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This study examines the uplink and downlink communication in a structured coded nonorthogonal multiple access (NOMA) in the context of cognitive radio networks (CRNs). Due to the ever-increasing demand for spectrum-efficient communication systems, NOMA has emerged as an effective approach to enhance spectral efficiency by allowing multiple users to share the same frequency resources. Furthermore, CRN also improves spectrum utilization by enabling dynamic spectrum access while primary users are present. This work presents a method that can maximize the spectral efficiency by combining NOMA and CRN mechanisms. The suggested system is evaluated in terms of throughput, spectral efficiency, and bit error rate (BER). The collected results show that the proposed strategy performs better in reducing data mistakes when two users access the spectrum at different signal-to-noise ratios (SNR), with a 7 dB improvement for 1st user and a 2.5 dB improvement for the 2nd user, respectively, in the downlink scenario. Next, the exact BER expressions for both coded and uncoded uplink NOMA systems are introduced. As a result, the proposed system demonstrates superior performance and needs only 11 dB to reach 1 × 10−6 of BER while the uncoded system cannot operate in this harsh environment and the BER is fixed at 0.25 dB.

While Transmission Control Protocol (TCP) works well with a low bit error rate (BER), the performance of TCP degrades significantly if the BER rises above a certain level. A study of the performance of TCP with high BER is required for the efficient design and deployment of such systems. In this paper, we address the problem of TCP performance in high BERs and analyze the issues by investigating the effect of BERs on system performance. We consider TCP Reno in our study to explore the system performance using extensive analysis of simulation and modeling. In the analysis, we consider the amount of datagram sent and retransmitted, mean throughput, link-layer overhead, TCP window size, FTP download response time, packet dropping and retransmission, and the TCP congestion avoidance mechanism. We validate simulation results by setting up a virtualized testbed using Linux hosts and a Linux router. The results obtained show that TCP throughput degrades significantly and eventually collapses at the packet drop probability of 10% (BER = 10−5). The FTP download response time is about 32 times longer than that of a perfect channel (no packet dropping). We found that TCP Reno cannot handle such a high BER to operate in wireless environments effectively. Finally, we provide recommendations for network researchers and engineers confronted with the challenge of operating TCP over noisy channels.

Two methods are proposed in this paper to estimate asymptotic and exact bit error rate (BER) in two-hop amplify-and-forward (AF) relay networks . Rayleigh-fading channels are considered and selection strategy is used to select the highest end-to-end signal-to-noise ratio relay among all relays. The first presented method unifies the BER analysis performance for both one and two hop networks in one scheme and this refers to as the unified BER (U-BER) . The second method, namely the optimal BER (O-BER), is developed to measure BER for an AF relay network that is optimized with respect to its energy and spectral efficiency. Expressions for asymptotic BER performance for (U-BER) and (O-BER) are derived. An expression for the exact BER for (U-BER) is also obtained. The proposed methods provide useful and efficient tools for analyzing the BER performance in AF relay networks . Analytical and simulated results are compared to validate the BER calculation.

Internet of Things (IoT) enables the inter-connectivity of different “things” using which wide range of items and devices can communicate with each other and their external environment. 5G technology offers enhanced quality of service with high-data transmission rates, which necessitates the implementation of IoT in 5G architecture. Free space optics (FSO) is considered as a promising technology that can offer high-speed information transmission links and therefore is an optimal choice for wireless networks to satisfy the full potential of 5G technology offering 100 Gbit/s or more speed. By implementing 5G features in IoT, the coverage area and performance of IoT will be enhanced using high-speed FSO links. This work proposes the development of high-speed long-reach FSO link for the implementation of 5G and IoT. We investigate a long-haul, single-channel polarization division multiplexed 16-level quadrature amplitude modulation (PDM-16-QAM) based FSO link at 160 Gbit/s incorporating digital signal processing with coherent detection at the receiver terminal. The results show that the proposed system demonstrates a good bit error rate performance under different weather conditions. The proposed system can be deployed for high-speed, long-haul, spectral efficient, robust information transmission links in future 5G wireless networks under dynamic weather conditions.

Emerging 5G and future 6G mobile networks are expected to cater for high mobility scenarios ranging from vehicle-to-vehicle communications to unmanned aerial vehicles and airborne platforms. Communications in this type of deployments suffer from severe Doppler shifts which require new modulation waveforms. Orthogonal time frequency space (OTFS) modulation has recently been proposed as a promising technology for coping with high Doppler channels. OTFS converts a time-varying fading channel into a time-independent channel in the two-dimensional delay-Doppler (DD) domain. The transmit symbols are multiplexed into a nearly constant channel with a complex channel gain in the DD domain. In this paper, we consider a high Doppler airborne communication network where relative mobile node speeds can be above 1200 m/s. The considered system represents a mobile ad-hoc network where the airborne mobile nodes can join or leave the network. Furthermore, each node is equipped with an antenna array that supports directed communication among mobile nodes. The Doppler shifts in this airborne communication network are in the order of 52-72 kHz and may potentially be even higher depending on the selected carrier frequency and the relative speed among the airborne platforms. As such, OTFS modulation is used in this work to efficiently compensate for the high Doppler shifts in the DD domain. In particular, a comprehensive performance assessment in terms of bit error rate (BER) is conducted to reveal the potential of OTFS modulation in dealing with such extreme transmission scenarios. The impact of physical layer parameters, number of delay-Doppler bins in the DD domain used for OTFS modulation, directed versus two-ray channels, and the combination of multiple-input multiple-output (MIMO) systems with OTFS modulation on the BER is assessed. It is shown that both OTFS modulation over a two-ray channel as well as MIMO-OTFS modulation provide a reliable airborne communication network with low BER.

Visible light communication (VLC) is a promising wireless high-data-rate transmission technology that uses visible light. Optical Orthogonal Frequency Division Multiplexing (OOFDM)-based systems, especially asymmetrically clipped optical OFDM (ACO-OFDM), face challenges such as high peak-to-average power ratio (PAPR), which causes signal distortion, power inefficiency, and degraded bit error rate (BER) performance. Previous methods like clipping, tone reservation, and standard companding tried to minimize PAPR, but at the expense of increased complexity or BER loss. To mitigate these shortcomings, in this paper, a hybrid scheme is proposed that combines nonlinear companding techniques (NCT) with other precoding schemes—discrete cosine transform (DCT), discrete Hartley transform (DHT), Walsh–Hadamard transform (WHT), and Vandermonde-like matrix (VLM). Simulation results indicate that the presented approach substantially reduces PAPR by up to 6.73 dB while maintaining or even improving BER performance. The proposed approach is an effective solution to high-performance ACO-OFDM-based VLC systems.

This paper presents for non-coherent Optical Code Division Multiple Access (OCDMA) systems a new optical code namely Two-Dimensional Half Spectral/Spatial Zero Cross Correlation (2D-HSSZCC) code based on a One-Dimensional Zero Cross Correlation (1D-ZCC) code already developed using block matrices characterized by a high capacity. The results of simulation show that the use of the new (2D-HSSZCC) code eliminates totally the Multiple Access Interferences (MAI) due to the zero cross correlation flexibility, and less complexity of the code construction which produces a very low bit error rate of closely (4×10 ) at 1 Gbps for four users with a low power source of −12.60 dBm to reach a high data rate and high number of simultaneous users upper to closely 149, save an effective power around −1.35 dBm, −3.3d Bm compared between those provides by (Two-Dimensional dynamic cyclic shift (2D-DCS) code and Two-Dimensional Dimensional Diluted Perfect Difference (2D-DPD) and (1D-ZCC) code, and increase the cardinality percentage upper to 1.58, 2.19, 2.33 and 3.9 times comparing to (2D-DCS) code, 2D-DPD code, 1D-ZCC code and Two-Dimensional Flexible Cross Corelation/Modified Double Weight (2D-FCC/MDW) code. On the other hand, 2D-HSSZCC code is comparied with other codes which has it same property namely Two-Dimensional zero cross correlation/multi diagonal (2D-ZCC/MD) and (2D-MD) codes where the increased percentage in system capacity was 1.38 and 1.05 times, respectively. Finally, the results obtained in part 1 (with Matlab software) were confirmed and validated with the Optisystem software, the proposed system gave a better BER minimum value around 10 and a maximum value of the Q factor of around 9.4 at 622 Mbps of data rate when the number of simultaneous users increases.

Recently, free-space optical (FSO) communication systems utilizing unmanned aerial vehicle (UAV) relays have garnered significant attention. Integrating UAV relays into FSO communication and employing cooperative diversity techniques not only fulfill the need for long-distance transmission but also enable flexible adjustments of relay positions based on the actual environment. This paper investigates the performance of a parallel-UAV-relay-based FSO communication system. In the considered system, the channel fadings include atmospheric loss, atmospheric turbulence, pointing errors, and angle-of-arrival fluctuation. Using the established channel model, we derive a tractable expression for the probability density function of the total channel gain. Then, we derive closed-form expressions of the system outage probability (OP) and average bit error rate (ABER). Moreover, we also derive the asymptotic OP and ABER for a high-optical-intensity regime. Our numerical results validate the accuracy of the derived theoretical expressions. Additionally, the effects of the number of relay nodes, the field of view, the direction deviation, the signal-to-noise ratio threshold, the atmospheric turbulence intensity, the transmit power, and the transmission distance on the system’s performance are also discussed.

As the applications of unmanned aerial vehicles (UAV) expand, reliable communication between UAVs and ground control stations is crucial for successful missions. However, adverse weather conditions caused by atmospheric gases, clouds, fog, rain, and turbulence pose challenges by degrading communication signals. Although, some recent studies have explored the nature of signal attenuation caused by atmospheric weather variations, studies that compare the attenuation from various weather conditions and analyze the effect on available bandwidth are missing. This work aimed to address this research gap by thoroughly investigating the impact of atmospheric weather conditions on the bandwidth available for UAV communications. Quantitative and qualitative performance analyses were performed for various weather conditions using metrics such as attenuation and the bit error rate of the received signals associated with different modulation schemes and frequencies, using a linearly segmented attenuation model. The results indicate that atmospheric gases and clouds/fog affect wireless signal propagation; however, the effect of rain on the propagation distances and operating frequencies considered in this study was the most severe. Based on the influence of power transmission, operating frequency, modulation schemes, distance, and adverse weather conditions on the bit error rate and bandwidth suboptimization, we propose an algorithm to select the maximum operating frequency for reliable UAV link operation.

This study introduces a novel approach to bolstering quantum key distribution (QKD) security by implementing swift classical channel authentication within the SARG04 and BB84 protocols. We propose mono-authentication, a pioneering paradigm employing quantum-resistant signature algorithms—specifically, CRYSTALS-DILITHIUM and RAINBOW—to authenticate solely at the conclusion of communication. Our numerical analysis comprehensively examines the performance of these algorithms across various block sizes (128, 192, and 256 bits) in both block-based and continuous photon transmission scenarios. Through 100 iterations of simulations, we meticulously assess the impact of noise levels on authentication efficacy. Our results notably highlight CRYSTALS-DILITHIUM’s consistent outperformance of RAINBOW, with signature overheads of approximately 0.5% for the QKD-BB84 protocol and 0.4% for the QKD-SARG04 one, when the quantum bit error rate (QBER) is augmented up to 8%. Moreover, our study unveils a correlation between higher security levels and increased authentication times, with CRYSTALS-DILITHIUM maintaining superior efficiency across all key rates up to 10,000 kb/s. These findings underscore the substantial cost and complexity reduction achieved by mono-authentication, particularly in noisy environments, paving the way for more resilient and efficient quantum communication systems.