Tuesday 28 June 2022

3GPP Explains TSG CT Work on UAS Connectivity, Identification and Tracking

Drones, technically Unmanned Aerial Vehicles/Systems or UAVs/UASs, have been a subject of interest for a very long time due to the wide variety of use cases they can offer. In the recent issue of 3GPP Highlights newsletter, Lena Chaponniere, 3GPP Working Group CT1 Vice-Chair has written an article about TSG CT work on UAS Connectivity, Identification and Tracking. Interestingly, the 3GPP abbreviation for UAS is slightly different, Uncrewed Aerial Systems.

Quoting from the newsletter: 

One of the defining drivers of 5G is the expansion beyond traditional mobile broadband to provide solutions meeting the needs of vertical industries.

A very good example of 3GPP rising up to this challenge is the work done in Release 17 to use cellular connectivity to support Uncrewed Aerial Systems (UAS), thereby enabling this vertical to benefit from the ubiquitous coverage, high reliability, QoS, robust security, and seamless mobility provided by the 3GPP system.

A key component of this work took place in CT Working Groups, which under the leadership of Sunghoon Kim (CT Work Item rapporteur) and Waqar Zia (rapporteur of new specifications TS 29.255 and TS 29.256) developed the necessary protocols and APIs to meet the service requirements specified in 3GPP SA1 and the architectural enhancements specified in 3GPP SA2, as part of the Release 17 Work Item on ‘ID_UAS’.

The key functions of the 3GPP architecture for ID_UAS are depicted in the following figure:

The work in CT Working Groups focused on specifying support for the following features:

UAV remote identification: The CAA (Civil Aviation Administration)-Level UAV ID was introduced in the 3GPP system. It is a globally unique, electronically and physically readable, and tamper resistant identification which allows the receiving entity to address the correct USS for retrieval of UAV information and can be assigned solely by the USS, via means outside the scope of 3GPP, or assigned by the USS with assistance from 3GPP system, whereby the USS delegates the role of “resolver” of the CAA-Level UAV ID to the UAS NF.

AV USS authentication and authorization (UUAA): The first step for the owner of the UAV is to register the UAV with the USS, via a procedure outside the scope of 3GPP, which can take place offline or using internet connectivity. During this procedure, the CAA-level UAV ID is configured in the UAV and the aviationlevel information (e.g. UAV serial number, pilot information, UAS operator, etc.) is provided to the USS.

The UE at the UAV then registers with the 3GPP system by using existing procedures for 3GPP primary authentication, with the MNO credentials stored in the USIM.

After successful authentication of the UE, the UUAA procedure is performed, to enable the 3GPP Core Network to verify that the UAV has successfully registered with the USS. In 5GS, this procedure can take place during the 3GPP registration, or during the establishment of a PDU session for UAS services.

For the former, CT1 extended the registration procedure in TS 24.501 to enable the UE to indicate its CAA-Level UAV ID into a new container (Service-level-AA container) included in the Registration Request message, which triggers the AMF to initiate UUAA with the USS by invoking the Nnef_Authentication service toward the UAS NF, as specified by CT4 in new specification TS 29.256, and the UAS NF to invoke the Naf_Authentication service toward the USS, as specified by CT3 in new specification TS 29.255.

For the latter, CT1 extended the PDU session establishment procedure in TS 24.501 to enable the UE to indicate its CAA-Level UAV ID via the Service-level-AA container included in the PDU Session Establishment Request message, which triggers the SMF to initiate UUAA with the USS via the UAS NF by invoking the services mentioned above. In order to enable exchanging the authentication messages between the UE and the USS, CT1 specified a new Session Management procedure in TS 24.501, in which the SMF sends a Service-level Authentication Command to the UE in a Downlink NAS Transport message. The UE replies to this command with a Service-level Authentication Complete carried in an Uplink NAS Transport message. In EPS, the UUAA procedure takes place during PDN connection establishment, and the information exchanged to that end between the UAV and the PGW is carried in the Service-level-AA container included in the ePCO

C2 communication over cellular connectivity: C2 communication over cellular connectivity consists of the UAV establishing a user plane connection to receive C2 messages from a UAVC, or to report telemetry data to a UAVC. Authorization for C2 communication by the USS is required and includes authorization for pairing of the UAV with a UAVC, as well as flight authorization for the UAV.

C2 communication authorization may be performed:

  • during the UUAA procedure (if UUAA is carried out at PDU session/PDN connection establishment) when the UAV requests establishment of a PDU Session/PDN connection for both UAS services and C2 communication
  • during PDU session modification/UE requested bearer resource modification when the UAV requests to use an existing PDU session/PDN connection for C2 communication
  • during a new PDU session/PDN connection establishment, if the UAV requests to use a separate PDU Session/PDN connection for C2 communication

To support this, CT1 extended the PDU session establishment and modification procedures in TS 24.501 to enable inclusion of the CAA-level UAV ID and an application layer payload containing information for UAVC pairing and for UAV flight authorization in the Service-level-AA container carried in the PDU Session Establishment Request and PDU Session Modification Request messages. The ePCO Information Element in TS 24.008 was also extended to enable it to include the above-mentioned information.

UAV location reporting and tracking: UAV location reporting and tracking was specified by CT3 and CT4 by re-using the existing Nnef_EventExposure service specified in TS 29.522 with the UAS NF acting as NEF/SCEF and interacting with other network functions (e.g. GMLC and AMF/MME) to support UAV tracking. The following tracking modes were specified:

  • UAV location reporting mode: the USS subscribes to the UAS NF UAV to be notified of the location of the UAV, and can indicate the required location accuracy and whether the request is for immediate reporting or deferred reporting (e.g. periodic reporting)
  • UAV presence monitoring mode: the USS subscribes for the event report of UAV moving in or out of a given geographic area
  • List of Aerial UEs in a geographic area: the USS requests the UAS NF for reporting a list of the UAVs in given geographic area and served by the PLMN.

The PDF of newsletter is available here.

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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 13 June 2022

Tutorial on 4G/5G Mobile Network Uplink Working and Challenges

People involved with mobile technology know the challenges with uplink for any generation of mobile network. With increasing data rates in 4G and 5G, the issue has become important as most of the speeds are focused on download but upload speeds are quite poor.

People who follow us across our channels know of many of the presentations we share across them from various sources, not just ours. One such presentation by Peter Schmidt looked at the uplink in details. In fact we recommend following him on Twitter if you are interested in technical details and infrastructure.

The details of his talk as follows:

The lecture highlights the influences on the mysterious part of mobile communications - sources of interference in the uplink and their impact on mobile communication as well as practices for detecting sources of RF interference.

The field strength bar graph of a smartphone (the downlink reception field strength) is only half of the truth when assessing a mobile network coverage. The other half is the uplink, which is largely invisible but highly sensitive to interference, the direction from the end device to the base stations. In this lecture, sources of uplink interference, their effects and measurement and analysis options will be explained.

Cellular network uplink is essential for mobile communication, but nobody can really see it. The uplink can be disrupted by jammers, repeaters, and many other RF sources. When it is jammed, mobile communication is limited. I will show what types of interference sources can disrupt the uplink and what impact this has on cellular usage and how interference hunting can be done.

First I explain the necessary level symmetry of the downlink (from the mobile radio base station - eNodeB to the end device) and the uplink (from the end device back to the eNodeB). Since the transmission power of the end device and eNodeB are very different, I explain the technical background to achieving symmetry. In the following I will explain the problems and possibilities when measuring uplink signals on the eNodeB, it is difficult to look inside the receiver. In comparison, the downlink is very easy to measure, you can see the bars on your smartphone or you can use apps that provide detailed field strength information etc. However, the uplink remains largely invisible. However, if this is disturbed on the eNodeB, the field strength bars on the end device say nothing. I will present a way of observing which some end devices bring on board or can be read out of the chipset with APPs. The form in which the uplink can be disrupted, the effects on communication and the search for uplink sources of disruption will complete the presentation. I will also address the problem of 'passive intermodulation' (PIM), a (not) new source of interference in base station antenna systems, its assessment, measurement and avoidance.

The slides are available here. The original lecture was in German, a dubbed video is embedded below:

If you know of some other fantastic resources that we can share with our audience, please feel free to add them in the comments.

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Monday 6 June 2022

2G/3G Shutdown may Cost Lives as 4G/5G Voice Roaming is a Mess

You have probably heard me a complaining about the pace of VoLTE rollout, 2G/3G shutdowns, 4G Voice roaming, etc. This post highlights all these issues coming together in a dangerous way. People often ask me why is it that it's always just me highlighting the issues. The answer is that there are other people but their voice may not reach you. In this post, I am highlighting presentations by Rudolf van der Berg, Project and programme manager at Stratix Consulting.

Let's start with Rudolf's post from LinkedIn:

Stop the shutdown of 2G and 3G networks to save lives. This is the urgent call I make today and I hope you can help me spread it! Please call on people you know in politics, regulators and emergency services to demand a stop! Call on anyone you know in the GSMA, 3GPP, handset makers (Apple, Samsung, Qualcomm, MediaTek), network builders (Ericsson, Nokia, Huawei) to re-engineer VoLTE to an interoperable standard.

Emergency calls (112, 911) should work anywhere in the world on any phone. For GSM and 3G voice calling it did. You could fly anywhere and call emergency services and in the EU we have the roaming regulation that demands calling like at home. Voice over 4G and 5G hasn't been properly standardized and isn't interoperable between networks, devices, chipsets and firmware. People need to be able to make and receive telephone calls around the world, to each other and to emergency services. Unfortunately even according to sector itself emergency services are at risk from VoLTE. A consumer today can't know whether a phone they bought will make VoLTE calls at home or abroad, nor whether it can reach emergency services. That can't be right!

So please help EENA 112 and me share this message! Thank you #eena2022 (Slide 4 contains a mistake, T-Mo USA hasn't decided on 2G shutdown yet. that is good for availability of 911, though fundamental point remains. Apologies.)

The video and slides are embedded below:

The slides contain many useful references and links, you can download directly from here.

Back in April, iBASIS hosted a VoLTE and 5G Roaming Roundtable. You can watch the video here and download the presentation and whitepaper as well. It contains talks from Kaleido Intelligence, iBASIS, KPN, Bouygues Telecom and Telus. 

The slide from Dutch MNO KPN above highlights the VoLTE Roaming issues they are observing. Other operators will face this issue sooner or later as well. 

The Regulators, GSMA and 3GPP have to come together to fix this important issue for once and all so no lives are lost because of this. Hopefully someone is listening!

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