Showing posts with label 5G. Show all posts
Showing posts with label 5G. Show all posts

Tuesday, 19 May 2020

5G Dynamic Spectrum Sharing (DSS)

5G Dynamic Spectrum Sharing is a hot topic. I have already been asked about multiple people for links on good resources / whitepapers. So here is what we liked, feel free to add anything else you found useful as part of comments.


Nokia has a nice high level overview of this topic which is available here. I really liked the decision tree as shown in the tweet above. I am going to quote a section here that is a great summary to decide if you want to dive deeper.

DSS in the physical layer
DSS allows CSPs to share resources dynamically between 4G and 5G in time and/or frequency domains, as shown on the left of Figure 3. It’s a simple idea in principle, but we also need to consider the detailed structure at the level of the resource block in order to understand the resource allocations for the control channels and reference signals. A single resource block is shown on the right side of Figure 3.

The 5G physical layer is designed to be so similar to 4G in 3GPP that DSS becomes feasible with the same subcarrier spacing and similar time domain structure. DSS is designed to be backwards compatible with all existing LTE devices. CSPs therefore need to maintain LTE cell reference signal (CRS) transmission. 5G transmission is designed around LTE CRS in an approach called CRS rate matching.

5G uses demodulation reference signals (DMRS), which are only transmitted together with 5G data and so minimize any impact on LTE capacity. If all LTE devices support Transmission Mode 9 (TM9), then the shared carrier has lower overheads because less CRS transmission is required. The control channel transmission and the data transmission can be selected dynamically between LTE and 5G, depending on the instantaneous capacity requirements.


The second resource is this Rohde & Schwarz webinar here. As can be seen in the tweet above, it provides nice detailed explanation.

Finally, we have a Comprehensive Deployment Guide to Dynamic Spectrum Sharing for 5G NR and 4G LTE Coexistence, which is a nice and detailed whitepaper from Mediatek. Quoting a small section from the WP for anyone not wanting to go too much in deep:

The DSS concept is based on the flexible design of NR physical layer. It uses the idea that NR signals are transmitted over unused LTE resources. With LTE, all the channels are statically assigned in the time-frequency domain, whereas the NR physical layer is extremely flexible for reference signals, data and control channels, thus allowing dynamic configurations that will minimize a chance of collision between the two technologies. 

One of the main concepts of DSS is that only 5G users are made aware of it, while the functionalities of the existing LTE devices remain unaffected (i.e. LTE protocols in connected or idle mode). Therefore, fitting the flexible physical layer design of NR around that of LTE is needed in order to deploy DSS on a shared spectrum. This paper discusses the various options of DSS implementation, including deployment challenges, possible impacts to data rates, and areas of possible improvements.

NR offers a scalable and flexible physical layer design depicted by various numerologies. There are different subcarrier spacing (SCS) for data channels and synchronization channels based on the band assigned. This flexibility brings even more complexity because it overlays the NR signals over LTE, which requires very tight coordination between gNB and eNB in order to provide reliable synchronization in radio scheduling.

The main foundation of DSS is to schedule NR users in the LTE subframes while ensuring no respective impact on LTE users in terms of essential channels, such as reference signals used for synchronization and downlink measurements. LTE Cell Reference Signals (CRS) is typically the main concept where DSS options are designated, as CRS have a fixed time-frequency resource assignment. The CRS resources layout can vary depending on the number of antenna ports. More CRS antenna ports leads to increased usage of Resource Elements (REs). CRS generates from 4.76% (1 antenna port) up to 14.29% (4 antenna ports) overhead in LTE resources. As CRS is the channel used for downlink measurements, avoiding possible collision with CRS is one of the foundations of the DSS options shown in figure 1. The other aspect of DSS design is to fit the 5G NR reference signals within the subframes in a way to avoid affecting NR downlink measurements and synchronization. For that, DSS considers the options shown in figure 1 to ensure NR reference signals such as Synchronization Signal Block (SSB) or Demodulation Reference Signal (DMRS) are placed in time-frequencies away from any collision with LTE signals.

MBSFN, option 1 in figure 1, stands for Multi-Broadcast Single-Frequency Network and is used in LTE for point-to-multipoint transmission such as eMBMS (Evolved Multimedia Broadcast Multicast Services). The general idea of MBSFN is that specific subframes within an LTE frame reserve the last 12 OFDM symbols of such subframe to be free from other LTE channel transmission. These symbols were originally intended to be used for broadcast services and are “muted” for data transmission in other LTE UE. Now this idea has been adjusted for use in a DSS concept, so that these reserved symbols are used for NR signals instead of eMBMS. While in general LTE PDCCH can occupy from 1 to 3 symbols (based on cell load), the first two OFDM symbols of such MBSFN subframe are used for LTE PDCCH, and DSS NR UE can use the third symbol. Using MBSFN is completely transparent to legacy LTE-only devices from 3GPP Release 9 onwards, as such LTE UE knows that these subframes are used for other purposes. In this sense this is the simplest way of deploying DSS. This method has disadvantages though. The main one is that if MBSFN subframes are used very frequently and it takes away resources from LTE users, heavily reducing LTE-only user throughput. Note that option 1 shown in figure 1 does not require LTE MBSFN Reference Signals to be used, because the MBSFN subframe is used to mute the subframe for DSS operation only, and LTE CRS shall only be transmitted in the non-MBSFN region (within the first two symbols) of the MBSFN subframe.

The two other options illustrated in figure 1 are dealing with non-MBSFN subframes that contain LTE reference signals. Option 2 is ‘mini-slot’ based; mini-slot scheduling is available in NR for URLLC applications that require extremely low latency. The symbols can be placed anywhere inside the NR slot. In respect to DSS, mini-slot operation just eliminates the usage of the symbols that contain LTE CRS and schedule only free ones for NR transmission. The basic limitation of this method comes from the concept itself. It is not very suitable for eMBB applications as too many resources are outside of NR scheduling. However it still can be utilized in some special cases like 30 kHz SSB insertion which will be described later in this paper.

Option 3 is based on CRS rate matching in non-MBSFN subframes, and it is expected to be the one most commonly used for NR data channels. In this option, the UE performs puncturing of REs used by LTE CRS so that the NR scheduler knows which REs are not available for NR data scheduling on PDSCH (Physical Downlink Shared Channel). The implementation of this option can be either Resource Block (RB)-level when the whole RB containing LTE CRS is taken out of NR scheduling, or RE-level where NR PDSCH scheduling avoids particular REs only. The end result of this method is that the scheduler will reduce the NR PDSCH transport block size as the number of REs available for scheduling become less in a slot.


Personally, I am not a big fan of DSS mainly because I think it is only useful in a very few scenarios. Also, it helps operators show a 5G logo but doesn't provide a 5G experience by itself. Nevertheless, it can come in handy for the coverage layer of 5G.


In one of the LinkedIn discussions (that I try and avoid mostly) somebody shared this above picture of Keysight Nemo DSS lab test results. As you can see there is quite a bit of overhead with DSS.

Thursday, 14 May 2020

A Look into 5G Virtual/Open RAN - Part 4: Intra-gNB DU Handover


In the previous posts of this series I described O-RAN interfaces and protocols, connection establishment and connection release procedures. Now it is time to look at handovers.

As mentioned in one of the earlier posts the gNB-CU CP will be in charge of controlling hundreds of gNB-DUs in a similar way like the 3G RNC was in charge of controlling hundreds of UMTS NodeBs. As a result the most common 5G SA intra-system handovers will be intra-gNB handovers. These handovers can further be classified into intra-gNB-DU handovers (inter- as well as intra-frequency) and inter-gNB-DU handovers.

Due to the virtualization of RAN network functions we will also find another form of switching transmission path, which is a change of the gNB-CU UP during the call without mobility of the UE. This scenario I will discuss later in a separate blog post.

Today I want to focus on the intra-gNB DU handover. Here the UE moves from one cell to another one within the same distributed unit as shown in the figure below.



A prerequisite is the successful establishment of a NR RRC connection and a F1AP UE Context between the gNB-DU and the gNB-CU CP.

The F1AP transports all RRC messages between these two entities. Indeed, it transports the PDCP blocks and the gNB-DU is not aware that these PDCP blocks contain RRC messages. However, for better illustration I have not shown the PDPC part in the ladder diagram.

What we see in step 1 is a NR RRC Reconfiguration message that contains RRC measurement configurations to be enabled on the UE side. A typical trigger event for intra-frequency handovers is the A3 event that is already known from LTE RRC.

Once the UE detects a better neighbor cell meeting the A3 criteria it sends a RRC Measurement Report to the gNB-CU CP (step 2).

In step 3 the gNB-CU CP orders the gNB-DU to perform a F1AP UE Context Modification. The purpose is to allocate radio resources for the UE in the target cell and to prepare the cell change.

The gNB-DU replies with F1AP UE Context Modification Response. This messages contains the new C-RNTI and a large block of lower layer configuration parameters (e.g. for RLC and MAC layer) that need to be sent to the UE and thus, need to be transported to the gNB-CU CP before, because it is the only RAN function capable to communicate with the UE using the RRC protocol.

Hence, in step 5 we see another downlink RRC message transfer. This time it is used to transport the handover command towards the UE. The handover command is a NR RRC Reconfiguration message and it contains the new C-RNTI (new UE identity within the cell) as well as the physical cell ID of the target cell and the full set of lower layer configuration parameters previously provided by the gNB-DU.

When the gNB-CU CP receives the RRC Reconfiguration Complete message sent by the UE in step 6 the handover is successfully completed and the UE is now served by the cell with NR PCI 2.

As mentioned before there is neither XnAP (communication between two neighbor gNBs) nor NGAP (communication between gNB and AMF) involved in this handover procedure.

Monday, 11 May 2020

5G Remote Surgery and Telehealth Solutions


One of the most controversial 5G use cases is the remote surgery. In this post I want to quickly look at the history and what is possible. Before I go to that, here is a short summary video that I am embedding upfront.



As far as I can recall, Ericsson was the first vendor that started talking about remote surgery. This is a tweet from back in 2017.


Huawei didn't want to be far behind so they did one at MWC Shanghai in 2018. Their tweet with video is embedded below.


In January 2019, South China Morning Post (SCMP) showed a video of a remote surgery on an animal. While the video and the article didn't provide many details, I am assuming this was done by Huawei as detailed here. The video of the surgery below.



This was followed by Mobile World Congress 2019 demo where a doctor used 5G to direct surgery live from a stage at MWC to Hospital Clinic Barcelona over 3 miles away. The team of doctors was removing a cancerous tumor from a patient's colon. This video from that is embedded below.



Vodafone New Zealand had a silly remote surgery of a dog video but looks like they have removed it.  Nothing can beat this Telecom Italia ad embedded below.



There are some realistic use cases. One of them being that with 5G the number of cables / wires in a hospital can be reduced saving on the disinfection.
NTT Docomo showcased 5G Mobile SCOT (Smart Cyber Operating Theater) which is an Innovative solution to enable advanced medical treatment in diverse environments. You can read more details here.

There are lots of other things going on. Here is a short list:
  • April 2020: Because of Coronavirus COVID-19, NT Times has an article on Telemedicine Arrives in the U.K.: ‘10 Years of Change in One Week’ - even though this does not involve 5G, it just shows that we are moving in that direction.
  • February 2020: 5G-aided remote CT scans used to diagnose COVID-19 patients in China (link)
  • February 2020: Verizon teamed with Emory Healthcare to test new 5G use cases for the medical industry at the latter’s Innovation Hub in Atlanta, in a bid to discover how the technology can be used to improve patient care. The collaboration will explore applications including connected ambulances; remote physical therapy; medical imaging; and use of AR and VR for training. (link)
  • February 2020: Vodafone 5G Healthcare – Conference & Experience Day (link)
  • November 2019: TIM enables first live remote-surgery consultation using 5G immersive reality (link)
  • October 2019: Along with a hospital in Malaga, Telefónica has presented what it claims is the first expert assistance system for medical interventions that runs on 5G. (link and video)
  • September 2019: Mobile Future Forward 2019 - World's First Remote VR Surgery Demo conducted on Sept 4th, 2019 in Seattle by Chetan Sharma, James Youngquist, Evie Powell, Nissim Hadar, David Colmenares, and Gabe Jones. (link)

Finally, a nice video on Benefits of 5G for Healthcare Technology by T-Mobile



Related Posts:

Wednesday, 6 May 2020

Virve 2.0 - Finland's 4G/5G Public Safety Network

State Security Networks Group Finland (Erillisverkot) safeguards the Finnish society by offering authorities and critical operators engaged in critical infrastructure and services secure and reliable ICT services. Much like in the civilian world, communication between authorities includes transferring images and video material to an increasing degree, which results in ever-growing data transfer volumes and, subsequently, new kinds of demands for all communication networks. 


Virve is a means of ensuring communication and cooperation between authorities and other partners across organisational borders into the future. It also entails the introduction of a higher service standard, as the transfer to broadband, estimated to take place in 2022, will make it possible to transfer video material, images and data. This will mean that it will be possible to send video material in a reliable and secure way in the case of accidents, for example. The radio network Virve, based on Tetra technology, will reach the end of its lifecycle by the end of the 2020s. The current Virve network will be used simultaneously with the new Virve 2.0 network until, at least, 2025.


Erillisverkot will acquire the broadband Virve 2.0 radio access network as a service from Elisa and the core systems from Ericsson. Separate networks will ensure the continuity of critical communications and operational capability of public safety in all situations in the future.

I would assume this would be MOCN, similar to the UK deployment of ESN networks as shown here.

Virve 2.0 subcribers will use Elisa’s public radio network, which the operator is expanding to become Finland’s largest data and voice network.

About 80 million messages pass through the Virve system every week. Elisa is committed to increasing the coverage, capacity and verification of its mobile network to meet the requirements of Virve 2.0.

The new online services will provide support for critical communication between public authorities and other parties.

The addition of image, video, and other wireless broadband services alongside existing Virve services will enable a better and more up-to-date view of the day-to-day operations of authorities and other actors.

The IoT enables automatic monitoring of rescue personnel and mobile use of surveillance cameras and drones.

The Virve 2.0 radio network service will be in use from 2021 and will include the 4G and 5G technologies and the internet of things. The contract is for ten years.

Finally, a recent advert of Elisa explaining 5G to outside world



Further Study:
  • Erillisverkot: Obstacles for MCX Broadband and how to overcome them [PDF]
  • Erillisverkot: Virve Broadband Plans for the Future - Critical Communications Europe 2019 [PDF]
  • 5G-XCast Whitepaper: Rapidly Deployable Network System for Critical Communications in Remote Locations [PDF]
  • Erillisverkot: White paper - Virve 2.0 RFI Summary of responses [PDF]
  • Erillisverkot: Factsheet - What is Virve 2.0? [PDF]

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Monday, 20 April 2020

A Look at the same RRC Message in LTE and 5G Stand-alone Call Scenarios


Some weeks ago the differences in 4G LTE RRC (3GPP 36.331) and 5G NR RRC (3GPP 38.331) and how both protocols interact in EN-DC call scenarios have been discussed in another blog post.

Now I would like to share a visual comparison of the RRC (Connection) Setup Complete message as it is seen in LTE (including EN-DC) and 5G stand-alone (SA) radio connections.

From the figure below one can see that although this message fulfills the same purpose in both radio access technologies its particular contents may look quite differently.

Different variants of RRC (Connection) Setup Complete message in LTE and 5G stand-alone call scenarios

Sunday, 19 April 2020

SCF Releases 5G Functional API to Enable Open Small Cells Ecosystem


The Small Cell Forum (SCF) announced the publication of documents focused on stimulating a competitive ecosystem for vendors of 5G-era small cell hardware, software and equipment. The expanded set of specifications contained in these documents are:
According to the press release:

Expanding upon the 5G Physical Layer API specification, published in July 2019, the new specifications enable small cells to be constructed piece-by-piece using components from different vendors, in order to address the diverse mixture of 5G use cases relatively easily, a common goal to all of the specifications made by Small Cell Forum.

The new release also includes two completely new specifications, SCF223: 5G NR FAPI P19 FrontEnd Interface Specification and SCF224: Network Monitor Mode API for Small Cells.


According to Dr. Prabhakar Chitrapu, Chair of SCF, “FAPI helps Equipment Vendors to mix PHY & MAC Software from different suppliers via this open FAPI interface. So, FAPI is an 'internal' interface.”

“5G-nFAPI (network FAPI) is a 'network' interface and is between a Distributed Unit and Centralised Unit  of a Split RAN/Small Cell network solution. An open specification of this interface (nFAPI) will help network architects by allowing them to mix distributed and central units from different vendors.”

SCF nFAPI is enabling Open RAN ecosystem in its own way by allowing any small cell CU/DU (S-CU / S-DU) to connect to any small cell radio unit (S-RU)

Here is a video playlist from SCF that explains the new API's



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Sunday, 12 April 2020

Spectrum for 5G NR beyond 52.6 GHz

3GPP TR 38.807: Study on requirements for NR beyond 52.6 GHz has recently been revised with all the new information post WRC-19. There is a section that details potential use cases for this new spectrum.


Quoting from the specs:

The relatively underutilized millimeter-wave (mmWave) spectrum offers excellent opportunities to provide high speed data rate, low latency, and high capacity due to the enormous amount of available contiguous bandwidth. However, operation on bands in frequencies above 52.6GHz will be limited by the performance of devices, for example, poor power amplifier (PA) efficiency and larger phase noise impairment, the increased front-end insertion loss together with the low noise amplifier (LNA) and analog-to-digital converter (ADC) noise. In addition, bands in frequencies above 52.6GHz have high propagation and penetration losses challenge. Even so, various use cases are envisioned for NR operating in frequencies between 52.6GHz and 114.25GHz. Some of the use cases are illustrated in Figure 5.1-1 and following section provide detailed description of the uses cases. It should be noted that there is not a 1-to-1 mapping of use cases and wireless interfaces, e.g. Uu, slidelink, etc. Various wireless interfaces could be applicable to various uses cases described.

  • High data rate eMBB
  • Mobile data offloading
  • Short-range high-data rate D2D communications
  • Vertical industry factory application
  • Broadband distribution network
  • Integrated access backhaul (IAB)
  • Factory automation/Industrial IoT (IIoT)
  • Augmented reality/virtual reality headsets and other high-end wearables
  • Intelligent Transport Systems (ITS) and V2X
  • Data Center Inter-rack Connectivity
  • Smart grid automation
  • Radar/Positioning
  • Private Networks
  • Critical medical communication

There is quite detailed information for each use case in the document that I am not detailing here.


It also details information on the allocation within the frequency range 52.6 GHz to 116 GHz in ITU Radio Regulation (see table below). The column with comments contains (a subset of) information on protection requirements for incumbent services. For the full details please refer to the Radio Regulations.

Quoting from the specs:

Within the range 52.6 to 116 GHz, the frequency bands 66-76 GHz (including 66-71 and 71-76 GHz) and 81-86 GHz are being studied under WRC-19 Agenda Item 1.13 for potential IMT identification. Results of sharing and compatibility studies, potential technical and regulatory conditions are included in Draft CPM Report, and the final decisions are to be made in WRC-19 with respect to IMT identification or no IMT identification, along with the corresponding technical and regulatory conditions.

For 66-71 GHz, Studies were carried out for the ISS, MSS (Earth-to-space) indicating that sharing is feasible, with a need for separation distance in the order of few kilometers for the case of MSS (space-to-Earth). The need for studies addressing interference from IMT towards RNS is still under debate. Thus, final conclusions in the regulatory and technical conditions for this band cannot be drawn.

For 71-76 GHz, studies were carried out for the FS, RLS and FSS (space-to-Earth) indicating that sharing with FS and FSS is feasible. However, additional limits of the IMT BS and UE unwanted emissions is needed to protect RLS in the adjacent frequency band 76-81 GHz.

For 81-86 GHz, studies were carried out for the FS, FSS (Earth-to-space), RAS (in band and adjacent band), EESS (passive) and RLS. Studies are not needed for the SRS (passive), as this service is dealing with sensors around other planets and no interference issue is expected. Studies were also not carried out for the MSS. The results of those studies indicate that sharing with FS, FSS and RAS (in band and adjacent band) is feasible. Notice that additional limits of the IMT BS and UE unwanted emissions would be needed to ensure protection of EESS (passive) in the adjacent frequency band 76-81 GHz and RLS in the adjacent frequency band 86-82 GHz.

An interesting paper looking at Waveforms, Numerology, and Phase Noise Challenge for Mobile Communications Beyond 52.6 GHz is available here.


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Saturday, 4 April 2020

5G eXtended Reality (5G-XR) in 5G System (5GS)


We have been meaning to make a tutorial on augmented reality (AR), virtual reality (VR), mixed reality (MR) and extended reality (XR) for a while but we have only managed to do it. Embedded below is video and slides for the tutorial and also a playlist of different use cases on XR from around the world.

If you are not familiar with the 5G Service Based Architecture (SBA) and 5G Core (5GC), best to check this earlier tutorial before going further. A lot of comments are generally around Wi-Fi instead of 5G being used for indoors and we completely agree. 3GPP 5G architecture is designed to cater for any access in addition to 5G access. We have explained it here and here. This guest post also nicely explains Network Convergence of Mobile, Broadband and Wi-Fi.





XR use cases playlist



A lot of info on this topic is from Qualcomm, GSMA, 3GPP and 5G Americas whitepaper, all of them in the links in the slides.


Related Posts:

Wednesday, 1 April 2020

A Look into 5G Virtual/Open RAN - Part 2


In the first blog post of this series the different virtual RAN functions, interfaces and protocols have been discussed. Now it is time to have a look at a set of procedures that are required for the establishment of an UE connection in virtual 5G RAN.

The Big Picture

In 5G standalone RAN the crucial elements for user plane payload transport of an UE connection are  GTP/IP transport tunnels and a dedicated radio bearer on the radio interface.

When looking at the 5G RAN there are two of such tunnels: one on NG-U (aka N3) that is controlled by NGAP, and one on F1-U that is controlled by F1AP - see figure 1.

On behalf  of these two tunnels payload data can be transported between the 5G core network User Plane Function (UPF) to the gNB Distributed Unit (gNB-DU) and vice versa. For the transport over the 5G RAN fronthaul (realized e.g. as eCPRI) and across the radio interface a dedicated radio bearer (DRB) for the user plane transport must be configured by the gNB Central Unit for the Control Plane (gNB-CU CP).

As in LTE it is the RRC protocol that establishes this DRB. However, due to the virtualization the different protocol layers for the air interface are also distributed and the gNB-DU is in charge of all the lower layer PHY/RLC/MAC parameters (e.g the c-RNTI), while the gNB-CU CP assigns higher layer parameters of PDCP and RRC like the DRB-ID. Since only the gNB-CU CP can send downlink RRC messages to the UE the lower layer parameters from the DU first need to be sent in uplink direction to the gNB-CU CP.

Beside this parameter exchange the F1AP is also responsible for the tunnel management of the F1-U Tunnel.

The downlink tunnel endpoint information is provided by the gNB-DU using F1AP, but the uplink tunnel endpoint terminates at the gNB-CU UP and thus, its endpoint parameters are received by the gNB-CU CP when it exchanges information with the gNB-CU UP on behalf of the E1AP protocol.

Figure 1: Network Functions, Protocols and Parameters involved in Setup of User Plane Data Transmission Resources
(click on the image to see full size)
A similar situation we see for the NG-U tunnel that is controlled by NGAP, the protocol for communication between gNB-CU CP and the Access and Mobility Management Function (AMF) in the 5G core. Neither the gNB-CU CP nor hte AMF have direct access to the NG-U tunnel endpoints. Hence, E1AP is used again to transmit the downlink tunnel parameters to the gNB-CU CP while the uplink tunnel endpoint parameters must be sent by the UPF to the Session Management Function (SMF) using the Packet Forwarding Control Protocol (PFCP) and later by the SMF to the AMF over the service-based interface where the tunnel endpoint parameters are embedded in a JavaScript Object Notation (JSON) container.

By the way, JSON is a quite generic format for exchanging and storing different kind of data. Between the AMF and the SMF JSON is used to transport Non-Access Stratum Session Management messages (defined in 3GPP 24.501).

The Ladder Diagram

Having the Big Picture in mind it is now easier to look at the ladder diagram with the individual RAN messages for UE connection setup - shown in Figure 2.

It looks complicated, because the F1AP messages carry RRC plus NAS messages in uplink and downlink direction, but when understanding the underlying logic it is easy.

Figure 2: 5G VRAN Successful UE Connection Setup
(click on the image to see full size)

The very first step (in the figure: step 0) is the random access procedure executed on the MAC layer involving the UE and the gNB-DU.

After successful random access the UE sends the NR RRC Setup Request message. This is the Initial UL RRC Message transported by the F1AP from the gNB-DU to the gNB-CU CP. Actually the F1AP carries PDCP transport blocks and inside the PDCP the NR RRC messages are found, but to keep it simple I do not show the PDCP header in the ladder diagram.

Beside RRC Setup Request there are also some other initial NR RRC messages and RRC response messages possible (see step 1 and 2).

More RRC messages are transported over F1AP until the RRC Connection establishment is complete.

The NR RRC Setup Complete message also transports the initial NAS message and the reception of this message by the gNB-CU CP triggers the setup of a F1AP UE context. The concept of UE context management in F1AP is the same as in NGAP or - when looking back into the E-UTRAN - in S1AP.

The GTP/IP transport tunnel on F1-U is established during F1AP UE Context Setup assisted by E1AP Bearer Context Setup procedure that provides the necessary tunnel endpoint parameters.

In the same manner the NG-U tunnel is established by the NGAP Initial UE Context Setup procedure.

Additional NAS messages (especially for session management) and NR RRC Reconfiguration are exchanged to establish the end-to-end UE connection through the core network. And that's it.

Monday, 9 March 2020

How LTE RRC (4G) and NR RRC (5G) Protocols are used in Parallel in EN-DC (5G NSA)

Last week I had a fruitful discussion with a fellow blogger on the web, Martin Sauter (@mobilesociety) regarding a post in which he compared features of LTE RRC (3GPP 36.331) and NR RRC (3GPP 38.331).

It was Martin's impression that the NR RRC protocol is primarily designed to be used in the 5G standalone mode. However, as I wrote in a comment to his post the NR RRC protocol is already used in EN-DC radio connections.

The reason is that the UE must be informed about Hundreds of lower layer 5G parameters (physical, MAC, RLC) that are needed for the payload transmission over 5G frequencies. Indeed, when it comes to user plane data transmission the gNB works almost independently and the UE must handle LTE and NR radio links in parallel.So it has two different radio units (even if combined into a single radio chip set). This double-functionality is also one important reason why 5G smartphones are quite expensive. It is a lot of software and know-how that sits inside these chips.

How much surplus code is really necessary to enable 5G technology becomes visible when looking at trace data using a state-of-the-art protocol test and monitoring tool.

When reading the 3GPP 36.331 (LTE RRC) standard document one might have the impression that just a few 5G parameters have been incorporated into this protocol to support EN-DC connections.

However, when looking into the details of e.g. the nr-SecondaryCellGroupConfig-r15 it turns out that some this single information element is indeed a huge block of NR information (total size: 1111 Byte)

It is an entire 5G RRC message (rRCReconfiguration) that is piggybacked by the LTE rrcConnectionReconfiguration message, because in 5G non-standalone mode this is the only way to transmit 5G signaling information to the UE. And as highlighted in the upper part of the screenshot there are a couple of NR RRC messages transported in so-called NR-RRCContainers* during the EN-DC Establishment Procedure.

And what about 5G standalone mode? For this radio access technology the 3GPP 38.331 Rel. 15 protocol is suitable as well. Hence, some parameters mentioned in the standard paper will never be seen in EN-DC. A perfect example is S-NSSAI (Single Network Slice Selection Assistance Information), because network slicing requires the connection with a 5G core network as a prerequisite. 


(click on image for larger version)

* This is not an 3GPP term, but coined by the developers of the decoding engine.

Wednesday, 4 March 2020

A Look into 5G Virtual/Open RAN - Part 1

Although it is understood in general that virtualization and increasing complexity are inherent characteristics of 5G networks many people are surprised when they realize the significant differences of 5G RAN architecture and signaling procedures compared to what they know from LTE or UTRAN.

In this blog post series I want to highlight some details that are not immediately visible when reading the 3GPP specs.

Figure 1 shows a virtualized gNB and the protocols it uses to communicate with its internal entities as well as with the UE and peer entities in neighbor network elements/functions.

Figure 1: Virtual Network Functions and Protocols in 5G RAN
(click on the image to see full size)

The core of the whole thing is the gNB-Central Unit for the Control Plane (gNB-CU CP). This function communicates directly with the UE using the NR RRC protocol. It also "talks" to the 5G Core Network represented by the AMF using the NGAP, a protocol very similar to the S1AP known from E-UTRAN. Neighboring 5G base stations are contacted using the XnAP, neighboring eNBs can be reached by using X2AP.

The other virtual functions of the gNB are the Central Units for User Plane (gNB-CU UP) and the Distributed Units (gNB-DU). While the gNB-CU UP is responsible for handling the transport of payload the gNB-DUs deal with all the allocation of radio resources, especially the scheduling. As a result the lower layer radio interface protocols, especially RLC and MAC terminate in the gNB-DUs.

For the RAN monitoring tools and the 3GPP Minimization of Drive Test (MDT) feature this means that RRC and Logged Measurement Reports sent by UEs will be available at gN-CU CP while all uplink radio quality measurements and call-related user plane metrics is only available at the gNB-DU - see figure 3.

Figure 2: Distribution of un-correlated RAN measurement tasks among different gNB virtual functions
(click on the image to see full size) 

And today, there is no 3GPP-standardized procedure to correlate this measurement information collected by different virtual gNB functions.

The full impact of the 5G RAN virtualization becomes even more evident when looking at Figure 3. It shows a single gNB-CU CP in charge of controlling several gNB-CU UPs and gNB-DUs.

In a live network deployment a single gNB-CU CP will control hundreds of gNB-DUs and maybe several gNB-CU UPs. This is why it is misleading to compare the connectivity of a gNB-CU CP with that of a LTE eNB. Rather it could be compared with a UTRAN RNC controlling a similar number of 3G base stations.


Figure 3: 5G RAN Connectivity
(click on the image to see full size)

Looking back into figure 1 we see that the F1AP is used for communication between gNB-CU CP and its gNB-DUs while the E1AP is the protocol that connects the gNB-CU CP with surrounding gNB-CU UPs.

Call-related control plane procedures of F1AP and E1AP are very similar to what is known from NGAP. There is a UE context established between the gNB-CU CP and the gNB-DU. On F1-U a GTP tunnel is established for user plane transport. At the same time an E1 Bearer Context in gNB-CU CP and gNB-CU UP keeps track of the most relevant user plane transport parameters.

All in all for setting up a single subscriber connection in the virtualized 5G RAN there are significantly more signaling transactions necessary than in E-UTRAN. Figure 4 shows a practical example.

Figure 4: 5G RAN Call Trace in NETSCOUT Session Analyzer
(click on the image to see full size)
The volume and complexity of signaling information is increasing when the UE moves or is redirected to virtual functions within one gNB e.g. due to load balancing.

The next blog post of this series will dive deeper into details of such call scenarios.

Stay tuned...

Sunday, 1 March 2020

5G Private and Non-Public Network (NPN)


Private Networks have been around for a while and really took off after 4G was launched. This is due to the fact that the architecture was simplified due to the removal of CS core and also the advancements in silicon, storage, computation, etc. allowed creation of smaller and more efficient equipment that simplified private networks.

While private networks imply an isolated network for selected devices that are allowed to connect on to the network, Non-Public Networks are much broader in scope. Chief among them is the ability of certain devices to be capable of working on Private as well as Public Network or roaming between them.

I recently ran a workshop on 'Introduction to Private 4G & 5G Networks' with a well known Industry analyst Dean Bubley. One of the sections looked at the Network Architecture based on the 3GPP standards. This tutorial is a part of that particular section. Slides and video embedded below. There are also some interesting videos on YouTube that show how and why Private Networks are needed and some use cases. The playlist is embedded in the end.






Playlist of Private Networks Use Cases.



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Friday, 21 February 2020

EPS Fallback in 5G Standalone Deployments

It can be expected that later this year some mobile network operators will launch their initial 5G standalone (5G SA) deployments.

Nevertheless there will remain areas with temporary or permanently weak 5G NR coverage. One possible reason might be that even when 5G and LTE antennas are co-located, which means: mounted at the same remote radio head, the footprint of the 5G NR cell is significantly smaller when it uses a higher frequency band than LTE - see figure 1.

Figure 1: Smaller footprint of co-located 5G NR cell with higher frequency
Especially UEs making Voice over New Radio (VoNR) calls from the 5G cell edge have a high risk of experiencing bad call quality, in worst case a call drop. To prevent this the UE is forced  during the voice call setup towards 5G core network (5GC) to switch to a LTE/EPS connection where the radio conditions are better for the voice service.

The same procedure for which the term "EPS Fallback" was coined by 3GPP also applies when the UE is served by a 5G cell that is not configured/not optimized for VoNR calls or when the UE does not have all needed VoNR capabilities.

Figure 2: Two options for EPS fallback

When looking at the RAN there are two options for executing the EPS Fallback as shown in figure 2.

In option A the 5G radio connection is released after the initial call attempt is successfully finished and with the 5G RRC Release the UE is ordered to reselect to a 4G cell where a new radio connection is started for the VoLTE call. In this case the UE context is transferred from the AMF to the MME over the N26 interface. 3GPP seems to use also the term "RAT fallback" for this option.

Option B is to perform a 5G-4G inter-RAT handover. Here the session management and user plane tunnels in the core network are handed over from SMF/UPF to MME/S-GW in addition. This is realized with the GTPv2 Forward Relocation procedure on N26 interface.

All in all the EPS fallback is expected to cause an additional call setup delay of approximately 2 seconds.

For the inter-RAT handover case it is easy to detect from signaling information that an EPS fallback was triggered. In the source-eNodeB-to-target-eNodeB-transparent-container sent by the gNB to the eNB a boolean "IMS voice EPS fallback from 5G" indicator will be found that is set to "true". This container is named according to the receiving entity and will be carried by the NGAP Handover Preparation, GTPv2 Forward Relocation Request and the S1AP Handover Request messages.

If a redirection for Voice EPS Fallback is possible or not is indicated in the NGAP Initial Context Setup Request, Handover Request (during 5G intra-system handover) and Path Switch Request Acknowledge (after Xn handover) messages, all sent by the AMF to the gNB.

Further the NGAP protocol provides the cause value "IMS voice EPS fallback or RAT fallback triggered" in the PDU Session Resource Modify Response message indicating that a requested VoNR session cannot be established.  





Wednesday, 12 February 2020

AI your Slice to 5G Perfection


Back in November, The Enhanced Mobile Broadband Group in CW (Cambridge Wireless) held an event on 'Is automation essential in 5G?'. There were some thought provoking presentations and discussions but the one that stood out for me was by Dan Warren from Samsung


The slides are embedded below but I want to highlight these points:
  • Some Network Functions will be per slice whereas others will be multi-slice, the split may not be the same for every slice
  • Two slices that have the same 'per slice vs multi-slice' functional split may be different network hardware topologies
  • Enterprise customers will likely want a 'service' contract that has to be manifested as multiple slices of different types. 
  • Physical infrastructure is common to all slices
The last point is very important as people forget that there is a physical infrastructure that will generally be common across all slices.

Again, when you apply Artificial Intelligence (AI) to optimize the network functions, does it do it individually first and then end-to-end and if this is applied across all slices, each of which may have a different functionality, requirement, etc. How would it work in practice?




As Dan says in his tweet, "It is hard to implement AI to optimise a point solution without potentially degrading the things around it.  Constantly being pushed to a bigger picture view => more data => more complexity"

Let me know what you think.

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Friday, 31 January 2020

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


Prof. Andy Sutton has shared quite a few presentations and talks on this blog. His presentations from the annual 'The IET 5G Seminar' has made it to the top 10 for the last 3 years in a row. His talk from 2019, 2018 & 2017 is available for anyone interested.

The title of this year's conference was '5G 2020 - Unleashed'. The details are available here and the video of all the talks are here. As always, the slides and video is embedded below.

Slides



Video


There are a lot of bands that keep on getting mentioned, especially in relation to backhaul. Here is a summary of these bands that would come handy.



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Sunday, 26 January 2020

NTT Docomo's Vision on 5G Evolution and 6G


NTT Docomo released a whitepaper on 5G Evolution and 6G. In a press release they announced:

NTT DOCOMO has released a white paper on the topic of 6G, the sixth-generation mobile communications system that the company aims to launch on a commercial basis by 2030. It incorporates DOCOMO's views in the field of 5G evolution and 6G communications technology, areas that the company has been researching since 2018. The white paper summarizes the related technical concepts and the expected diverse use cases of evolving 5G and new 6G communication technologies, as well as the technology components and performance targets.

Mobile communication systems typically evolve into the next generation over a period of roughly ten years; DOCOMO commenced its research into the commercial launch of 5G in 2010. In 2018, the company conducted successful radio wave propagation experiments at frequencies of up to 150 GHz, levels which are expected to enable the much faster and larger-capacity communications that 6G will require.

DOCOMO will continue to enhance the ultra-high-speed, large-capacity, ultra-reliable, low-latency and massive device-connectivity capabilities of 5G technology. It will continue its research into and development of 5G evolution and 6G technology, aiming to realize technological advances including:

  • the achievement of a combination of advances in connectivity, including ultra-high speed, large capacity and low latency
  • the pioneering of new frequency bands, including terahertz frequencies
  • the expansion of communication coverage in the sky, at sea and in space
  • the provision of ultra-low-energy and ultra-low-cost communications
  • the ensuring of highly reliable communications
  • the capability of massive device-connectivity and sensing

Visitors to DOCOMO Open House 2020 will be able to view conceptual displays incorporating DOCOMO's vision of the evolution of 5G technologies into 6G. The event will take place in the Tokyo Big Sight exhibition complex in Tokyo on January 23 and 24. DOCOMO also plans to hold a panel session entitled "5G Evolution and 6G" on January 24.

Videos from Docomo Open House are embedded below, along with a previous talk by Takehiro Nakamura from 6G Summit.


6G has become a hot topic, especially after China announced back in November that they are working on 6G. We have some interesting tweets on 6G as well.

This one from Stefan Pongratz, Dell'Oro group shows the timeline for 5G, Pre-6G and 6G



This one provides a timeline all the way from Release 99 up till 21



Finally, here is a tweet highlighting the 6G research



Finally, the paper acknowledges the 5G challenges and focus areas for 5G evolution, before focusing on 6G.
The mmWave coverage and mobility needs improvement, while the downlink is able to provide very high data rates, the uplink is struggling to be better than 4G. Also, there are some very extreme requirements for industrial use cases, 5G has yet to prove that it can meet them.

Finally, here is another view from iDate Digiworld comparing 5G vs 6G in terms of performance, spectrum and network.



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