• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권1호
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• pp.253-271
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• 2017

In this paper, considering that perfect channel state information (CSI) is hard to achieve in practice, the downlink capacity of distributed antenna systems (DAS) with imperfect CSI and multiple receive antennas is investigated over composite Rayleigh fading channel. According to the performance analysis, using the numerical calculation, the probability density function (PDF) of the effective output SNR is derived. With this PDF, accurate closed-form expressions of ergodic capacity and outage probability of DAS with imperfect CSI are, respectively, obtained, and they include the ones under perfect CSI as special cases. Besides, the outage capacity of DAS in the presence of imperfect CSI is also derived, and a Newton's method based practical iterative algorithm is proposed to find the accurate outage capacity. By utilizing the Gaussian distribution approximation, another approximate closed-form expression of outage capacity is also derived, and it may simplify the calculation of accurate outage capacity. These theoretical expressions can provide good performance evaluation for downlink DAS for both perfect and imperfect CSI. Simulation results verify the effectiveness of the theoretical analysis, and the system capacity can be improved by increasing the receive antennas, and decreasing the estimation error or path loss. Moreover, the system can tolerate the estimation error variance up to about 0.01 with a slight degradation in the capacity.

• 한국멀티미디어학회논문지
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• 제24권5호
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• pp.676-683
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• 2021

Wi-Fi Round-trip timing (RTT) based location estimation technology estimates the distance between the user and the AP based on the transmission and reception time of the signal. This is because reception instability and signal distortion are greater than that of a Received Signal Strength Indicator (RSSI) based fingerprint in an indoor NLOS environment, resulting in a large position error due to multipath fading. To solve this problem, in this paper, we propose an end-to-end based WiFi Trilateration Net (WTN) that combines neural network-based RTT correction and trilateral positioning network, respectively. The proposed WTN is composed of an RNN-based correction network to improve the RTT distance accuracy and a neural network-based trilateral positioning network for real-time positioning implemented in an end-to-end structure. The proposed network improves learning efficiency by changing the trilateral positioning algorithm, which cannot be learned through differentiation due to mathematical operations, to a neural network. In addition, in order to increase the stability of the TOA based RTT, a correction network is applied in the scanning step to collect reliable distance estimation values from each RTT AP.

• ETRI Journal
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• 제26권6호
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• pp.565-574
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• 2004

Differential unitary space-time modulation (DUSTM) has emerged as a promising technique to obtain spatial diversity without intractable channel estimation. This paper presents a study of the application of DUSTM on multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems with frequency-selective fading channels. From the view of a correlation analysis between subcarriers of OFDM, we obtain the maximum achievable diversity of DUSTM on MIMO-OFDM systems. Moreover, an efficient implementation strategy based on subcarrier reconstruction is proposed, which transmits all the signals of one signal matrix in one OFDM transmission and performs differential processing between two adjacent OFDM blocks. The proposed method is capable of obtaining both spatial and multipath diversity while reducing the effect of time variation of channels to a minimum. The performance improvement is confirmed by simulation results.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 하계종합학술대회 논문집(1)
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• pp.236-239
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• 2000

OFDM Transmission system can effectively reduce ISI(Inter Symbol Interference) caused by multipath fading, especially in the case of broad band data transmission. Nevertheless, the delayed waves existing in a symbol degrade the transmission Performance at the receiver. Therefore when OFDM transmission system applies to mobile radio communication system, we have to remove the influence without intricacy. This paper proposes and design a new scheme in order to estimate propagation characteristics using the characteristics of distinctive OFDM signal which is inserted pilot signal periodically in frequency axis before IFFT at the transmitter Moreover, we introduce a cancellation scheme of delayed signal on the basis of the proposed estimation technique. Using these schemes, it is possible to estimate and cancel the Interference of the delayed signal before FFT at the receiver.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2004년도 하계종합학술대회 논문집(1)
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• pp.79-82
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• 2004

In this paper, we analyze the performance of high-rate OFDM(Orthogonal Frequency Division Multiplexing) in the JTC(Joint Technical Committee) channel models using transmit diversity. In this thesis, each independent channel characteristic antennas in the transmitter are analyzed. Also, Equalization method through the channel estimation in the realistic fading channel environments is applied for BEE 802.11a WLAN system performance. From the simulation results, BER through transmit diversity of WLAN system is evaluated in AWGN channel and multipath channel environments.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2005년도 추계종합학술대회
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• pp.73-76
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• 2005

Preamble based synchronization result in performance degradation due to the high time variation in the power delay profile of the channel in fast varying channel. Since most of the timing metric that exploit the preamble is not based on theoretical back ground, it is not easy to find out the reason. In this paper, the behavior of the timing metric in the multipath fading channel is explained.

• 한국방송∙미디어공학회:학술대회논문집
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• 한국방송공학회 2008년도 추계학술대회
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• pp.165-168
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• 2008

이 연구는 HDTV 방송 서비스를 제공하기 위해 새로이 주목받고 있는 Ka대역에서의 강우로 인한 위성신호의 감쇠량을 추정하였다. 강우 자료는 서비스 가입자 수를 고려하여 최대 인구 밀집 지역인 서울지역을 기준으로 서울대학교 AWS에서 측정한 2003년부터 2007년까지의 최근 5년간의 10분 강우강도를 ITU-R 기준인 분 강우강도로 변환하였고, 이를 ITU-RP. 618-9의 강우 추정 모델에 적용하여 감쇠 량을 도출하였다. 또한 도출된 감쇠 값을 최근 우리나라 기후변화의 추이를 반영하여 기상청에서 획득한 자료로부터 도출된 1990년부터 1999년의 서울지역의 감쇠 량과 비교 분석하였다. 본 연구를 바탕으로 우리나라 전 지역을 하나의 강우 단위로 일괄 적용하는 ITU-R P.837-5의 단점을 극복할 수 있으며, 강우의 지역적 편이가 매우 높은 우리나라의 강수 특성을 유연하게 반영할 수 있다.

• 디지털산업정보학회논문지
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• 제16권2호
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• pp.27-33
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• 2020

Backward compatibility is one of the key issues for radio equipment supporting IEEE 802.11, the typical wireless local area networks (WLANs) communication protocol. For a successful packet decoding with the backward compatibility, the frame format detection is a core precondition. This paper presents a novel frame format detection method based on a deep learning procedure for WLANs affiliated with IEEE 802.11. Considering that the detection performance of conventional methods is degraded mainly due to the poor performances in the symbol synchronization and/or channel estimation in low signal-to-noise-ratio environments, we propose a novel detection method based on convolutional neural network (CNN) that replaces the entire conventional detection procedures. The proposed deep learning network provides a robust detection directly from the receive data. Through extensive computer simulations performed in the multipath fading channel environments (modeled by Project IEEE 802.11 Task Group ac), the proposed method exhibits superb improvement in the frame format detection compared to the conventional method.

• 한국정보통신학회논문지
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• 제2권4호
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• pp.553-558
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• 1998

We present in this paper the ture union bound of the performance of chip level detection for coded DS/CDMA system operating in Rician fading channels such as LEO satellite mobile radio where the maximum doppler frequency is very high. The main objective of this paper is to calculate the exact doe union bound of BER performance of different performance of different quadrature detectors and to find a optimum spreading factor as a function of fade rate. The rationale of using multiple chip detection is to reduce the effective fade rate or variation. We considered chip level differential detection, chip level maximum likelihood sequence estimation, noncoherent detection and coherent detection with perfect channel state information as a reference.

• Journal of information and communication convergence engineering
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• 제3권3호
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• pp.115-118
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• 2005

In this study, the proposed algorithm is a correlativity signal in a mobile wireless channel that has estimated the direction of arrival. The proposed algorithm applied the space average method in a MUSIC algorithm. The diagonal matrix of the space average method was changed to inverse the matrix and to obtain a new signal correlation matrix. The existing algorithm was analyzed and compared by applying a proposed signal correlation matrix to estimate the direction of arrival in a MUSIC algorithm. The experiment resulted in a proposed algorithm with a min-norm method resolution at more than $5^{\circ}$. It improved more than $2^{\circ}$ in a MUSIC algorithm.