• International journal of advanced smart convergence
• /
• v.7 no.4
• /
• pp.27-39
• /
• 2018

Since the global positioning system (GPS) has been included in mobile devices (e.g., for car navigation, in smartphones, and in smart watches), the impact of personal GPS log data on daily life has been unprecedented. For example, such log data have been used to solve public problems, such as mass transit traffic patterns, finding optimum travelers' routes, and determining prospective business zones. However, a real-time analysis technique for GPS log data has been unattainable due to theoretical limitations. We introduced a machine learning model in order to resolve the limitation. In this paper presents a new, three-stage real-time prediction model for a person's daily route activity. In the first stage, a machine learning-based clustering algorithm is adopted for place detection. The training data set was a personal GPS tracking history. In the second stage, prediction of a new person's transient mode is studied. In the third stage, to represent the person's activity on those daily routes, inference rules are applied.

• JSTS:Journal of Semiconductor Technology and Science
• /
• v.14 no.6
• /
• pp.810-817
• /
• 2014

An on-chip current sensor with fast response time for the peak-current-mode buck regulator is proposed. The initial operating points of the peak current sensor are determined in advance by the valley current level, which is sensed by a valley current sensor. As a result, the proposed current sensor achieves a fast response time of less than 20 ns, and a sensing accuracy of over 90%. Applying the proposed current sensor, the peak-current-mode buck regulator for the mobile application is realized with an operating frequency of 2 MHz, an output voltage of 0.8 V, a maximum load current of 500 mA, and a peak efficiency of over 83%.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.35 no.11B
• /
• pp.1667-1675
• /
• 2010

This paper presents a high efficiency DC-DC buck converter for mobile device. The circuit employes simplified compensation circuit for its portability and for high efficiency at stand-by mode. This device operates at PFM mode when it enters stand-by mode(light load). In order to place the compensation circuit on chip, the capacitor multiplier method is employed, such that it can minimize the compensation block size of the error amplifier down to 30%. The measurement results show that the buck converter provides a peak efficiency of 93% on PWM mode, and 92.3% on PFM mode. The converter has been fabricated with a $0.35{\mu}m$ CMOS technology. The input voltage of the buck converter ranges from 2.5V to 3.3V and it generates the output of 3.3V.

• Journal of Digital Convergence
• /
• v.18 no.7
• /
• pp.215-222
• /
• 2020

The aim of this study was to develop a mobile application 'Beat Processing Device (BPD)' to record and quantify the data for the performance accuracy of rhythm production. BPD has been developed in three phases. First, we reviewed studies that used rhythm as main intervention strategy to improve cognitive functioning of older adults, and derived four basic rhythm idioms. Second, we developed an iOS-based mobile application, optimized the device, the instrument tone, and the measurement variables through preliminary test. Lastly, we tested the mobile application by comparing the performance data obtained from MIDI and BPD from 60 older adults. The device was shown to be reliable and consistent with other mode of measurement and analysis. Conclusively, BPD can be a useful tool for assessing rhythm production ability in the course of cognitive skills training.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.9 no.10
• /
• pp.4015-4033
• /
• 2015

The future mobile networks consist of hyper-dense heterogeneous and small cell networks of same or different radio access technologies (RAT). Integrating mobile networks of different RATs to provide seamless and smooth mobility service will be the target of future mobile converged network. Generally, handover from high-speed networks to low-speed networks faces many challenges from application perspective, such as abrupt bandwidth variation, packet loss, round trip time variation, connection disruption, and transmission blackout. Existing inter-RAT handover solutions cannot solve all the problems at the same time. Based on the high-layer convergence sublayer design, a new receiver-aided soft inter-RAT handover is proposed. This soft handover scheme takes advantage of multihoming ability of multi-mode mobile station (MS) to smooth handover procedure. In addition, handover procedure is seamless and applicable to frequent handover scenarios. The simulation results conducted in UMTS-WiMAX converged network scenario show that: in case of TCP traffics for handover from WiMAX to UMTS, not only handover latency and packet loss are eliminated completely, but also abrupt bandwidth/wireless RTT variation is smoothed. These delightful features make this soft handover scheme be a reasonable candidate of mobility management for future mobile converged networks.

• Journal of electromagnetic engineering and science
• /
• v.14 no.1
• /
• pp.9-14
• /
• 2014

This paper discusses the resonant characteristics, such as the resonant frequencies and Q factors, as well as tuning methods of the resonant frequency of the triple-mode dielectric resonators, for their possible application to compact bandpass filters for mobile communication systems. The resonators include spheres and cylindrical rods that can be applied to compact bandpass filters. These high Q ceramic resonators can replace the conventional coaxial type resonators, which are large sized and also have relatively low Q values. Both simulated and measured results show that the Q values of the sphere and rod reach 27,000 and 24,000, respectively. Decoupling of degenerate modes is also briefly discussed.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.6 no.2
• /
• pp.610-628
• /
• 2012

Dual carrier frequency offsets (CFOs) occur in multiple-input single-output (MISO)-mode DVB-T2 systems, where signals are transmitted simultaneously from two distributed transmitters in a single frequency network (SFN). In this paper, we first derive an optimal compensation frequency for dual CFOs. We also propose an algorithm that optimizes the compensation frequency for the MISO-mode DVB-T2 application. Its performance is compared with the conventional scheme by using a full DVB-T2 simulator.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.3 no.2
• /
• pp.291-304
• /
• 1999

In this work, a mathematical modeling of SAW coupled mode in SAW resonator filter, which is very useful in analyzing the characteristics of periodic electrode structure such as SAW reflective array and inter-digital transducers. was considered by mathematical analytic approach. The design and simulation method for resonator filter was also proposed by equivalent transduction matrix using this mathematical modeling. In order for a designer to simulate, and to design the coupled mode SAW resonator filters effectively that could be applied to mobile communication system, a design simulator for coupled mode filter was implemented by graphic user interface, and it was investigated by designing and analyzing practical SAW coupled mode resonator filter from a view point of application of this simulator.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.23 no.5
• /
• pp.570-582
• /
• 2012

In the communication, a reconfigurable antenna using two PIN diodes is presented for quad-band(GSM900/GSM1800/GSM1900/UMTS) mobile handset applications. The proposed antenna has a size $45{\times}11{\times}6mm^3$. By independently adjusting the on/off states of two PIN diodes located on the radiating element, the proposed structure can be operated in the PIFA and loop mode, respectively. The PIN diodes are replaced by conducting tape in order to verify the concept. In regards to the fabricated reconfigurable antenna, when operating in the PIFA mode, the measured results show that the 7 dB bandwidth is 8.62 %. which covers the GSM900(880~960 MHz) band. When operating in the loop mode, the measured results show that the 7 dB bandwidth is 26.36 %, which covers the GSM1800(1,710~1,880 MHz), GSM1900(1,850~1,990 MHz), and UMTS(1,920~2,170 MHz) bands, respectively.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.47 no.3
• /
• pp.51-57
• /
• 2010

A dual-mode direct conversion receiver is developed in $0.13\;{\mu}m$ RF CMOS process for IEEE 802.11n based wireless LAN and IEEE 802.16e based mobile WiMAX application. The RF receiver covers the frequency band between 2.3 and 2.7 GHz. Three-step gain control is realized in LNA by using current steering technique. Current bleeding technique is applied to the down-conversion mixer in order to lower the flicker noise. A frequency divide-by-2 circuit is included in the receiver for LO I/Q differential signal generation. The receiver consumes 56 mA at 1.4 V supply voltage including all LO buffers. Measured results show a power gain of 32 dB, a noise figure of 4.8 dB, a output $P_{1dB}$ of +6 dBm over the entire band.