• Journal of the Korean Ceramic Society
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• v.43 no.2 s.285
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• pp.131-135
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• 2006

In this study, the dielectric, magnetic and transport properties of $Gd_{0.33}Sr_{0.67}FeO_3$ have been analyzed. The dielectric loss anomaly was found to be around 170 K. The activation energy corresponding to relaxation process of this dielectric anomaly was 0.17 eV. From the temperature dependence of the characteristic frequency, we concluded that the elementary process of the dielectric relaxation peak observed is correlated with polaron hopping between $Fe^{3+}\;and\;Fe^{4+}$ ions. The electrical resistivity displayed thermally activated temperature dependence above 200 K with an activation energy of 0.16 eV. In addition, the temperature dependence of thermoelectric power and resistivity suggests that the charge carrier responsible for conduction is strongly localized.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.7
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• pp.573-581
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• 2014

We proposed a hopping phase estimator to demodulate the received signals without any hopping information in frequency hopping spread spectrum systems. The demodulation process in this paper is as follows: hopped frequency tracking is accomplished by choosing a frequency component with maximum amplitude after taking discrete Fourier transform and a hopping frequency estimator which estimates the phase generated by hopped frequency is established through difference product and down-sampling. We obtained the probability density function and variance performance of the proposed estimator and confirmed that the analysis and the simulation results were agreed with each other.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.5
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• pp.376-382
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• 2001

Magnetic and transport properties in the ceramic specimen of L $a_{0.7}$S $r_{0.3}$Fe $O_3$ with orthohombic structure has been investigated. Weak ferromagnetism has been observed in a ceramic sample of L $a_{0.7}$S $r_{0.3}$Fe $O_3$. Large dielectric relaxation of Debye type is observed in paramagnetic states within the temperature range of 130K~200K. From the temperature dependence of the characteristic frequency, we concluded that the elementary process of the dispersion is related to holes hopping between F $e^{3+}$ and F $e^{4+}$ ions. The temperature dependencies of thermoelectric power and Dc conductivity suggest that the charge carrier responsible for the conduction are strongly localized. These experimental results have been interpreted in terms of a hopping process involving small polaron.n.laron.n.

• Journal of information and communication convergence engineering
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• v.6 no.1
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• pp.47-50
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• 2008

A novel high channel efficiency transceiver based on a fast acquisition frequency synthesizer has been designed. The direct digital synthesis (DDS) technique is applied and a simple memory look-up table is incorporated to expedite channel acquisition. The technique simplifies the frequency control process in the transceiver and thus reduces the channel switching time. As a result, the channel efficiency is improved. The designed transceiver is ideal for frequency hopping mobile communication applications.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.17 no.1
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• pp.38-46
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• 1992

In this thesis, a high speed code synchronization circuit is implemented, which is applicable to frequency hopping FSK tranceiver within 68-88 MIBz band- width. synchronization Process consists of two steps, initial synchronization and tracking. A modified matched filter method using two channel passive correlators matched with short hopping frequencies, synchronization prcfix. is proposed for initial synchronization. To increase probability of initial synchronization, prefix are transmitted repeatedly. The outputs of correlators are sent to synchronization decision circuit, and code start time Is extracted by synchronizatlon decision circuit-Modified matched fitter method makes it possible to reduce complexity in hardware and obtain code acquisition rapidly.Clock recovery circuit regenerates PN code clock for tracking.

• Korean Journal of Materials Research
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• v.6 no.12
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• pp.1242-1247
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• 1996

Spatially fixed bichromophoric systems with nonidentical chromophores have been extensively employed for studies of electron transfer and excitation transfer. Excitation hopping behavior between two naphthy1 moieties on 7,14-dihydro-7,14-ethanodibenz[a,h] anthracene(DEA)has been explored by the time-resolved fluorescence anisotropy measurements. The experimentally obtained value of the hopping rate in DEA agrees at least qualitatively with that calculated on the basis of the Dexter's theory, but disagrees with that calculated on the basis of the Forster's theory, indicates that for a pair of donor and acceptor with inter-chromophore separation as short as 4.5 $\AA$, excitation transfer via electron exchange is a predominant process.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.11
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• pp.3655-3673
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• 2014

Rendezvous is a process of two or more cognitive radio nodes gathering on the same channel at the same time for a negotiation to establish data communications. This paper discusses rendezvous issues in cognitive radio networks. It details why rendezvous is an issue in cognitive radio networks and how rendezvous works. It classifies channel access methods, and details sequence-based channel-hopping methods. It surveys existing works on blind rendezvous and compares the proposed algorithms in terms of the maximum time to rendezvous. This paper discusses the properties that an efficient channel-hopping rendezvous algorithm should have and illustrates common issues in the existing rendezvous methods. It also explains open research issues in the rendezvous area.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.36S no.7
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• pp.9-15
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• 1999

In this paper, we propose a bit synchronizer which is suitable for frequency hopping systems. The proposed bit synchronizer is an ADPLL in which the digital loop filter is combined with an error symbol detecting circuit. Suppressing the tracking process, when hop mute and impulse noises are detected, improves the performance of the digital loop filter and enhances the probability of the frequency hopping system. Simulation results demonstrate an improved performance of the proposed bit synchronizer compared with existing ones.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.8B
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• pp.1532-1539
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• 1999

In this paper, we propose a bit synchronizer which is suitable for frequency hopping systems. The proposed bit synchronizer is an ADPLL in which the digial loop filter is combined with an error symbol detecting circuit using an adaptive window. Suppressing the tracking process when hop mute and impulse noises are detected improves the performance of the digital loop filter and enhances the probability of the frequency hopping system. The simulation results demonstrate an improved performance of the proposed bit synchronizer compared with existing ones.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.324-329
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• 2005

Dynamic Encoding Algorithm for Searches (DEAS) which is known as a fast and reliable non-gradient optimization method, was proposed [1]. DEAS reaches local or global optimum with binary strings (or binary matrices for multi-dimensional problem) by iterating the two operations; bisectional search (BSS) and unidirectional search (UDS). BSS increases binary strings by one digit (i.e., 0 or 1), while UDS performs increment or decrement of binary strings in the BSS' result direction with no change of string length. Because the interval of UDS exponentially decreases with increment of bit string length (BSL), DEAS is difficult to escape from local optimum when DEAS falls into local optimum. Therefore, this paper proposes hopping UDS (HUDS) which performs UDS by hopping as many as BSL in the final point of UDS process. HUDS helps to escape from local optimum and enhances a probability searching global optimization. The excellent performance of HUDS will be validated through the well-known benchmark functions.