Free 6G Training

Last year we announced the launch of Free 5G Training. It was successful beyond our imagination. While we have just over 1,300 Twitter followers, on LinkedIn, we have over 30,000. The 5G for Absolute Beginners Udemy course already has over 6,000 students. This was a good enough motivation for us to launch a 6G equivalent with world's first 6G training course.

Back in November, we soft-launched the Free 6G Training website/blog along with Twitter and LinkedIn. The initial engagement and following are already very encouraging. 

We also created 'An Introduction to 6G Training Course' here. 6G Candidate technologies, that require most details and is the main area of focus for 6G will be added as and when I find time and have enough material.

There is also a new 6G Wireless R&D LinkedIn group that has been started to share information and discuss doubts, etc. I am hoping many people will be able to join.

If you are a 6G expert or researcher or have ideas on how I can do better or want to contribute with articles, presentations, videos, etc., please feel free to get in touch on LinkedIn.

One final thing, along with all this, the 3G4G page has a section on '6G and Beyond-5G Wireless Technology'. I add links to all publicly available whitepapers and other good material out there. 

It may also be useful to know that the 3G4G page has a search box on top that searches across all our channels and can be helpful in finding information on any mobile technology related topic.

NWDAF in 3GPP Release-16 and Release-17

We looked at Network Data Analytics Function, NWDAF, in detail here. While the 3GPP Release-16 work just starting back then, we have now completed Rel-16 and looking at Release 17. 

The 5G Core (5GC) supports the application of analytics to provide Intelligent Automation of the network, In Rel-16 the set of use cases that are proposed for the NWDAF has been widely expanded. 

In an earlier post, we looked at the ATIS webinar discussing Release-16 & forthcoming features in Rel-17. Puneet Jain, Director of Technical Standards at Intel and 3GPP SA2 Chairman talked briefly about NWDAF. The following is from his talk:

Release-16 provides support for Network Automation and Data Analytics.  Network Data Analytics Function (NWDAF) was defined to provide analytics to 5G Core Network Functions (NFs) and to O&M. It consists of several services that were defined in 3GPP Rel-16 and work is now going in Release 17 to further extend them. 

In release 16 Slice load level related network data analytics and observed service experience related network data analytics were defined. NF load analytics as well Network Performance analytics was also specified. NWDAF provides either statistics or prediction on the load communication and mobility performance in the area of interest. 

Other thing was about the UE related analytics which includes UE mobility analytics, UE communication analytics, Expected UE behavior parameter, Related network data analytics and abnormal behavior related network data analytics.

The NWDAF can also provide user data congestion related analytics. This can be done by one time reporting or continuous reporting in the form of statistics or prediction or both to any other network function. 

QoS sustainability analytics, this is where the consumer of QoS sustainability analytics may request NWDAF analytics information regarding the QoS change statistic for a specific period in the past in a certain area or the likelihood of QoS change for a specific period in future, in certain areas. 

In Release 17, studies are ongoing for network automation phase 2. This includes some leftover from Release 16 such as UE driven analytics, how to ensure that slice SLA is guaranteed and then also new functionality is being discussed that includes things like support for multiple NWDAF instance in one PLMN including hierarchies, how to enable real-time or near-real-time NWDAF communications, how to enable NWDAF assisted user pane optimization and last which is very interesting is about interaction between NWDAF and AI model and training service owned by the operator.

This article on TM Forum talks about NWDAF deployment challenges and recommendations:

To deploy NWDAF, CSPs may encounter these challenges:

• Some network function vendors may not be standards compliant or have interfaces to provide data or receive analytics services.
• Integrating NWDAF with existing analytics applications until a 4G network is deployed is crucial as aggregated network data is needed to make decisions for centralized analytics use cases.
• Many CSPs have different analytics nodes deployed for various use cases like revenue assurance, subscriber/marketing analytics and subscriber experience/network management. Making these all integrated into one analytics node also serving NWDAF use cases is key to deriving better insights and value out of network data.
• Ensuring the analytics function deployed is integrated to derive value (e.g., with orchestrator for network automation, BI tools/any UI/email/notification apps for reporting).

Here are some ways you can overcome these challenges and deploy efficient next-generation analytics with NWDAF:

• Mandate a distributed architecture for analytics too, this reduces network bandwidth overhead due to analytics and helps real-time use cases by design.
• Ensure RFPs and your chosen vendors for network functions have, or plan to have, NWDAF support for collecting and receiving analytics services.
• Look for carrier-grade analytics solutions with five nines SLAs.
• Choose modular analytics systems that can accommodate multiple use cases including NWDAF as apps and support quick development.
• Resource-efficient solutions are critical for on-premise or cloud as they can decrease expenses considerably.
• Storage comes with a cost, store more processed smart data and not more raw big data unless mandated by law.
• In designing an analytics use case, get opinions from both telco and analytics experts, or ideally an expert in both, as they are viewed from different worlds and are evolving a lot.

This is such an important topic that you will hear more about it on this blog and elsewhere.

Related Posts:

• The 3G4G Blog: ATIS Webinar on '5G Standards Developments in 3GPP Release 16 and Beyond'
• The 3G4G Blog: Automating the 5G Core using Machine Learning and Data Analytics
• The 3G4G Blog: Artificial Intelligence - Beyond SON for Autonomous Networks
• 3G4G: 5G Service Based Architecture (SBA) 

Banana and Egg gets 5G Telesurgery

Last year I wrote a detailed post on '5G Remote Surgery and Telehealth Solutions' here. Since then many people with little or no understanding of how the technology works have got in touch with me to educate me about all the 5G remote surgeries taking place. 

I am always prepared to learn new things and looked at both of these surgeries (detailed below) with open mind. I was still unable to see the 5G angle here. In fact in the case of banana, I don't even know if 5G was used.

Back in 2014, a BBC article detailed how a surgeon in Canada has performed over 20 remote surgeries with the help of a robot including colon operations and hernia repairs. The article goes on to ask, "The technology behind long-distance surgery is now mature enough to be used more widely, allowing people to access world-leading expertise and better healthcare without having to travel. Could it become the norm in hospitals?"

The first case is from Aug 2020 as shown in the video above where Doctor Liu Rong from a hospital in Beijing takes on the challenge of remotely controlling a medical robot in distant Qingdao City via the 5G network to finish an egg membrane suture surgery in 90 minutes.

The question here is that where exactly was 5G used and why? Did both the ends have 5G or just one end? Etc. I was unable to find a schematic to show the end-to-end details that would provide credibility to such a scenario.

To explain what I mean, when Vodafone UK launched 5G, they demonstrated low latency by giving an example of Haptic tackle using TeslaSuit. You can read the details and watch the video here. 

As you can see, the end-to-end solution architecture is nicely explained as shown in this picture. I would expect a similar kind of schematic for the surgery scenario. While I can clearly understand the use case for sports outdoor, I am not able to understand the use case for the surgery indoors. Where was the access point? What frequency was used? Was this Standalone or Non-Standalone network? And many other questions like these. 

The second case was a more recent one. The video is embedded below.

Even though the video mentions 5G and many other sites (see this LinkedIn post with nearly 2.5 million views) that have picked this up mention 5G, the original Instagram video does not mention 5G. In all likelihood there is no 5G connection with this one.

Surely there will be a real life 5G remote surgery use case someday that will capture our imagination but not today.

Related Posts:

• The 3G4G Blog: 5G Remote Surgery and Telehealth Solutions 
• The 3G4G Blog: Real-life 5G Use Cases for Verticals from China 

Some Cool Gadgets from CES 2021

 

With all the disruption on events and conferences due to Covid-19 pandemic, it wasn't a surprise that CES 2021 was completely digital. It was also moved by a week so it did disrupt a few smaller events here and there. I thought it may be worth sharing a few quick videos to give you an idea about the big announcements out there. BBC has a nice detailed coverage of the whole event here.

Let's start with this short 4 mins video from CNET that quickly shows all the best devices from CES 2021.

The next is this slightly longer 12 minute video that has 20 awesome gadgets for smart homes.

Finally, there is this 11 minute plus video that is a summary of all new mobile phone technology. It's not as polished as the ones before but still good enough.

In addition, here are some links for you to watch the keynotes from relevant to our industry:

Samsung gets full marks for making a short event highlights video here. In addition, they have a press conference video and a detailed keynote video. All details are on their CES microsite here.

TCL's rollable phone and tablet is nicely captured by CNET here. Their CES microsite is here.

LG Electronics may want to learn a few tricks from Samsung as far as making microsites and videos are concerned. They CES micro site is here. The full press conference is here while Engadget summarises the keynote in just over 9 mins here. LG Wing video here makes an interesting viewing.

Finally, here are 3 links that have summarised the best/weird gadgets from CES and yes there are overlaps in their choices

• DigitalTrends: The 15 coolest gadgets at CES 2021
• Pocket-lint Best of CES 2021 Awards: The 15 top gadgets, TVs, laptops and more
• Wired: The best (and strangest) new gadgets from CES 2021
• Mobile World Live - Mobile Mix: Viva Las Living Room

If you want to share something, feel free to comment.

Related Posts:

• Free 6G Training: Summary of CW '6G devices of 2030' Seminar
• The 3G4G Blog: Multi-SIM Terminology
• The 3G4G Blog: Embedded SIM (eSIM) and Integrated SIM (iSIM)
• The 3G4G Blog: The Futuristic Concept of 'Smart & Intelligent' Batteries
• The 3G4G Blog: CW Seminar: The present, the future & challenges of AR/VR (#CWFDT) 

UE Radio Capability Signaling Optimization (RACS) in Rel. 16

The data volume of UE Radio Capability Information defined in 3GPP 38.306 is already high and will further increase starting with Rel. 16 due to additional supported bands and other features.

Due to this 3GPP has standardized in Release 16 what is called UE Radio Capability Signaling Optimization (RACS) for both, E-UTRAN/EPS and NG RAN/NGC networks. 

Release 16 RACS does not apply to NB-IoT.

The first key element of this feature set is the introduction of a new UE Radio Capability ID that is structured as defined in 3GPP 23.003 and shown in figure 1 below:

Figure 1: UE Radio Capability ID according to 3GPP 23.003

The components of this new ID are:

•    TF - Type Field (TF): identifies the type of UE radio capability ID.

            Type = 0 -> manufacturer-assigned UE radio capability ID
            Type = 1 -> network-assigned UE radio capability ID

•  The Vendor ID is an identifier of UE manufacturer and only present if TF = 0. The vendor IDs are provided by Internet Assigned Numbers Authority (IANA). The complete list of assigned numbers is publicly available here: https://www.iana.org/assignments/enterprise-numbers/enterprise-numbers

•  The Version ID configured by the UE Capability Management Function (UCMF) that is part of the EPS/5GC. The Version ID value makes it possible to detect whether a UE Radio Capability ID is current or outdated.

·      The Radio Configuration Identifier (RCI) identifies the UE radio configuration.

The PLMN-assigned UE Radio Capability ID is assigned to the UE using the Non-Access Stratum UE Configuration Update Command or Registration Accept message (figure 2).

Figure 2: PLMN-assigned UE Radio Capability Update according to 3GPP 23.743

The new UCMF (UE radio Capability Management Function) stores All UE Radio Capability ID mappings in a PLMN and is responsible for assigning every PLMN-assigned UE Radio Capability ID.

Due to introduction of the UMCM in the core networks the new Nucmf service-based interface is defined for the 5GC and new S17 reference point is defined for the EPS as shown in figure 3.

Figure 3: Network Architecture with UCMF according to 3GPP 21.916

Each UE Radio Capability ID stored in the UCMF can be associated to one or both UE radio capabilities formats specified in 3GPP TS 36.331 [LTE RRC] and 3GPP TS 38.331 [NR RRC]. The AMF must only be able ot handle the NR RRC format while the MME uses the LTE RRC format. Which format is required by the UCMF is configurable.

If at any time the AMF/MME has neither a valid UE Radio Capability ID nor any stored UE radio capabilities for the UE, the AMF/MME may trigger the RAN to provide the UE Radio Capability information and subsequently request the UCMF to allocate a UE Radio Capability ID.

In NG RAN the UE Capability Request can be requested by the AMF as a flag in any NGAP Downlink NAS Transport message or by sending a NGAP UE Radio Capability Check Request (for checking compatibility of IMS voice capabilities). This triggers a NR RRC UE Capability Transfer procedure and subsequently NGAP UE Radio Capability Info Indication or NGAP UE Radio Capability Check Response (for IMS voice support parameters).

Using the NGAP UE Capability ID Mapping procedure the NG RAN node is able to request the most recent UE Capability ID mapping information from the core network functions AMF/UCMF. The same functionality is implemented in S1AP for signaling between eNB and MME/UCMF.

If the volume of the LTE/NR RRC UE Capability to be sent by the UE is larger than the maximum supported size of a PDCP SDU (specified in 3GPP 38.323) then the UE Capability Info can be transported in LTE/NR RRC using a chain of UL Dedicated Message Segment messages.

Figure 4: RRC UL Dedicated Segment Message transporting UE Radio Capability Information according to 3GPP 36.331 and 38.331

Each of these message will have a dedicated segment number and the last one has the rrc-MessageSegmentType =  “lastSegment”, which triggers reassembly of the orignal UE Capabability information in the receiving entity.

5G for Content Acquisition and Distribution

The Cambridge Wireless (CW) Content Production & Delivery group recently delivered a two part webinar series exploring ‘5G for content acquisition and distribution’ These online events introduced participants to the state of play with 5G for content distribution and production and the path to delivering the benefits 5G.

Aspirational discussion of benefits of 5G for content production and distribution needs to be turned into operational reality. 5G will enhance what is possible to be achieved with current mobile systems and the advantages to distribution and consumption are obvious through bigger pipes and enhanced agility to support ever evolving content and application platforms. The possibilities for content production and acquisition are also exiting but may be less obvious. 5G will allow service and capacity to be delivered where required through use of small cell and potentially highly localised private 5G networks, edge computing and support of a wide range of equipment and applications (not just those use cases directly involved in content acquisition).

The first session on 24 Nov 2020 in the series considers the role of 5G for content distribution and security. It covers the role of 5G for the creation of a more varied and vibrant ecosystem for content and the desire of some content creators for greater focus on security.

Henry Johnson, Director, Plum Consulting, '5G opportunities in the provision of content distribution' - 5G services promise to provide connectivity performance in terms of bandwidth and latency which have hitherto been possible only with fixed network connectivity. This session will look into the capabilities and potential limitations of 5G services once deployed and what that might mean for content delivery to consumers. [PPT presentation]

Malcolm Brew, University of Strathclyde, ‘5G-enabled remote broadcast’ - Malcolm will share some Strathclyde’s insights over the last 10 years in working with BBC and Ofcom on ‘Spectrum Sharing’ and how this has recently been lead to working in an IBC Accelerator Program ‘5G In Remote Production’ [PDF] 

For limited time, the recording is available here.

The 3G4G Blog: LTE / 5G Broadcast Evolution - https://t.co/nMM6VvxGbg via @5Gxcast #3G4G5G #IEEE5G #5GIEEE #eMBMS #LTEBroadcast #MissionCriticalComms pic.twitter.com/aSxdsFkX9A

— 3G4G (@3g4gUK) August 29, 2019

The following is the description from session 2, on 2nd Dec 2020:

Join the CW Content Production and Delivery Group’s aspirational discussion of benefits of 5G for content production and distribution needs to be turned into operational reality.

There is no doubt 5G will enhance what is possible to be achieved with current mobile systems and the advantages to distribution and consumption are obvious through bigger pipes and enhanced agility to support ever evolving content and application platforms.

The possibilities for content production and acquisition are also exciting, but may be less obvious. 5G will allow service and capacity to be delivered where required through use of small cell and potentially highly localised private 5G networks, edge computing and support of a wide range of equipment and applications (not just those use cases directly involved in content acquisition).

Ian Wagdin, Senior Technology Transfer Manager, BBC R&D, '5G in Content Production, work in standards and deployments' - A look at what’s here and what’s coming and how 5G may impact broadcast workflows. [PDF]

Paola Sunna, Technology and Innovation Department, EBU, '5G for Content Production' - EBU perspective on 5G for professional content production and challenges/ambitions in the Horizon 2020 project 5G-RECORDS. [PDF] 

For limited time, the recording is available here.

A nice talk looking at 5G and Broadcast - 'BBC, 5G and me' by Ed King, Principal Architect, BBC at @TheIET #5GUnleashed 2020 conference - https://t.co/RtTIxZnvN4#Free5GTraining #eMBMS #5Gbroadcast pic.twitter.com/j0d6r7Xqeq

— 5G Training (@5Gtraining) March 6, 2020

Other Recent News / Articles / Videos on 4G/5G Broadcast:

• SoftBank Corp. Showcases 5G-powered Entertainment and Advanced Technologies at Pop Culture Complex (link)
• 5G TODAY: BAVARIA’S BROADCAST TRIALS (link)
• Webinar: The role of broadcast and multicast in 5G-TOURS: High-quality video services distribution (link)
• Delivering Media with 5G Technology: FeMBMS, 5G-Xcast and beyond (link)
• 5G TODAY: 5G Broadcast trial using FeMBMS (link)
• 5G Today: On the Road to 5G Broadcast (link)

Related Posts:

• The 3G4G Blog: LTE / 5G Broadcast Evolution
• The 3G4G Blog: 5G Dynamic Spectrum Sharing (DSS)
• The 3G4G Blog: Multicast Operation on Demand (MooD) and Service Continuity for eMBMS 

Top Videos on 3G4G YouTube Channel

We made quite a few videos last year for our YouTube channel. In fact we crossed over 10K subscribers last year. Here are couple of playlists, one for the Top 5 videos of 2020 and other is Top 10 videos of all time. Hopefully you like them and subscribe to our channel

Top 5 3G4G videos from 2020

Top 10 3G4G videos from all time

 Let us know which ones are your favourite.

Related Posts:

• The 3G4G Blog: Top 10 Posts for 2020 and Top 5 Videos
• Connectivity Technology Blog: Top 5 Posts for 2020
• Operator Watch Blog: Top 5 Posts for 2020
• Telecoms Infrastructure Blog: Top 5 Posts for 2020 

Top 10 Posts for 2020 and Top 5 Videos

Here are the posts, from most popular to the tenth most popular, in descending order of popularity 

1. 5G Dynamic Spectrum Sharing (DSS), May 2020

2. EPS Fallback in 5G Standalone Deployments, Feb 2020

3. How MOCN RAN-Sharing Works, Jan 2020

4. Prof. Andy Sutton: Backhauling the 5G Experience, Jan 2020

5. Key Technology Aspects of 5G Security by Rohde & Schwarz, July 2020

6. Positioning Techniques for 5G NR in 3GPP Release-16, Oct 2020

7. 5G Private and Non-Public Network (NPN), March 2020

8. A Look into 5G Virtual/Open RAN - Part 1, March 2020

9. Interfacing HSS and UDM in 5GS with UDICOM (a.k.a NU1 / Nhss), Sep 2020

10. NTT Docomo's Vision on 5G Evolution and 6G, Jan 2020

There was another post, in the top 5 but I have listed it below. It was an announcement about the Free 5G Training site we launched early this year.

Bonus post*: Free 5G Training, Jan 2020

In addition to the above, we have a very popular and active YouTube channel, here are the top 5 videos that we posted in 2020. 

1. Advanced: Private Networks & 5G Non-Public Networks

2. Intermediate: Vehicle to Everything (V2X) Introduction

3. Beginners: UICC & SIM

4. Part 6: Standalone and Non-Standalone 5G - 5G for Absolute Beginners

5. Beginners: Industry 4.0 & 5G

Related Posts:

• Connectivity Technology Blog: Top 5 Posts for 2020
• Operator Watch Blog: Top 5 Posts for 2020
• Telecoms Infrastructure Blog: Top 5 Posts for 2020 
• The 3G4G Blog: Top 10 posts for 2019
• The 3G4G Blog: Top 10 posts for 2018
• The 3G4G Blog: Top 10 posts for 2017 and some other 3G4G info 

Challenges and Future Perspectives of Industrial 5G

Andreas Mueller, Head of communication and network technology at Bosch Corporate Research and Chair of 5G ACIA recently spoke at 'What Next for Wireless Infrastructure Summit' by TelecomTV about Industrial 5G. The following is paraphrased from his presentation 'Industrial 5G: Remaining challenges and future perspectives' which is embedded below: 

5G has the potential to become the central nervous system of the factory of the future, enabling unprecedented levels of flexibility, efficiency, productivity and also ease of use.  At the same time it's also a very special application domain so in many cases there are very demanding QoS requirements. 

Industrial applications have multi-faceted requirements where one case may require very low latencies and high reliabilities for instance, while for others we may need very high data rates (for example HD cameras). There is no single use case with a single set of requirements but many different use cases with very diverse requirements which also have to be supported in many cases at the very same time. 

As we need only a local network with local connectivity, this performance is required only in a very controlled environment; inside a factory, inside a plant. This allows for specific optimizations and makes certain things easier but we also always have brownfields deployments in many cases that means we have to live what we have in place today so that's typically wired communication in some cases it's wi-fi and similar wireless solutions and we have to be able to smoothly integrate a 5G network into this existing infrastructure

The developments towards Industrial 5G started about three years ago i would say and in the meantime it really has become a hot topic everybody is talking about industrial 5G. It has become a focused topic in standardization in 3GPP and some key capabilities already have been standardized which have been briefly outlined in the presentation. 

Good progress has also been made in the ecosystem development so we've established the 5G Alliance for Connected Industries and Automation two and a half years ago which serves as a global forum for bringing all relevant stakeholders together and for driving industrial 5G and we have 76 members today which includes major players from the telco industry but also from the industrial domain and also of course some universities and so on. We have seen the advent of non-public networks (NPN) so for the first time it will be possible for a manufacturers to deploy and operate such non-public networks inside a factory which are to some extent decoupled from the public networks.

If we look at the standardization timeline this is what you get. The first version of 5G release 15 of 3GPP was approved mid last year and it still had a very strong focus on consumer application and enhanced mobile broadband. If you buy 5G today, this is what you get then. Release-16 has for the first time had a very strong focus on industrial applications this has been approved in June this year and it includes features like ultra reliable low latency communication, non-public networks, time-sensitive communication. It means support for time-sensitive networking 5G and also native layer 2 transport so that we don't necessarily need internet protocol but we can directly transmit ethernet frames over a 5G network which again is very important especially for the industrial domain.

Last week’s TSG Plenary meetings have approved a firm Release-17 timeline. https://t.co/DoHTBQo5ZV pic.twitter.com/MSW8nnZgEA

— 3GPP Live (@3GPPLive) December 14, 2020

Release 17 is currently underway and it will come along with several enhancements of these features. It also has a stronger focus on positioning which is again very important in manufacturing because knowing where things are is a very valuable information and it will be in this new transmission mode called NR RedCap which is somewhere somewhere in between this high-end mobile broadband mode and also this low-end a massive machine type communication and this might be especially suitable for industrial sensors for example and then of course the journey will continue with Release 18 which is still being defined but with a high probability i would say it will more focus on massive iot applications that means tiny little sensors for example which have to be connected using very low energy and low costs and not just the natural next step.

5G NR-RedCap (New Radio Reduced Capability Device) is now the official name of NR-Light (or NR-Lite before that). Assuming this was also being discussed in 3GPP as NR-RedCom (New Radio Reduced Complexity Device) earlier. Can anyone confirm 🤔 pic.twitter.com/WZUaJSgQ8s

— 3G4G (@3g4gUK) December 20, 2020

So many things have been done already towards supporting these industrial applications but if you look at factories today there are only very few of them which already make use of 5g and that's because there are still some challenges to be overcome some of them are listed here first of all having the features in the standard is nice but they also have to be implemented in the chipsets and infrastructure components and that still say test takes some time especially if we consider that really 16 is the first release which really has many of the features that make a difference to the industrial domain

Here is a list of the features that can be prioritised for future 5G releases or even for 6G. As Release-17 has just been delayed slightly, quite possible that some of the features expected in 5G may get pushed on to Beyond 5G and even 6G.

Here is the embedded talk

An interview by Dr. Andreas Müller regarding Bosch 5G activities is available here (in German)

Related Posts:

• The 3G4G Blog: 5G and Industry 4.0
• The 3G4G Blog: What is Industrial IoT (IIoT) and how is it different from IoT?
• Free 6G Training: 6G Localization and Sensing – Technologies, Opportunities and Challenges
• The 3G4G Blog - Ultra Reliability: 5x9s (99.999%) in 3GPP Release-15 vs 6x9s (99.9999%) in 3GPP Release-16
• The 3G4G Blog: 5G Private and Non-Public Network (NPN)
• The 3G4G Blog: Real-life 5G Use Cases for Verticals from China
• The 3G4G Blog: Positioning Techniques for 5G NR in 3GPP Release-16 
• 3G4G: Introduction to NR-Light a.k.a. NR-Lite 

Conditional Handover (Rel. 16) Explained

Although a couple of SON mobility robustness features have been introduced in LTE radio networks it is still a common problem in some network areas that a high number of handover failures leads to higher drop rates and large numbers of RRC Re-Establishments.

Often these problems occur due to quickly changing radio conditions in the handover preparation phase or after handover execution attempt. 

SON algorithms cannot cope with these dynamic changes of the environment, but improvement is possible if the UE itself is enabled to constantly monitor the radio quality during the handover procedure and finally select the best possible target cell from a list of candidate neighbors. This new feature defined in 3GPP Release 16 for both, NG RAN (5G SA NR) as well as E-UTRAN (LTE), is called "Conditional Handover". The figure below illustrates how it works.

(click on the picture to enlarge)

Step 1 is the RRC Measurement Report indicating that handover to a neighbor cell is required. However, this message contains a list of candidate neighbor cells.

In the figure it is assumed that each of these candidate cells is controlled by a different gNB. Hence, 3 XnAP Handover Preparation procedures are performed and each potential target gNB allocates radio resources for the UE and provides a handover command (NR RRC Reconfiguration message) that is sent back to the source gNB (step 2).

In step 3 the source gNB builds the conditional handover command, which is a NR RRC Reconfiguration message that contains a list of conditional reconfiguration options plus additional RRC measurement configurations that enable the UE to find out which of the possible target cells is the best fit. 

In step 4 the UE makes its handover decision and moves to the cell controlled by target gNB 1.

Here it sends in step 5 the NR RRC Reconfiguration Complete message. 

The target gNB 1 detects the handover completion based on the reception of the NR RRC Reconfiguration Complete message, performs NGAP Path Switch procedure (not shown in figure) and triggers the release of the UE context in source gNB on behalf of sending the XnAP UE Context Release message (step 6).

With this information the source gNB also detects the successful handover completion and orders in step 7 the release of the radio resources provided by target gNB 2 and 3 to which it sends the new XnAP Conditional Handover Cancel message.

As mentioned before the conditional handover is also possible for LTE radio connections. In this case X2AP is used instead of XnAP and LTE RRC instead of NR RRC.

The conditional handover can be performed for all kind of intra-eNB/gNB handover and X2/Xn handover. However, S1/N2 (NG-C) conditional handover is not allowed.