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.

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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