• Journal of Broadcast Engineering
• /
• v.22 no.3
• /
• pp.350-365
• /
• 2017

Steganography is a technique for secret data communication, which is not perceived by third person between a receiver and a transmitter. It has been developed for thousands of years for the transmission of military, diplomatic or business information. The development of digital media and communication has led to the development of steganography techniques in modern times. Technic of image steganography include the LSB, which fixes the number of embedded bits into a pixel, and PVD, which exploits the difference value in the neighboring pixel pairs. In the case of PVD image steganography, a large amount of information is embedded fluidly by difference value in neighboring pixel pairs and the designed range table. However, since the secret information in order is embedded, if an error of the number of embedded bits occurs in a certain pixel pair, all subsequent information will be destroyed. In this paper, we proposes the method, which improve the vulnerability of PVD property about external attack or various noise and extract secret information. Experimental process is comparison analysis about stego-image, which embedded various noise. PVD shows that it is not possible to preserve secret information at all about noise, but it was possible to robustly extract secret information for partial noise of stego-image in case of the proposed PVD image steganography with locally-fixed number of embedding bits.

• Journal of the Institute of Convergence Signal Processing
• /
• v.14 no.4
• /
• pp.261-269
• /
• 2013

This paper describes the design and development of VSI (VLBI standard interface) optical adapter for transmitting VLBI(Very long baseline interferometry) observation data with optical signal. VSI cable comprised of 80-line is being used for observed data transmission with maximum length of 5-meter between playbacks (Mark5B, VERA2000) and raw VLBI data buffer (RVDB), RVDB and VLBI correlation subsystem (VCS) in Daejeon correlator. It has a plan to conduct the data processing for 16-stations and introduce the 14 RVDB systems in near future. And data loss frequently occurred because of trouble of VSI cable MDR80 connector. By considering the data loss by connector error of VSI cable, RVDB system extension plan, effective space usage and long distance data transmission(e-VLBI), the VSI optical adapter was proposed and developed for effectively transmitting and receiving VLBI data through optical signal. In order to confirming the performance of developed VSI optical adapter, the experiments for data transmission was conducted between playback and RVDB system, and confirmed that data transmission was clearly done without any data loss.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.40 no.7
• /
• pp.1397-1404
• /
• 2015

Recently, high data rate transmission is required in maritime communication. In this paper, we consider multiple input multiple output (MIMO) spatial multiplexing (SM). However, the performance of SM is severly degraded due to spatial channel correlation and line-of-sight (LOS) component. In the maritime communication, the MIMO channel correlation and LOS are critical due to the lack of scatteres around the transmitter and/or the receiver. When the feedback of channel information is available, precoding can enhance the error performance by exploiting the channel information. However, it is difficult to derive closed-form solution considering both the correlation and LOS. In this paper, we present open-loop precoding-based spatial multiplexing transmission method by showing that the effect of performance for the correlation and LOS. It is shown that the open-loop precoding can mitigate the performance degradation due to the LOS as well as the correlation. Consequently, we expect that the proposed open-loop precoding can be adopted to the maritime communication system.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.34 no.11C
• /
• pp.1085-1097
• /
• 2009

We present a structure and design method of the D8PSK modem compatible with the VDL mode-2 standard and performance test results of the developed modem. In VDL mode-2, the raised cosine filter is used only in the transmitter and a general low pass filter is used in the receiver. Consequently, we can not achieve ISI reduction but can have better spectrum characteristics. Although there is 1~2 dB performance degradation with an un-matched filter compared to that with a matched filter, it is more important to minimize adjacent channel interference in narrow band communications. The transmit signal is generated digitally to avoid the problems(I/Q imbalance and DC offset etc.) of analog modulators. In addition the digital down converter using digital IF sampling technique is adopted for the receiver. This paper contains the overall configuration, design method and simulation results based in part on the previously proposed structures and algorithms. It is confirmed that the modem transmits and receives messages successfully at a speed of max. 870 km/h over ranges of up to 310 km through the ground and in-flight communication tests.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.33 no.6C
• /
• pp.429-437
• /
• 2008

Multiple-input multiple-output (MIMO) techniques can be used for the spectral efficiency enhancement of the cellular systems, which can be categorized into spatial multiplexing (SM) and spatial diversity schemes. MIMO systems suffer a severe performance degradation due to the intercell interference from the adjacent cells as the mobile terminal moves toward the cell boundary. Therefore for the spectral efficiency enhancement, an appropriate transmission scheme for the given channel environment and reception scheme which can mitigate the intercell interference are required. In this paper, we propose an adaptive signal transmission/reception scheme for the spectral efficiency improvement of $M_R{\times}M_T$ MIMO systems, present the decision criteria for the adaptive operation of the proposed scheme, and demonstrate the performance gain. The proposed scheme performs adaptive transmission using spatial multiplexing and spatial diversity, and adaptive reception using maximal ratio combining (MRC) and intercell spatial demultiplexing (ISD) when the spatial diversity transmission is used at the transmitter. Spatial multiplexing/demultiplexing is performed at the high signal-to-interference ratio (SIR) range, and the transmit diversity in conjunction with the adaptive reception uses either conventional MRC or ISD which can mitigate the $M_R-1$ interference signals, based on the mobile location. For the performance evaluation of the proposed adaptive scheme, the probability density function (pdf) of the effective SIR for the transmission/reception methods in consideration are derived for $M_R{\times}M_T$ MIMO systems. Using the results, the average effective SIR and spectral efficiency are presented and compared with simulation results.

• Journal of Communications and Networks
• /
• v.16 no.2
• /
• pp.227-237
• /
• 2014

Throughput scaling laws for two coexisting ad hoc networks with m primary users (PUs) and n secondary users (SUs) randomly distributed in an unit area have been widely studied. Early work showed that the secondary network performs as well as stand-alone networks, namely, the per-node throughput of the secondary networks is ${\Theta}(1/\sqrt{n{\log}n})$. In this paper, we show that by exploiting directional spectrum opportunities in secondary network, the throughput of secondary network can be improved. If the beamwidth of secondary transmitter (TX)'s main lobe is ${\delta}=o(1/{\log}n)$, SUs can achieve a per-node throughput of ${\Theta}(1/\sqrt{n{\log}n})$ for directional transmission and omni reception (DTOR), which is ${\Theta}({\log}n)$ times higher than the throughput with-out directional transmission. On the contrary, if ${\delta}={\omega}(1/{\log}n)$, the throughput gain of SUs is $2{\pi}/{\delta}$ for DTOR compared with the throughput without directional antennas. Similarly, we have derived the throughput for other cases of directional transmission. The connectivity is another critical metric to evaluate the performance of random ad hoc networks. The relation between the number of SUs n and the number of PUs m is assumed to be $n=m^{\beta}$. We show that with the HDP-VDP routing scheme, which is widely employed in the analysis of throughput scaling laws of ad hoc networks, the connectivity of a single SU can be guaranteed when ${\beta}$ > 1, and the connectivity of a single secondary path can be guaranteed when ${\beta}$ > 2. While circumventing routing can improve the connectivity of cognitive radio ad hoc network, we verify that the connectivity of a single SU as well as a single secondary path can be guaranteed when ${\beta}$ > 1. Thus, to achieve the connectivity of secondary networks, the density of SUs should be (asymptotically) bigger than that of PUs.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.23 no.4
• /
• pp.475-483
• /
• 2012

This paper presents new type of the hybrid supply modulator for the next reconfigurable transmitters. The efficiency of the hybrid supply modulator is one of the most important performance. For enhancement the efficiency, multi-switching structure in the hybrid supply modulator is employed. Additionally, input envelope signal sensing stage is employed for implementation multi-mode operation. To compare the performance of the proposed hybrid supply modulator, the conventional hybrid supply modulator is also designed. The measured efficiency of the proposed hybrid supply modulator is 85 %/84 %/79 % for EDGE/WCDMA/LTE signals which have 384 kHz/3.84 MHz/5 MHz bandwidth, respectively. The efficiency of the proposed hybrid supply modulator is higher than the conventional hybrid supply modulator. Therefore, this structure shows good candidate for the reconfigurable transmitters.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.23 no.4
• /
• pp.491-498
• /
• 2012

Recently, many papers have been proposed in order to improve the OFDM system performance in T-DMB DOCR (Digital On Channel Repeater), by using removing the feedback signal so that the transmitter power can be increased or by using the equalizer to remove ICI. Despite these efforts, however, signal quality at the receiving terminal has not been improved because of constellation smearing in T-DMB DOCR. In this paper, in order to suppress constellation smearing, we propose an effective equalizer algorithm that can improve system performance. We perform adaptive channel estimation and non-coherent decision directed noise cancellation method that can estimate the channel subsequently during data symbols period in the frequency domain. So we can obtain better quality of the signal at the receiving terminal. In order to secure QoS(Quality of Service) required in T-DMB handsets, we evaluate SNR and BER in T-DMB DOCR(Digital On Channel Repeater) and verified by simulation. In this simulation results, this system is satisfied the performance of BER=$10^{-5}$ at less than SNR=14 dB at the receiver after compensation of phase noise -18 dBc.

• Korean Journal of Optics and Photonics
• /
• v.22 no.4
• /
• pp.191-197
• /
• 2011

In this paper, we have designed an integrated triplexer which is the basic component for a FTTH(Fiber To The Home) system which can transmit CATV and voice/data at the same time in a single fiber. The integrated triplexer can be fabricated with a novel technique of "Micro-Block Stacking (MBS)" method which automatically aligns the optical components in the optical beam pass using accurate ceramic holders. We analyze the displacement of the optical focus according to the tolerances of the component dimensions and the assembly process using code V simulator. For the transmitter, the most serious shift of the focal points is caused by the displacements of the LD spot. So the focal point moves up to $72{\mu}m$ from the center point for ${\pm}25{\mu}m$, ${\pm}25{\mu}m$, ${\pm}30{\mu}m$ displacements. For the receiver the most serious shift of the focal points is caused by the displacements of a 0.8mm ball lens (for the analog receiving part) and a micro ball lens (for the digital receiving part), and the focal point moves up to $55{\mu}$ for ${\pm}55{\mu}m$, ${\pm}5{\mu}m$, ${\pm}55{\mu}m$ micro ball lens displacements.

• The Korean Journal of Pain
• /
• v.6 no.2
• /
• pp.231-236
• /
• 1993

Clonidine, a centrally-acting antihypertensive agent known to reduce central sympathetic outflow and modulate presynaptic transmitter's release, has shown to suppress central noradrenergic hyperactivity induced by immobilization stress in animals, by decreasing the MAC of halothane and the dose of narcotics required to prevent reflex cardiovascular response to noxious stimuli, and to have potent analgesic properties in humans. These characteristics suggest that clonidine might be a useful adjunct to the anesthetic management of patients with preexisting hypertension. Accordingly, we determined the clinical efficacy and safety on analgesia, sedation and hemodynamic stability in the perioperative period. Thirty patients(ASA physical status II-III) with a history of arterial hypertension, scheduled for elective orthopedic surgery were randomly assigned to two groups. We applied CPA-clonidine patch($6.9\;mg/cm^2$, 0.2 mg delivered daily) or placebo patch to each groups, 48 hours prior to induction of anesthesia. Antihypertensive medication was continued until the morning of the scheduled surgery. All patients received premedication of atropine and lorazepam, and induced anesthesia with thiopental and succinylcholine, and maintained with enflurane and 50% nitrous oxide, while sustaining the BP and pulse rate at acceptable range. For the relief of pain postoperatively, diclofenac and fentanyl were administered intramuscularly on demand. The results were as follows: 1) The change of hemodynamic responses in clonidine group was less compared to the placebo group. 2) Intraoperative anesthetic requirement for enflurane in clonidine group were significantly lower than placebo group. 3) Postoperative analgetic requirement in clonidine group were significantly lower than placebo group. In clonidine group, 5 cases out of 15 cases were required no analgetics, and the incidence of administration of additional fentanyl was decreased to 5 cases, comparing with 10 cases in placebo group.