3,372 research outputs found
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
Initial Plant Growth in Sand Mine Spoil Amended with Peat Moss and Fertilizer Under Greenhouse Conditions: Potential Species for Use in Reclamation
No full textThe Great Lakes Basin exhibits the largest collection of freshwater sand dunes in the world. Sand dunes are ecologically important and support a unique assemblage of flora and fauna. Sand dunes are also economically valuable. However, when sand dunes are mined, soil quality is drastically reduced. Therefore, soil quality improvements followed by revegetation maybe necessary for successful reclamation. This study evaluates the germination and initial growth of 2 legume species, sundial lupine (Lupinus perennis) and Illinois bundleflower (Desmanthus illinoensis), and 2 warm-season grass species, Indian grass (Sorghastrum nutans) and little bluestem (Schizachyrium scoparium), in the presence of 2 soil amendments (inorganic fertilizer and sphagnum peat moss) added to spoil from a local sand mine. We sowed species in pots and propagated them under greenhouse conditions. Results indicate that sundial lupine and Illinois bundleflower exhibited the greatest germination and growth among species. Peat moss had the greatest overall impact on germination and growth while the addition of fertilizer positively affected initial growth. Based on these results, sundial lupine is recognized as a primary candidate for sand mine reclamation, while Illinois bundleflower is also recommended as an appropriate species for revegetation efforts. We recommend using soil amendments that are functionally equivalent to peat in increasing soil water holding capacity. We further suggest that fertilization may be accomplished by including legumes in plant species mixes used for revegetation. Results presented here may help to identify appropriate species and soil amendments for the reclamation of former sand mines or restoration of freshwater sand dunes
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+)
Validity of the 16-metre PACER and six-minute walk test in adults with Down syndrome
No full textPurpose: The purpose was to establish criterion-related validity of the 16-metre PACER and six-minute walk distance (6MWD) tests to VO2 peak as well as predictors of VO2 peak in adults with Down syndrome (DS).
Methods: Adults with DS (24 males and 19 females) aged 18–50 years performed the three aerobic tests on non-consecutive days during a one-week period. To assess validity, peak oxygen uptake was measured directly on a motorized treadmill. Pearson–product moment correlations were performed. Predictors of VO2 peak were assessed with a stepwise multiple regression analysis. Agreement between PACER and VO2 peak was assessed by Bland–Altman plot.
Results: Linear regression revealed that the PACER (R2 = 0.86) and the 6MWD (R2 = 0.75) were significantly related to VO2 peak (p 0.7; p < 0.05). PACER, 6MWD and BMI are significant predictors of VO2 peak (p < 0.05).
Conclusion: The 16-metre PACER and 6MWD are valid field tests for predicting aerobic capacity in adults with D
Groupwise Multiuser Detection in a Multirate DS-CDMA System
No full textThis report presents the performance of groupwise successive interference cancellation (GSIC) within a direct sequence code division multiple access system (DS-CDMA). Within the groups, matched filter and PIC receivers are used for detection of the users. A multirate DS-CDMA system model, based on a single rate system is presented. Although the study of multiuser detection for single rate systems has resulted in several structures, multiuser receivers designed specifically for a DS-CDMA variable spreading factor multirate system are shown to be benificial. Since they can exploit the specific properties of these systems. The bit error rate performance of matched filter, parallel interference cancellation and GSIC receivers are compared in AWGN channel. The GSIC receiver is seen to perform best. The various GSIC receiver variants are then simulated in a Rayleigh fading channel to investigate how they will perform in a realistic mobile environment. Finally the impact of fixed delay is studied.Applied SciencesElectrical EngineeringTelecommunications and Traffic-Control Systems Grou
Multibeam Adaptive Antenna Array Applied to DS-CDMA Communication Systems
No full textIn this thesis, the multibeam adaptive antenna array has been investigated for application to DS/CDMA The objective is to design an adaptive controller and a beamformer for an Adaptive Antenna Array suitable for the wideband DS/CDMA environment. The research was in accordance with the current research on third generation mobile communications systems in development in Europe…Applied SciencesInformation Technology and SystemsTelecommunications and Traffic Control Systems Grou
Performance Analysis of DS, SFH and Hybrid DS/SFH CDMA in an Micro - and Macro cellular Environment with Fading and Shadowing: Task report
No full textIn this report, a performance analysis of DS, SFH and Hybrid DS/SFH in terms of biterror probability, throughput and delay are presented. The modulation techniques used are BPSK and QPSK. The effect of Selection Diversity and Forward Error Correction (FEC) Codeon the performance are also investigated. A comparison between the CDMA techniques is made in macro- and micro cellular environment.Applied SciencesElectrical EngineeringTelecommunications and Traffic Control Systems Grou
Reduced-rank adaptive least bit-error-rate detection in hybrid direct-sequence time-hopping ultrawide bandwidth systems
No full textDesign of high-efficiency low-complexity detection schemes for ultrawide bandwidth (UWB) systems is highly challenging. This contribution proposes a reduced-rank adaptive multiuser detection (MUD) scheme operated in least bit-errorrate (LBER) principles for the hybrid direct-sequence timehopping UWB (DS-TH UWB) systems. The principal component analysis (PCA)-assisted rank-reduction technique is employed to obtain a detection subspace, where the reduced-rank adaptive LBER-MUD is carried out. The reduced-rank adaptive LBERMUD is free from channel estimation and does not require the knowledge about the number of resolvable multipaths as well as the knowledge about the multipaths’ strength. In this contribution, the BER performance of the hybrid DS-TH UWB systems using the proposed detection scheme is investigated, when assuming communications over UWB channels modeled by the Saleh-Valenzuela (S-V) channel model. Our studies and performance results show that, given a reasonable rank of the detection subspace, the reduced-rank adaptive LBER-MUD is capable of efficiently mitigating the multiuser interference (MUI) and inter-symbol interference (ISI), and achieving the diversity gain promised by the UWB systems
Arbitrary spin conformal fields in (A)dS
No full textAbstractTotally symmetric arbitrary spin conformal fields in (A)dS space of even dimension greater than or equal to four are studied. Ordinary-derivative and gauge invariant Lagrangian formulation for such fields is obtained. Gauge symmetries are realized by using auxiliary fields and Stueckelberg fields. We demonstrate that Lagrangian of conformal field is decomposed into a sum of gauge invariant Lagrangians for massless, partial-massless, and massive fields. We obtain a mass spectrum of the partial-massless and massive fields and confirm the conjecture about the mass spectrum made in the earlier literature. In contrast to conformal fields in flat space, the kinetic terms of conformal fields in (A)dS space turn out to be diagonal with respect to fields entering the Lagrangian. Explicit form of conformal transformation which maps conformal field in flat space to conformal field in (A)dS space is obtained. Covariant Lorentz-like and de-Donder like gauge conditions leading to simple gauge-fixed Lagrangian of conformal fields are proposed. Using such gauge-fixed Lagrangian, which is invariant under global BRST transformations, we explain how the partition function of conformal field is obtained in the framework of our approach
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