• Journal of Internet Computing and Services
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• v.6 no.5
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• pp.133-141
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• 2005

In this paper, we designed about OFDM/QPSK image transmission system simulator embedded watermark in wireless channel environment. Channel environment used OFDM/QPSK still image transmission system considering AWGN, Multi-path fading. And, we analyzed effect of still image and watermark information in considered channel environment. Watermark information is coded by DM-SS (Direct Matric/Spread Spectrum) image watermarking scheme, Also, we used interleaving scheme for mitigating the degradation in watermarking data under wireless channel. As a results, we could know that PSNR of watermark image improved of about 1dB by 54.2371dB then apply interleaving in same multi-path fading environment.

• Journal of Internet Computing and Services
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• v.10 no.1
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• pp.33-41
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• 2009

Signals transmitted from access point (AP) or stations in different wireless LANs (WLAN) interfere each other when the WLANs are closely installed. When they are configured to use the same channel, signals from an WLAN get collided with signals from other WLANs so that the delay increases to user stations and the throughput decreases. In this paper, we propose a method in which an AP in a basic service set (BSS) detects other BSSs using the same channel and switches to a different channel not being occupied by any other BSS. We can avoid using the same channel with other BSS in spacially overlapped BSS environment. The proposed scheme is simulated and its characteristics are described with the analysis of the result. The results measured in terms of throughput show that the problems in overlapped wireless LANs can be resolved with the proposed method.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.12
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• pp.4432-4450
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• 2014

It is widely observed that in practical wireless cooperative communication systems, different links may experience different fading characteristics. In this paper, we investigate into the outage probability and channel capacity of two-way amplify-and-forward (TWAF) relaying systems operating over a mixed asymmetric Rician and Rayleigh fading scenario, with different amplification policies (AP) adopted at the relay, respectively. As TWAF relay network carries concurrent traffics towards two opposite directions, both end-to-end and overall performance metrics were considered. In detail, both uniform exact expressions and simplified asymptotic expressions for the end-to-end outage probability (OP) were presented, based on which the system overall OP was studied under the condition of the two source nodes having non-identical traffic requirements. Furthermore, exact expressions for tight lower bounds as well as high SNR approximations of channel capacity of the considered scenario were presented. For both OP and channel capacity, with different APs, effective power allocation (PA) schemes under different constraints were given to optimize the system performance. Extensive simulations were carried out to verify the analytical results and to demonstrate the impact of channel asymmetry on the system performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.5
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• pp.964-973
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• 2015

Ship Area Network(SAN) can monitor the status of ship in real time and minimize the maintenance costs by connecting various devices to the network. In particular, among researches on SAN, Wireless Sensor Network using sensor nodes that is low-cost, low-power, and multifunctional has a number of advantages. In this paper, we propose cluster-based multi-channel algorithm considering the energy efficiency in wireless sensor network in a ship. The proposed algorithm shows the result of improvement of throughput and energy efficiency, because it reduces interference between clusters by using channel allocation algorithm that is distributed and dynamic.

• Journal of Communications and Networks
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• v.14 no.1
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• pp.51-62
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• 2012

The exponential growth in wireless services has resulted in an overly crowded spectrum. The current state of spectrum allocation indicates that most usable frequencies have already been occupied. This makes one pessimistic about the feasibility of integrating emerging wireless services such as large-scale sensor networks into the existing communication infrastructure. Cognitive radio is an emerging dynamic spectrum access technology that can be used for flexibly and efficiently achieving open spectrum sharing. Cognitive radio is an intelligent wireless communication system that is aware of its radio environment and that is capable of adapting its operation to statistical variations of the radio frequency. In ad hoc cognitive radio networks, a common control channel (CCC) is usually used for supporting transmission coordination and spectrum-related information exchange. Determining a CCC in distributed networks is a challenging research issue because the spectrum availability at each ad hoc node is quite different and dynamic due to the interference between and coexistence of primary users. In this paper, we propose a novel CCC selection protocol that is implemented in a distributed way according to the appearance patterns of primary systems and connectivity among nodes. The proposed protocol minimizes the possibility of CCC disruption by primary user activities and maximizes node connectivity when the control channel is set up. It also facilitates adaptive recovery of the control channel when the primary user is detected on that channel.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.8
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• pp.4227-4240
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• 2019

In this paper, we present our proposed magnetic induction based wireless communication system. The proposed system is designed to perform communication as well as distance measurement in underground environments. In order to improve the communication quality, we propose and implement the adaptive channel compensation technique. Based on the fact that the channel may be fast time-varying, we keep track of the channel status each time the data is received and accordingly compensate the channel coefficient for any change in the channel status. By using the proposed compensation technique, the developed platform can reliably communicate over distances of 10m while the packet error rate is being maintained under 5%. We also implement the distance measurement block that is useful for various applications that should promptly estimate the location of nearby nodes in communication. The distance between two nodes in communication is estimated by generating a table describing pairs of the magnetic signal strength and the corresponding distance. The experiment result shows that the platform can estimate the distance of a node located within 10m range with the measurement error less than 50cm.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.23 no.1
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• pp.37-43
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• 2023

Compressed still image or video bitstreams require protection from channel errors in a wireless channel. Embedded Zerotree Coding(EZW), SPIHT could have provided unprecedented high performance in image compression with low complexity. If bit error is generated by dint of wireless channel transmission problem, the loss of synchronization on between encoder and decoder causes serious performance degradation. But wavelet zerotree coding algorithms are producing variable-length codewords, extremely sensitive to bit errors. The idea is to partition the lifting coefficients. A many partition of lifting transform coefficients distributes channel error from wireless channel to each partition. Therefore synchronization problem that caused quality deterioration in still image and video stream was improved.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.2
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• pp.95-101
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• 2011

In wireless X networks where all transmitters send the independent messages to all receivers, the theoretical bound on the degrees of freedom (DOF) and interference alignment (IA) scheme for its achievability are given by Cadambe and Jafar [1]. However, IA scheme for wireless X network may be infeasible in practice unless the transmitters have the perfect channel information. In addition, if the transmitter with single antenna uses time-varying channel coefficients as a beamforming vector, the infinite channel extension is required to achieve the theoretical bound on the DOF of wireless X networks with perfect IA scheme. In this paper, we consider K-user MIMO X network where K transmitters and K receivers have M antennas each. While the beamforming vectors have been constructed with multiple channel uses over multiple time slot in the earlier work, we consider the beamforming vectors constructed only by a spatial signature over unit time. Accordingly the channel information at the transmitters can be available instantaneously. Then we propose the perfect IA scheme with no channel extension. Based on our sum-rate analysis and the simulation results, we confirm that our proposed scheme can achieve MK/2 DOF which is quite close to the theoretical bound on the DOF region of wireless X networks.

• 전자공학회논문지 IE
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• v.48 no.2
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• pp.61-70
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• 2011

IEEE 802.11 wireless network supports control frames like RTS/CTS(Request To Send / Clear To Send). Because they is defend to frame collection problems. It helps to solve the frame collection problem but decreases the throughput rate. Also, control frame makes False Node Problem. This problem is makes to other wireless nodes don't work and don't find channels in the same cell and near cells. We proposed a reformed new control frame for efficiency throughput rate and solution of False Node Problem. New control frame is to have added to 4 bytes of channel detection ability at the RTS frames. Channel detection ability supported to check channel at the wireless node start to transmit data frame, We expect that channel detection ability make prevent False Node Problem for increase to access number to channel. We perform comparative analysis in terms of delay(sec) and load(bits/sec) with reform RTS/CTS method which proves the efficiency of the proposed method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.5B
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• pp.463-468
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• 2009

In VANET(Vheicle Ad hoc Network), the researches based on the wireless LAN are conducting and the method based on 802.11a is being adapted in IEEE 802.11p WAVE(Wireless Access in Vehicular Environments). However, wireless LAN which uses a single channel in a competition can cause transmission delays because of a frequent collision and a use of CSMA/CA to avoid competition in VANET requiring a fast access. In this paper, we designed CMMP (Clustering based Multi-channel MAC protocol) adequate to VANET and then confirmed the appropriate channel conditions in a V2V communication on the basis of this protocol. The simulation results showed that a packet collision and a transmission delay by the use of an existing single channel based on the contention decreased more than 60% by CMMP.