7,584 research outputs found
Superseded - Human vs Machine Spoofing
No full textThis Item has been replaced. Please see Wester, M; Wu, Z; Yamagishi, J. (2015). Human vs Machine Spoofing, [dataset]. University of Edinburgh. https://doi.org/10.7488/ds/258
Ant-Colony Based Near-ML Space-Time Multiuser Detection for the STBC Assisted DS-CDMA Uplink
No full textIn this contribution, a novel Ant Colony Optimization (ACO) based Space-Time (ST) Multiuser Detection (MUD) algorithm was proposed in order to improve the Bit Error Ratio (BER) versus Signal-to-Noise Ratio (SNR) performance achieved by the Space-Time Block Code (STBC) assisted two transmit antenna aided fully loaded DS-CDMA system directly employing an ACO based MUD algorithm. Our simulation results demonstrate that the proposed ACO based MUD algorithm enables the fully loaded system to approach the single user performance associated with a second-order diversity gain. Furthermore, the complexity of the improved ACO based MUD algorithm is a factor of 1018 lower than that of the Maximum Likelihood (ML) MUD, when K = 32 users are supported by the STBC G2 assisted DS-CDMA systems employing Gold codes having a length of 31 chips
Blind Multi-User Equalisation for a Dispersive DS-CDMA Downlink under Carrier Frequency Offset Conditions
No full textWe address blind multiuser detection in a DS-CDMA downlink channel in the presence of carrier frequency offset. The synchronous users are separated by re-establishing orthogonality of their spreading sequences in a shared equaliser at the chip level. The adaptation algorithm is based on a constant modulus criterion of the various users, for which a stochastic gradient descent algorithm can be derived. We show that the resulting filtered-error filtered-regressor algorithm requires modifications in order to cope with carrier offset, and propose an combined blind multiuser equaliser with blind carrier frequency offset estimation. Simulations demonstrating the algorithm's convergence and BER performance are presented
Studies on the activity of superoxide dimutase in Miscanthus floridulus grown near a copper smelter in Taiwan.
No full textPerformance 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
Layered Steered Space–Time-Spreading-Aided Generalized MC DS-CDMA
No full textAbstract—We present a novel trifunctional multiple-input– multiple-output (MIMO) scheme that intrinsically amalgamates space–time spreading (STS) to achieve a diversity gain and a Vertical Bell Labs layered space–time (V-BLAST) scheme to attain a multiplexing gain in the context of generalized multicarrier direct-sequence code-division multiple access (MC DS-CDMA), as well as beamforming. Furthermore, the proposed system employs both time- and frequency-domain spreading to increase the number of users, which is also combined with a user-grouping technique to reduce the effects of multiuser interference
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
Multiple-Symbol Differential Sphere Detection Aided Successive Relaying in the Cooperative DS-CDMA Uplink
Full text linkThe conventional amplify-and-forward cooperative system is capable of achieving a superior performance with the aid of Multiple-Symbol Differential Sphere Detection (MSDSD), when compared to conventional differential detection (CDD) for transmission over time-selective channels. However, the conventional broadcast/cooperative twin-phase based relaying protocol encounters a 50% throughput loss imposed by half-duplex relaying. For combating this problem, in this paper, we create a MSDSD aided successive relaying based cooperative DS-CDMA system. We demonstrate that given the target BER of 10-4 , a diversity gain of up to 10 dB is achieved over the benchmark schemes employed without a throughput loss
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+)
Despreading chip waveform design for coherent delay-locked tracking in DS/SS systems
No full textIn this paper, the effect of unmatched despreading chip waveforms for locally generated early and late despreading codes in a coherent delay-locked loop (CDLL) for DS/SS systems is investigated. Linear and nonlinear theories are employed to evaluate the performance of the CDLL. Based on linear theory, optimum despreading chip waveforms are pursued in the sense of minimizing root mean square (RMS) tracking error with both time limited (full response) and time unlimited constraints. Nonlinear analysis shows that the use of designed chip waveforms reduces RMS tracking error and increase mean time to lose lock (MTLL). Both rectangular and Sine chip pulse-shaping waveforms are considered, as two widely used examples. It is also found that the designed despreading chip waveforms are optimized for any specified early-late spacing.Computer Science, Information SystemsEngineering, Electrical & ElectronicTelecommunicationsCPCI-S(ISTP)
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