4,150 research outputs found
Differential space-time modulation schemes for smart antenna aided generalized multicarrier DS-CDMA systems
Get PDFAbstract—Differential space-time modulation (DSTM) schemes were proposed for detection without any knowledge of the Channel State Information (CSI), which is an attractive feature in the presence of fast fading channels, where accurate channel estimation is a challenging task. In this contribution we invoke two DSTM schemes for improving the achievable performance in the downlink of a generalized MC DS-CDMA system employing smart antennas, namely the Differential Space-Time Spreading (DSTS) scheme and the Differential Steered Space-Time Spreading (DSSTS) scheme. In the MC DS-CDMA system considered the transmitter employs multiple antenna arrays and each of the antenna arrays consists of several antenna elements. Furthermore, the generalized MC DS-CDMA system employs both time- and frequency (TF) domain spreading, where a user-grouping technique is employed for reducing the effects of multiuser interference
Performance of Broadband Multicarrier DS-CDMA using Space-Time Spreading-Assisted Transmit Diversity
No full textIn this contribution multicarrier direct-sequence code-division multiple-access (MC DS-CDMA) using space–time spreading (STS)-assisted transmit diversity is investigated in the context of broadband communications over frequency-selective Rayleigh-fading channels. We consider the issue of parameter design for the sake of achieving high-efficiency communications in various dispersive environments. Furthermore, in contrast to conventional MC DS-CDMA schemes employing time (T)-domain spreading only, in this contribution we also investigate broadband MC DS-CDMA schemes employing both T-domain and frequency (F)-domain spreading, i.e., employing TF-domain spreading. The bit-error rate (BER) performance of STS-assisted broadband MC DS-CDMA is investigated for downlink transmissions associated with the correlation based single-user detector and the decorrelating multiuser detector. Our study demonstrated that when appropriately selecting the system parameters, broadband MC DS-CDMA using STS-assisted transmit diversity constitutes a promising downlink transmission scheme. This scheme is capable of supporting ubiquitous communications over diverse communication environments without BER performance degradation. Index Terms—Broadband system, code-division multiple access (CDMA), frequency-domain spreading, frequency-selective fading, multicarrier direct-sequence code-division multiple-access (MC-DS-CDMA), multicarrier CDMA, multicarrier modulation, multiuser detection, space–time spreading (STS), transmit diversity
Adaptive Minimum-BER Linear Multiuser Detection for DS-CDMA Signals in Multipath Channels
No full textThe problem of constructing adaptive minimum bit error rate (MBER) linear multiuser detectors is considered for direct-sequence code division multiple access (DS-CDMA) signals transmitted through multipath channels. Based on the approach of kernel density estimation for approximating the bit error rate (BER) from training data, a least mean squares (LMS) style stochastic gradient adaptive algorithm is developed for training linear multiuser detectors. Computer simulation is used to study the convergence speed and steady-state BER misadjustment of this adaptive MBER linear multiuser detector, and the results show that it outperforms an existing LMS-style adaptive MBER algorithm first presented at Globecom'98 by Yeh, Lopes and Barry
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कठिन शब्द : भूमि, कोटा, प्रतिरूप, विकास, व्यवसाय, कृष
Measurement of the branching fractions of Ds+→η'X and Ds+→η'ρ+ in e+e-→Ds+Ds-
No full textÇetin, Serkant Ali (Dogus Author)We study Ds+ decays to final states involving the η' with a 482 pb-1 data sample collected at s=4.009 GeV with the BESIII detector at the BEPCII collider. We measure the branching fractions B(Ds+→η'X)=(8.8±1.8±0.5)% and B(Ds+→η'ρ+)=(5.8±1.4±0.4)% where the first uncertainty is statistical and the second is systematic. In addition, we estimate an upper limit on the non-resonant branching ratio B(Ds+→η'π+π0)<5.1% at the 90% confidence level. Our results are consistent with CLEO's recent measurements and help to resolve the disagreement between the theoretical prediction and CLEO's previous measurement of B(Ds+→η'ρ+)
TRANSCEIVER FOR DS/CDMA MIMO ANTENNA SYSTEMS UTILIZINGFULL RECEIVER DIVERSITY
No full text1. 청구범위에 기재된 발명이 속한 기술분야본 발명은 다수의 송신안테나에서 동시에 독립적인 데이터를 전송하고 다수의 수신 안테나를 이용하여 수신하는 미모(MIMO: Multiple-Input Multiple-Output) 안테나를 사용하는 디에스/시디엠에이(DS/CDMA : Direct Sequence / Code Division Multiple Access) 통신 시스템에 관한 것임.2. 발명이 해결하려고 하는 기술적 과제본 발명은, 다수의 송수신 안테나를 사용하는 DS/CDMA MIMO 안테나 시스템에서 여러 개의 확산 코드와 송신 안테나 마다 다른 스크램블링 코드를 이용하여 동시에 전송되는 각 데이터 심볼이 서로 다른 서명수열을 갖도록 함으로서 수신단에서 완전한 수신다이버시티 이득을 얻을 수 있는 전송 시스템을 제공하고자 함.3. 발명의 해결방법의 요지 본 발명은, 전송하고자 하는 원본 데이터를 전달받아 이를 다수의 데이터로 병렬시켜 소정 개수의 확산 코드로 확산하고 다시 송신 안테나 고유의 스크램블링 코드로 스크램블링하여 상기한 다수의 송신안테나에서 데이터를 전송하는 송신수단; 및 상기 다수의 수신 안테나를 통해 수신되는 데이터에 대해 상기 전송수단에서 이루어진 확산 및 스크램블링을 감안한 역확산 처리를 통해 상기 원본 데이터를 복원하는 수신수단을 포함함.4. 발명의 중요한 용도본 발명은 무선통신 시스템에 이용됨.스크램블링, 시디엠에이, 디에스/시디엠에이, 미모 안테나, 다이버시
CONTINUOUS VARIABLE-STRUCTURE CONTROLLER FOR BLDDSM POSITION CONTROL WITH PRESCRIBED TRACKING PERFORMANCE
No full textThe continuous, accurate, and robust sliding mode tracking controller based on a disturbance observer for a brushless direct drive servo motor (BLDDSM) is presented. Although the conventional sliding mode control (SMC) or variable structure control (VSC) can give the desired tracking performance, there exists an inevitable chattering problem in control which is undesirable for a direct drive system. With the proposed algorithm, not only are the chattering problems removed, but also the prescribed tracking performance can be obtained by using the efficient compensation of the disturbance observer. The design of the sliding mode tracking controller for the prescribed, accurate, and robust tracking performance without the chattering problem is given based on the results of the detailed stability analysis. The usefulness of the proposed algorithm is demonstrated through the computer simulation for a BLDDSM under load variations
Morphohistometric Investigation and bcl-2 Expression in the Placenta of Chromosomally Abnormal Pregnancy
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