6G, the next generation of mobile cellular technology, is set to revolutionize the way we connect, communicate, and interact with our devices and the world around us. With promises of ultra-high-speeds, low latency, and unprecedented capabilities, 6G holds the key to unlocking a new era of connectivity. In this article, we delve into the vision, requirements, challenges, and technology roadmap that define the path to 6G.
Mobile Communication Evolution
Mobile communications have been undergoing a generational change every ten years or so. However, the time difference between the so-called “G’s” is also decreasing. While fifth-generation (5G) systems are becoming a commercial reality, there is already significant interest in systems beyond 5G, which we refer to as the sixth-generation (6G) of wireless systems.
Each generation of mobile technology, from the first to the fifth (5G), has been designed to meet the needs of end users and network operators. Each generation also introduces new services with more stringent requirements, that the current generations cannot meet.
As the world moves towards a more connected future, the demand for faster and more reliable wireless communication has become more urgent. With 5G technology barely settling in, the race to develop 6G technology is already underway. 6G technology is poised to offer even faster speeds, lower latency, and more bandwidth than its predecessor. This ebook will explore the concept of 6G technology, its potential applications, and the challenges that come with its development.
Future network technologies (5G, 6G, etc.) are expected to enable fundamentally new applications that will transform the way humanity lives, works, and engages with its environment. Many rich multimedia applications in the form of high-fidelity holograms and immersive reality, tactile/haptic-based communications, and the support of mission-critical applications for connecting all things are being discussed.
Drivers for 6G Systems: Lifestyle and Societal Changes
According to the ITU-T, the three most important driving characteristics linked to the next decade of lifestyle and societal changes, impacting the design and outlook of 6G networks, are: 1) High-Fidelity Holographic Society; 2) Connectivity for All Things; and 3) Time Sensitive/Time
The future Networks will have new use cases which requires massive connectivity, reliability, real-time and throughput requirements, which are huge challenges to current communication networks.
To support such applications, even larger system bandwidths than those seen in 5G are required along with new physical layer (PHY) techniques, as well as higher layer capabilities that are not present today.
- Extended reality and Holographic Telepresence
Video is increasingly becoming the mode of choice for communications today and is evolving to augmented reality (AR). As such, video resolution capability is increasing at a rapid rate. For instance, user equipment (UE) devices supporting 4k video require a data rate of 15.4 Mb/s (per-UE). In addition, a UE’s viewing time is also increasing to the point where it is now the norm for end-users to watch complete television programs, live sports events, or on-demand streaming.
Future networks will provide new services Extended reality and Holographic Telepresence that will provide ultimate multimedia experience. Extended Reality (XR) is an all-encompassing term that includes augmented reality (AR), virtual reality (VR), and mixed reality (MR) technologies that provide truly immersive experience.
Holograms and multisense communications are the next frontiers in this virtual mode of communication. When it is deployed, holographic presence will enable remote users as a rendered local presence. Hologram is a next-generation media technology that can present gestures and facial expressions by means of a holographic display.
It has attracted great attention and opened new horizons in various fields including entertainment, medicine, science, education, and manufacturing industries. For instance, technicians performing remote troubleshooting and repairs, doctors performing remote surgeries, and improved remote education in classrooms could benefit from hologram renderings.
Mobile devices will take various form factors, such as augmented reality (AR) glasses, virtual reality (VR) headsets, and hologram devices. Users will be even able to go beyond observation, and actually interact with the digital twins, using VR devices or holographic displays. A digital twin is a replicate of physical entities, including people, devices, objects, systems, and even places, in a virtual world.
The proliferation of AR/VR and holographic applications will require a system capacity above 1 Tbps. The content to display can be obtained by means of real-time capture, transmission, and 3D rendering techniques. The data transmission rates for holograms are very substantial. Besides the standard video properties, such as color, depth, resolution, and frame rate, holographic images will need transmission from multiple viewpoints to account for variations in tilts, angles, and observer positions relative to the hologram. For example, Datarate requirements of a 3D holographic display: a raw hologram, without any compression, with colors, full parallax, and 30 fps, would require 4.32 Tbps.
- Smart healthcare
Nextgen NWs will revolutionize the health-care sector, through reliable remote monitoring system and even remote surgery.
Remote surgery and real-time tactile feedback are two important technological advancements that have the potential to revolutionize the field of surgery. Remote surgery involves the use of robotics and telecommunication technologies to perform surgical procedures from a remote location. Real-time tactile feedback refers to the provision of sensory feedback to the surgeon in real-time during a surgery, enabling them to perceive the surgical site more accurately and respond more effectively.
While remote surgery has been successfully performed in several instances, the lack of tactile feedback has been a major limitation of this approach. Real-time tactile feedback is essential for the surgeon to accurately judge the amount of force applied, the texture of tissues, and the progress of the procedure. Providing this feedback requires deeper perception, more real-time feedback, and response, which can be achieved through the use of advanced sensors and haptic feedback systems.
Remote surgery and Real-time tactile feedback which requires deeper perception, more real-time feedback and response. Therefore, the eHealth services will require to meet their stringent Quality of Service (QoS) requirements, i.e., continuous connection availability (99.99999% reliability), ultralow latency (sub-ms), and mobility support.
- Industry 4.0
Next-generation Networks will fully realize the Industry 4.0 revolution started with 5G, i.e., the digital transformation of manufacturing through cyber physical systems and IoT services. Industrial control requires real-time operations with guaranteed µs delay jitter, and Gbps peak data rates for AR/VR industrial applications (e.g., for training, inspection). Advanced robotics scenarios in manufacturing need a maximum latency target in a communication link of 100 μs and round-trip reaction times of 1 ms.
Ultrareliable transmissions are assumed to have a success rate of “five nines,” i.e., 99.999%. Industrial IoT systems could require even higher reliability, such as 99.99999%, since the loss of information could be catastrophic in some cases.
- Autonomous driving
Enabled by vehicle-to-vehicle (V2V) or vehicle-to-infrastructure (V2I) communication and coordination, autonomous driving can result in a large reduction of road accidents and traffic jams. However, latency in the order of a few ms will likely be needed for collision avoidance and remote driving. Thus, advanced driver assistance, platooning of vehicles, and fully automated driving are the key application areas that 6G aims to support, and mature, with the first components to be implemented in the Third Generation Partnership Project (3GPP)
- Connected autonomous unmanned systems
The evolution towards fully autonomous transportation systems offers safer traveling, improved traffic management, and support for infotainment. Future networks will help in the deployment of connected autonomous unmanned systems such as UAVs. UAVs help in many fields such as commerce, science, agriculture, recreation, law and order, product delivery, surveillance, aerial photography, and disaster management. Moreover, the UAV will be used to support wireless broadcast and high rate transmissions when the cellular base station (BS) is absent or not working. It will promote the real deployment of self-driving cars (autonomous cars or driverless cars).
Connecting autonomous vehicles demands unprecedented levels of reliability and low latency (i.e., above 99.99999% and below 1 ms, respectively), even in ultra-high mobility scenarios (up to 1000 km/h), to guarantee passenger safety.
Next generation networks vision: Redefining Connectivity, Ubiquitous, Intelligent, and Green
The goal of future generation networks is to meet the future communication needs of the information societies such as Smart infrastructures, Smart City, Smart Grid, Smart Health, and Smart Transportation. The future will be a completely data-driven society in which people and things are connected universally, almost instantaneously (milliseconds) to form an incredibly fully connected utopian world. It will also be key enabling technology to fully realize the Industry 4.0 revolution i.e., the digital transformation of manufacturing through cyber physical systems and IoT services
Beyond speed: Understanding the broader vision of 6G, which goes beyond mere speed improvements and encompasses transformative use cases like augmented reality, autonomous systems, and the Internet of Things (IoT).
Ubiquitous connectivity: Exploring the vision of ubiquitous connectivity, where 6G aims to provide seamless connectivity even in remote areas, underwater, and in space.
The future Network is required to be ubiquitous, providing connectivity to everyone and everything, everywhere, every time. It will Omnipresent allow hundreds of billions of machines in space-air-ground-sea domain to create, share, and process data seamlessly. It will provide three-dimensional coverage and connection to all types of terrain and space, including unmanned systems deployed in the deep indoors, deep sea or deep space, human/unmanned aerial vehicles in the middle and high altitude, and autonomous robots in the harsh environment. The media interaction will evolve towards high fidelity AR/VR interaction, and holographic information interaction, and wireless holographic communication so that people can enjoy fully immersed holographic interactive experience at any time and place.
The future Network will be completely automated and intelligent network that provides everything as a service and a completely immersive experience. The advances in AI will drive large applications in wireless communications improving the performance and reduce capital expenditure (CAPEX) and operational expenditure (OPEX). Further all the connected machines are becoming smart through embedded AI. Examples of connected machines include autonomous space-air-ground-sea platforms and systems, smart home appliances, smart sensors installed in various infrastructures, construction machineries, and factory equipment.
The Network will evolve from “connected things” to “connected intelligence” providing Intelligent connectivity services from the core to the end devices of the network. “Intelligent Connectivity” will meet two requirements at the same time: on the one hand, all the related connected devices in the network itself are intelligent, and the related services have been intelligent; on the other hand, the complex and huge network itself needs intelligent management.
Future networks will have high-density deployment of base stations and the ultra-high throughput, ultra-large bandwidth and ultra-large number of ubiquitous wireless nodes, which will bring unprecedented challenges to energy consumption. The future network generations will need to transition to Green Communication Systems and Networks to solve the challenging issues related to energy efficiency in communication systems and networks. Energy-efficient techniques will comprise of energy-efficient node design and operations (component level), efficient node-to-node interaction, and efficient node data management (system level).
Future Network Requirements: Demanding the Impossible
Skyrocketing data rates: Analyzing the need for mind-boggling data rates in 6G to support bandwidth-hungry applications and services.
Ultra-low latency: Exploring the significance of ultra-low latency in enabling real-time interactions for applications like remote surgery, autonomous vehicles, and tactile internet.
Massive device connectivity: Discussing the requirement for 6G to accommodate the massive number of devices expected to be connected, leading to the concept of “Internet of Everything.”
The transfer from one generation to another improves the QoS metrics, includes new services, and provides new features. The key drivers of future networks are high bit rate, high reliability, low latency, high energy efficiency, high spectral efficiency, new spectrums, green communication, intelligent networks, network availability, and convergence of communications, localization, computing, control, and sensing. It will support high Volume spectral efficiency to support space-air-ground-sea domain systems.
Future Ubiquitous always-on broadband global network coverage requires integration of terrestrial wireless with satellite systems. The explosive growth in the number of connected machines will require future generation network to support more than 107 devices per square kilometer. The most important requirement is the capability of handling massive volumes of data and very high-data-rate connectivity per device. Intelligent applications (Big-Data based) require massive data transmission.
The peak rate, which is one of the key technical indicators is expected to reach tens of terabits per second. AR/VR anytime and anywhere means that we want to meet the high-speed demand at anytime and anywhere, which requires not only super-high peak rate, but also super-high coverage performance. Furthermore, in order to achieve high fidelity immersive AR/VR, not only the peak rate of Tb/s, but also the lower interaction delay, i.e., both high throughput and low delay, are required.
It will provide instant holographic connectivity anytime and anywhere. The latency requirement will hit the sub-ms, and thousands of synchronized view angles will be necessary, as opposed to the few required for VR/AR. For support of latency-sensitive services requiring extreme reliability, e.g., industrial automation, emergency response, and remote surgery, we intend to improve reliability by 100 times compared to 5G so that the error rate is 10−7. It will provide Connected intelligence with machine learning capability. Next generation networks will require very high energy efficiency at least 100x with respect to 5G, to enable scalable, low-cost deployments, with low environmental impact, and better coverage, and the ability to support battery-free IoT devices.
Challenges: Overcoming the Hurdles
Spectrum crunch: Investigating the challenges posed by the scarcity of available spectrum and exploring potential solutions like utilizing higher frequency bands and advanced spectrum sharing techniques.
Energy efficiency: Highlighting the need for energy-efficient 6G networks to address the growing concerns of sustainability and environmental impact.
Security and privacy: Examining the heightened security and privacy requirements in 6G, considering the increasing number of connected devices and potential vulnerabilities.
For deep understanding of 6G technology and applications please visit: 6G Technology: Next Generational Leap of Wireless Communication
Technology Roadmap: Building the Future
Emerging technologies: Exploring the cutting-edge technologies expected to drive 6G, such as terahertz communications, advanced antenna systems, and AI-enabled networks.
Standardization and collaboration: Discussing the importance of global collaboration and standardization efforts in shaping the development and deployment of 6G.
Timeline and milestones: Outlining the anticipated timeline for 6G development, including key milestones and the expected rollout of commercial networks.
Future networks will face many challenges: more complex and huge networks, more types of terminals and network devices, and more complex and diverse business types. In order to meet these demands, radically new communication technologies, network architectures, and deployment models will be needed. Meanwhile, AI will play a critical role in designing and optimizing 6G architectures, protocols, and operations. All the network instrumentation, management, physical layer signal processing, resource management, service-based communications, and so on will be incorporated by using AI.
This network will be an organic whole, that is, it needs a unified standard protocol architecture and technical system to truly realize the ubiquitous connectivity of space-air-ground-sea integration. “Intelligent Connectivity” will demand of intellectualization of communication systems: intellectualization of network elements and network architecture, intellectualization of connecting objects (intellectualization of terminal devices), and information support of intellectualized services.
Several breakthroughs need to be made in key areas, including new signal sampling mechanism, new channel coding and modulation mechanism, terahertz communication theory and technology, AI-based wireless communication theory and technology. Green communications and networking will comprise of sustainable, energy-efficient, energy-aware, and environmentally aware communications and networking
- Novel disruptive and energy-efficient communication technologies
Spectrum is the basis and scarce resource of mobile communication. 5G systems are characterized to a significant degree by the use of the mmWave spectrum complemented by large antenna arrays. To reach Terabytes per second data rates, it is inevitable to operate at higher and higher frequency bands through Terahertz and optical communication. However, we note that not all 6G services will be suitable to be offered in the new bands. The existing bands for 4G and 5G will continue and maybe reframed for 6G. In this spirit, the spectrum from 100 GHz to 1 THz is being considered as a candidate for 6G systems.
- Energy-efficient Terahertz (THz)-Communications.
Terahertz (THz)-band communications are celebrated as a key enabling technology for next-generation wireless systems that promises to leverage the large available bandwidths at the THz band to achieve a terabit/second data rate. The frequency range from 140 to 350 GHz is typically referred to as the sub-THz band even though, strictly speaking, “high mmWaves” might be the
more appropriate nomenclature. The two key advantages of this band are: 1) the existence of many tens of GHz of bandwidth that is currently lying unused and 2) the ability to develop ultramassive multiple-input multiple-output (MIMO) antenna arrays within a reasonable form factor.
Many challenges need to be addressed prior to the widespread introduction of THz communications. For instance, the THz band’s high propagation losses and power limitations result in very short communication distances.
Supporting devices will transfer large amounts of data in both directions, causing high energy consumption by the electronic circuitries of the equipment in use. Therefore, physical layer for these systems must be designed carefully in order to reduce energy consumption per bit. Researchers have shown that for short-range communications, M-ary quadrature amplitude modulation is the most energy-efficient technique that can lead up to 90% reduction in consumed energy.
Recently, major advancements in transceiver design are closing the so-called THz gap. Nowadays semiconductor technologies based on InP, GaAs, SiGe, and even CMOS are capable of generating power in the mW range with acceptable efficiency at low THz band. This paves the way for several applications at the THz band, ranging from indoor wireless communications, to vehicular and drone-to-drone communications, device-to-device (D2D) communications, and nano-communications.
Other Thz challenges are 1) transporting the signal within the integrated system and to the antenna with low loss; 2) packaging of the integrated system without significant loss, and maintaining proper heat dissipation; 3) lowering the mixer phase-noise; 4) low power multi-Giga-samples-per-second analog-to-digital converters (ADCs) and digital-to-analog convertors (DACs); and lastly 5) low power digital input/output (IO) to DACs and ADCs to transfer data at Tbps data rate with acceptable power consumption.
- Ultra-Massive MIMO Systems (UM-MIMO) and Holographic MIMO Surfaces
Ultra-Massive MIMO (UM-MIMO) and Holographic MIMO Surfaces are two emerging technologies in wireless communication that promise to revolutionize the way we communicate wirelessly.
UM-MIMO is a technique that employs a very large number of antennas at the base station to serve multiple users simultaneously. The use of a large number of antennas enables the base station to create a very large number of virtual channels, which can be used to serve multiple users with high data rates. UM-MIMO has the potential to significantly increase the capacity and spectral efficiency of wireless communication systems.
THz allows a massive number of antennas to be embedded at in a few square millimeters. Very dense ultra-massive multiple-input multiple-output (UM-MIMO) antenna systems can provide the required beamforming gains necessary to overcome the distance problem. It will enhance energy efficiency as it is known to reduce the radiated power by a factor proportional to the square root of the number of deployed antennas, while keeping the information rate unaltered. The exact performance of THz UM-MIMO systems, however, is dictated by the exact channel conditions and the corresponding accuracy in channel state information. Similarly, efficient beamforming schemes are required, so as to overcome the high path loss and account for the distance dependent and frequency-dependent THz channel characteristics. In order to design efficient THz communication systems in practice, accurate yet tractable THz multipath channel models need to be developed for both indoor and outdoor environments.
Holographic MIMO Surfaces (HMS) is another emerging technology that utilizes a large number of passive reflecting elements to enable wireless communication. Unlike UM-MIMO, HMS does not require active antennas at the base station. Instead, it employs a large number of small passive reflecting elements that are arranged in a specific pattern to focus the electromagnetic waves in a specific direction. This enables the creation of a virtual MIMO array that can be used to serve multiple users simultaneously.
The key advantage of HMS is that it can provide a more energy-efficient and cost-effective solution compared to UM-MIMO. Since the reflecting elements do not require any power supply, the overall power consumption of the system is significantly reduced. Additionally, the use of passive reflecting elements makes HMS more robust against interference and multi-path fading.
Holographic MIMO Surfaces (HMIMOS) aim at going beyond massive MIMO, being based on low cost, size, weight, and low power consumption hardware architectures that provide a transformative means of the wireless environment into a programmable smart entity. HMIMOS refers to a low-cost transformative wireless planar structure comprising of subwavelength metallic or dielectric scattering particles, which is capable of impacting electromagnetic waves according to desired objectives. Following the recent breakthrough on the fabrication of programmable metamaterials, reconfigurable intelligent surfaces have the potential to materialize seamless connections and intelligent software-based control of the environment in wireless communication systems when coated on the otherwise passive surfaces of various objects
- Visible Light Communications
The move to even higher frequency bands are free-space optical (including infrared) links, either through the use of laser diodes or light-emitting diodes (LEDs) commonly assumed for visible light communications (VLCs). Both of these approaches have been explored for a number
of years, but it is only recently that integration into cellular and other wireless systems seems to increasingly become a realistic option.
OWC technologies, such as light fidelity, visible light communication, optical camera communication, and FSO communication used more widely to meet the demands. Communication based on optical wireless technologies can provide very high data rates, low latencies, and secure communications. Visible light communications have been proposed to complement RF communications by piggybacking on the wide adoption of cheap Light Emitting Diode (LED) luminaries.
The Li-Fi is a wireless communication system in which light is used as a carrier signal instead of traditional radio frequency as in Wi-Fi. Li-Fi is a technology that utilizes a Light Emitting Diode (LED) to transmit data wirelessly. In the future LiFi would make possible the extensive deployment of visible light communication for a wide range of short and medium-range communication applications including wireless, local, personal, and body area networks (WLAN, WPAN, and WBANs), vehicular networks, underwater networks and machine-to-machine (M2M) communication among others. This is also energy efficient way as LED lights require so little energy, they can be powered by a standard ethernet cord or solar cells charging batteries.
- Full-duplex communication
Advances in signal-processing electronics now support full-duplex network communications on the same frequency. With full-duplex communications, the transceivers will be capable of receiving a signal while also transmitting, because of carefully designed self-interference-suppression circuits. Full-duplex passive suppression and digital cancellation (PSDC) communication mode is more energy-efficient than the plain passive suppression full-duplex mode. Experimental results show that, the full-duplex DSDC mode achieves up to 40 percent increased energy efficiency compared to half-duplex.
- Novel channel estimation techniques (e.g., out of band estimation and compressed sensing).
Channel estimation for directional communications will be a key component of communications at mmWaves and Terahertz frequencies. However, it is difficult to design efficient procedures for directional communications, considering multiple frequency bands and possibly a very large bandwidth. Therefore, 6G systems will need new channel estimation techniques. For example, out-of-band estimation (e.g., for the angular direction of arrival of the signal) can improve the reactiveness of beam management, by mapping the omnidirectional propagation of sub-6 GHz signals to the channel estimation for mmWave frequencies. Similarly, given the sparsity in terms of angular directions of mmWave and Terahertz channels, it is possible to exploit compressive sensing to estimate the channel using a reduced number of samples.
- Sensing and network-based localization.
Extremely wideband waveforms in the THz band would enable accurate ranging between transmitter and receiver with sub-centimeter-scale accuracy. This will greatly improve the accuracy of distance-based positioning systems. The use of pencil-point sharp beams steered in both azimuth and elevation will greatly improve angular resolution and triangulation accuracy of 3D position estimation. Future networks will exploit a unified interface for localization and communications to (i) improve control operations, which can rely on context information to shape beamforming patterns, reduce interference, and predict handovers; and (ii) offer innovative user services, e.g., for vehicular and eHealth applications.
- Innovative network architectures
The heterogeneity of future network applications and the need for 3D coverage calls for new cell-less architectural paradigms, based on the tight integration of different communication technologies, for both access and backhaul, and on the disaggregation and virtualization of the Networking equipment.
- Tight integration of multiple frequencies and communication technologies and cell-less architecture.
Multiple 6G devices will support a number of heterogeneous radios in the devices. This enables multi connectivity techniques that can extend the current boundaries of cells, with users connected to the network as a whole (i.e., through multiple complementary technologies) and not to a single cell. The cell-less network procedures will guarantee a seamless mobility support, without overhead due to handovers (which might be frequent when considering systems at Terahertz frequencies),and will provide QoS guarantees that are in line with the most challenging mobility requirements.
- 3D network architecture.
Future 6G heterogeneous architectures to provide three-dimensional (3D) coverage, thereby complementing terrestrial infrastructures with non-terrestrial platforms (e.g., drones, balloons, and satellites). The 3D Base Stations will be provided through low orbit satellites and UAVs to provide cellular connectivity. Despite such promising opportunities, there are various challenges to be solved before flying platforms can effectively be used in wireless networks, e.g., air-to-ground channel modeling, topology and trajectory optimization, resource management and energy efficiency.
- Advanced access-backhaul integration.
The massive data rates of the new access technologies will require an adequate growth of the backhaul capacity. Moreover, Terahertz and VLC deployments will increase the density of access points, which need backhaul connectivity to their neighbors and the core network. The huge capacity of terrahetz and VLC technologies can thus be exploited for selfback hauling solutions, where the radios in the base stations provide both access and backhaul.
Using FSO, it is possible to have very long range communications even at a distance of more than 10,000 km. FSO supports high-capacity backhaul connectivity for remote and non-remote areas, such as the sea, outer space, underwater, isolated islands; FSO also supports cellular BS connectivity.
- Disaggregation and virtualization of the networking equipment
6G networks will bring disaggregation to the extreme by virtualizing Medium Access Control (MAC) and Physical (PHY) layer components which currently require dedicated hardware implementations and realizing low-cost distributed platforms with just the antennas and minimal processing. This will decrease the cost of networking equipment, making a massively dense deployment economically feasible.
- Energy-harvesting strategies for low power consumption network operations.
Incorporating energy harvesting mechanisms into 5G infrastructures currently faces several issues, including coexistence with the communications, and efficiency loss when converting harvested signals to electric current. Given the scale expected in 6G networks, it is necessary to design systems where both the circuitry and the communication stack are developed with energy-awareness in mind. One option is using energy harvesting circuits to allow devices to be self powered, which could be critical for example to enable off-grid operations, long-lasting IoT devices and sensors, or long stand-by intervals for devices and equipment which are rarely used.
- Green Hardware: Energy-efficient storage, cloud computing, edge computing and data centers
Future wireless communication systems are expected to realize an intelligent and software reconfigurable paradigm, where all parts of device hardware will adapt to the changes of the wireless environment. The hardware for wireless communications systems needs to be designed explicitly accounting for its energy consumption, and to adopt major architectural changes, such as the cloud-based implementation of the radio access network.
- Green Data Centers
Due to the large number of networked computers and storage devices in data centers, novel communication technologies are required to facilitate accessing and processing of data. In data centers, servers are typically arranged in multiple racks, and wired connections are often sought for convenience. Wiring a massive number of servers, however, increases the size of data centers and reduces system efficiency. To the contrary, wireless links can reduce system costs and yield more energy efficient data centers by eliminating the need for power-hungry switches. Such links should be complemented by efficient networking solutions and scheduling mechanisms, that allocate channels to servers based on the traffic demand.
- Green and Intelligent Radio
The high data rates make THz communications a strong candidate for wireless data centers. Furthermore, the reconfigurability of THz antenna arrays can be leveraged to support multiple inter-rack and intra-rack communication links. THz UM-MIMO transceivers with high power, low noise figures, and good sensitivity can thus be optimized in such static environments.
- Integrating Intelligence in the Network
The complexity of 6G communication technologies and network deployments will require intelligent techniques in cellular networks. 6G deployments to be much denser (i.e., in terms of number of access points and users), more heterogeneous (in terms of integration of different technologies and application characteristics), and with stricter performance requirements with respect to 5G. Therefore, intelligence will play a more prominent role in the network.
AI will need to be embedded in all system components in 6G networks which allows all system components to obtain and evaluate a massive amount of real-time information. In this way, system can handle complex optimization tasks across layers to optimize the system parameters and overall system performance.
AI can Improve performance of handover operation taking into account network deployments and geographical environments; optimize network planning involving base station (BS) location determination; Reduce network energy consumption; Predict, detect, and enable self-healing of network anomalies.
- Learning techniques for data selection and feature extraction.
The large volume of data generated by future connected devices (e.g., sensors in autonomous vehicles) will put a strain on communication technologies, which could not guarantee the required quality of service. It is therefore fundamental to discriminate the value of information to maximize the utility for the end users with (limited) network resources. In this context, machine learning (ML) strategies can evaluate the degree of correlation in observations, or extract features from input vectors and predict the a-posteriori probability of a sequence given its entire history.
- Inter-user inter-operator knowledge sharing.
Spectrum and infrastructure sharing is beneficial in cellular networks, to maximize the multiplexing capabilities. With learning-driven networks, operators and users can also share learned/processed representations of specific network deployments and/or use cases, for example to speed up the network configuration in new markets, or to better adapt to new unexpected operational scenarios. The tradeoffs in latency, power consumption, system overhead, and cost will be studied in 6G, for both on-board and edge cloud-assisted solutions.
- User-centric network architecture.
Future networks will be ML-driven networks which envision distributed artificial intelligence, to implement a fully-user-centric network architecture. Distributed methods can process ML algorithms in real time, i.e., with a sub-ms latency, thereby yielding more responsive network management. In this way, end terminals will be able to make autonomous network decisions based on the outcomes of previous operations, without communication overhead to and from centralized controllers. Unsupervised learning and knowledge sharing will promote real-time network decisions through prediction.
There is need to identify major research and development challenges in the development of energy-sustainable, and environment-friendly future green networking technologies. Some of the research areas are
- Modeling of THz frequencies
The propagation characteristics of the mmWave and sub-mmWave (THz) is subject to atmospheric conditions; therefore, absorptive and dispersive effects are seen. The atmospheric condition is frequently changeable and thus quite unpredictable. In order to design efficient THz communication systems in practice, accurate yet tractable THz multipath channel models need to be developed for both indoor and outdoor environments. Therefore, the channel modeling of this band is relatively complex, and this band does not have any perfect channel model.
- Energy efficient Terahertz communications technology
Given that research on THz communications is still in its infancy because no THz network has yet been built, let alone a multi-functional network. In order to support THz communication, the following aspects need further research: (1) Transistor and hardware materials with excellent high frequency characteristics. The most potential material employed for hardware design is graphene which has high thermal and electrical conductivities and plasmonic effects. (2) Robust beam forming and scanning algorithms such as hybrid beamforming approaches. (3) Low-complexity, low-power hardware circuits. (5) Energy efficient modulation schemes and low-density channel codes. (6) Ultra-massive MIMO system. Nano antennas will play an important role in MIMO systems. (7) Powerful synchronization schemes.
- Energy efficient THz hardware
We require a new design for the transceiver architecture for the THz communication systems. The transceiver must be able to operate at high frequencies, and we need to ensure the full use of very widely available bandwidths. A very small gain and an effective area of the distinct THz band antennas is another challenge of THz communication. Health and safety concerns related to THz band communications also need to be addressed.
Other Thz challenges are 1) transporting the signal within the integrated system and to the antenna with low loss; 2) packaging of the integrated system without significant loss, and maintaining proper heat dissipation; 3) lowering the mixer phase-noise; 4) low power multi-Giga-samples-per-second analog-to-digital converters (ADCs) and digital-to-analog convertors (DACs); 5) low power digital input/output (IO) to DACs and ADCs to transfer data at Tbps data rate with acceptable power consumption and Low cost, energy-efficient antenna and RF designs
- Energy Efficient waveforms, channel coding, and protocols
Compared with the current 5G system, the next generation channel coding mechanism research needs to meet the new and more complex heterogeneous wireless communication needs scenarios and business needs in the future. Several typical scenarios need to be considered: ultra-high throughput (Tb/s level), ultra-wide bandwidth channel, ultra-high frequency channel, visible light channel, high altitude/space channel, ocean/deep sea channel, deep earth channel and other complex propagation environments and more heterogeneous and diverse business types
Supporting devices will transfer large amounts of data in both directions, causing high energy consumption by the electronic circuitries of the equipment in use. Therefore, physical layer for these systems must be designed carefully in order to reduce energy consumption per bit.
Efficient operation of a wireless system is highly dependent on the design of a proper waveform. While OFDM remains a strong candidate waveform for THz systems, it is necessary to explore alternative waveforms to support GHz-wide channels, reduce PAPR, and withstand the THz hardware limitations. Moreover, it is necessary to develop proper design of signals, channels, and protocols, which are effective yet of low complexity for THz operation.
- Complexity in resource management for 3D networking
The 3D networking extended in the vertical direction. Hence, a new dimension was added. Moreover, multiple adversaries may intercept legitimate information, which may significantly degrade the overall system performance. Therefore, new techniques for resource management and optimization for mobility support, routing protocol, and multiple access are essential. Scheduling needs a new network design.
- Spectrum and interference management
Due to the scarcity of the spectrum resources and interference issues, it is very important to efficiently manage the spectra employing the spectrum-sharing strategies and innovative spectrum management techniques. Efficient spectrum management is important for achieving the maximum resource utilization with QoS maximization. The researchers have to address concerns, such as how to share the spectrum, and how to manage the spectrum mechanism in the heterogeneous networks that synchronize the transmission at the same frequency. Researchers also need to investigate how the interference can be cancelled using the standard interference cancellation methods, such as parallel interference cancellation, and successive interference cancellation.
- Autonomous wireless systems
The system will provide full support to automation systems such as autonomous car, UAVs, and Industry 4.0 based on AI. To make autonomous wireless systems, we need to have the convergence of many heterogeneous sub-systems, such as autonomous computing, interoperable processes, system of systems, machine learning, autonomous cloud, machines of systems, and heterogeneous wireless systems
- Cross-layer design and optimization for green communications and computing:
The layered structure of the present IP suite with duplicate lower-layer functionality needs to be enhanced to guarantee deterministic throughput and low latency requirements. Therefore, a new cross-layer protocol design that merges the traditional network and transport layers and combines the functionalities of both layers can be considered. This combined layer may ensure better control over IP and transport layers by taking into account application requirements as well as the network state.
- Antenna, lens, and beamforming architecture
Moving up to THz range frequency means drastic increase in path-loss. Consequently, unprecedentedly massive antenna arrays are necessary to compensate for the path-loss. Designing such arrays that will operate with high efficiency at THz frequency poses many challenges to designing the feed network and the antenna elements to support GHz-wide bandwidth. Moreover, the use of ultra-massive arrays results in very focused beams, similar to laser beams. As a result, communication links at these frequencies will depend on LoS and focused-reflected paths, not on scattering and diffracting paths. It is of great importance to optimize the beamforming architecture to provide high dynamic-range and high flexibility at a reasonable cost and energy consumption.
- Energy Harvesting and Management
Energy harvesting technologies and the use of new materials will greatly improve the system energy efficiency and realize sustainable green networks.
The consistent computation demands for AI processing and increasing proliferation of IoT devices are posing significant challenges to the energy efficiency of communication equipment. Therefore, energy-efficient communication technologies will shine in future networks where communication distance is much shorter. There have been numerous efforts spent on energy harvesting and management researches over the past decade.
A technology called symbiotic radio (SR) offers a possible solution to the energy problem, which integrates passive backscatter devices with active transmission system. A typical example of SR is ambient backscatter communication, in which network devices utilize ambient RF signals to transmit information without requiring active RF transmission, making battery-free communication possible. Smart energy management is another promising mechanism with the goal of dynamically optimizing the balance between energy demand and supply
- Green wireline, optical, and wireless communications and networks
Green networking mainly deals with the design, development, and deployment of ecofriendly ICT infrastructure that help reduce greenhouse gas (GHG) emission by using energy efficient technologies to power the networking devices, designing energy efficient networks, deploying energy efficient devices (also called green devices), and deploying green routing and switching. Recent studies have identified that adaptive link rate, proxy and caching services, energy‐aware ICT infrastructure, and energy‐aware applications are the major dimensions of green networking by which energy saving can be achieved.
- Adaptive link rate: By adapting the link rate based on the current network conditions, energy consumption can be reduced. For example, in wireless communication systems, the use of adaptive modulation and coding schemes can help to adjust the transmission rate according to the channel conditions, thereby reducing energy consumption.
- Proxy and caching services: By caching frequently accessed content and providing it locally, the need to fetch content from the network can be reduced, which results in energy savings. For example, web caching techniques can be used to store frequently accessed web pages on a local server, which can reduce the number of requests made to the origin server and hence save energy.
- Energy-aware ICT infrastructure: By designing ICT infrastructure with energy efficiency in mind, energy consumption can be reduced. For example, the use of energy-efficient servers, switches, and routers can help to reduce the energy consumption of data centers.
- Energy-aware applications: By designing applications that are energy-efficient, energy consumption can be reduced. For example, video streaming applications can be designed to adapt the video quality based on the available network bandwidth, which can reduce the energy consumption of the device.
Energy-efficient and energy-aware heterogeneous networks, self-organized, and low-power sensor networks. Green network concepts and architectures
Green fixed access communications and networking, green optical communications and networking, green wireless access networks, green cellular base stations, green circuits, devices and terminals, software for green communications, computing, and relevant systems. hierarchical and distributed techniques for energy distribution and management, energy harvesting, novel network concepts and architectures lowering the overall footprint of ICT (such as compressed sensing, network coding and interference alignment, and so on), green ad hoc and sensor networks, green cognitive communications and computing, energy-efficient smart home networking, green smart grid communications, green cloud computing and data centers, electromagnetic pollution mitigation, advanced signal processing techniques for energy-efficient transmission systems, resource-efficient cross-layer optimization methods, and opportunistic spectrum sharing without causing harmful interference pollution.
As we look ahead to the future of mobile cellular technology, 6G represents a paradigm shift that promises to reshape our digital landscape. By understanding the vision, requirements, challenges, and technology roadmap of 6G, we can appreciate the immense possibilities and transformative impact that this next generation of connectivity will bring to our lives.
References and Resources
- Towards 6G Networks: Use Cases and Technologies, Marco Giordani, Member, IEEE, Michele Polese, Member, IEEE, Marco Mezzavilla, Senior Member, IEEE, Sundeep Rangan, Fellow, IEEE, Michele Zorzi, Fellow, IEEE
- Zhao Y J, Yu G H, Xu H Q. 6G Mobile Communication Network: Vision, Challenges and Key Technologies (in Chinese). Sci Sin Inform, ISSN 1674-7267, Pre-published, https://doi.org/10.1360/N112019-00033. (http://engine.scichina.com/doi/10.1360/N112019-00033 )
- Samsung 6G Vision https://cdn.codeground.org/nsr/downloads/researchareas/6G%20Vision.pdf
- Next Generation Terahertz Communications: A Rendezvous of Sensing, Imaging, and Localization Hadi Sarieddeen, Member, IEEE, Nasir Saeed, Senior Member, IEEE, Tareq Y. Al-Naffouri, Senior Member, IEEE and Mohamed-Slim Alouini, Fellow, IEEE https://arxiv.org/pdf/1909.10462.pdf
- A Survey on Green 6G Network: Architecture and Technologies TONGYI HUANG1, WU YANG2, JUN WU1, (Member, IEEE), JIN MA1, XIAOFEI ZHANG3, AND DAOYIN ZHANG3