• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.39B no.12
• /
• pp.842-855
• /
• 2014

Recently, the progress of smart phone market has retarded by oversupply therefore wearable computer has been the focus of new growth engine. Wearable computing system is a complex fusion of a variety of technologies such as wireless network, embedded, sensor and new material. Because these technologies involves utilization and mobility in addition to quality characteristic in existing software, application of ISO/IEC 9126 is not perfect when assessing quality of wearable computer. In this study, author suggested new quality assessment model for wearable computer by sorting quality attribute in ISO/IEC 9126 and adding new quality attribute. For this, author investigated features and functional requirements related to wearable computer. and then author suggested quality standard and metrics by identifying quality characteristic. Author confirmed practicality of quality assessment model by using suggested model in scenario and comparing quality assessment of three goods such as company S, L, G. This quality assessment model is expected to use guidelines for assessing quality of wearable computer.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.33 no.4A
• /
• pp.342-351
• /
• 2008

In this paper, a new handover procedure for OFDM-based multi-hop relay systems is proposed to reduce the handover overhead by distinguishing inter-cell handover event from intra-cell handover event at the level of physical layer using a hierarchical design concept of preamble. A Subcell ID concept for identifying RS in a cell is proposed in the design of hierarchical manner, in addition to the existing Cell ID for identifying BS. The decision on either inter-cell handover or intra-cell handover is made by the signal quality measure of CBINR(Carrier of BS to Interference and Noise Ratio) and CRINR(Carrier of RS to Interference and Noise Ratio), provided by the hierarchical preamble. The proposed handover procedure can simplify scanning procedure and skip/simplify network re-entry procedure (capability negotiation, authorization, registration), resulting in a significant reduction of handover overhead.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.33 no.4A
• /
• pp.387-393
• /
• 2008

In this paper, we present an SDR (Software Defined Radio) handset modem platform which supports communication systems such as HSDPA (High Speed Downlink Packet Access), and WiBro (Wireless Broadband Portable Internet). The proposed SDR platform employs DSPs (Digital Signal Processors), FPGAs (Field Programmable Gate Arrays), and microprocessors in such a way that the various communication functions like HSDPA and WiBro can be programmed and downloaded to the hardware platform. The proposed SDR platform can be used for functional verification of the physical layers of the mobile handset system in the mobile communication network. We first demonstrate the receiving structure of the physical layer of the HSDPA and WiBro system. Then, the hardware implementation of the proposed SDR platform is shown with functions and optimized signal flows required at each mode. Finally, the link performance of each mode operating on the proposed SDR platform is presented through the internal loopback tests with the test vectors. The experimental performance has been compared with the computer simulation results.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.38A no.1
• /
• pp.33-43
• /
• 2013

This paper proposes a distributed MAC protocol called Carrier Sensing Multiple Access with Collision Resolution (CSMA/CR) considering fully-connected single hop network environments for next-generation wireless LAN with high density of stations. The proposed CSMA/CR is compatible with the conventional MAC protocols by observing the operation of CSMA/CA and is able to detect a collision promptly without RTS/CTS exchange by applying the technique of CSMA/CD to wireless environments. Moreover, once a collision is detected, the dedicated resource is allocated to the next transmission and so the collision that may occur again is resolved. We investigate some implementation issues for the practicality of CSMA/CR and compare it with the typical distributed MAC protocols. The simulation results show that the proposed CSMA/CR has a low overhead as detecting a collision without the RTS/CTS exploitation and achieves always the best throughput regardless of the number of access stations, by using the reservation-based collision resolution technique.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.38B no.12
• /
• pp.954-961
• /
• 2013

In this paper, we propose a new learning method using a variable learning to improve pattern recognition in the FCSR(Fast Commit Slow Recode) learning method of the Fuzzy ART. Traditional learning methods have used a fixed learning rate in updating weight vector(representative pattern). In the traditional method, the weight vector will be updated with a fixed learning rate regardless of the degree of similarity of the input pattern and the representative pattern in the category. In this case, the updated weight vector is greatly influenced from the input pattern where it is on the boundary of the category. Thus, in noisy environments, this method has a problem in increasing unnecessary categories and reducing pattern recognition capacity. In the proposed method, the lower similarity between the representative pattern and input pattern is, the lower input pattern contributes for updating weight vector. As a result, this results in suppressing the unnecessary category proliferation and improving pattern recognition capacity of the Fuzzy ART in noisy environments.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.38C no.11
• /
• pp.939-954
• /
• 2013

Korean military is developing the next generation military satellite communications system in order to achieve the requirements of future military satellite communication such as high speed, high capacity, survivability, all IP networking, and on-the-move. In this paper, we survey and analyze the research interests about optimal resource allocation and IP networking such as MF-TDMA, random access, satellite IP routing, and PEP. Conventional researches have focused on the increase in channel throughput and efficiency. In addition to these measurements, we consider heterogeneous satellite terminals, full mesh topology, distributed network, anti-jamming, and the like which are the special characteristics of the next generation military satellite communications system. Based on this, we present key research issues and evaluation on the issues by simulation.

• Journal of Communications and Networks
• /
• v.15 no.5
• /
• pp.476-485
• /
• 2013

In this paper, the effective capacity of a multiple-input multiple-output (MIMO) system in two different cases with receive antenna selection (RAS) and transmit antenna selection (TAS) schemes is investigated. A closed-form solution for the maximum constant arrival rate of this network with statistical delay quality of service (QoS) constraint is extracted in the quasi-static fading channel. This study is conducted in two different cases.When channel state information (CSI) is not available at the MIMO transmitter, implementation of TAS is difficult. Therefore, RAS scheme is employed and one antenna with the maximum instantaneous signal to noise ratio is chosen at the receiver. On the other hand, when CSI is available at the transmitter, TAS scheme is executed. In this case, one antenna is selected at the transmitter. Moreover, an optimal power-control policy is applied to the selected antenna and the effective capacity of the MIMO system is derived. Finally, this optimal power adaptation and the effective capacity are investigated in two asymptotic cases with the loose and strict QoS requirements. In particular, we show that in the TAS scheme with the loose QoS restriction, the effective capacity converges to the ergodic capacity. Then, an exact closed-form solution is obtained for the ergodic capacity of the channel here.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.42 no.2
• /
• pp.444-452
• /
• 2017

Recently, a demand of Internet-of-things (IoT) rises dramatically and an interest in Low Power Wide Area (LPWA) grows larger accordingly. In this paper, performance in LoRa which is included in LPWA standard is analyzed. Particularly, after measuring Received Signal Strength Indication (RSSI) of received signal on Line-of-sight (LoS) and Non-line-of-sight (NLoS) environment and it is compared with RSSI which theoretical path loss model is applied to. Among many path loss models, the simulation for theoretical RSSI use Log-distance, Two-ray model and Okumura-Hata model that is based on the test database. Consequently, the result of Okumura-Hata model is the most similar with the measured RSSI. When a network based on LoRa is built, this result can used to decide optimal node arrangement.

• The Transactions of the Korean Institute of Electrical Engineers D
• /
• v.51 no.11
• /
• pp.521-527
• /
• 2002

The Hemodialysis system is the device for the patients who have suffered from end stage renal failure as the kidney which removes the waste products in a human body. The existing hemodialysis is based on a 8-bit micro-controller and it is not a touch-screen type but a manual type. This paper is focused on hemodialysis system based on high control and expension embedded system. The whole system consists of main control unit and sub control unit(dialysis control unit, blood control unit, monitoring control unit, networking unit). The dialysis control unit, blood control unit, monitoring control unit are processed by 3 microcontrollers and network unit is for monitoring a renal failure patient's condition. For the evaluation of the system performance, the saline was pured into blood unit and then water removal rate, conductivity and temperature of hemodialysis liquid were measured 10 times in an each state suing the UF pump in the fluid unit varing the quantity of saline to 1000cc, 2000cc, 3000cc and 4000cc. As a result, the rates of water removal are 98.6% in condition of 000cc saline, 96.9% in 2000cc, 98.9% in 3000cc and 98.3% in 4000cc. The conductivities of hemodialysis liquid are 99.6% in the first to third condition and 99.7% in the forth condition. The temperatures of hemodialysis liquid are 99.8% in the first to third condition and 99.6% in th forth condition.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.15 no.10
• /
• pp.889-895
• /
• 2002

Wafer level packaging is gain mote momentum as a low cost, high performance solution for RF-MEMS devices. In this work, the flip-chip method was used for the wafer level packaging of RF-MEMS devices on the quartz substrate with low losses. For analyzing the EM (electromagnetic) characteristic of proposed packaging structure, we got the 3D structure simulation using FEM (finite element method). The electric field distribution of CPW and hole feed-through at 3 GHz were concentrated on the hole and the CPW. The reflection loss of the package was totally below 23 dB and the insertion loss that presents the signal transmission characteristic is above 0.06 dB. The 4-inch Pyrex glass was used as a package substrate and it was punched with air-blast with 250${\mu}{\textrm}{m}$ diameter holes. We made the vortical feed-throughs to reduce the electric path length and parasitic parameters. The vias were filled with plating gold. The package substrate was bonded with the silicon substrate with the B-stage epoxy. The loss of the overall package structure was tested with a network analyzer and was within 0.05 dB. This structure can be used for wafer level packaging of not only the RF-MEMS devices but also the MEMS devices.