Monday, 16 December 2019

5G Integrated Access and Backhaul (IAB) Enhancements in Rel-17


It's been a while since I last wrote about IAB on this blog here. At that time 3GPP Release-16 was being discussed. Since then things have moved on. While Release-16 is being prepared for final release soon, Release-17 study and work items have just been agreed upon.

IAB is included as part of Rel-16 but there isn't a comprehensive document or presentation easily available to details all that it will contain. Similarly the enhancements for Release-17 are available only superficially. Qualcomm is well known for making some really excellent presentations available on 5G. One of their presentations from January (here) has some details on IAB (pg. 32 - 35). There was also an excellent presentation by Navid Abedini, Qualcomm from IEEE Sarnoff Symposium, 2019 which is embedded at the end.


In a 3GPP RAN#84 discussion document RP-191181, Samsung has provided a comprehensive summary of what is being done as part of Rel-16 and what did not make in that:
  • Rel-16 IAB aims at basic operations
    • Architecture and protocol design
    • IAB integration procedure 
    • Routing, BAP and BH configuration
    • CP and UP data transmission  via IAB
    • Topology support: 
      • Spanning Tree (ST) and Directed acyclic graph (DAG) 
      • Intra-Donor adaptation is prioritized
  • The following cannot  be supported in Rel-16
    • Mobile IAB
    • Topology support: Mesh
  • Some functionalities in Rel-16 may not be completed due to time constrains e.g. 
    • Topology adaptation between IAB donors
    • Mechanisms for efficient control signaling transmission
Ericsson also provides a good summary in RP-190971 regarding Release 16 IAB and Rel-17 enhancements:
  • IAB Rel-16 provide basic support for multi-hop and multi-path relaying. 
  • The solution supports 
    • QoS prioritization of traffic on the backhaul link
    • Flexible resource usage between access and backhaul
    • Topology adaptivity in case link failure
  • In Rel-17 it would be possible to further evolve the IAB solution targeting increased efficiency and support for new use cases


Meanwhile in the recently concluded RAN#86, AT&T provided a good detailed summary on what enhancements are required for IAB as part of Rel-17 in RP-192709
  • Duplexing enhancements
    • Multiplexing beyond TDM (FDM/SDM/multi-panel Tx/Rx) including multi-parent scenarios, case 6/7 timing alignment, power control/CLI optimizations
  • Topology enhancements
    • Mobile IAB: CP/UP split + Group mobility 
    • Inter-CU topology adaptation
    • Mesh-connectivity between IAB nodes for local control/user plane routing
  • User plane enhancements
    • Multi-hop scheduling enhancement – exchange of benefit metric between IAB nodes to enable radio-aware multi-hop scheduling to improve throughput performance
  • Network Coding
    • Study benefits compared to duplication over redundant backhaul routes

We will have to wait and see what makes it into the enhancements and what don't. Meanwhile here is a video from Navid Abedini, Qualcomm from IEEE Sarnoff Symposium, 2019
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Monday, 9 December 2019

5G Evolution with Matthew Baker, Nokia


I wrote a summary of CW (Cambridge Wireless) TEC conference here a couple of months back. The last session was on "Getting ready for Beyond-5G Era". Matthew Baker, Head of Radio Physical Layer & Co-existence Standardization, Nokia Bell Labs was one of the speakers. His talk provided a summary of 3GPP Rel-15 and then gave a nice and short summary of all the interesting things coming in Rel-16 and being planned for Rel-17. The slides from his presentation is embedded below:



Nokia also created a short video where Matthew talks about these new features. It's embedded below:



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Wednesday, 4 December 2019

Challenges of 5G Inter-Node Handovers

In all mobile communication networks handovers are the most complex signaling procedures, because multiple network elements (or network functions) are involved. Thus, it is logical that dual connectivity with two different base stations contributing to the radio connection simultaneously are even more complicated. And in EN-DC these two base stations are often covering different footprints using different carrier frequencies.This leads to a situation where we have more options for performing a handover in detail compared with plain LTE handover scenarios before.

The two signaling scenarios presented below illustrate in which different ways a change of the LTE master eNodeB can be performed during an ongoing EN-DC radio connection by using the X2 interface. In a very similar way it is also possible to perform S1 handover from old to new MeNB.

The pros and cons of these options have been discussed already by Martin Sauter in his Wireless Moves blog.

Inter-MeNB Handover without 5G Inter-Site Anchor

Figure 1 shows the easiest way of handing over the signaling connection from one MeNB to another one. Here it is up to the new MeNB to decide if and how the 5G part of the radio connection is continued.

Figure 1: X2 Handoverof EN-DC connection without 5G inter-site anchor

The handover is triggered when the UE sends a RRC Measurement Report (step 1) indicating that a stronger 4G cell than the currently used primary cell was measured. From its neighbor list the current MeNB detects that this better cell belongs to a neighbor eNB.

To provide both, the the Master Cell Group (MCG) and Secondary Cell Group (SCG) parameters to this neighbor eNB the old MeNB queries the SCG configuration parameters from the old SgNB by performing the X2AP SgNB Modification procedure (step 2+3).

Then it sends the X2AP Handover Request message to the target MeNB (step 4) including all information necessary to continue the 5G radio link in case the target MeNB decides to go for this option.

However, what comes back from the target MeNB is a plain LTE handover command (LTE RRC Connection Reconfiguration message [step 6]) embedded in the X2AP Handover Request Acknowledge message (step 5).

Due to this the old MeNB releases all 5G resources and the UE context in the SgNB (steps 7 + 10).

After the UE  successfully connected via radio interface with the target cell in the new MeNB the S1AP Path Switch procedure is executed to re-route the GTP/IP-Tunnels on S1-U (step 8) and releases the X2 UE context in the old MeNB (step 9)

The new MeNB then waits for a new inter-RAT measurement event B1 (step 11) before starting a new SgNB addition procedure (step 12).  Once the SgNB addition is successfully completed including all necessary reconfigurations/modifications on RRC and S1 the payload transmission over 5G resources is continued.

Inter-MeNB Handover with 5G Inter-Site Anchor

Now figure 2 shows what happens when the new MeNB decides to keep the existing UE context in the SgNB while the RRC measurement results and parameters are identical with what was presented above. 
Figure 2: X2 Handoverof EN-DC connection with 5G inter-site anchor

The difference in the call flow starts at step 5 when the new MeNB after receiving the X2AP Handover Request (step 4) starts the X2AP SgNB Addition procedure towards the SgNB (old = new!). The SgNB-UE-X2AP-ID earlier requested in step 2+3 acts as the reference number for the existing context that is going to be continued.

After adding the SgNB UE context successfully the new MeNB sends the X2AP Handover Request Acknowledge message including an UE Context Kept = "true" flag and the Handover Command (step 8).

After the UE successfully connected to the target cell of the new MeNB the S1AP Path Switch procedure is performed and the temporary X2 UE context between old and new MeNB is released (step 10).

The big advantage of handling the handover in this way: The duration of the interruption of the payload transmission over 5G radio resources is minimalized and subscriber experience is significantly better compared to the scenario in figure 1.

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Monday, 2 December 2019

Guest Post: Exploring Network Convergence of Mobile, Broadband and Wi-Fi

This is a guest post by Ben Toner, Founder and Director, Numerous Networks


Are multiple networks better than one?

How many articles have you read with a title similar to "Which technology is better, 5G or Wi-Fi6?" If, like me, you regularly use Wi-Fi and cellular (I still use 4G though) then you might find it hard to take sides.

Enter Network Convergence - the concept of bringing multiple networks together to get the best of them all. Imagine, as an end user, not having to decide which network to use but instead feeling satisfied that your data was traversing the best combination of networks at that moment in time.

Imagine a business traveler being connected to Wi-Fi which is slow or busy while trying to take that all important conference call while sitting in an airport. Because you are roaming you want to use that Wi-Fi but you do not want to compromise the video call quality. If your network and device could work together to use just enough cellular data to supplement the slow Wi-Fi so that you stayed within your daily roaming quota but never lost a moment in the video call - then you would probably be very happy with that service. Better still, as you start walking off, if the call transitioned from Wi-Fi to cellular with no dropouts or hangup then you might be delighted!

Earlier I underlined best because that in itself is somewhat complicated.  The example above is easy to desribe but quite hard for to achieve within a framework where all possible scenarios are handled that well, for every user. The common questions which need to be factored into any such choice are:
  • What do I as the end user want? 
  • What performance can each network deliver. 
  • How important is the transfer of content at that time and 
  • How much am I willing to pay for it (how many MB of my data plan am I willing to use?). 

This is one of the challenges that we cannot easily solve today, but technology is being developed to help in that process. The operators and device vendors are working within standardisation to develop technology which can provide such a converged service. However at this time there is still a rules mechanism behind it all which does not really describe how user input and preference is going to be captured.

In the last 10 years I have witnessed many battles within service providers when deciding what "one size fits all" service to offer everyone when deciding how to make service provider Wi-Fi available to their customers; all fuelled by my points above.

A lot of concepts are well designed and somewhat mature but deciding exactly what will be implemented in standards is currently ongoing.

In the following slides and video I introduce this whole concept of Network Convergence. The following content introduces the concept and then takes a detailed look at the ATSSS; technology being defined in 3GPP. I also have highlighted the technologoies you can get hold of today to try out network convergence.

I encourage you all to download the example technologies and try convergence for yourself. I'm eager to hear opinions of what technologies work best for each of you. And better still, what is not being provided which you think should be...

Looking forward to your feedback and answering your questions...





Ben Toner
Founder and Director, Numerous Networks


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Wednesday, 27 November 2019

Private 4G / 5G Cellular Networks and Bring Your Own Spectrum


With 4G maturing, private cellular networks are finally getting the attention that they deserve and has been promised for quite a while. In a Industry Analyst event, Nokia announced that they are running 120+ private networks including transportation, Energy, Public sector, Smart cities, manufacturing and logistics, etc. (tweet below). The Enterprise Business division is now accounting for 5% of the revenue.
Ray Le Maistre, Editor-in-Chief at Light Reading, in an opinion on Telecoms.com pointed out:

One of the more immediate revenue stream opportunities right now is wireless private networks, and the good news is that this opportunity doesn’t require 5G. Instead, the potential looks set to be enhanced by the availability of a full set of 5G standards (including the yet-to-be concluded core network specs) and the maturity of associated technology.

 In the meantime, 4G/LTE has already been the cellular foundation for an increasingly thriving wireless private networks sector that, according to ABI Research, will be worth $16.3 billion by 2025

 Another market sizing prediction, this time by SNS Telecom & IT, pitches annual spending on private 4G and 5G networks at $4.7 billion by the end of 2020 and almost $8 billion by 2023. 

 However this plays out, there’s clear anticipation of growing investment. What’s particularly interesting, though, is which organizations might pocket that investment. That’s because enterprises and/or organizations looking to benefit from having a private wireless network have a number of options once they decide to move ahead with a private network – here are three permutations that look most likely to me:
  1. Build and run it themselves – technology vendors get some sales in this instance
  2. Outsource the network planning, construction and possibly even the day-to-day. management of the network to a systems integrator (SI) – the SI and some vendors get the spoils. It’s possible here, of course, that the SI could be a technology vendor.
  3. Outsource to a mobile network operator – the operator and some vendors will get some greenbacks.
For sure there will be other permutations, but it shows how many different parts of the ecosystem have some skin in the game, which is what makes this sector so interesting.

 What’s also interesting, of course, is what the enterprises do with their private networks: Does it enhance operations? Help reduce costs? Create new business opportunities? All of the above?

 Let’s not forget the role of the regulators in all of this. In the US the private wireless sector has been given a shot in the arm by the availability of CBRS (Citizens Broadband Radio Service) shared spectrum in the currently unlicensed 3.5 GHz band: This has given rise to numerous trials and deployments in locations such as sports stadiums, Times Square and even prisons.

 In Germany, the regulator has set aside 100MHz of 5G spectrum for private, industrial networks has caused a storm and even led to accusations from the mobile operators that the move ramped up the cost of licenses in the spectrum auction held earlier this year.

 In the UK, Ofcom is making spectrum available in four bands:
  • the 1800 MHz and 2300 MHz shared spectrum bands, which are currently used for mobile services;
  • the 3.8-4.2 GHz band, which supports 5G services, and
  • the 26 GHz band, which has also been identified as one of the main bands for 5G in the future.
Slide shared by Mansoor Hanif, CTO, Ofcom at TIP Summit 2019

 The process to enable companies and organizations (Ofcom has identified manufacturers, business parks, holiday/theme parks and farms as potential users) in the UK to apply for spectrum will go live before the end of this year, with Ofcom believing that thousands of private networks could be up and running in the coming years.

Dean Bubley from Disruptive Analysis recently spoke about BYOSpectrum – Why private cellular is a game-changer at TAD Summit. The talk is embedded below and is definitely worth listening:



TelecomPaper reported:

The German Federal Ministry for Economic Affairs and Energy said that companies can start to apply to use 5G frequencies in the 3.7-3.8 GHz range on industrial campuses. Local frequencies enable firms to build their own private networks, rather than rely on telecommunications providers to build networks. 

 The Automotive Industry Association (VDA) and other industry associations including the VCI, VDMA and ZVEI have welcomed the allocation of frequencies for industrial campuses. According to VDA, several dozen companies have already registered their interest in such frequencies with the Federal Network Agency. 

 The firms believe that 5G can replace existing networks, including WLAN, provide improved coverage of entire company premises, enable full control over company data and reduce disruption to public mobile networks.

 The spectrum licences will be allocated based on the applicant's geographic footprint and use of a certain area. Prices also take account the area covered by the network, as well as the amount of bandwidth used and duration of the licence.

The formula for the prices is very interesting as shown in the tweet below



In Japan, NTT Docomo is working in co-operation with industry partners to help them to create their own private 5G networks. More announcements on this are expected at MWC next year.



Finally, I am running an Introduction to Private 4G /5G Networks Workshop with Dean Bubley on 04 Feb 2020. If this is an area of interest, consider attending it.



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Friday, 22 November 2019

5G Call Drops in EN-DC: A Thread for Service Quality?

As explained in the post about EN-DC setup the addition of 5G NR radio resources to an ongoing LTE connection provides additional bandwidth for user plane data transmission. And it seems to be fair to say that at least in social media today 5G speed test results, especially throughput measurements, are treated as the benchmark for EN-DC service performance. Hence, it is also logical that a loss of the physical 5G radio link (5G drop) could have a serious impact on user experience.

I write "could", because as a matter of fact many 5G drops will not be recognized by subscribers using non-realtime services including HTTP streaming.

Due to the dual connectivity of LTE Master eNodeB (MeNB) and Secondary gNodeB (SgNB) the signaling trigger points indicating a 5G drop are also a bit more complex compared to what we know from LTE. Indeed, both network nodes are able to release 5G radio resources abnormally using three different X2AP message flow scenarios as shown in figure 1.

Figure 1: Three Basic Signaling Flows for Abnormal Release of 5G Radio Resources

Which of these individual message flows will be found in the trace data depends on which of the two base stations is the first one that detects a problem on the 5G radio link.

A particular case that is seen quite often in live networks is illustrated in figure 2.

Figure 2: 5G Drop due to SGC Failure in UE

Here the trigger is a LTE RRC SCG Failure Information NR message sent by the UE to the MeNB. Thus, the MeNB requests the release of 5G radio resources, which is acknowledged and executed by the SgNB.

In addition (not show in the figures) also the GTP/IP-Tunnel for user plane transport between S-GW and gNB is released by the MeNB after successful completion of the X2AP SgNB Release procedure.

For the UE the 5G drop is not as serious as a drop of the LTE radio connection would be. It is just a fallback on plain LTE, so to say. And after the switching the GTP/IP-Tunnel back to a downlink endpoint at the eNB 4G payload transmission continues.

The longer the overall duration of the radio connection the higher is the risk that the 5G radio resources are lost during an EN-DC call. One of my favorite cases is a subscriber with a radio connection that last a bit more than two and a half hours - see figure 3.

Figure 3: Location Session Record of a Single Subscriber indicating a total number 340 SgNB Drops over 2:33 Hours

Thanks to the smart algorithms of NETSCOUT's TrueCall geolocation engine there is high confidence that she or he sits in an indoor environment, but is served by an outdoor 5G cell. Thus, the penetration loss of the 5G signal is significant. Due to the higher frequency the path loss has also higher impact on the 5G than on the 4G radio signal. This seems to be the main reason why the 5G radio link drops as often as 340 times, which leads to an overall 5G (SgNB) Drop Rate of 83% for this connection.

However, the impact on the subscriber experience might not be a serious one as a different KPI, the 5G EN-DC Duration Rate indicates. According to the Duration Rate 99.99% of all the time 5G radio resources have been available for the subscriber. This is possible, because as also shown in figure 2 within a relatively short time new 5G radio resources are allocated again to this connection. Even if the subscriber is watching e.g. a Netflix video the buffering of already downloaded data on the end user device should be sufficient to conceal the short interruption of the data transfer over 5G resources.

With rising amount of EN-DC traffic it might be rather problematic for the network to handle the additional signaling load originating from the frequent 5G additions and releases. In extreme cases this may even lead to congestion due to CPU overload in RAN nodes or virtual network functions.

For realtime services like Voice over New Radio (VoNR) the entire situation changes. Here even short interruptions of the user plane radio transmission can be perceived by subscribers so that the above discussed 5G Duration Rate KPI will become insufficient to estimate the service quality. Hence, this will drive the demand for a fully integrated view of 5G RAN and Core KPIs covering both, signaling and application quality. 
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Tuesday, 19 November 2019

Cell-free Massive MIMO and Radio Stripes


I wrote about "Distributed Massive MIMO using Ericsson Radio Stripes" after MWC 2019 here. I found it a very interesting concept and it will certainly take a few years before it becomes a reality.

Emil Björnson, Associate Professor at Linköping University have produced couple of videos on this topic. I am embedding both of them below for anyone who may be interested.

"A New Look at Cell-Free Massive MIMO" - based on technical paper from PIMRC 2019 on how to design Cell-free Massive MIMO systems that are both scalable and achieve high performance.



Worth noting the following about this video (based on video comments):
  • There are some minor issues with the sudio
  • Cell-free Massive MIMO is particularly for stadiums, streets, and places with many users or where it is hard to provide sufficient network quality with other methods.
  • This concept is still 4-5 years away from being ready to be practically deployed. It should be ready for later part of 5G, probably 5.5G

"Reinventing the Wireless Network Architecture Towards 6G: Cell-free Massive MIMO and Radio Stripes" looks at the motivation behind Cell-free Massive MIMO and how it can be implemented in 6G using radio stripes.



Worth noting the following on this video (based on video comments):

  • It may be possible that multiple frequency bands can be handled in the same radio stripe. If it is found to be possible then every other antenna  processing unit could manage a different band.
  • In principle, you can make the stripe as long as you need. But you probably need to divide it into segments since the power is supplied from one end of a stripe and it will only reach a limited distance (roughly up to 1 km). There are many implementation ideas and it remains to be seen what works out well in practice.

I am looking forward to see it work as it can solve coverage issues in many tricky scenarios.

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Thursday, 7 November 2019

Introduction to 5G ATSSS - Access Traffic Steering, Switching and Splitting


Last month we made a short tutorial on 5G and Fixed-Mobile Convergence (FMC). One of the features covered in that was ATSSS. It deserved a bit more detail so we made a short tutorial on this feature.

Access Traffic Steering, Switching and Splitting or ATSSS for short is being standardized as part of 3GPP Rel-16 and allows traffic steering across multiple accesses at a finer granularities than a PDU session.  It is an optional feature both on the UE and the 5GC network. ATSSS introduces the notion of Multi Access PDU session, a PDU session for which the data traffic can be served over one or more concurrent accesses (3GPP access, trusted non-3GPP access and untrusted non-3GPP access). The simplest way to visualize it is as shown below:


The presentation and video is embedded below:







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Sunday, 27 October 2019

R&S Webinar on LTE-A Pro and evolution to 5G


Rohde & Schwarz recently uploaded a webinar video on their YouTube channel. I found it really useful. It's embedded below.

Topics covered:

  • LTE-M / NB-IoT
    • feMTC
    • UE Category M2
    • OTDOA based positioning
  • UE Categories
  • Unlicensed Spectrum Overview
  • LTE in Unlicensed Spectrum
    • LWA, LWIP
    • LAA, eLAA
    • Wi-Fi
    • LBT
    • LWA mobility
  • Carrier Aggregation Enhancements
  • Multi-user superposition transmission (MUST)
  • Single cell - point to multipoint transmission (SC-PTM)
    • SC-PTM Channel Structure
    • SC-PTM Channel Flow
  • Massive MIMO
  • V2X Overview
    • eNB scheduling - transmission mode 3
    • Distributed scheduling - transmission mode 4
    • Direct communication
  • LTE Advanced Pro (Release 15)
    • Further NB-IoT Enhancements
    • Even further enhanced MTC - eMTC4 (Rel-15)



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Tuesday, 22 October 2019

From traditional RAN to Open RAN - O-RAN: Goals and Challenges


My Open RAN tutorial has recently gained popularity with recent announcements from Altiostar, Mavenir, Parallel Wireless, Telefonica and Vodafone. With TIP Summit in few weeks time, I am hoping for a lot more curious people to discover that blog post and video.

Olivier Simon, Director, Radio Innovation, Orange spoke about "O-RAN: Goals and Challenges" at Open Networking Summit Europe 2019. In his presentation, he explained how O-RAN will trigger more intelligence and openness in the RAN domain. He talked about which use cases will require this new architecture and why O-RAN is coming at the right time. Major architectural change are necessary in the next years in order to improve E2E latency and benefit from the flexibility of virtualized network functions. O-RAN will provide the right framework in order to perform this transformation in an open manner and keeping at the same time economies of scale thanks to a global adoption.


The presentation also touches on O-RAN Software Community. The O-RAN Alliance recently partnered with the Linux Foundation to establish the O-RAN-Software Community (O-RAN-SC), to provide that open source software application layer to the RAN. O-RAN-SC will foster development of an open source infrastructure platform for running 5G RAN solutions.

The key aspects of ORAN-SC are:
  • New Open Community focused on RAN Software in collaboration with O-RAN Alliance
  • Set up for collaboration across OPNFV, ONAP, Akraino and other Open Source projects

Here is the video of the conference embedded below:



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