• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.1A
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• pp.17-24
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• 2012

In this paper, we described a received signal model in terms of the starting point of FFT window and derive a post-detection SINR for the receiver with MMSE filter and the corresponding filter coefficients in order to mitigate the effects of interferences caused by time and frequency selective fading channels and time difference of arrival (TDoA) in OFDMA-based Mesh Networks. In addition, we proposed an MMSE Bidirectional Successive Detection (BSD) technique which can suppress the effects of interferences among multi-nodes without any redundant FFT operations. It was shown by simulation that the proposed interference suppression technique has not an error floor at higher average SNR than 30dB in terms of 64QAM uncoded BER contrary to the conventional techniques.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.12C
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• pp.1131-1137
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• 2009

In this paper, a resource management technique for digital duplexing (DD) systems using orthogonal frequency division multiple access (OFDMA) is proposed. The proposed technique can reduce the dynamic range of the signal received at the subscriber station (SS) and minimize the effects of inter-symbol interference (ISI) and inter-carrier interference (ICI) due to the time difference of arrival (TDoA) without using a cyclic suffix. It is shown by computer simulation that the proposed technique can reduce the number of bits for an analog-to-digital converter (ADC) and increase the signal-to-interference and noise ratio (SINR) significantly.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.6C
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• pp.495-505
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• 2010

In this paper, the effect of Near-Far Problem (NFP) among distributed nodes in OFDMA-based Wireless Mesh Networks (WMNs) is analyzed by investigating statistical characteristics of Time Difference of Arrival (TDoA) and Desired-to-Undesired power Ratio (DUR). In order to overcome the effects of Inter-Symbol Interference (ISI), Inter-Carrier Interference (ICI), and Inter Link Interference (ILI), caused by TDoA in WMNs, we derive effective SINR for each subcarrier, and then, propose the optimal starting point of FFT window which can minimize BER for each subcarrier. In addition, we propose a subcarrier-based Zero Forcing - 2 Dimensional Ordered Successive Interference Cancellation (ZF-2DOSIC) technique for signal detection in WMNs with TDoA. It is verified by simulation that the effective SINR and uncoded BER performances of the proposed signal detection technique for OFDMA-based WMNs are significantly improved, compared with those of conventional technique.

• Proceedings of the KIEE Conference
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• 2005.07d
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• pp.3049-3051
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• 2005

본 논문은 UWB(Ultra Wide Band) 펄스 기반의 단일 송수신을 통한 근거리 무선측위 시스템 및 방법에 관한 것으로서, UWB 펄스의 높은 시간 분해능을 이용하여 근거리에서 높은 정밀도를 가지고 태그의 위치를 획득할 수 있다. 특히, 마스터-슬레이브 형태로 구성된 비콘(beacon)들 간의 사전 설정을 통해 마스터 비콘과 무선측위 대상인 태그 사이의 단일 송수신만으로 ToA(Time of Arrival) 및 TDoA(Time Difference of Arrival) 기법을 적용할 수 있도록 하며, 이로써 태그의 신호 송신을 최소화하여 태그의 저전력 동작을 가능케하는 UWB기반 단일송수신을 통한 근거리 무선측위 시스템이다.

• The Journal of the Acoustical Society of Korea
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• v.39 no.1
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• pp.47-56
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• 2020

The sound source localization technique has various application fields in the era of internet-of-things, for which the probe size becomes critical. The localization methods using the acoustic intensity vector has an advantage of downsizing the layout of the array owing to a small finite-difference error for the short distance between adjacent microphones. In this paper, the acoustic intensity vector and the Time Difference of Arrival (TDoA) method are compared in the viewpoint of the localization error in the far-field. The comparison is made according to the change of spacing between adjacent microphones of the three-dimensional microphone array arranged in a tetrahedral shape. An additional test is conducted in the reverberant field by varying the reverberation time to verify the effectiveness of the methods applied to the actual environments. For estimating the TDoA, the Generalized Cross Correlation-Phase transform (GCC-PHAT) algorithm is adopted in the computation. It is found that the mean localization error of the acoustic intensimetry is 2.9° and that of the GCC-PHAT is 7.3° for T₆₀ = 0.4 s, while the error increases as 9.9°, 13.0° for T₆₀ = 1.0 s, respectively. The data supports that a compact array employing the acoustic intensimetry can localize of the sound source in the actual environment with the moderate reflection conditions.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.8C
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• pp.742-749
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• 2009

In this paper, we propose mitigation techniques using time-domain shortening filter (TSF) and frequency-domain shortening filter (FSF) to overcome inter-block interference (IBn and inter-carrier interference (ICn due to the time difference of arrival (TDoA) and carrier frequency offset (CFO) between downlink and uplink signals from access point (AP) and subscriber station (SS) in synchronous digital duplexing (SDD)/orthogonal frequency division multiple access (OFDMA) systems for indoor wireless communication. The proposed TSF and FSF maximize SIR for shortening in time (SIRST) and SINR for shortening in frequency (SINRSF), respectively, by using channel impulse responses and timing information among stations, obtained from mutual ranging procedure. It is verified by computer simulation that the proposed TSF and FSF reduce effectively the effects of IBI and ICI in the SDD/OFDMA systems.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.12
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• pp.1069-1078
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• 2013

In this paper, we propose a distributed time synchronization technique for OFDMA- based wireless mesh communication systems. The proposed technique employs the bio-inspired algorithm for self-time synchronization in the physical layer. To achieve the network synchronicity, the proposed technique updates the transmission time and the FFT window using the TDoA information of received signals from the neighbor nodes. The proposed technique can achieve fast self-synchronization among nodes with a simple algorithm, without the need of a centralized controller. The performance of the proposed time synchronization technique is evaluated by simulation in terms of convergence speed and convergence probability.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.25 no.4
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• pp.611-614
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• 2021

In this paper, we propose a widerange array microphone for lecturer tracked with Frequency Modulated Continuous Waveform (FMCW) radar sensor. Time Difference-of-Arrival (TDoA) is often used as audio tracking, but the tracking accuracy is poor because the frequency of the voice is low and the relative frequency change is large. FMCW radar has a simple structure and is used to detect obstacles for vehicles, and the resolution can be archived to several centimeter. It is shown that the sensor is useful for detecting a speaker in open area such as a lecture, and we propose an wide range 4-element array microphone beamforming system. Through some experiments, the proposed system is able to adequately track the location and showed a 8.6dB improvement over the selection of the best microphone.

• IEMEK Journal of Embedded Systems and Applications
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• v.8 no.1
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• pp.51-59
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• 2013

This paper researches location estimating method in CDMA system. Previously proposed positioning algorithms are difficult to estimate accurate position in indoor environments, and possible to limited position. This paper proposes enhanced algorithm using received PN pilot signals from base stations to enhance previous algorithms. For estimating position, we set the threshold value and use over the threshold value in received signals. After selecting signals, we estimate position using TDOA algorithm. And the cases which TDOA algorithm cannot use to estimate position, we use Pattern Matching algorithm. The proposed method system showed the improved performance in estimating parameters and locating positions by computer simulations.

• Journal of Institute of Control, Robotics and Systems
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• v.14 no.6
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• pp.608-614
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• 2008

This paper describes a location tracking system to guide landing process of an Unmanned Helicopter(UMH) exploiting MIT Cricket nodes. For automatic landing of a UMH, a precise positioning system is indispensable. However, GPS(Global Positioning System) is inadequate for tracking the three dimensional position of a UMH because of large positioning errors. The Cricket systems use Time-Difference-of-Arrival(TDoA) method with ultrasonic and RF(Radio Frequency) signals to measure distances. They operate in passive mode in that a listener attached to a moving device receives distance signals from several beacons located at fixed points on ground. Inevitably, this passive type of implementation causes large disturbances in measuring distances between beacons and the listener due to wind blow from propeller and turbulence of UMH body. To cope with this problem, we proposed active type of implementation for positioning a UMH. In this implementation, a beacon is set up at UMH body and four listeners are located at ground area at least where the UMH will land. A pair of Ultrasonic and RF signals from the beacon arrives at several listeners to calculate the position of the UMH. The distance signals among listeners are synchronized with a counter value appended to each distance signals from the beacon.