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Um, Jungsun,Park, Jaehyun,Chun, Joohwan,Park, Seungkeun IEEE 2016 IEEE Transactions on Vehicular Technology VT Vol.65 No.8
<P>In the TV white space, geolocation database techniques are utilized to manage white space devices (WSDs) or secondary users' operations over the digital terrestrial TV (DTT) receiver protection, in which the location-specific maximum power of WSDs is calculated based on location probability. The multiple antennas can also be utilized for WSDs to protect the DTT receivers and simultaneously increase the WSDs' system performance. However, due to the lack of channel information at the transmitter, conventional multiple-antenna-based cognitive radio (CR) techniques cannot be applied to WSD transceivers. In this paper, we develop the transmission strategies for multiple-antenna-based WSDs operating on the geolocation database framework. We analyze the achievable throughput when the WSD receiver exploits zero-forcing (ZF) linear processing under imperfect channel estimation and, based on the analytic results, propose a dynamic WSD transmission strategy in which the number of active transmit antennas and the associated antenna indexes are determined according to the WSD operational parameters obtained from the geolocation database.</P>
Implementation of platform for long-term evolution cell perspective resource utilization analysis
Um, Jungsun,Kim, Igor,Park, Seungkeun Electronics and Telecommunications Research Instit 2021 ETRI Journal Vol.43 No.2
As wireless communication continues to develop in limited frequency resource environments, it is becoming important to identify the state of spectrum utilization and predict the amount needed in future. It is essential to collect reliable information for data analysis. This paper introduces a platform that enables the gathering of the scheduling information of a long-term evolution (LTE) cellular system without connecting to the network. A typical LTE terminal can confirm its assigned resource information using the configuration parameters delivered from a network. However, our platform receives and captures only the LTE signal over the air and then enables the estimation of the data relevant to scheduling for all terminals within an LTE cell. After extracting the control channel signal without loss from all LTE subframes, it detects valid downlink control information using the proposed algorithm, which is based on the error vector magnitude of depatterned symbols. We verify the reliability of the developed platform by comparing it with real data from mobile phones and service operators. The average difference in resource block utilization is only 0.28%.
5 ㎓ 비면허대역 무선랜과의 상호공존을 위한 LTE 시스템의 채널접속방법에 관한 연구
엄중선(Jungsun Um),유성진(Sungjin Yoo),박승근(Seungkwon Park) 한국전자파학회 2015 한국전자파학회논문지 Vol.26 No.4
무선 트래픽이 급증함에 따라 활용 가능한 주파수 자원을 확보하고, 기존 사용자와 공동으로 주파수를 사용하기 위한 상호공존 기술에 대한 관심이 높아지고 있다. 이동통신 무선접속표준을 제정하는 3GPP에서도 면허대역에서 제공되던 이동통신시비스를 5 ㎓ 비면허대역으로 확장하기 위한 표준기술 개발을 시작하였다. 캐리어 집성기술을 기반으로 면허대역의 보조 캐리어로 5 ㎓ 대역을 활용하는 시나리오를 가정하고 있으며, 기존 Wi-Fi 시스템과 상호공존할 수 있는 기술개발이 핵심 요구사항으로 정의되었다. 3GPP에서는 각국의 기술기준을 모두 만족할 수 있는 단일 기술개발을 목표로 삼고 있으므로, 현재 유럽 기술기준의 Listen-Before-Talk 기반 Frame based Equipment와 Load based Equipment 채널접속방법을 Wi-Fi와 주파수 자원을 공유하기 위한 기술로 우선 검토하고 있다. 본 논문에서는 두 가지 방식에 대하여 설명하고, 비면허대역 LTE 표준에 적용하는 경우, 구현 및 표준관점에서의 고려할 사항을 정의하고 있다. 또한, 세 가지 동작 시나리오에서 파일전달지연시간과 전송률의 성능지표로 두 방식의 성능을 비교 분석한다. With explosion of wireless traffic it is required to further investigate the technologies on acquiring available spectrum resources and on sharing frequency with existing users. In 3GPP, it is started to study on feasibility and functional requirement of LTE standard in order to extend cellular services offered on only licensed band to 5 ㎓ unlicensed band. Operating scenario on LTE in unlicensed band is focused on carrier aggregation with licensed band, and the coexistence with Wi-Fi services in 5 ㎓ band is concerned as a major requirement. For a single global solution framework for licensed assisted access to unlicensed spectrum, listen-before-talk(LBT) mechanism of European regulation for fair access to channel under the coexistence environments is currently examined in 3GPP. In this paper, we evaluate two types of LBT, frame based equipment and load based equipment, with considering LTE carrier aggregation feature and performances of file transferred time and throughput.
SDR-Based Frequency Interference Emulator in the Space-Time Domain and Its Application
Hyungoo Yoon,Jungsun Um,Jin-Soo Park,Byung-Jun Jang 한국전자파학회JEES 2018 Journal of Electromagnetic Engineering and Science Vol.18 No.1
In this study, we propose a software-defined radio-based frequency interference emulator in the space-time domain. This emulator can easily model actual interference environments because of the versatile programming capability of the universal software radio peripheral and LabVIEW. As an example of an interfering network using the contention-based multiple access scheme in the time domain, we emulate a coordinated Wi-Fi network that consists of one access point and two Wi-Fi nodes. Results show that our emulator can successfully model multiple interfering signals in the Wi-Fi network and easily adjust various space–time domain parameters.
Yunbae Kim,Ganguk Hwang,Jungsun Um,Sungjin Yoo,Hoiyoon Jung,Seungkeun Park IEEE 2016 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.15 No.5
<P>As a promising solution for handling super dense wireless networks, wireless local area networks (WLANs) have been intensively considered due to their wide availability. However, the contention-based MAC protocol in WLANs should be modified because of its inefficiency. To this end, we consider a recently proposed novel MAC protocol called the renewal access protocol (RAP). With the RAP, we analyze two strategies for resolving collisions efficiently and achieving optimal throughput performance in super dense WLANs: strategies without and with grouping. First, we analyze the asymptotic behavior of the RAP itself (i.e., without grouping) as the number of terminals goes to infinity. We show that the RAP can achieve optimal throughput even in super dense WLANs and the relevant optimal access probability can be derived in a closed form. Second, we propose a grouping strategy in the RAP called the grouped RAP (G-RAP). While a grouping strategy in the IEEE 802.11ah standard is based on time division, our G-RAP is based on transmission attempts. So the G-RAP does not waste channel resources. We show that the G-RAP achieves the optimal network throughput for any group structure if terminals use the optimal access probability that we derive. Our analytical results are validated by simulation.</P>