The preinstalled white light emitting diodes (WLEDs) inside buildings can be exploited as an optical source in visible light communications (VLC) motivated by high optical efficiency and low cost. One of the main challenges for VLC is LED nonlinear distortion, which has a detrimental effect on system performance. Estimation and compensation of the LED nonlinear behavior can be accomplished using predistortion or postdistortion techniques. Three compensation techniques are adopted to mitigate the effect of LED nonlinearity on layered asymmetrically clipped optical, orthogonal frequency division multiplexing. Their performance and efficiency are discussed and compared with the aid of error vector magnitude and bit error rate (BER) in an additive white Gaussian noise channel. The obtained results reveal that polynomial-based predistorters and postdistorters can overcome the LED nonlinear behavior with extra SNR of only 0.25 dB at BER of 1 0 − 3 . Furthermore, the look-up-table-based predistorter can provide the same BER with lower SNR penalty than the previous two systems.

Visible light communication (VLC) depends on light emitting diodes (LEDs) for data transmission. This is one of the strengths of VLC motivated by high optical efficiency and low cost. However, LEDs impose nonlinear effects on the transmitted signal and limit overall system performance, especially in the case of multicarrier modulation systems. This paper extends to the layered asymmetrically clipped optical, orthogonal frequency division multiplexing (LACO-OFDM) and investigates the impact of LED nonlinearity on system performance. The effect of the second-order nonlinear distortion in addition to the clipping noise is presented and analyzed at different power values assuming different strengths of nonlinearity. With a variable number of layers, the system performance is explored considering a nonlinear LED model. Finally, the impact of nonlinearity is investigated in the case of ACO-OFDM for the sake of comparison, bearing in mind that ACO-OFDM represents the first layer of LACO-OFDM.

Due to their numerous advantages, Wavelet transform processor-based acoustic wave devices constitute an interesting approach for various engineering disciplines, such as signal analysis, speech synthesis, image recognition and atmospheric and ocean wave analysis. The major aim of this paper is to review the most recent methods for implementing wavelet transform processor-based surface acoustic wave devices. Accordingly, the goal of this paper is to compare different models, and it will provide a generalized model with small insertion loss values and side lobe attenuation, making it suitable for designing multiplexer filter banks and also to ease the way for the continued evolution of device design. In this paper, a generalized framework on surface acoustic wave devices is presented in terms of mathematical equations, types of materials, crystals types, and interdigital transducer design in addition to addressing some relevant problems.

Long-range wide area network (LoRaWAN) is a promising low-power network standard that allows for longdistance wireless communication with great power saving. LoRa is based on pure ALOHA protocol for channel access, which causes collisions for the transmitted packets. The collisions may occur in two scenarios, namely the intra-spreading factor (intra-SF) and the inter-spreading factor (inter-SF) interference. Consequently, the SFs assignment is a very critical task for the network performance. This paper investigates a smart SFs assignment technique to reduce collisions probability and improve the network performance. In this work, we exploit different architectures of artificial neural networks for detecting collisions and selecting the optimal SF. The results show that the investigated technique achieves a higher prediction accuracy than traditional machine learning algorithms and enhances the energy consumption of the network.

<p><em>Various schematics for colpitts oscillator with fixed ultra-high frequency using either LC tank circuits or one port surface acoustic wave resonator are presented. Four circuits used to achieve 433.9 MHz oscillating frequency, Two of them using NPN Bipolar junction transistor, while the others using operational amplifier with high speed, gain and accuracy. A comparison between using passive elements as a source of resonance frequency and using SAW resonator is introduced. Another comparison between using an equivalent lumped circuit instead of SAWR package in oscillator design is also introduced. Two different software tools are used to achieve the required simulation. Proteus and ADS tools are used in simulation with AC, S-parameters and hybrid simulation. This paper is considered a direct application for SAW resonators in wide bandwidth ASK Transmitter / Receiver.</em></p>