Phase noise impact on the performance of contention resolution slotted random access schemes

Cost‐effective satellite terminals (STs) that are designed for a large scale deployment in the Internet of things (IoT) applications are constrained by consumer‐grade local oscillators (LOs) to lower the costs, on the one hand, and by limited equivalent isotropic radiated power (EIRP) due to limited peak transmit power and/or low antenna gain, on the other hand. To close the link budget with the low EIRP constraint, STs can resort to adopting robust forward error correcting (FEC) schemes and/or limiting the transmission baud rate, hence increasing the link margin with respect to the required receiver threshold. In general, the LOs at the terminal side are responsible for injecting multiplicative phase distortions to the transmitted signal, known as phase noise (PN). The PN caused by low‐cost LOs could be significant, especially for low baud rates, thus affecting the demodulator performance. Random access (RA) techniques are particularly encouraged on the return link in networks with low‐cost terminals and bursty/low‐duty cycle types of traffic. The state‐of‐the‐art time‐slotted RA techniques are often evaluated considering high EIRP at the terminal side and high baud rates. This paper investigates the impact of the PN in time‐slotted RA techniques and optimizes different carrier phase estimation (CPE) algorithms. Furthermore, it evaluates the impact of CPE errors on RA performance for a wide range of baud rates and typical STs phase noise masks.     

Cramer-Rao bounds of SNR estimates for BPSK and QPSK modulatedsignals

We derive Cramer-Rao lower bounds (CRLBs) for the estimation of signal-to-noise ratio (SNR) of binary phase-shift keying (BPSK) and quaternary phase-shift keying (QPSK) modulated signals. The received signal is corrupted by additive white Gaussian noise (AWGN). The lower bounds are derived for non-data-aided estimation where the transmitted symbols are unknown at the receiver. The bounds are compared to those for data-aided estimations (known symbols at the receiver). It is shown that at low SNR there is a significant difference between the bounds for non-data-aided and data-aided estimations     

γ Irradiation of Bulk MgB2 Superconductor

Current–voltage (I–V) characteristics of MgB₂ bulk sintered superconductor, prepared from the commercially available powder (Alfa-Aesar), have been investigated before and after several γ irradiations up to 5000 MR. A minor increase in the normal state resistance of the sample was observed up to 5000 MR without any change in its critical temperature (T _c ). I–V characteristics before and after γ irradiation with different doses up to 5000 MR were shown and fitted to the expression V∝I ^β(T,B) where β approaches unity near T _c before and after γ irradiation. A decrease in the critical currents (I _c ) with γ irradiation up to 1000 MR was observed; after which they start to increase with higher irradiations up to 5000 MR without exceeding the critical currents before irradiation.     

An evaluation of machine learning and artificial intelligence models for predicting the flotation behavior of fine high-ash coal

In this study, five different machine learning (ML) and artificial intelligence (AI) models: random forest (RF), artificial neural networks (ANN), the adaptive neuro-fuzzy inference system (ANFIS), Mamdani fuzzy logic (MFL) and a hybrid neural fuzzy inference system (HyFIS) were employed to predict the flotation behavior of fine high ash coal in the presence of a novel “hybrid” ash depressant consisting of polyacrylamide chains grafted onto aluminium hydroxide nanoparticles: Al(OH)₃-PAM (Al-PAM). A total of 51 flotation tests were conducted on coal samples with 38% ash-content and a P₈₀ of approximately 49?μm. Different influencing variables of coal flotation including polymer dosage, pH, polymer conditioning time, sodium metasilicate dosage (commercial dispersant), and the impeller speed were used as inputs for the models. The combustible recovery and ash content of coal reported to the concentrate were used as response variables (outputs). For AI model development, 80% of the total data was used for training phase and 20% was used for testing phase. Coefficient of determination (R²) and root-mean-square error (RMSE) were used as performance indicators of the models. The MFL model showed the best accuracy for the prediction of the combustible recoveries and the froth ash contents for this specific feed. However, in case of any significant change in the characteristics of the feed, these models would have to be re-trained using the data obtained through further physical experimentation and/or process model simulations. Moreover as these models are trained on laboratory scale data, these are only good for the predictions at laboratory scale.     

Factors Affected by Machine Settings and Fabric Properties in Knitwear Production. Part I: Seam Shrinkage and Thread Consumption

This paper investigates the combined effects of machine variables and compressional parameters of knitted fabrics on seam shrinkage and thread consumption during chain-stitch sewing. The approach is based on the analysis of energies and the formation of dimensionless groups. It also briefly discusses the factors which affect the dynamic peak, average thread tension and the movements of the pressure bar as an appendix.     

Digital video broadcasting‐return channel via satellite linear modulation with turbo coding

The digital video broadcasting, return channel via satellite second generation (DVB‐RCS2) linear modulation scheme offers significantly better performance than that of the first generation (DVB‐RCS) both at the physical layer and at the link layer. The DVB‐RCS2 design allows for optimizing the link margin by implementing adaptive coding and modulation (ACM) in the return link, controlled by the central system controller, resembling the ACM as supported for the DVB‐S2‐based forward link. The gain of the return link ACM complements performance improvements at layers 1 and 2. The performance enhancement of the DVB‐RCS2 comes with a higher computational complexity compared with that of the DVB‐RCS but mainly at the gateway, whereas the computational load increase of the terminal is minimal. Copyright © 2013 John Wiley & Sons, Ltd.     

Generalized raised-cosine filters

Data transmission over bandlimited channels requires pulse shaping to eliminate or control intersymbol interference (ISI). Nyquist filters provide ISI-free transmission. Here we introduce a phase compensation technique to design Nyquist filters. Phase compensation can be applied to the square-root of any zero-phase bandlimited Nyquist filter with normalized excess bandwidth less than or equal to one. The resulting phase compensated square-root filter is also a Nyquist filter. In the case of a raised-cosine spectrum, the phase compensator has a simple piecewise-linear form. Such a technique is particularly useful to accommodate two different structures for the receiver, one with a filter matched to the transmitting filter and one without a matched filter. We also use the phase compensation technique to characterize a more general family of Nyquist filters which subsumes raised-cosine spectra. These generalized raised-cosine filters offer more flexibility in filter design. For instance, the rate of asymptotic decay of the filter impulse response may be increased, or the residual ISI, introduced by truncation of the impulse response, may be minimized. Design examples are provided to illustrate these choices     

Solar energy—A look into power generation,challenges, and a solar‐powered future

Sun is an inexhaustible source of energy capable of fulfilling all the energy needs of humankind. The energy from the sun can be converted into electricity or used directly. Electricity can be generated from solar energy either directly using photovoltaic (PV) cells or indirectly using concentrated solar power (CSP) technology. Progress has been made to raise the efficiency of the PV solar cells that can now reach up to approximately 34.1% in multi‐junction PV cells. Electricity generation from concentrated solar technologies has a promising future as well, especially the CSP, because of its high capacity, efficiency, and energy storage capability. Solar energy also has direct application in agriculture primarily for water treatment and irrigation. Solar energy is being used to power the vehicles and for domestic purposes such as space heating and cooking. The most exciting possibility for solar energy is satellite power station that will be transmitting electrical energy from the solar panels in space to Earth via microwave beams. Solar energy has a bright future because of the technological advancement in this field and its environment‐friendly nature. The biggest challenge however facing the solar energy future is its unavailability all‐round the year, coupled with its high capital cost and scarcity of the materials for PV cells. These challenges can be met by developing an efficient energy storage system and developing cheap, efficient, and abundant PV solar cells. This article discusses the solar energy system as a whole and provides a comprehensive review on the direct and the indirect ways to produce electricity from solar energy and the direct uses of solar energy. The state‐of‐the‐art procedures being employed for PV characterization and performance rating have been summarized . Moreover, the technical, economic, environmental, and storage‐related challenges are discussed with possible solutions. Furthermore, a comprehensive list of future potential research directions in the field of direct and indirect electricity generation from solar energy is proposed.