• ETRI Journal
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• v.28 no.2
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• pp.227-230
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• 2006

There has been a growing need for increased capacity in cellular systems. This has resulted in the adoption of the code division multiple access (CDMA) system as a multiple channel access method. Thus, it is important to obtain the phase offsets of binary codes in the CDMA system because distinct phase offsets of the same code are used to distinguish signals received at the mobile station from different base stations. This letter proposes an efficient algorithm to compute the phase offset of a binary code in the CDMA system through the use of the basic facts of number theory and a new notion of the subcodes of a given code. We also formulate the algorithm in a compact form.

• Journal of Korea Technology Innovation Society
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• v.3 no.1
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• pp.127-138
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• 2000

This pape applies the multi-attribute utility theory for estimating the non-economci value of technology. The technology of the code division multiple access in mobile communications is used as a case study. The technology of the code division multiple access in mobile communications is used as a case study. The result shows that the multi-attribute utility theory is a useful method for es-tinmating the non-economic value of technology and gaining an insight into the importance of tech-nology innovation.

• ETRI Journal
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• v.28 no.4
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• pp.513-516
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• 2006

Experimental demonstration of bipolar spectral encoding code-division multiple-access with modified pseudorandom noise codes is presented. Bipolar spectral encoding is achieved with an erbium-doped fiber amplifier amplified spontaneous emission source and arrayed waveguide gratings. The bit-error rate performance of 1.25 Gbps signal transmission over 80 km single mode fiber is measured in a multiple-user environment.

• Journal of Satellite, Information and Communications
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• v.7 no.3
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• pp.26-29
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• 2012

In this paper, we propose a Single Carrier Frequency Division Multiple Access(SC-FDMA) scheme with greatly enhanced tolerance of timing offset among the users. The type of the proposed scheme is similar to code spread Multiple Carrier Direct Spread Code Division Multiple Access(MC DS CDMA). The proposed scheme performs partial Discrete Fourier Transform(DFT) in order to solve high Peak to Average Power Ratio(PAPR) of the MC DS CDMA before Inverse Fast Fourier Transform(IFFT). Exploiting the property Properly Scrambled Walsh-Hadamard(PSW) code has zero correlation despite ${\pm}1$ chip timing offset, the proposed scheme achieves Multiple Access Interference free performance with the timing offset up to ${\pm}1$ OFDM symbol duration with low PAPR. In contrast, the other existing schemes in comparison undergo severe performance degradation even with small timing offset in multipath fading channel.

• ETRI Journal
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• v.26 no.1
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• pp.13-20
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• 2004

We propose a new optical code division multiple access (OCDMA) scheme for reducing multiple access interference (MAI) and enhancing performance for optical subscriber access networks using modified pseudorandom noise (PN)-coded fiber Bragg gratings with bipolar OCDMA decoders. Through the bipolar OCDMA decoder and the modified PN codes, MAI among users is effectively depressed. As the data are encoded either by a unipolar signature sequence of the modified PN code or its complement according to whether the data bit is 1 or 0, the bit error ratio (BER) can be more improved with the same signal to interference plus noise ratio over the conventional on-off shift keying-based OCDMA system. We prove by numerical analysis that the BER of the proposed bipolar OCDMA system is better than the conventional unipolar OCDMA system. We also analyze the spectral power distortion effects of the broadband light source.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.3 no.2
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• pp.22-29
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• 1992

In recent years there has been increased interest in a class of multiple-access techniques known as code division multiple-access(CDMA). As the trend for ever increasing data transmission rate and high error performance continues while conserving bandwidth, the needs arise for good highrate R=b/v convolu- tional codes such as punctured codes. In this paper, the packet error propability has been analyzed in code division multiple-access packet radio system which utilize punctured convolutional code and hard-decision Viterbi decoding.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.6C
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• pp.649-655
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• 2009

Mean acquisition time (MAT) is the most important performance measure for code acquisition systems, where a shorter MAT implies a better code acquisition performance. Keshavarzian and Salehi proposed the multiple-shift (MS) algorithm for code acquisition in optical code division multiple access (O-CDMA) systems. Performing two steps acquisition, the MS algorithm has a shorter MAT than that of the conventional serial-search (SS) algorithm. In this paper, we propose a rapid code acquisition algorithm for O-CDMA systems. By using an efficient combination of local signals, correlation value, and the sign of correlation value, the proposed algorithm can provide a shorter MAT compared with that of the MS algorithm. The simulation results show that the proposed algorithm presents a shorter MAT than that of the MS algorithm.

• Journal of IKEEE
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• v.16 no.1
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• pp.51-55
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• 2012

In this paper, we propose to employ a ternary sequence as a cyclic code shift keying (CCSK) modulation sequence. And we simulate the performance in a frequency hopping spread spectrum/time division multiple access (FHSS/TDMA) system with CCSK. Wireless channel is modeled as Rayleigh fading channel. From the simulation results, it is demonstrated that the system adopting the ternary sequence as a CCSK sequence has higher performance than that with a random sequence.

• ETRI Journal
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• v.26 no.3
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• pp.265-268
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• 2004

We develop a simple exact solution method for return link capacity allocation scheduling in a satellite interactive network using a hybrid code-division multiple access / time-division multiple access (CDMA/TDMA) scheme.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.5
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• pp.121-127
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• 2013

When input power is small, nonideal symmetric balance incomplete block design(BIBD) code design is effective in the spectral-amplitude-code(SAC) optical code-division multiple-access (OCDMA) system. But the number of simultaneous users is not sufficient. To overcome this property, we propose 2-D BIBD codes, where nonideal BIBD codes are used as spectral code and ideal BIBD codes are used as spatial codes. Analytical results show that the number of simultaneous users increases significantly.