• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.9
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• pp.1513-1527
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• 2011

This paper investigates the capacity rate problems for a joint decode-and-forward (JDF) based two-way relaying with network coding. We first characterize the achievable rate region for a conventional three-node network scenario along with the calculation of the corresponding maximal sum-rate. Then, for the goal of maximizing the system sum-rate, opportunistic relay selection is examined for multi-relay networks. As a result, a novel strategy for the implementation of relay selection is proposed, which depends on the instantaneous channel state and allows a single best relay to help the two-way information exchange. The JDF scheme and the scheme using relay selection are analyzed in terms of outage probability, after which the corresponding exact expressions are developed over Rayleigh fading channels. For the purpose of comparison, outage probabilities of the amplify-and-forward (AF) scheme and those of the scheme using relay selection are also derived. Finally, simulation experiments are done and performance comparisons are conducted. The results verify that the proposed strategy is an appropriate method for the implementation of relay selection and can achieve significant performance gains in terms of outage probability regardless of the symmetry or asymmetry of the channels. Compared with the AF scheme and the scheme using relay selection, the conventional JDF scheme and that using relay selection perform well at low signal-to-noise ratios (SNRs).

• Journal of Communications and Networks
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• v.13 no.3
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• pp.232-239
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• 2011

This paper investigates the user selection problem of successive zero-forcing precoded multiuser multiple-input multiple-output (MU-MIMO) downlink systems, in which the base station and mobile receivers are equipped with multiple antennas. Assuming full knowledge of the channel state information at the transmitter, dirty paper coding (DPC) is an optimal precoding strategy, but practical implementation is difficult because of its excessive complexity. As a suboptimal DPC solution, successive zero-forcing DPC (SZF-DPC) was recently proposed; it employs partial interference cancellation at the transmitter with dirty paper encoding. Because of a dimensionality constraint, the base station may select a subset of users to serve in order to maximize the total throughput. The exhaustive search algorithm is optimal; however, its computational complexity is prohibitive. In this paper, we develop two low-complexity user scheduling algorithms to maximize the sum rate capacity of MU-MIMO systems with SZF-DPC. Both algorithms add one user at a time. The first algorithm selects the user with the maximum product of the maximum column norm and maximum eigenvalue. The second algorithm selects the user with the maximum product of the minimum column norm and minimum eigenvalue. Simulation results demonstrate that the second algorithm achieves a performance similar to that of a previously proposed capacity-based selection algorithm at a high signal-to-noise (SNR), and the first algorithm achieves performance very similar to that of a capacity-based algorithm at a low SNR, but both do so with much lower complexity.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.8 no.6
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• pp.528-533
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• 2015

In the construction of USN environment, the implementation of a safe sensor network using wireless communications can be said to be the most important factor in the entire system. Although USN communication uses wireless communications to enhance accessability and non-contact capability, this results in the security vulnerability, thus endangering the system. In this regard, we propose a security protocol that can be effectively applied to USN, a multi-sensor network. The proposed protocol is a method using an individual chaotic system, and it is a security protocol to synchronize the main chaotic system mounted on each sensor and prepared key values into the initial values, and to communicate with the use of the synchronized values as symmetric keys. The communication protocol proposed in this paper is expected to yield good results as a new method to resolve security problems of USN and program capacity limitations of sensor nodes if subsequent studies continue to be carried out.

• Journal of Communications and Networks
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• v.14 no.2
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• pp.188-194
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• 2012

Cognitive networks (CNs) are capable of enabling dynamic spectrum allocation, and thus constitute a promising technology for future wireless communication. Whereas, the implementation of CN will lead to the requirement of an increased energy-arrival rate, which is a significant parameter in energy harvesting design of a cognitive user (CU) device. A well-designed spectrum-sensing scheme will lower the energy-arrival rate that is required and enable CNs to self-sustain, which will also help alleviate global warming. In this paper, spectrum sensing in a multi-user cognitive ad hoc network with a wide-band spectrum is considered. Based on the prospective spectrum sensing, we classify CN operation into two modes: Distributed and centralized. In a distributed network, each CU conducts spectrum sensing for its own data transmission, while in a centralized network, there is only one cognitive cluster header which performs spectrum sensing and broadcasts its sensing results to other CUs. Thus, a wide-band spectrum that is divided into multiple sub-channels can be sensed simultaneously in a distributed manner or sequentially in a centralized manner. We consider the energy consumption for spectrum sensing only of an analog-to-digital convertor (ADC). By formulating energy consumption for spectrum sensing in terms of the sub-channel sampling rate and whole-band sensing time, the sampling rate and whole-band sensing time that are optimal for minimizing the total energy consumption within sensing reliability constraints are obtained. A power dissipation model of an ADC, which plays an important role in formulating the energy efficiency problem, is presented. Using AD9051 as an ADC example, our numerical results show that the optimal sensing parameters will achieve a reduction in the energy-arrival rate of up to 97.7% and 50% in a distributed and a centralized network, respectively, when comparing the optimal and worst-case energy consumption for given system settings.

• The Journal of the Korea institute of electronic communication sciences
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• v.13 no.6
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• pp.1263-1268
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• 2018

In this paper, a video analysis is proposed to implement video surveillance system with deep learning object detection and probabilistic data association filter for tracking multiple objects, and suggests its implementation using GPU. The proposed video analysis technique involves object detection and object tracking sequentially. The deep learning network architecture uses ResNet for object detection and applies probabilistic data association filter for multiple objects tracking. The proposed video analysis technique can be used to detect intruders illegally trespassing any restricted area or to count the number of people entering a specified area. As a results of simulations and experiments, 48 channels of videos can be analyzed at a speed of about 27 fps and real-time video analysis is possible through RTSP protocol.

• The KIPS Transactions:PartC
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• v.11C no.1
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• pp.141-148
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• 2004

Recently, the demand of broadband communications such as high-speed internet, HDTV, 3D-HDTV and ATM backbone network has been increased drastically. For transmitting the broad-bandwidth data using wireless network, it is needed to use ka-band frequency. However, the use of this ka-band frequency is seriously affected to the received data performance by rain fading and atmospheric propagation loss at the Ka-band satellite communication link. So, we need adaptive MODEM to endure the degraded performance by channel environment. In this paper, we will present the structure and design of the 155Mbps adaptive Modem adaptively compensated against channel environment. In order to compensate the rain attenuation over the ka-band wireless channel link, the adaptive coding schemes with variable coding rates and the multiple modulation schemes such as trellis coded 8-PSK, QPSK, and BPSK are adopted. And the blind demodulation scheme is proposed to demodulate without Information of modulation mode at the multi-mode demodulator, and the fast phase ambiguity resolving scheme is proposed. The design and simulation results of adaptive Modem by SPW model are provided. This 155Mbps adaptive MODEM was designed and implemented by single ASIC chip with the $0.25\mu{m}$ CMOS standard cell technology and 950 thousand gates.

• The KIPS Transactions:PartC
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• v.8C no.6
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• pp.821-830
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• 2001

H.323 proposes to use Mobile IP and H.323 ad hoc conference signaling to provide Handoff function to a mobile terminal. But H.323 ad hoc conference signaling has a drawback. It requires an H.323 endpoint to do a complex conference signaling which makes inter-operability between H.323 endpoints difficult and takes the longer signaling time. In this paper, we propose an Handoff signaling using H.323 rerouting(Third party initiated Pause and Rerouting). H.323 rerouting signaling only requires an H.323 endpoint to do H.323 basic signaling in reestablishing media channel, and makes inter-operability more easier and provides the faster Handoff. To do this, our H.323 GK has derived H.245 control channel using tunneling for all H.323 calls including the fast connect calls which enable endpoints communicate each other if they don\`t have H.245 control channel. In order to evaluate the performance of the proposed signaling, we have conducted an experiment that compares a call transfer signaling using H.323 rerouting with ad hoc conference signaling in inter-operability and signaling delay. The results of our experiment shows that the call transfer signaling can inter-operate with four H.323 endpoints among five H.323 endpoints of other vendors and reduces the signaling delay average 1.4 sec.

• KIPS Transactions on Computer and Communication Systems
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• v.7 no.2
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• pp.49-58
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• 2018

A certificate is a means to certify users by conducting the identification of the users, the prevention of forgery and alteration, and non-repudiation. Most people use an accredited certificate when they perform a task using online banking, and it is often used for the purpose of proving one's identity in issuing various certificates and making electronic payments in addition to online banking. At this time, the issued certificate exists in a file form on the disk, and it is possible to use the certificate issued in an existing device in a new device only if one copies it from the existing device. However, most certificate duplication methods are a method of duplication, entering an 8-16 digit verification code. This is inconvenient because one should enter the verification code and has a weakness that it is vulnerable to security issues. To solve this weakness, this study proposes a method for enhancing security certificate duplication in a multi-channel using TCP and BLE. The proposed method: 1) shares data can be mutually authenticated, using BLE Advertising data; and 2) encrypts the certificate with a symmetric key algorithm and delivers it after the certification of the device through an ECC-based electronic signature algorithm. As a result of the implementation of the proposed method in a mobile environment, it could defend against sniffing attacks, the area of security vulnerabilities in the existing methods and it was proven that it could increase security strength about $10^{41}$ times in an attempt of decoding through the method of substitution of brute force attack existing method.

• Geophysics and Geophysical Exploration
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• v.22 no.4
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• pp.225-238
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• 2019

Migration velocity analysis (MVA) for creating optimum depth-domain velocities in seismic imaging was applied to marine long-offset multi-channel data, and the effectiveness of the MVA approach was demonstrated by the combinations of conventional data processing procedures. The time-domain images generated by conventional time-processing scheme has been considered to be sufficient so far for the seismic stratigraphic interpretation. However, when the purpose of the seismic imaging moves to the hydrocarbon exploration, especially in the geologic modeling of the oil and gas play or lead area, drilling prognosis, in-place hydrocarbon volume estimation, the seismic images should be converted into depth domain or depth processing should be applied in the processing phase. CMP-based velocity analysis, which is mainly based on several approximations in the data domain, inherently contains errors and thus has high uncertainties. On the other hand, the MVA provides efficient and somewhat real-scale (in depth) images even if there are no logging data available. In this study, marine long-offset multi-channel seismic data were optimally processed in time domain to establish the most qualified dataset for the usage of the iterative MVA. Then, the depth-domain velocity profile was updated several times and the final velocity-in-depth was used for generating depth images (CRP gather and stack) and compared with the images obtained from the velocity-in-time. From the results, we were able to confirm the depth-domain results are more reasonable than the time-domain results. The spurious local minima, which can be occurred during the implementation of full waveform inversion, can be reduced when the result of MVA is used as an initial velocity model.

• Journal of Korea Multimedia Society
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• v.6 no.2
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• pp.340-351
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• 2003

We introduce our experiences of the design and implementation of the Page Together system that has expanded hyperlink metaphor to utilize human resources in the web. This system supports that a user connects with others in the web, communicates through video/audio channel, navigates same web pages simultaneously and cooperates some work on Internet. For these functions, it comprises Collaborative Browsing Module (CBM), Multimedia Conferencing Module(MCM) Data Conferencing Module(I)CM) and Multi Protocol Interface(MPI). We adopted three standard protocols, IEC, H.323 and T.120 for each nodule and it allows developers to use them easily. We also defined MPI to synchronize information of session among modules. Each module exchanges information each other in session creating process and session terminating process. After a session is created once, each module works independently as its won protocol. Interferences among modules are reduced as minimizing to exchange information. We also introduce a web site that provides web board service based on the Page Together system. A user may post a notice with a link to himself/herself on our web board. After then, if someone read that notice and has any question about it, he or she can try to connect to the writer as clicking the link in that notice and communicate each other. This service site shows that our system can be applied to diverse internet services such as distance teaming and distance conference.