• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.2
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• pp.337-342
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• 2001

This paper provides a comprehensive study of the effect of time delay on adaptive transmission methods. By adaptive we mean that the transmission of data is made adaptive according to channel conditions. That is, the modulation level at the transmitter is carefully controlled for maximizing bandwidth efficiency, on the basis of the observation of instantaneous channel characteristics. By making use of the simulator developed for the present work, a large number of channel propagation environments including the models proposed in 3GPP were submitted to the simulator and the performance with respect to both time delay and SNR is observed. The results show that the performance is very sensitive to channel delay and in some cases the performance shows irreducible BER (IBER). A large amount of delay together with a high fading rate greatly affects the performance of adaptive transmission systems.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.6
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• pp.42-47
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• 2012

Followed by a paper on the Pig and Bone orthopedic prosthetic, this experiment using Phantom and Bone MRI imaging I, II of orthopedic prosthetic metal effect combines magnetic resonance imaging on metal signal-to-noise ratio(Signal to noise : SNR) and CNR(Contrast to noise: CNR), fat signal suppression(Fat-suppression) images was compared. Specimen trees to measure the reliability of the experimental reproducibility tests and statistical analysis using the SPSS statistical package was applied program SPSS(IBM SPSS Statistice 19) by * P = 0.000 < significance level $({\alpha})$ = 0.01 as a significant there was a correlation(** P < 0.01). SNR and CNR results did not directly proportional to the Titanium, Stainless, Clip CNR and fat signal suppression of the order of images of blood specimens was found to be close to the image. The impact of orthopedic prosthetic metals on magnetic resonance imaging in the diagnostic value of Titanium is relatively high and are meant more.

• ETRI Journal
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• v.38 no.1
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• pp.90-99
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• 2016

In this work, we investigate differentially encoded blind transceiver design in low signal-to-noise ratio (SNR) regimes for orthogonal frequency-division multiplexing (OFDM) signaling. Owing to the fact that acquisition of channel state information is not viable for short coherence times or in low SNR regimes, we propose a time-spread frequency-encoded method under OFDM modulation. The repetition (spreading) of differentially encoded symbols allows us to achieve a target energy per bit to noise ratio and higher diversity. Based on the channel order, we optimize subcarrier assignment for spreading (along time) to achieve frequency diversity of an OFDM modulated signal. We present the performance of our proposed transceiver design and investigate the impact of Doppler frequency on the performance of the proposed differentially encoded transceiver design. To further improve reliability of the decoded data, we employ capacity-achieving low-density parity-check forward error correction encoding to the information bits.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.10A
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• pp.1473-1479
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• 2000

This paper presents the performance evaluation of an adaptive QAM scheme under flat and frequency selective fading channels for indoor wireless communication systems. The QAM modulation is combined with differential encoding and the demodulation process is carried out noncoherently. The adaptation is performed by varying the modulation level of QAM, depending upon received signal strength. The adaptation mechanism allows a 2- or 3-bit increase or decrease at a time, if the channel condition is considered to be significantly good or bad. Simulation results show that the average number of bits per symbol (ABPS) for each symbol block transmitted over a flat fading channel is higher than 5.0 and the BER performance is better than 10^-4 for a SNR value higher than 30 dB. For frequency selective fading channels, an oversampling technique in the receiver was employed. The BER performance obtained for frequency selective fading channels is better than 10^-4 with a SNR value of 40 dB and ABPS is found to be approximately 5.5. Therefore, this scheme is very useful in that it provides both very high bandwidth efficiency and acceptable performance with moderate SNR values over flat and frequency selective fading channels. In addition, this scheme provides reduced receiver complexity by way of noncoherent detection.

• Journal of Satellite, Information and Communications
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• v.5 no.1
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• pp.1-5
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• 2010

Recently, the transmission amount of information that each single person requires is growing by development of electron information communication technology. So in this paper we analysis the phase noise characteristics to obtain a most suitable of SNR performance request characteristic by BER on CATV transmission system that satisfy performance request DOCSIS 2.0 standard. Especially we get the parameter value of PLL that satisfy phase noise characteristic request standard using developed simulator. Presented method can be used to obtain a performance request standard connection performance request standard of high speed CATV transmission system in the future.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.14 no.12
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• pp.4664-4681
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• 2020

Modulation recognition (MR) plays a key role in cognitive radar, cognitive radio, and some other civilian and military fields. While existing methods can identify the signal modulation type by extracting the signal characteristics, the quality of feature extraction has a serious impact on the recognition results. In this paper, an end-to-end MR method based on long short-term memory (LSTM) and the gated recurrent unit (GRU) is put forward, which can directly predict the modulation type from a sampled signal. Additionally, the sliding window method is applied to fast-changing mixed-modulation signals for which the signal modulation type changes over time. The recognition accuracy on training datasets in different SNR ranges and the proportion of each modulation method in misclassified samples are analyzed, and it is found to be reasonable to select the evenly-distributed and full range of SNR data as the training data. With the improvement of the SNR, the recognition accuracy increases rapidly. When the length of the training dataset increases, the neural network recognition effect is better. The loss function value of the neural network decreases with the increase of the training dataset length, and then tends to be stable. Moreover, when the fast-changing period is less than 20ms, the error rate is as high as 50%. As the fast-changing period is increased to 30ms, the error rates of the GRU and LSTM neural networks are less than 5%.

• Nuclear Engineering and Technology
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• v.54 no.12
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• pp.4652-4659
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• 2022

Among the detector materials available at room temperature, thallium bromide (TlBr), which has a relatively high atomic number and density, is widely used for gamma camera imaging. This study aimed to verify the usefulness of TlBr through quantitative evaluation by modeling detectors of various compound types using Monte Carlo simulations. The Geant4 application for tomographic emission was used for simulation, and detectors based on cadmium zinc telluride and cadmium telluride materials were selected as a comparison group. A pixel-matched parallel-hole collimator with proven excellent performance was modeled, and phantoms used for quality control in nuclear medicine were used. The signal-to-noise ratio (SNR), contrast to noise ratio (CNR), sensitivity, and full width at half maximum (FWHM) were used for quantitative analysis to evaluate the image quality. The SNR, CNR, sensitivity, and FWHM for the TlBr detector material were approximately 1.05, 1.04, 1.41, and 1.02 times, respectively, higher than those of the other detector materials. The SNR, CNR and sensitivity increased with increasing detector thickness, but the spatial resolution in terms of FWHM decreased. Thus, we demonstrated the feasibility and possibility of using the TlBr detector material in comparison with commercial detector materials.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.37.1-37.1
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• 2020

Cosmic-ray protons (CRp) are efficiently produced at starburst galaxies (SBGs), where the star formation rate (SFR) rate is high. In this talk, we present estimates of gamma-ray and neutrino emissions from nearby SBGs, M82, NGC253, and Arp220. Inside the starburst nucleus (SBN), CRp are accelerated at supernova remnant (SNR) shocks as well as at stellar wind (SW) termination shocks, and their transport is governed by the advection due to starburst-driven wind and diffusion mediated by turbulence. We here model the momentum distributions of SNR and SW-produced CRp with single or a double power-law forms. We also employ two different diffusion models, where CRp are resonantly scattered off large-scale turbulence in SBN or self-excited waves driven by CR streaming instability. We then calculate gamma-ray/neutrino fluxes. The observed gamma-ray fluxes by Fermi-LAT, Veritas, and H.E.S.S are well reproduced with double power-law distribution for SNR-produced CRp and the CRp diffusion by self-excited turbulence. The estimated neutrino fluxes are <~10-3 of the atmospheric neutrino flux in the energy range of Eneutrino <~100 GeV and <~10-1 of the IceCube point source sensitivity in the energy range of Eneutrino >~60 TeV.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.3
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• pp.460-465
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• 2007

In this paper, the pipelined A/D converter with multi S/H stage structure is proposed for high resolution and high-speed data conversion rate. In order to improve a resolution and operational speed, the proposed structure increased the sampling time that is sampled input signal. In order to verify the operation characteristics 20MS/s pipelined A/D converter is designed with two S/H stage. The simulation result shows that INL and DNL are $0.52LSB{\sim}-0.63LSB$ and $0.53LSB{\sim}-0.56LSB$, respectively. Also, the designed Analog-to-Digital converter has the SNR of 43dB and power consumption is 18.5mW.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.12B
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• pp.1244-1250
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• 2010

This paper presents a detection and ranging algorithm for a high-speed targets in the high PRF radar. We show, unlike the conventional methods, it firstly estimates Doppler frequency with a quasi-periodic pulse train prior to range processing. The estimated Doppler frequency can compensate the phase error enbeded in the received signal, which makes the signal integrated coherently in the range direction and localizes the target's signiture in low SNR. We present the derivation of the proposed algorithm and discuss how the system parameters such as the range/Doppler sampling condition, processing time and Doppler estimation error affect the performance of the proposed algorithm, which is verified by simulations.