visual speaker identification (AVSI). The VSR estimation is formulated using a~ Gaussian fuzzy membership function (GFMF) to measure lighting variations. The variance parameters of GFMF are optimized in order to maximize the performance of the overall AVSI. The experimental results show that the proposed method outperforms the score-based reliability measuring technique.
A new method of explicitly adaptive time delay estimation (EATDE) algorithm is proposed for estimating a varying time delay parameter. The proposed method is based on the Haar wavelet transform of cross-correlations. The proposed algorithm can be viewed as a gradient-based optimization of lowpass filtered cross-correlations, but requires less computational power. The algorithm shows a global convergence property for wide-band signals with uncorrelated noises. A convergence analysis including mean behavior, mean-square-error behavior, and steady-state error of delay estimate is given. Simulation results are also provided to demonstrate the performance of the proposed algorithm.
Yu Min HWANG Gyeong Hyeon CHA Jong Kwan SEO Jae-Jo LEE Jin Young KIM
This paper proposes a novel wavelet de-noising scheme regarding the existing burst noises that consist of background and impulsive noises in power-line communications. The proposed de-noising scheme employs multi-level threshold functions to efficiently and adaptively reduce the given burst noises. The experiment results show that the proposed de-noising scheme significantly outperformed the conventional schemes.
Youngsoo KIM Sangbae JEONG Daeyoung KIM
In this paper, an efficient node-level target classification scheme in wireless sensor networks (WSNs) is proposed. It uses acoustic and seismic information, and its performance is verified by the classification accuracy of vehicles in a WSN. Because of the hard limitation in resources, parametric classifiers should be more preferable than non-parametric ones in WSN systems. As a parametric classifier, the Gaussian mixture model (GMM) algorithm not only shows good performances to classify targets in WSNs, but it also requires very few resources suitable to a sensor node. In addition, our sensor fusion method uses a decision tree, generated by the classification and regression tree (CART) algorithm, to improve the accuracy, so that the algorithm drives a considerable increase of the classification rate using less resources. Experimental results using a real dataset of WSN show that the proposed scheme shows a 94.10% classification rate and outperforms the k-nearest neighbors and the support vector machine.
Namseok CHANG Na-young KIM Joonhyuk KANG Youngok KIM Hyunbeom LEE
Instead of pilot tones, the impulse sample is exploited for channel estimation in Impulse Postfix OFDM systems [1]. As the magnitude of impulse sample is increased, the accuracy of channel estimation can be enhanced, but it may significantly increase the PAPR of generated OFDM symbols. In this letter, based on the statistical analysis of the generated OFDM symbol, we propose a decision scheme for determining the magnitude of impulse sample. By using the proposed scheme, we can determine the magnitude of impulse sample that provides the enhancement of BER performance as well as the avoidance of PAPR increase. The validation of the proposed scheme is demonstrated by computer simulations.
In this paper, multiuser detector (MUD) based on radial basis function (RBF) is proposed and simulated for a multicode DS/CDMA system in an AWGN and a multipath fading channels. The performance of RBF-based MUD is compared with that of many suboptimal multiuser detectors in terms of bit error probability. To obtain simulation results, importance sampling technique is employed. From the simulation results, it is confirmed that the RBF-based MUD outperforms decorrelating detector, and achieves near-optimum performance under various environments. The results in this paper can be applied to design of MUD for a multicode DS/CDMA system.
Tae-Hyoung KIM Kwang-Jin LEE Uk-Rae CHO Hyun-Geun BYUN
This paper describes a digital impedance controller (DIC) [1] for high-speed signal interface. The proposed DIC provides the wide range impedance control covering from 23 Ω to 140 Ω with 3.29% maximum quantization error. The maximum quantization error of the proposed DIC is 2.26% with RQ ranging from 23 Ω to 53 Ω, the same range covered by conventional scheme. The high resolution and wide range impedance control is implemented by using automatic gate voltage optimization. The amount of jitter caused by quantization error is 6.9 ps while 13.8 ps in conventional scheme. The data input valid window is 623 ps at 0.75200 mV and maximum eye open is 641 mV meaning about 10% improvement at 1.5 Gbps/pin DDR3 SRAM interface.
Modern digital systems design requires us to explore a large and complex design space to find a best configuration which satisfies design requirements. Such exploration requires a sound representation of design space from which design candidates are efficiently generated, each of which then is evaluated. This paper proposes a plan-generation-evaluation framework which supports a complete process of such design space exploration. The plan phase constitutes a design space of all possible design alternatives by means of a formally defined representation scheme of attributed AND-OR graph. The generation phase generates a set of candidates by algorithmic pruning of the design space in an attributed AND-OR graph with respect to design requirements as well as architectural constraints. Finally, the evaluation phase measures performance of design candidates in a pruned graph to select a best one. A complete process of cache design is exemplified to show the effectiveness of the proposed framework.
Yu Min HWANG Sun Yui LEE Isaac SIM Jin Young KIM
With the increasing demand of Internet-of-Things applicability in various devices and location-based services (LBSs) with positioning capabilities, we proposed simple and effective post-processing techniques to reduce positioning error and provide more precise navigation to users in a pedestrian environment in this letter. The proposed positioning error reduction techniques (Technique 1-minimum range securement and bounce elimination, Technique 2-direction vector-based error correction) were studied considering low complexity and wide applicability to various types of positioning systems, e.g., global positioning system (GPS). Through the real field tests in urban areas, we have verified that an average positioning error of the proposed techniques is significantly decreased compared to that of a GPS-only environment.
Yu Min HWANG Jun Hee JUNG Yoan SHIN Jin Young KIM Dong In KIM
In this letter, we study a scenario based on decoupled RF energy harvesting networks (DRF-EHNs) that separate energy sources from information sources to overcome the doubly near-far problem and improve harvesting efficiency. We propose an algorithm to maximize energy efficiency (EE) while satisfying constraints on the maximum transmit power of the hybrid access point (H-AP) and power beacon (PB), while further satisfying constraints on the minimum quality of service and minimum amount of harvested power in multi-user Rayleigh fading channel. Using nonlinear fractional programming and Lagrangian dual decomposition, we optimize EE with four optimization arguments: the transmit power from the H-AP and PB, time-splitting ratio, and power-splitting ratio. Numerical results show that the proposed algorithm is more energy-efficient compared to baseline schemes.
In this paper, outage performance of a turbo-coded CDMA system is analyzed and simulated in a multiple-beam satellite channel. From the simulation results, it is confirmed that turbo coding provides considerable coding gain over an uncoded system. And, it is demonstrated that Max-Log-MAP decoding algorithm is most promising in terms of performance and complexity.
Younghyun KIM Miyoung KIM Youngsong MUN
Internet engineering task force (IETF) has proposed hierarchical mobile IPv6 (HMIPv6) in order to reduce a frequent location registration of a mobile node in mobile IPv6 (MIPv6). All traffics toward a mobile node must be transmitted through a MAP in HMIPv6. This brings unnecessary packet latency because of the increased processing cost of packet at the MAP. At this point, the processing cost of packet at the MAP is influenced by the packet arrival rate for a mobile node, cell mobility rate and the number of mobile nodes in MAP domain. In this paper, we analyze the MAP's performance considering the above elements. For this, we compare total cost of HMIPv6 with total cost of MIPv6 as MAP's capability after we define Markov chain model for performance analysis. Also, we define network's total profit as total cost of MIPv6 minus total cost of HMIPv6. Then, we can find optimal capability of MAP such that total profit has maximum value. Also, we use the blocking probability by the MAP's capability as performance estimation element. As a conclusion, we can observe both HMIPv6's performance by the MAP's capability and optimal capability of the MAP, and blocking probability form a relationship of trade off between them.
In this paper, we propose a new minimum-bandwidth line code, MB810+ (MB810 plus), which is designed by statistically controlling the ASV (Alternate Sum Variation) or the DSV (Digital Sum Variation) of a line code. The proposed MB810+ retains dc-free and minimum-bandwidth characteristics, whereas it consumes only 2k gates for implementing the encoder and decoder, respectively. Therefore MB810+ can be used as a line code for high-speed data, of which speed is limited by processing delays.
JongGeun OH DongYoung KIM Min-Cheol HONG
This letter introduces a non-local means (NLM) denoising algorithm that uses a weight function based on a switching norm. The noise level and local activity are incorporated into the NLM denoising algorithm which enhances performance. This is done by selecting a norm among l1, l2, and l4 norms to determine a weighting function. The experimental results show the capability of the proposed algorithm. In addition, the proposed algorithm is verified as effective for enhancing the performance of other NLM algorithms.
ChaYoung KIM JinHo AHN ChongSun HWANG
Gossip-based reliable broadcast protocols with reasonably weak reliability properties scale well to large groups and degrade system performance gracefully even if node failure or message loss rates increase compared with traditional protocols. However, although many distributed applications require highly steady performance only by allowing causality to be used asynchronously, there is no existing gossip-based protocol offering causally ordered delivery property more lightweight than totally ordered delivery one. This paper presents an application-level broadcast algorithm to guarantee causally-ordered delivery semantics based on peer to peer interaction models for scalability, reasonable reliability and stable throughput. Processes propagate each message with a vector time stamp much like the spread of rumor in society for a fixed number of rounds. Upon receipt of these messages, correct processes immediately deliver the corresponding messages to the application layers in a causal order. Simulation results show that the proposed algorithm outperforms the existing ones in terms of delivery throughput.
Yong-Qian CHEN Young-Kyoung KIM Sang-Jo YOO
Sensor node localization is an important issue in wireless sensor networks (WSNs) due to the dynamic nature of sensor deployment. Generally, in wireless sensor network localization, the absolute positions of certain anchor nodes are required based on the use of global positioning systems, then all the other nodes are approximately localized using various algorithms based on a coordinate system of the anchors. This paper proposes a neighbor position-based localization algorithm (NPLA) that can greatly enhance the positioning accuracy when compared with current overlapping connectivity localization algorithms that attempt to use the observation of connectivity to a set of anchors to determine a node's position. The proposed method localizes the sensor nodes using both the anchors' positions and neighbor node information. However, unlike existing overlapping-based methods, the proposed NPLA does not assume the same radio transmission range. A simulation study is used to demonstrate the positioning accuracy of the proposed method with different anchor and sensor node densities.
Seok-Woo JANG Gye-Young KIM Hyung-Il CHOI
In this paper, we propose a method to estimate affine motion parameters from consecutive images with the assumption that the motion in progress can be characterized by an affine model. The motion may be caused either by a moving camera or moving object. The proposed method first extracts motion vectors from a sequence of images and then processes them by adaptive robust estimation to obtain affine parameters. Typically, a robust estimation filters out outliers (velocity vectors that do not fit into the model) by fitting velocity vectors to a predefined model. To filter out potential outliers, our adaptive robust estimation defines a flexible weight function based on a sigmoid function. During the estimation process, we tune the sigmoid function gradually to its hard-limit as the errors between the input data and the estimation model are decreased, so that we can effectively separate non-outliers from outliers with the help of the finally tuned hard-limit form of the weight function. The experimental results show that the suggested approach is very effective in estimating affine parameters.
Ju-Young KIM Ki-Hong KIM Hee-Chul HWANG Duk-Gyoo KIM
A novel image enhancement algorithm that can efficiently detect a small target of panoramic infrared (IR) imagery is proposed. Image enhancement is the first step for detecting and recognizing a small target in the IR imagery. The essence of the proposed algorithm is to utilize the independent histogram equalization (HE) separately over two sub-images obtained by decomposing the given image through the statistical hypothesis testing (SHT). Experimental results show that the proposed algorithm has better discrimination and lower false alarm rate than the conventional algorithms.