• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.29 no.10A
• /
• pp.1159-1166
• /
• 2004

This paper follows up the previous work on the linearly constrained, modified minimum mean-squared error(MMSE) detection for direct-sequence code-division multiple-access DS-CDMA) systems in fading channels. We find a condition to avoid the breakdown of joint modified MMSE detection and pilot symbol-aided channel estimation (PSACE). The linearly constrained, modified MMSE solution is theoretically shown to be robust against time variations in Rayleigh fading channels. This fact is consistent with the simulation results. We also show that under some conditions the linearly constrained, modified MMSE detection maximizes the output signal-to-interference-plus-noise ratio.(SINR)

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.33 no.1C
• /
• pp.102-109
• /
• 2008

The higher data rate of mobile communications has been required for various multimedia services. In DS-CDMA system, one of the solutions to increase the throughput is to use multicode. However, multipath channel destorys the orthogonality of spreading codes, which causes the intercede interference(ICI). ICI gives severe effect on multicode DS-CDMA for BER performance. Conventionally, multicode DS-CDMA system uses the Rake receiver with turbo code, which cannot overcome error floor caused by ICI. In this paper, we propose frequency domain turbo equalization based on minimum mean squared error(FDTE-MMSE) for multicode DS-CDMA in frequency selective channel and evaluate its BER performance by computer simulation. The simulation results show that FDTE-MMSE gives much better performance in high Eb/N0 than the Rake receiver with turbo code in multipath length L>1.

• The Transactions of the Korea Information Processing Society
• /
• v.7 no.10
• /
• pp.3218-3225
• /
• 2000

In this paper, the performance of the MMSE multiauser deteclor was analyzed with the SNR from the standpoint of the exproient, according to the multiuser, In was analyzed not only at the AWGN channel, but at the fading channel also. With the result of this test, the MMSE multiuser detector showed better performance of multi-connection interference in comparison with comon deterctors. However, its disadvantageis that the hardware turns out to be too complicated and that it requires too many calculations. Because of multi-connectioninterference that happens as a result of spreading code horizontally, the DS/CDMA system, which contatins the same frequency and time, turns out to thve interference according to the quality of the call and the number of users. In order to solve these problems, an adaptive MMSE multiuser detector is suggested. To increase the system's processing gain, the hardware's complexity can be reduced by establishing the number of taps wirhin the detector.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2009.05a
• /
• pp.447-450
• /
• 2009

In this paper, binary pulse-antipodal modulation (2PAM) direct-sequence (DS) ultra-wideband (UWB) system is applied to multiple input multiple output (MIMO) system using vertical bell lab layered space-time (V-BLAST) structure to achieve high-data-rate communications over indoor wireless channels. The relationship between antenna dimension and BER performance of 2PAM DS UWB MIMO system is discussed. In the receiver of UWB-MIMO system, various MIMO detection algorithms such as zero-forcing (ZF), ZF-ordered successive interference cancellation (OSIC), minimum-mean-square-error (MMSE), MMSE-OSIC and maximum likelihood (ML) are comparatively studied.

• Proceedings of the IEEK Conference
• /
• 2002.06a
• /
• pp.69-72
• /
• 2002

In this paper, adaptive minimum mean-squared error (MMSE) multiuser detector combined with decision-feedback detector (DFD) is considered fur near-far resistant DS-CDMA system. To provide a reliable input to the adaptive MMSE detector, multiple-access interference (MAI) is regenerated using bit estimates from DFD and subtracted from the received signal. In the adaptive MMSE detector, the effect of the imperfect cancellation is compensated by a least mean square (LMS) algorithm. Through the numerical results, it is shown that, in a near-far situation, the proposed scheme provides superior performance to the matched filter (MF) receiver, adaptive MMSE detector, and DFD in terms of the bit error rate (BER).

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.10A
• /
• pp.1034-1041
• /
• 2007

In this paper, we propose a FD USE (frequency domain minimum mean square error) equalizer algorithm for MBOK DS-UWB (M-ary bi-orthogonal keying direct sequence UWB) systems considered as a PHY proposal for high-speed wireless communication in IEEE 802.15.TG3a. The conventional FD MMSE equalization scheme has a structural limit due to insertion of the cyclic prefix (CP) in all transmit packets, but the proposed scheme is able to equalize the channel effect without CP. In order to overcome channel estimation error by multipath delay, we introduce a moving FFT and a moving average scheme. Compared with conventional FD MMSE equalizer and the traditional TD (time domain) MMSE-RAKE receiver, the proposed FD MMSE equalizer has better BER performance and we demonstrate this result by computer simulation.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.25 no.10A
• /
• pp.1540-1547
• /
• 2000

In this paper, the performance of the MMSE multiuser detector is compared with the conventional detector with respect to the signal-to-noise ratio, the number of users and the Nakagami parameter under AWGN as well as Nakagami fading channel. The results show that the MMSE multiuser detector is superior to the conventional detector with respect to cancelling the multiple access interference. However, its drawback is the hardware's complexity. To solve this drawback, the advanced MMSE multiuser detector is presented, and its performance is analyzed. The number of taps in the advanced MMSE multiuser are independent of the processing gain. Thus, the system engineer can choose the appropriate number of taps in the detector to achieve a optimal trade-off between the hardware complexity and the performance of system.

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

• 한국노년학
• /
• v.39 no.4
• /
• pp.801-824
• /
• 2019

As becoming an aging society, there is a rising interest on dementia. But Dementia prevention program, executed at the national level, is in insufficient state. In this study, to design and diffuse Dementia prevention program, this study conduct Cognition improvement program and evaluate cognitive function in aspects of Discrimination, Organization, Thinking, Memorizing, and Concentration capacity. So that this study try to investigate how this Cognition improvement program will affect in detail to cognitive function in senior people. This study designed Silver Cognition program for 5 aspects of cognitive function; Discrimination, Organization, Thinking, and Concentration capacity. And this studyrecruited experimental group with control group, and conducted the program to them for 3 months. At the start and the end of the program, this study evaluated their MMSE-DS score, Geriatric depression scale, Quality of life score, and cognitive function test score by survey. Finally, this study compared and analyzed these first and second score to find the effects of this program to cognitive function. As the results compared between first and second score of MMSE-DS test, Geriatric depression scale, Quality of life scale, and cognitive function test, Silver Cognition program has a significant effects to improve cognitive function, MMSE-DS score and Geriatric depression scale. As the results of the test on cognitive function in 5 aspects, cognitive function is more improved in the order of Memorizing, Thinking, Concentration, Discrimination, and Organization capacity. After the Silver Cognition program, Memorizing and Thinking capacity have most improvement. But aging of brain function is faster in these two capacity, so if more concentrated education is conducted for these two capacity, then it will bring better effects for prevention of dementia.

• 한국노년학
• /
• v.40 no.2
• /
• pp.325-340
• /
• 2020

Early diagnosis and intervention of dementia is critical to minimize future risk and cost for patients and their families. The purpose of this study was to develop and validate Figure-Copy Test(FCT), as a new dementia screening test, that can measure neurological damage and cognitive impairment, and then to examine whether the grading precesses for screening can be automated through machine learning procedure by using FCT imag es. For this end, FCT, Korean version of MMSE for Dementia Screening (MMSE-DS) and Clock Drawing Test were administrated to a total of 270 participants from normal and damaged elderly groups. Results demonstrated that FCT scores showed high internal constancy and significant correlation coefficients with the other two test scores. Discriminant analyses showed that the accuracy of classification for the normal and damag ed g roups using FCT were 90.8% and 77.1%, respectively, and these were relatively higher than the other two tests. Importantly, we identified that the participants whose MMSE-DS scores were higher than the cutoff but showed lower scores in FCT were successfully screened out through clinical diagnosis. Finally, machine learning using the FCT image data showed an accuracy of 73.70%. In conclusion, our results suggest that FCT, a newly developed drawing test, can be easily implemented for efficient dementia screening.