This work investigates the performance of a downlink non-orthogonal multiple access (NOMA) based coordinated low-earth orbit (LEO) satellite system. Two LEO satellites are assumed to coordinate their transmissions to serve three users simultaneously using NOMA protocol, where only one user lies in the intersection of the footprints of the two satellites. We investigate the reliability of the proposed architecture, which is expressed in terms of the outage probability (OP). We derive closed-form expressions of the users’ OPs taking into considerations different realistic losses effects on the link budget including receiver antenna gain, satellite antenna gain, antennas pointing errors, shadowing, small-scale fading, and large-scale free space path loss. The channels between satellites and the three users are assumed to follow shadowed-Rician (SR) fading. The mathematical analysis is verified by the extensive representative Monto-Carlo simulations. Finally, we demonstrate the impact of the system parameters on the considered system as well as the superiority of the NOMA scheme over conventional OMA system.

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.

Long-range wide area network (LoRaWAN) is a promising low-power network standard that allows for long-distance wireless communication with great power saving. $L$ oRa 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.

In this paper, we provide a sparse image restoration algorithm with a SSIM-based objective function. The proposed technique is a modification to the SSIM-inspired OMP (iOMP) and, and it has two parallel sparse restoration paths. One of them is ${\mathcal{L}}_2$-sense OMP and the other is $\text{SSIM}$-sense OMP (iOMP). Both paths intersects only at the starting point and gives different quality levels after each iteration. This distinction enables us to select the coefficients of the best quality and to avoid the uncertainty issue of iOMP. From the point of view of the SSIM levels, the conducted experiments proved that, the proposed methodology works better than iOMP and OMP. Also, the performance of this method is checked for significance by the t-test, and the obtained results proved that the method works well especially for large images and the data-independent based dictionary.

This paper implies a prototype for a broad-band log periodic dipole antenna (LPDA) with dimensions of 20 × 40 × 0.508 mm³ equipped with directors. The LPDA is based on Roger’s RT5880 with εr = 2.2. The 4-arms with alternative stubs constitute the LPDA, which is evenly spaced on both lines. At the substrate’s back, the 50Ω main feeder line is placed on partial ground. The directors are also incorporated and studied in a regular matrix at a predetermined distance to improve gain, further reduce side lobes, and widen the frequency band. The performance of the antenna covers a wide spectrum of millimeter waves ranging from 26 up to 44 GHz. The realized gain for the antenna is 8.97, 11.96, 13.96, and 14.29 dB at 28 GHz, 35 GHz, 38 GHz, and 43 GHz, respectively. The total gain is 14.29 dB as a peak gain. The antenna was designed and tested for 5G communication applications in autonomous vehicles, and the design cost for the antenna is low in comparison to dielectric lenses. The model exhibits symmetrical radiation patterns for the antenna range. The results of the simulations and the testing of the implemented antenna elements coincide quite well. The proposed design outperforms earlier work in this field.