• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.3
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• pp.684-691
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• 1996

Since the period of a spreading code in DS/SS communication systems is generally long, it is necessary to make the code acquisition as fast as possible. The code acquisition time can be sued as a measure to evaluate the performance of code acquisition systems. The search rate of serial search codee acquisition system used in the coventional CDMA cellular system is lower than that of the matched filter technique. In order to reduce the code acquisition time, this paper proposes hybrid code acquisition system composed filters combined with serial search blocks. In the proposed system, the matched filter sweeps possible code phases fast and the acquired phase information is verified by the serial search block. The mean and the variance of its acquisition time are calculated and compared with those of double dwell serial search system. The results indicate better performance of the proposed system by yielding its small vaues of the mean and the variance of code acquisition time.

• Proceedings of the KIEE Conference
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• 2004.11c
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• pp.196-199
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• 2004

This paper presents a structure of the searcher using the space diversity in array antenna system operating in the DS/CDMA signal environments. The new technique exploits the fact that the In-phase and Quadrature components of interferers can respectively be viewed as independent Gaussian noise at each antenna element in most practical CDMA (Code Division Multiple Access) signal environments. The proposed PN acquisition scheme is a single dwell serial PN acquisition system consisting of two stage, that is, the searching stage and the verification stage. The searching stage correlates the received signals with the local PN oscilator for obtaining the synchronous energy at the entire uncertainty region. The verification stage compares the searching energy with the optimal threshold, which is pre-designed in the Lock-Detector, and decides whether the acquisition is successful or fail. In this paper, we analyzed the relationship of both diversity order and the mean acquisition time. In general, It is known that the mean acquisition time decreases significantly as the number of antenna elements increases. But, the enhancement of the performance is saturated in terms of PN acquisition scheme. Therefore, to decrease the mean acquisition time, we must design the optimal array antenna system by considering the operating SNR range of the receiver, the detection probability, and the false alarm probability. The performance of the proposed acquisition scheme is analyzed in frequency-selective Rayleigh fading channels. In this paper, the effect of the number of antenna elements on acquisition scheme is considered in terms of the detection probability, false alarm probability. and the mean acquisition time.

• Proceedings of the IEEK Conference
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• 2000.06a
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• pp.189-192
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• 2000

In this paper, we consider a code acquisition of W-CDMA signals over multipath Rayleigh fading channel when double-dwell serial search code acquisition is used for initial synchronization. We derive the detection and false alarm probability, and mean acquisition time mathematically by taking into account of multiple H$\_$l/ cells and double-dwell serial search. It is noteworthy that the more the number of the post-detection integration, the shorter the mean acquisition time in low SNR.

• Proceedings of the IEEK Conference
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• 2000.09a
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• pp.233-236
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• 2000

In this paper, we consider a code acquisition of W-CDMA signals over multipath Rayleigh fading channel when double-dwell serial search code acquisition is used for initial synchronization. We derive the detection and false alarm probability, and mean acquisition time mathematically by taking into account of multiple H$_1$ cells and double-dwell serial search. It is noteworthy that the more the number of the post-detection integration, the shorter the mean acquisition time in low SNR.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.34S no.8
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• pp.10-19
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• 1997

In this paper, perfodrmance of matched-filter (MF) acquisition scheme is analyzed for a direct-sequence/code-division-multiple-access (DS/CDMA) system in a microcellular environment. Mean acquistion time is used as a performance measure. It is demonstrated that acquisition performance is enhanced using interference suppression filter in a Rician fading channel. To apply for multiuser environments, multiple access interference is considered in the performance analysis. From the numerical results, it is shown that mean acquistion time decreases with the increasing SNR/chip, and acquisition performance is improved as the number of taps of interference suppression filter. It is also shown that mean acquisition time increases with the number of users in the system, and acquistion performance is degraded as the icrease of narrowband interference bandwidth. The analysis in this paper can be applied to a DS/CDMA overlay environment.

• ETRI Journal
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• v.29 no.1
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• pp.1-7
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• 2007

In this paper, we analyze the performance of double-dwell hybrid initial acquisition in a direct sequence ultra-wideband (DS-UWB) system via detection, miss, false alarm probabilities, and mean acquisition time. In the analysis, we consider the effect of the acquisition sequence as well as the deployment scenario of the abundant multipath components over small coverage of the piconet in the DS-UWB system. Based on the simulation, we obtain various performance measures for the mean acquisition time by varying parameters such as the total number of hypotheses to be searched, subgroup size, and dwell time. We thereupon suggest the optimum parameter set for the initial acquisition in the DS-UWB system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.7A
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• pp.696-701
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• 2006

In this paper, we analyze the performance of double-dwell hybrid initial acquisition in DS-UWB system via detection, miss, false alarm probabilities and mean acquisition time. In the analysis, we consider the effect of the acquisition sequence, and deployment scenario of the abundant multipath components over the small coverage of the piconet in DS-UWB system. Based on the simulation, we obtain various performance on the mean acquisition time by varying the parameters, such as the total number of hypotheses to be searched, subgroup size, and dwell time. Then, we suggest the optimum parameter set for the initial acquisition in DS-UWB system.

• Investigative Magnetic Resonance Imaging
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• v.26 no.2
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• pp.125-134
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• 2022

Purpose: The aim of this study was to investigate the change in signal sensitivity over different acquisition start times and optimize the scanning window to provide the maximal signal sensitivity of [1-¹³C]pyruvate and its metabolic products, lactate and alanine, using spatially localized hyperpolarized 3D ¹³C magnetic resonance spectroscopic imaging (MRSI). Materials and Methods: We acquired 3D ¹³C MRSI data from the brain (n = 3), kidney (n = 3), and liver (n = 3) of rats using a 3T clinical scanner and a custom RF coil after the injection of hyperpolarized [1-¹³C]pyruvate. For each organ, we obtained three consecutive 3D ¹³C MRSI datasets with different acquisition start times per animal from a total of three animals. The mean signal-to-noise ratios (SNRs) of pyruvate, lactate, and alanine were calculated and compared between different acquisition start times. Based on the SNRs of lactate and alanine, we identified the optimal acquisition start timing for each organ. Results: For the brain, the acquisition start time of 18 s provided the highest mean SNR of lactate. At 18 s, however, the lactate signal predominantly originated from not the brain, but the blood vessels; therefore, the acquisition start time of 22 s was recommended for 3D ¹³C MRSI of the rat brain. For the kidney, all three metabolites demonstrated the highest mean SNR at the acquisition start time of 32 s. Similarly, the acquisition start time of 22 s provided the highest SNRs for all three metabolites in the liver. Conclusion: In this study, the acquisition start timing was optimized in an attempt to maximize metabolic signals in hyperpolarized 3D ¹³C MRSI examination with [1-¹³C] pyruvate as a substrate. We investigated the changes in metabolic signal sensitivity in the brain, kidney, and liver of rats to establish the optimal acquisition start time for each organ. We expect the results from this study to be of help in future studies.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.7A
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• pp.682-688
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• 2006

In this paper, a soft-decision method for initial PN code acquisition in pilot-channel aided Direct Sequence Code Division Multiple Access (DS-CDMA) systems is proposed in order to improve the acquisition performance. We apply this technique to the conventional hybrid search algorithm and analyze it in terms of mean code acquisition time. For the analysis, we present mathematical model of proposed algorithm and also perform the simulation under IMT-2000 channel models. Numerical results show that our proposed scheme outperforms the conventional one by 0.2 - 0.4 sec with respect to the mean code acquisition time because the soft decision technique can mitigate the possible decline in search performance caused by the use of a hard-decision technique.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.6
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• pp.22-27
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• 2011

This paper presents an efficient technique to reduce PN code acquisition time considerably by adjusting threshold values in direct sequence spread spectrum (DS-SS) systems. The proposed algorithm employs a pre-dump mode prior to a search mode, and the pre-dump mode determines threshold values of both search and verification modes depending on its correlation energy, which can improve not only the rejection performance of false code phases in the search mode but also that in the verification mode. The proposed method can reduce the mean code acquisition time by about 40% without increase of hardware costs compared with the conventional technique.