• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.7
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• pp.1229-1236
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• 2016

In underwater acoustic multipath channel, a performance of underwater acoustic (UWA) communication systems is affected by dynamic variation of boundary and high temporal and spatial variability of the channel conditions. Time and spatial variations of UWA channel induce a carrier frequency offset (CFO) since a phase and a frequency of received signal mismatch with a transmitting signal. Therefore, a performance of a phase shift keying underwater acoustic communication system is degraded. In this study, we have analyzed a performance of CFO estimation and compensation using a phase code in time and spatial variation channel. A constant amplitude zero autocorrelation (CAZAC) signal is applied as a phase code signal and its performance is evaluated in water tank. The bit error rate of a quadrature phase shift keying (QPSK) system with a phase code is improved about 4 to 10 times better than that without a phase code.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.11A
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• pp.1087-1094
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• 2008

In this paper, we propose the acquisition method of the Cyclic-Prefix CDMA using Good-Autocorrelation-Sequence (GAS-CP-CDMA) system. The sequences for GAS-CP-CDMA are m-sequence and constant amplitude zero autocorrelation code (CAZAC) with good autocorrelation property. The GAS-CP-CDMA system is proposed for interference cancellation in multi-user and -path environment in co-cell. However, the reliable initial acquisition in multi-path fading channel and multi-user system environment is crucial. In this paper, non-coherent power detector and threshold value are used for discriminating signal acquisition. The sequence used for computer simulation is CAZAC. The simulation results show proper threshold value depends on the number of users. Through the computer simulation, we draw setting up method of the optimum threshold value for the GAS-CP-CDMA system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.11C
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• pp.641-648
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• 2011

Frequency domain equalization is the most promising technology that has relatively low complexity in multipath channel. A frame of single carrier system with frequency domain equalization (SC-FDE) has cyclic prefix to mitigate effect of delay spread. After synchronization and equalization procedure on the SC-FDE system, common phase offset (CPO) that can introduce performance degradation caused by phase mismatch between transmitter and receiver oscillators is remained. In this paper, common phase offset tracking in frequency domain is proposed. To track CPO, constant amplitude zero autocorrelation code sequence as training sequence is adopted. By using numerical results, performance of mean square error is evaluated. The results show that MSE of CPO has similar performance compare to the time-domain estimation and there is no need of domain conversion.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.11A
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• pp.1079-1086
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• 2008

In this paper, we propose a Cyclic-Prefix Code Division Multiple Access system that uses Sequences with Good Autocorrelation property(GAS-CP-CDMA) and analyze the uplink signal-to-noise ratio performance of that system. Phase-shifted sequences are used for differentiating users. The signals of the GAS-CP-CDMA system experience no (or very little) interferences from co-cell signals because of the good autocorrelation property, but user signals of adjacent cells may yield interferences. The frequency reuse factor in the ordinary CDMA system is around 0.6 and the interference from adjacent cells is about 40 percent of the total interference in the conventional CDMA system. Our numerical analysis shows that the frequency reuse factor and user capacity versus signal-to-noise ratio of the GAS-CP-CDMA system are improved comparing to the conventional CDMA system. The uplink user capacity of the proposed system can be increased up to about twice of that of the conventional CDMA system.