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Femto Cell 전파환경에서의 전송가능 대역폭 평가방법에 관한 연구
하덕호(Deock-Ho Ha) 한국정보기술학회 2017 한국정보기술학회논문지 Vol.15 No.4
It is very important thing to search a practicable transmission bandwidth which can aim the upper limit of code rate in urban mobile communications. Usually, the measurement method of analysing the practicable transmission bandwidth can be conducted by Fourier transform analysis for the measured time delay distribution data. But this measuring method is very difficult because of the requirement of synchronization between the transmit and receiving end. Another method of deciding the practicable transmission bandwidth is to utilize the frequency correlation coefficient calculated from the two field strength signals with each different frequencies. This calculating method of frequency correlation coefficients is also not so good recommendable method because of its incorrectness due to the characteristic of field strength distribution. In this paper, we proposed and analyzed the standard deviation value calculated from difference decibel value between the two field strength signals with each different frequencies. From the simulation results, it can be seen that the dB standard deviation value of received signal strength is suitable estimation parameter because the dB standard deviation values can be correctly indicated a proportional value from 7.18 to 0.37 due to the variation ratio of directed wave components(-30~+20dB).
Cognitive UWB 펄스에 의한 시스템 성능 개선
하덕호(Deock-Ho Ha) 한국정보기술학회 2013 Proceedings of KIIT Conference Vol.2013 No.5
본 논문에서는, 스펙트럼 사용 효율을 높이기 위한 기술로서 UWB 시스템에서 사용되지 않는 주파수를 감지하여 이를 효율적으로 공유하여 사용할 수 있는 무선통신방식을 소개한다. 이 방식은 UWB(Ultra-WideBand)시스템에 인지적 기술(Cognitive Radio Technology) 기술을 적용한 방식으로, 컴퓨터 시뮬레이션을 통하여 원하는 마스크를 충족시키고 타 시스템으로부터의 간섭을 회피하여 성능이 개선됨을 확인하였다. UWB 기기들은 기존의 동일한 무선주파수대역을 공동으로 사용하기 때문에 상호 간섭에 의한 장애가 발생하게 되는데, 본 방식은 다양한 무선 응용 기술들이 혼재된 상황은 주파수 자원의 효율적 이용에 활용될 것으로 기대된다.
하덕호(Deock-Ho Ha) 한국정보기술학회 2015 한국정보기술학회논문지 Vol.13 No.6
Recently, it is also executing the spectrum auction policy in our country. Thus the 700/800MHz band is expected to be sold by auction and then frequency reallocation should be realized soon. Therefore, if the conventional analog frequency band of 800MHz is to be redistributed by the government spectrum policy and new CDMA mobile radio frequency band is reallocated, it is necessary to analyse and understand the mutual interference problems between adjacent wireless systems. In this paper, we proposed a solution of the interference problems from the analysis of measurement data concerned to the mixing interference signal in the conventional 800MHz frequency band of CDMA system. Especially, to solve the spurious emission problems and find the spurious emission objects we analysed radio propagation environments from the actual field test and then presented the solution of removing the spurious emissions from the analyzing the cause of spurious emission occurrences.
RTLS 시스템에서 속도 적응형 Hybrid(TDOA-RSSI) 방식에 의한 위치추정오차 개선
하덕호(Deock-Ho Ha) 한국정보기술학회 2012 한국정보기술학회논문지 Vol.10 No.6
In this paper, in order to improve the location estimation error existing in RTLS(Real Time Location Service) system for the mobility individual, we proposed a method of speed-adaptive location estimation that the transmitting signaling period is adaptively changed according to the varying speed of a mobility individual for each location interval. To get the more accurate location estimation values, we analyzed both the location values measured by Hybrid(TDOA and RSSI) method by using AeroScoutTM RTLS system and the estimated value obtained from the theoretical calculation by using the Least Square Method. Finally, we compared the analyzed values with a real location of mobility individual. From the experimental results based on our proposed method, it can be seen that the location estimation error for the real location of a mobility individual can be improved.
실내무선전파환경을 고려한 수정된 UWB 채널모델 시뮬레이터 구현
하덕호(Deock-Ho Ha),이영환(Young-Hwan Lee) 한국정보기술학회 2011 한국정보기술학회논문지 Vol.9 No.4
In this paper, we implement a novel UWB channel model simulator modifying by the conventional UWB channel model(IEEE 802.12 SG3a) parameters and also try to improve the UWB system performance applying by the modified channel parameters. First of all, we find the newly modified channel parameters adopting by the characteristic which the circularly polarized wave has markedly fading reduction effect compared to the linearly polarized wave in the indoor LOS and NLOS environment. And also, we modify main channel parameters(cluster arrival rate, ray arrival rate, cluster decay factor, ray decay factor) based on measured data for establishing the correct channel model corresponding to various polarized waves. Finally, in oder to verify the modified channel parameters, we analyse the performance improvement of UWB system.
차량 충돌 방지용 24㎓ 레이더 주파수대의 근거리 전파손실특성
하덕호(Deock-Ho Ha),류지열(Jee-Youl Ryu),김성운(Sung-Un Kim),최연욱(Yeon-Wook Choi) 한국정보기술학회 2011 한국정보기술학회논문지 Vol.9 No.8
In this paper, we describe the short range propagation loss characteristic of 24㎓ frequency band used for automotive collision avoidance radar (ACAR). To investigate the radio propagation characteristic of ACAR signals, we used 24㎓ UMCW (Un-Modulated Continuous Wave) signals using by several polarized antenna combinations. To detect the accurate message data for safety guiding ACAR, we analyze and investigate the optimum receiving condition from the short range UMCW signal of the 24㎓ frequency. From the measurement analysis, it can be clearly seen that the short range UMCW signal can be encountered to multipath interference due to scattering rays from the ground plane and adjacent moving obstacles. In addition, it was also found that the received signal strength of circularly co-polarized antenna shows the most strong envelopes and best fading reduction effect.
실내 LOS 무선채널 모델에서의 인지(Cognitive Radio) 기반 UWB 시스템 성능 개선
하덕호(Deock-Ho Ha)) 한국정보기술학회 2013 한국정보기술학회지 Vol.11 No.1
UWB 기기들은 기존의 다른 많은 무선기기와 동일한 무선주파수대역을 공동으로 사용하기 때문에 상호 간섭에 의한 장애가 발생하게 된다. 본 논문에서는, 스펙트럼 사용 효율을 높이기 위한 기술로서 UWB 시스템에서 비어 있는 주파수 채널를 감지하여 이를 효율적으로 공유하여 사용할 수 있는 무선통신기술을 소개한다. 제안된 UWB(Ultra-WideBand) 시스템에 인지적 기술(Cognitive Radio technology) 기술을 적용한 방식으로, 실내 가시거리 환경(LOS)을 고려한 컴퓨터 시뮬레이션을 통하여 원하는 마스크를 충족시키고 타 시스템으로부터의 간섭을 회피하여 성능이 개선됨을 확인하였다. 제안된 방식은 다양한 무선 응용 기술들이 혼재된 상황에서 주파수 자원의 효율적 이용에 활용될 것으로 기대된다.
차세대 차량용 무선통신(WAVE) 기술에 적합한 무선채널 모델
하덕호(Deock-Ho Ha) 한국정보기술학회 2014 한국정보기술학회논문지 Vol.12 No.4
In order to estimate the accuracy of system performance improvement and ensure the traffic safeties in next generation vehicular wireless communications, it is the most important thing to adopt the more accurate channel modeling for the vehicle-to-vehicle and vehicle-to-infrastructure wireless communication channels. This is the because the channel modeling is directly related to the traffic safety and its efficiency in Wireless Access in Vehicular Environment(WAVE) technology developments. In this paper, we analysed the microscopic effects of wireless propagation model which can be insisted on estimating the more accurate system performance and ensuring the traffic safety in WAVE technology. Firstly, we defined the typical conventional empirical model of the urban radio propagations, and then analysed the characteristic of data transmission and traffic safety sensitivities for the microscopic and macroscopic propagation characteristics. From the computer simulation analysis results, it can be seen that the radio channel modeling suitable for WAVE technology is to be considered with all characteristics of path loss, shadow fading, and fast fading effects.