• Title, Summary, Keyword: Diversity

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Transmit Diversity Using Windowing Scheme in OFDM System (OFDM 시스템에서 윈도윙 기법을 이용한 송신 다이버시티)

  • Kim, Yong-June;Rim, Min-Joong;Lim, Dae-Woon
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.32 no.9A
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    • pp.871-877
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    • 2007
  • In this paper, we propose a new transmit diversity scheme using window functions in orthogonal frequency division multiplexing (OFDM) system. Transmit diversity of the scheme is varied with window functions and the condition of the window function to maximize transmit diversity is derived. The proposed scheme can be considered as a generalization of the diversity schemes such as cyclic delay diversity (CDD), orthogonal transmit diversity (OTD), and frequency switched transmit diversity (FSTD).

Analysis on the Impact of Multiple-Antenna Transmit Schemes on Multiuser Diversity

  • Lee, Myoung-Won;Mun, Cheol;Yook, Jong-Gwan
    • Journal of electromagnetic engineering and science
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    • v.6 no.4
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    • pp.222-228
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    • 2006
  • In this paper, the performance of a multiuser diversity system combined with a multi-element transmit antenna system is analyzed under the assumption of independent Rayleigh fading. A measure of system .level performance is an average channel capacity as a function of the number of users and antennas. Average channel capacity is obtained from the instantaneous signal-to-noise ratio(SNR) distribution combined by both transmit diversity(TD) at each link and multiuser diversity at system level. Numerical results show that closed-loop antenna techniques provide an additional gain with multiuser diversity system due to array gain, even though space diversity gain reduces multiuser diversity gain. On the other hand, the space-time block coding(STBC) that provides full order space diversity gain only has a destructive influence on multiuser diversity.

Circular Polarization Diversity in Indoor Wireless Mobile Environments

  • Ha, Deock-Ho;Ko, Yeon-Hwa;An, Jae-Sung;Kim, Tai-Hong
    • Journal of electromagnetic engineering and science
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    • v.4 no.3
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    • pp.128-136
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    • 2004
  • In this paper,. with the aim of achieving the expected performance improvement for a polarization diversity system, we analyzed two-branch polarization diversity at the receiving end of a mobile link which a transmitter emits circularly polarized wave. In this analysis, to calculate the correlation coefficient considered by XPD(cross polarization discrimination) between the two received signals, a simple theoretical model of circular polarization diversity is adopted. From the analysis results, it is clearly seen that the correlation coefficient of circular polarization diversity evaluated by the XPD is less than that of conventional linear polarization diversity. And also, we designed and implemented a circular polarization diversity system with micro-strip antenna. By using the circular polarization diversity system, we analyzed the measured data in indoor NLOS(Non-Line-Of-Sight) environments. From this analysis results, it is also clearly seen that the diversity effect of circular polarization diversity system shows better performance compared to the conventional linear diversity system by about 3 dB high.

The Fabrication and Performance Estimation of Circularly Polarization Diversity System for Multipath Fading Reduction (다중경로페이딩 경감을 위한 원편파 다이버시티 시스템 제작 및 성능 평가)

  • 이주현;김판신;안재성;김태홍;고연화;김흥진;하덕호
    • Proceedings of the IEEK Conference
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    • pp.609-612
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    • 2003
  • For combating multipath fading in wireless radio environment, diversity schemes is useful. In this paper, for performance improvement of polarization diversity system, we analyzed a two-branch polarization diversity at the receiving end of a mobile link when the transmitter emits a circularly polarized wave. And In order to calculate the correlation coefficient considering the XPD(cross polarization discrimination) between the received signals for the two diversity branches, a simple theoretical model of circular polarization diversity is adopted and calculate correlation coefficient. From the analysis results, it is seen that the correlation coefficient of circular polarization diversity evaluated by the XPD is less than that of vertical polarization diversity. And also, we designed and fabricated circular polarization diversity system with microstrip antenna. we analyzed data measured in indoor NLOS environment using fabricated circular polarization diversity system. From the measurement results, it is clearly seen that the diversity effect of circular polarization diversity system is higher 3dB than vertical polarization diversity system.

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The Effects of Perception Levels of Diversity on Team Performance: Moderating Effects of Conflict (다양성 지각 정도가 팀의 성과에 미치는 영향: 갈등의 조절효과를 중심으로)

  • Yun, Jun Hee;Shin, Ho-Chul
    • Journal of the Korean Society for Quality Management
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    • v.41 no.2
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    • pp.289-300
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    • 2013
  • Purpose: The results of prior studies investigating main effects between diversity and team performance are neither clear nor consistent. This study seeks to provide more evidence for a direct link between these two. The present study also attempts to close a gap in the literature by examining conflict as a moderator of the relationship between diversity and team performance. Methods: As suggested by Williams and O'Reilly(1998), this study examines the effects of perception levels of three specific types of diversity (social category diversity, value diversity, and informational diversity) and two contextual moderators (task conflict and relationship conflict) on team performance. Results: The results show that perception levels of all three types of diversity are significantly related to team performance in the current sample of 313. Results also indicate that relationship conflict significantly interacted with the perception levels of diversity in relating to team performance. Results for task conflict, however, fails to support the hypothesis. Conclusion: The results suggest that the effects of diversity on team functioning depend on how diversity is perceived by team members, rather than actual diversity seen by team members. Theoretical and practical implications are reviewed, and limitations of the study and suggestions for future research are addressed.

Performance Analysis of Angle Time Transmit Diversity in Urban Area (도심환경에서 각도-시간 송신다이버시티의 성능분석)

  • Park, Byeong-Hoon
    • The Transactions of the Korean Institute of Electrical Engineers P
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    • v.60 no.4
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    • pp.200-205
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    • 2011
  • In multipath fading channel, diversity is essential to mitigate the impairments. In this paper, we have proposed the angle diversity scheme called ATTD(Angle Time Transmit Diversity) instead of Alamouti's STTD(Space Time Transmit Diversity) and have analyzed the performance of the proposed scheme when signal powers caused by the transmission to different angles are different. Based on it, we have measured the wireless vector-channel in the urban area, which has lots of high-story buildings, using the data collected from the 8 by 4 smart array antenna system that we made. According to the measured data, the received signals from different angles have different signal powers. Our performance analysis results show that the proposed scheme has better performance than the space diversity scheme when the received path signal power is at least -7dB compare to the strongest path signal power.

The Analysis of Protection Ratio and Its Effect of Interference-to-Noise Ratio for Digital Microwave System with Diversity

  • Suh Kyoung-Whoan;Jang Won-Gyu
    • Journal of electromagnetic engineering and science
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    • v.6 no.3
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    • pp.189-195
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    • 2006
  • In this paper, the derivation of the protection ratio for the digital microwave system with diversity is newly suggested for a basic guidance of initial planning for frequency coordination, and computational results are presented for an actual radio frequency band. The net filter discrimination has been also examined to see the effect of the adjacent channel protection ratio caused by adjacent channel interference. In addition, the protection ratios for the space or frequency diversity system are analyzed in terms of diversity improvement factors to find out an equivalent allowable noise-to-interference ratio (N/I) from degraded fade margin. According to results for 6.2 GHz system, with the space diversity of 25 m distance between antennas or the frequency diversity of ${\Delta}f/f=0.05$, under 64-QAM and 60 km at BER $10^{-6}$, the protection ratio can be greatly reduced in comparison to the non-diversity system. So, assuming that only the same protection ratio as the non-diversity system is kept, it is shown that the system with diversity may get more interference level of N/I allowing from 9.0 to - 5.9 dB or from 6.0 to - 4.3 dB for the space or frequency diversity. In consequence, it is concluded that the diversity system is more robust or tolerable for interferences or fades, which may play an important role in overcoming N/I to some extent.

SER Analysis of QAM with Space Diversity in Rayleigh Fading Channels

  • Kim, Chang-Joo;Kim, Young-Su;Jeong, Goo-Young;Mun, Jae-Kyung;Lee, Hyuck-Jae
    • ETRI Journal
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    • v.17 no.4
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    • pp.25-35
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    • 1996
  • This paper derives the symbol error probability for quadrature amplitude modulation(QAM) with L-fold space diversity in Rayleigh fading channels. Two combining techniques, maximal ratio combining(MRC) and selection combining(SC), are considered. The formula for MRC space diversity is obtained by averaging the symbol error probability of M-ary QAM in an additive white Gaussian noise(AWGN) channel over a chi-square distribution with 2L degrees of freedom. The obtained formula overcomes the limitations of the earlier work, which has been limited only to deriving the symbol error rate(SER) of QAM with two branch MRC space diversity. The formula for SC space diversity is obtained by averaging the symbol error probability of M-ary QAM in an AWGN channel over the distribution of the maximum signal-to noise ratio among all of the diversity channels for SC space diversity has been reported yet. Analytical results show that the probability of error decreases with the order of diversity gain per additional branch decreases as the number of branches becomes larger. On the other hand, the performance of 16 QAM with MRC becomes much better than that of SC as the number of branches becomes larger. By giving the order of diversity, L, and the number of signal points, M, we have been able to obtain the SER performance of QAM with general space diversity. These results can be used to determine the order of diversity to achieve the desired SER in land mobile communication system employing QAM modulation.

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Bandwidth-efficient Cooperative Diversity with Rotated Constellations and Its Performance Analysis

  • Lei, Weijia;Xie, Xianzhong;Li, Xiangming
    • KSII Transactions on Internet and Information Systems (TIIS)
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    • v.4 no.6
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    • pp.989-1005
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    • 2010
  • Cooperative diversity is a technique with which a virtual multiple antenna array is established among the single antenna users of the wireless network to realize space diversity. Signal space diversity (SSD) is a bandwidth-efficient diversity technique, which uses constellation rotation and interleaving techniques to achieve diversity gain. A new cooperative diversity scheme with rotated constellations (RCCD) is proposed in this paper. In this scheme, data are modulated by using a rotated constellation, and the source and the relays transmit different components of the modulated symbols. Since any one of the components contains full information of the symbols, the destination can obtain multiple signals conveying the same information from different users. In this way, space diversity is achieved. The RCCD scheme inherits the advantage of SSD - being bandwidth-efficient but without the delay problem of SSD brought by interleaving. The symbol error rate of the RCCD scheme is analyzed and simulated. The analysis and simulation results show that the RCCD scheme can achieve full diversity order of two when the inter-user channel is good enough, and, with the same bandwidth efficiency, has a better performance than amplify-and-forward and detect-and-forward methods.

Capacity of Multiuser Diversity with Cooperative Relaying in Wireless Networks (협동 릴레이와 다중 사용자 다이버시티를 이용하는 무선 통신 네트워크의 용량 분석)

  • Joung, Hee-Jin;Mun, Cheol;Seo, Jeong-Tae;Yoo, Kang-Hee
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.33 no.6C
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    • pp.423-428
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    • 2008
  • We consider the use of cooperative diversity in a multiuser wireless data network. This paper provides an analysis of the interaction between cooperative diversity and multiuser diversity on downlink channels. By using approximation of the signal-to-noise ratio (SNR) distribution of each cooperative diversity link by Gamma distribution, an analytic expression is derived for the average throughput of a single-cell wireless system with multiple cooperative diversity links combined with a fair-access scheduler. The proposed analytic approach is verified through comparisons with simulated results and shows that cooperative diversity makes the detrimental impacts on multiuser diversity.