An efficient joint algorithm for reducing PAPR of SC-FDMA system in cognitive radio networks

Cognitive radio (CR) has been proposed as a solution for the spectrum scarcity problem. This paper investigates single-carrier frequency division multiple access (SC-FDMA) for cognitive radios. Recently, SC-FDMA has been suggested as a candidate for multicarrier based CR systems. In this paper, we propose enhanced techniques to reduce the peak to average power ratio (PAPR) in SC-FDMA for Cognitive Radio Network (CRN). We start by showing the effect of two standard PAPR reduction techniques (interleaver based and selective mapping) to reduce the PAPR in SC-FDMA based CR. Then, a proposed joint algorithm interleaver with selective mapping in a way that is suitable for SC-FDMA based CR will be proposed that results in a lower PAPR than using them individually. Simulation results show that the SC-FDMA with proposed techniques has a lower PAPR when compared with the conventional SC-FDMA system for CRN, while the complexity of the system slightly increases. Results also reveal that the no. of interleavers and SLM sequences must be chosen carefully in order to limit the PAPR with slightly increases in the complexity of the system.

     

Effect of Calcium and Potassium on Antioxidant System of Vicia faba L. Under Cadmium Stress

Cadmium (Cd) in soil poses a major threat to plant growth and productivity. In the present experiment, we studied the effect of calcium (Ca(2+)) and/or potassium (K(+)) on the antioxidant system, accumulation of proline (Pro), malondialdehyde (MDA), and content of photosynthetic pigments, cadmium (Cd) and nutrients, i.e., Ca(2+) and K(+) in leaf of Vicia faba L. (cv. TARA) under Cd stress. Plants grown in the presence of Cd exhibited reduced growth traits [root length (RL) plant(-1), shoot length (SL) plant(-1), root fresh weight (RFW) plant(-1), shoot fresh weight (SFW) plant(-1), root dry weight (RDW) plant(-1) and shoot dry weight (SDW) plant(-1)] and concentration of Ca(2+), K(+), Chlorophyll (Chl) a and Chl b content, except content of MDA, Cd and (Pro). The antioxidant enzymes [peroxidase (POD) and superoxide dismutase (SOD)] slightly increased as compared to control under Cd stress. However, a significant improvement was observed in all growth traits and content of Ca(2+), K(+), Chl a, Chl b, Pro and activity of antioxidant enzymes catalase (CAT), POD and SOD in plants subjected to Ca(2+) and/or K(+). The maximum alleviating effect was recorded in the plants grown in medium containing Ca(2+) and K(+) together. This study indicates that the application of Ca(2+) and/or K(+) had a significant and synergistic effect on plant growth. Also, application of Ca(2+) and/or K(+) was highly effective against the toxicity of Cd by improving activity of antioxidant enzymes and solute that led to the enhanced plant growth of faba bean plants.     

Study the effect of PAPR on wideband cognitive OFDM radio networks

Cognitive radio (CR) technology is viewed as a novel approach for maximizing the utilization of the radio electromagnetic spectrum. Spectrum sensing methods are often used for finding free channels to be used by CR. Recently, Orthogonal Frequency Division Multiplexing system (OFDM) has been suggested as a candidate technology for multicarrier-based CR systems. However, one problem that appears in OFDM systems is the high Peak to Average Power Ratio (PAPR). In this paper, the effect of PAPR reduction of the primary signal on the performance of the multiband joint detection for wideband spectrum sensing and the profit of the primary user will be investigated. Moreover, the optimal solutions for the multi-band joint detection for the non-cooperative and cooperative schemes will be analyzed by considering the primary user’s PAPR reduction. Also, the wideband cooperative spectrum sensing to improve the signal detection with high reduction in the PAPR will be suggested. Simulation results show that the PAPR reduction decreases the total price of the primary user and the aggregate opportunistic throughput of the secondary user. The cooperative scheme is effective in improving the performance in terms of the aggregate opportunistic throughput with PAPR reduction.     

Hard and softened combination for cooperative spectrum sensing over imperfect channels in cognitive radio networks

Recently, cognitive radio (CR) access has received much attention to overcome spectrum scarcity problem. Spectrum sensing methods are often used for finding free channels to be used by CR. In this paper, the problem of cooperative spectrum sensing will be investigated in CR networks over realistic channels. This problem is not clarified until now by taking into account the error effect on the decision reporting. The analytical expressions of the hard and softened one bit and two bits hard combination scheme for cooperative spectrum sensing will be derived. These expressions are investigated to compare with simulation results. The analysis and simulation results show that the performance of cooperative spectrum sensing is limited by the probability of reporting errors. Moreover, it is shown that there is a significant performance loss when a final decision regarding to primary user’s (PU) state made at the fusion depends on a set of local spectrum sensing information that are distorted by imperfect reporting channels during transmission. The probability of detection is degraded due to imperfect reporting channel by 16.5% and 12.2% with one bit hard combination and softened two bits hard combination, respectively. To reduce this performance loss, Amplify and Forward (AAF) relying mechanism will be proposed. The probability of detection is improved by 8% and 9.3% with one bit hard combination and softened two bits hard combination, respectively using AAF relaying mechanism.     

Performance of SDM/COFDM system in the presence of nonlinear power amplifier

The performance of Space Division Multiplexing/ Companded Orthogonal Frequency Division Multiplexing (SDM/COFDM) system will be evaluated in the presence of nonlinear amplifier. The evaluation comes from decreasing high dynamic range that is resulted from characteristics of OFDM and nonlinearity of power amplifier. The high dynamic range means high Peak to Average Power Ratio (PAPR). The reduction of dynamic range or PAPR is made by using a compander in this system, which is effective that is because of Gaussian distribution of OFDM signal where large OFDM signal only occurs infrequently. System simulation models are employed using Rapp??s nonlinear power amplification model. The simulation results show that the compander can provide better performance in comparison to a system that does not employ the compander, i.e., SDM/OFDM system. The effect of main parameter for the compander will be studied. Comparisons between the performances of our system and SDM/OFDM system that is used clipping technique for reduction of PAPR will be made. All these results are made at different modulation techniques and different sub-carriers     

Controlled release of polymer conjugated agrochemicals. System based on poly(methyl vinyl ether‐alt‐maleic anhydride)

Controlled release formulations were prepared by using commercially available poly(methyl vinyl ether‐alt‐maleic anhydride) (I) and 2,4‐dichlorophenoxy acetic acid herbicide (2,4‐D). The copolymer (I) was reacted with various diamines to produce amido‐amine containing carboxylate copolymers. The produced copolymers were reacted with the acid chloride of herbicide 2,4‐D as model herbicide for carboxylic group functionalized herbicides. The formulations produced were characterized by IR and elemental analyses. The release of the herbicide 2,4‐D from the formulations was studied under different aqueous medium conditions and the effect of copolymer microstructure on release profiles was investigated. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 415–421, 2001     

Integrated Microwave and Optical Scanning Probe for Magnetic Resonance Imaging

We demonstrate a scanning microwave near-field probe based on a slit aperture that is capable of performing spatially-resolved magnetic resonance measurements in the frequency range of 3–90 GHz. We demonstrate local electron spin resonance (ESR), ferromagnetic resonance (FMR), and spin-wave resonance (SWR) studies on model materials. The probe can serve as a local contactless heater as well. We demonstrate also a further application, a dual microwave/optical near-field probe that can be useful in contactless measurements of photoconductivity and fluorescence under microwave irradiation.