• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.9
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• pp.2494-2504
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• 1996

This paper describes about the spread specturm radio wave propagation characteristics in urban microcells. The experiments are carried out with respect to the mean excess delay, the RMS delay spread, and the received maximum peak power in the two kinds of geogrphical areas, LOS area and N-LOS area, especially whose variations are observed while varying the transmission distance and tilting the transmitting antenna. The typical results obtained in pariticular urban sites in Seoul are 300-600 nsec of mean excess delay and about 75 nsec of averaged RMS delay spread for LOS area, and 270-280 nsec of mean excess delay and about 100 nsec for N-LOS area. With the transmitting antenna gilted, obsered in the experiments are increase in RMS delay spread as expected, but increase of the received power at N-LOS areas in particular.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.5 no.4
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• pp.47-63
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• 1994

An important parameter in characterizing mobile communication channel is delay spread. This paper presents the results of measured delay profiles and calculated distribution funcations of delay spread for typical cellular service environments at Taejon and vicinities. The measurement system uses 1023 chip length, 5 Mbps PN code and sliding correlation method. It has been evaluated by using commercial hardware channel simulator for reliability of out data. As results the value of mean delay spread is 2.08 $\mu\textrm{s}$for suburban area. 2.12 $\mu\textrm{s}$ for urban area and 1.3 $\mu\textrm{s}$ for national/local road. Delay spread is less then 3.4$\mu\textrm{s}$, 2.8$\mu\textrm{s}$ and 1.5 $\mu\textrm{s}$ for probability of 50% and 4.5$\mu\textrm{s}$, 4.2$\mu\textrm{s}$ and 2.9$\mu\textrm{s}$ for probability of 90% at each tested site. The difference of delay spread is within 7% between going and returning status along same street. In this experiment, we found delay spread for suburban area is larger than reported foreign test results.

• The Journal of the Acoustical Society of Korea
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• v.41 no.2
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• pp.184-191
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• 2022

Underwater acoustic wave in shallow water is propagated through multipath that has a large delay spread causing Inter-Symbol Interference (ISI) and these characteristics deteriorate the performance in the communication system. In order to analyze the communication performance and investigate the correlation with multipath delay spread in a reverberant environment, an underwater acoustic communication experiment using Binary Phase-Shift Keying (BPSK) signals with symbol rates from 100 sym/s to 8000 sym/s was conducted in a 5 × 5 × 5 m³ water tank. The acoustic channels in a well-controlled tank environment had the characteristics of dense multipath delay spread due to multiple reflections from the interfaces and walls within the tank and showed the maximum excess delay of 40 ms or less, and the Root Mean Squared (RMS) delay spread of 8 ms or less. In this paper, the performances of Bit Error Rate (BER) and output Signal-to-Noise Ratio (SNR) were analyzed using four types of communication demodulation techniques. And the parameter, Symbol interval to Delay spread Ratio in reverberant environment (SDR_rev), which is the ratio of symbol interval to RMS delay spread in the reverberant environment is defined. Finally, the SDR_rev was compared to the BER and the output SNR. The results present the reference symbol rate in which high communication performance can be guaranteed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.3
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• pp.216-221
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• 2013

In this paper, wireless channel characteristics of massive MIMO system is analyzed by comparing angular spread, cross polarization discrimination(XPD) and delay spread of dual polarized 4 and 128 transmit array antenna systems, by using 3D rat-tracing simulator, Wireless Insite in microcell environments. The analysis shows that increasing the number of transmit antennas results in the smaller angular spread and delay spread, and the higher value of XPD.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.17 no.5
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• pp.79-84
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• 2017

This paper is a multi-input multi-path (Multiple-input multiple-output: MIMO) using a space-alternating generalized expectation maximization(SAGE) algorithm in the parameter channel and determine the channel estimation performance. Estimated by the algorithm, SAGE time-varying channel environment, the channel parameters estimated from the parameters of the channel measured in the island region 781 of the band in order to compare the performance and compares the original data. This allows you to check the performance of the algorithm SAGE and is highly stable to delay spread (Delay Spread), the diffusion angle of arrival (Arrive of Angular Spread) performance in terms of accuracy down through the SAGE algorithm for estimating a more general calculation parameters.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.8A
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• pp.777-784
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• 2010

Recently, the necessity of underwater communication and demand for transmitting and receiving various data such as voice or high resolution image data are increasing as well. The performance of underwater acoustic communication system is influenced by characteristics of the underwater communication channels. Especially, ISI(inter symbol interference) occurs because of delay spread according to multi-path and communication performance is degraded. In this paper, we study the OFDM technique to overcome the delay spread in underwater channel and by using CP, we compensate for delay spread. But PAPR which OFDM system has problem is very high. Therefore, we use DFT-spread OFDM method to avoid nonlinear distortion by high PAPR and to improve efficiency of amplifier. DFT-spread OFDM technique obtains high PAPR reduction effect because of each parallel data loads to all subcarrier by DFT spread processing before IFFT. In this paper, we show performance about delay spread through OFDM system and verify method that DFT spread OFDM is more suitable than OFDM for underwater communication. And we analyze performance according to two subcarrier mapping methods(Interleaved, Localized). Through the simulation results, performance of DFT spread OFDM is better about 5~6dB at $10^{-4}$ than OFDM. When compared to BER according to subcarrier mapping, Interleaved method is better about 3.5dB at $10^{-4}$ than Localized method.

• Journal of ILASS-Korea
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• v.25 no.3
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• pp.119-125
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• 2020

In this paper, we used Helmholtz solver based on 3D finite element method to quantitatively analyze the effects of change of gain, time delay and time delay spread, which are the main variables of flame transfer function, on combustion instability in gas turbine combustor. The effects of the variable of flame transfer function on the frequency and growth rate, which are the main results of combustion instability, were analyzed by applying the conventional heat release fluctuation model and modified one considering the time spread. The analysis results showed that the change of gain and time delay in the same resonance mode affected the frequency of the given resonance modes as well as growth rate of the feedback instability, however, the effect of time delay spread was not relatively remarkable, compared with the dominant effect of time delay.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.11
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• pp.78-87
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• 1996

in urban cross-roads with dense buildings, receiving power and delay spread were computed when doing these, we were able to develope codes to be executed in a very fast time by combining image method and algorithm for propagation paths compairing with ray launching technique. And receiving power and delay spread could be viewed in 3-dimensional picture by virtue of computing electric fields in arbitrary receiving point. For numerical computation, receiving power of wide and anrrow band and delay spread were computed, and extension method of ray numbers was facilitated for handling infinite number of rays.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.1
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• pp.225-234
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• 2018

Domestic urban areas are experiencing serious traffic congestion problems due to continuous population growth and increased traffic volume. In order to solve the problem of traffic congestion, the study of great depth underground double deck tunnels using underground space is being actively carried out in the urban areas. The characteristics of great depth underground double deck tunnels are low in cross section, so the spread of fire smoke is expected to spread faster than the road tunnel in case of fire. Therefore, it is necessary to provide a fire smoke delay device which delays the spread of fire smoke when a fire occurs in a tunnels. In the previous study, the diffusion effect was analyzed according to the blocking area when the fire smoke spread delay device was operated through the 3D CFD in the study of preventing the smoke spread in the case of the tunnel fire. A study on fire smoke diffusion delay device using spring elasticity which is excellent in applicability to a tunnel and economical value is studied. In this study, fire smoke spread delay system was developed to fire smoke delay was experimentally analyzed. Fire smoke delay effect of fire smoke delay device appeared. Therefore, it is considered that the can minimize the damage of the victims when installed in the great depth underground double deck tunnels.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.5A
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• pp.593-601
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• 2000

In a multi-bandwidth CDMA system, the performance of multiple order selection combining rake receivers are analyzed according to the spreading bandwidth of the system and the delay spread of the Rayleigh fading channel. The results for various channel environments indicate a tradeoff between total received signal energy and multipath fading immunity. Increasing the occupied bandwidth of the system(wide-bandwidth spreading) gives better performance for small delay spread environments, while gathering more energy(narrow-bandwidth spreading)gives better performance for large delay spread environments. It is shown that the performance difference between low and high order selection combining grows larger as the spreading bandwidth increases. It is also noted that performance degrades by increasing the bandwidth above a certain point and the optimum spreading bandwidth for each channel environment decreases as the delay spread of the channel increases.