• Journal of Satellite, Information and Communications
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• v.12 no.4
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• pp.110-114
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• 2017

Using a small mobile wireless network as a supplement to the disaster safety network can be useful for eliminating small radio shadowing areas, reducing traffic overloads in disaster areas, and quickly building a disaster communication network in difficult access areas. Potable base station is needed to build a small mobile wireless network, and the portable base station using TVWS(TV White Space) is effective in terms of utilization of radio frequency resources and construction cost of wireless networks. In this paper, we design and implement a power amplifier for portable base station operating in TVWS. The implemented power amplifier operates at 470 ~ 698MHz. The gain of the implemented amplifier is more than 20.1dB, the input/output return loss is more than 11.4dB, and the isolation is more than 39.9dB when the output is off. The IMD characteristic of the power amplifier has characteristics of 61.0dBc with 18.8dBm output at 470MHz, 59.3dBc wih 18.6dBm output at 550MHz and 56.5dBc with 19.0dBm output at 690MHz. The power amplifier implemented in this paper can be used as a power amplifier for portable base station.

• Journal of Korea Multimedia Society
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• v.15 no.8
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• pp.1031-1037
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• 2012

In this paper, we propose the interference probability according to distance between mobile stations and the maximal power of interfering transmitter as parameters which are used for analysis to co-exist in co-channel of different systems. In order to analyze interfering between each systems, we consider two cases. First, WiBro is an interfering transmitter and WLAN is a victim receiver. Second, WLAN is an interfering transmitter and WiBro is a victim receiver. When the interfering transmitter is WiBro or WLAN, interference probability according to distance between systems is analyzed by setting transmit power of 25 and 23 dBm, respectively. Analyzed coexistence results under various co-use scenarios may be widely applied into the technique developed to get the coexisting condition for wireless devices using many communication protocols in same frequency.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.12
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• pp.1165-1171
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• 2011

In this paper, we investigate hidden node problem to effectively utilize TV band devices(TVBDs) in the TV white space(TVWS), and also to protect digital television(DTV) service in Korea. Firstly, we classify the radio propagation environment into an urban area, a basin area, and a coastal area based on geographical characteristics. Thereafter, we measure and analyze local shape based hidden node attenuation at eight segmented positions in each geographic area. Because commercial buildings as well as residential and commercial buildings in Korea are located in closer proximity to each other than in other countries, hidden node margin should be more than 38 dB in order to safely protect DTV service in Korea.

• Review of KIISC
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• v.19 no.5
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• pp.68-72
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• 2009

최근 들어 기학급수적으로 증가하는 방송 및 통신 시스템으로 인해 무선 주파수 자원의 고갈 문제가 심각하게 대두되고 있다. 이와 같은 주파수 고갈과 비효율적인 주파수 사용 문제를 해결하기 위해 유휴 주파수를 합리적으로 이용하기 위한 인지무선(Cognitive radio) 기술이 많은 관심을 받고 있다. 본 고에서는 TV 주파수 대역 내 유휴자원(White space)을 대상으로 주파수 공유 기술인 인지무선 기술을 적용하기 위해 현재 표준화가 진행 중인 IEEE 802.22 WRAN을 중심으로 인지 무선네트워크를 위한 보안 표준화 현황을 살펴본다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.8C
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• pp.529-535
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• 2011

After permission for utilization of TV white space by FCC, a lot of attentions are focused on spectrum sensing, and various spectrum sensing methods have been proposed. However, they do not consider real environment, thus they are hard to achieve the required performance. In this paper, we propose resolutions for the problem which could be occurred in implementation of spectrum sensing module and verify performance of the proposed methods with computer simulation. The first proposed method utilizes channel status information to separate received signal and spurious for reducing false alarm probability caused by system internal spurious. The another proposed scheme is subband normalization method to prevent miss detection caused by multiple narrow band signals with different received signal strength. The simulation results verify that we can prevent false alarm cause by spurious components with the proposed system internal spurious cognition. Moreover, the proposed subband normalization method shows that it could overcome performance degradation caused by received signal strength difference.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.9
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• pp.1864-1869
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• 2012

We make an interference analysis to obtain a critical ctiteria for coexisting availability of WLAN and WiBro between adjacent channels can be used in TVWS(TV White Space). To meet this analysis, we set the various transmission parameters including the emission and blocking mask, antenna height and gain, transmission power and bandwidth, channel model etc. And, based on these parameters, we analyze on performances according to a variation of guard band, a number of service user and allowable transmit power of the user operating in the adjacent channels. In this paper, we consider a urban environment and apply a Extended Hata-SRD for WLAN and an interference link and Extended Hata model for WiBro, respectively. With these results, we can see how each system can be shared in an adjacent channel.

• Journal of Communications and Networks
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• v.18 no.3
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• pp.476-483
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• 2016

Super Wi-Fi is a Wi-Fi-like service exploiting TV white space (WS) which is expected to achieve larger coverage than today's Wi-Fi thanks to its superior propagation characteristics. Super Wi-Fi has been materialized as an international standard, IEEE 802.11af, targeting indoor and outdoor applications, and is undergoing worldwide field tests. This paper demonstrates the true potential of indoor Super Wi-Fi, by experimentally comparing the signal propagation characteristics of Super Wi-Fi and Wi-Fi in the same indoor environment. Specifically, we measured the wall and floor attenuation factors and the path-loss distribution at 770MHz, 2.401 GHz, and 5.540 GHz, and predicted the downlink capacity of Wi-Fi and Super Wi-Fi. The experimental results have revealed that TVWS signals can penetrate up to two floors above and below, whereas Wi-Fi signals experience significant path loss even through a single floor. It has been also shown that Super Wi-Fi mitigates shaded regions of Wi-Fi by providing almost-homogeneous data rates within its coverage, performs comparable to Wi-Fi utilizing less bandwidth, and always achieves better spectral efficiency than Wi-Fi. The observed phenomena imply that Super Wi-Fi is suitable for indoor applications and has the potential of extending horizontal and vertical coverage of today's Wi-Fi.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.10
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• pp.7-12
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• 2011

The effect of frequency interference situation between WiBro and WLAN in TV White Space band was taken into account in this paper. We assumed the using frequency in each system is applied in co-channel. When it comes to co-channel interference case, the minimum distance between WiBro ME and WLAN UE should be at least 210m if the maximum transmitter power of WiBro UE of 25dBm is limited. Analysis results of this paper can provide efficient reference and guideline to make spectrum plan for deploying WiBro and WLAN in TVWS.

• International Journal of Computer Science & Network Security
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• v.23 no.4
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• pp.55-68
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• 2023

In recent years, the Television White Space (TVWS) has attracted the interest of many researchers due to its propagation characteristics obtainable between 470MHz and 790MHz spectrum bands. The plenty of unused channels in the TV spectrum allows the secondary users (SUs) to use the channels for broadband services especially in rural areas. However, when the number of SUs increases in the TVWS wireless network the aggregate interference also increases. Aggregate interferences are the combined harmful interferences that can include both co-channel and adjacent interferences. The aggregate interference on the side of Primary Users (PUs) has been extensively scrutinized. Therefore, resource allocation (power and spectrum) is crucial when designing the TVWS network to avoid interferences from Secondary Users (SUs) to PUs and among SUs themselves. This paper proposes a model to improve the resource allocation for reducing the aggregate interface among SUs for broadband services in rural areas. The proposed model uses joint power and spectrum hybrid Firefly algorithm (FA), Genetic algorithm (GA), and Particle Swarm Optimization algorithm (PSO) which is considered the Co-channel interference (CCI) and Adjacent Channel Interference (ACI). The algorithm is integrated with the admission control algorithm so that; there is a possibility to remove some of the SUs in the TVWS network whenever the SINR threshold for SUs and PU are not met. We considered the infeasible system whereby all SUs and PU may not be supported simultaneously. Therefore, we proposed a joint spectrum and power allocation with an admission control algorithm whose better complexity and performance than the ones which have been proposed in the existing algorithms in the literature. The performance of the proposed algorithm is compared using the metrics such as sum throughput, PU SINR, algorithm running time and SU SINR less than threshold and the results show that the PSOFAGA with ELGR admission control algorithm has best performance compared to GA, PSO, FA, and FAGAPSO algorithms.

• Journal of Periodontal and Implant Science
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• v.52 no.4
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• pp.312-324
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• 2022

Purpose: The role of hard-type crosslinked hyaluronic acid (HA) with particulate bone substitutes in bone regeneration for combined inlay-onlay grafts has not been fully investigated. We aimed to evaluate the effect of hard-type crosslinked HA used with bone substitute in terms of new bone formation and space maintenance. Methods: A 15-mm-diameter round defect was formed in the calvaria of 30 New Zealand White rabbits. All animals were randomly assigned to 1 of 3 groups: the control group (spontaneous healing without material, n=10), the biphasic calcium phosphate (BCP) graft group (BCP, n=10), and the BCP graft with HA group (BCP/HA, n=10). The animals were evaluated 4 and 12 weeks after surgery. Half of the animals from each group were sacrificed at 4 and 12 weeks after surgery. Samples were evaluated using micro-computed tomography, histology, and histomorphometry. Results: The BCP group showed higher bone volume/tissue volume (BV/TV) values than the control and BCP/HA groups at both 4 and 12 weeks. The BCP and BCP/HA groups showed higher bone surface/tissue volume (BS/TV) values than the control group at both 4 and 12 weeks. The BCP group showed higher BS/TV values than the control and BCP/HA groups at both 4 and 12 weeks. No statistically significant difference in newly formed bone was found among the 3 groups at 4 weeks. The BCP group showed significantly higher new bone formation than the BCP/HA group at 12 weeks. Conclusions: Hard-type crosslinked HA did not show a positive effect on new bone formation and space maintenance. The negative effect of hard-type crosslinked HA may be due to the physical properties of HA that impede osteogenic potential.