• ETRI Journal
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• v.36 no.2
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• pp.317-320
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• 2014

A balanced RF duplexer with low interference in an extremely narrow bandgap is proposed. The Long-Term Evolution band-7 duplexer should be designed to prevent the co-existence problem with the WiFi band, whose fractional bandgap corresponds to only 0.7%. By implementing a hybrid bulk acoustic wave (BAW) structure, the temperature coefficient of frequency (TCF) value of the duplexer is successfully reduced and the suppressed interference for the narrow bandgap is performed. To achieve an RF duplexer with balanced Rx output topology, we also propose a novel balanced BAW Rx topology and RF circuit block. The novel balanced Rx filter is designed with both lattice- and ladder-type configurations to ensure excellent attenuation. The RF circuit block, which is located between the antenna and the Rx filter, is developed to simultaneously function as a balance-tounbalance transformer and a phase shift network. The size of the fabricated duplexer is as small as $2.0mm{\times}1.6mm$. The maximum insertion loss of the duplexer is as low as 2.4 dB in the Tx band, and the minimum attenuation in the WiFi band is as high as 36.8 dB. The TCF value is considerably lowered to $-16.9ppm/^{\circ}C$.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.6
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• pp.1449-1454
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• 2015

Virtualization lacks capabilities for enabling the application to scale efficiently because of new applications components which are raised to be configured on demand. In this paper, we propose an architecture that affords mobile app based on nomadic smartphone using not only mobile cloud computing-cloudlet architecture but also a dedicated platform that relies on using virtual private mobile networks to provide reliable connectivity through LTE(Long Term Evolution) wireless communication. The design architecture lies with how the cloudlet host discovers service and sends out the cloudlet IP and port while locating the user mobile device. We demonstrate the effectiveness of the proposed architecture by implementing an android application responsible of real time analysis by using a vehicle to applications smartphone interface approach that considers the smartphone to act as a remote users which passes driver inputs and delivers outputs from external applications.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.11
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• pp.3876-3895
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• 2014

Recently, Heterogeneous Network (HetNet) with Coordinated Multi-Point (CoMP) scheme is introduced into Long Term Evolution-Advanced (LTE-A) systems to improve digital services for User Equipments (UEs), especially for cell-edge UEs. However, Radio Resource Management (RRM), including Resource Block (RB) scheduling and Power Allocation (PA), in this scenario becomes challenging, due to the intercell cooperation. In this paper, we investigate the RRM problem for downlink transmission of HetNet system with Joint Processing (JP) CoMP (both joint transmission and dynamic cell selection schemes), aiming at maximizing weighted sum data rate under the constraints of both transmission power and backhaul capacity. First, joint RB scheduling and PA problem is formulated as a constrained Mixed Integer Programming (MIP) which is NP-hard. To simplify the formulation problem, we decompose it into two problems of RB scheduling and PA. For RB scheduling, we propose an algorithm with less computational complexity to achieve a suboptimal solution. Then, according to the obtained scheduling results, we present an iterative Karush-Kuhn-Tucker (KKT) method to solve the PA problem. Extensive simulations are conducted to verify the effectiveness and efficiency of the proposed algorithms. Two kinds of JP CoMP schemes are compared with a non-CoMP greedy scheme (max capacity scheme). Simulation results prove that the CoMP schemes with the proposed RRM algorithms dramatically enhance data rate of cell-edge UEs, thereby improving UEs' fairness of data rate. Also, it is shown that the proposed PA algorithms can decrease power consumption of transmission antennas without loss of transmission performance.

• JSTS:Journal of Semiconductor Technology and Science
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• v.14 no.6
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• pp.802-809
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• 2014

This paper presents a dual-mode bias modulator (BM) for complementary metal oxide semiconductor (CMOS) power amplifiers (PAs). The BM includes a hybrid buck converter and a normal buck converter for an envelope tracking (ET) mode for high output power and for an average power tracking (APT) mode for low output power, respectively. The dual-mode BM and CMOS PA are designed using a $0.18-{\mu}m$ CMOS process for the 1.75 GHz band. For the 16-QAM LTE signal with a peak-to-average power ratio of 7.3 dB and a bandwidth of 5 MHz, the PA with the ET mode exhibited a poweradded efficiency (PAE) of 39.2%, an EVM of 4.8%, a gain of 19.0 dB, and an adjacent channel leakage power ratio of -30 dBc at an average output power of 22 dBm, while the stand-alone PA has a PAE of 8% lower at the same condition. The PA with APT mode has a PAE of 21.3%, which is an improvement of 13.4% from that of the stand-alone PA at an output power of 13 dBm.

• The Journal of the Korea institute of electronic communication sciences
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• v.7 no.1
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• pp.135-139
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• 2012

A majority of 4G Mobile communication manufacturers have launched separated-type base stations composed of DU (digital unit) and RU (ratio unit). DUs are usually installed in the central office, while RUs with antennas are installed on the top of building or pole. Therefore, the allowable distance between DU and RU is very important for cell planning. In this paper, we analyze the allowable distance between DU and RU induced by closed-loop MIMO (mulitple input multiple output) technology in 4G FDD (frequency division duplexing) mobile communication systems. In conclusion, the distance limit between DU and RU is dependent on the frequency of the wireless communication, and the allowable distance is about 11 km when assuming the operating frequency is 2 GHz.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.9
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• pp.2967-2981
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• 2014

Device-to-Device (D2D) communication is a technology component for long-term evolution-advanced (LTE-A). In D2D communication, users in close proximity to each other can communicate directly without going through a base station; such direct communication can improve spectral efficiency. Although D2D communication brings improvement in spectral efficiency, it also causes interference to the cellular network as a result of spectrum sharing. In particularly, D2D communication can generate interference for each D2D pair when the common wireless medium in a co-located limited area is accessed. Even though the interference management for between the D2D pair and cellular networks has been proposed, the interference reducing methods have still not been fully studied for the D2D pairs. In this paper, we investigate the problem of D2D pair coexistence in which interference is considered between D2D pairs. Using a signal to interference model for a target D2D pair, we provide an analysis of the aggregated throughput of a dense D2D network. For a target D2D pair, we assume that the desired signal and interference signals obey multipath fading and shadow fading. Through analysis, we demonstrate the effect of cluster size such as the number of D2D pairs and the size of the considered area on the network performance. The analytical results are compared with computer simulations. Our work can be used for a rough guideline for controlling the system throughput in a dense D2D network environment.

• Journal of the Korea Convergence Society
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• v.10 no.10
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• pp.107-115
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• 2019

Effective construction safety management systems are desperately required for reducing damage caused by increasing safety accidents in construction sites. Safety accidents in construction sites can effectively protect if proactive measures are taken to prevent unauthorized worker access the expected hazardous area. In this study, we have developed a IoT(Internet of Things)-based dangerous zone alarming system for safety management in construction sites, which can be operated at low cost in large-scale sites as well as small and medium-sized construction sites. The development system utilizes a Zigbee-based beacon technology and cellular mobile communication technology to detect when authorized workers, unauthorized field workers or outsiders approaches hazardous zones. If somebody approaches the dangerous zones the system notifies immediately to the safety manager with a danger warning signal. It is expected that this system can effectively prevent safety accidents when applied to construction sites.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.5
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• pp.2241-2248
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• 2011

This paper describes the design of a palette-type 60watt high power amplifier module using gallium nitride(GaN) devices with high power and efficiency performances for WiMAX and LTE systems. The line-up for the high gain amplifier module consists of the pre-amplifier stage with low power and high gain, 8watt GaN driving amplifier stage, and 60watt GaN high power amplifier stage of Doherty structure with two 30watt GaN devices. The obtained gain is 61.4dB with an excellent gain flatness of ${\pm}$0.075dB over 2.5~2.68GHz. GaN devices and the Doherty structure are adopted for the improvement of high efficiency and output power. The measurement for the fabricated high power amplifier module of palette type is performed using the widely known WiMAX signal all over the world. In the example of RRH(remote radio head) application of the fabricated amplifier module, the measured efficiency is 37~38% with the 10watts of modulated output power. It is shown that when the fabricated amplifier module is activated with a digital predistorter(DPD), the measured ACLR is better than 46dBc under the 10watts of modulated output power.

• Journal of Broadcast Engineering
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• v.18 no.2
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• pp.215-224
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• 2013

With the rising popularity of smart-phones, the supply of Internet protocol television is largely increased and it causes the wireless communication network load to be increased. To overcome such an overloading problem, 3GPP is now working on the standardization of MBMS since LTE Release 6 specification. MBMS has good performance in bandwidth efficiency by sharing the same bandwidth with the mulitple MBMS users having the same content. According to the proposed algorithm, in heterogeneous networks having a dispersed Single-cell MBMS where 3GPP network and Wi-Fi network are mixed, if the number of MBMS users, who are belonging to cells supporting a dispersed Single-cell MBMS, is more than a specified threshold, the MBMS priority policy is operated. Otherwise, the Wi-Fi priority policy is executed. As the simulation results show both the increase of total available bandwidth ratio and the decrease of network usage cost, it is confirmed that the proposed scheme allows the network efficiency to be maximized.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.32 no.1
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• pp.78-88
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• 2022

Objectives: To develop the smart sensor to protect worker's health from chemical exposure by adopting ICT (Information and Communications Technology) technologies. Methods: To develope real-time chemical exposure monitoring system, IoT (Internet of Things) sensor technology and regulations were reviewed. We developed and produced smart sensor. A smart sensor is a system consisting of a sensor unit, a communication unit, and a platform. To verify the performance of smart sensors, each sensor has been certified by the Korea Laboratory Accreditation Scheme (KOLAS). Results: Chemicals (TVOC; Total Volatile Organic Compounds, Cl₂: Chlorine, HF: Hydrogen fluoride and HCN: Hydrogen cyanide) were selected according to a priority logic (KOSHA Alert, acute poisoning statistics, literature review). Notifications were set according to OEL (occupational exposure limit). Sensors were selected based on OEL and the capabilities of the sensors. Communication is designed to use LTE (Long Term Evolution) and Wi-Fi at the same time for convenience. Electronic platform were applied to build this monitoring system. Conclusions: Real-time monitoring system for OEL of hazardous chemicals in workplace was developed. Smart sensor can detect chemicals to complement monitoring of traditional workplace environmental monitoring such as short term and peak exposure. Further research is needed to expand the scope of application, improve reliability, and systematically application.