After setteling the LEO satellite in the given circuit, the ground station needs to communicate with it for the received of information and control of its subsystems. Due to the fact that satellite communication channels are influenced by shadowing conditions, if a line of sight (LOS) signal exists between the receiver and the transmitter, then the radio channels conditions are good and the Additive White Gaussian Noise channel is modeled as Rician distribution. However, under poor conditions and in the lack of LOS, channel model is Rayleigh, and due to the radio link conditions the channel will be switched between these two models. In a proper model, the time varying behavior of the station – satellite radio link should be considered. The importance attached to this issue is due to its considerable effect on the selection of modulation type, design of channel access method, and error control. In this view, the present study has sought to momentarily determine the range of variations in error probability. Through calculations and simulation, the Bit Error Rate received during the satellite trajectory has been obtained for any given moment and its range of variations has been determined.

Spatial diversity is one of the most effective techniques to combat fading in wireless channels that can be implemented through antenna arrays. In this paper the hybrid decode-amplify-forward protocol with best relay selection (HDAF-S)in a cooperative system with multiple parallel relays with independent non-identically channels is considered and tight upper and lower bounds on bit error rate (BER) of this protocol is derived. It is shown that the BER of this protocol outperforms the BER of amplify and forward (AF) protocol but cannot exceeds the performance of decode and forward (DF) protocol. Then through asymptotic analysis for high SNR regime, it is shown that the HDAF-S protocol achieves full diversity order. Then the BER performance of HDAF protocol with n-th best relay selection (HDAF-nS) in independent and identically distributed channels is analyzed and tight upper and lower bounds on the BER are derived. Asymptotic analysis shows that this protocol cannot achieve full diversity order and it is shown that the diversity order decreases as n increases. The analytical results are validated through simulations.

The Nonorthogonal Multiple Access (NOMA) technique is one of the key enablers of next-generation cellular communications, facilitating the sharing of the same resources among users. The effectiveness of NOMA relies heavily on implementing a robust power allocation strategy that considers diverse influential factors. To address this challenge, we propose an innovative multi-objective power allocation scheme for downlink NOMA systems using the Multi-Objective Particle Swarm Optimization (MOPSO) algorithm. This approach simultaneously optimizes users' sum data rates and average bit error rates (BERs). The performance of the proposed method is analyzed in comparison to two benchmark approaches of Fixed Power Allocation (FSPA) and Greedy Algorithm-based Power Allocation (GAPA). The results confirm that, although our method offers comparable performance to these approaches regarding energy efficiency and sum data rate, it provides remarkable BER gain compared to these benchmarks.

Free-Space Optical (FSO) Communication has many advantages such as high bandwidth and high security and can also be a good alternative to radio communication systems. The main problem with the use of FSO is the presence of atmospheric phenomena such absorption, scattering and turbulence. This effect causes not only the weakening of the laser light transmission but also causes the multipath phenomena and behavior similar to the fading in the radio communication channels. In this paper, a model is presented to investigate the FSO attenuation and turbulence effect on its performance. Designing of an FSO system using a combination of methods such as Aperture averaging, Multiple Input Single Output (MISO) and Line code 1B4B to reduce the effects of turbulence has been examined and the behavior of system using error probability rate (BER) diagram and the probability of cutting (Outage) in different climatic conditions has also been simulated. Link budget analysis shows that an FSO system with 4 transmitters each with 200mW of optical power and a receiver with at least 25cm optical aperture can communicate data, in the moderate turbulence condition, with a maximum range of 10 km and a BER better than 10-6.

This paper proposes an analytical model for evaluating the performance of dense wavelength division multiplexing (DWDM) for all optical orthogonal frequency division multiplexing (AO-OFDM) optical wireless channel. The investigated performance for proposed system is evaluated for the parameters bit error rate (BER) and Q factor. The constellation diagrams, and bit error rate (BER) of the received signals are specified. The effect of atmospheric attenuation of the outdoor wireless optical communication system was induced (channel impairments) such as medium rain, light rain, and dust to find their effects on system performance carrier wavelength. The results show the BER and constellation diagram under different weather conditions for different transmission distance using Quadrature Amplitude Modulation (QAM) AO-OFDM-optical wireless channel (OWC).

In this article, we present new research on the impact of various optical filters on the functionality of an orthogonal Optical Frequency Division Duplexing (OFDM) system for the first time. This paper focused on long-haul optical systems using four Quadrature Amplitude Modulation (4-QAM) methods for OFDM systems. The analysis demonstrates the impact of choosing a Gaussian, Rectangular, or Trapezoidal optical Filter on the effectiveness of the optical system used for long-distance high data rate transmission. Compared with other systems for long-distance transmission using various filter types, 4-QAM OFDM showed a high Bit Error Rate (BER) performance. Significant findings like transmitting Power received Power, and Error Vector Magnitude (EVM) is compared with the system's propagation length.

This paper demonstrates the design of an Arrayed Waveguide Gratings (AWG) based optical switch. In the design both physical and network layer analysis is performed. The physical layer power and noise analysis is done to obtain Bit Error Rate (BER). This has been found that at the higher bit rates, BER is not affected with number of buffer modules. Network layer analysis is done to obtain performance in terms of packet loss rate and average delay. Analysis presented in the paper clearly reveals that there is a minimum amount of power required, which is necessary for the satisfactory performance of switch both at physical and network layer.

Orthogonal Frequency Division Multiplexing (OFDM) is a multicarrier modulation technique which is used for supporting high data rates. In this modulation scheme, Fourier transform is used to provide orthogonality between subcarriers. Since the channel is multi-path, a cyclic prefix having a length greater than channel delay spread is added to each OFDM symbol. The cyclic prefix removes the inter symbol interference, but, since it does not carry useful information, it decreases spectrum efficiency. In wavelet-based OFDM, there is no need for cyclic prefix. Wavelets have suitable localization, finite length and orthogonality both in time and frequency domains. Therefore, they could be used to generate suitable waveform for transmission through a fading channel. In this paper, a comparison has been made between performances of the Fourier transform and orthogonal wavelet families in OFDM-based systems in order to improve. Also, in order to select optimum filter order in these systems, the effect of increasing filter order is investigated. Simulation results show that wavelet transforms outperform the Fourier transform in terms of bit error rate (BER) and system efficiency and wavelet transforms with smaller filter orders should be used.

Scalable High Efficiency Video Coding (SHVC) is the scalable extension of the latest video coding standard H. 265/HEVC. Video rate control algorithm is out of the scope of video coding standards. Appropriate rate control algorithms are designed for various applications to overcome practical constraints such as bandwidth and buffering constraints. In most of the scalable video applications, such as video on demand (VoD) and broadcasting applications, encoded bitstreams with variable bit rates are preferred to bitstreams with constant bit rates. In variable bit rate (VBR) applications, the tolerable delay is relatively high. Therefore, we utilize a larger buffer to allow more variations in bitrate to provide smooth and high visual quality of output video. In this paper, we propose a fuzzy video rate controller appropriate for VBR applications of SHVC. A fuzzy controller is used for each layer of scalable video to minimize the fluctuation of QP at the frame level while the buffering constraint is obeyed for any number of layers received by a decoder. The proposed rate controller utilizes the well-known structural similarity index (SSIM) as a quality metric to increase the visual quality of the output video. The proposed rate control algorithm is implemented in HEVC reference software and comprehensive experiments are executed to tune the fuzzy controllers and also to evaluate the performance of the algorithm. Experimental results show a high performance for the proposed algorithm in terms of rate control, visual quality, and rate-distortion performance.