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.

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.

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.

In recent years, there has been considerable interest in the use of CDMA in mobile communications. Bit error rate is one of the most important parameters in the evaluation of CDMA systems. In this paper, we develop a technique to find an accurate approximation to the probability of bit error for asynchronous direct-sequence code division multiple-access (DS/CDMA) systems by modeling the multiple access interference (MAI) as an improved Gaussian process. The channel is modeled as a multipath flat Rayleigh fading channel. Numerical results are obtained by using the improved Gaussian approximation (IGA) and compared to the standard Gaussian approximation (SGA).

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 effect of IQ imbalance on adaptive MQAM modulation in MIMO systems with direct conversion receivers is investigated in this paper. A continues power, discrete rate adaptive modulation scheme in using MIMO system with perfect channel information in both transmitter and receiver is considered. The selected adaptation mechanism changes the transmit power and transmit constellation size under an average transmit power and instantaneous bit error rate (BER) constraints to obtain the maximum average spectral efficiency. First, a closed from expression for the BER of MQAM modulation under the effect of IQ imbalance is introduce. Then, the impact of IQ imbalance on the BER of adaptive modulation in MIMO system is studied. This effect is also investigated for the different configuration of trancmit-recive antenna. The analytic results are compared with the Mont Carlo simulation results to verify the analytic expression.

One of the most important challenges that threaten the reliability of network-based chips is soft errors. Such problems occur mainly in buffers on the chip networks. Given that these buffers make up between 50 and 90 percent of the area of routers, the likelihood of soft forms is high. In addition, the increase in chip technology size (from 130 nm to 22 nm) has caused the rate of occurrence of single-event upsets to be 6 to 7 times higher. The shrinking size of the technology has also increased the likelihood of converting single-event upset errors set to multi-event upsets, so it is predicted that by 2021 most soft errors of the multi-event reversal type will occur. Many different methods of avoiding and tolerating soft errors do not have the ability to deal with multi-event events due to different patterns. On the other hand, the rate of crosstalk fault is increasing. The purpose of this paper is to provide a method that, while improving the tolerance of single-event reversal events in buffers, is also able to tolerate multi-event upsets. The proposed method, called Priority Flit, is based on the different importance of tailer and data flits. In other words, the fault tolerance method against soft errors in tailor and data is different. The second one is leafing and the second one is based on crosstalk avoidance and Hamming code. Results show improvements in terms of hardware and performance with respect to the state-of-the-art mechanism.