Towards Enabling Haptic Communications over 6G

Version	Summary	Created by	Modification	Content Size	Created at	Operation
1		Muhammad Zafar	--	5552	2023-07-28 10:10:38	\|
2	format	Jason Zhu	-3 word(s)	5549	2023-07-28 10:14:41	\| \|
3	format	Jason Zhu	Meta information modification	5549	2023-07-28 10:15:06	\|

This entry is adapted from the peer-reviewed paper 10.3390/electronics12132955

The developments in communication networks enable many applications including high quality audio/video sharing. Mobile communication has become an essential component of present-day life. It plays an important role in the economy, health, education, and many other industries. Most of the population is connected through mobile communication networks globally. After successfully connecting billions of smartphones and laptops through mobile internet, the focus of mobile internet has now been diverted towards the ubiquitous connectivity of multiple devices and machines, hence creating the Internet of Things (IoT). This transition has led mankind towards remote communication between a human being and some kind of physical device. Such data-intensive communications can result in mediums where the human beings can interact with each other remotely by touch (haptic communication) or actuation.

haptic communication tactile internet teleoperation

1. Resource Allocation in Tactile Internet

The increasing demand for multimedia services and the proliferation of devices have caused radio resources to become increasingly scarce ^[1]. As a result, it has become increasingly important and difficult to properly allocate radio resources for D2D-assisted haptic communications in order to guarantee the latency and reliability requirements of the control loop necessary for providing users an immersive experience ^[2]. The transmission of the haptic stream contains the control signal on the downlink and the feedback signal on the uplink ^[3].

In ^[4], the authors pose D2D connectivity as a key technology for the efficiency of the cellular network through wireless systems of the fifth generation. In accordance with recent research progress, the authors implement D2D communication and its usage scenarios, present an explanation of D2D communication centered on spectrum division, duplexing and number of steps, level of control, and address interruption and architecture dimensions of D2D communication. They also highlight very recent research to acquaint the reader with the current developments in this regard. The technologies protected by these works comprise of file distribution, vehicular contact, web networks, video streaming, advertisement, and real-time applications. They also summarized the methods and models used and their standards. Finally, the authors explain the issues defined in various parts of D2D literature and state the very latest developments.

In ^[5], the authors discuss the use of backscatter communications (BsC) and non-orthogonal multiple access (NOMA) to improve the energy efficiency and capacity of wireless communications systems in the beyond 5G (B5G) era. The paper proposes the use of coded cooperative-NOMA in combination with BsC and presents simulation results showing the improved performance of the proposed method compared to traditional NOMA and BsC systems. The paper suggests that the combination of BsC and coded cooperative-NOMA can be a promising approach for improving energy efficiency and increasing capacity in B5G wireless communications systems.

The authors in ^[6] note that there is a need for potential communication services to co-exist with several current devices. Few of the implementations will require a smooth and quick association with different networks. A novel infrastructure is therefore required with new practices and features for various senses such as 3D-video, responsiveness (for example touch, sound, and feel). The packet distribution principle must always be imminent allowing for tremendous low latency and extreme precision latency. The extremely low latency criteria would allow the 2030 network to be decentralized. In addition, with the full application of TI services, the interaction between human avatars, etc., is possible. The reorganization of the network would result in a generalization of its function and a reform of network management concepts. Satellite networks can be commonly used for content distribution facilities, which at the same time is questionably effective for the introduction of new infrastructure needing extreme low delays due to the inherent constraints on the speed of light. Unmanned aerial vehicles (UAVs) and tethered UAVs can be extensively used as a flying application for low-density regions and difficult to access areas for delivering ultra-low delays in service.

In ^[7], the authors provide an extensive overview of the development of the telecommunications infrastructure through software-defined 5G/6G networks. They describe circumstances for the 5G/6G rollout, key technologies, and software defined networking (SDN). The SDN design offered open network access by modifying variations between machines on the network. Under the conventional IT network architecture, the routing process in the network which resolved the problem of complicated network design can be conveniently described. They then gave the future network design based on SDN, based on the principles of 5G/6G network design. Moreover, they discussed the new methods of allocating resources and managing them. Radio environment maps (REMs) may play a significant role in potential network analysis, because of the presence of innovative spectrum discovery and monitoring processes. While they have looked into the latest connectivity management technologies for 5G/6G networks and addressed how to fairly address the connected state mobility problem in extremely dense networks via SDN. The writers published a concise survey on SDN related conflict control of cellular 5G/6G networks. In addition, they provided a detailed overview of the interference graph (IG) abstraction which the SDN controller can use to configure network segments with several functional constraints. Furthermore, the writers outlined the study problems and accessible concerns on 5G/6G-based SDN networks and described potential paths for the next work.

In ^[8], multiple radio resource allocation for the haptic communication in the 5G enabled LTE-A networks is investigated. The radio resource allocation for the haptic communication system is a challenging task due to multiple constraints of the multiple access scheme in LTE-A networks. first, the requirements of the radio resource allocation for haptic communications are identified. After that, the problem is translated into the resource allocation problem which tackles the uplink and downlink constraints of the 5G LTE-A network. To reduce the complexity of the problem, the optimization problem is first decomposed and transform into binary integer programming. Extensive simulations have been conducted to show the effectiveness of the proposed scheme and results show that the resource allocation performed well for the 5G LTE-A network.

In ^[9], a novel radio resource allocation framework named Hap-SliceR for the 5G framework with haptic communication is proposed. This approach allocates the radio resources to the 5G network in a flexible way to utilize the maximum spectrum of radio resources. The Hap-SliceR strategy is based on the reinforcement learning for dynamic radio spectrum slicing. For this purpose, first, the radio resource slicing problem is modelled by using the Markov decision process and then solve it by mean of Q-learning. However, this Q-learning approach is computationally slow. Therefore, increasing the efficiency of radio resource slicing through post-decision requires learning that exploits the system dynamics. After that, the novel algorithm for network slicing is proposed that first identifies the requirements of the network and then formulate the unique allocation problem by considering the constraints of downlink and uplink multiple access schemes in LTE-A networks.

In ^[10], the key requirements and the solutions of haptic communication from a radio resource allocation perspective are proposed. The radio allocation problem is to deal with two different types of problems: symmetric and perceptual coding design. Due to the combinational nature of the problem, it becomes complex. To solve this issue, the problem is first decomposed and solved by using binary integer programming for resource block allocation. Furthermore, the resource allocation problem is solved by using greedy heuristic algorithms and by using the canonical duality theory and Hungarian method, near optimal solutions are proposed. The results acquired from simulations show that the proposed method outperforms the different classical algorithms.

2. Channel Modeling

The authors argue in ^[11] that network slicing is an effective way that meets the varied demands of 5G mobile networks, delivering the necessary stability and scalability related to potential network deployment. The study comprises of the basic principles underlying mapping committed and mutual slices, in addition to application-specific factors when the network slicing method is used across the Core Network (CN) and Radio Access Network (RAN). Special attention has been paid to linking RAN principles to network slicing. They also state that robust network slicing capacity has been discovered to meet the complex specifications of the upcoming 5G networks. When constructing network slicing based 5G networks, they emphasize on the problems that occur. Authors concentrate on the technical dimensions of the network’s co-existence of devoted and mutual pieces. The authors discuss in detail the deployment possibilities of a modular wireless access system with an emphasis on network slicing and consequences on 5G mobile network architecture. Authors concentrate on the technological elements of the dedicated and reciprocal items co-existence of the network. The authors discuss in detail the implementation possibilities of an adaptable wireless access network with a focus on network slicing and effects on 5G mobile network design.

In ^[12], the authors present a specific and in-depth look at fundamental possibilities, problems and solutions to the development of potential spectrum wireless, sensing and positioning technologies over 100 GHz that will probably be a part of the 6G age. The paper identified recent legislative and standard group actions intended for promoting potential wireless schemes utilizing multi-GHz frequency channels over 100 GHz that can accommodate data rates of 100 Gbps. Authors state that a large number of exciting technologies should support future THz levels because computing power increases at the same pace to exceed the human brain’s processing power. Many THz wireless applications will allow new perception, sensing, imaging, networks, and positioning abilities to be used by new human interfaces, autonomous vehicles, and automated devices, all empowered by THz’s very high bandwidth and very short wavelength, which seems to be an assuring spectrum for coming wireless communications past the millimetre wave (mmWave) system. They also demonstrated how directional steerable antennas would allow mobile communication into the THz range, where the joint antenna gains will exceed the weather losses that were previously thought to be expensive. Antenna array systems would take advantage of new methods and physical designs such as three-dimensional noise modeling, beam shaping, hybrid beam shaping, and silence shafts, as these have demonstrated to provide substantial performance advantages, and also would resolve design restrictions such as the size of RF modules with a considerable number of antenna components. The authors review past work and introduced new measures of propagation over 100 GHz, analysis of cross-polarization discrimination, and measurements of partition failure for common building material.

In ^[13], the authors offered a comprehensive review of emerging technologies, including Machine Learning (ML), Quantum Computing (QC), and Quantum ML (QML). They also introduce their goal for the QC-and QML-assisted platform to allow wireless networks beyond 5G. First, the target facilities provided by evolving 5G communication networks and the complexities of accessible examination for the 5G communication networks were discussed. Afterwards, the latest trends in communications given by quantum, QC-aided, ML-aided, QC reinforced by ML, and QML were thoroughly reviewed. A system for 6G communication networks focused on ML, QML, and QC-aided has been suggested. Comprehensive discussions on numerous promising innovations, accessible science problems, and potential avenues for the study were given in the sense of the proposed system. Most specifically, the current 6G architecture has defined and addressed various potential supporting technology for network-organization, air device, network-edge, and user-side. The authors also describe network organization and-edge levels: the position of the suggested system for smart preemptive caching, smart MEC, resource allocation, multi-objective routing optimization, comprehensive IoT management, interoperability coordination, big data analytics, safe link security, and data privacy safety features have been addressed and suggested exhaustively.

In ^[14], the authors outlined wireless communication work and rulemaking beyond 100 GHz, examined current D band (110–170 GHz) transmission measurements, given NYU WIRELESS 140 GHz channel sounder architecture, and proposed tentative 140 GHz penetration failure measurements for different building resources. Penetration failure and total penetration loss of 140 GHz common resources that are not well studied are calculated and contrasted to 28 and 73 GHz common materials. The authors also describe a 140 GHz indoor measurement program that will be used to shape predictive indoor channel templates for different RX and TX antenna arrangements and multi-frequency divisions in combination with the previous 73 and 28 GHz indoor measurements performed at NYU WIRELESS. For mmWave indoor wireless network architecture, position tests, and a likely gigabyte Wi-Fi with the Internet of Things, the processing data and subsequent models can aid ^[15].

The current system of human-machine contact is outlined in ^[16], which focuses on the various approaches of emotion detection. Simultaneously, from the point of view of communication, the gap between the current human-machine interaction scheme and the proposed emotion communication scheme is compared. The authors then define the communication system of emotions and summarize the main technologies desired in the system. The authors described the design of the emotion communication system focused on the four principles: selection, coordination, interpretation and evaluation of the emotion that is desired in an emotion communication system. To meet the communication’s consistency criteria for both sides when the emotion is conveyed as a kind of multimedia knowledge, the authors suggest an emotion transmission procedure that delivers high-level consistent support for emotion communication. Finally, the authors examine the actual performance of a pillow robot-based speech emotion communication scheme and demonstrate the viability and efficacy of transmitting an emotion.

The TI envisages full-time remote infrastructure control through Tactile sensors (haptics) and assisted by immersive audiovisual inputs in real-time. Applications such as telehealth or Industry 4.0 would need end-to-end intervals of up to 5 ms (minimum observable by the naked eye) and ultra-high-speed communications. VR video streaming needs to overcome many challenges to achieve the real time (maximum 5 ms end to end latency) and quality (5 Gbps) required by the TI.

The aim of ^[17] is to identify areas of accessible research and obstacles to allow VR for the Tactile Web. The authors established four fields of open science problems after a theoretical and practical assessment of state-of-the-art VR video streaming solutions. First, it is necessary to optimize and improve transport and application protocols. The authors believe that the research in this area is moving in the direction of adaptive streaming where tiles, prediction of viewport and infrastructure need to be thoroughly revised. Secondly, edge infrastructure will be necessary for moving computer-intensive tasks from lightweight VR customers and intelligently prefixing material to minimize latency. Second, it is important to synchronize the multi-sensor system (VR + haptics). Finally, to subjectively benchmark solutions, new evaluation infrastructures and new methods need to be created.

Sustained focus is important in the awareness, conditioning and locomotion of everyday human activities. An increase in persistent attention shows likely effects in several areas, including the management of mental ailments, such as attention deficit disorder, and the preparation of some employees, such as aircraft pilots, who function under high mental load conditions. The authors argue in ^[18] that through preparation, vigilant monitoring can be improved. Nonetheless, a technique to fully utilize the human haptic pathway in the course of preparation has not been explored by any comprehensive research. Thanks to the fundamental focus function and exclusive features of the haptic system, haptics-mediated attention coaching provides tremendous promise. Training in haptics-mediated care is a cross-disciplinary study involving cognitive neuroscience, haptics, and psychophysiology. Exploring the neural and psychological attention methods in tasks that use the haptic channel can also foster an understanding of the mechanism of neuroplasticity in humans. The authors propose an innovative use of haptic tools that improve the ability of the human brain to maintain continued attention through the haptic channel. Since haptic experiences, such as the ability to control power, are a natural human feeling, the existing computer games may theoretically be revamped by adding realistic force feedback simulations, raising the cautious workload of players.

3. Haptic Communications Security

In ^[19], the authors discuss the security requirements for the 6G networks and describe a solution that emphasizes the insertion of trust to address distributed denial of service (DDoS) attacks into the networks. The authors argue that security risks will increase in a world where digital devices and hackers remain within the borders of the digital world. In particular, hacking can be harmful when cars, houses, vessels, harbor transportation facilities, transportation hubs and storehouses, energy supply grids, energy production and storing systems are linked to a digital network. If hacking is possible, many real-world crimes may be possible such as theft of goods, razing other’s property, and many other crimes.

The authors suggest in ^[20] that trust should be embedded in the network itself as an inherent function to automate backtracing of attacks, avoid successful distributed denial of service attacks and additional security functionality using cloud-based automation to support inexpensive and low-power devices. The authors further argue that security at the Internet level will not be enough when the physical and digital worlds intersect narrowly due to the heavy dependency on information security from physical security.

In ^[21], for 5G/6G wireless networks, the authors are proposing a new multiple access method for broad wireless communication, called Delta orthogonal multiple access (DOMA). The authors state how each cohort of cellular wireless methods has been differentiated by a different multiple access approach. First-generation (1G) networks focused primarily on multiple access frequency division (FDMA), while second, third and fourth-generation systems used Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA) and Orthogonal Frequency Division Multiple Access (OFDMA) techniques respectively.

For 5G cellular networks, although many deployments and standardization attempts are nevertheless underway, the authors foresee no innovative multiple access technologies that use significantly wider spectrum ranges (up to 60 GHz) and the introduction of Non orthogonal Multiple Access Scheme (NOMA) in addition to the existing Orthogonal Frequency Division Multiple Access (OFDMA). By adopting higher frequency spectrum bands such as mmWave bands in 5G, air interface would pose significant propagation problems due to extreme path-loss and need for beam orientation. This can be partly mitigated with the ultra-dense utilization of access points, which requires complex management and collaboration between dispersed APs to minimize the effects of co-channel interference resulting from overlapping adjacent cell coverage areas.

4. Communication Protocols

In ^[16], the authors suggest an emotion communication system based on NLOS mode to disrupt the constraint of the conventional human-machine contact framework. They describe the emotion first as one form of multimedia that is comparable to audio and video formats. It is not only possible to recognize the emotional knowledge, but also to transmit it over long distances. Instead, because of the real-time needs of the interactions between the participating parties, and emotional contact procedure is suggested that offers reliable support for emotional communication. An emotion communication system is developed for the pillow robot voice, where the pillow robot serves as a visualization tool for consumer emotion. Eventually, in the landscape of a long-distance contact among a pair of mother-child people, the real-time operation of the whole communication mechanism to determine the viability and efficacy of emotion communication is investigated.

The authors research and analyze the latest migration strategies provided by virtualization platforms such as docker and Kernel-based Virtual Machine (KVM) in ^[22] and suggest an application-level migration protocol that avoids the former’s disadvantages. In a latency-sensitive application such as a gaming program, the server needs to be transferred throughout the gameplay sessions between various hosts. The authors introduce the implementation of the suggested protocol as a proof of concept to the users and research the transition in depth. They further research and analyze different migration approaches and suggest a framework for application-level migration, now referred to as Agile Cloud Migration (ACM). The framework is designed to rapidly and regularly deploy concurrent and latency-sensitive applications through multiple internet servers. The protocol requires certain application architecture designs such as engine isolation from its state to optimize the migration, and while keeping the entire migration process transparent to the user. Using theoretical approximations, the measurements of transfer time are deliberated in detail and proven using the measurements made on the concrete implementation of the ACM protocol.

Taking advantage of the recent advances in 5G and ultralow latency networking, AI in general, and robotics, the authors emphasize in ^[23] the advent of a radically new Web that will allow digital capabilities to be delivered. The authors present their perspective on an innovative internet generation, the Internet of Skills, where sophisticated ultra-low latency, AI, and advances in robotics can allow skills to be distributed throughout the world securely and cost effectively. They identify the technical challenges that need to be solved to enable such a dream, i.e., the creation of a 5G Tactile Network, unified haptic codecs, and AI to allow zero-latency networks to be viewed. They claim that the Web of Skills will revolutionize business processes and company functionality by allowing the distribution of physical experiences locally (and globally) and will transform the way teaching, training, and communication are conducted in the customer world. They claim that it would become a catalyst for skill set transfer making it an essential technology for service-driven markets. Finally, they discuss social challenges related to the Internet of Skills, emphasizing both business and societal opportunities enabled by the novel concept of the Internet of Skills.

5. Performance Evaluation Parameters

In ^[24], the author projected a framework for Distributed Event-Triggered Communication and Control (ETCC) of Linear Multi-Agent System (MAS) under the TI for the data reduction of every agent. Firstly, the proposed work reflects the ETCC data reduction scheme both for the communication and controller update to each agent under the TI. This framework highlights that with this arrangement, the ultra-low latency and data reduction are reinforced as the output feedback of ETCC. The proposed work proves that the agreement of MAS can be accomplished asymptotically. Finally, it is revealed that the proposed communication and control approach satisfies in the reduction of mutually the frequency of the communication and controller updates as well as excluding Zeno behavior.

In ^[25], the authors discuss the design challenges and their solutions to enabling the TI. This first focuses on the requirements of haptic communications in the context of TI and then highlights the design challenges of TI over cellular networks. This focuses on designing such an architecture that enables haptic communications without changing the existing architecture of the communication system with efficient network slicing and resource allocation, by achieving ultra-reliable connectivity along with the reduction in round-trip latency. The latency rate is increased by using optical transport as a backhaul medium and by increasing the computational power of the nodes.

In ^[26], a novel approach to reduce the round-trip latency and network congestion is proposed. This problem is catered to by introducing small scale clouds which consist of a small number of cells. The edge computing facilities are present in the micro-cloud, and this micro-cloud is connected with the mini-clouds which have furthermore computation capabilities. By introducing multi-level clouding results in reducing the round-trip latency and network congestion. This high latency rate will encourage the TI by which the emotions can be transferred in real-time.

The TI structure defined networks in the core of the cellular network and mobile edge computing in multilevels to reduce round-trip latency as discussed in ^[27]. This approach uses the motivation behind the software define networks which have centralized core controller with a global knowledge of the network along with the concept of network function visualization. The results show that the round-trip latency is decreased with the decrease in the bandwidth and by shifting the communication process from the core network controller to the mini-cloud unit.

In ^[28], the authors proposed the key architecture changes in the existing 5G cellular network to enhance the cost, energy efficiency, stability, security, and latency. For this purpose, the authors’ proposed the decomposition of a mobile cellular network function and allocate it to the cloud network. To implement this concept the software defines network and network visualization concepts are used in which cloud computing is involved to reduce the computational complexities which result in the reduction of end-to-end latency.

In ^[29], the authors highlight the key networking solutions to enabling the TI in the flexible 5G networks and beyond. This focuses on the recent progress in the area of TI and its enabling technologies. The state-of-the-art techniques discussed in most of the literature is to integrate the software-define radios and network function virtualization along with edge-fog computing to overcome the issue of 1 ms latency rate, which enables TI.

An approach to achieve the goal of 1 ms latency over the 5G network is proposed in ^[30]. The authors proposed that the centralized controller in the network with global information of the entire system overcome the issue of 1 ms round-trip latency. This system architecture employs software defined network along with multi-level mobile edge computing to enable TI. The modular testbed to test the large variety of haptic communications applications is discussed in ^[31]. Haptic systems are tested based on characteristics and validation of many aspects of end-to-end delay. Therefore, a testbed using multi-block testbed architecture is proposed by the authors. In this architecture, depending on the use case to be tested, the blocks are reconfigured and add/remove module options are available. Moreover, the testbed tools are designed to extract the information of the latency of sub-blocks and modules in use to support the research and development.

In ^[32], authors propose a queueing function for a pair of Power Domain Non-orthogonal multiple access (PDNOMA) based TI users in C-RANs. Authors consider a more practical scenario between end-to-end TI users by incorporating RRH and BBU queueing delays. To minimize these delays, the problem is first treated as a non-convex optimization problem. Then it is solved by successive convex approximation (SCA) and the difference between two convex functions (DC). This solution allows controlling the delays encountered among TI users. By using the proposed queueing model these delays between TI users are significantly improved enabling less usage of transmission power for each transmission between users. In ^[33], a resources allocation (RA) algorithm using admission control (AC) is proposed for users which are using TI services in OFDMA based C-RAN network. To maximize user experience, delays encountered due to BBUs, RRHs and front hauls are minimized. This is possible when RA is considered a non-convex problem. To solve it, successive convex approximation (SCA) is applied which reduces transmission power consumption. The performance of this algorithm is evaluated by the service acceptance ratio (SAR).

6. Virtual Reality

Virtual Reality (VR) haptic technology offers an extra feature to the VR technology by letting users feel the virtual environment via the sense of touch, in addition to visual and aural perception. One method to achieve this haptic feature is to add a passive haptic device to the VR.

In ^[34], the framework of haptic retargeting is proposed, which supports passive haptics for multiple virtual objects by using a single physical prop. This task will be achieved by providing the haptic feedback in a VR environment by warping up the virtual space by matching the location of a prop in someone’s surroundings. The warping has been achieved by using three methods: body, word and hybrid warping, which allows passive haptics in a VR that is different from the physical one. These three techniques of warping enable a better sense of presence in VR.

In ^[17], the challenges in the VR video streaming technologies for the TI are discussed. To achieve the real-timeliness and high quality, the network must have an ultra-low latency rate that can be possible by TI. However, it is still a challenging task in VR to achieve ultra-high-speed video streaming. For this purpose, the authors suggest that some areas of the TI must be addressed by the researchers properly, i.e., transport and application protocols, edge infrastructure, and VR and haptic devices must be synchronized.

The control strategies for the haptic interface in VR are proposed in ^[35]. The force and position control strategies have been used to improve the haptic interface in VR. Furthermore, the three-stage energy compensation controller was used to avoid the instability caused by the energy leakage. This technique efficiently controls the haptic rendering destabilization, but loses control sometimes in the position control mode and may increase the instability threshold. Therefore, the energy compensation controller along with fuzzy impedance controller gives better position control and improves stability in the haptic interface.

7. Advantages and Challenges of Communication Technologies

Sixth-generation (6G) networks are the next generation of wireless communication networks, and they are expected to offer significantly higher speeds, capacity, and performance than previous generations of networks. While 6G is still in the development stage and its exact features and capabilities have not yet been fully determined, it is expected to incorporate a variety of different communication technologies, including aerial, ground, and underwater communications.

Aerial communication refers to the transmission of information through the air, typically using wireless technologies such as radio waves or microwaves. In the context of 6G networks, aerial communication is likely to continue to play a significant role in providing coverage and capacity for a wide range of applications, including mobile communication, IoT, and machine-to-machine (M2M) communication ^[36]^[37].

Ground communication refers to the transmission of information through cables or wires that are physically connected on the ground. In the context of 6G networks, ground communication is likely to continue to play a role in providing high-bandwidth, high-capacity communication for applications that require low latency and high reliability, such as industrial control and automation ^[38]^[39].

Underwater communication refers to the transmission of information under water, typically using sound waves or light waves. In the context of 6G networks, underwater communication is likely to play a role in providing communication for a variety of underwater applications, such as offshore oil and gas exploration, military operations, and ocean monitoring ^[40]^[41].

7.1. Advantages of Aerial Communication in 6G

Wide coverage: aerial communication technologies can cover large geographical areas, making them useful for long-distance communication and for providing coverage in remote or hard-to-reach areas ^[42].
High speed: aerial communication technologies are expected to offer significantly higher speeds in 6G networks, making them suitable for applications that require fast communication ^[43].
Flexibility: aerial communication technologies can be easily deployed and relocated, making them suitable for use in dynamic environments ^[44].
High capacity: aerial communication technologies are expected to offer significantly higher capacity in 6G networks, which can support the transmission of large amounts of data ^[45].

7.2. Challenges of Aerial Communication in 6G

Interference: aerial communication technologies are vulnerable to interference from other sources, such as other wireless devices or physical obstacles ^[46].
Limited bandwidth: the available bandwidth for aerial communication is limited, which can affect the quality and capacity of the communication ^[47].
Weather: aerial communication technologies can be affected by weather conditions, such as rain, fog, and thunderstorms, which can reduce the quality and reliability of the communication ^[48].
Security: aerial communication technologies are generally less secure than ground-based technologies, as they are easier to intercept or disrupt ^[49].
Energy efficiency: aerial communication technologies can be energy-intensive, which can be a challenge for applications that require long-term or continuous operation ^[50].

7.3. Advantages of Ground Communication in 6G

Reliability: ground communication technologies are generally more reliable than aerial communication technologies, as they are less vulnerable to interference and weather conditions ^[51].
Security: ground communication technologies are generally more secure than aerial communication technologies, as they are harder to intercept or disrupt ^[52].
High bandwidth: ground communication technologies are expected to offer significantly higher bandwidth in 6G networks, which can support high-quality and high-capacity communication ^[53].
Low latency: ground communication technologies can offer low latency, which is important for applications that require real-time communication ^[54].

7.4. Challenges of Ground Communication in 6G

Limited coverage: ground communication technologies are limited to the physical location of the cables or wires, which can make it difficult to provide coverage in remote or hard-to-reach areas ^[55].
Inflexibility: ground communication technologies are generally less flexible than aerial communication technologies, as they require the physical installation and maintenance of cables or wires ^[55].
Cost: the installation and maintenance of ground communication technologies can be costly, especially in large or complex networks ^[55].
Vulnerability to physical damage: ground communication technologies are vulnerable to physical damage, such as cuts or breaks in the cables or wires, which can disrupt the communication ^[55].
Limited mobility: ground communication technologies are generally less mobile than aerial communication technologies, as they are tethered to the ground ^[55].

7.5. Advantages of Underwater Communication in 6G

Security: underwater communication technologies are generally more secure than aerial or ground communication technologies, as they are harder to intercept or disrupt ^[56].
Low interference: underwater communication technologies are less vulnerable to interference from other sources, as there are fewer sources of interference ^[56].
Long range: underwater communication technologies can support long-range communication, as sound waves can travel long distances through water ^[56].
High data rates: underwater communication technologies are expected to offer significantly higher data rates in 6G networks, which can support the transmission of large amounts of data in real-time ^[56].

7.6. Challenges of Underwater Communication in 6G

Limited coverage: underwater communication technologies are limited to the physical location of the water, which can make it difficult to provide coverage in areas that are not near bodies of water ^[57].
Complexity: underwater communication technologies can be complex to design and implement, as they need to account for the unique properties of water and the underwater environment ^[57].
Cost: underwater communication technologies can be costly to develop and maintain, due to the specialized equipment and expertise required ^[57].
Environmental factors: underwater communication technologies can be affected by environmental factors such as temperature, pressure, and salinity, which can affect the quality and reliability of the communication ^[57].
Limited bandwidth: the available bandwidth for underwater communication is generally limited, which can affect the capacity and quality of the communication ^[57].
Latency: underwater communication technologies can have high latency due to the slow speed of sound in water, which can be a challenge for applications that require real-time communication ^[57].

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