In 2015, the 5th generation (5G) mobile communication was officially approved by the International Telecommunication Union (ITU) as IMT-2020. Since then, 3GPP, the international organization responsible for 5G standards, is actively developing specifications for the complete 5G System (5GS). 3GPP Release 15 provides the first full set of deployable standards for the 5GS, and the evolution and expansion of 5GS are now being standardized in Release 16 and 17, respectively. The 5GS is designed to handle extremely high traffic from the vast number of devices more efficiently along with enhanced capabilities in providing real-time services, including mission-critical services, using a flexible architecture tailored to customer needs. This paper describes an overview of the 3GPP 5GS core capabilities and future directions.
3GPP 5G Standards Overview
3GPP started a preliminary study for the development of 5G specification in Release 14 and proceeded with the complete set of 5G specifications in earnest in Release 15 (late 2018) and Release 16 (mid 2019 for completion of 80% of features). In Release 15, 5G basic features including New Radio (NR), massive machine-type communications (mMTC), ultra-reliable low-latency communications (URLLC), vehicle to everything (V2X) phase 2, service-based architecture, etc., were defined as the 5G Phase 1 specification. In Release 16, additional features, for example, enhancing 5G system, industrial IoT, URLLC enhancements, are standardized as the 5G Phase 2 specification. As shown in Fig. 1, the 5G specification is officially scheduled to release its Phase 1 in June 2018 and, at the time of writing this paper, the Phase 2 specification is expected to freeze in June 2020 and complete in September 2020. Release 17 is scheduled to deliver in September 2021.
The scope of Release 15 covers both non-standalone 5G radio systems integrated with LTE networks and standalone 5G with a new radio system complemented by a next-generation core network (see Fig. 2). Release 15 also focuses on supporting enhanced mobile broadband (eMBB) among three 5G usage scenarios (eMBB, mMTC, URLLC) defined by ITU  with following capabilities:
- >10 Gb/s peak data rates for eMBB
- >1 M/km2connections for mMTC
- <1 ms latency for URLLC
As the next major release for 5G specification, the 3GPP Release 16 provides an initial complete 5GS set of standards resulting from around 25 studies on various topics such as V2X phase 3, 5G satellite access, network slicing, security enhancements , novel radio techniques and the IoT.
Release 17 targets further 5G system enhancements to expand the mobile ecosystem for supporting new services/protocols/devices, new spectrum bands and business models covering topics such as Multimedia Priority Service, V2X application layer services, 5G satellite access, and Local Area Network (LAN) support in 5G.
Benefit of 5G over 4G
What is 5G and how does it differ from 4G? This is a question that is paramount on the minds of the general public. When we speak of 5G we really mean 5G radio technology and not so much about the core network that is also an integral part of the entire 5G system. Currently, 4G radio technology is robust and matured, i.e., enhanced over the last ten years and widely deployed. The real benefits of 5G radio technology will take time to realize until it matures and is widely deployed in the next ten years. It should be noted that 5G isn’t replacing 4G any time soon. In fact, both will coexist for many years and work together. 5G capable phones will support both 4G and 5G technology. Here is a list of key differences of 4G vs. 5G from a technical standpoint:
- Radio frequency spectrum – 3GHz vs. 30-300 GHz
- Spectrum efficiency – 3 times better (more bits per Hz)
- Data transmission/speed – up to 1 Gbps vs. 50 Gbps
- Lower latency – 50ms vs. 1ms
- Connection density – 10 times higher in 5G
The 5G radio’s key benefits in the spectrum it operates in are higher speeds, less latency, and capacity for a larger number of connected devices along with less interference and better efficiency. One disadvantage in higher frequency band for 5G would be its broadcast range as signal does not travel long distance in higher frequency bands, and does not penetrate buildings very well. This will require large number of cell sites to be deployed for 5G. In the day-to-day experience, users will not experience a big difference using 5G technology, other than downloading videos faster. The biggest benefits of 5G will not be apparent right away but developments are underway to offer fancy features which we can’t even foresee right now as 5G technology matures and is widely deployed. Unlike previous generations of mobile networks, 5G technology is expected to fundamentally transform the role that telecommunications technology plays in the society. The next section explains key features of 3GPP 5G standards.
5G Core Technology Features and Services
Some 5G key features to look into are new radio capabilities, network slicing, ultra-reliable low-latency communications, enhance security, high-capacity for large-scale internet of things devices, and enhanced core network using service-based architecture. These features allow operating more flexible and dynamic networks to uniformly enable user services with different needs. These 5G features enables supporting various value-added real-time services such as self-driving car, smart city, augmented reality and virtual reality (AR/VR), online interactive learning and 3D video.
5G Deployment Options: The integration of the new radio technology NR in 5G with the ones of the previous generation 4G Long Term Evolution (LTE) was studied in different options in 3GPP Technical Report (TR) 33.801  with two general possibilities as shown in Fig. 2: Standalone (SA) options consist of only one generation of radio access technology, 4G LTE or 5G NR. Non-Standalone (NSA) options have both generations of radio access technologies (4G LTE and 5G) by means of dual connectivity. The most important options are for NSA the so-called Option 3 with the LTE eNB (i.e., evolved Node B) as master node and the 5G gNB, which is a 3GPP 5G Next Generation base station that supports the 5G NR, as secondary node, and both connected to the 4G core network (Evolved Packet Core, EPC). This allows a fast deployment in the operator networks that already deployed 4G LTE and from User Equipment (UE, the phone in 3GPP language) only a 5G radio needs to be added. The evolution in the core network to the 5G core is more difficult. For SA, the most important option is the so-called Option 2, where the 5G gNB is directly connected to the 5G core. While all 5G benefits can be used directly with this option, it is more beneficial with green field operators who start deploying 5G without any legacy network, since interworking with 4G requires much more effort.
Network Slicing using NFV: One of the new features of the 5GS, is call network slicing which enables operators to manage their network resources in unique ways based on customer traffic needs. The network slicing feature is an end-to-end feature which is supported both on the radio access network (RAN) and 5G core. It allows partitioning the network resources via creation of Network Slices (NSs) consisting of dedicated network resources that are needed to do the job, rather than using the entire network and wasting resources, as done previously when there was only a single monolithic network whose resources could not be partitioned resulting in under or over utilization of resources. For example, NSs can be created to address different requirements on functionality (i.e., priority, charging, policy control, security, and mobility), or different requirements on performance (i.e., latency, mobility, availability, reliability and data rates), or a NS can be created to serve only specific users (i.e., multimedia priority service users, public safety users, corporate customers, roamers, or hosting an mobile virtual network operator). The network slice behavior in terms of features and services can be described with the Slice/Service type as part of the slice identifier. So far there are four Slice/Service types specified  for eMBB, URLLC, mMTC and V2X .
The 5G network nodes can be virtualized and sliced through the use of cloud computing working in the same fashion as virtual machines (see Fig. 3). This concept is called network function virtualization (NFV) which has gained importance to allow operators to reduce capital expenditure (no need for dedicated hardware for the network nodes) and ability to tailor the network nodes easily through just software updates. The NFV standards are conducted by the ETSI NFV Industry Specification Group, founded in November 2012.
Service Based Architecture (SBA) – cloud native architecture: The SBA functionality is described in TS 23.501  and the procedures are documented in TS 23.502 . 5G SBA is based on technologies known from the internet, i.e., the Service-Oriented Architecture (SOA) and Representational State Transfer (REST). SOA consists of the three components Service Repository, Service Consumer and Service Provider. A Service Producer publishes its service(s) to the Service repository and a Service Consumer queries the Service Repository for a Service Provider for a specific Server. Then the Service Consumer queries or subscribes to events of the requested service. Network Functions (NF) of SBA can act according to one or more roles of the three, depending of the NF, i.e., they can consume a service from one NF but notify other NFs as a producer at the same time. Without going into details, SBA in 5G defines a variety of NFs as shown in Fig. 4, here are the most important ones: Access and Mobility management Function (AMF), Session Management Function (SMF), User Plane Function (UPF), Policy Control Function (PCF), Network Exposure Function (NEF), Network Repository Function (NRF), Unified Data Management (UDM), Unified Data Repository (UDR), Authentication Server Function (AUSF), Application Function (AF), Network Slice Selection Function (NSSF).
New studies have been proposed in 3GPP for Release 17 and work has started on them. Some of them are mentioned here which are proposed for enhancement of the 5G core network.
- Proximity-based services: To study applicability of direct mode device-to-device capability of the proximity-based service feature that is used in mission critical services, for commercial applications like virtual reality interactive services.
- 5G multicast-broadcast services: To study the applicability of The Multicast/Broadcast Multimedia Subsystem (MBMS) feature of 3G/4G for supporting multicast requirements/use cases for cellular IoT, Public Safety, V2X etc.
- Network automation for 5G: To study applicability of the Release 15 functionality called network data analytics function (NWDAF) responsible for analyzing data of any part of the network, for enabling Artificial Intelligence related services.
- Edge Computing in 5G: To study the applicability of the mobile edge computing technology for improving response times for real-time applications based on URLLC, V2X, AR/VR, satellite access in 5GS, and content delivery network, etc., use cases.
- Support of non-public private networks: To study the applicability of the Release 16 feature called “Vertical LAN”, which offered specific industry (verticals) solutions for companies/factories like redundant transmissions and URLLC, to be available to private networks.
- Enhancement of network slicing: To study further enhancements of the Release 16 network slicing feature.
- Support of satellite access: To study the architecture enhancements in the 5G core for using satellite access in 5G.
Prof. Song was supported by the faculty research fund of Sejong University in 2020.