EVM and Achievable Data Rate Analysis of Clipped OFDM Signals in Visible Light Communication

Orthogonal frequency division multiplexing (OFDM) has been considered for visible light communication (VLC) thanks to its ability to boost data rates as well as its robustness against frequency-selective fading channels. A major disadvantage of OFDM is the large dynamic range of its time-domain waveforms, making OFDM vulnerable to nonlinearity of light emitting diodes (LEDs). DC biased optical OFDM (DCO-OFDM) and asymmetrically clipped optical OFDM (ACO-OFDM) are two popular OFDM techniques developed for the VLC. In this paper, we will analyze the performance of the DCO-OFDM and ACO-OFDM signals in terms of error vector magnitude (EVM), signal-to-distortion ratio (SDR), and achievable data rates under both average optical power and dynamic optical power constraints. EVM is a commonly used metric to characterize distortions. We will describe an approach to numerically calculate the EVM for DCO-OFDM and ACO-OFDM. We will derive the optimum biasing ratio in the sense of minimizing EVM for DCO-OFDM. Additionally, we will formulate the EVM minimization problem as a convex linear optimization problem and obtain an EVM lower bound against which to compare the DCO-OFDM and ACO-OFDM techniques. We will prove that the ACO-OFDM can achieve the lower bound. Average optical power and dynamic optical power are two main constraints in VLC. We will derive the achievable data rates under these two constraints for both additive white Gaussian noise (AWGN) channel and frequency-selective channel. We will compare the performance of DCO-OFDM and ACO-OFDM under different power constraint scenarios

EVALUATE THE EFFECT OF SOME FACTORS AFFECTING SOLUBILIZATION OF PHOSPHORUS IN RHIZOSPHERE

The aim of this work was to conduct pot experiment to study the ability of plant roots on solubilizing various sources of phosphorus and factors that may facilitate or inhibit their activity. A split medium – split root technique experiment was conducted to study the effect of CaCO3, pH, organic matter (humic acid) and bentonite on the pH, P solubility in the medium and P concentration in bean plants (Vicia faba var. balady). The changes in pH of the lower solution was recorded, also the root exudate was collected in 500 ml of CaCl2 solution 0.5 × 10-4 M and pH 6.85.  Results showed that the highest recorded total dry weight was found when both N forms were applied in the ratio of 1:4 NO-3: NH+4 or NO-3 alone. The mechanism of solubilizing rock phosphate by exudating protons or organic, amino and other organic compounds is possible at the root surface even in alkaline soil as long as the rock phosphate material was added near the root and organic matter was added to limit the fixing power of the inorganic components as CaCO3 and excess soluble Ca. Also, the availability of P from rock phosphate sources depends on its reactivity value

10 Gbps Mobile Visible Light Communication System Employing Angle Diversity, Imaging Receivers, and Relay Nodes

Over the last decade, visible light communication (VLC) systems have typically operated between 50 Mbps and 3.4 Gbps. In this paper, we propose and evaluate mobile VLC systems that operate at 10 Gbps. The enhancements in channel bandwidth and data rate are achieved by the introduction of laser diodes (LDs), angle diversity receivers (ADR), imaging receivers, relay nodes and delay adaptation techniques. We propose three mobile VLC systems; an ADR relay assisted LD-VLC (ADRR-LD), an imaging relay assisted LD-VLC (IMGR-LD) and select-the-best imaging relay assisted LD-VLC (SBIMGR-LD). The ADR and imaging receiver are proposed for the VLC system to mitigate the intersymbol interference (ISI), maximise the signal to noise ratio (SNR) and reduce the impact of multipath dispersion due to mobility. The combination of IMGR-LD with a delay adaptation technique adds a degree of freedom to the link design, which results in a VLC system that has the ability to provide high data rates under mobility. The proposed IMGR-LD system achieves significant improvements in the SNR over other systems in the worst case scenario in the considered real indoor environment

Factors Affecting Solubilization of Rock Phosphates in Soils

The aim of this work was to conduct laboratory and pot experiments to study the ability of plant roots on solubilizing various sources of rock phosphate and factors that may facilitate or inhibit their activity. The effect of adding organic matter or sulphur in solubilizing rock phosphate added to alkaline and calcareous soil was studied. A split medium – split root technique experiment was conducted to study also the effect of N form, soil type, source and nature of rock phosphate on the pH, P solubility in the medium and P uptake by bean plants (Vicia faba var. balady). Results show that the highest NaHCO3 extractable P of incubation experiment were found for both soils treated with superphosphate. The behavior of rock phosphates in the two soils indicated slight solubilization in the alluvial soil and no remarkable change of extractable P in the calcareous soil as compared to the control. Regarding the effect of N form and P on growth and root exudates of bean plants, results indicated that the highest recorded total dry weight was found when both N forms were applied in the ratio of 1:4  :  or   alone. Results of root exudate analyses for amino acid content indicated the presence of several amino acids and variations in the amount were only with lysine. The highest content (115 μδ/100 ml) was in the root exudate of the complete nutrient solution (Hoagland solution) and the lowest value (24 μδ/100 ml) in the exudates of bean plants fed with as the only N form. The rock phosphate from Abou zaabal gave the highest P content in acid soil in the presence of plant. The highest drop in pH value in the collected solutions was when NH4+ alone was the N source

IEEE Access Special Section Editorial: Optical Wireless Technologies for 5G Communications and beyond

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