4,532 research outputs found
On the Performance of Band-Limited Asynchronous DS-CDMA over Nakagami-m Channels
No full textIn this paper we investigated the BER performance of DS-CDMA using various chip-waveforms, which include three time-limited chip-waveforms and two band-limited chipwaveforms. Closed-form formulae were derived for evaluating the achievable bit-error rate performance with the aid of the standard Gaussian approximation, when communicating over a Nakagami-m channel. The time-limited waveforms impose a low implementational complexity, since they maybe oversampled and read from a look-up table. However, they are outperformed by the frequency-domain raised-cosine waveform as well as the optimum waveform specifically designed by Cho and Lehnert for achieving the lowest possible bit error rate. Index Terms—Code-division multiple-access, chip waveform, Gaussian approximation, Nakagami, band-limited, normalized bandwidth
Kinetics calculation under space-dependent feedback in analytic function expansion nodal method via solution decomposition and Galerkin scheme
No full textTo develop kinetics calculational capability of the analytic function expansion nodal methodology for space-dependent feedback problems, a novel method with the time-dependent solution decomposed into an analytic part and a polynomial correction part is proposed. The analytic part consists of the analytic solutions of the "quasi-static" diffusion equation and the polynomial part is determined by applying a Galerkin scheme. The results tested on several benchmark problems (two-dimensional and three-dimensional) show that 1 node/assembly calculation and a large time-step size can be used for high accuracy. The new feedback calculation method removes almost all the errors induced from space-dependent feedback. Also, it is shown that the coarse group rebalance acceleration scheme and conventional techniques for kinetics calculation (exponential transformation for time variable and bilinear weighting for control rod cusping problem) can be easily incorporated into the method
The analytic function expansion nodal (AFEN) method with half-interface averaged fluxes in mixed geometry nodes for analysis of pebble bed modular reactor (PBMR) cores
No full textThe analytic function expansion nodal (AFEN) method has been successfully applied to the rectangular and hexagonal geometries in the cartesian coordinates system. In this paper, we extended the AFEN method to the cylindrical geometry in the R-Z coordinates for the analysis of pebble bed modular reactors (PBMRs). To treat the mixed geometry of rectangular and triangular nodes appearing in the lower periphery of the reactors, we used half-interface averaged fluxes as nodal unknowns. Numerical results obtained attest to their accuracy and applicability to practical problems
Precise BER Formulas for Asynchronous QPSK-Modulated DS-CDMA Systems Using Random Quaternary Spreading Over Rayleigh Channels
No full textPrecise bit-error-ratio (BER) analysis of an asynchronous QPSK-modulated direct-sequence code-division multiple-access system using random quaternary spreading sequences for transmission over Rayleigh channels is performed based on the characteristic-function approach. Its accuracy is verified by our numerical simulation results and also compared with those of the Gaussian approximation. Index Terms—Asynchronous direct-sequence code-division multiple-access (DS-CDMA), bit-error-ratio (BER), precise, QPSK, quarternary spreading, Rayleigh
Initial Synchronisation in the Multiple-Input Multiple-Output Aided Single- and Multi-Carrier DS-CDMA as well as DS-UWB Downlink
No full textIn this thesis, we propose and investigate code acquisition schemes employing both colocated and cooperative Multiple Input/Multiple Output (MIMO) aided Single-Carrier (SC) and Multi-Carrier (MC) Code Division Multiple Access (CDMA) DownLink (DL) schemes. We study their characteristics and performance in terms of both Non-Coherent (NC) and Differentially Coherent (DC) MIMO scenarios. Furthermore, we also propose iterative code acquisition schemes for the Direct Sequence-Ultra WideBand (DS-UWB) DL. There is a paucity of code acquisition techniques designed for transmit diversity aided systems. Moreover, there are no in-depth studies representing the fundamental characteristics of code acquisition schemes employing both co-located and cooperative MIMOs. Hence we investigate both NC and DC code acquisition schemes in the co-located and cooperative MIMO aided SC and MC DS-CDMA DL, when communicating over spatially uncorrelated Rayleigh channels. The issues of NC initial and post-initial acquisition schemes as well as DC schemes are studied as a function of the number of co-located antennas by quantifying the attainable correct detection probability and mean acquisition time performances. The research of DS-UWB systems has recently attracted a significant interest in both the academic and industrial community. In the DS-UWB DL, initial acquisition is required for both coarse timing as well as code phase alignment. Both of these constitute a challenging problem owing to the extremely short chip-duration of UWB systems. This leads to a huge acquisition search space size, which is represented as the product of the number of legitimate code phases in the uncertainty region of the PN code and the number of legitimate signalling pulse positions. Therefore the benefits of the iterative code acquisition schemes are analysed in terms of the achievable correct detection probability and mean acquisition time performances. Hence we significantly reduce the search space size with the aid of a Tanner graph based Message Passing (MP) technique, which is combined with the employment of beneficially selected generator polynomials, multiple receive antennas and appropriately designed multiple-component decoders. Finally, we characterise a range of two-stage iterative acquisition schemes employing iterative MP designed for a multiple receive antenna assisted DS-UWB DL scenario
Exact BER Performance of Asynchronous DS-CDMA Systems using Quadriphase Spreading and QPSK Modulation over Rayleigh Channels
No full textAn accurate closed-form expression is derived for calculating the average BER in an asynchronous DS-CDMA system using random complex-valued spreading sequences for transmission over Rayleigh channels. This accurate solution is based on the Characteristic Function (CF) approach and only requires a single numerical integration. Our numerical simulation results verify its accuracy, and also demonstrate the relative inaccuracy of the Gaussian approximation
Prognostic nutritional index and prognosis in renal cell carcinoma: A systematic review and meta-analysis
No full textPurpose: To perform a systematic review and meta-analysis of the Prognostic Nutritional Index (PNI) as a prognostic factor for renal cell carcinoma (RCC). Materials and methods: Eligible studies that evaluated the prognostic impact of pretreatment PNI in RCC patients were identified by comprehensive searching the electronic databases PubMed, Cochrane Central Search library, and EMBASE. The end points were overall/cancer-specific survival (OS/CSS) and recurrence-free/disease-free survival (RFS/DFS). Meta-analysis using random-effects models was performed to calculate hazard ratios (HRs) with 95 % confidence intervals (CIs). Results: In total, 9 retrospective, observational, case-control studies involving 5,976 patients were included for final analysis. Eight studies evaluated OS/CSS, and 5 evaluated RFS/DFS. Our results showed that lower PNI was significantly associated with unfavorable OS/CSS (HR = 1.68, 95% CI 1.44-1.96, P < 0.001, I2 = 9.2%, P = 0.359) and RFS/DFS (HR = 1.98, 95% CI 1.57-2.50, P < 0.001, I2 = 18.2%, P = 0.299) in patients with RCC. Subgroup and meta-regression analysis based on ethnicity, study sample size, presence of metastasis, PNI cut-off value, Newcastle–Ottawa quality assessment scale (NOS) score, and gender ratio all showed that lower PNI was associated with poorer OS/CSS and RFS/DFS. Funnel plots and Egger's tests indicated significant publication bias in OS/CSS (P = 0.001), but not in RFS/DFS (P = 0.757). Conclusion: This meta-analysis indicated that lower PNI was a negative prognostic factor and associated with tumor progression and poorer survival of patients with RCC. Therefore, PNI could be a potential prognostic predictor of treatment outcomes for patients with RCC
New Rotor Parameter Estimation for a Flux and Speed Control of Induction Machine Considering Saturation Effects
No full textDeadbeat Current Control for a Voltage-Fed PWM Invetter with Delayed Input Voltage Feedback
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