• Journal of Communications and Networks
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• v.15 no.6
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• pp.589-600
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• 2013

In this paper, we propose a new feedback scheme called mode selection-based feedback by scheduling probability prediction (SPP-MF) for channel state feedback in OFDMA downlink system. We design the scheme such that it determines the more desirable feedback mode among selective feedback by scheduling probability prediction (SPP-SF) mode and bitmap feedback by scheduling probability prediction (SPP-BF) mode, by calculating and comparing the throughputs of the two modes. In both feedback modes, each user first calculates the scheduling probability of each subchannel (i.e., the probability that a user wins the scheduling competition for a subchannel) and then forms a feedback message based on the scheduling probability. Specifically, in the SPP-SF mode, each user reports the modulation and coding scheme (MCS) levels and indices of its best S subchannels in terms of the scheduling probability. In the SPP-BF mode, each user determines its scheduling probability threshold. Then, it forms a bitmap for the subchannels according to the scheduling probability threshold and sends the bitmap along with the threshold. Numerical results reveal that the proposed SPP-MF scheme achieves significant performance gain over the existing feedback schemes.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.10 no.3
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• pp.37-48
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• 2000

서울Visual cryptography scheme is a simple method in which can be directly decoded the secret information in human visual system without performing any cryptographic computations. This scheme is a kind of secret sharing scheme in which if a secret of image type is scattered to n random images(slides) and any threshold (or more) of them are stacked together the original image will become visible. In this paper we consider (2, n) visual cryptography scheme and propose a new construction method in which the number of expanded pixels can be reduced by using the sample matrix. The proposed scheme can futhermore distribute the multiple secret image to each group according to the difference of relative contrast.

• ETRI Journal
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• v.32 no.2
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• pp.333-335
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• 2010

This letter proposes a non-coherent blind time-of-arrival (TOA) estimation scheme for impulse radio ultra-wideband systems. The TOA estimation is performed in two consecutive phases: the Rayleigh-quotient theorem-based coarse-signal acquisition (CSA) and the iterative-threshold-test-based fine time estimation (FTE). The proposed scheme serves in a blind manner without demanding any a priori knowledge of the channel and the noise. Analysis and simulations demonstrate that the proposed scheme significantly increases the signal detection probability in CSA and ameliorates the TOA estimation accuracy in FTE.

• Journal of Communications and Networks
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• v.16 no.1
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• pp.56-66
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• 2014

We propose a novel opportunistic access scheme for cognitive radios in an interweave cognitive system, that considers the channel gain as well as the predicted idle channel probability (primary user occupancy: Busy/idle). In contrast to previous work where a cognitive user vacates a channel only when that channel becomes busy, the proposed scheme requires the cognitive user to switch to the channel with the next highest idle probability if the current channel's gain is below a certain threshold. We derive the threshold values that maximize the long term throughput for various primary user transition probabilities and cognitive user's relative movement.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.32A no.1
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• pp.166-178
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• 1995

An accurate threshold voltage extraction scheme for MOS transistors is presented. In contrast to alternative methods recently reported in the literature, this scheme does not need matched replica of the transistor under test, and thus can be applied more effectively and accurately to raal-time on-chip applications where threshold voltage measurements are required for many transistors with various geometries and bias conditions. The proposed scheme is accurately implemented in a matching-free way using a ratio-indepentent switched-capacitor subtracting amplifier and a dynamic current mirror. Nonideal effects associated with these circuits have been investiggated and compensated.

• ETRI Journal
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• v.27 no.6
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• pp.802-805
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• 2005

A dynamic bandwidth allocation (DBA) scheme, an inter -optical network unit (ONU) bandwidth scheduling, is presented to provide quality of service (QoS) to different classes of packets in Ethernet passive optical networks (EPONs). This scheme, referred to as TADBA, is based on efficient threshold reporting from, and adaptive polling order rearranging of, ONUs. It has been shown that the network resources are efficiently allocated among the three traffic classes by guaranteeing the requested QoS, adaptively rearranging the polling orders, and avoiding nearly all fragmentation losses. Simulation results using an OPNET network simulator show that TADBA performs well in comparison to the available allocation scheme for the given parameters, such as packet delay and channel utilization.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.12 no.6
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• pp.81-92
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• 2002

In some practical circumstances, the ability of a signer should be restricted. In group signature schemes, a group member of a group may be allowed to generate signatures up to a certain number of times according to his/her position in the group. In proxy signature schemes, an original signer may want to allow a proxy signer to generate a certain number of signatures on behalf of the original signer. In the paper, we present signature schemes, called c-times signature schemes, that restrict the signing ability of a signer up to c times for pre-defined value c at set-up. The notion of c-times signature schemes are formally defined, and generic transformation from a signature scheme to a c-times signature scheme is suggested. The proposed scheme has a self-enforcement property such that if a signer generates c+1 or more signatures, his/her signature is forged. As a specific example, we present a secure c-times signature scheme $^c$DSA based on the DSA (Digital Signature Algorithm) by using a threshold scheme. Our transformation can be applied to other ElGamal-like signature schemes as well.

• Journal of information and communication convergence engineering
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• v.9 no.4
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• pp.391-395
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• 2011

Cognitive radio (CR) technique is a useful tool for improving spectrum utilization by detecting and using the vacant frequency bands while avoiding interference to the primary user. The sensing performance in a CR network can be improved by allowing some CR users to perform cooperative spectrum sensing. In this paper, we propose a new sensing algorithm that utilizes an adaptive energy threshold for cooperative spectrum sensing in which a changeable energy threshold is adopted by the CR users for improving local sensing performance. Through the proposed scheme, the reliability of global decision can be enhanced mainly due to the improvement in local sensing performance.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.15 no.12
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• pp.4617-4632
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• 2021

IEEE 802.11ax is a protocol being developed for high-density Wireless Local Area Networks (WLAN). Several algorithms have been proposed to improve the level of spatial reuse applied in IEEE 802.11ax. However, these algorithms are tentative and do not specify how to select the transmit power and carrier sense threshold in practice; It is unclear when and why the tuned parameters lead to better network performance. In this paper, we restricted the scale of transmit power tuning to prevent the case of backfire in which spatial reuse will result in transmission failure. If the restrictions cannot be satisfied, spatial reuse will be abandoned. This is why we named the proposed scheme as Arbitration based Spatial Reuse (ASR). We quantified the network performance after spatial reuse, and formulate a corresponding maximum problem whose solution is the optimal carrier sense threshold and transmit power. We verified our theoretical analysis by simulation and compared it with previous studies, and the results show that ASR improves the throughput up to 8.6% compared with 802.11ax. ASR can avoid failure of spatial reuse, while the spatial reuse failure rate of existing schemes can up to 36%. To use the ASR scheme in practice, we investigate the relation between the optimal carrier sense threshold and transmit power. Based on the relations got from ASR, the proposed Relation based Spatial Reuse (RSR) scheme can get a satisfactory performance by using only the interference perceived and the previously found relations.

• Journal of Electrical Engineering and Technology
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• v.13 no.5
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• pp.2080-2085
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• 2018

There have been numerous studies that extract the R-peak from electrocardiogram (ECG) signals. All of these studies can extract R-peak from ECG. However, these methods are complicated and difficult to implement in a real-time portable ECG device. After filtration choosing a threshold value for R-peak detection is a big challenge. Fixed threshold scheme is sometimes unable to detect low R-peak value and adaptive threshold sometime detect wrong R-peak for more adaptation. In this paper, a simple and robustness algorithm is proposed to detect R-peak with less complexity. This method also solves the problem of threshold value selection. Using the adaptive filter, the baseline drift can be removed from ECG signal. After filtration, an appropriate threshold value is automatically chosen by using the minimum and maximum value of an ECG signals. Then the neighborhood searching scheme is applied under threshold value to detect R-peak from ECG signals. Proposed method improves the detection and accuracy rate of R-peak detection. After R-peak detection, we calculate heart rate to know the heart condition.