By Magnus Hylén | Rohde & Schwarz

With 5G NR and the completely different operation modes (non-standalone and standalone) the air interface procedures and all protocol layers are getting extra complicated. To have the ability to perceive the message content material from related Radio Useful resource Management (RRC) we labored on a human-readable answer. R&S®ROMES4 comprises now a built-in professional decoder that extracts RRC message info and robotically interprets it into the structured RRC connection management, measurement and mobility features, presenting them as readable RRC occasions and key efficiency indicators (KPI).

Overview

The arrival of 5G New Radio (5G NR) has made radio community layouts far more complicated than they have been for legacy 4G/LTE networks.
Totally new frequency band ranges (together with mmWave) and new community architectures that enable twin connectivity create new alternatives but additionally pose challenges for radio community design in addition to the evaluation and optimization of those networks.

Consumer tools (UE) can both join standalone over LTE or 5G NR networks and over each with non-standalone connectivity.
5G has larger flexibility, making it much more difficult to grasp and analyze radio networks. With the rising variety of community interfaces and radio entry community (RAN) configurations, system consultants and radio engineers want extra experience and develop strategies and instruments to optimize or troubleshoot 5G and 4G networks.

Analytical challenges

We’re going to take a more in-depth take a look at radio useful resource management (RRC) layer 3 signaling in 5G NR and 4G LTE cellular networks and analyze the connection management, measurement configuration and mobility procedures.
The RRC reconfiguration message comprises important info. The message can embrace measurement configurations, handover info, in addition to add and launch cells for provider aggregation and twin connectivity.

A pattern RRC layer 3 LTE protocol evaluation:

The sequence begins with a measurement report from the UE within the uplink adopted by an RRC connection reconfiguration message within the downlink. The underlying procedures may be discovered within the message content material and it’s good to be a 3GPP protocol professional to decipher all of the essential info.

LTE and 5G NR RRC reconfiguration messages are among the lengthiest within the protocol stack and it will possibly take time to totally perceive them. A protocol professional can decipher these messages and acquire the perception seen within the screenshot under:

1. The measurement report is triggered by a earlier Occasion A3 reporting configuration. The LTE RAN will act upon the Occasion A3 message and provoke a handover try that’s signaled by the RRC reconfiguration message.
2. 2. Analyzing the extension fields within the subsequent RRC reconfiguration message confirms that including SCells will activate provider aggregation.

This is only one RRC signaling sequence out of the tons of {that a} machine can generate over the course of an hour and analyzing all of them is tiresome work, even for consultants.

The answer – let the instrument be the professional

Letting a instrument equivalent to R&S®ROMES4 do the be just right for you is a great various. The built-in professional decoder extracts RRC message info and robotically interprets it into the structured RRC connection management, measurement and mobility features, presenting them as RRC occasions and key efficiency indicators (KPI) together with all different logged UE diagnostic info.
Under is our earlier LTE handover within the layer 3 view with the good RRC occasions seen with a inexperienced background within the supply RRC message.

The signaling sequence is now simpler to grasp, even for non-experts.
The good RRC occasions clarify:

1. LTE -MR Occasion A3 triggered the measurement report and gives the measured cell high quality outcomes for the PCells, neighbor cell(s) and SCells (SFL).
2. 2. LTE eNB acts upon an MR Occasion A3 and initiates an RRC reconfiguration whereas R&S®ROMES4 detects the next good RRC occasions:
   a) Handover try for LTE PCell: handover to a brand new major cell on the identical frequency (inter-frequency handover)
   b) RB AddMod: RLC and PDCP configuration of the info radio bearer
3. 3. The subsequent RRC reconfiguration prompts provider aggregation, as indicated by the MCG add LTE SCell occasion.

Evaluation samples

An enormous set of parameters can be found to regulate mobility features, equivalent to handovers and twin connectivity. Excessive mobility efficiency ranges in cellular networks require that parameters be fine-tuned to geographical circumstances, frequency bands and even cell-specific circumstances. So, a cellular community will want loads of tuning all through its lifecycle.
Measurement reporting configurations may be occasion pushed or periodic. An Occasion A3 is the widespread intra-frequency handover set off, indicating {that a} neighbor cell has offset of x dB relative to the serving cell. the subsequent instance depicted under exhibits an LTE-MR Occasion A3 triggering a measurement report for the PCI 483 neighbor cell with an RSRP of -83 dBm and a serving cell with -87 dBm, that means the neighbor cell is 4 dB higher. NodeB responds with an RRC reconfiguration message and a handover to the brand new cell.

In an earlier RRC reconfiguration message you will discover the Occasion A3 configuration to cross-check the reporting circumstances and ensure that the offset [dB] plus hysteresis [dB] are actually 4 dB.

LTE was the primary mobile expertise with a self-organizing community (SON) operate: the automated neighbor relation (ANR) characteristic. Community operators around the globe welcomed this characteristic, since considerably diminished the trouble wanted to handle neighbor cell relations, which have been very difficult in legacy 2G and 3G networks.
ANR is embedded within the total LTE measurement high quality procedures with particular person measurement reporting configurations. ANR can instruct the UE to report neighbor cells with a detrimental offset earlier than they’re detected as handover candidates by different Occasion A3 configurations.
Within the instance under the Occasion A3 parameters offset plus hysteresis are as a substitute -12 dB.

R&S®ROMES4 makes it simple to differentiate between Occasion A3 measurement reviews used to set off handovers and people used for SON features. A number of cases of Occasion A3 SON are reported however the detrimental offset prevents a handover resolution within the NodeB.

Lacking neighbor issues are the commonest reason behind dropped calls and poor connection high quality. When a UE sends measurement reviews to the first cell indicating a greater neighbor cell and no response comes from the NodeB (i.e. no RRC reconfiguration), the UE will most likely will drop the connection resulting from poor sign high quality and begin the RRC re-establishment course of.

Relationships with neighbor cells might not be outlined within the major cell resulting from a suboptimal ANR operate. Different causes might embrace heavy site visitors hundreds in a neighboring cell.

R&S®ROMES4 has the ‘No MR response’ KPI to make it simpler to detect conditions with no response from the UE measurement and rapidly determine such issues.

The KPI helps discover issues and decoded RRC MR occasions assist perceive them.
Occasion A3 outlined for SON (detrimental offset) just isn’t considered for the ‘No MR response’ KPI, because it doesn’t set off a NodeB response.