• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.9 s.100
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• pp.932-940
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• 2005

In this paper, a planar half-circle shape ultra-wideband(UWB) antenna fed by CPW is designed, fabricated and measured for UWB communications. Within the UWB band(3.1 GHz${\~}$10.6 GHz), 5.15 GHz${\~}$5.825 GHz frequency band is used by IEEE 802.1la WLAN applications. It may be necessary to notch out this band to avoid interference with IEEE 802.1la WLAN. Therefore, we have proposed three kinds of UWB antennas having a notch function, such as a rectangular slot, a hat-shaped slot a circle-shaped slot. The notch frequency of the proposed antenna can be adjusted by controlling the slot length or slot width. From the measured results, the proposed antennas show a good gain flatness except the IEEE 802.1la WLAN frequency band and have a reasonable agreement with simulated results.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.6
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• pp.1333-1340
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• 2015

IEEE 802.11 MAC(Media Access Control) defines DCF(Distributed Coordination Function) for data transmission control. BEB(Binary Exponential Backoff) algorithm of DCF has a problem that if the number of stations connected are over a certain threshold, it degrades network performance because of packet collisions caused from the minimum contention window size. To cope with this problem, we proposed a novel algorithm, named as VBS(Variable Backoff Stage) algorithm, which adjusts the rate of backoff stage increment depending on the number of stations associated with an AP(Access Point). Analytic model of proposed algorithm was derived and simulations on the BEB and the VBS algorithms have been conducted on the OFDM (Orthogonal Frequency Division Multiplexing) method. Simulation results showed that when the rate of backoff state increment was 5 and 10, the number of retransmission were reduced to 1/5 and 1/10 comparing to that of BEB, respectively. Our algorithm showed improvement of 19% and 18% in network utilization, respectively. Packet delay was reduced into 1/12.

• Journal of Advanced Navigation Technology
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• v.13 no.2
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• pp.238-243
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• 2009

Now, the production process systems are largely based on automatic system using the wired network. The production process systems using wired network has disadvantage that it is expensive when the installed and replaced equipment. The each equipment happens to repair cost for control and management in production processes. And the replaced equipment has also the additional expense and breaks production process. These problems are solved through wireless communication between the industrial equipments. So, we propose wireless production process system based on IEEE 802.15.4 technology. It solves a complicated space and stops by replaced equipment in the factory. Then we simulated and analyzed IEEE 802.15.4 for Industrial Equipment based on Wireless Network.

• The Journal of the Korea Contents Association
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• v.9 no.2
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• pp.10-17
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• 2009

This paper analyze the effect of frequency offset for the IEEE 802.15.4b LR-WPAN(Low-Rate Wireless Personal Area Network) with 915MHz bandwidth noncoherent DSSS O-QPSK based receiver system, and presents a compensation method with addition of differential filter to the system for compensation of frequency offset problem. DSSS PSSS-ASK and DSSS O-QPSK modulation techniques are accepted within the regularization of IEEE 802.15.4b. These new method can obtain 250kbps transmission rate. The DSSS O-QPSK modulation method that is used in this paper has no BER variation below 40ppm(frequency offset 36.6kHz), but if the offset frequency become high above 40ppm, then the system cannot have stable receiving condition due to worse BER. To solve this problem, we present a more stabilized receiver system at maximum frequency offset ${\pm}80ppm$ using MDDF unti a correlator of DSSS O-QPSK modulator. Moreover computer simulation results will be presented to evaluate the performance of the proposed algorithm unde various AWGN and frequency offset environment.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37B no.9
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• pp.723-733
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• 2012

In wireless ad hoc networks, packet loss and latency are frequently occurred by movement of node. As the number of transmission hops increases in these networks, the throughput is increasingly deteriorated. In this paper, we design the wireless ad hoc network system based on IEEE 802.16j MMR (Mobile Multi-hop Relay), which improves the network performance. Our wireless ad hoc network system used adaptively the nearest BS and Farthest BS scheduling algorithms for efficient data transmission and chose the optimal path that minimize data loss and latency. In order to evaluate performance of the wireless ad hoc network system based on IEEE 802.16j MMR, we used the LWX (Light Wimax) model of NS-2 simulator. Through the simulation, we analyzed the network performance for various scenarios.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.5
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• pp.425-432
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• 2014

The Enhanced Distributed Channel Access (EDCA) function of IEEE 802.11e standard defines contention window (CW) for different Access Category (AC) limits to support Quality-of-Service (QoS). However, it have been remained the problem that the collision probability of transmission is increasing in congested network. Several different solutions have been proposed but the collision occurs among same priority queue within the same station to compete the channel access. This paper presents an APCA (Advanced Priority Collision Avoidance) algorithm for EDCA that increases the throughput in saturated situation. The proposed algorithm use reserved field's bits of FC(Frame Control) using IEEE 802.11e standard's RTS/CTS (Request to Send / Clear to Send) mechanism to avoid data collision. The simulation results show that the proposed algorithm improves the performance of EDCA in packet loss. Using Jain's fairness index formula, we also prove that the proposed APCA algorithm achieves the better fairness than EDCA method under network congested condition.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.2 s.332
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• pp.75-80
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• 2005

In this paper, 2-stage power amplifier has been designed for 5.8GHz wireless LAN application. The power amplifier PldB output power has 21.6dBm at 5.8GHz frequency. Also the power amplifier shows 17.6dB gain and -17.8dB input return loss at 5.725GHz to 5.825GHz. The OFDM modulation and transmission block have been modeled in order to analyse the relationship between the power amplifier distortion and output ACPR for the IEEE 802.11a wireless LAN. The nonlinear characteristic of the power amplifier has been modeled as AM-to-AM and AM-to-PM using the behavioral model, and the output spectrum is analysed with the phase distortion variation. Also, amplifier back-off value from PldB to satisfy the required IEEE 802.11a standard spectrum mask has been simulated with phase distortion, and the simulation data have been compared to the measurement result collected by using the pre-distortion technique.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.1
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• pp.175-181
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• 2015

In this paper, we develop a 2.4GHz ISM band wireless communication platform prototype based on embedded linux which support can be u-Hospital service. The developed system is available connecting between ARM920T processor board and FPGA board and linking IEEE 802.11b PHY board, AD/DA(10Bit) and RF(2.4GHz) board for wireless access. It is also can be utilized for the embedded system design with IEEE 802.11b/g Access Point(Option: IEEE 802.11a/b/g) test due to the Embedded Linux. Also, the developed system is possible to test and verify the radio access technology, Modem(OFDM etc) and IP(Intellectual Property) circuit. And make the most use of the system, we search for a expansion to that home and mobile healthcare, wellness service application.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.47 no.4
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• pp.63-70
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• 2010

In IEEE 802.11e system providing differentiated services, there exist some problems as follows; collision probability increase due to the increase in the number of nodes by employing CSMA/CA transmission mode, transmission speed declining tendency towards the worst of it, which is caused by different transmission mode and decrease of TCP transmission rate as the result of the link occupancy by UDP when TCP shares the link with UDP by the TCP’s flow control characteristic. In this thesis, the initial minimum and maximum CW are set differently according to the number of connected nodes in the network to avoid collisions and TXOP is adjusted according to the channel state, in which ACs with low priority but better channel state will get gradually more chances to transmit leading to optimal channel capacity. Also, by allowing higher priority for ACK frames which control the TCP transmission, the flow control becomes better because that reduces the channel occupancy by UDP flow, and by this, fair transmission is obtained from the result of the more fair transmission and active resource allocation.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2010.10a
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• pp.722-725
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• 2010

In this paper, BER performance and error convergence speed of layered LDPC(Low Density Parity Check) decoder which supports IEEE 802.16e WiMAX standard is analyzed, and optimal design conditions for hardware implementation are derived. A LDPC decoder is modeled and simulated at AWGN channel with QPSK modulation by Matlab. The parity check matrix(PCM) for IEEE 802.16e standard which has block lengths of 576, 1440, 2304 and code rates of 1/2, 2/3A, 2/3B, 3/4A, 3/4B, 5/6 are used. Fixed-point simulation results show that fixed-point bit-width should be more than 8 bits for acceptable decoding performance.