• Journal of Communications and Networks
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• v.9 no.4
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• pp.482-489
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• 2007

In this paper, two frequency domain signal processing techniques for pulse shape modulation(PSM) ultra wideband(UWB) systems are presented. Firstly, orthogonal detection of UWB PSM Hermite pulses in frequency domain is addressed. It is important because time domain detection by correlation-based receivers is severely degraded by many sources of distortion. Pulse-shape, the information conveying signal characteristic, is deformed by AWGN and shape-destructive addition of multiple paths from the propagation channel. Additionally, because of the short nature of UWB pulses, timing mismatches and synchronism degrade the performance of PSM UWB communication systems. In this paper, frequency domain orthogonality of the Hermite pulses is exploited to propose an alternative detection method, which makes possible efficient detection of PSM in dense multipath channel environments. Secondly, a ranging method employing the Cepstrum algorithm is proposed. This method is partly processed in the frequency domain and can be implemented without additional hardware complexity in the terminal.

• Proceedings of the Optical Society of Korea Conference
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• 1991.06a
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• pp.121-125
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• 1991

A basic coherent optical transmission was demonstrated using FSK modulation and heterodyne detection scheme. Optical frequency of DFB LD light source at the transmitter side was stabilized with Fabry Perot etalon and bias feedback circuit. A tunable external cavity LD was used as a local oscillator at the receiver. Heterodyned output signal at IF frequency of 2GHz was measured and discussed.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.3 no.1 s.4
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• pp.117-125
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• 2004

Space-time coding and modulation exploit the presence of multiple transmit antennas to improve performance on multipath Rayleigh fading channels. In this paper, we propose the Trellis-Coded Differential Space Time Modulation-OFDM system with multiple symbol detection. The Trellis-code perform the set partition with unitary group codes. The Viterbi decoder containing new branch metrics is introduced in order to improve the bit error rate (BER) in the differential detection of the Unitary differential space time modulation. Also, we describe the Viterbi algorithm in order to use this branch metrics. Our study shows that such a Viterbi decoder improves BER performance without sacrificing bandwidth and power efficiency.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.4
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• pp.1954-1971
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• 2017

In this work, first, a multiuser detection (MUD) algorithm based on component-level soft interference cancellation and linear minimum mean square error (CLSIC-LMMSE) is proposed, which can enhance the bit error ratio (BER) performance of the traditional SIC-LMMSE-based MUD by mitigating error propagation. Second, for non-binary low density parity check (NB-LDPC) coded high-order modulation systems, when the proposed algorithm is integrated with partial mapping, the receiver with iterative detection and decoding (IDD) achieves not only better BER performance but also significantly computational complexity reduction over the traditional SIC-LMMSE-based IDD scheme. Extrinsic information transfer chart (EXIT) analysis and numerical simulations are both used to support the conclusions.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.1
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• pp.45-51
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• 2016

In this paper, we develop an iterative maximum likelihood (ML) receiver for generalized spatial modulation systems. In the proposed ML receiver, to mitigate the deleterious effect of channel information errors on symbol detection, the instantaneous covariance matrix of effective noise is estimated, which is then used to obtain improved ML solutions. The estimated covariance matrix is updated through multiple iterations to enhance the estimation accuracy. The simulation results show that the proposed ML receiver outperforms the conventional ML detection scheme, which does not take the effect of channel information errors into account.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.7
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• pp.13-23
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• 2009

In this paper, the network performance of a turbo coded optical code division multiple access (CDMA) system with cross-layer, which is between physical and network layers, concept is analyzed and simulated. We consider physical and MAC layers in a cross-layer concept. An intensity-modulated/direct-detection (IM/DD) optical system employing pulse position modulation (PPM) is considered. In order to increase the system performance, turbo codes composed of parallel concatenated convolutional codes (PCCCs) is utilized. The network performance is evaluated in terms of bit error probability (BEP). From the simulation results, it is demonstrated that turbo coding offers considerable coding gain with reasonable encoding and decoding complexity. Also, it is confirmed that the performance of such an optical CDMA network can be substantially improved by increasing e interleaver length and e number of iterations in e decoding process. The results of this paper can be applied to implement the indoor optical wireless LANs.

• The Journal of the Acoustical Society of Korea
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• v.39 no.4
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• pp.237-245
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• 2020

In decades, active sonar, which transmits signals and detects incident signals reflected by underwater targets, has been significantly studied since passive sonar in Anti-Submarine Warfare (ASW) detection performance becomes lowered, as underwater threats become their radiated noise reduced. In general, active sonar using Hull-Mounted Sonar (HMS) adjusts vertical tilt (depression) and sequentially transmits multiple Linear Frequency Modulation (LFM) subpulses which have non-overlapped bands, i. e. 1 kHz ~ 2 kHz, 2 kHz ~ 3 kHz, in order to reduce shadow zones. Recently, however, Generalized SFM (GSFM), which is generalized form of SFM, is proposed, and it is confirmed that subpulses of GSFM have orthogonality among each other depending on setting of GSFM parameters. Hence, in this paper, we applied GSFM to active target detection using HMS to improve the performance by the signal processing gain obtained from enlarged bandwidths of GSFM subpulses compared to those of LFM subpulses. Through simulation, we verified that when the number of subpulses is three, the matched filter gain of GSFM is approximately 5 dB higher than that of LFM.

• Structural Engineering and Mechanics
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• v.69 no.4
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• pp.407-416
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• 2019

This paper develops a wireless sensor for online fatigue crack detection and failure warning based on crack-induced nonlinear ultrasonic modulation. The wireless sensor consists of packaged piezoelectric (PZT) module, an excitation/sensing module, a data acquisition/processing module, a wireless communication module, and a power supply module. The packaged PZT and the excitation/sensing module generate ultrasonic waves on a structure and capture the response. Based on nonlinear ultrasonic modulation created by a crack, the data acquisition/processing module periodically performs fatigue crack diagnosis and provides failure warning if a component failure is imminent. The outcomes are transmitted to a base through the wireless communication module where two-levels duty cycling media access control (MAC) is implemented. The uniqueness of the paper lies in that 1) the proposed wireless sensor is developed specifically for online fatigue crack detection and failure warning, 2) failure warning as well as crack diagnosis are provided based on crack-induced nonlinear ultrasonic modulation, 3) event-driven operation of the sensor, considering rare extreme events such as earthquakes, is made possible with a power minimization strategy, and 4) the applicability of the wireless sensor to steel welded members is examined through field and laboratory tests. A fatigue crack on a steel welded specimen was successfully detected when the overall width of the crack was around $30{\mu}m$, and a failure warnings were provided when about 97.6% of the remaining useful fatigue lives were reached. Four wireless sensors were deployed on Yeongjong Grand Bridge in Souht Korea. The wireless sensor consumed 282.95 J for 3 weeks, and the processed results on the sensor were transmitted up to 20 m with over 90% success rate.

• Journal of Communications and Networks
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• v.5 no.2
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• pp.124-134
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• 2003

In this paper, we investigate the error probability performance of noncoherently detected orthogonal modulation combined with Alamouti space-time block coding. We find that there are two types of pair-wise error probabilities that characterize the performance. We employ methods that allow a direct evaluation of exact, closed-form expressions for these error probabilities. Theoretical as well as numerical results show that noncoherent orthogonal modulation combined with space-time block coding (STBC) achieves full spatial diversity. We derive an expression for approximate average bit error probability for-ary orthogonal signaling that allows one to show the tradeoff between increased rate and performance degradation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.7
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• pp.665-671
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• 2015

The performance of fault diagnostics for a planetary gearbox depends on vibration modulation characteristics, which can vary with manufacturing & assembly tolerance, and load condition. In this paper, a fault diagnostics technique that considers vibration modulation characteristics is proposed for the effective fault detection of planetary gearboxes in wind turbines. For identifying the vibration modulation characteristics in practice, re-sampled vibration signals are processed with narrow band-pass filters. Thereafter, the optimal position of the vibration extraction window is identified for effective detection of faulty signals under the varying vibration modulation characteristics. The proposed diagnostics technique makes it possible to perform robust diagnostics of the planetary gearbox with regard to the changeable vibration modulation effect. For demonstrating the proposed fault diagnostics technique, a 2-kW WT testbed is designed with two DC motors and gearboxes. A faulty gear with partial tooth breakage is machined and assembled into the gearbox.