• Journal of Korean Society of Industrial and Systems Engineering
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• v.28 no.3
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• pp.115-120
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• 2005

In this paper, we propose a personal-computer-based wireless data access system, which use DS/SS(Direct Sequence Spread Spectrum) method and the ISM band of 2.44GHz radio frequency. By applying hi-directional transmission between wireless handy terminals and PCs or servers, it can be easily connected with any kinds of database systems such as Oracle, MS-SQL and MS-ACCESS. Therefore, it could be economically adopted as peripheral equipments for ERP or SCM systems.

• Journal of Communications and Networks
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• v.7 no.1
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• pp.29-35
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• 2005

This paper deals with the problem of multiuser detection over a direct-sequence code-division multiple access (DS-CDMA) channel with incomplete channel state informations (I-CSI). We devise and assess two novel recursive detectors based on the expectation conditional maximization (ECM) algorithm and the generalized likelihood ratio (GLR) principle, respectively. Both receivers entail an affordable computational complexity. Moreover, the performance assessment, conducted via Monte Carlo techniques, shows that they achieve satisfactory performance levels and outperform linear detectors.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.1
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• pp.539-542
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• 2005

In this paper, we propose a wireless data access system, which used direct sequence spread spectrum method and the ISM band with 900MHz radio frequency. By applying bi-directional transmission between wireless transmitter and receiver, it can be effectively connected with any kinds of RF-ID with 900MHz ISM band. Therefore it could economically be used as peripheral equipments for RF-ID system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.1A
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• pp.34-43
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• 2007

In the IEEE 802.15.3 Medium Access Control (MAC) protocol, Simultaneously Operating Piconets (SOPs) are linked by the parent/child (P/C) or parent/neighbor (P/N) configuration, which work on a Time Division Multiple Access (TDMA) basis. This provides interference mitigation but the overall throughput is limited because the SOPs share the channel time exclusively. The protocol is not efficient for SOPs if we focus on the combination of interference mitigation and high throughput maintenance. In this paper Public Channel Time Allocation (Public CTA) is proposed, which is able to greatly reduce the inter-piconet interference (IPI) and achieve greater throughput without much loss of link success probability (LSP) in the SOPs. The simulation results based on the SOPs of Direct Sequence Ultra Wideband (DS-UWB) system demonstrate that the proposed scheme effectively supports the coexistence of SOPs, and it can not only significantly improve the overall throughput of SOPs but also maintain high LSP.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.36S no.8
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• pp.8-16
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• 1999

In this paper, the performance of a hybrid DS/SFH-SS(direct-sequence/slow-frequency-hopped spread-spectrum) system with coherent BPSK modulation over Nakagami fading channel in the presence of multiple tone jamming is analyzed. Because the Nakagami m-distribution can describe not only Rayleigh fading but also more general fluctuations involving a specular component by adjusting the value of the fading index m. It is known that for m=1 corresponds to Rayleigh fading, for $1/2{\le}m{\le}1$ corresponds to the worst case fading condition, for m>1 corresponds to Rician fading, and for $m{\to}{\infty}$ corresponds to the nonfading condition. The bit error probability is derived over Nakagami model and numerical evaluations are presented for some combinations of system parameters. The results show that as m increases, the bit error probability is better. Also, at a low JSR(jamming-to-signal power ratio), a pure DS-SS system can achieve lower bit error probability than a hybrid DS/SFH-SS system. But at a high JSR, a hybrid DS/SFH-SS system is shown to be superior to a pure DS-SS system. Therefore, it is demonstrated that without increasing the total system bandwidth, the performance of a hybrid DS/SFH-SS is superior to that of a pure DS-SS system in the presence of multiple tone jamming.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.1
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• pp.47-55
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• 1994

This paper investigates the performance analysis of the packet DS/SS receiver with a PJED(phase-jump error detector) using the block signal processing(BSP) methods. The conventional packet DS/SS block receiver has a high probability of mistaking the phase-jump detection, which causes the frequency estimation error. The conventional receiver uses a Matched-Pulse Timing Extractor which has a complicated structure. The proposed packet DS/SS block receiver with the PJED which uses libearity of the phase has little probability of mistaking the phase-jump detection. The proposed Matched Pulse Timing Extractor gas the more simple structure but obtains the same performance on the exact matched-pluse timing as the conventional one does. The simulation results show that the proposed receiver gives about 2dB improvement in the BER compared with the conventional receiver.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.6C
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• pp.423-433
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• 2005

We present power(in frequency domain) and rate adaptation(in time domain) schemes in multicarrier (MC) direct-sequence code-division multiple-access(DS/CDMA) communications. Utilizing channel state information from the receiver, the adaptation schemes allocate power the user's sub-band with the largest channel gain. In the time domain, the transmission data rate is adapted for a desired transmission quality. In the case of single-user channels, a closed-form expression is derived for an optimal time domain power adaptation that minimizes the average bit error rate(BER). Channel inversion power adaptation is found to provide nearly optimal performance in this case, as the number of sub-bands or available average transmission power increase. Analysis and simulation results show the BER performance of the proposed power and rate adaptations with fixed average transmission power significantly improves the performance over the power allocation in the frequency domain only. Also, we compare the performance of the proposed power and rate adaptation schemes in MC-DS/CDMA systems with that of power and rate adapted single carrier DS/CDMA systems with RAKE receiver.

• Korean Journal of Breeding Science
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• v.40 no.4
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• pp.387-393
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• 2008

Over 7 individual rice (Oryza sativa L.) plants per a line were sowed and sampled by pooled sampling method for genomic DNA extraction. The 5,400 flanking sequence tags (FSTs) were analysed by adaptor PCR and direct sequencing. FST analysis showed that the intragenic FSTs, the intergenic FSTs, and the original insertional sequences including hot spot covered 48.1% (2,597), 25.6% (1,383), and 25% (1,350), respectively. The 2,597 intragenic FSTs were used for genotyping to determine whether they are heterozygous or homozygous, and 1,393 core lines were selected. Among them, 422 knockout genes were distributed on chromosome 3, while 56 - 157 intragenic FSTs scattered on other chromosomes. Among 1,393 FSTs, known genes such as transcription factor covered 59.4% (827), while unknown genes such as expressed protein covered 40.6% (566). RT-PCR indicated that some core lines had no expression or decreased expression level in their knockout genes. It means that core lines are very useful knockout lines for functional genomic studies.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.5B
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• pp.931-941
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• 2000

We propose a serial acquisition scheme using antenna arrays for initial acquisition of direct sequence spread spectrum (DS-SS) signals, which can lower substantially the range of detectable signal-to-noise ratio (SNR). The proposed scheme uses the sum of the independent decision samples form psedo-noise (PN) co-phased noncoherent I-Q matched filters (MFs) associated with antenna arrays as a decision variable in order to enhance SNR of the resulting signal. We analyze its mean acquisition time performance under an additive white Gaussian noise (AWGN) channel and a flat Rayleigh fading channel by deriving the expressions for the probabilities of detection and false alarm. From mumerical results, we see that the acquisition performance of the proposal scheme becomes improved continually as the number of antennas increses.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.16 no.11
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• pp.1054-1062
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• 1991

In this paper a communication system using direct sequence spread spectrum (DS/SS) technique is constructed to transmit burst format data over power line channel with impulsive noise and narrowband interferences. Fast code synchronization is acquired by digital matched filter and data decision is accomplished by sampling pulses. In order to examine the performance of the power line communication system, but error rate and packet loss rate are measured over the simulation channel with various noise sources. When the packet composed of 1-bit preamble and 63-bit data is transmitted under very high burst impulsive noise, the bit error rate is about 10$^3$-10$^4$ and the packet loss rate is below 0.07.