• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.13 no.4
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• pp.193-200
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• 2013

Recently, network coding has been actively studied to increase the spectral efficiency of two-way relay wireless channels such as cellular systems as well as broadcasting systems. In this paper, we derive the average transmission capacity and the outage probability of a network coding system, which utilizes two-way data transmission via the best relay rather than multiple relays. Since the data unbalance between the forward and the reverse link in two-way communication systems exists, we include the asymmetric link as well as the symmetric link in the analysis. It is noticed that the space diversity gain increases as the increase of the number of relays. Also we obtain 11.4 dB signal-to-noise ratio (SNR) gain with 9 relays compared to that with single relay in symmetrical link at the given conditions. In asymmetrical links, we denotes that the outage probability is more sensitive to the number of relays rather than data unbalance between the links.

• Journal of the Korea Society for Simulation
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• v.18 no.3
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• pp.123-131
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• 2009

Wireless networks have several unique features : node mobility, restricted bandwidth, time-variable bandwidth, large latency, and high bit error rates time due to channel fading. These features at wireless networks intend to decrease the performance TCP protocols are used in wireless networks. Lots of studies have been done for finding appropriate wireless transport protocols for current wireless communications. However, related studies have not provided good performance or some protocols have a good performance only in specific circumstances. Thus, these are not suitable for general wireless circumstance. Therefore, we propose a new wireless transport protocol which provides better performance than the previous ones. And we'd like to solve a problem that previous protocols cannot maintain their connections even though they have multiple paths until another path is successfully set up. To solve these problems, a new protocol ATP-M is proposed which is designed on already known TCP-M and ATP protocols. With NS-2 computer simulation, it is shown that this newly proposed protocol has better system throughput than TCP, TCP-M and ATP protocols.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.4
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• pp.667-672
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• 2003

Smart antennas will be used mon widely for the higher data rate and the larger number of users as the demand of wireless multimedia service is increased. Therefore, the BER performance is analyzed in this paper for DS-CDMA and MC-CDMA systems using smart antennas. A reverse link channel is simulated assuming the frequency selective Rayleigh fading. The simulation results are presented based on the characteristics of DS-CDMA and MC-CDMA systems according to the signal spectrum bandwidth and the method of adaptive beamforming. The BER performances of both systems are improved as the beam width of smart antennas is decreased. Also, it is shown that the performance of MC-CDMA system is much better than that of DS-CDMA system as the number of users is increased.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.12A
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• pp.1122-1127
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• 2010

In this paper, we propose a relay-based DF cooperative communication scheme using repetitive transmission algorithm for wireless LAN environments on D-STBC. Additional transmission diversity gain can be obtained by repetitive transmission algorithm. However, in comparison with conventional schemes, data rate is decreased in half. We consider data modulation constellation twice higher than conventional schemes. Further, system complexity is decreased and performance degradation is minimized because repetitive transmission algorithm is adapted between source and relay node. We show the uncoded BER performance of the proposed algorithm over HiperLAN/2 Rayleigh fading channel.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.12B
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• pp.1251-1258
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• 2010

Orthogonal Frequency Division Multiplexing (OFDM) has been investigated as promising technology for future broadband communication. In this paper, we propose a power allocation algorithm for a frequency selective fading channel. However, many investigated algorithms that perform high computation overhead are not appropriate for sensor network systems due to hardware limitations. The proposed algorithm significantly reduces computational overhead and satisfies the power budget. Throughput of the algorithm is comparable to the optimum solution. Simulation results support the claim stated.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.2
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• pp.286-293
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• 2000

This paper treats performance analysis and improvement of DSRC physical layer which is discussed for standardization at the ISO TC-204 WG-15. DSRC is a short range wireless communication for which distance is less than 100m between RSU and O BE, since DSRC requires cheap and simple modulation technique, ASK is being developed as standard modulation system among PSK, FSK and ASK in our country. This paper analyzes the performance of DSRC physical layer system which is at the first stage of development under Rician fading channel, more sepcifically, the validity of the system and the performance limitations are shown. Both equalizer and antenna diversity techniques are simulated to improve the ASK system performance.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.6
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• pp.14-21
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• 2011

In this paper, we propose an efficient symbol mapping method based on LLR (log-likelihood ratio) statistic for HARQ employing CoRe (constellation rearrangement) with 64QAM. The signal constellations for 64QAM with limited number of retransmissions are selected by the proposed mapping rule. Then we determine the transmission order of selected constellations. The proposed scheme reduces the performance deviation between transmit symbols so as to improve the system performance. Through simulation results, the proposed and existing CoRe mapping methods are compared with respect to error rate and throughput in MIMO-OFDM system over fading channel and we confirm the applicability of the proposed scheme in practical wireless communications environment.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.1
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• pp.106-112
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• 2007

A new space-time cooperative communication relaying strategy with assistant or management terminals is proposed in multi-hop wireless communication systems. More than one relaying terminals are included in one cooperative group to share the state information such as frame error rate and channel information. Among the cooperative group, the best ones are selected to send bit information using space-time codes. An implementation for the proposed scheme is also presented using a TDMA cooperative protocol. Receive signal to transmit signal ratio($E_r/E_s$) and computer simulation show the strategy outperform the conventional cooperative system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.1A
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• pp.109-114
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• 2007

A new space-time cooperative communication relaying strategy with assistant or management terminals is proposed in multi-hop wireless communication systems. More than one relaying terminals are included in one cooperative group to share the state information such as frame error rate and channel information. Among the cooperative group, the best ones are selected to send bit information using space-time codes. An implementation for the proposed scheme is also presented using a TDMA cooperative protocol. Receive signal to transmit signal ratio($E_r/E_s$) and computer simulation show the strategy outperform the conventional cooperative system.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.5
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• pp.429-436
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• 2017

Since the telemetry performance using the time-delayed data dissipates the wireless channel resources, we propose the spectral efficient retransmission scheme in this paper. In the proposed scheme, the telemetry data is retransmitted based on triggered memory to improve the spectral efficiency. The proposed scheme minimizes the error caused by multipath fading, antenna pattern as well as the error caused by the flight events. In the flight simulation data, we show the proposed scheme improves the telemetry performance based on spectral efficient retransmission.