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Technology Migration:Possible scenarios for the introduction of 5G

June 28, 2018

Unlike previous generations of mobile technologies, 5G is expected to fundamentally transform the role that telecom technology plays in society. 5G is also expected to drive economic growth and enable large-scale digitalisation, creating an ecosystem where not only all people, but all devices are connected as well. It is not a coincidence that governments around the world, particularly in the most advanced economies such as China, the European Union, Japan, Korea and the US, are working to accelerate the introduction of 5G technology. Given the variety of business models and services that 5G systems can support, mobile operators can explore different strategies to introduce these services. Further, global reach and economies of scale (for network equipment and devices) are two key performance indicators of a telecom network, thus it is important to ensure that they are upheld, even as different operators may follow different 5G introduction and deployment options.


5G drivers and use cases

While previous generations of mobile networks were purpose-built for delivering communications services such as voice and messaging (2G) or mobile broadband (4G), 5G will have flexibility and configurability at the heart of its design. This will enable mobile operators to serve the internet of things (IoT) use cases, and support ultra-reliable, low latency connections and enhanced mobile broadband (eMBB). New use cases designed to support smart cities, smart agriculture, logistics and public safety agencies will deeply impact every aspect of people’s lives.

5G has three major use-case classes – eMBB IoT (mIoT) and ultra-reliable low latency. The requirements of these use case classes and the use cases within each class vary significantly. For example, smart meters will require only periodic transmission of a relatively small volume of traffic while enhanced mobile broadband will require bursty/continuous transmission of larger traffic volumes.

The spectrum bands earmarked for the deployment of 5G can be divided into three macro categories – sub-1 GHz, 1-6 GHz and above 6 GHz. The sub-1 GHz bands can be used to support IoT services and extend mobile broadband coverage from urban areas to suburban and rural areas. This is because the propagation properties of a signal at these frequencies enable 5G to create very large coverage areas and allow deep in-building penetration. The 1-6 GHz bands offer a useful mix of coverage and capacity for 5G services. There is a reasonable availability of mobile broadband spectrum within this range, which could be used for initial 5G deployments. Spectrum bands above 6 GHz provide significant capacity owing to the very large bandwidth that can be used for mobile communications to enable eMBB applications. On the down side, using high spectrum bands (the “millimetre wave”) significantly reduces the coverage size of each cell and its susceptibility to blocking.

There are many options of 5G introduction and different spectrum bands will be needed to support the range of 5G applications. Operators must, therefore, consider the feasibility of the various options and their interoperability with other options to ensure that their networks deliver the service effectively while supporting global interoperability.

5G network deployment options

As with the previous generations, 3GPP (the 3rd Generation Partnership Project) defines both a new 5G core network, referred to as 5GC, and a new radio (NR) access technology called 5G NR. Unlike previous generations where both access and core networks of the same generation had to be deployed [for example, evolved packet core (EPC) and long term evolution (LTE) together formed a 4G system], 5G allows the integration of elements from different generations in various configurations (standalone using only one radio access technology and non-standalone combining multiple radio access technologies).

In a standalone scenario, 5G NR or the evolved LTE radio cells and the core network are operated separately. This means that the NR or evolved LTE radio cells are used both for the control plane and the user plane. The standalone option is simple to manage and may be deployed as an independent network using normal inter-generation handover between 4G and 5G for service continuity. On the other hand, in a non-standalone scenario, the NR radio cells are combined with LTE radio cells using dual-connectivity to provide radio access and the core network may be EPC or 5GC depending on the operator. This scenario may be adopted by those operators that want to leverage existing 4G deployments, combining LTE and NR resources with existing EPC, and/or those that want new 5GC to deliver 5G mobile services.

5G migration path

There are several possible “paths” operators can follow to introduce 5G and then migrate it to the target configuration(s). These options include –

Evolved packet system (EPS) to standalone NR under 5GC: In this scenario, the operator migrates directly from EPS to a standalone scenario with inter-RAT mobility mechanisms used to move devices between 4G LTE under EPC coverage and 5G NR under 5GC coverage. One of the key benefits of this option is that standalone architecture can help leverage 5G end-to-end network capabilities supported by NR and 5GC, providing customised services, especially to the vertical industry, in an effective and efficient way.

EPS to non-standalone LTE and NR under EPC: The E-UTRA is extended to allow compatible devices to use dual connectivity to combine LTE and NR radio access. One of the key advantages of this option is that it only requires the development of NR specifications as non-standalone access as part of E-UTRA connected to EPC.

Non-standalone to non-standalone LTE and NR under 5GC, and standalone LTE under 5GC: This is applicable to early 5G devices. In this path, 5GC is deployed so that the full advantage of 5G end-to-end network capabilities can be delivered to the users. This path enables operators to provide initial 5G use cases such as mobile broadband, leveraging LTE and EPC installed base, while new use cases can be addressed on clean-slate 5GC architecture.

Non-standalone LTE and NR under EPC to non-standalone LTE and NR under EPC and standalone NR under 5GC: This can be used to move devices between 5G non-standalone LTE and NR under EPC coverage and 5G NR under 5GC coverage. This path enables operators to cater to all use cases on clean-slate 5GC architecture. However, the operator may need to consider migration of initial use cases served by EPC to 5GC.

Non-standalone LTE and NR under EPC to non-standalone NR and LTE under 5GC and standalone NR under 5GC: In this path, the 5GC core network is used to replace the EPC in serving 5G use cases (if 5GC replaces EPC completely then legacy 4G user equipment or UEs with 4G only subscription will no longer be served). This means that users can fully utilise 5G end-to-end network capabilities. This path also enables operators to address all use cases on clean-slate 5GC architecture.

Other migration steps: These include non-standalone LTE and NR under 5GC to non-standalone NR and LTE under 5GC; standalone LTE under 5GC to non-standalone NR and LTE under 5GC; EPS to non-standalone; and EPS to non-standalone LTE and NR under 5GC.

In sum

The various options and migration steps available for deploying 5G allow operators to choose from different strategies as per their specific market situation, business models and competition needs. Other industry stakeholders including customers will also benefit from the collaborative actions taken by operators  to ensure service continuity, service and network interoperability, and unlock economies of scale. s

Based on a white paper, “Road to 5G: Introduction and Migration”, by GSMA.




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