• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.10A
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• pp.1563-1570
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• 1999

This paper relates to the soft decision method with erasure technique in digital terrestrial television broadcasting system. The proposed decoder use the CSI derived from using the pilots in receiver. The active real(I) and imaginary(Q) data are transferred to the branch metric calculation block that decides the Euclidean distance for the soft decision decoding and also the estimated CSI values are transferred to the same block. After calculating the Euclidean distance for the soft decision decoding, the Euclidean distance of branch metric is multiplied by CSI. To do so, new branch metric values that consider each carrier state information are obtained. We simulated this method in better performance of about 0.15dB to 0.17dB and 2.2dB to 2.9dB in Rayleigh channel than that of the conventional soft decision Viterbi decoding with or without bit interleaver where the constellation is QPSK, 16-QAM and 64-QAM.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.6
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• pp.648-653
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• 2011

In this paper, coordinated space division multiple access(SDMA) technology is proposed to mitigate inter-cell interference by using partial channel state information in cooperative wireless communications system with limited feedback. Each AT selects an optimal cluster transmission mode and sends it back to a cluster scheduler, and at the cluster scheduler, ATs are scheduled within a AT group with the identical cluster transmission mode, and the optimal transmission mode and the corresponding scheduled ATs are determined to maximize scheduling priority. Also, in order to enhance multiuser diversity gain, an extended transmission feedback method is proposed to feed back multiple preferred cluster transmission modes at each AT. It is shown that the proposed coordinated SDMA scheme outperforms existing non-coordinated SDMA schemes in terms of the average system throughput.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2018.10a
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• pp.464-466
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• 2018

In this paper, a dense cellular network is considered in which each base station equipped with multiple antennas simultaneously communicates with multiple single-antenna users. Based on limited feedback, each user feeds back its quantized channel state information (CSI) to its associated transmitter, and the transmitter broadcasts multiple data streams prepared for the scheduled users using a space-division multiple access scheme. As the amount of CSI is limited at the transmitter, the downlink throughput increases with the number feedback bits. However, the increased number of feedback bits requires the correspondingly increased amount of uplink resources. Thus, an appropriate balance between the downlink throughput and the uplink resource usage should be considered in realistic systems. A net spectral efficiency defined in this context is used in this paper, and the optimal number of feedback bits that maximizes the net spectral efficiency is analyzed. This paper particularly focuses on the case when the received signal power is much smaller than the noise power.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.17 no.2
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• pp.168-180
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• 1992

Commumication technology has been continuously developed to overcome the distance and time for the transmission of information to the human society. Wireless mobile communication, which had been used mostly in the military and police is widely used these days for enterprise and individuals. Therefore the domestic usage of the advanced mobile phone service are progressively gaining wide popularity. The modulation techniques used usually in mobile communications were the analog techniques such as AM and FM, but they are getting replaced by the digital techniques, However, the major disadvantage of the digital communications is the increase of the transmission bandwidth. Therefore, it is very important to use efficiently the limited frequency bandwidth. The domestic research and development on the subject seems quite limited and in order to establish the technology of the digital mobile communications. This thesis presents the design of the frequency hopping synthesizer providing 124 channels with a channel spcing of 200KHz. VCD used in the synthesizer employs a semi-rigid cable for higher purity of signal spectrum, and a hybrid pgase detector is realized with a sample hold phase detector in conjuction with a tri-state phase detedctor.

• Journal of Communications and Networks
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• v.18 no.3
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• pp.375-386
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• 2016

Most existing studies on broadcast services in orthogonal frequency division multiplexing (OFDM) systems have focused on how to allocate the transmission power to the subcarriers. However, because a broadcasting system must guarantee quality of service to all users, the performance of the broadcast service dominantly depends on the channel state of the user who has the lowest received signal-to-noise ratio among users. To reduce the effect of the worst user on the system performance, we propose a joint delivery scheme of unicast and broadcast transmissions in OFDM systems with broadcast and unicast best-effort users. In the proposed joint delivery scheme, the BS delivers the broadcast information using both the broadcast and unicast subcarriers at the same time in order to improve the performance of the broadcast service. The object of the proposed scheme is to minimize the outage probability of the broadcast service while maximizing the sum-rate of best-effort users. For the proposed joint delivery scheme, we develop an adaptive power and subcarrier allocation algorithm under the constraint of total transmission power. This paper shows that the optimal power allocation over each subcarrier in the proposed scheme has a multi-level water filling form. Because the power allocation and the subcarrier assignment problems should be jointly solved, we develop an iterative algorithm to find the optimal solution. Numerical results show that the proposed joint delivery scheme with adaptive power and subcarrier allocation outperforms the conventional scheme in terms of the outage probability of the broadcast service and the sum-rate of best-effort users.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.12
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• pp.2812-2817
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• 2013

In this paper, an outage probability for the best relay selection in decode-and-forward relaying systems in the presence of interference is analyzed over Rayleigh fading channels. Based on the outage performance results, we propose a method to determine effective relay candidates for the best relay selection, where the effective relay candidates represent the relays except for relays that make no contribution to improving the performance. in all possible relays given in the system. By determining the effective relay candidates, the feedback overhead of channel state information and the energy consumption of relays can be significantly reduced while minimizing the performance degradation. In this paper, we provide important parameters that affect the determination of the effective relay candidates.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.29 no.2
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• pp.417-429
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• 2019

WPA2-PSK uses a 4-way handshake protocol based on a shared secret to establish a secure session between a client and an AP. It has various security problems such as eavesdropping attacks and the secure session establishment process is inefficient because it requires multiple interactions between client and AP. The WPA3 standard has recently been proposed to solve the security problem of WPA2, but it is a small improvement using the same 4-way handshake methodology. OAuth 2.0 token authentication is widely used on the web, which can be used to keep an authenticated state of a client for a long time by using tokens issued to an authenticated client. In this paper, we apply the dual-token based randomized token authentication technology to the Wi-Fi security protocol to achieve an efficient Wi-Fi security protocol by dividing initial authentication and secure session establishment. Once a client is authenticated and equipped with dual tokens issued by AP, it can establish secure session using them quickly with one message exchange over a non-secure channel.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.2
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• pp.714-720
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• 2021

The ITL (information theoretic learning) based on the kernel density estimation method that has successfully been applied to machine learning and signal processing applications has a drawback of severe sensitiveness in choosing proper kernel sizes. For the maximization of correntropy criterion (MCC) as one of the ITL-type criteria, several methods of adapting the remaining kernel size ( ) after removing the term have been studied. In this paper, it is shown that the main cause of sensitivity in choosing the kernel size derives from the term and that the adaptive adjustment of in the remaining terms leads to approach the absolute value of error, which prevents the weight adjustment from continuing. Thus, it is proposed that choosing an appropriate constant as the kernel size for the remaining terms is more effective. In addition, the experiment results when compared to the conventional algorithm show that the proposed method enhances learning performance by about 2dB of steady state MSE with the same convergence rate. In an experiment for channel models, the proposed method enhances performance by 4 dB so that the proposed method is more suitable for more complex or inferior conditions.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.24 no.7
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• pp.935-941
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• 2020

People estimation is important to provide IoT services. Most people counting technologies use camera or sensor data. However, the conventional technologies have the disadvantages of invasion of privacy and the need to install extra infrastructure. This paper proposes a method for estimating the number of people using a Wi-Fi AP. We use channel state information of Wi-Fi and analyze that using deep learning technology. It can be achieved by pre-installed Wi-Fi infrastructure that reduce cost for people estimation and privacy infringement. The proposed algorithm uses a k-binding data for pre-processing process and a 1D-CNN learning model. Two APs were installed to analyze the estimation results of six people. The result of the accurate number estimation was 64.8%, but the result of classifying the number of people into classes showed a high result of 84.5%. This algorithm is expected to be applicable to estimate the density of people in a small space.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.15 no.11
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• pp.3950-3969
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• 2021

Radio Frequency (RF)-based indoor localization technologies play significant roles in various Internet of Things (IoT) services (e.g., location-based service). Most such technologies require that all the devices comply with a specified technology (e.g., WiFi, ZigBee, and Bluetooth). However, this requirement limits its application scenarios in today's IoT context where multiple devices complied with different standards coexist in a shared environment. To bridge the gap, in this paper, we propose a cross-technology localization approach, which is able to localize target nodes using a different type of devices. Specifically, the proposed framework reuses the existing WiFi infrastructure without introducing additional cost to localize Non-WiFi device (i.e., ZigBee). The key idea is to leverage the interference between devices that share the same operating frequency (e.g., 2.4GHz). Such interference exhibits unique patterns that depend on the target device's location, thus it can be leveraged for cross-technology localization. The proposed framework uses Principal Components Analysis (PCA) to extract salient features of the received WiFi signals, and leverages Dynamic Time Warping (DTW), Gradient Boosting Regression Tree (GBRT) to improve the robustness of our system. We conduct experiments in real scenario and investigate the impact of different factors. Experimental results show that the average localization accuracy of our prototype can reach 1.54m, which demonstrates a promising direction of building cross-technology technologies to fulfill the needs of modern IoT context.