• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.10
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• pp.838-844
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• 2013

In this paper, we propose a novel spectrum sensing scheme based on sensing time partitioning for cognitive radio systems in high traffic environments. Specifically, we partition a sensing time into K sub-sections, and then, propose a spectrum sensing scheme that determines if a primary user signal is present based on the sensing results on the partitioned sub-sections. From numerical results, it is confirmed that the proposed scheme outperforms the conventional schemes in high traffic environments.

• Journal of Communications and Networks
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• v.14 no.6
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• pp.614-618
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• 2012

Smart grid is widely considered to be a next generation power grid, which will be integrated with information feedback communications.However, smart grid communication technologies are subject to inefficient spectrum allocation problems. Cognitive radio networks can solve the problemof spectrumscarcity by opening the under-utilized licensed bands to secondary users. In this paper, adaptive cognitive radio spectrum sensing and sharing algorithms are developed for smart grid environments. Simulation results are presented to demonstrate the effectiveness of the proposed scheme in comparison with other existing schemes.

• Journal of Communications and Networks
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• v.16 no.3
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• pp.335-343
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• 2014

This paper considers the crucial problem of deploying wireless relays for achieving a connected wireless sensor network in indoor environments, an important aspect related to the management of the sensor network. Several algorithms have been proposed for ensuring full sensing coverage and network connectivity. These algorithms are not applicable to indoor environments because of the complexity of indoor environments, in which a radio signal can be dramatically degraded by obstacles such as walls. We first prove theoretically that the indoor relay placement problem is NP-hard. We then predict the radio coverage of a given relay deployment in indoor environments. We consider two practical scenarios; wire-connected relays and radio-connected relays. For the network with wire-connected relays, we propose an efficient greedy algorithm to compute the deployment locations of relays for achieving the required coverage percentage. This algorithm is proved to provide a $H_n$ factor approximation to the theoretical optimum, where $H_n=1+{\frac{1}{2}}+{\cdots}+{\frac{1}{n}}={\ln}(n)+1$, and n is the number of all grid points. In the network with radio-connected relays, relays have to be connected in an ad hoc mode. We then propose an algorithm based on the previous algorithm for ensuring the connectivity of relays. Experimental results demonstrate that the proposed algorithms achieve better performance than baseline algorithms.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.17 no.11
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• pp.1271-1278
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• 1992

In this paper, a practical model for evaluating and comparing the bit error rates(BERs) due to adjacent channel mutual interference in a synchronous and asynchronous frequency hopped spread spectrum multiple access(FH-SSMA) radio communication systems is proposed. After implementing the actual FH radio in both the sychronous and asynchronous case, the BER is computed and measured. An experiment of this system in mobile tactical environments reveals that the performance in the asynchronous case is lower than that of the synchronous case. The computer simulation model is an efficient tool for designing practical FH radios in mobile communication environments.

• Proceedings of the IEEK Conference
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• 2000.07a
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• pp.144-147
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• 2000

In this paper, we propose two receiver structures of the impulse radio (IR) system to improve its performance in multipath environments. Recently, the impulse radio system has drawn much attention for future high-speed wire-less communication services. The conventional IR receiver directly correlates received signals with the ideal reference waveform, which results in performance degradation in multipath environments. The Key idea of the proposed receiver structures is to reflect the multipath Characteristics into the IR receiver. One is to deconvolve the received waveform with estimates of the multipath gains to obtain the transmitted waveform while the other is to modify the reference waveform of the correlator according to the estimates of the multipath gains. We examine the performance of the proposed schemes for the statistical indoor wireless communication channel model using computer simulation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.5
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• pp.479-485
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• 2013

In this paper, we propose a smart farming system using the visible light communication based on the software defined radio (SDR) technology and the conventional RF radio. The proposed system can continuously monitor growth environments of the LED plant factory and automatically control the LED plant factory to keep optimal growth environments. Furthermore, by creating a database from various growth factors, the LED plant factory can be efficiently managed.

• Journal of information and communication convergence engineering
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• v.9 no.2
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• pp.166-171
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• 2011

This paper investigates the design issues of spectrum sensing in the cognitive radio (CR) networks of opportunistic unlicensed spectrum access. The cognitive radios can perform a communication using the incumbent user spectrum band without the interference caused by the cognitive radio users. In this case, the cognitive radios must know the real-time radio environments of the incumbent user spectrum band using the spectrum sensing, beacon signal, and geo-location database access. Then in this paper, we are going to provide spectrum sensing issues which include the sensing techniques, the regulatory requirements, the analysis of DTV detection threshold, and main considerations associated with the spectrum sensing design in cognitive radio systems. Also, this paper introduces design trade-offs in order to optimize the sensing parameters such as sensing time and sensing complexity.

• Journal of Advanced Navigation Technology
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• v.19 no.6
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• pp.630-635
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• 2015

Since, the existing analog village broadcasting system had been affected by the climate change such as rain and had some problems likes as short range, it had been changed to the digital system and its standardizations required to be developed from now. In order to deploy the efficient digital wireless village broadcasting system, some propagation profiles as well as service coverages should be analyzed in various radio environments. In this paper, we have set up the transmission power as a parameter and estimated the service coverage area ratio as well as the area ratio interfered into the nearby village in rural, suburban and urban environments using spectrum management intelligence system (SMIS). This paper provides the basic data to establish a standard using the radio propagation characteristics and received power for village broadcasting system in various environments.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.7
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• pp.1755-1763
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• 1998

The rain attenuatio of a radio channel above 10 GHz can have impact on the availability of the radio channel. The severity of the rain impairments increases with frequency and varies with regional location. This paper presents an estimation method for rain attenuation for millimeter-wave propagation in domestic environments. the dropsize distribution is assumed to be exponential, and the measurement data in the various countries which are simlar to the domestic environments are compared with the theoretical one by varying the dropsize distribution. A rain-rate conversion model which can convert .tau.-minutes rain-rate data to 1-minute rain-rate data for domestic environments is also discussed. Using the converted domestic rain-rate data, probabilty distributions of rain attenuation are computed.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.4 no.3
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• pp.243-257
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• 2010

Rapid developments in wireless sensor networks have extended many applications, hence, many studies have developed wireless sensor network positioning systems for indoor environments. Among those systems, the Global Position System (GPS) is unsuitable for indoor environments due to Line-Of-Sight (LOS) limitations, while the wireless sensor network is more suitable, given its advantages of low cost, easy installation, and low energy consumption. Due to the complex settings of indoor environments and the high demands for precision, the implementation of an indoor positioning system is difficult to construct. This study adopts a low-cost positioning method that does not require additional hardware, and uses the received signal strength (RSS) values from the receiver node to estimate the distance between the test objects. Since many objects in indoor environments would attenuate the radio signals and cause errors in estimation distances, knowing the path loss exponent (PLE) in an environment is crucial. However, most studies preset a fixed PLE, and then substitute it into a radio propagation loss model to estimate the distance between the test points; such method would lead to serious errors. To address this problem, this study proposes a Path Loss Exponent Estimation Algorithm, which uses only four beacon nodes to construct a radio propagation loss model for an indoor environment, and is able to provide enhanced positioning precision, accurate positioning services, low cost, and high efficiency.