• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.8
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• pp.1894-1912
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• 2012

This paper proposes a system called Wireless Link based on Global Communication Channel (WLGCC) to enhance the spectrum sharing between digital broadcasting (DB) services and the cognitive radio (CR) system in the licensed band of 470-790 MHz. The WLGCC aims to enhance the spectrum sensing and geolocation database (GLD) spectrum sharing methods in the CR system. Spectrum sensing can be enhanced by receiving the status of the used frequencies from the WLGCC, thereby eliminating the need for a low detection threshold (i.e., avoiding the hidden node problem). In addition, the GLD can be enhanced by providing a reliable communication link between the database and the CR device in the form of an unused TV white space that is reserved as the proposed Global Communication Channel (GCC). This paper analyzes the coexistence of the new WLGCC system and the DB service in terms of avoiding additional interference. Specifically, we mathematically determine the WLGCC parameters, such as the in-band and out-of-band power levels, and operation coverage, and verify them using Monte Carlo simulation. The results show that WLGCC does not degrade the existing DB service and reliably transmits information of the vacant (or used) frequency bands to the CR.

• Journal of Communications and Networks
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• v.12 no.5
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• pp.433-441
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• 2010

Multihop transmission is a promising technique that helps in achieving broader coverage (excellent network connectivity) and preventing the impairment of wireless channels. This paper proposes a cluster-based multihop wireless network that makes use of the advantages of multihop relaying, i.e., path loss gain, and partial relay selection in each hop, i.e., spatial diversity. In this partial relay selection, the node with the maximum instantaneous channel gain will serve as the sender for the next hop. With the proposed protocol, the transmit power and spectral efficiency can be improved over those in the case of direct transmission and conventional multihop transmission. Moreover, at a high signal-to-noise ratio (SNR), the performance of the system with at least two nodes in each cluster is dependent only on the last hop and not on any of the intermediate hops. For a practically feasible decode-and-forward relay strategy, a compact expression for the probability density function of the end-to-end SNR at the destination is derived. This expression is then used to derive closed-form expressions for the outage probability, average symbol error rate, and average bit error rate for M-ary square quadrature amplitude modulation as well as to determine the spectral efficiency of the system. In addition, the probability of SNR gain over direct transmission is investigated for different environments. The mathematical analysis is verified by various simulation results for demonstrating the accuracy of the theoretical approach.

• Journal of the Korea Institute of Military Science and Technology
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• v.18 no.5
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• pp.602-611
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• 2015

Even though GNSS provides highly accurate navigation information all over the world, it is vulnerable to jamming in the electronic warfare due to its weak signal power. The United States and Korea have plans to use terrestrial navigation systems as back-up systems during outage of GNSS. In order to develop back-up systems of GNSS, an M&S software platform is necessary for performance evaluation of various vehicle trajectories and integrated navigation systems. In this paper a design method of an M&S software is proposed for evaluation of multiple radio positioning integration systems. The proposed M&S software consists of a navigation environment generation part, a navigation algorithm part, a GUI part and a coverage analysis part. Effectiveness of the proposed design method is shown by implementing an M&S software for the GPS, DME and eLoran navigation systems.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.1
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• pp.26-33
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• 2013

Femto-cells are low power/cost, micro-base stations and are main components in heterogeneous networks. However, some of technical issues arise when femto-cells are initially installed. One approach to resolve the problems is to control the transmission (TX) power autonomously via SON(Self-Organized Network) scheme. By controlling the femto-cell TX power, the system throughput performance can be improved or the system overhead is highly reduced. Generally, the TX power for maximizing the system throughput and that for reduced system overhead may not be identical. Therefore, we propose a TX power control scheme by which we can improve the system throughput and reduce the system overhead, simultaneously. When we apply the proposed method, the simulation results show that the system overhead can be reduced by up to 41% compared to the performance of the method which maximizes throughput performance only, and the throughput performance can be improved by up to 63% compared to that of the method which only optimizes the coverage area.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.12
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• pp.1110-1116
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• 2013

A 3D-ray tracing tool is a software considering reflection, penetration, and diffraction of the signals to provide accuracy. To provide communication resources effectively, communication standards adopt Heterogeneous Networks (HetNets) that includes small cells. A 3D performance evaluation methodology becomes more and more important since the coverage of the small cell networks is narrower than that of the macro cell networks. It is difficult to directly apply conventional 2D mathematical models due to the complexity of small cell network; since they have many considerations such as topography, placement of buildings and 3D beamforming techniques. In this paper, we introduce an effective performance evaluation methodology for small cell networks using 3D-ray tracing tool. From simulation results, we conclude that new performance evaluation methodologies by using 3D-ray tracing tool is more suitable than conventional methodology for small cell networks.

• The KIPS Transactions:PartC
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• v.17C no.6
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• pp.491-498
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• 2010

Wi-Fi based vehicle-to-infrastructure (V2I) communication is an emerging solution to improve the safety, traffic efficiency, and comfort of passengers. However, due to the high mobility of vehicles and the limited coverage of Wi-Fi APs, the V2I system may suffer from frequent handoffs although roadside APs can support cost effective Internet connectivity. Such problem of V2I systems can be overcome with Mobile AP (MAP) platform. The MAPs yield longer service duration by moving along with vehicles, yet they provide a lower link capacities than the roadside APs. In this paper, we propose a new association control mechanism that effectively determines whether the vehicle will select a fixed roadside-AP or a nearby MAP in mobile vehicular network environments. We consider both the achievable link bandwidth and available connection duration as a selection criterion and provide their run-time estimation method. Extensive simulation using real traces show significant performance improvements.

• Journal of KIISE:Information Networking
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• v.35 no.3
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• pp.227-234
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• 2008

The development of wireless network technology allows high data rate seamless communication irrespective of the place and time in various emerging mobile service environment. Unlike wired networks, however, wireless networks utilize expensive limited bandwidth. MBS(Multicast Broadcast Service), which is supported by mobile WiMAX system based on IEEE802.16e, overcomes this problem using a shared downlink channel for efficiently supporting a number of users. However. the coverage and throughput of the system are significantly affected by the channel condition. In this paper we propose on MBS system employing Mobile Multi-Hop Relay(MMR) and adaptive modulation and coding(AMC) scheme. The result of NS-2 computer simulation shows that the throughput and transmission time are substantially improved by the proposed approach compared to the existing MBS system.

• KIISE Transactions on Computing Practices
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• v.22 no.4
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• pp.184-188
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• 2016

The cleaning robot is popularly used as a home appliance. The state-of-the-art cleaning robot can clean more efficiently by using information gathered from its sensor, which is difficult for low-price cleaning robots due to limitation in this aspect. In this paper, we suggested a method for the moving pattern of cleaning robot based on grammatical evolution. Optimized program is generated by using moving pattern grammar, which is defined by Backus-Naur form. In addition, conditional probability is used between each of the grammar elements during the program creation process. The proposed method is evaluated by robot simulation in order to verify its performance and further compare it with existing algorithms. The experiment results showed that the proposed method is better than the compared algorithms.

• Journal of Korea Society of Industrial Information Systems
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• v.17 no.7
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• pp.9-16
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• 2012

In order to extend cell coverage and to cope with shadow areas, a relay-assisted wireless communications system has been widely studied. In this paper, we propose new equalization method for single carrier (SC) frequency domain equalizer (FDE) in amplify-and-forward (AF) relaying multi-path networks to improve the performance at shadow areas. The performance of SC-FDE system in 3-slot based multi-path networks can be improved considerably with the diversity gain which we obtain by equalizing the combined signal from relays by means of the minimum mean square error (MMSE) criteria. We find the weighting coefficients of maximum ratio combining (MRC) and the tap coefficients of MMSE equalizer for SC-FDE in AF relaying multi-path networks. Simulation results show that the proposed system considerably outperforms the conventional SC-FDE system.

• Journal of Korea Multimedia Society
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• v.13 no.11
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• pp.1657-1666
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• 2010

Underwater wireless sensor networks (UWSN) need stable efficient data transmission methods because of environmental characteristics such as limited energy resource, limited communication bandwidth, variable propagation delay and so on. In this paper, we explain an enhanced hybrid transmission method that uses a hexagon tessellation with an ideal cell size in a two-dimensional underwater wireless sensor network model (2D) that consists of fixed position sensors on the bottom of the ocean. We also propose an energy efficient sensing and communication coverage method for effective data transmission in a three-dimensional underwater wireless sensor network model (3D) that equips anchored sensors on the bottom of the ocean. Our simulation results show that proposed methods are more energy efficient than the existing methods for each model.