1,721,023 research outputs found
Impact of pilot pattern on carrier frequency recovery for TETRA-like multitone modulations
No full textAn efficient receiver structure for sweep-spread-carrier underwater acoustic links
Full text linkIn this paper, we present an improved receiver architecture for sweep-spread-carrier modulation, a spread-spectrum technique proposed to effectively contrast the effects of time dispersion over multipath propagation channels in underwater acoustic wireless links. The proposed structure is capable of taking advantage of the energy received from all propagation paths rather than only from the strongest path, as envisaged in the pioneering paper introducing this modulation technique. A hardware version of the modem was implemented in the laboratory and its behavior was assessed and compared, using standard propagation models, to that exhibited by the traditional single-path-based scheme in terms of bit error rate. Results are presented showing that gains of a few decibels can be achieved in signal-to-noise-plus-interference ratio. Issues relevant to carrier/symbol synchronization, channel estimation, and sensitivity to Doppler distortion are also addressed
Maximum Likelihood Frequency Estimation and Preamble Identification in OFDMA-based WiMAX Systems
No full textIn multi-cellular WiMAX systems based on orthogonal frequency-division multiple-access (OFDMA), the training preamble is chosen from a set of known sequences so as to univocally identify the transmitting base station. Therefore, in addition to timing and frequency synchronization, preamble index identification is another fundamental task that a mobile terminal must successfully complete before establishing a communication link with the base station. In this work we investigate the joint maximum likelihood (ML) estimation of the carrier frequency offset (CFO) and preamble index in a multicarrier system compliant with the WiMAX specifications, and derive a novel expression of the relevant Cramer-Rao bound (CRB). Since the exact ML solution is prohibitively complex in its general formulation, suboptimal algorithms are developed which can provide a reasonable trade-off between estimation accuracy and processing load. Specifically, we show that the fractional CFO can be recovered by combining the ML estimator with an existing algorithm that attains the CRB in all practical scenarios. The integral CFO and preamble index are subsequently retrieved by a suitable approximation of their joint ML estimator. Compared to existing alternatives, the resulting scheme exhibits improved accuracy and reduced sensitivity to residual timing errors. The price for these advantages is a certain increase of the system complexity
Frequency Estimation in OFDM Direct-Conversion Receivers Using a Repeated Preamble
Full text linkThis paper investigates the problem of carrier frequency offset (CFO) recovery in an OFDM receiver affected by frequency-selective in-phase/quadrature (I/Q) imbalances. The analysis is based on maximum-likelihood (ML) methods and relies on the transmission of a training preamble with a repetitive structure in the time domain. After assessing the accuracy of the conventional ML (CML) scheme in a scenario characterized by I/Q impairments, we review the joint ML (JML) estimator of all unknown parameters and evaluate its theoretical performance. In order to improve the estimation accuracy, we also present a novel CFO recovery method that exploits some side-information about the signal-to-interference ratio. It turns out that both CML and JML can be derived from this scheme by properly adjusting the value of a design parameter. The accuracy of the investigated methods are compared with the relevant Cramer-Rao bound. Our results can be used to check whether conventional CFO recovery algorithms can work properly or not in the presence of I/Q imbalances and also to evaluate the potential gain attainable by more sophisticated schemes
Anaerobic acidogenic digestion of a dephenolized olive mill wastewater in a biofilm reactor packed with ceramic filters
No full textAnaerobic digestion of sludges coming from biological wastewater treatment plants
No full textOrganic pollutants such as PAHs, PCBs and pesticides tend to accumulate in the primary and secondary sludges of biological plants treating domestic and industrial wastewaters. Thus, those sludges have to be submitted to a dedicated treatment, that generally consists in their thermal destruction. Anaerobic digestion could represent an alternative technology for the decontamination of such sludges. In fact, it can mediate the biodegradation of the occurring contaminants, the depletion of pathogenic microrganisms and the production of a biogas with a high content of methane. The effects of the anaerobic digestion (both under mesophilic and thermophilic conditions) on the final decontamination and disinfection of a sludge coming from a domestic water treatment plant and spiked with a mix of xenobiotics were investigated along with the possibility of enhancing the process by adding yeast extract. Methane production and xenobiotic removal were more efficient under mesophilic conditions while a complete disinfection of the sludge was achieved at 55°C. Yeast extract allowed to obtain better performances under mesophilic conditions both in terms of sludge decontamination and disinfection
Biofilm reactors packed with ceramic filters or granular activated carbon for the acidogenic digestion of olive mill wastewaters
No full textRECOVERY OF OLIVE MILL WASTEWATER POLYPHENOLS THROUGH LIQUID-SOLID EXTRACTION
No full textThe recovery of polyphenols from olive mill wastewaters (OMWs) conjugates the reduction of the waste phytotoxicity to the obtainment of high-added value molecules. To this aim, liquid-solid extraction can represent an economical and environmental friendly approach, since it can combine simple procedures to the use of non-toxic desorbing solvents. In this work, the adsorption and desorption features of four resins, namely Amberlite XAD7 and XAD16, IRA96 and Isolute ENV+, towards the phenolic fraction of an OMW were studied. Methanol and ethanol, also acidified with HCl 0.5% v/v, were tested as the desorbing phase. The OMW had a total phenol content (on Folin-Ciocalteu method basis) of about 3.4 g/L. Adsorption isotherms related to total phenols and to the single monocyclic detected ones (measured via reverse-phase HPLC-DAD) were determined by filling 50 mL-flasks with 10 mL of an OMW dilution (10÷100%) and with 0.7 g of resin (dry weight) and by shaking the flasks at 180 rpm for 2 hours at room temperature. Freundlich and Langmuir isotherms were used to interpolate the experimental data, which better fitted with the former model. The highest phenolic fraction adsorption was achieved with resin ENV+ resin (up to about 80%), which allowed the almost complete adsorption of hydroxytyrosol, i.e. the highest added-value detected phenol in the OMW (0.59 g/L). The efficiencies of the desorbing step were evaluated by recovering the resins employed in the dephenolization of the not-diluted OMW: after liquid-solid phases separation, the flasks were refilled with 14 mL of solvent and shacked under the same conditions reported above. Comparable results were observed by employing ethanol or methanol. The highest desorption was obtained with acidified ethanol, by which almost all the adsorbed phenolic fraction was recovered from resins ENV+, XAD7 and XAD16, while about its 82% was recovered from IRA96. Considering the integrated adsorption-desorption processes, the 84, 69, 65 and 59%, respectively, of the OMW total phenols were obtained; however, XAD16 gave rise to the highest specific recovery of hydroxytyrosol (77%). The obtained results were validated by employing other two OMWs in identical adsorption-desorption experiments, carried out with ethanol and acidified ethanol as the solvent: again, the latter desorbing phase allowed higher polyphenol recoveries and ENV+ was confirmed to be the most performing resin
Chemical-biotechnological integrated process for the dephenolization of olive mill wastewater and its acidogenic fermentation in a packed bed biofilm reactor
No full textPolyhydroxyalkanoates (PHAs) are biopolymers whose costs are not competitive with those of fossil fuel-based plastics. The exploitation of organic waste in PHA biotechnological production is of great interest in the perspective of reducing their costs. To this aim, a three-stage integrated anaerobic-aerobic process fed with olive mill wastewaters (OMWs) was proposed (Dionisi et al., 2005). In its first step, the waste is digested under acidogenic conditions in order to obtain a volatile fatty acids (VFAs) enriched effluent to be fed to the following PAH producing aerobic steps.
OMW polyphenols, which contribute to the waste phytotoxicity, are natural antioxidants whose exploitation can concern several industrial fields.
Thus, an integrated chemical-biotechnological process for the recovery of OMW polyphenols by liquid-solid extraction and for the continuous acidogenic fermentation of the dephenolized waste was developed.
The employed OMW (pH = 4.5) had a total phenol content (on Folin-Ciocalteu method basis) of 4.6 g/L, while COD and VFA concentrations were 55 and 8.4 gCOD /L, respectively. As a result of the adsorption pre-treatment, carried out with resin Amberlite XAD16 as the solid phase (0.7 g/L, contact time = 2 hours), the 90% of OMW polyphenols were removed together with the 25% of the COD, while VFA concentration and pH did not vary appreciably. Almost all the adsorbed phenolic fraction was desorbed by using ethanol as the solvent. The resulting wastewater was processed in a biofilm reactor packed with ceramic filters developed in a recent study (Beccari et al., 2009). On the basis of the results obtained from a preliminary batch experiment, the pH of the influent flow was correct to 7.0 and the reactor was thermostated at 25°C and fed with an OLR of about 6 gCOD/L/day. The process effluent, whose pH was 6.2, had a total VFA and COD concentrations of 19.02 and 25.94 gCOD/L, respectively. A significant enhancement in terms of VFA production yield with respect to the former experience (Beccari et al., 2009) was achieved. In particular, butyric and acetic acids were the main detected VFAs in the obtained effluent where they represented the 28 and 27%, respectively, of the whole VFA mixture.
Beccari M. et al. (2009) J Chem Technol Biotechnol 84:901-908.
Dionisi D. et al. (2005) Wat Res 39:2076-2084
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