• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.7 s.110
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• pp.629-637
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• 2006

It is important to design the high-speed communication system in the hostile channel. Due to the frequency diversity, FD-OFDM that can be used for the high-speed communication is more robust to the noise or interference than ordinary OFDM. However, even the FD-OFDM becomes degraded in th ε strong narrow band interference channel. In this paper, we propose an AFD-OFDM system and analyze the communication performances in order to find out the more robust communication system in the hostile channel. So, the AFD-OFDM system can cover the drawback of the FD-OFDM and improve the BER performance than FD-OFDM. From the simulation results, FD-OFDM shows better performance than the ordinary OFDM. Furthermore, AFD-OFDM shows more excellent performance than FD-OFDM in the strong narrow interference channel.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.3
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• pp.365-370
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• 2016

Recently, There are increasing number of studies that apply multi-carrier method, a land mobile communication method, to underwater channel environment in order to enhance the performance of underwater communication. Therefore, in this paper, in order to design a new system with improved communication performance compared to the multi-carrier method in underwater communication, we present that the RS(Resource Spreading) FMT-OFDM system has a diversity and repetition effect from resource spreading. Moreover, we verify the performance of RS FMT-OFDM system and existing FMT-OFDM system through simulations after modeling communication channels and setting the system parameter based on the data measured from the real sea. Our result indicate that, compared to the existing FMT-OFDM system, there has been an improvement in communication performance by 12dB based on BER $10^{-3}$ we also discovered that communication performance improves as the resource spreading rate increases.

• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.6
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• pp.1121-1128
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• 2019

In this paper, we introduce the combination of OFDM(Orthogonal Frequency Division Multiplexing) and MIMO(Multiple-Input Multiple-Output) technology, and explain that this combination seems to be very preferable when designing very high-rate wireless mobile systems. The application of OFDM, with the block diagrams of an OFDM modulator and demodulator and a MIMO-OFDM system, are described. The several diversities are studied at the receiver, analyzed the performances of diversity in OFDM-MIMO system and simulated results.

• Journal of the Optical Society of Korea
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• v.20 no.5
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• pp.557-562
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• 2016

In this paper, for the first time, the transmission performances of long-haul 100-Gb/s direct detection optical OFDM (DDO-OFDM) and coherent optical OFDM (CO-OFDM) wavelength division multiplexing (WDM) systems are compared by simulation. It provides specific guides for system parameter selection to get a high-performance and cost-effective OFDM WDM system. Specifically, the comparison involves three aspects: launched power is investigated to achieve better system performance; laser linewidth is numerically investigated to choose cost-effective laser; system dispersion tolerances with different laser linewidths are analyzed to further reveal the advantages and disadvantages of these two detecting methods, direct detection and coherent detection, in long-haul OFDM WDM system.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.8
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• pp.2783-2795
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• 2014

Orthogonal frequency division multiplexing with offset quadrature amplitude modulation (OFDM-OQAM) technique has drawn significant interests in recent years. However, most of the existing OFDM peak-to-average ratio (PAPR) reduction schemes cannot be used in the OFDM-OQAM system directly. In this paper, a modified scheme called overlapped segmental clipping (OS-clipping) is proposed to deal with the high PAPR problem specifically in the OFDM-OQAM system. For the proposed OS-clipping scheme, the input signals are divided into a number of overlapped segments and then the clipping operation is processed on each segment. Simulation results show that the modified scheme used in the OFDM-OQAM system can provide better performance than conventional clipping scheme directly used in the OFDM-OQAM system, and even outperforms conventional clipping scheme applied in the OFDM system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.12
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• pp.1715-1720
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• 2016

In the upcoming 5-generation mobile communication system, various techniques for improving the power efficiency and spectral efficiency have been proposed. 5G mobile communication system also have been studied a lot of multi-carrier-based modulation techniques like the 4G mobile communication system. In this paper, we analyzed the conventional system structure of the Zero-tail DFT-s-OFDM and UW (Unique Word) -DFT-s-OFDM system based on DFT-s-OFDM system in these techniques. UW and zero are added and used each system, and CP is removed. the result of quality of systems for simulation, OOB(Out of Band) power of Zero-tail DFT-s-OFDM and UW-DFT-s-OFDM use the less time resource as long as CP length, also both systems are reduced about 11dB than DFT-s-OFDM system. In these result, Zero-tail DFT-s-OFDM and UW-DFT-s-OFDM system are more effective than DFT-s-OFDM system.

• Journal of Satellite, Information and Communications
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• v.3 no.2
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• pp.48-53
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• 2008

In the future, satellite communication systems, such as ISDB in Japan and DVB in Europe, are required to support higher transmission date rate for providing multimedia services including HDTV, high rate data communication etc. Considering the effectiveness of OFDM technique in efficient usage of frequency bandwidth and its robustness to the multi-path fading, several OFDM based standards have been proposed for satellite communication. However, the problem of high Peak to Average Power Ratio is one of the main obstacles for the implementation of OFDM based system. Many PAPR reduction schemes have been proposed for OFDM systems. Among these, the partial transmit sequences (PTS) is attractive as they obtain better PAPR property by modifying OFDM signals without distortion. In this paper, considering the complexity issue, we present a simplified minimum maximum (minimax) criterion and Sub-Optimal PTS algorithm to optimize the phase factor. This algorithm can be dynamically made tradeoff`f between performance and complexity on demand. In addition, we integrate guided scrambling (GS) with this method. Simulation in multiple antenna based OFDM system proves that the proposed Hybrid schemes can get much more PAPR reduction and do not require transmission of side information (SI). Thus it is helpful when implementing OFDM technique in satellite communication system.

• 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.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.3A
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• pp.189-197
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• 2011

OFDM systems are much studied for the recent high speed wireless optical communication system. OFDM system has basically high PAPR and ICI easily generated because of non-linearity and RF impairments. In the wireless optical communication system, optical output power driven by current of LED is not linear so that transmission signals are distorted. Therefore, research about reception performance of this nonlinear optical output emitted by non-linear LED transfer function and OFDM signal has been conducted. Nonlinear effect of LED is different from nonlinear effect of OFDM system in the conventional radio communication system, which degrades the BER performance. In this paper, we apply non-linear transfer function of recently studied LED into OFDM system. So, for reducing the PAPR and suppressing the ICI in frequency domain of receiver, we suggest a new PAPR reduction technique to reduce non-linear distortion of LED and an adaptive ICI suppression algorithm so that BER performance may be improved. Also, the proposed method is verified through simulation results.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.11
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• pp.2062-2068
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• 2006

In his paper, embedded system implementation for IEEE802.l1p based OFDM-DSRC is presented. After the IEEE802.11p physical layer specification is introduced and BER performance of the modem is evaluated by simulation, implementation aspects of the system such as system architecture, design method and implementation results are addressed. Implemented embedded system for the OFDM-DSRC communication consists of FPGA, flash memory, ARM9 CPU Core, peripherals, etc. from the results, it is shown that the implemented system operates well according to IEEE802.11p specification. It is expected that implemented embedded system shall be used for wireless communication system such as ITS application by enhancing system optimizing.