Merge remote-tracking branch 'origin/fix-delta-mcs' into integration_2026_w13 (!3912)
Fix Delta MCS mode, reimplement UL power control This change set fixes the "delta-MCS" mode, and reimplements the UL power control loops at gNB, i.e., for PUSCH and PUCCH. It further adds new T traces to log PUSCH/PUCCH power infrmation, and cleans up code. The "delta-MCS" mode in OAI refers to configuring a UE with deltaMCS in the PUSCH-PowerControl IE (see TS 38.331). In this mode, the UE adjusts the PUSCH power for transmissions to take into account for MCS (see TS 38.213 Sec. 7.1). In other words, the target SNR can be set to a somewhat low value, and the UE will still use the right power for UL transmissions. Note that the spec only foresees this adjustment of UL power when using one layer. In contrast, in the "normal" mode, the gNB sends TPC commands to keep a UE at a fixed target SNR (default: 20dB), regardless of the MCS or number of layers. Future work is planned to completely remove this fixed target SNR, which is not done in this MR yet. Further, there is a new power control loop implementation. Prior to this MR, on each UL transmissions, the gNB uses the SNR to decide about TPC sent to a UE in the next transmissions. The new implementation relies on averaging the SNR, and a "TPC in flight" average to account for the slow reaction of the average SNR. The sum of both quantities is the current SNR that is used by the UE. See the commit messages or documentation for more information. Further cleanup to group data (e.g., power control configuration, refactoring of code to save space, ...) is done. Two new T traces GNB_MAC_PUSCH_POWER_CONTROL and GNB_MAC_PUCCH_POWER_CONTROL are added; documentation exists to explain how to graphically plot corresponding graphs.
This commit is contained in:
Jaroslava Fiedlerova
+45
-9
@@ -67,6 +67,43 @@ happen.
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Say we have 0% PDCCH success rate (radio link failure scenario) but `pdcch_cl_adjust` is 0 indicating
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perfect PDCCH channel. it would take ~18 PDCCH failures to reach maximum aggregation level.
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## Power control
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The gNB tracks the average SNR used by the UE for PUSCH/PUCCH, and sends TPC
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commands to maintain the UE at a specific target SNR. Internally, it maintains
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an average of measured SNR and RSSI. It also updates `tpc_in_flight`, which
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tracks TPC changes that don't show up in the average yet. For instance, imagine
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that the target SNR of 15 changes to 20. Three successive TPC commands need to
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be sent (+3, +1, +1), but it will take time to show up in the average SNR. To
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account for this, `tpc_in_flight` is updated by the TPCs sent, and an average
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will make it go down back to zero at the same pace as the average SNR
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approaches the target SNR. The sum of average SNR and `tpc_in_flight` sums up
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to the actual, current SNR, which approximates the target SNR. The power
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control tries to keep the SNR within -1<=targetSNR<=+2dB to avoid too many TPC
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changes. On each DTX, `tpc_in_flight` is lowered by 1dB, correspondingly
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lowering the current SNR by 1dB, which result in "boosting" the UE's target
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SNR.
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For PUCCH, the gNB will try to keep the UE at the target SNR as configured by
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`pucch_TargetSNRx10`.
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For PUSCH, two modes are available currently. Both have in common that
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`pusch_TargetSNRx10` is used to configure a specific target SNR, but the
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meaning of the target SNR changes depending on the mode. (For the following,
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note that as per 38.213 Sec 7.1, the number of PRBs used for a PUSCH
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transmission is always taken into account by the UE).
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1. the "normal" mode (default), in which the gNB tries to keep the UE at the
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target SNR, regardless of MCS (and layers) used. This is the default.
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Depending on the target MCS and number of layers, the target SNR should be
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placed in the 20-30dB range.
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2. the "deltaMCS" mode (`deltaMCS=1`, see below). In this mode, the UE accounts
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for the MCS in the power used for PUSCH transmissions automatically (see
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delta_TF factor in TS 38.213 Sec 7.1) when using only one layer. Thus it is
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sufficient to set a lower target SNR (5-10dB). As the spec foresees that
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this only works for one layer, it is suggested to disable SRS to disable
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multi-layer operation in UL.
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## Periodic output and interpretation
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The scheduler periodically outputs statistics that can help you judge the radio
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@@ -81,8 +118,8 @@ Example:
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UE RNTI 2460 CU-UE-ID 2 in-sync PH 28 dB PCMAX 24 dBm, average RSRP -74 (8 meas), average SINR 40.0 (32 meas)
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UE 2460: CQI 15, RI 2, PMI (14,1)
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UE 2460: UL-RI 2 TPMI 0
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UE 2460: dlsch_rounds 32917/5113/1504/560, dlsch_errors 211, pucch0_DTX 1385, BLER 0.19557 MCS (1) 23 CCE fail 3
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UE 2460: ulsch_rounds 3756/353/182/179, ulsch_errors 170, ulsch_DTX 285, BLER 0.33021 MCS (1) 27 (Qm 8 dB) NPRB 5 SNR 31.0 dB CCE fail 0
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UE 2460: dlsch_rounds 32917/5113/1504/560, dlsch_errors 211, pucch0_DTX 1385 (SNR 19.8+0.2 dB), BLER 0.19557 MCS (1) 23 CCE fail 3
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UE 2460: ulsch_rounds 3756/353/182/179, ulsch_errors 170, ulsch_DTX 285, BLER 0.33021 MCS (1) 27 (Qm 8 dB) NPRB 5 SNR 31.0 (-1.0) dB CCE fail 0
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UE 2460: MAC: TX 1530943191 RX 194148 bytes
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UE 2460: LCID 1: TX 651 RX 3031 bytes
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UE 2460: LCID 2: TX 0 RX 0 bytes
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@@ -139,6 +176,8 @@ The fourth and fifth line show HARQ-related information:
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and ACK/NAK cannot be conveyed properly or DL DCIs are missed by the UE. This
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is also something that should be very small compared to `A` in
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`dlsch_rounds`.
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* `(SNR x+y dB)`: PUCCH SNR where `x` is the average PUCCH SNR and `y` the
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difference to the target (positive: above SNR, negative: below)
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* `DLSCH BLER` is the current measured block-error rate of the DLSCH. Basically
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a moving average of `B`/`A` in `dlsch_rounds`. This is something that should always
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be close to the target bler that the MAC scheduler uses. typically 10-30% if
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@@ -162,10 +201,9 @@ The fourth and fifth line show HARQ-related information:
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fluctuate a lot but when doing high throughput with iperf, it indicates the
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number of PRBs that the UE is actually able to use with its power budget and
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should be high.
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* ULSCH `SNR`: the current SNR that the gNB receives the UE signal with. It
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should be close to the target in the gNB configuration file,
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`pusch_TargetSNRx10`, which should be around 10 times the value shown in the
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log
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* ULSCH `SNR`: the current SNR that the gNB receives the UE PUSCH signal with.
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This value should be close to the target SNR; in paranthesis, the difference
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to the target SNR.
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* Both ULSCH/DLSCH `CCE fail`: lists the number of failed CCE attempts. If this
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number gets high, it signifies that the scheduler tried to scheduled this UE,
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but could not allocate the DCI.
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@@ -276,9 +314,7 @@ configuration](../RRC/rrc-usage.md) as well for SIB configuration.
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* `disable_harq` (default 0=false): flag whether to disable HARQ completely
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(useful for NTN operation, see <../RUNMODEM.md>). **this is a Rel-17 feature
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and you need to have a capable UE for this**
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* `use_deltaMCS` (default 0=false): flag whether to enable deltaMCS (**this is not fully tested
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and might not work** and you might need to adjust other parameters such as
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target SNRs)
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* `use_deltaMCS` (default 0=false): flag whether to enable deltaMCS
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* `num_dlharq` (default 16): number of HARQ processes to use in DL (other valid
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options are 2, 4, 6, 8, 10, 12, 32; **32 is a Rel-17 features**)
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* `num_ulharq` (default 16): as `num_dlharq` for UL (other valid option is 32;
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