Intensive development of the Fifth-Generation Mobile communications system (aka 5G) has been pushed forward worldwide as an extensive advancement of the existing mobile communication systems based on comprehensive researches of market trends and future demands to the mobile communication systems towards 2020s. This article summarizes an overview of requirements for 5G and relevant technologies that are derived from variety of use cases , ,  surveyed by number of 5G research organizations and academic societies.
Studies on high speed, high capacity, massive number of connections, ultra-low latency, and ultra-high reliability
5G use cases and their requirements have already been studied by 5G research organizations, academic institutes and telecommunications firms, and published as their white papers . All of these dedicated efforts have converged to a common framework of use cases and network requirements. As an example, use cases and the requirements taken from a white paper published by ‘2020 and Beyond Ad Hoc group’ of the Association for Radio Industries and Businesses (ARIB) in 2014 are shown in Figure 1 and Figure 2 below.
(1) High Speed, High Capacity
Since LTE has been widely used worldwide already and LTE-Advanced is being developed in various nations or regions as well, certain level of demands for high speeds and high capacity communications caused by growing communication traffic as the consequence of increasing number of smartphones with enriched applications would be satisfied for the time being.
However if you talk about the 2020s, further advancement of the communications system would be inevitable in which substantial penetration of wearable devices, enriched video contents provided by 4K or 8K video systems etc. should be taken into account. It will not only be so important for entertainment or advertising cases, but also for use cases for such as security, healthcare and education.
For these use cases, it is predicted that the communication traffic will be beyond 1000s times higher in the 2020s than in the 2010s and 5G systems should enlarge its capacity in order to support this demand accordingly.
In addition, ultra-high speed transmission of up to 10Gps will be needed to allow users to make accesses to ultra-high capacity contents.
(2) Massive connected devices
Up to now, communications amongst people or communications between people and their targeting objects to utilize variety of service contents on servers have been main scenarios supported by communication systems. However, as has been represented by emerging Internet of things (IoT) or Machine to Machine (M2M) communications, massive number of objects will be starting to communicate each other sooner or later.
Number of communication modules establishing communications between gas and electric meters are gradually increasing. In parallel to that, demands for sensors expected to be utilized in agriculture, livestock industries or construction industry are being developed as well.
In the next decade, further penetration of these sensors will progress and variety of things will be connected by variety of communication modules, which will provide better user benefit, higher security with reduced cost.
For the use cases in transportation systems such as automobiles or trains, expectation to roll of the mobile communication systems seems so high. Among these use cases, there seems especially high interest in car driving support including autonomous driving, in-car entertainment or ensuring safety.
It is also expected that remote controlling facilities or securing devices for houses, electric appliances or equipment in offices would be widely used. Variety of wearable devices will be available and help different kinds of support to human activities will be provided. For the moment wearable glasses would be one of the typical example and tactile communication services will become a reality in near future. As another example, sensors embedded in clothes for healthcare purposes are being considered.
Taking into account these various use cases, the commutation systems in 2020s should support massive number of devices which number could be more than 100 folded compared to the ones in the existing systems.
(3) Ultra-low latency and ultra-high reliability
LTE or LTE Advanced (corresponding to IMT-Advanced in Figure 2) has achieved short transmission latency in the order of 10 milliseconds, it is said that more drastic reduction of the latency would be required for certain use cases, for instance, tactile communications.
In some use cases, both low latency and high reliable communications will be required. Examples for these use cases will be found in the case of communication between cards to avoid accidents or remote controlling of robots. As the consequence, end-to-end latency of few milliseconds or less than one millisecond for radio access part will be required. For the communication reliability, success rate of 99.999 percent could be the target.
It should also be mentioned that deploying communication networks providing both ultra-low latency and ultra-high relatability to every use case will be technically feasible but would not be realistic because of its cost required. Accordingly careful consideration to choose appropriate use cases for these sophisticated requirements will be highly recommended.
(4) Energy Saving, Cost Saving
Energy saving is the top priority in every industry or society in recent years, and the ICT industry is not an exemption. The ICT industry’s energy consumption share to the whole industry increases as its growth and it cannot be regarded as marginal. Energy saving would results in cost saving as well.
Cost saving has been a fundamental requirements and historically set as a qualitative target in every previous generation of mobile communications systems and will also be important for 5G. Considering the contrast between ongoing remarkable increase of communication traffic and saturating business income of telecommunication firms, extra cost saving is regarded as the fundamental factor of 5G deployments.
At the moment, definitions, requirements, nor metrics for energy saving and cost saving have not yet been finalized. Even so, those are considered to be very important requirements for 5G.
5G Radio Technology
Leading candidates: Utilization of the higher frequency bands and massive element antenna technologies
A considerable number of 5G research organizations are actively promoting researches related to network and radio technology in order to deploy 5G and a number of component technology candidates have already been on the candidate list. This article will not discuss all of the technical details though, some of the most interesting radio transmission related technologies being developed worldwide, i.e. utilization of higher frequency bands in mobile communications and massive element antenna technologies, are picked up and their overviews are given.
(1) Utilization of High Frequency bands
It will be difficult to achieve the above-mentioned 5G requirements for high speed and high capacity if we only rely on enhancing the current radio access technology. Therefore, it is essential to apply small cell deployment more and utilizing wider frequency spectrum. In this regard, frequency bandwidths of several hundred megahertz or more would be necessary if we try to achieve transmission speeds of 10Gbps.
However it should be also the fact that finding additional new spectrum of few hundreds MHz or more for 5G in the bands from several hundred MHz to 3GHz is almost impossible since the band is extensively used by existing radio systems or services, including mobile communication systems, everywhere on the globe.
As a result, expectation of utilizing higher spectrum bands in the submillimeter or the millimeter with technical breakthrough to utilize the spectrum becomes high. Specifically saying, a number of researches are being made with frequency spectrum up to 100GHz as possible candidate bands for 5G.
Up until now, it has been said that utilizing the higher frequency bands for mobile communications is a big challenge because of the propagation properties of electromagnetic waves in these frequency bands, that is relatively large propagation loss in the air and consequent reduced cell sizes of mobile communication systems due to their rectilinear advancing property with resultant shadowing effect caused by buildings, vegetation or even human bodies.
Therefore there should be new technical factors to overcome these drawbacks. One of the expected technologies the industry pays the most attention to, which will be discussed in the next section, is the use of the massive element antenna technology for radio transmission.
In order to develop technologies utilizing the higher spectrum bands for 5G, a comprehensive understanding of the mobile transmission environment in higher frequencies is essential. Moreover propagation models applicable in simulation tools for system performance evaluation will be the key. For the moment, experts in these areas of academia, industries, and reach projects are working on research to elaborate relevant measurement tools, analyzers, and the propagation models.
(2) Massive element Antenna Technologies
Massive element antenna technology will enable what is called beamforming technology, which combines radio waves and forms a single sharp beam. The beam is able to compensate the propagation loss in higher frequencies and ensuring a transmission area of several hundred meter radius.
Two types of multi-antenna technologies have been applied in LTE and LTE-Advanced that could be a basis to massive element antenna technology in 5G. These technologies utilize multiple propagation paths available in a radio communication link between a mobile station and a base station. One is Single-User MIMO (SU-MIMO) forming plural antenna beams targeting different directions and achieve high speed data transmission via data multiplexing across the plural propagation paths. The other is Multi-user MIMO, which makes the space multiplexing scheme in SU-MIMO as a set of dedicated communication links for each of multiple mobile stations and improves the system capacity.
Towards 5G, aggressive use of massive number of antennas allowing increased multiplexing capability and aiming for higher data rate with improved system capacity, so called Massive-MIMO, is being planned
For the moment, horizontal beam forming has been applied in the existing systems however 3GPP standardization activities are working for both horizontal and vertical beam forming schemes and Massive-MIMO as the succeeding antenna beam forming technology for 5G would have the same scheme.
As has been stated, 5G is expected to use millimeter waves or submillimeter waves, and applying multi antenna technologies in these higher frequency spectrum would have advantage since physical sizes of the antenna elements as well as spans of the elements are proportional to wave length of the radio signals, which is inverse proportional to the frequency, and this would result in compact antenna devices in these higher frequency bands. As the consequence, even when massive number of antenna elements are applied, size of the antenna portion would be reasonably compact but still gives higher antenna gain thanks for the sharp antenna beam formed by these massive elements .
Beside these technologies mentioned above, quite a lot state of the art technologies, such as radio signal processing methods dedicated to use cases, shortened radio frame structure with optimized network structure providing ultra-low transmission delay and technologies evolved from the existing or on-going technical standards are being proposed for 5G. As a reference, overview of probable 5G radio wireless component technologies are shown in Figure 3 below .
5G mobile network technologies
Studies centered on network softwarization
Considering actual deployment of 5G mobile communication networks, not only wireless networks but also fixed network aspect should be involved and importance of technology development regarding architecture of the whole communication network should be taken into account.
In Japan, the 5GMF network committee has the mission to carry out above mentioned studies. The committee has payed special attention to end-to-end communication quality and has identified necessity of developing fixed network technologies to accommodate reduced transmission latency or wider bandwidth properties in the radio access portion, and desirable extremely flexible resource control as in the radio access networks as essential requirements of 5G networks.
In order to satisfy these requirements, the following four areas are regarded as focus area of 5G mobile architecture research; 1) Network softwarization, 2) Mobile fronthaul and backhaul 3) Mobile edge computing (MEC), 4) Management and orchestration. A strategy to elaborate researched in these areas has been elaborated.
As for Network softwarization, it implies softwarization of wider area beyond ordinary SDN and NFV. It involves concept of well-known slicing, which is a set of reserved network resources consist of communication networks, data processing units, with the following extensions; 1) Horizontal extension to make conventional MEC in the context of NFV to involve the UE and the cloud and softwarizing them, 2) Vertical extension from not only contains control planes in the context of SDN but also data plans as well, and lastly, 3) a flexible configuration of hardware and software portion corresponds to each application.
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As there have been a growing desire to go forward towards 5G, a considerable number of research promotion entities have been established and extensive research activities are going on in global wise. This paper summarizes use cases, requirements as well as some of the important enabling technologies of 5G. In Japan, initial research of 5G was commenced in the ‘ARIB 2020 and Beyond Ad Hoc’ and the work has been extended to include network related area and succeeding works are being proceeded actively by the Fifth Generation Mobile Communication Promotion Forum.