• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.10C
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• pp.981-990
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• 2006

In this paper, we introduce the concept of a subcarrier-based virtual multiple antennas (SV-MIMO) for OFDM cellular systems, where the multiple antenna techniques are performed on a set of subcarriers, not on the actual multiple antennas. The virtual multiple antenna system can support multiple users simultaneously as well as reduce inter-cell interference (ICI) form adjacent cells with a single antenna. Also, this technique is easily extended to multiple antenna environments. The virtual multiple antenna techniques can be divided into a virtual smart antenna technique and a virtual MIMO technique. Especially, this method effectively reduces ICI at cell boundary with frequency reuse factor equal to 1, and can support flexible resource allocation depending on the amount of interference. It is shown by simulation that the proposed method is superior to conventional method under the same condition of data transmission.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.4
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• pp.1208-1222
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• 2014

Due to the low utilization and scarcity of frequency spectrum in current spectrum allocation methodology, cognitive radio networks (CRNs) have been proposed as a promising method to solve the problem, of which spectrum sensing is an important technology to utilize the precious spectrum resources. In order to protect the primary user from being interfered, most of the related works focus only on the restriction of the missed detection probability, which may causes over-protection of the primary user. Thus the interference probability is defined and the interference-aware sensing model is introduced in this paper. The interference-aware sensing model takes the spatial conditions into consideration, and can further improve the network performance with good spectrum reuse opportunity. Meanwhile, as so many fading factors affect the spectrum channel, errors are inevitably exist in the reporting channel in cooperative sensing, which is improper to be ignored. Motivated by the above, in this paper, we study the throughput tradeoff for interference-aware cognitive radio networks over imperfect reporting channel. For the cooperative spectrum sensing, the K-out-of-N fusion rule is used. By jointly optimizing the sensing time and the parameter K value, the maximum throughput can be achieved. Theoretical analysis is given to prove the feasibility of the optimization and computer simulations also shows that the maximum throughput can be achieved when the sensing time and the parameter of K value are both optimized.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.6
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• pp.1828-1847
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• 2014

Coordinated multi-point (CoMP) transmission has been regarded as a potential technology for LTE-Advanced. In frequency division duplexing systems, channel quantization is applied for reporting channel state information (CSI). Considering the dynamic number of cooperation base stations (BSs), asymmetry feature of CoMP channels and high searching complexity, simply increasing the size of the codebook used in traditional multiple antenna systems to quantize the global CSI of CoMP systems directly is infeasible. Per-cell codebook based channel quantization to quantize local CSI for each BS separately is an effective method. In this paper, the theoretical upper bounds of system throughput are derived for two codeword selection schemes, independent codeword selection (ICS) and joint codeword selection (JCS), respectively. The feedback overhead and selection complexity of these two schemes are analyzed. In the simulation, the system throughput of ICS and JCS is compared. Both analysis and simulation results show that JCS has a better tradeoff between system throughput and feedback overhead. The ICS has obvious advantage in complexity, but it needs additional phase information (PI) feedback for obtaining the approximate system throughput with JCS. Under the same number of feedback bits constraint, allocating the number of bits for channel direction information (CDI) and PI quantization can increase the system throughput, but ICS is still inferior to JCS. Based on theoretical analysis and simulation results, some recommendations are given with regard to the application of each scheme respectively.

• Korean Journal of Construction Engineering and Management
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• v.13 no.1
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• pp.24-35
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• 2012

RFID-based logistics is increasingly adopted in various areas of the construction industry as a technology that can improve effectiveness and efficiency of construction logistics. However, the technology is not widely adopted yet compared to the potential of RFID applications in the construction industry that the existing research has shown. Since the validation and verification of the benefit from RFID applications were biased toward the productivity of managers, more wide aspect of validation and verification is necessary. Therefore, the objective of this paper is to show how much impact the RFID-based logistics management system can have on resource leveling and allocation that have a direct impact on a construction project as well as the managers' productivity improvement that was shown by the existing research. This paper also discusses issues arisen during the test process.

• Journal of Energy Engineering
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• v.29 no.2
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• pp.23-29
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• 2020

In this study, the last 10 years of news data on fine dust was collected and 80 topics are selected through LDA analysis. As a result, weather-related information made up the main words for the topic, and we can see that fine dust becomes a big issue below 10 degrees Celsius. The frequency of exposure to the media and the maximum concentration of fine dust are correlated with positive. Topics related to fine dust reduction measures and the government's comprehensive measures over the past decade, topics related to products such as air purifiers related to fine dust, topics related to policies protecting vulnerable people from fine dust, and topics on fine dust reduction through R&D were found to be major topics. Measures against fine dust as a social issue can be seen to be closely related to the government's policy.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.12 no.1
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• pp.45-50
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• 2012

In the current wireless communication technology, the digital radio system replaces the analog radio broadcasting. Since the in-band digital radio systems are used in the existing analog radio frequency band, interference problems of digital radio are caused. It is important to effectively analyze the interference. In this paper, to analyze SINR and BEP (bit error probability) of digital radio system, we propose the analysis method considering angular effect. The angular effect means a method to analyze the interference when the receiver is located in different directions around the transmitter. These results are able to give basic information for the allocation of digital radio networks.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.17 no.2
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• pp.1-6
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• 2017

Due to the recent advances in IoT technologies, reducing power consumption in battery-based IoT devices becomes an important issue. An IoT device is a kind of real-time systems, and processor voltage scaling is known to be effective in reducing power consumption. However, recent research has shown that power consumption in memory increases dramatically in such systems. This paper aims at combining processor voltage scaling and low-power NVRAM technologies to reduce power consumption further. Our main idea is that if a task is schedulable in a lower voltage mode of a processor, we can expect that the task will still be schedulable even on slow NVRAM memory. We incorporate the NVRAM memory allocation problem into processor voltage scaling, and evaluate the effectiveness of the combined approach.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.12
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• pp.39-44
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• 2010

In LTE-Advanced systems, every sector uses the entire range of the frequency resource, and when the UEs are located at a cell edge, user throughputs degrade due to the interferences from the adjacent cells. In this paper, we propose a combined scheme for inter-cell interference avoidance and power control. In the proposed algorithm, the sectors consist of the right edge, the left edge and the center for resource allocation and we control the transmission power to improve the user throughputs at the edge of each cell. Using a system level simulation, we analyze low 5th percentile and average user throughputs of the UEs who are located the cell, center and edge when the inter-cell interference avoidance and the power control are combined.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.7A
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• pp.1028-1036
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• 2000

In this paper, an error-resilient image compression technique using wavelet transform is proposed. The zerotree technique that uses properties of statistics, energy and directions of wavelet coefficients in the space-frequency domain shows effective compression results. Since it is highly sensitive to the propagation of channel errors, evena single bit error degrades the whole image quality severely. In the proposed algorithm, the image is encoded by the SPIHT(Set Partitioning in Hierarchical Trees) algorithm using the zerotree coding technique. Encoded bitstreams are partitioned into some blocks using the subband correlations and then fixed-length blocks are made by using the effective bit reorganization algorithm. finally, an effective bit allocation technique is used to limit error propagation in each block. Therefore, in low BER the proposed algorithm shows similar compression performance to the zerotree compression technique and in high BER it shows better performance in terms of PSNR than the conventional methods.

• Journal of Digital Contents Society
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• v.14 no.2
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• pp.191-197
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• 2013

To complete the "anywhere" mobile service there should not be shaded areas. However, it is never economical to deploy BS's (Base Stations) in a low population density area due to the low resource utilization. We propose a design technique to install RS's(Relay Stations) which are cheaper than BS's and find the condition in which the proposed technique is acceptible. The proposed design technique aims to allocate the frequency and time resources to RS's to minimize the transmission rate degradation due to interferences between RS's as well as to maximize the parallelism in transmission. We showed by simulation that the proposed technique achieves cost benefits when the expected traffic is less than 20.32 percent of the total BS capacity. The proposed technique is compatible with the IEEE 802.16j, thus can be extended to multi-hop configuration.