• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.12
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• pp.1049-1055
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• 2018

This paper proposes the Signal Quality Indicator (SQI) to certify the wired communication channels connected between sub-systems embedded in guided flight systems. The communication signals can be distorted due to the poor interconnections of wired channels, the interference from the signals passing through the adjacent routed channels, and additive white Gaussian noises. As the ways to find out the condition of the communication channels, we present the Hamming distance based SQI (H-SQI) and the Euclidean distance based SQI (E-SQI). Two SQIs are compared in terms of the SQI resolution performance and the required number of hardware resources for implementations. The E-SQI requires the 10 times FPGA resources and an additional analog-digital converter over the H-SQI in spite of its outstanding SQI resolution performance. Moreover, the H-SQI could have the enough SQI resolution performance to find out the channel condition by increasing the oversampling rate, so the H-SQI is the more adequate than the E-SQI for the SQI of the guided flight systems.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.7
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• pp.716-725
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• 2002

In this paper, we showed the applicability of power symmetric MSSI(Mid-Span Spectral Inversion) to the long-haul WDM system with the channel interference due to FWM(Four Wave Mixing). And we showed the degree of performance improvement. We used 1 dB EOP(Eye-Opening Penalty) criterion so as to evaluate the degree of compensation dependent on the variation of chirp parameter of optical pulse for the various input power in high speed tansmission system. And we evaluated the maximum input power of channel be able to be the signal to crosstalk noise (SNR) above 20 dB in the transmission link with the channel interference due to FWM. Consequently the proposed MSSI compensation method is capable to transmitting the total 68 WDM channels simultaneously with a 0.4 nm channel spacing and 5.3 dBm maximum input power in a 10 Gbps transmission link. Therefore the proposed power symmetric MSSI compensation method may be very useful for the implementation of long-haul wideband WDM transmission systems with relatively high power and improved performance.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.5
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• pp.1-6
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• 2007

In wireless mesh networks (WMNs), the end-to-end throughput of a flow decreases drastically according to the traversed number of hops due to interference among different hops of the same flow in addition to interference between hops of different flows with different paths. This paper proposes a distributed multi-channel assignment scheme based on hops (DMASH) to improve the performance of a static WMN. The proposed DMASH is a novel distributed multi-channel assignment scheme based on hops to enhance the end-to-end throughput by reducing interference between channels when transmitting packets in the IEEE 802.11 based multi-interface environments. The DMASH assigns a channel group to each hop, which has no interference between adjacent hops from a gateway in channel assignment phase, then each node selects its channel randomly among the channel group. Since the DMASH is a distributed scheme with unmanaged and auto-configuration of channel assignment, it has a less overhead and implementation complexity in algorithm than centralized multi-channel assignment schemes. Simulation results using the NS-2 showed that the DMASH could improve remarkably the total network throughput in multi-hop environments, comparing with a random channel assignment scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.11A
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• pp.878-891
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• 2011

We consider the throughput-maximization problem for both the up- and downlink in a wireless network with interference channels. For this purpose, we design an iterative and distributive uplink algorithm based on Lagrangian relaxation. Using the uplink power prices and network duality, we achieve throughput-maximization in the dual downlink that has a symmetric channel and an equal power budget compared to the uplink. The network duality we prove here is a generalized version of previous research [10], [11]. Computational tests show that the performance of the up- and downlink throughput for our algorithms is close to the optimal value for the channel orthogonality factor, ${\theta}{\in}$(0.5, 1]. On the other hand, when the channels are slightly orthogonal (${\theta}{\in}$(0, 0.5]), we observe some throughput degradation in the downlink. We have extended our analysis to the real downlink that has a nonsymmetric channel and an unequal power budget compared to the uplink. It is shown that the modified duality-based approach is thoroughly applied to the real downlink. Considering the complexity of the algorithms in [6] and [18], we conclude that these results are quite encouraging in terms of both performance and practical applicability of the generalized duality theorem.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.11A
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• pp.1072-1078
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• 2008

In this paper, we propose an efficient superposition coding multiplexing(SCM) method based on power allocation in descending order for fading broadcast channels in which per-user minimum and maximum rate constraints are considered in order to maximize the transmission effectiveness. It consists of three steps as follows. In the first step, a user group is selected to maximize the number of users with whom a transmitter can communicate instantaneously. In the second step, per-user power allocation for each user is done in descending order of transmit power by determining a maximum allowable interference power from all subsequent interfering users in order to guarantee its corresponding minimum rate, and then a residual power is calculated. The final step is performed if some power remains even after the second step. In this step, additional power allocation is performed up to the maximum transmit power to provide the maximum rate to the corresponding user, again in ascending order, starting from the last user in descending order. But, this method does not require power reallocation to subsequent users because tentative power allocation in the second step has been performed in descending order to guarantee the minimum rate for each user, taking into account the maximum allowable interference power from all the subsequent users. Therefore, the proposed method gets more efficient in term of computational complexity when per-user minimum as well as maximum rate constraints exist, especially as the number of users increases.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2011.10a
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• pp.255-258
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• 2011

Wi-Fi is a rapidly spreading communications network with Smart phone's publication, the technology has become Ubiquitous-based core network which is connected to personal computers, laptops, and tablet PC. Wi-Fi can send currently a variety of data standard due to developed wireless LAN communications network. One of Wi-Fi standard protocols, which is IEEE 802.11n, use 2.4GHz and 5GHz band. 2.4GHz band is used for 802.11b/g protocol because wavelength is long, diffraction and receiving distance is enough to connect other device. 5GHz band has more available channels to use than 2.4GHz band, so there is no frequency interference of other wireless device such as Bluetooth, RFID. Moreover, there is low interference between channels due to small users in each bandwidth level. In the thesis, we are going to analyze 802.11a/b/g protocol which has used since the beginning of Wi-Fi protocol and 802.11n protocol which is used lately. Furthermore, we look into development and direction for standardization of the next generation wireless LANs which are 802.11ac and 802.11ad. In addition, we will consider for the security, vulnerabilities and its countermeasure in Wireless LAN.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.4B
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• pp.613-623
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• 2000

Digital TV tuner for 8-VSB modulation was developed with satisfying the requirements of ATSC. The double frequency conversion and the active tracking filter in the front-end were used to reduce interference of the adjacent channels and multi-channels, which suppress If beat and image band. However, it was impossible to get frequency mapping between tracking filter and first VCO(Voltage Controlled Oscillator) in the double conversion digital TV tuner differing from conventional NTSC tuner. This paper, therefore, suggests the available structure and a new method for automatic frequency selection by obtaining the mapping of frequency characteristic over tracking voltage and the combined hardware which compose of Micro-controller, EEPROM, D/A(Digital-to-Analog Converter), OP amp and switch driver to solve above problems.

• Journal of Digital Convergence
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• v.10 no.9
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• pp.375-381
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• 2012

If a mobile station requests a channel allocation in its mobile networks, the switching center assigns a channel to a mobile station that belongs to each base station. There are three kinds of channel allocation schemes; a fixed channel allocation, a dynamic channel allocation and a hybrid combination of these two forms. In assigning a good frequency, it is our intention to provide quality service to our customers as well as to use resources efficiently. This paper proposes methods of assigning frequencies that minimize interference between channels and that also minimize the amount of searching time involved. In this paper, we propose an algorithm to per specific equipment, regardless of the number of channels that can be used as a general-purpose system, such as base stations, control stations, central office model is proposed, the existing operators manner similar to the fixed channel allocation based statistics and assigned when the conventional method and the improved method is proposed. Different ways and compared via simulations to verify the effectiveness of the proposed approach.

• Journal of IKEEE
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• v.3 no.1 s.4
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• pp.133-140
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• 1999

When the current optical communication system is used for the DWDM, it raise the serious interference because an interval between the adjacent channels is narrow. The FBG filter for the DWDM is able to reduce the interferences between the adjacent channels. In this paper, therefore, we find the reflection spectrums for the three types of induced index changes, that is, uniform, Gaussian apodized, and raised-cosine apodized. From the obtained results in this paper, we can see that uniform FBG does not fit, and that the smaller the maximum induced index change ${\sigma}$ is and the larger the value of parameter C in the raised-cosine apodized FBG and G in the Gaussian apodized FBG are, the fitter they are on the narrow filter for DWDM. But, we can also see that the raised-cosine apodized FBG has more excellent property than the Gaussian apodized FBG because it has the narrower maximum reflection spectrum band and the lower sidelobes than the other.

• Journal of Navigation and Port Research
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• v.37 no.3
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• pp.269-273
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• 2013

Underwater acoustic channels are generally recognized as one of the most difficult communication media because of the multipath propagation, dispersion, and so on. MIMO (Multiple-input multiple-output) techniques have been actively pursued in underwater acoustic communications recently to increase the data rate over the bandwidth-limited channels. The transmit diversity techniques can be applied in this case, and one of them is Alamouti's scheme. In this paper the performances of the transmit diversity technique are evaluated via experiment. Two transmitters and two receivers were used in experiment, and the experiment was performed in indoor water tank. The error rate 5~8% was confirmed in experimental results, and these are the improved values than the error rate 14.8% for SISO(Single-input single-output) channel under same data rate condition.