• ETRI Journal
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• v.27 no.6
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• pp.810-813
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• 2005

This letter presents an analytical framework for a performance analysis of the imperfect direct-sequence code division multiple access (DS-CDMA) closed-loop power control (CLPC) loop with loop delay, channel estimation error, and power control command bit error as the parameters under a Rayleigh flat fading environment. The proposed model is verified through a comparison between analytical results and simulation ones.

• Proceedings of the IEEK Conference
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• 2000.07a
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• pp.501-504
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• 2000

In this paper, performance of a pseudonoise (PN) code tracking loop is analyzed and simulated for a direct-sequence/code-division multiple access ( DS/CDMA) system with imperfect power control in a multipath fading channel. A noncoherent first-order delay-locked loop (DLL) is considered as a PN code tracking loop. Power control error is modeled as a log-normally distributed random variable. From the simulation results, it is shown that for smaller discriminator offset, tracking jitter performance is improved while MTLL performance is degraded. It is shown that large power control error and heavy shadowing substantially degrade the PN tracking performance. The analysis in this paper can be applicable to design of PN code tracking loop for a DS/CDMA system.

• 전자공학회논문지 IE
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• v.43 no.2
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• pp.70-74
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• 2006

The performance of conventional direct sequence code division multiple access (DS-CDMA) systems is decreased under environments such as additive white Gaussian noise (AWGN), channel distortion and interference noise due to multiple access user. By means of this parameter, auto correlation value of pseudo noise spreading sequence is decreased at receiver. This techniques which are based on correlation of between signature waveform signal. In this paper, to improve correlation property, we proposed the binary chirp DS-CDMA techniques which combine the DS-CDMA and chirp modulation. The proposed system which is based on binary chirp symbol has a good correlation value. Thus, we called BC DS-CDMA. To evaluate the system's performance, we compare the performance of the proposed systems with DS-CDMA systems under AWGN channel and halogen noise which exists on the powerline. The simulation results show that the proposed method has better performance than conventional technique.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.9A
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• pp.2131-2140
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• 1998

Signal-to-interference ratio (SIR)-based dynamic code allocation method to be rioritized for handoff call is proposed and evaluated in a direct sequence-code division multiple access (DS-CDMA) cellular systm. Proposed method allocates a code to a mobile terminal according to the restidual capacity computed by SIR in the base station. We consider the voice activity detection to increase the system capacity. We evaluate the performance of proposed method with computer simulation. And the handoff decision function that controls handoff of mobile terminal is interodcued. The proposed method provide much improvement in the forced termination probability and handoff call fail probability.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.3B
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• pp.251-258
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• 2002

In this paper, an adaptive convolutional coding method in multicarrier direct sequence code division multiple access (DS/CDMA) systems is considered. In order to accommodate a number of coding rates easily and make the encoder and decoder structure simple, we use the rate compatible punctured convolutional (RCPC) code. To achieve maximum data throughput, an adaptive rate system based on the channel state information (the SINR estimate) is proposed. We show that the proposed adaptive rate convolution coded multicarrier DS/CDMA systems can enhance spectral efficiency and provide frequency diversity.

• Proceedings of the IEEK Conference
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• 2000.09a
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• pp.33-36
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• 2000

DS-CDMA (direct sequence-code division multiple access) 시스템에서 여러 사용자가 동일 주파수 대역을 공유함으로써 다중 접속 간섭 (multiple access interference; MAI)이 발생하고 시스템의 성능을 크게 제한한다. 이러한 다중 접속 간섭을 제거하여 전송 신호의 질을 높이고 용량을 증대시키는 중요한 신호 처리 기술 가운데 하나가 적응 간섭 억제 기술이다. 적응 간섭 억제 기술 가운데 CMA (constant modulus algorithm) 기반의 블라인드 적응 간섭 억제기는 훈련수열을 필요로 하지 않고 빠른 수렴을 통하여 간섭을 효과적으로 제거할 수 있으나, 다중 경로 환경에서 심벌간 간섭 (intersymbol interference; ISI)이 증대되어 기존의 적응 수신기보다 악화된 성능을 보인다. 본 논문에서는 CMA를 기반으로 훈련 수열 없이 빠른 수렴을 하며 MAI와 ISI를 효과적으로 제거하기 위한 다이버시티 결합기 구조의 적응 간섭 억제기를 제한한다. 다중 경로 페이딩 채널 환경에서 기존의 블라인드 적응간섭 억제기와의 성능 비교 결과, 제안된 방식이 다중경로에 의한 ISI의 영향을 효과적으로 제거하여 우수한 성능을 얻을 수 있음을 확인하였다.

• Proceedings of the KIEE Conference
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• 2004.07d
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• pp.2559-2561
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• 2004

This paper proposes the new signal-to-noise ratio(SNR) that is different from the conventional signal-to-noise ratio (SNR) in direct-sequence code-division multiple-access communication system employing offset quadrature phase-shift keying(OQPSK) and using a chip waveform. The conventional SNR value is so different from a real SNR value. Therefore, we propose a new SNR equation approximated to real SNR. The multiple-access interference(MAI) in DS-CDMA communication system has an effect on SNR performance and MAI is concerned with the correlation functions of the chip waveform. For this reason, we considered all possible correlations of chip waveforms. In conclusion, the SNR value of proposed method is enclosed to the real SNR value.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.8
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• pp.697-703
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• 2013

We propose an efficient frequency-time domain resource allocation scheme in multi-carrier (MC) direct-sequence code-division multiple-access (DS/CDMA) communications. We consider, as a power allocation strategy in the frequency domain, transmitting each user's DS waveforms over the user's sub-band with the largest channel gain. We then consider rate adaptation in the time domain, where the data rate is adapted such that a desired transmission quality is maintained. We analyze the achievable average data rate of the proposed scheme with fixed average transmission power, and compare the performance to single carrier DS/CDMA systems with power and rate adaptations.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.5A
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• pp.500-508
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• 2008

Direct-sequence ultra-wideband(DS-UWB) system is being considered as one of promising transmission technologies for wireless personal area networks(WPANs). Due to relatively low spreading factors and huge bandwidth of transmit signal, a DS-UWB receiver needs to be equipped not only with a rake receiver but also with an equalizer, of which the equalizer is not required for traditional direct-sequence code division multiple access(DS-CDMA) systems. The number of rake fingers is limited in practice, influencing the performance of the subsequent equalizer. In this paper, we derive a decision feedback equalizer(DFE) for DS-UWB systems based on the minimum mean square error(MMSE) criterion, and investigate the impact of various parameters on the DFE performance in realistic scenarios. In particular, we propose an approach to improving the performance of the DFE using additional channel estimates for multipaths not combined in the rake receiver, and discuss how the accuracy of channel estimation affects desirable DFE configuration. Moreover, we present simulation results that show the impact of turbo equalization on the DFE performance.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.4
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• pp.160-164
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• 2004

In DS/CDMA(direct sequence code division multiple access) system using the approximated analytic chip waveforms are applied. Proposed chip waveforms are classified into 2 types: uniform chip waveforms with uniform envelope and non-uniform chip waveforms with non-uniform envelope. It has confirmed that the similarity of the approximated analytical chip waveforms is compared using chip waveforms, envelope, phase, correlation, and bandwidth properties.