Showing posts with label LTE. Show all posts
Showing posts with label LTE. Show all posts

Wednesday 24 January 2024

UE Assistance Information in LTE and 5G

I have been asked about the UE Assistance Information (UAI) RRC message a few times before. Generally I have always pointed people back to the LTE/5G specifications but here is a concise video that the telecoms technology training company Mpirical have shared recently:

If you want to dig further into details then please see the RRC specifications: 36.331 for LTE and 38.331 for 5G. 

Over the years I have added quite a few short tutorials from Mpirical on this blog, do check them out below.

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Wednesday 13 September 2023

Private Networks Introductory Series

Private Networks has been a hot topic for a while now. We made a technical introductory video which has over 13K views while its slides have over 25K views. The Private Networks blog that officially started in April is now getting over 2K views a month. 

In addition, there are quite a few questions and enquiries that I receive on them on a regular basis. With this background, it makes sense to add these Introductory video series by Firecell in a post. Their 'Private Networks Tutorial Series' playlist, aiming to demystify private networks, is embedded below:

The playlist has five videos at the moment, hopefully they will add more:

  • Introduction to different kinds of mobile networks: public, private and hybrid networks
  • Different Names for Private Networks
  • Drivers and Enablers of Private Networks
  • Mobile Cellular vs Wi-Fi Private Networks
  • Architecture of Mobile Private Networks

I also like this post on different names for private networks.

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Thursday 3 August 2023

Tutorial: A Quick Introduction to 3GPP

We recently made a beginners tutorial explaining the need for The 3rd Generation Partnership Project (3GPP), its working, structure and provides useful pointers to explore further. The video and slides are embedded below.

You can download the slides from here.

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Wednesday 12 July 2023

Small Data Transmission (SDT) in LTE and 5G NR

One of the features that was introduced part of 5G NR 3GPP Release 17 is known as Small Data Transmission (SDT). When small amount of data, in case of an IoT device, needs to be sent, there is no need to establish data radio bearers. The information can be sent as part of signalling message. A similar approach is available in case of 4G LTE. 

Quoting from Ofinno whitepaper 'Small Data Transmission: PHY/MAC', 

The SDT in the 3GPP simply refers to data transmission in an inactive state. Specifically, the SDT is a transmission for a short data burst in a connectionless state where a device does not need to establish and teardown connections when small amounts of data need to be sent.

In the 3GPP standards, the inactive state had not supported data transmission until Release 15. The 3GPP standards basically allowed the data transmission when ciphering and integrity protection are achieved during the connection establishment procedure. Therefore, the data transmission can occur after the successful completion of the establishment procedure between the device and network.

The problem arises as a device stays in the connected state for a short period of time and subsequently releases the connection once the small size data is sent. Generally, the device needs to perform multiple transmissions and receptions of control signals to initiate and maintain the connection with a network. As a payload size of the data is relatively smaller compared with the amounts of the control signals, making a connection for the small data transmission becomes more of a concern for both the network and the device due to the control signaling overhead.

The 3GPP has developed the SDT procedure to enable data transmission in the inactive state over the existing LTE and NR standards. The device initiates the SDT procedure by transmitting an RRC request message (e.g., SDT request message) and data in parallel instead of transmitting the data after the RRC request message processed by a network. Additional transmission and/or reception are optional. The device performs this SDT procedure without transition to the connected state (i.e., without making a connection to the network).

The SDT enables for the network to accept data transmission without signaling intensive bearer establishment and authentication procedure required for the RRC connection establishment or resume procedure. For example, in the SDT procedure, the device needs only one immediate transmission of a transport block (TB) that contains data and RRC request message. Furthermore, the device does not need to perform procedures (e.g., radio link monitoring) defined in the connected state since the RRC state is kept as the inactive state. This results in improving the battery life of the device by avoiding control signaling unnecessary for transmission of small size data.

The principle of the SDT is very simple. The network configures radio resources beforehand for the data transmission in the inactive state. For example, if the conditions to use the configured radio resources satisfy, the device transmits data and the RRC request message together via the configured radio resources. In the 3GPP standards, there are two types of the SDT depending on the ways to configure the radio resources: (1) SDT using a random access (RA) and (2) SDT using preconfigured radio resources. 

Figure 2 (top) illustrates different types of the SDT referred in 3GPP LTE and NR standards. The SDT using the random access in LTE and NR standards is referred to as an EDT (early data transmission) and RA-SDT (Random Access based SDT), respectively. For both the EDT and the RA-SDT, the device performs data transmission using shared radio resources of the random access procedure. Thus, the contention with other devices can occur over the access to the shared radio resources. The shared radio resources for the SDT are broadcast by system information and are configured as isolated from the one for a nonSDT RA procedure, i.e., the legacy RA procedure. On the other hands, the CG-SDT uses the preconfigured radio resources dedicated to the device. The SDT using the preconfigured radio resource is referred to as transmission via PUR (Preconfigured Uplink Resource) in the LTE standards. The NR standards refers the SDT using the preconfigured radio resource as CG-SDT (Configured Grant based SDT). The network configures the configuration parameters of the preconfigured radio resources when transiting the device in the connected state to the inactive state. For example, an RRC release message transmitted from the network for a connection release contains the configuration parameters of PUR or CG-SDT. No contention is expected for the SDT using the preconfigured radio resource since the configuration parameters are dedicated to the device. 

You can continue reading the details in whitepaper here. Ofinno has another whitepaper on this topic, 'Small Data Transmission (SDT): Protocol Aspects' here.

3GPP also recently published an article on this topic here. Quoting from the article:

With SDT it is possible for the device to send small amounts of data while remaining in the inactive state. Note that this idea resembles the early GSM systems where SMS messages where sent via the control signalling; that is, transferring small amounts of data while the mobile did not have a (voice) connection.

SDT is a procedure which allows data and/or signalling transmission while the device remains in inactive state without transitioning to connected state. SDT is enabled on a radio bearer basis and is initiated by the UE only if less than a configured amount of UL data awaits transmission across all radio bearers for which SDT is enabled. Otherwise the normal data transmission scheme is used.

With SDT the data is transmitted quickly on the allocated resource. The IoT device initiates the SDT procedure by transmitting an RRC request message and payload data in parallel, instead of the usual procedure where the data is transmitted after the RRC request message is processed by a network.

It is not only the speed and the reduced size of the transmitted data which make SDT such a suitable process for IoT devices. Since the device stays in the inactive state, it does not have to perform many tasks associated with the active state. This further improves the battery life of the IoT device. Additional transmission and/or reception are optional.

There are two ways of performing SDT:

  1. via random access (RA-SDT)
  2. via preconfigured radio resources (CG-SDT)

Random Access SDT

With RA-SDT, the IoT device does not have a dedicated radio resource, and it is possible that the random access message clashes with similar RA-SDT random access messages from other IoT devices. The device gets to know the radio resources for the RA procedure from system information messages, in a similar way to non RA-SDT devices. However, the RA radio resources for SDT and non SDT devices are kept separate; that is, these device types do not interfere with each other in random access

The RA-SDT procedure can be a two-step or a four-step random access procedure. In two-step procedure the payload data is already sent with the initial random access message, whereas in four-step procedure the device first performs contention resolution with the random access request - random access response message pair, and then sends the UL payload with RRC Resume Request. The procedure may continue with further uplink and downlink small data transmissions, and then it is terminated with an RRC Release from the network.

Below are the signalling diagrams for both two-step and four-step RA-SDT procedures. Note that in both cases the UE stays in the RRC inactive state during the whole process.

Configured Grant SDT

For CG-SDT, the radio resources are allocated periodically based on the estimation of the UE’s traffic requirements. This uplink scheduling method is called Configured Grant (CG). With CG-SDT there will be no message clashes with other IoT devices since the radio resources are dedicated for each device. The resource allocation is signalled to the IoT device by the network when the device leaves the connected state.

If the amount of data in the UE's tx buffer is larger than a defined limit, then the data transmission is done using the normal non-SDT procedure.

For SDT process, the device selects the CG-SDT as the SDT type if the resources for the CG-SDT are configured on the selected uplink carrier. If the resources for the CG-SDT are unavailable or invalid, the RA-SDT or the non-SDT RA procedure will be chosen if those are configured. If no SDT type configuration is available then a normal non-SDT data transmission is performed.

With IoT devices proliferating, it makes sense to optimise data transfer and anything else that will reduce the power consumption and let the battery in the devices last for much longer.

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Saturday 24 December 2022

3GPP Release 17 Description and Summary of Work Items

An updated (looks final) version of 3GPP TR 21.917: Release 17 Description; Summary of Rel-17 Work Items was added to the archive earlier this month. It is a fantastic summary of all the Rel-17 features. Quoting the executive summary from the specs:

Release 17 is dedicated to consolidate and enhance the concepts and functionalities introduced in the previous Releases, while introducing a small number of brand new Features.

The improvements relate to all the key areas of the previous Releases: services to the industry (the "verticals"), including positioning, private network, etc.; improvements for several aspects of 5G supporting Internet of Things (IoT), both in the Core Network and in the Access Network, of proximity (direct) communications between mobiles, in particular in the context of autonomous driving (V2X), in several media aspects of the user plane related to the entertainment industry (codec, streaming, broadcasting) and also of the support of Mission Critical communications. Furthermore, a number of network functionalities have been improved, e.g. for slicing, traffic steering and Edge-computing.

The Radio interface and the Access Network have been significantly improved too (MIMO, Repeaters, 1024QAM modulation for downlink, etc.). While most of the improvements target 5G/NR radio access (or are access-agnostic), some improvements are dedicated to 4G/LTE access. Such improvements are clearly identified in the title and in the chapters where they appear.

Note: To avoid terminology such as "even further improvements of…", the successive enhancements are now referred to as "Phase n": "phase 2" refers to the first series of enhancements, "Phase 3" to the enhancements of the enhancements, etc. In this transition Release, the "Phase n" way of referring to successive enhancements has not always been used consistently nor enforced.

As for the new Features, the main new Feature of this Release is the support of satellite access, and a dedicated chapter covers this topic.

Note that the classifications, groupings and order of appearance of the Features in this document reflect a number of choices by the editor as there is no "3GPP endorsement" for classification/order. This Executive Summary has also been written by the editor and represents his view.

The following list is from the table of contents to provide you an idea and if it interests you, download the technical report here

5 Integration of satellite components in the 5G architecture
5.1 General traffic (non-IoT)
5.1.1 SA and CT aspects
5.1.2 RAN aspects
5.2 NB-IoT/eMTC support for Non-Terrestrial Networks

6 Services to "verticals"
6.1 Introduction
6.2 Generic functionalities, to all verticals
6.2.1 Network and application enablement for verticals Enhanced Service Enabler Architecture Layer for Verticals Enhancements for Cyber-physical control Applications in Vertical domains (eCAV) Enhancements of 3GPP Northbound Interfaces and APIs
6.2.2 Location and positioning RAN aspects of NR positioning enhancements Enhancement to the 5GC LoCation Services-Phase 2
6.2.3 Support of Non-Public and Private Networks Enhanced support of Non-Public Networks Enhancement of Private Network support for NG-RAN
6.3 Specific verticals support
6.3.1 Railways Enhancements to Application Architecture for the Mobile Communication System for Railways Phase 2 Enhanced NR support for high speed train scenario (NR_HST) NR_HST for FR1 NR_HST for FR2 NR Frequency bands for Railways Introduction of 900MHz NR band for Europe for Rail Mobile Radio (RMR) Introduction of 1900MHz NR TDD band for Europe for Rail Mobile Radio (RMR)
6.3.2 Mission Critical (MC) and priority service Mission Critical Push-to-talk Phase 3 Mission Critical Data Phase 3 Mission Critical security Phase 2 Mission Critical Services over 5GS Enhanced Mission Critical Communication Interworking with Land Mobile Radio Systems (CT aspects) Mission Critical system migration and interconnection (CT aspects) MC services support on IOPS mode of operation MCPTT in Railways Multimedia Priority Service (MPS) Phase 2
6.3.3 Drone/UAS/UAV/EAV Introduction General aspects 5G Enhancement for UAVs Application layer support for UAS Remote Identification of UAS
6.3.4 Media production, professional video and Multicast-Broadcast Communication for Critical Medical Applications Audio-Visual Service Production Multicast-Broadcast Services (MBS) Multicast-broadcast services in 5G NR multicast and broadcast services 5G multicast and broadcast services Security Aspects of Enhancements for 5G MBS Study on Multicast Architecture Enhancements for 5G Media Streaming 5G Multicast-Broadcast User Service Architecture and related 5GMS Extensions Other media and broadcast aspects
6.4 Other "verticals" aspects

7 IoT, Industrial IoT, REDuced CAPacity UEs and URLLC
7.1 NR small data transmissions in INACTIVE state
7.2 Additional enhancements for NB-IoT and LTE-MTC
7.3 Enhanced Industrial IoT and URLLC support for NR
7.4 Support of Enhanced Industrial IoT (IIoT)
7.5 Support of reduced capability NR devices
7.6 IoT and 5G access via Satellite/Non-Terrestrial (NTN) link
7.7 Charging enhancement for URLLC and CIoT
7.8 Messaging in 5G

8 Proximity/D2D/Sidelink related and V2X
8.1 Enhanced Relays for Energy eFficiency and Extensive Coverage
8.2 Proximity-based Services in 5GS
8.3 Sidelink/Device-to-Device (D2D)
8.3.1 NR Sidelink enhancement
8.3.2 NR Sidelink Relay
8.4 Vehicle-to-Everything (V2X)
8.4.1 Support of advanced V2X services - Phase 2
8.4.2 Enhanced application layer support for V2X services

9 System optimisations
9.1 Edge computing
9.1.1 Enhancement of support for Edge Computing in 5G Core network
9.1.2 Enabling Edge Applications
9.1.3 Edge Computing Management
9.2 Slicing
9.2.1 Network Slicing Phase 2 (CN and AN aspects)
9.2.2 Network Slice charging based on 5G Data Connectivity
9.3 Access Traffic Steering, Switch and Splitting support in the 5G system architecture; Phase 2
9.4 Self-Organizing (SON)/Autonomous Network
9.4.1 Enhancement of data collection for SON/MDT in NR and EN-DC
9.4.2 Autonomous network levels
9.4.3 Enhancements of Self-Organizing Networks (SON)
9.5 Minimization of service Interruption
9.6 Policy and Charging Control enhancement
9.7 Multi-(U)SIM
9.7.1 Support for Multi-USIM Devices (System and CN aspects)
9.7.2 Support for Multi-SIM Devices for LTE/NR

10 Energy efficiency, power saving
10.1 UE power saving enhancements for NR
10.2 Enhancements on EE for 5G networks
10.3 Other energy efficiency aspects

11 New Radio (NR) physical layer enhancements
11.1 Further enhancements on MIMO for NR
11.2 MIMO Over-the-Air requirements for NR UEs
11.3 Enhancements to Integrated Access and Backhaul for NR
11.4 NR coverage enhancements
11.5 RF requirements for NR Repeaters
11.6 Introduction of DL 1024QAM for NR FR1
11.7 NR Carrier Aggregation
11.7.1 NR intra band Carrier Aggregation
11.7.2 NR inter band Carrier Aggregation
11.8 NR Dynamic Spectrum Sharing
11.9 Increasing UE power high limit for CA and DC
11.10 RF requirements enhancement for NR FR1
11.11 RF requirements further enhancements for NR FR2
11.12 NR measurement gap enhancements
11.13 UE RF requirements for Transparent Tx Diversity for NR
11.14 NR RRM further enhancement
11.15 Further enhancement on NR demodulation performance
11.16 Bandwidth combination set 4 (BCS4) for NR
11.17 Other NR related activities
11.18 NR new/modified bands
11.18.1 Introduction of 6GHz NR licensed bands
11.18.2 Extending current NR operation to 71 GHz
11.18.3 Other NR new/modified bands

12. New Radio (NR) enhancements other than layer 1
12.1 NR Uplink Data Compression (UDC)
12.2 NR QoE management and optimizations for diverse services

13 NR and LTE enhancements
13.1 NR and LTE layer 1 enhancements
13.1.1 High-power UE operation for fixed-wireless/vehicle-mounted use cases in LTE bands and NR bands
13.1.2 UE TRP and TRS requirements and test methodologies for FR1 (NR SA and EN-DC)
13.1.3 Other Dual Connectivity and Multi-RAT enhancements
13.2 NR and LTE enhancements other than layer 1
13.2.1 Enhanced eNB(s) architecture evolution for E-UTRAN and NG-RAN
13.2.2 Further Multi-RAT Dual-Connectivity enhancements
13.2.3 Further Multi-RAT Dual-Connectivity enhancements

14 LTE-only enhancements
14.1 LTE  inter-band Carrier Aggregation
14.2 LTE new/modified bands
14.2.1 New bands and bandwidth allocation for 5G terrestrial broadcast - part 1
14.3 Other LTE bands-related aspects

15 User plane improvements
15.1 Immersive Teleconferencing and Telepresence for Remote Terminals
15.2 8K Television over 5G
15.3 5G Video Codec Characteristics
15.4 Handsets Featuring Non-Traditional Earpieces
15.5 Extension for headset interface tests of UE
15.6 Media Streaming AF Event Exposure
15.7 Restoration of PDN Connections in PGW-C/SMF Set
15.8 Other media and user plane aspects

16 Standalone Security aspects
16.1 Introduction
16.2 Authentication and key management for applications based on 3GPP credential in 5G (AKMA)
16.3 AKMA TLS protocol profiles
16.4 User Plane Integrity Protection for LTE
16.5 Non-Seamless WLAN offload authentication in 5GS
16.6 Generic Bootstrapping Architecture (GBA) into 5GC
16.7 Security Assurance Specification for 5G
16.8 Adapting BEST for use in 5G networks
16.9 Other security aspects

17 Signalling optimisations
17.1 Enhancement for the 5G Control Plane Steering of Roaming for UE in Connected mode
17.2 Same PCF selection for AMF and SMF
17.3 Enhancement of Inter-PLMN Roaming
17.4 Enhancement on the GTP-U entity restart
17.5 Packet Flow Description management enhancement
17.6 PAP/CHAP protocols usage in 5GS
17.7 Start of Pause of Charging via User Plane
17.8 Enhancement of Handover Optimization
17.9 Restoration of Profiles related to UDR
17.10 IP address pool information from UDM
17.11 Dynamic management of group-based event monitoring
17.12 Dynamically Changing AM Policies in the 5GC
17.13 Other aspects

18 Standalone Management Features
18.1 Introduction
18.2 Enhanced Closed loop SLS Assurance
18.3 Enhancement of QoE Measurement Collection
18.4 Plug and connect support for management of Network Functions
18.5 Management of MDT enhancement in 5G
18.6 Management Aspects of 5G Network Sharing
18.7 Discovery of management services in 5G
18.8 Management of the enhanced tenant concept
18.9 Intent driven management service for mobile network
18.10 Improved support for NSA in the service-based management architecture
18.11 Additional Network Resource Model features
18.12  Charging for Local breakout roaming of data connectivity
18.13 File Management
18.14 Management data collection control and discovery
18.15 Other charging and management aspects

If you find them useful then please get the latest document from here.

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Wednesday 30 November 2022

Disaster Roaming in 3GPP Release-17

One way all operators in a country/region/geographic area differentiate amongst themselves is by the reach of their network. It's not in their interest to allow national roaming. Occasionally a regulator may force them to allow this, especially in rural or remote areas. Another reason why operators may choose to allow roaming is to reduce their network deployment costs. 

In case of disasters or emergencies, if an operator's infrastructure goes down, the subscribers of that network can still access other networks for emergencies but not for normal services. This can cause issues as some people may not be able to communicate with friends/family/work. 

A recent example of this kind of outage was in Japan, when the KDDI network failed. Some 39 million users were affected and many of them couldn't even do emergency calls. If Disaster Roaming was enabled, this kind of situation wouldn't occur.

South Korea already has a proprietary disaster roaming system in operation since 2020, as can be seen in the video above. This automatic disaster roaming is only available for 4G and 5G.

In 3GPP Release-17, Disaster Roaming has been specified for LTE and 5G NR. In case of LTE, the information is sent in SIB Type 30 while in 5G it is in SIB Type 15.

3GPP TS 23.501 section 5.40 provides summary of all the other information needed for disaster roaming. Quoting from that:

Subject to operator policy and national/regional regulations, 5GS provides Disaster Roaming service (e.g. voice call and data service) for the UEs from PLMN(s) with Disaster Condition. The UE shall attempt Disaster Roaming only if:

  • there is no available PLMN which is allowable (see TS 23.122 [17]);
  • the UE is not in RM-REGISTERED and CM-CONNECTED state over non-3GPP access connected to 5GCN;
  • the UE cannot get service over non-3GPP access through ePDG;
  • the UE supports Disaster Roaming service;
  • the UE has been configured by the HPLMN with an indication of whether Disaster roaming is enabled in the UE set to "disaster roaming is enabled in the UE" as specified in clause 5.40.2; and
  • a PLMN without Disaster Condition is able to accept Disaster Inbound Roamers from the PLMN with Disaster Condition.

In this Release of the specification, the Disaster Condition only applies to NG-RAN nodes, which means the rest of the network functions except one or more NG-RAN nodes of the PLMN with Disaster Condition can be assumed to be operational.

A UE supporting Disaster Roaming is configured with the following information:

  • Optionally, indication of whether disaster roaming is enabled in the UE;
  • Optionally, indication of 'applicability of "lists of PLMN(s) to be used in disaster condition" provided by a VPLMN';
  • Optionally, list of PLMN(s) to be used in Disaster Condition.

The Activation of Disaster Roaming is performed by the HPLMN by setting the indication of whether Disaster roaming is enabled in the UE to "disaster roaming is enabled in the UE" using the UE Parameters Update Procedure as defined in TS 23.502 [3]. The UE shall only perform disaster roaming if the HPLMN has configured the UE with the indication of whether disaster roaming is enabled in the UE and set the indication to "disaster roaming is enabled in the UE". The UE, registered for Disaster Roaming service, shall deregister from the PLMN providing Disaster Roaming service if the received indication of whether disaster roaming is enabled in the UE is set to "disaster roaming is disabled in the UE".

Check the specs out for complete details. 

From my point of view, it makes complete sense to have this enabled for the case when disaster strikes. Earlier this year, local governments in Queensland, Australia were urging the Federal Government to immediately commit to a trial of domestic mobile roaming during emergencies based on the recommendation by the Regional Telecommunications Independent Review Committee. Other countries and regions would be demanding this sooner or later as well. It is in everyone's interest that the operators enable this as soon as possible.

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Friday 26 August 2022

How Multiband-Cells are used for MORAN RAN Sharing

In the previous blog post I have explained the concept of multi-band cells in LTE networks and promised to explain a bit deeper how such cells can be used in Multi-Operator RAN (MORAN) scenarios. 

MORAN is characterized by the fact that all network resources except the radio carriers and the Home Subscriber Server (HSS) are shared between two or more operators. 

What this means in detail can be see in Step 1 of the figure below. 

The yellow Band #1 spectrum of the multi-band cell is owned by Network Operator 1 while the blue spectrum of Band #2 and Band #3 belongs to Network Operator 2.

Band #1 is the default band. This means if a UE enters the cell is always has to establish the initial RRC signaling connection on Band #1 as shown in step 1.

The spectrum owned by Network Operator 2 comes into the game as soon as a dedicated radio bearer (DRB), in the core network known as E-RAB, is established in this RRC connection. 

Then we see intra-frequency (intra-cell) handover to Band #2 where the RRC signaling connection is continued. Band #3 is added for user plane transport as a secondary "cell" (the term refers to the 3GPP 36.331 RRC specification). 

The reason for this behavior can be explained when looking a frequency bandwidths. 

The default Band #1 is a low frequency band with a quite small bandwidth, e.g. 5 MHz. as it is typically used for providing good coverage in rural areas. Band #2 is also a lower frequency band, but Band #3 is a high frequency band with maximum bandwidth of 20 MHz. So Band #3 brings the highest capacity for user plane transport and that is the reason for the handover to the spectrum owned by Network Operator 2 and the carrier aggregation used on these frequency bands. 

However, due to the higher frequency the footprint of Band #3 is lower compared to the other two frequency bands. 

For UEs at the cell edge (or located in buildings while being served from the outdoor cell) this leads quite often to situations where the radio coverage of Band #3 becomes insufficient. In such cases the UE typically sends a RRC measurement event A2 (means: "The RSRP of the cell is below a certain threshold."). 

If such A2 event is received by the eNB it stops the carrier aggregation transport and releases the Band #3 resources so that all user plane transport continues to run on the limited Band #2 resources as shown in step 3.

And now in the particular eNB I observed a nice algorithm starts that could be seen as a kind of zero-touch network operation although it does not need big data nor artificial intelligence. 

10 seconds after the secondary frequency resources of Band #3 have been deleted they are added again to the connection, but if the UE is still at the same location the next A2 will be reported soon and carrier aggregation will be stopped again for 10 seconds and then the next cycle starts.

This automation loop is carried out endlessly until the UE changes its location or the RRC connection is terminated. 

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Thursday 16 June 2022

What is a Multi-Band Cell?

Multi-band cells became very popular in modern RAN environment and beside many benefits they also come with some challenges for performance measurement and radio network optimization.

A multi-band cell consists of a default band that shall be used by UEs for initial cell selection and a set of additional frequency band carriers that typically become involved as soon as a dedicated radio bearer (DRB) for payload transmission is established in the radio connection.

The exact configuration of a multi-band cell including all available frequency bands is broadcasted in SIB 1 as shown in the example below.

Different from legacy RAN deployments where – to take the example of a LTE cell – a pair of PCI/eARFCN (Physical Cell Identity/eUTRAN Absolute Radio Frequency Number) always matches a particular ECGI (eUTRAN Cell Global Identity) the multi-band cell has many different PCI/eARFCN combinations belonging to a single ECGI as you can see in the next figure.

Now performance measurement (PM) counters for e.g. call drops are typically counted on the cell ID (ECGI) and thus, in case of mulit-band cells do not reveal on which frequency a radio link failure occurred.

However, knowing the frequency is essential to optimize the radio network and minimize connectivity problems. More detailed information must be collected to find out which of the different frequency bands performs well and which need improvement.

This becomes even more interesting if multi-band cells are used in MORAN RAN sharing scenarios.

In my next blog post I will have a closer look at this special deployment.

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Monday 27 September 2021

Maritime Communication (MARCOM) Services over 3GPP system

Maritime Communication Services over 3GPP System is one of the topics listed in the 3GPP Release-16 summary that I summarised here.

Maritime domain, one of 5G vertical domains in 3GPP, started to be considered since 2016 to enable 3GPP systems to play the role of mobile communication platform necessary for the digitalization and mobilization of the maritime domain that bring about the Fourth Industrial Revolution of the maritime businesses as well as maritime safety.

Compared to other vertical domains, the maritime domain has the radio communication environment that 3GPP hasn’t considered in detail, which means that maritime related issues and features were not in the scope of 3GPP standardization and some of existing 3GPP enabling technologies or solutions are not able to fully support the optimized performances required by the maritime domain in a way that has been guaranteed for on-land communication. In addition, on-board mobile users in a vessel would like to experience the same rich mobile communication services as they enjoy on land.

Furthermore, it is of the view that the capacity and rate for data transmission based on legacy maritime radio communication technologies are indeed not enough for e-Navigation described in IMO Strategy Implementation Plan (SIP) or Maritime Autonomous Surface Ships (MASS), which the International Maritime Organization (IMO), a United Nations specialized agency, have been working to provide to ship.

Considering that the maritime domain is one of 5G vertical domains that 3GPP take into account in order for 5G to be able to provide enhanced mobile broadband services or massive machine-type communication services etc. everywhere anytime in the world, it is desirable to study use cases and requirements for maritime communication services over 3GPP system so that 3GPP system can be a good candidate of innovative tools to help address the information gap between users on land and users at sea as well as the maritime safety and vessel traffic management etc. that IMO intends to achieve especially in 5G era.

3GPP TR 22.819, Feasibility Study on Maritime Communication Services over 3GPP system concluded in 2018 and a report is available here. The scope of the document says:

The present document aims to support the maritime communication services between users ashore and at sea or between vessels at sea over 3GPP system that are targeted to improve maritime safety, protect the maritime environment and promote the efficiency of shipping by reducing maritime casualty caused by human error, in particular, involving small ships and fishing vessels. In addition, the outcome of the technical report is expected to narrow the information gap between mobile users on land and shipboard users on vessels at sea by making it possible to provide the mobile broadband services.

The document describes use cases and potential requirements for services between shore-based users such as authorities and shipboard users in the maritime radio communication environment over 3GPP system. In addition, it deals with use cases to support Mission Critical Services between authorities on land and authorities at sea (e.g. maritime police) as well as use cases to support the interworking between 3GPP system and the existing/future maritime radio communication system for the seamless service of voice communication and data communication between users ashore and at sea or between vessels at sea.

Analysis is also made on which legacy services and requirements from the existing 3GPP system need to be included and which potential requirements need additional work for new functions to support maritime communication services over 3GPP system.

The first 3GPP Technical Specification (TS) 22.119 covering service requirements (Stage 1) is specified for the support of maritime communication (MARCOM) over 3GPP systems.

The maritime domain, one of the 5G vertical domains in 3GPP, is moving forward with the digitalisation and mobilisation of commercial as well as safety fields. Legacy 3GPP-based technologies and solutions can be beneficial to the digitalisation and mobilisation of the maritime domain though some of the legacy 3GPP enabling technologies and solutions may not be able to fully support the performances required by the maritime domain. The maritime radio environment was not originally considered by 3GPP when the technical specifications and solutions were standardised for LTE and 5G. 

However, most of the legacy mobile services and IoT services based on capabilities of EPS and 5GS specified in 3GPP specifications are applicable to maritime usage for the support of mobile broadband services, and for the support of IoT services or machine-type communication services in a vessel at sea. 

In addition, there are service scenarios and requirements specified in 3GPP specifications based on requirements of other related vertical domains (e.g. public safety domain, automotive domain, factory automation domain, and satellite industrial domain). Some requirements derived by service scenarios from these related vertical domains are applicable to the maritime domain. Thus, it is beneficial to use 3GPP enabling technologies developed to satisfy those requirements for the maritime domain in terms of the economy of scale.

For example, satellite access is one of the 3GPP radio access networks supported over the 5G system, so it is possible to provide seamless maritime mobile services by integrating multiple access technologies including satellite access depending on the service scenarios. In addition, Vertical LAN that can replace Ethernet-based access are applicable to indoor maritime mobile services inside a vessel.

Mission Critical (MC) Services specified in 3GPP specifications are applicable to commercial and maritime safety fields. Some similarities exist between the public safety domain and the maritime domain in terms of service scenarios that are essentially the same. For example, in some situations, mobile communication services are supported in spite of disconnected networks, i.e. off-network mode, or under isolated conditions. 

However, the maritime domain also has specific situations that do not happen in other vertical domains or in the legacy ICT industrial domain. New 3GPP enabling technologies dedicated to the maritime domain can be used to address such specific situations based on requirements derived from maritime use cases. Other vertical domains may benefit from such new 3GPP enabling technologies that consider maritime domain scenarios and may need more robust technologies or solutions than those that currently exist for those vertical domains.

The following specifications are relevant for MARCOM:

  • 3GPP TS 22.119, Maritime communication services over 3GPP system
  • 3GPP TS 22.179, Mission Critical Push to Talk (MCPTT); Stage 1
  • 3GPP TS 22.280, Mission Critical (MC) services common requirements
  • 3GPP TS 22.281, Mission Critical (MC) video
  • 3GPP TS 22.282, Mission Critical (MC) data

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Tuesday 7 September 2021

Future Railway Mobile Communication System (FRMCS)

I have been meaning to write on this topic for a very long time. The discussion started back in 2016 when the limitations of GSM-R were obvious and it was recognised that a successor will be needed sooner or later. The International Railway Union (UIC) published a user requirement specification in their paper “Future Railway Mobile Communication System - FRMCS”. This is available on 3GPP server as liaison statement S1-161250.

As 3GPP notes in their article, this was the trigger for them to go ahead and start the studies. Then in Release 16, 3GPP TS 22.289 "Mobile communication system for railways" outlined the requirements for railway communication, beyond the 3GPP Future Railway Mobile Communication System (FRMCS) Phase 1 specs. Details are available on this post here.

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The latest version of 3GPP TR 22.889, Study on Future Railway Mobile Communication System; Stage 1 is from Release 17. The introduction to the document clarifies:

The railway community is considering a successor communication system to GSM-R, as the forecasted obsolescence of the 2G-based GSM-R technology is envisaged around 2030, with first FRMCS trial implementations expected to start around 2020. 

The Future Railway Mobile Communication System (FRMCS) Functional Working Group (FWG) of the International Union of Railways (UIC) have investigated and summarised their requirements for the next generation railway communication system in the Future Railway Mobile Communication User Requirements Specification (FRMCS URS). The present document is based on this input given by the UIC/ETSI TC-RT 

Study on FRMCS Evolution (FS_eFRMCS), available as SP-201038 clarifies:

The UIC FRMCS programme was recently releasing stable version 5.0.0 of the User Requirement Specification, version 2.0.0 of the Functional Use Cases and a new specification item, version 1.0.0 of the Telecom On-Board System - Functional Requirements Specification, as a further step in the evolution of the FRMCS specifications. The UIC FRMCS Programme is developing all the technical conditions for the 5G FRMCS, with the main objective to make available a “FRMCS First Edition” ecosystem available for procurement by Q1 2025.

The UIC FRMCS 3GPP Task Force has been identifying and analyzing impact of this newly released set of FRMCS specifications on existing use cases and requirements collected in TR 22.889. The UIC FRMCS 3GPP Task Force analysis has concluded that refining existing use cases, defining new use cases such as merging railway emergency communications and real-time translation of conversation, and deriving potential new requirements, will be necessary to align FRMCS and 3GPP specifications. The potential impact on normative work is estimated to be limited and much less compared to the study work.

As approved in SA1#90-e (S1-202245), TR 22.889 has now been re-named to TR 22.989 from Rel-18 onwards (latest version is TR 22.989 v18.0.0) to make it visible to the Rail community to be able to follow the 3GPP normative work in line with their needs. It is of most importance for the Rail community that specifications from different organisations (i.e. UIC, 3GPP and ETSI) are all aligned.

Due to the expected 3GPP work overload in Release 18 (SA1 and downstream groups), it is proposed to reduce the scope of the present Rel-18 study to evolution of critical applications related use cases only already identified by UIC – what is really essential for the railways as part of the “FRMCS First Edition” and the migration phase from GSM-R to FRMCS. 

Study of non-essential use cases (e.g. evolution of performance and business use cases) shall be postponed to Rel-19.

This plan is from 2019 so quite likely that it is already outdated. It does provide an idea on different steps and trial plans. Some of this was also covered in the 5G RAN Release 18 for Industry Verticals Webinar detailed here.

Finally, as this image from Arthur D. Little highlights, there is a lot of other interest in addition to FRMCS for 5G in railway. Report here.

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Friday 15 January 2021

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:

UE Radio Capability ID
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 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.

Thursday 17 December 2020

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.