• Journal of Korea Society of Industrial Information Systems
• /
• v.17 no.2
• /
• pp.19-27
• /
• 2012

In railway tunnel environment, the reliability of a high-data-rate and real-time train-to-wayside communication should be maintained especially when high-speed train moves along the track. In China and Europe, the communication frequency around 900 MHz is widely used for railway applications. At this carrier frequency band, both of the solutions based on continuously laid leaky coaxial cable (LCX) and discretely installed base-station antennas (BSAs), are applied in tunnel radio coverage. Many available works have concentrated on the radio-wave propagation in tunnels by different kinds of prediction models. Most of them solve this problem as natural propagation in a relatively large hollow waveguide, by neglecting the transmitting/receiving (Tx/Rx) components. However, within such confined areas like railway tunnels especially loaded with train, the complex communication environment becomes an important factor that would affect the quality of the signal transmission. This paper will apply a full-wave numerical method to this case, for considering the BSA or LCX, train antennas and their interacted environments, such as the locomotive body, overhead line for power supply, locomotive pantograph, steel rails, ballastless track, tunnel walls, etc.. Involving finite-difference time-domain (FDTD) method and uni-axial anisotropic perfectly matched layer (UPML) technique, the entire wireless RF downlinks of BSA and LCX to tunnel space to train antenna are precisely modeled (so-called integrative modeling technique, IMT). When exciting the BSA and LCX separately, the field distributions of some cross-sections in a rectangular tunnel are presented. It can be found that the influence of the locomotive body and other tunnel environments is very significant. The field coverage on the locomotive roof plane where the train antennas mounted, seems more homogenous when the side-laying position of the BSA or LCX is much higher. Also, much smoother field coverage solution is achieved by choosing LCX for its characteristic of more homogenous electromagnetic wave radiation.

• Journal of the Korea Society of Computer and Information
• /
• v.15 no.3
• /
• pp.55-63
• /
• 2010

On Handoff, existing AP search has chosen one of various APs according to signal strength. However IEEE 802.11 uses Medium Access method with CSMA/CA(Carrier Sensing Multiple Access /Collision Avoidance) that competes to obtain a channel by sharing common medium. For that reason, network performance is heavily affected by the number of nodes and network congestion aside from signal strength. Consequently, in this paper we propose the method that choose one AP which ensures more improved network performance and set up a link, reflecting AP network information in Handoff area, on Handoff in the process of AP selection. We also demonstrate through simulation that it gets maximum performance even in the wireless network which many users concurrently access to, and it has considerable effects on aspects of resources and network management by distribution of users.

• Journal of the Institute of Convergence Signal Processing
• /
• v.5 no.4
• /
• pp.333-337
• /
• 2004

This paper describe a design of 5GHz OFDM baseband chip for IEEE 802.11a wireless LAN. The proposed device is consists of transmitter and receiver within a single FPGA chip. We applied single tap equalizer that use Normalized LMS algorithm to remove ISI that happen at high speed data transmission. And also, we used carrier wave frequency offset algorithm that use training symbol to remove ICI. The simulation results show the correct transmission without errors the between transmitter and receiver And we can remarkably reduce the number of register through the synthesized circuits by using DSP block and EMB(Embedded Memory Block). The target device for implementation of the synthesized circuits is Altera Stratix EPIS25FC672 FPGA and design platform is VHDL.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.48 no.6
• /
• pp.1-5
• /
• 2011

We present the Multi-band orthogonal frequency division multiplexing ultra-wideband (MB-OFDM UWB) technology for increasing the transmission reach of wireless speaker systems. The proposed scheme adopts the Reed-Solomon coding for preventing the random error perfectly and shows the SNR gain in low bit error rate (BER) especially. So, we can increase the maximum reach of MB-OFDM UWB technology since the receiver sensitivity is improved. The simulation environment includes most effects of realistic channel environments such as Additive White Gaussian Noise (AWGN), CM1 channel model, Sampling frequency offset (SFO), Carrier frequency offset (CFO) to improve the simulation accuracy. The simulation results show that the proposed scheme can give a maximum 2 dB SNR gain and increase the transmission reach up to 12.6m.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2013.10a
• /
• pp.1033-1036
• /
• 2013

A study about collision resolution is needed because huge file, video and multimedia information are transmitted to wireless LAN. CSMA/CR protocol guarantees fairness, but doesn't consider QoS. To practicalize CSMA/CR protocol in saturation fully-connected single hop network environments, this paper proposes method of collision compensation. previous CSMA/CR protocol chooses CR Slot only considering fairness, but this paper chooses front CR Slot for compensation of collision to station experiencing collisions. The station transmits jam signal and has channel priority of transmission. So transmitting efficiency and successful transmission probability rise. This proposed simple method can offer benefit to station experiencing collisions without additional hardware cost.

• Journal of the Institute of Electronics and Information Engineers
• /
• v.52 no.11
• /
• pp.12-19
• /
• 2015

In network-centric warfare, the communication network has played a significant role in defeating an enemy. Especially, the urgent and important data should be preferentially delivered in time. Thus, we proposed a priority MAC protocol based on CSMA/CA with Binary Exponential Back-off for tactical wireless networks. This MAC protocol suggested a PCW(Prioritized Contention Window) with differentiated back-off time by priority and a RBR(Repetitive Back-off Reset) to reset the remaining back-off time. The results showed that this proposed MAC has higher performance than those of DCF(Distributed Coordination Function) in the transmission success rate and the number of control packet transmission by reducing the packet collision. Thus, it produced more effective power consumption. In comparison with DCF, this proposed protocol is more suitable in high-traffic network.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.30 no.3
• /
• pp.215-222
• /
• 2019

A frequency hopping(FH) signal can change its carrier frequency during transmission and has spread-spectrum characteristics in these frequency bands. Therefore, FH signals are widely used in applications that require low-probability-of-intercept(LPI) and anti-jamming (AJ) abilities in wireless communication environments. In this study, the authors propose a method for generating hopping information (HI), which includes start time, dwell time, and hopping frequency for unknown FH signals. The proposed blind HI generation method produces signal detection information based on the spectrum data and then extracts HI using operational procedures for estimating the target FH signal's status, such as appearance, maintenance, and termination. Further, simulation results demonstrate that the proposed method provides accurate HI without detection omissions for various FH signals.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.17 no.6
• /
• pp.1105-1112
• /
• 2022

Field data monitoring systems such as renewable energy generation and smart farm integrated control are developing from PC and server to mobile first, and various wireless communication and application services have emerged with the development of IoT technology. Low-power wide-area networks are services optimized for low-power, low-capacity, and low-speed data transmission, and data collected in the field is transmitted to designated storage servers or cloud-based data platforms, enabling data monitoring. In this paper, we implement an IoT repeater that collects field data with a single device and transmits it to a wireless carrier cloud data flat using a low-power wide-area network, and a monitoring app using it. Using this, the system configuration is simpler, the cost of deployment and operation is lower, and effective data accumulation is possible.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.37 no.4
• /
• pp.302-307
• /
• 2001

The underwater background noise measured in Geoje and Tongyoung diving fishing ground from May to December, 2000 and analyzed to get optimum carrier frequency and transmitter power level for underwater wireless telephone design. The results obtained are summarized as follows: 1. At the Geoje and Tongyoung diving fishing ground, the lowest ambient noise band was 25~30kHz with 57dB and 52dB re 1$\mu$Pa, respectively. 2. At the Geoje and Tongyoung diving fishing ground, the lowest noise band during fishing activity was 67dB and 62dB re 1$\mu$Pa, respectively. 3. At the Geoje diving fishing ground, the noise of water jetter which is a digging machine for subbottom shells was 102dB re 1$\mu$Pa. 4. Considering the design parameters of underwater wireless telephone, it is found that the optimum carrier frequency band is around 30kHz and the transmitter source level should be at least 131dB re 1$\mu$Pa for 500m range telephone.

• Journal of Advanced Navigation Technology
• /
• v.5 no.1
• /
• pp.11-18
• /
• 2001

In this paper, we evaluated the performance of Orthogonal MC/FH-CDMA system considering the hit of frequency hopping patterns, and obtained the degree of the performance improvement by adopting TCM scheme under frequency selective Rayleigh fading channel. From the performance analysis, it is known that the error performance is improved, since delay time relative to symbol time is reduced as the number of carrier is increased. On the other hand, it is found that BER performance is improved about $5{\times}10^{-2}$ degree by adopting TCM scheme, and higher S/N is required if the QoS of voice (BER = $10^{-3}$) must be achieved.