편향된 QPSK를 이용한 머신 러닝 기반 채널 위상 추정에 대한 연구

왕한호(Hanho Wang),고균병(Kyunbyoung Ko) 한국콘텐츠학회 2023 한국콘텐츠학회 종합학술대회 논문집 Vol.2023 No.5

순차적 K-means 군집화를 이용한 고차 변조 신호에 대한 채널 추정기법

왕한호(Hanho Wang) 한국정보기술학회 2019 한국정보기술학회논문지 Vol.17 No.6

In this paper, we propose a channel estimation method for 16-QAM or higher-order modulated signals without using pilot signal transmission using Sequential K-means Clustering (SKC). The existing channel estimation method using K-means clustering can be applied only to QPSK with a constant absolute value of 1. However, the conventional techniques have a problem in that they can not be applied to a 16QAM or higher-order modulation method in which the absolute value of a complex number representing a data symbol is not the same. On the other hand, the proposed channel estimation scheme using SKC provides a new center point method called reference center point and solves the problem in conventional K-means clustering-based channel estimation schemes. In order to verify the performance of the channel estimation scheme using the SKC proposed in this paper, the mean square error and the symbol error rate are used as performance metrics. Through the performance evaluation results, it is confirmed that the proposed channel estimation method using SKC and the reference center are successfully applied to the channel estimation using the higher order modulation signal of 16QAM or more. Even though the pilot signal is not used, the channel estimation method is superior to the least square channel estimator Respectively.

군집화 알고리즘을 이용한 채널 추정 기법 및 성능 평가

왕한호(Hanho Wang) 한국정보기술학회 2018 한국정보기술학회논문지 Vol.16 No.2

Pilot signals must be transmitted in order to estimate the channel of the mobile terminal. However, since the pilot signals consume resources for transmitting data signals, the actual data rate is lowered. In this paper, utilizing a clustering technique used in the unsupervised deep learning field, we propose a pilotless channel estimation (PCE) scheme with only using data symbols. If QPSK symbols are transmitted through the multipath channel, their amplitude and phase changes in the channel. The clustering technique is applied to the wireless communication receiver to estimate the channel. Assuming the Rayleigh fading channel, we evaluate the performance of the PCE under the LTE system with the minimum resource allocation. We compare the performance of the PCE with the widely used least square channel estimator. The PCE performs 7㏈ better than the conventional channel estimation scheme with respect to the mean squared error (MSE). Due to the improvement of the MSE, we can obtain 2 ㏈-improved bit error rate performance even though pilot signals are unused.

선택 다이버시티를 사용하는 이중 편파 안테나 시스템의 오수신 확률 분석

왕한호(Hanho Wang) 한국정보기술학회 2015 한국정보기술학회논문지 Vol.13 No.1

Dual-polarization antenna systems are designed to multiplex two independent wireless communication channels by using polarization characteristics. The dual-polarization antenna systems can work in line-of-sight (LoS) channel environment differentiated from the conventional multiple input multiple output (MIMO) systems which can work only in multi-path channel. The most important performance metric to evaluate the capacity of a dual-polarization antenna system is the rotation angle between dual-polarization antennas in a transmitter and receiver pair. If the rotation angle is perfectly aligned, interference occurs in between vertical and horizontal antennas, which results in capacity degradation of the dual-polarization antenna system. In this paper, outage probability of a dual-polarization antenna system with selection diversity. Quantitative outage improvement by using the selection diversity is derived as a closed form expression.

이중 편파 안테나시스템의 오수신 확률 분석

왕한호(Hanho Wang),노고산(Gosan Noh),방승재(Seungjae Bahng),박윤옥(Youn Ok Park) 한국통신학회 2014 韓國通信學會論文誌 Vol.39 No.12(통신이론)

M2M 어플리케이션 지원을 위한 무선 결합 전송 플랫폼의 전송률 분석

왕한호(Hanho Wang),우중재(Choongchae Woo) 대한전기학회 2014 전기학회논문지 P Vol.63 No.3

Various M2M applications have different quality-of-service(QoS) requirements to be implemented practically. QoS requirements are normally data rate and delay constraint. However, there are limited number of wireless communication chip solutions which cannot support QoS requirements for all M2M application. Hence, aggregated usage of plural wireless communication chip solutions should be needed to implement M2M applications. In this paper, we consider the case that two wireless communication chips using random access protocol work together to transmit data of an M2M application. In such case, data rate and delay performance are mathematically analyzed. In our results, practical data rate can be improved from 2.5 to 7 times while delay constraints are satisfied if we simply use two wireless communication chips together.

타 단말 신호를 이용하는 K-means 기반 채널 추정 기법

왕한호(Hanho Wang) 한국정보기술학회 2020 한국정보기술학회논문지 Vol.18 No.11

Pilotless channel estimation (PCE) without transmitting a pilot signal increases a substantial data rate by estimating a channel using only data symbols. However, the existing PCE techniques have had a problem that a channel can be normally estimated only when received data symbols are evenly distributed over all symbol positions on a constellation of a modulation scheme. This paper proposes a PCE technique that estimates the channel by receiving both the desired user’s signal and the signal of another terminal in the downlink. By receiving signals from two terminals together and increasing the actual number of data symbols used for the PCE, improved channel estimation performance can be obtained. According to the results of this paper, when estimating the channel of the desired terminal using data symbols modulated with 16QAM, it is confirmed that the mean squared error of the estimated channel can be reduced by estimating channel including other user’s signal.

시변 채널에서 K-means 기반 채널 추정 기법의 성능 평가

왕한호(Hanho Wang) 한국정보기술학회 2022 한국정보기술학회논문지 Vol.20 No.1

PCE with a certain number of data symbols has superior mean squared error(MSE) performance compared to a least square(LS) channel estimator using pilot signal. However, in PCE studies conducted so far, only the channel estimation performance for the snapshot channel has been presented, but the performance in the time-varying channel has not been presented. Since the PCE is a channel estimator that estimates the channel based on the previous channel estimation, performance evaluation in the time-varying channel is essential. In this paper, the channel estimation performance of the PCE is evaluated in time-varying channel of a mobile communication environment. Through this evaluation, It is shown that the PCE has superior MSE performance with SNR gain between 4 and 6 dB compared to the LS channel estimator even in time-varying channels. In addition, mobility adaptive resource allocation scheme for the PCE is proposed, which makes the PCE provide the best MSE performance in a channel environment

인지무선통신 환경에서 슬롯-알로하 기법의 전송 효율 분석

왕한호(Hanho Wang),우중재(Choongchae Woo) 대한전기학회 2015 전기학회논문지 P Vol.64 No.1

In cognitive radios, exponentially distributed idle period(EIP) is considered in this paper. In the EIP case, durations of idle periods are be limited and varied by primary traffic arrivals. Accordingly, we first analyze the idle period utilization which can be achieved by the slotted ALOHA in cognitive radio communications. The idle period utilization is a newly defined performance metric to measure the transmission performance of the secondary network as effective time durations utilized for successful secondary transmissions in an idle period. Then, the idle period utilization is maximized through controlling the data transmission time. All technical processes are mathematically analyzed and expressed as closed form solutions.

OFDMA 기반 셀룰러 시스템에서 핸드오버 기법의 성능 Trade-Off 분석

왕한호(Hanho Wang) 대한전기학회 2013 전기학회논문지 P Vol.62 No.4

Handover is a technical methodology to support mobility of wireless communication users, which mainly affects the capacity of wireless communication systems and the quality of service (QoS) of link level signal. However, in OFDMA-based cellular systems, there are few published technical reports investigating handovers with respect to diversity gains and resource consumption depending on what handover technique is adopted. In this paper, we propose handover schemes exploiting transmit diversity and macro-diversity in order to increase capacity of OFDMA-based wireless communication systems, and analyze their performance. In cellular environments, depending on what handover scheme is selected, average signal-to-interference-and-noise ratio is calculated first for a handover user in order to evaluate the link level QoS. Through this technical evaluation for handover schemes, we conclude what handover scheme is suitable for OFDMA-based cellular systems.