• International Journal of Computer Science & Network Security
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• v.23 no.5
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• pp.172-178
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• 2023

In this paper, performance of autoencoder based OFDM communication systems is compared with IEEE 802.11a Wireless Lan System (Wi-Fi). The proposed autoencoder based OFDM system is composed of the following steps. First, one sub-carrier's transmitter - channel - receiver system is created by autoencoder. Then learning process of the one sub-carrier autoencoder generates constellation map. Secondly, using the plural sub-carrier autoencoder systems, parallel bundle is configured with inserting IFFT and FFT before and after the channel to configure OFDM system. Finally, the receiver part of the OFDM communication system was updated by re-learning process for adapting channel condition such as multipath channel. For performance comparison, IEEE802.11a and the proposed autoencoder based OFDM system are compared. For channel estimation, Wi-Fi uses initial long preamble to measure channel condition. but Autoencoder needs re-learning process to create an equalizer which compensate a distortion caused by the transmission channel. Therefore, this autoencoder based system has basic advantage to the Wi-Fi system. For the comparison of the system, additive random noise and 2-wave and 4-wave multipaths are assumed in the transmission path with no inter-symbol interference. A simulation was performed to compare the conventional type and the autoencoder. As a result of the simulation, the autoencoder properly generated automatic constellations with QPSK, 16QAM, and 64QAM. In the previous simulation, the received data was relearned, thus the performance was poor, but the performance improved by making the initial value of reception a random number. A function equivalent to an equalizer for multipath channels has been realized in OFDM systems. As a future task, there is not include error correction at this time, we plan to make further improvements by incorporating error correction in the future.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.3 no.4
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• pp.385-398
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• 2009

This paper aims to find a suitable solution to joint allocation of sub-channel and transmit power for multiple users in an IEEE 802.16e OFDMA/TDD cellular system. We propose the FASA (Fairness insured Aggressive Sub-channel Allocation) algorithm, which is a dynamic channel allocation algorithm that considers all of the users' channel state information conditionally in order to maximize throughput while taking into account fairness. A dynamic power allocation algorithm, i.e., an improved CHC algorithm, is also proposed in combination with the FASA algorithm. It collects the extra downlink transmit power and re-allocates it to other potential users. Simulation results show that the joint allocation scheme with the improved CHC power allocation algorithm provides an additional increase of sector throughput while simultaneously enhancing fairness. Four frames of time delay for CQI feedback and scheduling are considered. Furthermore, by addressing the difference between uplink and downlink scheduling in an IEEE 802.16e OFDMA TDD system, we can employ the uplink channel information directly via channel sounding, resulting in more accurate uplink dynamic resource allocation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.9
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• pp.3481-3485
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• 2010

In this paper, we propose a concept and model of an additional service system as a kind of convergence system of broadcast and telecommunication. The proposed system use existing back-bone network such as broadcasting or communication networks. For this, we derive channel capacity formula as an approximated closed-form expression in order to show how many reliable additional data can be transmitted through wireless fading channel. From the derived formula, we confirm that the channel capacity is varied according to channel and system parameters.

• Journal of Power System Engineering
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• v.17 no.1
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• pp.64-70
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• 2013

The heat transfer and friction factor characteristics of turbulent flows in three stationary channels have been investigated experimentally to check out the effect of divergence ratio. These are a constant cross-sectional channel and two diverging channels with ratio of divergence(Dho/Dhi) of 1.16 and 1.49. The measurement was conducted within the range of Reynolds numbers from 15,000 to 89,000 and the dimension of uniform cross-sectional test section is $100mm{\times}100mm$ at the cross section and 1,000 mm in length. The measurements of heat transfer coefficients and friction factors in the uniform channels were conducted as a reference. Because of the streamwise flow deceleration, the heat transfer and friction factor characteristics in the diverging channel were quite different from those of the constant cross-sectional channel. The effective friction factors and convective heat transfer coefficients increased with increasing the ratio of divergence of the channel.

• Journal of Advanced Navigation Technology
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• v.7 no.1
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• pp.51-58
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• 2003

Generally, multi-path is viewed as an undesirable feature of wireless communications. Therefore, diversity reception and adaptive array schemes are proposed to mitigate its effects. Recently, to increase the spectrum efficiency and the link reliability, multiple-input multiple-output (MIMO) scheme is devised to exploit multi-path in a scattering wireless channel. In this paper, we have evaluated the channel capacity of MIMO Multi-Carrier CDMA system in path correlation fading channel. And, the channel capacity of MIMO system is compared with single-input single-output (SISO) system. From the results, the MIMO multi-carrier CDMA system with path correlation yields better performance with respect to channel capacity than a SISO system.

• Proceedings of the KIEE Conference
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• 2004.11c
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• pp.240-242
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• 2004

A channel allocation algorithm of multi-user OFDM(orthogonal frequency division multiplexing) system is presented. The proposed algorithm is to reduce the complexity of the system, using the GNN(gradual neural network) with gradual expansion scheme and the algorithm attempts to allocate channel with good channel gain to each user. The method has lower computational complexity and less iteration than other algorithms.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.4 no.3
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• pp.643-652
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• 2000

In this paper, we analyze the BER performance of OFDM/QPSK system in frequency selective Rayleigh fading channel with impulsive noise and improve its performance by adopting convolutional coding. When the channel delay time is shorter than the guard band, the OFDM/QPSK system shows a good BER performance while, when the channel delay time becomes longer than the guard band, its BER performance is abruptly degraded. Moreover, when the transmitted signal is contaminated by a strong impulsive noise in the channel, the BER performance falls to about $10^{-1}$. Also, without channel coding technique, the system doesn't meet even the voice service requirement while it meets the data service requirement with convolutional coding in frequency selective Rayleigh fading channel with impulsive noise.

• Proceedings of the IEEK Conference
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• 2004.06a
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• pp.293-296
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• 2004

This paper proposes an architecture of channel estimation for multi-band OFDM UWB systems presented to IEEE 802.15.3a by Multi-band OFDM alliance(MBOA). The multi-band OFDM (MB-OFDM) systems should have channel estimation for compensation of signal distortion by multi-band channel. The moving-averaging estimation algorithm and multi-band equalization architecture for MB-OFDM UWB systems proposed in this paper was verified by the simulation. Simulation results show that MB-OFDM system with the proposed architecture have the performance improved by about 3.4 dB compared to system with no channel estimation in 0.1$\pi$ phase-rotated channel.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.580-584
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• 2004

In the present study, an evaluation technology for heating channel layout was investigated in SMC molding system design. Conventional design rules of cooling channel in injection molding process were applied to the present work. Finite element thermal analysis with ANSYSTM was performed to evaluate the temperature distribution of mold surface. SMC mold was manufactured to test the effect of a proposed heating channel layout system on the temperature distribution of mold surface and infrared camera was applied to a measurement of temperature. It was shown that infrared camera application was possible in a measurement of temperature distribution on mold surface.

• Proceedings of the IEEK Conference
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• 2003.07a
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• pp.35-38
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• 2003

We propose a switched beamforming to improve the reception performance of VSB system in severe Rayleigh fading channel. The VSB system has only about 3% of known training signal for the receiver in a data field and the reception performance of VSB receiver is degraded significantly when there are near-0 dB ghosts in receiving signal. The switched beamforming forms several beams in different directions and selects only one beam among them. For the selection of a beam with best channel condition for VSB equalizer, we extracted the channel profiles in time domain for all the beams by correlating the PN511 sequence in VSB field sync and selected optimal beam by comparing the channel profiles. The simulation results show that the proposed method improves the reception performance of VSB system in severe Rayleigh channel.