• Journal of Advanced Navigation Technology
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• v.20 no.5
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• pp.440-445
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• 2016

There is a scheme where secondary users (SU) use predicted spectrum holes for primary users (PU) not to utilize for efficient utilization of the limited spectrum resources in cognitive radio networks. In this paper, we propose an adaptive call admission control framework that minimizes spectrum hopping call dropped probability (SHDP) for satisfying SU quality of service (QoS). The scheme is based on a call admission control (CAC), bandwidth prediction and adaptive bandwidth assignment. The prediction model predicts not only the number of spectrum holes, but requested bandwidth of SU spectrum hopping call, and then the CAC minimizes SHDP via an adaptive bandwidth assignment in resources not being enough for reservation. We bring Wiener prediction model to predict the resources. Simulations are conducted to compare the performance of proposed scheme with an existing, and show its ability of minimizing the SHDP.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.7
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• pp.685-691
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• 2003

This paper newly analyzes the effect of the phase noise in the frequency synthesizer on the performance of SFH/M-NCFSK system by standard frequency deviation(equation omitted) when noncoherent FSK demodulation of the square-law detector is considered. We derive the SER in the SFH system and analyze the effect of phase noise on the SFH/M-NCFSK system performance according to the hopping frequency spacing (1/T$\_$h/) and the variation of the standard frequency deviation (equation omitted). The required SNR is about 13.4 dB to meet Ps=10$\^$-3/ when the standard frequency deviation is about 4.0 Hz and the hopping frequency spacing (1/T$\_$h/) in the SFH/2-NCFSK system is 30. So, there is about 2.4 dB power penalty than the phase noise-free system. If the hopping frequency spacing 1/T$\_$h/ is under 30, the error floor may happen and SER considerably grows up. We show that the analytic results closely match with the simulation results.

• Journal of Internet Computing and Services
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• v.12 no.2
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• pp.47-53
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• 2011

When some sensors under Wireless Sensor Networks fail or become energy-exhausted, redundant mobile sensors might be moved to recover the sensing holes. Within rugged terrain where wheeled sensors are unsuitable, other type of mobile sensors, such as hopping sensors, are needed. In this paper, we address the problem of relocating hopping sensors to the detected sensing holes. Recent study for this work considered the relocation using the shortest path between clusters; however, the shortest path might be used repeatedly and create other sensing holes. In order to overcome the mentioned problem, we propose relocation schemes using the most disjointed paths or multi-paths. Simulation results show that the proposed schemes guarantee more balanced migration distributions of efficient sensors and higher movement success ratios of required sensors than those of the shortest path-based scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.1
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• pp.14-24
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• 2017

In this paper, we propose a new EIM(erasure insertion method) based on the average-minimal-noise-power for HOM(higher order modulation) over AWGN(additive white Gaussian noise) under PBJ(partial-band jamming). Then we design SFH/SS(slow-frequency-hopping spread-spectrum) system by applying this method and formulate the PER(packet error rate) of the system. Based on this formula, we propose a new method to set the optimal threshold of the EIM and verify it at the designed 16-QAM SFH/SS system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.10A
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• pp.816-829
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• 2003

In this paper, we evaluate the performance of PN (Pseudo Noise) code based time hopping sequences for M-ary UWB (Ultra Wide Band) multiple access systems using the equicorrelated signal sets. In particular, we consider two different types of M-ary UWB systems in UWB indoor wireless multipath channels: The first type of the systems (System #1) has identical symbol transmission rate regardless of the number of symbols M since the length of signal pulse train is fixed while M increases, and the second type of the systems (System #2) has the same bit transmission rate regardless of M since the length of signal pulse train is extended according to the increase of M. We compare the proposed systems with those using the ideal random time hopping sequence in terms of the symbol error rate performance. Simulation results show that the PN code based time hopping sequence achieves quite good performance which is favorably comparable to that of the ideal random sequence. Moreover, as M increases, we observe that System #2 shows better robustness against multiple access interference than System # 1.

• Journal of the Korean Ceramic Society
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• v.39 no.9
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• pp.878-883
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• 2002

Electrical resistivity and thermoelectric power measurements on Mn-based $La_{2.1}Sr_{1.9}Mn_3O_{10}$ with layered perovskite structure as functions of temperature are presented. The experimental results demonstrate that the electronic transport in $La_{2.1}Sr_{1.9}Mn_3O_{10}$ is well described by the Emin-Holstein adiabatic small polaron model. The thermoelectric power data in the small polaron regime above Curie temperature is nearly equal to that predicted by nominal $Mn^{4+}$ valence arguments. This indicates that transport involves small polaron hopping.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.8
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• pp.988-995
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• 2019

In this paper, we propose the Tile Based Frequency Hopping - Chirp Spread Spectrum(TBFH-CSS) technique, which has excellent Low Probability of Intercept(LPI)/Anti-Jamming(AJ) performance. Conventional Frequency Hopping - Chirp Spread Spectrum(FH-CSS) technique uses only single chirp signal, that makes the follower jammer easy to find and jam. However, proposed TBFH-CSS uses various kind of chirp signals which are generated according to the structure of basis tile, it is composed the basis time unit and the basis bandwidth unit. The TBFH-CSS signal has variety signal period and signal bandwidth. Therefore, the follower jammer hard to find and difficult to jam the TBFH-CSS signal. We analysis the LPI/AJ performance of the TBFH-CSS technique when the follow jamming attack exist and compared with the performance of the conventional FH-CSS technique. From the analysis, we can see the proposed TBFH-CSS technique has better LPI/AJ performance than conventional technique.

• Korean Journal of Materials Research
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• v.24 no.11
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• pp.604-609
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• 2014

The thermoelectric power and dc conductivity of $La_{2/3+x}TiO_{3-{\delta}}$ (x = 0, 0.13) were investigated. The thermoelectric power was negative between 80K and 300K. The measured thermoelectric power of x = 0.13 increased linearly with increased temperatures and was represented by $S_0+BT$. The x = 0 sample exhibited insulating behavior, while the x = 0.13 sample showed metallic behavior. The electric resistivity of x = 0.13 had a linear temperature dependence at high temperatures and a T3/2 dependence below about 100K. On the other hand, the electric resistivity of x = 0 has a linear relation between $ln{\rho}/T$ and 1/T in the range of 200 to 300K, and the activation energy for small polaron hopping was 0.23 eV. The temperature dependence of thermoelectric power and the resistivity of x = 0 suggests that the charge carriers responsible for conduction are strongly localized. This temperature dependence indicates that the charge carrier (x = 0) is an adiabatic small polaron. These experimental results are interpreted in terms of spin (x = 0.13) and small polaron (x = 0) hopping of almost localized Ti 3d electrons.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.8
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• pp.1543-1548
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• 2009

In this paper, a high speed code synchronization circuit is proposed. for fast code synchronization, matched filler method is used for initial code acquisition with two channel correlators. Particular frequency patterns of the limited number having the information about PN code start time are composed and transmitted repeatedly to increase the probability of accurate initial synchronization. And digital frequency synthesizer is proposed. And it's performance is analyzed theoretically. The analysis show that fast frequency hopping is possible in frequency hopping system that use digital frequency synthesizer.

• Journal of the Korea Institute of Military Science and Technology
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• v.14 no.1
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• pp.69-73
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• 2011

In the defence wireless communications, conventional Anti-Jamming techniques(Frequency Hopping/Spread Spectrum or Direct Sequence/Spread Spectrum) are used to overcome a intentional interfering signals which are single/multitone or partial band jammer etc. DS/SS techniques is very strong on tone jamming signal but not to be on a partial band jammer. So FH/SS AJ performances are expected method of an substitution of DS/SS, however FH/SS could not have good performance on some BMTJ(Band Multi-tone Jammer). So this paper proposes FH-CSS (Frequency Hopped - Chirp Spread Spectrum) to get more robustness against jammers(BMTJ, PBNJ) and analyze the AJ performances.