• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.10B
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• pp.1246-1251
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• 2011

In this paper, BPSK-OFDM-based LED communication systems are applied to watermarking techniques, were studied on how to transfer the additional information data with at the same time as the transfer of LED communication data. For watermarking kasami code was used as spreading codes, and spread additional data is controlled by small signal level to be BPSK-OFDM does not affect the optical signal. BPSK-OFDM is added to an optical signal is transmitted. The performance of the spreading code as a kasami code is autocorrelation of the noise-free environment, under the noise environment was confirmed by autocorrelation. BPSK-OFDM-based LED communication system has been applied proposed technique throughout the simulation in analyzed to BER of BPSK-OFDM DER performance and watermark signal level according to signal size level of data. That was availability confirmed for watermarking data transmit techniques data as being analysis detection performance of watermarking information using LED communication according to the code.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.11a
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• pp.59-60
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• 2005

OFDM communication system is effective for the high data rate transmission in the frequency selective fading channel. Since OFDM has high PAPR, OFDM signal may be distorted by the nonlinear HPA. In this paper, we propose an combined SLM and PTS method for reducing the PAPR in OFDM communication system. Proposed method increased some system complex in comparison with exiting method..

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.11
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• pp.1026-1033
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• 2004

Clipping is a simple and convenient PAPR reduction method to prevent the high-speed OFDM communication system from the nonlinear distortion. However, it inherently produces clip noise so that BER performance can be degraded. Clipping noise can be divided into in-band and out-of-band clipping noise. In this paper, we study the clipping effect on the forward link of the OFDM-FDMA system. BER performance of OFDM-FDMA system using clipping method is theoretically analyzed. We also investigate the BER performance of the clipped OFDM-FDMA signal through the HPA. From the simulation results it can be quantified how much the BER performance of OFDM-FDMA system is degraded by the clipping method. From the study results, we can choose the appropriate IBO value and CR(clip ratio) to get the desired BER performance.

• International Journal of Computer Science & Network Security
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• v.24 no.9
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• pp.21-29
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• 2024

Precoding of the orthogonal frequency division multiplexing (OFDM) with Walsh Hadamard transform (WHT) is known in the literature. Instead of performing WHT precoding and inverse discrete Fourier transform separately, a product of two matrix can yield a new matrix that can be applied with lower complexity. This resultant transform, T-transform, results in T-OFDM. This paper extends the limited existing work on T-OFDM significantly by presenting detailed account of its computational complexity, a lower complexity receiver design, an expression for PAPR and its cumulative distribution function (cdf), sensitivity of T-OFDM to timing synchronization errors, and novel analytical expressions signal to noise ratio (SNR) for multiple equalization techniques. Simulation results are presented to show significant improvements in PAPR performance, as well improvement in bit error rate (BER) in Rayleigh fading channel. This paper is Part II of a three-paper series on alternative transforms and many of the concepts and result refer to and stem from results in generalized multicarrier communication (GMC) system presented in Part I of this series.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.6
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• pp.263-268
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• 2010

As the demand of high quality service in next generation wireless communication systems, a high performance of data transmission requires an increase of spectrum efficiency and an improvement of error performance in wireless communication systems. In this paper, we propose a multi-user multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system with cyclic delay diversity and block diagonalization procoding method to improve bit error rate (BER) performance with wireless local area network (WLAN) channel model C and D for 802.11n WLAN system. The results of mathlab simulation show the improvement of BER performance in 802.11n wireless indoor channel environment.

• Journal of IKEEE
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• v.22 no.3
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• pp.800-804
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• 2018

This paper presents a novel HF band differential quadrature phase-shift keying (DQPSK) orthogonal frequency-division multiplexing (OFDM) communication system. The system can deliver 3.6 kbps with a bandwidth of about 3 kHz. In a digital modem, OFDM with 32-point fast Fourier transform is used. In the system, each subcarrier uses DQPSK modulation. Hence, a demodulator does not require carrier phase recovery and symbol timing recovery. And, each subcarrier employs CRC error check code individually. By using CRC code for each subcarrier, bit error caused by multipath fading can be recovered simply.

• Journal of the Korean Institute of Intelligent Systems
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• v.19 no.1
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• pp.145-151
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• 2009

Orthogonal Frequency Division Multiplexing (OFDM) has been focused on as 4th generation communication method for realization of Ubiquitous Network in land mobile communications services, and has been a standard technology of Wireless Local Area Network (WLAN) for a High Date Rate communication. And in maritime data communication using high frequency (HF) band, 32-point FFT OFDM system is recommended by International Telecommunication Union (ITU). Maritime communication should be kept on connecting when maritime accident or the maritime disaster happen. Therefore, main device FFT should be operated with low power consumption. In this paper we propose a low power 32-point FFT algorithm using radix-2 and radix-4 for low power operation. The proposed algorithm was designed using VHSIC hardware description language (VHDL), and it was confirmed that the output value of Spartan-3 field-programmable gate array (FPGA) board corresponded to the output value calculated using Matlab. The proposed 32-point FFT algorithm will be useful as a leading technology in a HF maritime data communication.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.24 no.8
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• pp.1086-1094
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• 2020

AThis paper measured real sea area for performance analysis according to distance from west sea and south sea of Korea. The performance of the underwater OFDM system was analyzed by comparing the performance of the West and South Seas by adjusting the number of data repetitive transmissions and the pilot symbol placement interval parameters based on the real-sea data measured from the distance and Data rate of the West and South Sea vessels. In conclusion, when comparing the performance of the South Sea at the Data rate and distance, the BER performance of the South Sea was similar at the 5 km South Sea and 1 km West Sea under the same conditions. Placement interval of pilot symbol at 10 km of South Sea and 3 km of West Sea is (𝚫f, 𝚫t) = (6, 3) and the number of times the PRB is (R_f, R_t) = (2, 1) repeated. We confirmed that we can send high data over long distances in the South Sea.

• 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.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.14 no.4
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• pp.77-83
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• 2014

Visible light communication is a converging communication by technologies that enable solutions using the LED Lighting. There is a need to research about it in order to improve the performance of the wireless communication by using a Color LED and improve the efficiency of data. In this paper, Assume the General indoor communication environment and LED communication systems based on CSK-OFDM applied to a MIMO communication system, We studied about transmitting method of more efficient communication. After performing the simulation based on IEEE 802.15.7 Standardization, as a result of the analysis of performance, it was confirmed the there is a significant impact on the performance of SNR and BER performance by the transmitting method based on MIMO and external noise using the LED communication system based on CSK-OFDM.