• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.8
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• pp.1686-1692
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• 2012

Spreading sequence play an important role in wireless communications, such as in a CDMA(code division multiple access) communication system and multi-carrier spectrum communication system. Spreading sequences with low cross-correlation, in a direct-sequence spread spectrum communication system, help to minimize multiple access interference and to increase security degree of system. Analysis of cross-correlations between the sequences is a necessary process to design sequences. However it require lots of computing time for analysis of cross-correlations between sequences. In this paper we propose a method which is possible to compute effectively cross-correlation using subfield in the process of practical computation of cross-correlation between nonlinear binary sequences.

• The Journal of the Korea institute of electronic communication sciences
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• v.7 no.1
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• pp.61-67
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• 2012

Spreading sequence is used for spreading spectrum in CDMA. For the purpose of minimizing multiple access interference and expanding linear span of the sequences, it is desirable to use such sequences with low correlation and high linear span. To obtain large family size and high linear span, the values of the correlation function of the sequences is more complex. In this paper, we propose the extended Zeng sequences with large family size and high linear span and analyze the correlation of the sequences.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.2 no.4
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• pp.511-517
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• 1998

In this paper a new technique to generate spreading code sequences in the CDMA communication is introduced. It is an effective method to generate optimal code sequences using the orthogonality of wavelet packet basis set of subspaces. With a three-stage Quadrature Mirror Filter(QMF), generation of optimal code sequences has been demonstrated. Since these generated optimal code sequences are non-binary and have an arbitrary waveform which is different from that of the conventional PN-based Gold code sequences, a strong security against the intended interceptor is feasible. Encouraging good correlation properties are also achieved with this new method.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.11
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• pp.44-47
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• 2008

New Eight-phase Preferred Pairs (EPPs) that have Zero-Correlation Duration (ZCD) of (0.5N+1) chips are constructed for the periods of $N=4{\times}2n$ (n=1,2,3...). By using the chip-shift operation of the EPP, new eight-phase ZCD sequences are constructed in this paper. We certified its ZCD property by various correlation simulations. This new eight-phase spreading sequence can be used for Interference cancelled wireless personal area network(WPAN) based on approximately synchronized code-division-multiple-access(AS-CDMA) system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.2
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• pp.264-272
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• 2015

In this paper, we analyze the statistical characteristic and describe the anti-interference performance of the signal for the LPI-applied GNSS using encrypted spreading code. To do this, we analyze the correlation property of encrypted sequences theoretically having various symbol sets over complex root of unity. We derive the degradation of anti-interference performance of encrypted sequences comparing with Gold and Zadoff-Chu sequences using theoretical and experimental methods.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.36S no.9
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• pp.27-35
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• 1999

In this paper, we propose an error detection scheme of phase offsets for binary sequences including PN (Pseudo Noise) sequences based on the number theoretical approach. It is important to know phase offsets of spreading sequences in the CDMA (Code Division Multiple Access) mobile communication systems because phase offsets of the same spreading sequence are used to achieve the acquisition and are used to distinguish each base station. When the period of the sequence is not very long, the relative phase offset between the sequence and its shifted replica can be found by comparing them, but as the period of the sequence increases it becomes difficult to find the phase offset. The error detection failure probability of the proposed method is derived, and it is confirmed by the simulation results. We also discuss the circuit realization of the proposed method and show it can be easily implemented.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.10
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• pp.29-33
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• 2010

In this paper, a new family of wavelength-time codewords using modified time mapped prime sequences as a time spreading pattern is constructed. When $P_t$ = 3, we can construct $P_w^2$ wavelength-time codewords with low autocorrelation sidelobe and crosscorrelation of less than or equal to 1. When $P_t$ = 5 and $P_t$ = 7, the number of wavelength-time codewords of $P_w^2$ can be constructed with good crosscorrelation of 1 and autocorrelation of less than or equal to 2.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.1A
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• pp.10-17
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• 2000

In this paper, we evaluate the correlation properties and the optimization of PN sequence phase for multi-media DS/CDMA system with variable spreading gain (VSG) scheme. In multi-media multi-rate DS/CDMA systems, the optimization of PN sequence phase is not a tractable problem, since the sequences should be optimized against both sequences of the same length and other sequences with different length. Hence, we verify the correlation properties of PN sequence phase in multi-rate system environment and furthermore, we propose the new phase criterion, MIN-AIP (minimum-average interference parameter), to minimize the bit error rate (BER). As the results of performance evaluations, it is shown that the performance of MIN-AIP criteria gives the best results.

• Journal of Communications and Networks
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• v.7 no.1
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• pp.21-28
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• 2005

In this paper, we analyze the performance of code division multiple access (CDMA) systems with orthogonal frequency division multiplexing (OFDM) that employ random spreading sequences in an additive white Gaussian noise (AWGN) channel. We obtain the probability density function (pdf) of the multiple access interference and extend the results to OFDM-CDMA systems to determine the pdf of multiple access and inter-carrier interference in terms of the number of users, the spreading length, the number of sub-carriers, and the frequency offset. We consider the synchronous downlink of cellular multi-carrier CDMA and derive a Gaussian approximation of the multiple access and inter-carrier interference. Overall the effect of frequency offset is shown to vary with the system loading. The analysis in this paper is critical for further development into fading channels and frequency selective multipath channels.

• Proceedings of the IEEK Conference
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• 2002.07c
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• pp.2019-2022
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• 2002

This paper presents design of spreading codes for asynchronous DS-CDMA systems. We have been trying to generate maximal-period sequences based on one-dimensional maps with finite bits whose shapes are similar to piecewise linear chaotic maps. We propose an efficient search algorithm finding such mammal-period sequences. This algorithm makes it possible to find many kinds of maximal-period sequences with sufficiently long period for CDMA applications. We also investigate bit error rate(BER) in asynchronous DS-CDMA systems using the maximal-period binary sequences by computer simulations.