• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.6
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• pp.99-105
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• 2010

The most frequently used noise model for the performance analysis of a communication system is additive white Gaussian noise. However impulsive noise model is more practical for the real communication environments, currently the performance analysis of a communication system in impulsive noise is increasing. In this paper, therefore, the performance of a cooperative system, which is recently one of the most intensive research topics, is derived in impulsive noise. We analytically derive and compare the performance of two opportunistic cooperative diversity systems which have an amplify-and-forward (AF) relaying or a decode-and-forward (DF) relaying. It is noticed that the impulsive noise component is increases with decreasing the average number of impulses in impulsive noise, consequently the performance of two systems is degraded in high SNR region. Also it is shown that the performance of the opportunistic cooperative system with DF relaying is superior to that with AF relaying.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 1995.10a
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• pp.657-660
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• 1995

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.5C
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• pp.391-397
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• 2005

Since space time block code (STBC) technique of a transmission diversity technique was introduced, multiple input multiple output techniques using transmission diversity at the basestation for improving transmission data rate, have been studied extensively. Multiplexed STBC OFDM technique uses multiple groups of two transmit antennas and suppresses the interference signals of other STBC OFDM groups at the receivers. In this paper, I propose a new method of iterative decoding and maximal ratio receive combining technique for multiplexed STBC OFDM systems, and simulated and showed the results in comparison with the conventional methods.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.6C
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• pp.429-437
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• 2008

Multiple-input multiple-output (MIMO) techniques can be used for the spectral efficiency enhancement of the cellular systems, which can be categorized into spatial multiplexing (SM) and spatial diversity schemes. MIMO systems suffer a severe performance degradation due to the intercell interference from the adjacent cells as the mobile terminal moves toward the cell boundary. Therefore for the spectral efficiency enhancement, an appropriate transmission scheme for the given channel environment and reception scheme which can mitigate the intercell interference are required. In this paper, we propose an adaptive signal transmission/reception scheme for the spectral efficiency improvement of $M_R{\times}M_T$ MIMO systems, present the decision criteria for the adaptive operation of the proposed scheme, and demonstrate the performance gain. The proposed scheme performs adaptive transmission using spatial multiplexing and spatial diversity, and adaptive reception using maximal ratio combining (MRC) and intercell spatial demultiplexing (ISD) when the spatial diversity transmission is used at the transmitter. Spatial multiplexing/demultiplexing is performed at the high signal-to-interference ratio (SIR) range, and the transmit diversity in conjunction with the adaptive reception uses either conventional MRC or ISD which can mitigate the $M_R-1$ interference signals, based on the mobile location. For the performance evaluation of the proposed adaptive scheme, the probability density function (pdf) of the effective SIR for the transmission/reception methods in consideration are derived for $M_R{\times}M_T$ MIMO systems. Using the results, the average effective SIR and spectral efficiency are presented and compared with simulation results.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.4 s.119
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• pp.440-447
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• 2007

The switched diversity, although its performance is a little inferior to the selection diversity, is widely used due to its advantage that only one RF circuit is required for its operation without respect to the number of antennas in use. In this paper, we propose an application of the antenna switched diversity to a spread spectrum system with adaptive modulation and derived the optimal antenna switching threshold to maximize the average transmission bit rate. We also compared the performances of the proposed system with those of the two cases using a single antenna and the selection diversity with two antennas in terms of the average number of bits per symbol(BPS), the probability of no transmission, and the average BER. The performance analysis shows that, if the number of paths in a multipath channel environment increases, the performance of the proposed scheme becomes closer to that of the selection diversity based system in terms of the average BPS. Furthermore, the proposed scheme produces as almost high the probability of no transmission as the selection diversity based system for the case of low average SNR, although the former yields a little higher probability of no transmission than the latter fer the case of high average SNR.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.12A
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• pp.941-949
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• 2011

In a cooperative communication system with a source node and multiple relays equipping single antenna and a destination node equipping multiple antennas, the selective cooperative spatial multiplexing scheme can obtain spatial multiplexing gain and additional selection diversity gain. But it can degrade a bit error rate performance because some received symbols forwarded from particular relays may be lost by attenuation due to path-loss. We propose a relay and transmission mode selection scheme which selects minimum number of multiple relays having the channel capacity larger than a given data rate and transmission mode which switches spatial multiplexing and spatial diversity mode in cooperation phase to enhance the bit error rate performance. The proposed scheme achieves 1.5~2dB gain at the low SNR range compared with the conventional scheme by obtaining additional spatial diversity gain.

• Journal of Broadcast Engineering
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• v.13 no.2
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• pp.172-178
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• 2008

Orthogonal Frequency Division Multiplexing (OFDM) is one of the most promising technologies for high data rate wireless communications. OFDM has been adopted in wireless standards such as digital audio/video broadcasting. The combination of OFDM and cooperative diversity techniques can provide the diversity gain and/or increased capacity. In this paper, the cooperative coding using cyclic delay diversity (CDD) for multiuser OFDM systems is introduced. To improve the beneficial effects of relays's cooperation, CDD is adopted in cooperative transmission of relays. Simulation results show the bit error rate (BER) for various consideration. The proposed scheme provides improved performance compared to delay.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.18 no.2
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• pp.49-54
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• 2018

In this paper, we study the secrecy outage probability when using cooperative diversity and jammer in a relay system based on decode-and-forward. MRC method is used in receiver and eavesdroppers to obtain cooperative diversity. To use the MRC technique, direct links between the sender and receiver, and between the sender and the eavesdropper are used, respectively. Jammers are used to generate intentional noise siganls to increase security capacity. Jammers generate intentional noise, degrading the channel quality of the eavesdropper and helping physical layer security be realized. The secrecy outage probability is used to evaluate security performance. Assume that the system is under the Rayleigh fading channel.

• Proceedings of the Korea Information Processing Society Conference
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• 2000.10b
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• pp.1263-1266
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• 2000

In this paper, we propose a reliable Image transmission system with Decision Feedback Equalization (DFE), and use diversity combining techniques over multipath fading channels. It is shown that the proposed system has the features of simplicity in implementation with DFE and diversity combining techniques without modifying DFE. This study includes error concealment techniques for reconstruction of missing blocks in JPEG. To verify and compare the performance of our proposed system, the computer simulations have been performed in three diversity combining cases.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.4
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• pp.394-401
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• 2013

Recently there have been much interest in the performance improvement of maritime communication system. In the maritime communication system, the wireless channel is likely to be time-invariant and the retransmission scheme is not proper because it does not provide time diversity. For the improvement of reliability, we consider MIMO ARQ scheme using Alamouti-type signal which can provide space and time diversity. In this paper, we also propose the criterion of optimal retransmission order and provide its performance of error probability and packet throughput. The proposed MIMO ARQ scheme with optimal retransmission order has performance gain over random ordered MIMO ARQ and conventional Chase combining method. Therefore we expect that it can be adapted to the next generation maritime communication system.