• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.8
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• pp.845-854
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• 2003

In this paper, the characteristics of compensation for WDM channel signal distortion due to both chromatic dispersion and Ken effect in 1,000 km 200 Gbps(5${\times}$40 Gbps) WDM systems was investigated. The WDM system has a path-averaged intensity approximation(PAIA) mid-span spectral inversion(MSSI) as a compensation method. This system has a highly nonlinear dispersion shifted fiber(HNL-DSF) optical phase conjugator(OPC) in the mid-way of transmission line. In order to evaluate the degree of compensation, 1 dB eye opening penalty(EOP), bit error rate(BER) characteristics and power penalty of 10$\^$-9/ BER are used. It is confirmed that HNL-DSF is an useful nonlinear medium in OPC fur wideband WDM system with PAIA MSSI and that the optimal compensation for WDM channel distortion is achieved by the selection of pump light power of OPC, which equalize the conjugated light power into the second half fiber section with the input WDM signal light power depending on total transmission length, dispersion coefficient of fiber, OPC pump light wavelength, conversion efficiency of WDM channel in OPC.

• The Journal of the Acoustical Society of Korea
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• v.32 no.2
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• pp.95-103
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• 2013

An underwater acoustic (UWA) communication in shallow water is strongly affected by the water surface and the seabed acoustical properties. Every reflected signal to receiver experiences a time-variant scattering in sea surface roughness and a grazing-angle-dependent reflection loss in bottom. Consequently, the performance of UWA communication systems is degraded, and high-speed digital communication is disrupted. If there is a dominant signal path such as a direct path, the received signal is modeled statistically as Rice fading but if not, it is modeled as Rayleigh fading. However, it has been known to be very difficult to reproduce the statistical estimation by real experimental evaluation in the sea. To give an insight for this scattering and grazing-angle-dependent bottom reflection loss effect in UWA communication, authors conduct experiments to quantify these effects. The image is transmitted using binary frequency shift keying (BFSK) modulation. The quality of the received image is shown to be affected by water surface scattering and grazing-angle-dependent bottom reflection loss. The analysis is based on the transmitter to receiver range and the receiver depth dependent image quality and bit error rate (BER). The results show that the received image quality is highly dependent on the transmitter-receiver range and receiver depth which characterizes the channel coherence bandwidth.

• Journal of the Korea Society of Computer and Information
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• v.15 no.3
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• pp.65-72
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• 2010

We propose the asymmetric 2.5Gbps/622Mbps PON(Passive Optical Network) in order to reduce the bandwith of filter at receiver with inverse RZ(Return to Zero) code coded downstream and NRZ(Non Return to Zero) upstream re-modulation. I theoretically analyze BER(Bit Error Rate) performance and the power sensitivity with the optimal threshold level by performing simulation with MATLAB according to the types of downstream data. The results have shown that the optimal threshold level at the optical receiver could be saturated at 0.33 as the optical received power increase more than -26dBm to keep $10^{-12}$ of BER to a minimum. Also the power sensitivity is more improved by about 3dB by fixing the threshold level at 0.33 than the conventional receiver. The proposed system can be a useful technology for optical access networks with asymmetric upstream and downstream data rates because the optical receiver can be used without controlling threshold levels and that does not require a light source in optical network unit (ONU) and its control circuits in the optical line termination (OLT).

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.46 no.4
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• pp.148-156
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• 2009

This paper presents a new image rejection algorithm based on the analysis of the distortion of a single-frequency continuous-wave (CW) signal due to the I/Q mismatch. Existing methods estimated the gain mismatch and phase mismatch on RF receivers and compensated them However, this paper shows that the circular trajectory of a single-frequency CW signal is distorted elliptic-type trajectory due to the I/Q mismatch. Utilizing the analysis, we propose a I/Q mismatch compensation method. It has two processing steps. In the first processing step, the generated signal is rotated to align the major axis of the elliptic-type trajectory diagram with the x-axis. In the second processing step, the Q-channel signal in the regenerated signal is scaled to align the regenerated signal with the transmitted single-frequency CW signal. Simulation results show that a receiver using the proposed image rejection algorithm can achieve an image rejection ratio of more than 70dB. And, simulation results show that the bit error rate performances of receivers using the proposed image rejection algorithm are almost the same as those of conventional coherent demodulators, even in fading channels.

• Journal of IKEEE
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• v.24 no.1
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• pp.25-32
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• 2020

In this paper, we propose an image generator for OLED panel test that can compensate for color coordinates and luminance by using panel defect inspection and optical measurement while displaying images on OLED panel. The proposed image generator consists of two processes: the image generation process and the process of compensating color coordinates and luminance using optical measurement. In the image generating process, the panel is set to receive the panel information to drive the panel, and the image is output by adjusting the output setting of the image generator according to the panel information. The output form of the image is configured by digital RGB method. The pattern generation algorithm inside the image generator outputs color and gray image data by transmitting color data to a 24-bit data line based on a synchronization signal according to the resolution of the panel. The process of compensating color coordinates and luminance using optical measurement outputs an image to an OLED panel in an image generator, and compensates for a portion where color coordinates and luminance data measured by an optical module differ from reference data. To evaluate the accuracy of the image generator for the OLED panel test proposed in this paper, Xilinx's Spartan 6 series XC6SLX25-FG484 FPGA was used and the design tool was ISE 14.5. The output of the image generation process was confirmed that the target setting value and the simulation result value for the digital RGB output using the oscilloscope matched. Compensating the color coordinates and luminance using optical measurements showed accuracy within the error rate suggested by the panel manufacturer.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.42 no.6
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• pp.149-158
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• 2005

This paper proposed a blind watermarking method for video contents which satisfies both the invisibility and the robustness to attacks to prohibit counterfeiting, modification, illegal usage and illegal re-production of video contents. This watermarking algorithm targets MPEG compression system and was designed to control the amount of watermarking to be inserted according to the adaptive quantization scale code to follow the adaptive quantization of the compression system. The inserting positions of the watermark were chosen by considering the frequency property of an image and horizontal, vertical and diagonal property of a $8{\times}8$ image block. Also the amount of watermarking for each watermark bit was decided by considering the quantization step. This algorithm was implemented by C++ and experimented for invisibility and robustness with MPEG-2 system. The experiment results showed that the method satisfied enough the invisibility of the inserted watermark and robustness against attacks. For the general attacks, the error rate of the extracted watermark was less than $10\%$, which is enough in robustness against the attacks. Therefore, this algorithm is expected to be used effectively as a part in many MPEG systems for real-time watermarking, especially in the sensitive applications to the network environments.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.4 s.95
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• pp.380-388
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• 2005

This paper presents analysis results of the effects of RF filter characteristics on the system performance of impulse radio. The impulse radio system transmits modulated pulses having very short time duration and information can be extracted in receiver side based on cross-correlation between received and transmitted pulses. Accordingly, the pulse distortion due to in-band group delay variation can cause serious system performance degradation. In general, RF bandpass filters inevitably cause group delay difference to the signal passing through the filter which is proportional to its skirt characteristic due to its resonance phenomenon. For time as well as frequency domain analysis, small signal scattering parameter $S_{21}$ and its Fourier transform are used to characterize output pulse waveform under the condition that the input and output ports are matched. The output pulse waveform of the filter is predicted based on convolution integral between input pulse and filter transfer function, and resulting BER performances in the BPM and PPM based impulse radio system are calculated.

• International Journal of Computer Science & Network Security
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• v.23 no.10
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• pp.1-10
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• 2023

This paper proposes a method to extend Inter-Carrier Interference (ICI) canceling Orthogonal Frequency Division Multiplexing (OFDM) receivers for 5G mobile systems to spatial multiplexing 2×2 MIMO (Multiple Input Multiple Output) systems to support high-speed ground transportation services by linear motor cars traveling at 500 km/h. In Japan, linear-motor high-speed ground transportation service is scheduled to begin in 2027. To expand the coverage area of base stations, 5G mobile systems in high-speed moving trains will have multiple base station antennas transmitting the same downlink (DL) signal, forming an expanded cell size along the train rails. 5G terminals in a fast-moving train can cause the forward and backward antenna signals to be Doppler-shifted in opposite directions, so the receiver in the train may have trouble estimating the exact channel transfer function (CTF) for demodulation. A receiver in such high-speed train sees the transmission channel which is composed of multiple Doppler-shifted propagation paths. Then, a loss of sub-carrier orthogonality due to Doppler-spread channels causes ICI. The ICI Canceller is realized by the following three steps. First, using the Demodulation Reference Symbol (DMRS) pilot signals, it analyzes three parameters such as attenuation, relative delay, and Doppler-shift of each multi-path component. Secondly, based on the sets of three parameters, Channel Transfer Function (CTF) of sender sub-carrier number n to receiver sub-carrier number l is generated. In case of n≠l, the CTF corresponds to ICI factor. Thirdly, since ICI factor is obtained, by applying ICI reverse operation by Multi-Tap Equalizer, ICI canceling can be realized. ICI canceling performance has been simulated assuming severe channel condition such as 500 km/h, 8 path reverse Doppler Shift for QPSK, 16QAM, 64QAM and 256QAM modulations. In particular, 2×2MIMO QPSK and 16QAM modulation schemes, BER (Bit Error Rate) improvement was observed when the number of taps in the multi-tap equalizer was set to 31 or more taps, at a moving speed of 500 km/h and in an 8-pass reverse doppler shift environment.

• Journal of Intelligence and Information Systems
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• v.24 no.2
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• pp.21-35
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• 2018

Since the introduction of MP3 players, CD recordings have gradually been vanishing, and the music consuming environment of music users is shifting to mobile devices. The introduction of smart devices has increased the utilization of music through music playback, mass storage, and search functions that are integrated into smartphones and tablets. At the time of initial MP3 player supply, the bitrate of the compressed music contents generally was 128 Kbps. However, as increasing of the demand for high quality music, sound quality of 384 Kbps appeared. Recently, music content of FLAC (Free License Audio Codec) format using lossless compression method is becoming popular. The download service of many music sites in Korea has classified by unlimited download with technical protection and limited download without technical protection. Digital Rights Management (DRM) technology is used as a technical protection measure for unlimited download, but it can only be used with authenticated devices that have DRM installed. Even if music purchased by the user, it cannot be used by other devices. On the contrary, in the case of music that is limited in quantity but not technically protected, there is no way to enforce anyone who distributes it, and in the case of high quality music such as FLAC, the loss is greater. In this paper, the author proposes an audio watermarking technology for copyright protection of high quality stereo music. Two kinds of information, "Copyright" and "Copy_free", are generated by using the turbo code. The two watermarks are composed of 9 bytes (72 bits). If turbo code is applied for error correction, the amount of information to be inserted as 222 bits increases. The 222-bit watermark was expanded to 1024 bits to be robust against additional errors and finally used as a watermark to insert into stereo music. Turbo code is a way to recover raw data if the damaged amount is less than 15% even if part of the code is damaged due to attack of watermarked content. It can be extended to 1024 bits or it can find 222 bits from some damaged contents by increasing the probability, the watermark itself has made it more resistant to attack. The proposed algorithm uses quantization in DCT so that watermark can be detected efficiently and SNR can be improved when stereo music is converted into mono. As a result, on average SNR exceeded 40dB, resulting in sound quality improvements of over 10dB over traditional quantization methods. This is a very significant result because it means relatively 10 times improvement in sound quality. In addition, the sample length required for extracting the watermark can be extracted sufficiently if the length is shorter than 1 second, and the watermark can be completely extracted from music samples of less than one second in all of the MP3 compression having a bit rate of 128 Kbps. The conventional quantization method can extract the watermark with a length of only 1/10 compared to the case where the sampling of the 10-second length largely fails to extract the watermark. In this study, since the length of the watermark embedded into music is 72 bits, it provides sufficient capacity to embed necessary information for music. It is enough bits to identify the music distributed all over the world. 272 can identify $4*10^{21}$, so it can be used as an identifier and it can be used for copyright protection of high quality music service. The proposed algorithm can be used not only for high quality audio but also for development of watermarking algorithm in multimedia such as UHD (Ultra High Definition) TV and high-resolution image. In addition, with the development of digital devices, users are demanding high quality music in the music industry, and artificial intelligence assistant is coming along with high quality music and streaming service. The results of this study can be used to protect the rights of copyright holders in these industries.

• Journal of Intelligence and Information Systems
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• v.17 no.2
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• pp.97-107
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• 2011

Nowadays there are a lot of issues about copyright infringement in the Internet world because the digital content on the network can be copied and delivered easily. Indeed the copied version has same quality with the original one. So, copyright owners and content provider want a powerful solution to protect their content. The popular one of the solutions was DRM (digital rights management) that is based on encryption technology and rights control. However, DRM-free service was launched after Steve Jobs who is CEO of Apple proposed a new music service paradigm without DRM, and the DRM is disappeared at the online music market. Even though the online music service decided to not equip the DRM solution, copyright owners and content providers are still searching a solution to protect their content. A solution to replace the DRM technology is digital audio watermarking technology which can embed copyright information into the music. In this paper, the author proposed a new audio watermarking algorithm with two approaches. First, the watermark information is generated by two dimensional barcode which has error correction code. So, the information can be recovered by itself if the errors fall into the range of the error tolerance. The other one is to use chirp sequence of CDMA (code division multiple access). These make the algorithm robust to the several malicious attacks. There are many 2D barcodes. Especially, QR code which is one of the matrix barcodes can express the information and the expression is freer than that of the other matrix barcodes. QR code has the square patterns with double at the three corners and these indicate the boundary of the symbol. This feature of the QR code is proper to express the watermark information. That is, because the QR code is 2D barcodes, nonlinear code and matrix code, it can be modulated to the spread spectrum and can be used for the watermarking algorithm. The proposed algorithm assigns the different spread spectrum sequences to the individual users respectively. In the case that the assigned code sequences are orthogonal, we can identify the watermark information of the individual user from an audio content. The algorithm used the Walsh code as an orthogonal code. The watermark information is rearranged to the 1D sequence from 2D barcode and modulated by the Walsh code. The modulated watermark information is embedded into the DCT (discrete cosine transform) domain of the original audio content. For the performance evaluation, I used 3 audio samples, "Amazing Grace", "Oh! Carol" and "Take me home country roads", The attacks for the robustness test were MP3 compression, echo attack, and sub woofer boost. The MP3 compression was performed by a tool of Cool Edit Pro 2.0. The specification of MP3 was CBR(Constant Bit Rate) 128kbps, 44,100Hz, and stereo. The echo attack had the echo with initial volume 70%, decay 75%, and delay 100msec. The sub woofer boost attack was a modification attack of low frequency part in the Fourier coefficients. The test results showed the proposed algorithm is robust to the attacks. In the MP3 attack, the strength of the watermark information is not affected, and then the watermark can be detected from all of the sample audios. In the sub woofer boost attack, the watermark was detected when the strength is 0.3. Also, in the case of echo attack, the watermark can be identified if the strength is greater and equal than 0.5.