4G to 5G – The Transition Road

Evolution of the Mobile Telephony

In the past forty years mobile telephony has gone from the first generation of mobile telephony (1G), which was based on analog radio signals, to digital versions of 2G, 3G, 4G and 5G. The need for faster data transfer speeds, higher bandwidth, high spectral efficiency, simpler network architecture as well as a large number of requested services by users has propelled the development of new technologies. The fifth generation enables use of frequency bands from 400 MHz to 90GHz, up to 100 times faster data transfer speeds compared to 4G (> 10 Gbps), delays of less than 1 ms (at 4G delay about 10 ms), high reliability, connection of over a hundred times more devices to the network. It is based on prediction that in the next 10 years that a trillion devices will be connected to the network). It promises reduced power consumption and longer battery life. In frequency bands below 6 GHz, it offers bandwidth of 100 MHz, and above 6 GHz, bandwidth of 400 MHz. Using the carrier aggregation technique (as in 4G), in the band below 6 GHz, the bandwidth of 4x100 MHz can be enabled (at 4G max bandwidth is 100 MHz, obtained using the aggregation technique of carriers of 20 MHz each). Great attention is paid to wireless transmission over millimeter waves (mmWave). In addition to the millimeter waves, the technology also uses massive MIMO (Multiple Input Multiple Output), beamforming.

3GPP, IEEE and International Telecommunication Union ITU continue to work on standardization of 5G. 3GPP defined 5G NR (New Radio) in the release 15 specification, which represents the first phase of standardization of 5G technology, and the second phase ended with the release 16 specification.

Specifications

Release 15 was fully released in June 2019. It covers 5G System Phase 1 specifications, mMTC & IoT, Network slicing - API for 3rd Party. This release is what is implemented in most of the world.

Release 16 was fully released in July 2020. It covers 5G System Phase 2 - NR Radio enhancements for URLLC, Industry IoT, Vehicle to everything, UE power saving, MIMO enhancements, LTE-NR & NR-NR dual connectivity, LTE based 5G terrestrial broadcasts, 5G system enablers for new verticals like Industrial automation, non-Public Network, Mobile communication system for railways, Satellite access, NR-based access to unlicensed spectrum and  wireless - wireline convergence.

Release 17 was fully released in June 2022. It covers NR MIMO, Industrial IoT / URLLC enhancements, NR coverage enhancement, extended reality support, Multicast broadcast, RAN slicing, quality of experience, Network automation, edge computing in 5GC, proximity based service,  Network slicing, location services and  LAN-type services

Release 18 (also called 5G NR Advanced), Stage 2 functional freeze was fully released in June 2023. Key focus areas include: system architecture, services, security and privacy enhancements, new multimedia codecs,  management, orchestration and charging, Application Enablement & Critical Communication Applications, 5G Radio Layer 1 enhancements, Radio layer 2 & 3 Radio Resource Control enhancements, UTRAN/E-UTRAN/NG-RAN architecture & related net- work interfaces and Radio Performance and Protocol Aspects.

Release 19 is nearing Stage 1 completion at the date of writing of this paper. Four prominent work areas approved include : satellite architecture enhancement, Metaverse enhancements, energy saving, IMS-NG RTC enhancement.

High Level 4G vs 5G Comparison

5G entails major changes in the Core vis-à-vis 4G. MME from 4G is separated into 3 different functions namely AMF, SMF and UDM. UE states will be stored in UDM and Session states will be stored in SMF. AMF will be dedicated for processing tasks. UE processes are no longer dedicated to one AMF. They can be processed by any AMF connected to UDM. This allows dynamic scaling to manage high load conditions.

UPF in 5G performs the functions of S-GW and P-GW in 4G EPC. It directly connects to radio network (RAN). UPF can perform many functions. Technically, in 5G SMF can request any UPF in the path to perform any function, unlike in 4G where S-GW & P-GW have very specific defined functions.

PCF in 5G performs the role performed by PCRF in 4G. It is enhanced to perform below role apart from 4G PCRF role, handle more devices and dynamic change in device density, ability to handle network slicing and allowing devices to connect to different network slices. It is also cloud based micro services architecture allowing for upgrades without downtime.

AUSF along with UDM are evolution of HSS in 4G. AUSF takes care of authentication (3GPP and non-3GPP), whereas, UDM stores part of user data and handles authentication, user identification and authorization.

The other Network Functions NEF, NRF, NSSF, SDSF and UDSF are newly introduced in 5G. They are introduced for managing network function instantiation, network slicing and storing/ managing data in micro services based system.[i]

Migration from 4G to 5G

As experienced in 2G to 3G and 3G to 4G evolution, the evolution of network and subscribers is gradual. This leads to the necessity of adopting different 5G rollout techniques broadly classified into two categories Stand Alone (SA) and Non-Stand Alone (NSA).

Following options have been proposed:

Option 1: This is legacy deployment with 4G LTE network connected to 4G EPC and no 5G. Most of the operators currently follow this network deployment mode.

Option 2: This represents standalone 5G with UE connected to 5G NR and 5G NR connected to 5G Core. This is most suitable for any green field network operator rolling out 5G service. This will also enable the operator to offer most of the 5G use cases if sufficient spectrum is available.

Option 3, 3a, 3x: This option has multiple variations but the key feature of this option is UE can connect to either LTE network or 5G NR. Both LTE & 5G NR will in-turn connect to EPC. Core signalling used in this option is 4G EPC signalling.

Option 4, 4a: This option has multiple variations but the key feature of this option is both LTE & 5G NR networks connect to 5G Core. For this option , the operator must deploy enhanced LTE (eLTE) as a pre-requisite.

Option 5: This is a standalone deployment where standalone LTE RAN is connected to 5G Core. For this, LTE should be evolved LTE (eLTE) that can understand 5G core signalling. Most of the operators will not go for this option as most benefits of 5G will come from 5G NR.

Option 6: This is also a standalone deployment with 5G NR but it connects to EPC as the core network. As this will use legacy signalling interface which means 5G NR must support legacy core network signalling. It is unlikely to be chosen as any operator who has 4G EPC will also have LTE network and they will not phase out LTE network immediately and potentially chose from other options

Option 7, 7a, 7x: This represents non-stand alone deploy- ment where 5G core will be used with a mix of LTE and 5G NR. This option requires operator to upgrade existing LTE network to eLTE network for handling 5G core signalling.

Option 2, 4 belong to Stand Alone Deployment. Option 3a, 3x, 4a, 7, 7a, 7x belong to non-Stand Alone Deployment.

Comparison

The difference in Stand Alone and non Stand Alone deployment is largely on basis of coverage, network capabilities, terminal performance, 4G/5G inter working, complexity of deployment and cost.

Coverage: Theoretically 3.6GHz 5G NR should have larger propagation loss and penetration loss, hence it should have poorer coverage compared to LTE. However, with introduction of coverage enhancing features in 5G NR like massive MIMO, beam sweeping MIMO, larger control channel element and others, the coverage of 5G NR will be comparable to 1900 MHz LTE. Hence, in terms of coverage, there is not much expected difference in SA or NSA deployment as long as the number of base stations is similar.

Network capability: NSA is not expected to have same network capabilities as SA because it will mainly focus on eMBB applications. SA will be able to support capabilities like network slicing, more accurate and flexible QoS management compared to NSA.

Terminal Performance: In NSA, as terminal will need to support two radio links LTE & NR, hence possibility of interference is more compared to SA. Apart from this, it may also degrade performance of the terminal since it requires to run two radio links.

Power Consumption: NSA consumes higher power in download mode compared to SA. NSA and SA have com- parable power consumption in upload. However, considering normal user scenario, user will have heavy download. This means NSA will have higher power consumption compared to SA.

4G/ 5G inter working: For NSA, device will always be anchored to EPC or 5GC. Hence, there is no interworking or handover. The voice call can be always routed through 5G NR connected to LTE with LTE fallback.

LTE network. For SA deployment, there are two options for supporting voice call. Either the network supports VoNR or for voice call the device falls back on LTE network. The inter working will be easier in NSA as the handover is intra- system whereas in SA the hand over is inter-system with more latency/service disruption.

Network Deployment: In SA, the network deployment is simple and one step as it requires only one interface N26 to introduce interworking between a 5G and 4G network. In NSA, the network deployment is complex because it requires modification to existing 4G EPC as well as it requires a future step to move from NSA to SA 5G for exploiting all 5G use cases.

Advantages - Disadvantages of NSA Deployment

Advantages of NSA deployment include faster launch, operator can keep moving through gradual increase in performance, easy deployment due to familiarity to 4G, reduced cost

Disadvantages of NSA include; reduced 5G Use cases, higher power consumption, higher connection drops during inter RAT handovers

Conclusion

5G is designed to explore the new business opportunities of eMBB, mMTC, and URLLC scenarios. For operators who have the ambition to explore the vertical and enterprise markets as soon as possible, SA is recommended for large- scale deployment. For operators who are not willing to introduce the 5GC for initial NR deployment, NSA is a compromise between adding new capacity for eMBB and saving some cost of initial deployment. When it is necessary, the NSA NR can be evolved to SA NR.

5G promises to revolutionize the wireless networks, however there are concerns raised around ability of 5G to support true Internet of Everything applications on massive scale. Although initially it was thought that 5G rollout on large scale will happen on mmWave above 6GHz frequencies, it is evident that large deployment of 5G will be done on sub-6 GHz frequencies. There are many new Internet of Everything applications being developed everyday like virtual reality (AR/ VR), telemedicine, haptics, flying vehicles, brain- computer interface and connected autonomous systems. These applications will require the network to simultaneously have high reliability, low latency and high data rate. To overcome these challenges research on 6G has already started with 3GPP Rel 19 onwards. There are expectations on 6G standards to be finalized by 2028.

[i] A study of wireless network evolution from 4G to 5G: standalone vs non-standalone, Dhanashree Shukla, Dr. Sudhir D. Sawarkar