like feature combination preamble 3GPP Release 17 we have lots of new features like REDCAP, Power Saving Feature PEI, PDCCH Skipping, NTN, etc. In those features one of the most interesting features is the feature combination preamble so you guys must be thinking about why we need feature preamble combination because every UE has got set of preambles in RACH procedure so why such new feature introduced.
I already discuss the RACH procedure in detail you can check it out if you did not check also about REDCAP I explained in detail in this article
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So, let’s discuss in detail the feature combination preamble
FeatureCombintionPreamble is introduced for a special set of features (like REDCAP, SDT, MSG3 Repetitions spare etc) or combinations of features and can be defined under the RACH Config Common as per the test requirement.
If both RACH Configuration and feature combination preamble both defined under RACH Config Common then and UE supports the R17 or REDCAP UE then it selects the feature combination preambles instead of RACH preambles to send to the network.
Otherwise it does not support the R17 feature or feature priorities (explained below) not set under the SIB1 then UE selects the normal RACH config preambles and sends to the network.
FeatureCombinationPreamble is enables under RACH Config Common SIB1 so UE will give higher priority to the Feature Combination Preamble.
There is no difference in RACH Procedure it’s same there is the only difference that we are defining the special set of preambles to specific features for if REDCAP UE then we can set the feature priority to REDCAP define feature preambles for REDCAP under RACH Config Common then UE selects the REDCAP preambles.
One of the important elements under SIB1 for the feature preamble is feature priorities.
FeaturePriorities
indicates priorities for features, such as RedCap, Slicing, SDT, and MSG3-Repetitions for Coverage Enhancements. These priorities determine which FeatureCombinationPreambles the UE shall use when a feature maps to more than one FeatureCombinationPreambles, as specified in TS 38.321 [3].
A lower value means a higher priority. The network does not signal the same priority for more than one feature. The network signals a priority for all features that map to at least one FeatureCombinationPreambles.
The fetaurecombinationpreamble can be defined under intialUplinkBWP or under initialUplinkBWP AdditionalRACH Config-Common or also can define under intialUplinkredcapBWP and initialUplinkredcapBWP AdditionalRACH Config-Common.
SIB1 Configuration for FeatureCombinationPreamble.
FeatureCombinationPreambles The IE FeatureCombinationPreambles associates a set of preambles with a feature combination. For parameters that can be provided in this IE, the UE applies this field value when performing Random Access using a preamble in this featureCombinationPreambles, otherwise, the UE applies the corresponding value as determined by applicable Need Code, e.g.
Need S. On a specific BWP, there can be at most one set of preambles associated with a given feature combination per RA Type (i.e. 4-step RACH or 2-step RACH).
Also Read :- 5g-nsa-call-flow-non-stand-alone-and-log-analysis
FeatureCombinationPreambles information element:
FeatureCombinationPreambles-r17
startPreambleForThisPartition-r17 INTEGER (0..63),
numberOfPreamblesPerSSB-ForThisPartition-r17 INTEGER (1..64),
ssb-SharedRO-MaskIndex-r17 INTEGER (1..15) OPTIONAL, — Need S
groupBconfigured-r17 SEQUENCE {
ra-SizeGroupA-r17 ENUMERATED {b56, b144, b208, b256, b282, b480, b640,
b800, b1000, b72, spare6, spare5,spare4, spare3, spare2, spare1},
messagePowerOffsetGroupB-r17 ENUMERATED { minusinfinity, dB0, dB5, dB8, dB10, dB12, dB15, dB18},
numberOfRA-PreamblesGroupA-r17 INTEGER (1..64)
} OPTIONAL, — Need R
separateMsgA-PUSCH-Config-r17 MsgA-PUSCH-Config-r16 OPTIONAL, — Cond MsgAConfigCommon
msgA-RSRP-Threshold-r17 RSRP-Range OPTIONAL, — Need R
rsrp-ThresholdSSB-r17 RSRP-Range OPTIONAL, — Need R
deltaPreamble-r17 INTEGER (-1..6) OPTIONAL, — Need R…
3GPP Reference 38.301 V17.2.0
RedCap
If present, this field indicates that RedCap is part of this feature combination.
SmallData
If present, this field indicates that Small Data is part of this feature combination.
Nsag
If present, this field indicates NSAG(s) that are part of this feature combination.
msg3-Repetitions
If present, this field indicates that signaling of msg3 repetition is part of this feature combination. This field is not configured in a set of preambles that is configured with 2-step random-access type.
How do we know which feature preamble selected or not?
If UE selected the featurepreamble which is configured under SIB1 then we can check the PRACH Config Index message configuration there is one IE’s PRACH Feature Preamble in this, it will show the REDCAP feature preamble selected or SDT or MSG3 whatever you configured on SIB1.
Can we define multiple feature preambles under SIB1 for one UE?
Yes. We can define multiple featurecombination preambles under SIB1 for we can divide the feature preambles to different feature like MSG3 repetition we cam assignee starting 10 preambles then 5 preambles we can assignee for REDCAP feature under we can assignee to SDT it totally depends on the test requirement.
Also Read :- UE power on procedure in 5G: Initial Access or Cell Selection
How many feature preambles we have for one UE?
We have total 64 featureCombinationpreambles as per 3GPP specifications.
startPreambleForThisPartition-r17 INTEGER (0..63),
numberOfPreamblesPerSSB-ForThisPartition-r17 INTEGER (1..64),
what is featureCombinationPreamblesList?
featureCombinationPreamblesList specifies a series of preamble partitions associated with a combination of features and 4-step RA. The network does not configure this list to have more than 16 entries.
