International Journal of Computer and Applications

The next generation (NG) optical technologies will unveil certain unique features, namely ultra-high data rate, broadband multiple services, scalable bandwidth, and flexible communications for manifold end-users. Among the optical technologies, free space optical (FSO) technology is a key element to achieve free space data transmission according to the requirements of the future technologies, which is due to its cost effective, easy deployment, high bandwidth enabler, and high secured. In this article, we give the overview of the recent progress on FSO technology and the factors that will lead the technology towards ubiquitous application. As part of the review, we provided fundamental concepts across all types of FSO system, including system architecture comprising of single beam and multiple beams. The review is further expanded into the investigation of rain and haze effects toward FSO signal propagation. The final objective that we cover is the scalability of an FSO network via the implementations of hybrid multi-beam FSO system with wavelength division multiplexing (WDM) technology.

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A Survey of Free Space Optics (FSO) Communication Systems, Links, and Networks

SIMO optical wireless links with nonzero boresight pointing errors over M modeled turbulence channels

In this paper, we are interested in more efficient modulation techniques that achieve a good Bit Error Rate (BER) performance, bandwidth and power efficiencies for Free Space Optics (FSO) Communication Systems. The theoretical expressions of the BER versus the Signal-to-Noise Ratio (SNR), the bandwidth efficiency, and the normalized power requirements for NRZ-OOK, RZ-OOK, PPM, PAM, DPSK, BPSK, and QPSK modulation schemes for FSO communication systems are introduced, and a comparison between these modulation techniques is presented. The comparative study of the PPM and PAM schemes is also discussed and showed that for similar SNR, PPM offered improved BER performance. In addition, the BER performance under BPSK modulation is better compared to OOK, RZ-OOK, PAM, 2-PPM, 4-PPM, DPSK, and QPSK modulation techniques. And for FSO communication systems, although the power efficiency is inferior to PPM, OOK is more commonly used due to its efficient bandwidth usage, but PAM scheme is the bandwidth efficient modulation scheme in this research for more than two bits of information sent, while the PPM scheme is the power efficient modulation scheme for more than two bits of information sent.

Studying the BER performance, power- and bandwidth- efficiency for FSO communication systems under various modulation schemes

In recent years, underwater visible light communication (UVLC) has become a potential wireless carrier candidate for signal transmission in highly critical, unknown, and acrimonious water mediums such as oceans. Unfortunately, the oceans are the least explored reservoirs in oceanogeographical history. However, natural disasters have aroused significant interest in observing and monitoring oceanic environments for the last couple of decades. Therefore, UVLC has drawn attention as a reliable digital carrier and claims a futuristic optical media in the wireless communication domain. Counterparts of traditional communications, the green, clean, and safe UVLC support high capacity data-rate and bandwidth with minimal delay. Nevertheless, the deployment of UVLC is challenging rather than terrestrial basis communication over long ranges. In addition, UVLC systems have severe signal attenuation and strong turbulence channel conditions. Due to the fact that, this study provides an exhaustive and comprehensive survey of recent advancements in UVLC implementations to cope with the optical signal propagation issues. In this regard, a wide detailed summary and future perspectives of underwater optical signaling towards 5G and beyond (5GB) networks along with the current project schemes, channel impairments, various optical signal modulation techniques, underwater sensor network (UWSN) architectures with energy harvesting approaches, hybrid communication possibilities, and advancements of Internet of underwater things (IoUTs) are concluded in this research. 

https://ieeexplore.ieee.org/ielx7/6287639/9668973/09707771.pdf

Recent Trends in Underwater Visible Light Communication (UVLC) Systems

As wireless communication systems become ever-more important and pervasive parts of our everyday life; system capacity and quality of service issues are becoming more critical. In order to increase the system capacity and improve the quality of service, it is necessary that we pay closer attention to bandwidth and power efficiency issues. In this paper, the bandwidth and power efficiency issues in Free Space Optics (FSO) transmissions are addressed under Pulse Position Modulation (L-PPM) and Pulse Amplitude Modulation (M-PAM) schemes, and their performance in terms of power and bandwidth efficiencies and the Bit Error Rate (BER) versus Signal-to-Noise Ratio (SNR) are compared analytically. The comparative study of the L-PPM and MPAM schemes is discussed, and showed that for similar SNR, L-PPM scheme offered improved performance. For FSO communication systems, although the power efficiency is inferior to L-PPM scheme, On-Off Keying (OOK) modulation scheme is more commonly used due to its efficient bandwidth usage, but M-PAM is the bandwidth efficient modulation scheme in this research for more than “2” bits of information can be sent, while L-PPM is the power efficient modulation scheme for more number of bits can be sent, and it may be able to improve performance by increasing the number of bits in L-PPM scheme. General Terms Optical Communications, Modulation schemes, Bit Error Rate (BER), Signal to Noise Ratio (SNR), Bandwidth Efficiency, Power Efficiency.

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Performance Comparison between OOK, PPM and PAM Modulation Schemes for Free Space Optical (FSO) Communication Systems: Analytical Study

Intelligent reflecting surfaces (IRS)-aided multiuser millimeter-wave (mmWave) massive multiple input multiple output (mMIMO) systems have recently attracted a great interest as an attractive paradigm for the future 6G wireless communications. The main benefits of these systems include achieving a transmission in a cost-effective, energy-efficient and intelligent manner. In this paper, multi-IRS-aided systems are introduced as a promising technique to assist the adaptive cross entropy (ACE)-based hybrid precoding, which is a machine learning (ML) inspired energy-efficient hybrid precoding scheme that requires a small number of low-cost and energy-efficient switches and inverters. Extensive computer simulations have been conducted to evaluate the achievable sum-rate performance and the energy efficiency (EE) of the proposed multi-IRS-assisted mMIMO systems with ACE-based hybrid precoding architecture. For the sake of fair comparisons, the conventional precoding schemes are also evaluated. The simulation results demonstrate the remarkable advantages of the proposed scheme compared with the conventional state-of-the-art schemes. It is also shown that the EE can be further improved as the number of cascaded IRSs and their elements increase. This makes the proposed system a promising candidate for 6G wireless communications.

Multi-IRS-aided Millimeter-wave Massive MIMO with Energy-Efficient Hybrid Precoding Schemes

Intelligent reflecting surface (IRS)-assisted multiple input multiple output (MIMO) has recently been considered as a prospective candidate for the future 6G wireless systems. This is mainly due to its ability to significantly improve the energy efficiency and network coverage by intelligently adapting the wireless propagation environment. In this paper, a parallel multi-IRS-aided spatial modulation (SM) scheme with Frobenius norm-based IRS selection is proposed to improve the error performance by selecting a subset of IRSs with the largest norm values out of parallel multiple IRSs for the transmission between the source and destination. Extensive computer simulations have been conducted to evaluate the bit error rate (BER) performance of the proposed scheme, and the performance of the parallel multi-IRS-assisted SM and conventional SM schemes is also evaluated for the sake of fair comparison. The results show that the proposed scheme has remarkable advantages, such as power-efficiency, over its counterparts. It is also shown that the BER performance can be further improved as the number of selected IRSs and their elements are increased.

Frobenius Norm-Based IRS Selection Algorithm in Parallel Multi-IRS-assisted Spatial Modulation

Intelligent reflecting surface (IRS)-assisted beamspace millimeter-wave (mmWave) multiuser massive multiple input multiple output (MIMO) with interference-aware (IA) beam selection scheme is proposed in this paper. This proposed scheme is capable of intelligently reconfiguring the radio environment and utilizing the beam selection for the sake of reducing the number of required radio frequency $( R$F) chains without any noticeable performance degradation. To ensure a fair comparison, the achievable sum-rate and energy efficiency (EE) performance metrics of the proposed scheme are evaluated and compared to that of IRS-assisted fully-digital systems with zero-forcing $(Z$F) precoding and the conventional systems without the IRS technology. Simulation results demonstrate that the proposed IRS-assisted beamspace mmWave massive MIMO system with IA beam selection algorithm outperforms the conventional system without IRS. It is also shown that the performance improves when the number of reflecting elements is more than the total number of mobile users. Moreover, the proposed scheme can potentially offer higher EE than the conventional schemes. Therefore, this shows that the proposed system can be considered as an alternative solution for the future generation of wireless systems.

IRS-Assisted Beamspace Millimeter-wave Massive MIMO with Interference-Aware Beam Selection

In this article, signed quadrature spatial modulation (SQSM) scheme is intrinsically amalgamated with both fully digital geometric mean decomposition (GMD)‐based precoding technique and analog beamforming (ABF) for transmission over millimeter‐wave (mmWave) channel. Explicitly, the proposed scheme combines SQSM and GMD‐based hybrid beamforming (HBF) in downlink multiuser scenario, where the Frobenius norm‐based user selection algorithm is considered. This proposed scheme is denoted as multiuser steered SQSM (MUS‐SQSM). The ABF is used to mitigate the severity of the propagation loss in mmWave band by using power amplifiers and phase shifters. The performance of the proposed scheme in terms of both the bit error rate and the average mutual information is assessed in comparison to the conventional SQSM scheme performance. Simulation results show that significant improvements are realized by both the user selection algorithm and the application of ABF technique as the number of antenna array elements increases. It is also demonstrated that MUS‐SQSM scheme is robust against the channel estimation errors. Furthermore, the proposed MUS‐SQSM scheme with HBF benefits from the multiplexing gain of SQSM, the diversity gain of serving multiple users, and from the beamforming gain. All these gains increase the energy efficiency of the proposed model; thus, the proposed scheme can be considered in 5G wireless systems deployment.

Taissir YoussefElganimi

Papers

Performance Comparison between OOK, PPM and PAM Modulation Schemes for Free Space Optical (FSO) Communication Systems: Analytical Study

Multi-IRS-aided Millimeter-wave Massive MIMO with Energy-Efficient Hybrid Precoding Schemes

Frobenius Norm-Based IRS Selection Algorithm in Parallel Multi-IRS-assisted Spatial Modulation

IRS-Assisted Beamspace Millimeter-wave Massive MIMO with Interference-Aware Beam Selection

Multiuser steered signed quadrature spatial modulation for millimeter‐wave massive multiple‐input multiple‐output with hybrid beamforming