By Huawei's METIS project team
Future mobile and wireless communication systems will have to be highly versatile and scalable to provide high capacity with greatly enhanced efficiency in power consumption, cost, and spectrum usage. The METIS project will develop a brand new 5G system concept and lay the foundation for future mobile and wireless communication systems.
Challenges after 2020
In recent years, mobile and wireless communication has been developing rapidly. It has gone way beyond traditional voice, messaging, and data services and expanded into many new sectors such as e-banking, e-learning, e-health, and on-demand video/audio services. The emergence of the Internet of Things (IoT) also signifies that in addition to human-centric communication, machine-centric communication will be an important part of future wireless systems and will greatly improve people's life quality, working efficiency, and security.
Mobile and wireless communication is evolving at such an unprecedented speed that many challenges will arise accordingly. It is estimated that by 2020, the mobile data traffic will be boosted by 1000 times. Moreover, due to massive machine communication (MMC), 50 billion devices will be connected. The coexistence of human-centric communication and machine-centric communication will demand more diverse services from the mobile communication system. Such service diversification requires the mobile system to be more powerful and versatile in a lot of aspects, including throughput, delay, link density, as shown the figure on the following page, as well as cost, complexity, power consumption, and Quality of Service (QoS).
To tackle the above challenges, Huawei and its 28 European partners initiated the Mobile and Wireless Communications Enablers for the Twenty-twenty Information Society (METIS) project. Launched in November 2012, the METIS project aims to develop a brand new 5G system concept and the related key technologies in three years to support future explosive mobile data increase with very high cost- and power efficiency as well as spectrum usage efficiency. Huawei is a core member of the METIS project and is responsible for leading the wireless air interface research and development. Wireless air interface is a core technology component of the METIS project and is crucial to the success of 5G.
The vision of METIS
METIS envisions a future world where all people can access and share information and connect to anything at anytime, anywhere. This "all-connected world" with no boundaries for information flow will greatly promote socio-economic development. Compared to the traditional mobile and wireless communication systems, 5G must consume less energy and capital while providing much higher capacity and resource utilization efficiency. Moreover, the 5G system should be versatile to support different requirements such as availability, mobility, and QoS, and new application scenarios such as MMC. The 5G system must also be highly scalable to support a wide range of requirements and large traffic dynamics.
Compared to the traditional network, the 5G system designed by METIS will support 1000 times the mobile data traffic volume per area and 10 to 100 times the connected devices and user data rate. It will provide 10 times longer battery life for low power MMC than current networks. Its end-to-end (E2E) latency will be one fifth that of LTE Release 8.
Key technologies for 5G
To construct the 5G system concept, METIS will look into four technology components: radio link concepts, multi-mode and multi-antenna transmission, multi-radio access technology (RAT) and multi-layer network, and spectrum usage techniques.
Radio link concepts
To meet new requirements of future mobile applications, METIS will design a new air interface. The most challenging part for the air interface is to support various application scenarios from low power consumption sensors that demand low data rates to multimedia services that demand high-speed data rates. Therefore, new technologies related to transmission waveform, coding, modulation, and transceiver structures must be developed to improve the spectral efficiency in the physical layer, reduce power consumption, and enhance anti-interference capability and robustness of the wireless network. In addition, multiple access, media control, and wireless resource management will also be re-designed to increase the system efficiency.
Huawei Europe Research Center (ERC) is actively leading the research on this new air interface design, focusing on the coexistence between broadband applications (such as multimedia services) and narrowband applications (such as sensors) in the same frequency band. To achieve the most efficient use of the available frequency bandwidth in this heterogeneous multi-service scenario, the new air interface will be able to adaptively adjust the waveform according to transmission environments and conditions. Furthermore, a waveform with ultra-low out-of-band emission is used, allowing the development of flexible spectrum usage concepts. Such concepts will allow mobile operators to share the spectrum dynamically and adaptively with other non-communication/communication systems or with each other.
Multi-node and multi-antenna transmission
Multi-node and multi-antenna transmission technology will greatly boost the performance and capacity of the future wireless communications system. METIS will address the performance limits, architectural impact and development of algorithms and key technologies. New application scenarios like ultra dense networking (UDN) and MMC will also be targeted.
First, massive multi-antenna configuration will be addressed, based on beamforming, space division multiple access, and spatial multiplexing. The goal is to provide higher data rates and spectral efficiency, or to increase link reliability, coverage rate, and to reduce power consumption. Second, advanced multi-node coordination technology will be developed to significantly increase spectral efficiency and user throughput, and to improve link quality in unfavorable radio conditions. The novel air interfaces and new multi-node coordination methods will be integrated into practical systems. Third, multi-hop communications and wireless network coding will be studied, which use one or multiple relay nodes between the information source and the information destination. Such technologies should provide efficient means for backhauling, to extend coverage and reliability, or to transfer the processing/energy burden from the MMC devices to the network.
Multiple RAT and multi-layer network
The research on multi-RAT and multi-layer network involves many aspects and is crucial to efficient network deployment, operation and optimization, especially the deployment of heterogeneous multi-layer and multi-RAT networks. The first focus is on network coexistence, collaboration, and interference management. Providing solutions for UDN is challenging since interference dependencies between communicating entities in a UDN are especially complex. Another challenge is the increased degrees of freedom for interference management due to direct device-to-device (D2D) communications and MMC.
The second focus is the management of demand, traffic, and mobility. Mobile operators need to predict and utilize the information about users and devices, including users' location and environment information. Such information can help optimize the selection of the RAT and the network layers. Furthermore, novel mobility management concept will be proposed, especially for UDN, to decrease signaling overhead.
The third focus is on the functional network enablers, including defining new management interfaces, automatic integration and management of multiple types of network nodes, and efficient integration of nomadic cells in heterogeneous networks.
Spectrum usage techniques
METIS will propose new concepts for spectrum sharing to ensure sufficient spectrum beyond 2020. First, frequency bands up to 275GHz will be analyzed to identify new spectrum resources and to understand their characteristics. Additionally, future mobile and wireless communications scenarios will be studied to predict spectrum requirements beyond 2020. Ultimately, novel flexible spectrum sharing and management techniques will be developed to realize UDN operation at high frequency bands and network-assisted D2D communication that supports high mobility.
METIS's horizontal topics
The METIS project has outlined a series of "Horizontal Topics (HT)" to construct the 5G system concept. Each HT will integrate a series of new technology components to provide effective solutions for one or several application scenarios. So far, METIS has identified six such HTs.
Direct D2D communication
Direct D2D means direct commu-nication between two or more wireless devices without resorting to network infrastructure. D2D is different from other E2E transmission technology such as Bluetooth in that the wireless link between devices is still subject to network management, including wireless resource management and interference management. Therefore, D2D can increase network coverage, boost network availability and reliability, and offload backhaul to reduce cost. D2D can also improve spectrum utilization and increase network capacity per area.
With D2D enabled, the network can reduce unnecessary wireless links and optimize network resource allocation according to actual situations. Furthermore, D2D can improve service quality in densely populated networks. Finally, by developing novel resource and interference management techniques, D2D will be integrated to multi-dimensional networks including multi-RAT and multi-layer networks.
Massive Machine Communication (MMC)
MMC is an important part of the future mobile and wireless communication systems. MMC advancements will lead to connectivity solutions for the connection of tens of billions of devices, realizing flexible network up- and down-scaling. The major challenge is that machine-centric communication has a wide range of unique characteristics and requirements on traffic rates, latency, cost, network availability, and reliability, which are quite different from those of human-centric communication. Within METIS, new technologies will be developed to support MMC and create an "all-connected world".
Moving Networks (MN)
An MN consists of one or more nodes, each of which can be an automobile, bus, or any other moving entities. In such a network, a node can communicate with surrounding nodes including fixed or mobile nodes on or off the mobile subnet. The MN involves all technologies mentioned above, especially backhauling, mobility, and interference management, as well as models and technologies for spectrum and network sharing.
Ultra Dense Networks (UDN)
UDN is the main solution for high traffic rates. It increases network capacity, improves link efficiency and spectrum utilization while reducing power consumption. In fact, densification of infrastructure has already been used in current cellular networks, where the minimum distance between base stations is about 200 meters. In comparison, METIS plans to further increase the network density by several times.
UDN faces many technical challenges, including difficulties on mobility management and backhauling (including self-backhaul). METIS will develop advanced interference and mobility management concepts at the physical and network layers to support UDN. METIS will also assess the UDN in terms of cost, power consumption, and spectrum utilization.
Ultra Reliable Communication (URC)
URC aims to improve network availability. METIS will provide scalable and cost-effective solutions to support services that have extremely high demand on network availability and reliability such as telemetric services and automation. Currently, some purpose-built networks such as public security networks have been set up. These networks boast high reliability and security. METIS's new ideas and solutions will support the evolution and migration of such networks and allow their markets to benefit from the economy-of-scale advantages of the public mobile and wireless communications market.
METIS will investigate key concepts and enablers of network architecture, and design the whole system taking into account the features related to functionality, topology, and interfaces. In other words, a brand new 5G network architecture will be created, which integrates all above technology components and HTs.