A comprehensive review of performance analysis of RF-FSO hybrid communication systems

The combination of radio frequency (RF) and free-space optical (FSO) communication has grown in importance as a study area for wireless communication systems in recent years. This technology has the ability to address the rising need for high-speed, high-capacity wireless communication in a variety of applications by successfully integrating the benefits of both RF and FSO communication. The performance analysis of various communication systems based on RF-FSO hybrid technology is covered in detail in this research. An overview of the RF-FSO hybrid technology and its many architectures follows the introduction of the key features and benefits of RF and FSO communication. The performance analysis of several RF-FSO hybrid communication systems, including relay-assisted RF-FSO systems, cooperative diversity RF-FSO systems, and dual-hop RF-FSO systems, are discussed in detail. The performance metrics, such as bit error rate (BER), outage probability, and channel capacity, is analyzed and compared for these systems. Based on the analysis of existing literature, several key conclusions are drawn. First, RF-FSO hybrid technology can provide higher data rates and greater reliability than traditional communication systems. Secondly, the performance of the RF-FSO hybrid system, which combines the advantages of RF technology and FSO technology, has bright development prospects. Finally, the RF-FSO hybrid system can also be combined with other systems for better performance and wider application scenarios.


Introduction
Our daily lives now depend heavily on wireless communication, and the demand for high-speed, highcapacity wireless communication is rising quickly.The data rate, bandwidth, and transmission range of conventional wireless communication technologies like radio frequency (RF) and microwave are constrained [1].Free-space optical (FSO) communication, on the other hand, can provide high data rates, large bandwidth and system capacity, licensed spectrum, and anti-electromagnetic interference [1][2][3][4][5] but it is sensitive to atmospheric conditions such as atmospheric turbulence, pointing error, and atmospheric attenuation and has a limited transmission range [1][2][3][4][5][6][7][8].
Lately, a viable method to get around both technologies' drawbacks has emerged: RF and FSO communication hybrid technology.RF-FSO hybrid communication technology can combine the advantages of both [1][2][3][4][5][6][7] and provide high data rates, large bandwidth, and a long transmission range.It has the potential to meet the increasing demand for high-speed, high-capacity wireless communication in various applications.
The performance analysis of various communication systems based on RF-FSO hybrid technology is covered in detail in this research.The paper is organized as follows: Firstly introduce the key characteristics and advantages of RF-FSO communication technologies.Then discuss the performance analysis of several RF-FSO hybrid communication systems, including relay-assisted RF-FSO systems, cooperative diversity RF-FSO systems, and dual-hop RF-FSO systems.The performance metrics, such as bit error rate (BER), outage probability, and channel capacity, are analyzed and compared for these systems.The conclusion summarizes the challenges and future research directions of the RF-FSO hybrid technology.
It is anticipated that researchers and engineers working in the field of wireless communication will find this study to be a useful reference because it includes a thorough assessment of the performance analysis of many RF-FSO hybrid communication systems.

Advantages overview
RF-FSO communication uses a combination of RF and FSO links to transmit data.The RF link provides a reliable and continuous communication channel that can transmit data through obstacles and adverse weather conditions [1,6,7].On the other hand, the FSO link provides a high-speed and secure communication channel that is immune to interference from other RF sources [1][2][3][4][5].The combination of these two links provides a robust and reliable communication system that can operate in diverse environments.RF-FSO communication has several advantages over traditional RF or FSO communication.First, it provides high-speed communication with data rates up to several Gbps, which is much higher than traditional RF communication [1][2][3][4][5].Second, it is immune to interference from other RF sources, making it suitable for use in crowded RF environments [2,3].Third, it provides a secure communication channel because the FSO link cannot be intercepted without physical access to the transmitter and receiver, and it can be mitigated against environmental factors such as atmospheric turbulence [1][2][3][4][5][6][7][8].

Analysis and comparison of various technologies
Several RF-FSO hybrid communication system types, such as relay-assisted RF-FSO systems, cooperative diversity RF-FSO systems, and two-hop RF-FSO systems, have been presented recently.Several criteria, including bit error rate (BER), outage probability, and channel capacity, have been used to assess these systems' performance.This section mainly focuses on three RF-FSO systems: Relay-Assisted RF-FSO Systems, Cooperative Diversity RF-FSO Systems, and dual-hop RF-FSO Systems.

Relay-assisted RF-FSO systems
Relay-assisted RF-FSO systems refer to a hybrid communication system that integrates radio frequency (RF) and free-space optical (FSO) technologies with the help of a relay node.In this system, the relay node acts as a mediator between the source and destination nodes and provides a reliable connection by mitigating the effects of atmospheric turbulence and other environmental factors.Here is a detailed analysis of the advantages and disadvantages of a relay-assisted RF-FSO system: 3.1.1.Advantages.Increased Reliability: By overcoming the difficulties of FSO communication, the relay node offers a dependable communication link between the source and destination nodes.This improves the overall reliability of the system, especially in adverse weather conditions.
Extended Range: Compared to conventional RF or FSO systems, the system can achieve a larger communication range by deploying a relay node.This is so that the signals can be renewed and sent over a greater distance by the relay node.
Reduced Bit Error Rate (BER): By reducing the effects of atmospheric turbulence and other environmental conditions, the relay node improves system performance and lowers BER.
Flexibility: Relay-assisted RF-FSO systems are extremely adaptable and can be built to satisfy the unique communication requirements of many applications.For example, the system can be optimized for long-range, high-speed, or low-power communication.

Disadvantages. Complexity:
The relay-assisted RF-FSO system is more complex than traditional RF or FSO systems.This is because the system requires additional hardware and software to support the relay node and manage the communication between the nodes.
Cost: Relay-assisted RF-FSO systems are more expensive to deploy than conventional RF or FSO systems.This is due to the system's need for more infrastructure and hardware to support the relay node.
Power Consumption: The relay node uses extra energy, which can be problematic in remote or energy-restricted settings.
Interference: By introducing interference into the communication network, the relay node could reduce the system's performance.
In conclusion, compared to conventional RF or FSO systems, the relay-assisted RF-FSO system has a number of benefits, including increased reliability, a wider range, a lower BER, and flexibility.The system does have several disadvantages, though, including complexity, expense, power consumption, and interference.As a result, the system's deployment should be carefully assessed in light of the application's unique requirements.

Cooperative diversity RF-FSO systems
Cooperative diversity RF-FSO systems are a type of RF-FSO system that uses diversity techniques to improve the reliability of communication between the source and destination.This is achieved by using multiple transmit and receive antennas, as well as the cooperation of neighboring nodes to create a more robust and reliable link.
Compared to the relay-assisted RF-FSO system, cooperative diversity RF-FSO systems offer several advantages and disadvantages: 3.2.1.Advantages.Higher Reliability: Cooperative diversity RF-FSO systems use diversity techniques and cooperation between nodes to improve the reliability of communication links.In contrast, relayassisted RF-FSO systems may suffer from signal degradation and delays due to the use of a relay node.
Better Spectral Efficiency: Cooperative diversity RF-FSO systems can achieve higher spectral efficiency than relay-assisted RF-FSO systems because they do not require the use of a relay node, which can introduce additional delays and signal degradation.
Lower Power Consumption: Cooperative diversity RF-FSO systems can be more energy-efficient than relay-assisted RF-FSO systems because they do not require the use of a relay node, which can consume additional power.

Disadvantages.
Complexity: Cooperative diversity RF-FSO systems are more complex than relay-assisted RF-FSO systems because they require multiple antennas and cooperation between nodes.
Higher Implementation Cost: Due to the requirement for numerous antennas and additional signal processing hardware, cooperative diversity RF-FSO systems may be more expensive to implement than relay-assisted RF-FSO systems.
The reliability and effectiveness of RF-FSO communication systems can be increased, especially in difficult circumstances, with the help of cooperative diversity RF-FSO systems.However, their complexity and higher implementation cost may limit their practical use in some applications.

Dual-hop RF-FSO systems
Dual-hop RF-FSO system is a wireless communication system that combines radio frequency (RF) and free-space optical (FSO) technologies.This system is designed to overcome the limitations of traditional RF and FSO systems by providing a backup communication channel using the RF link in case the FSO link is disrupted.This ensures that communication is not lost, resulting in a more reliable system.
Additionally, the RF link can be used for long-distance transmission, increasing the transmission range of the system.Dual-hop RF-FSO systems offer greater flexibility in system design and implementation, making them a promising solution for various communication applications.However, they require additional hardware components and signal processing algorithms to ensure seamless integration between the RF and FSO links.
3.3.1.Advantages.Improved system reliability: Since wireless signals can be affected by obstacles, multipath fading, and atmospheric conditions, using a dual-hop RF-FSO system can improve the system's reliability.The RF link can be used to provide a backup communication channel in case the FSO link is interrupted.
Increased transmission range: The optical signal can be attenuated by atmospheric conditions including fog, rain, and snow on FSO lines.The use of a dual-hop RF-FSO system can increase the transmission range of the system by allowing the RF link to be used for long-distance transmission.
Improved system flexibility: A dual-hop RF-FSO system might offer more design and implementation freedom.The RF link can be utilized to increase the coverage area or give key applications a backup communication channel.

Disadvantages.
Increased system complexity: A dual-hop RF-FSO system is more complex than a single-hop RF or FSO system.To guarantee flawless integration between the RF and FSO lines, additional hardware elements and signal processing methods are needed.
Higher cost: In comparison to conventional RF or FSO systems, the cost of a dual-hop RF-FSO system may be higher due to the additional hardware and complexity.
A dual-hop RF-FSO system, in general, offers improved reliability, a larger transmission window, and more system flexibility, but at the cost of increased complexity and more expensive implementation.

Conclusion
This paper analyzes the defects of RF and FSO technology, summarizes the advantages of RF-FSO technology, and analyzes and compares the performance and advantages of several common RF-FSO technologies.Strategies including these kinds of systems can enhance the performance of RF-FSO hybrid communication systems.The particular requirements must be considered when choosing system designs since each technique has features of its own.
The dual-hop RF-FSO system has broader application scenarios and longer-term development potential.It can be utilized in conjunction with the current 5G network and the upcoming 6G network to offer a promising replacement for the current system.Moreover, the dual-hop RF-FSO can be used in deep space communication, which can reduce the impact of sun scintillation, and improve the outage probability performance in deep space communication to assist future sounding exploration.Dual-hop RF-FSO is worthy of further exploration due to its advantages.
The biggest drawback of RF-FSO technology at the moment is that it is sensitive to atmospheric factors, which can weaken and distort signals.The RF and FSO beam alignment can also be challenging and calls for exact pointing and tracking devices.Researchers are investigating cutting-edge methods like adaptive optics and sophisticated modulation algorithms to overcome these issues and enhance the performance and reliability of RF-FSO systems.
The shortcoming of this paper is that it does not analyze and compare more RF-FSO technologies, but only discusses three currently common technologies.In the future, it is expected that RF-FSO technology will continue to evolve and become more robust and efficient.One potential area of development is the integration of machine learning and artificial intelligence to optimize the alignment of the RF and FSO beams and enhance the adaptability of the system to changing atmospheric conditions.Overall, the continued advancements in RF-FSO technology have the potential to greatly improve wireless communication and enable new applications in areas such as 5G and 6G networks, autonomous vehicles, and smart cities.