• The Journal of the Acoustical Society of Korea
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• v.42 no.6
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• pp.491-499
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• 2023

Scattering by Sea surface roughness occurs due to sea level roughness, communication performance deteriorates by causing frequency spread in communication signals and time variation in communication channels. In order to compare the difference in time variation of underwater acoustic communication channel according to the surface roughness, an experiment was performed in a tank owned by Hanyang University Ocean Acoustics Lab. Artificial surface roughness was created in the tank and communication signals with three bandwidths were used (8 kHz, 16 kHz, 32 kHz). The measured surface roughness was converted into a Rayleigh parameter and used as a roughness parameter, and statistical analysis was performed on the time-varying channel characteristics of the surface path using Doppler spread and correlation time. For the Doppler spread of the surface path, the Weighted Root Mean Square Doppler spread (w_fσ_ν) that corrected the effect of the carrier frequency and bandwidth of the communication signal was used. Using the correlation time of the surface path and the energy ratio of the direct path and the surface path, the correlation of total channels was simulated and compared with the measured correlation time of total channels. In this study, we propose a method for efficient communication signal design in an arbitrary marine environment by using the time-varying characteristics of the sea surface path according to the sea surface roughness.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.5
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• pp.988-994
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• 2004

In this paper we analyze the effects of frequency offset, doppler spread, sampling and oscillator phase noise in mobile channels on orthogonal frequency division multiplexing(OFDM)system, Since this kind of distortions cause subcarrier interference which can be seen as additional noise, performance of OFDM system is degraded. We show the limitation of maximum carrier frequency offset and doppler frequency to maintain designated SNR, and analyze characteristics of the performance of OFDM systems considering the oscillator phase noise.

• ETRI Journal
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• v.44 no.4
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• pp.543-559
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• 2022

To determine a suitable waveform for Internet of Things (IoT) transmission over low-Earth orbit (LEO) satellites, this paper reports the results of a performance comparison between chirp spread spectrum (CSS)-based LoRa and direct sequence spread spectrum (DSSS)-based Ingenu. The performance of both waveforms was measured in terms of the packet error rate, throughput, and packet loss rate, considering the Doppler effect caused by the high speed of LEO satellites and the interference among multiple terminals. Simulation results indicate that the DSSS scheme is more suitable than the CSS scheme for high-traffic IoT services because of its robustness against interference among multiple terminals. However, the CSS scheme is more suitable than the DSSS scheme for high-mobility IoT services because of its robustness against the Doppler effect. We discuss various solutions, such as the preprocessing of Doppler effect and avoidance of packet collision, to enhance the performance of the DSSS and CSS schemes. The simulation results of the proposed solution show that the enhanced DSSS scheme can be a proper waveform in IoT transmission over LEO satellites for both the high-traffic and high-mobility services.

• 한국ITS학회:학술대회논문집
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• 2008.11a
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• pp.543-547
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• 2008

• ETRI Journal
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• v.38 no.4
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• pp.634-644
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• 2016

Channel-based radio-frequency fingerprinting such as a channel impulse response (CIR), channel transfer function (CTF), and frequency coherence function (FCF) have been recently proposed to improve the accuracy at the physical layer; however, their empirical performance, advantages, and limitations have not been well reported. This paper provides a comprehensive empirical performance evaluation of RF location fingerprinting, focusing on a comparison of received-signal strength, CIR-, CTF-, and FCF-based fingerprinting using the weighted k-nearest neighbor pattern recognition technique. Frequency domain channel measurements in the IEEE 802.11 band taken on a university campus were used to evaluate the accuracy of the fingerprinting types and their robustness to human-induced motion perturbations of the channel. The localization performance was analyzed, and the results are described using the spatial and temporal radio propagation characteristics. In particular, we introduce the coherence region to explain the spatial properties and investigate the impact of the Doppler spread in time-varying channels on the time coherence of RF fingerprint structures.

• ETRI Journal
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• v.30 no.6
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• pp.765-773
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• 2008

Spatial correlation is a result of insufficient antenna spacing among multiple antenna elements, while temporal correlation is caused by Doppler spread. This paper compares the effect of spatial and temporal correlation in order to investigate the performance of multiuser scheduling algorithms in multiple-input multiple-output (MIMO) broadcast channels. This comparison includes the effect on the ergodic capacity, on fairness among users, and on the sum-rate capacity of a multiuser scheduling algorithm utilizing statistical channel state information in spatio-temporally correlated MIMO broadcast channels. Numerical results demonstrate that temporal correlation is more meaningful than spatial correlation in view of the multiuser scheduling algorithm in MIMO broadcast channels. Indeed, the multiuser scheduling algorithm can reduce the effect of the Doppler spread if it exploits the information of temporal correlation appropriately. However, the effect of spatial correlation can be minimized if the antenna spacing is sufficient in rich scattering MIMO channels regardless of the multiuser scheduling algorithm used.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.1
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• pp.29-37
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• 2005

One of the principal disadvantages of multicarrier modulation technique is the sensitivity to the frequency offset introduced by Doppler shift. This frequency offset introduces inter-carrier interference (ICI) among the multiplicity of carriers in the multicarrier modulated signal. However, Doppler spread induced by temporal channel variations can Provide another means for diversity. In this paper, we propose a modified multicarrier code division multiple access (CDMA) system to exploit Doppler diversity as well as multipath diversity. The key work of our framework is a canonical time-frequency-based decomposition of the mobile wireless channel into series of independent fading channel. The decomposition naturally leads to a time-frequency generalization of the Rake receiver that exploits both multipath and Doppler diversity.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 2004.07a
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• pp.379-379
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• 2004

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.7 no.5
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• pp.131-138
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• 2008

The channel parameters such as RMS delay spread and Doppler frequency have an effect on performance of system. This paper investigates the effect between the Inter-Code Interference (ICI) and the frequency diversity gain in the multi-rate MC-CDMA system. The multi-rate MC-CDMA system has achieved the more variable data rate than the MC-CDMA and moreover it has the better performance than the OFDMA system, because it has achieved the frquency diversity gain. However, the frequency diversity gain and ICI have a trade-off relationship by using the spreading code. Therefore, we have improved the system performance by efficient choice of system parameters. In order to evaluate the effectiveness of the frequency diversify gain and the ICI effect, we perform simulations by altering the Doppler frequency and RMS delay spread.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.3A
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• pp.235-239
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• 2008

In this paper, we study a simulation model for cooperative MIMO (multiple-input multiple-output) channels and present a cooperative one-ring channel model which is extended from the geometrical one-ring and two-ring scattering models. Assuming that the source, the destination and the relay are surrounded by an infinite number of scatters, we derive a reference model for the cooperative one-ring channel and propose a simulation model based on the reference model provided in the paper. Then we show how modeling parameters of the simulation model are determined to match the correlation functions for the respective models. With numerical investigation, we also show that the correlation functions for the reference and the simulation are well matched.