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fixeria gerrit-no-reply at lists.osmocom.orgfixeria has uploaded this change for review. ( https://gerrit.osmocom.org/c/osmo-bsc/+/24804 )
Change subject: power_control: constrain BS power reduction on BCCH carrier
......................................................................
power_control: constrain BS power reduction on BCCH carrier
BS Power Control is not allowed on the BCCH/CCCH carrier, unless
the BTS is operating in the BCCH carrier power reduction mode.
Allow constrained BS power reduction (up to 6 dB) on active logical
channels iff BCCH carrier power reduction mode is enabled.
Take into account that the maximum power difference between a timeslot
used for BCCH/CCCH and the timeslot preceding it shall not exceed 3 dB.
Change-Id: I2cc6a86731984f586ef35b43a8d3de631f7d8a2f
Related: SYS#4919, SYS#4918
---
M doc/manuals/chapters/power_control.adoc
M include/osmocom/bsc/gsm_data.h
M src/osmo-bsc/bts.c
M src/osmo-bsc/lchan_fsm.c
4 files changed, 62 insertions(+), 0 deletions(-)
git pull ssh://gerrit.osmocom.org:29418/osmo-bsc refs/changes/04/24804/1
diff --git a/doc/manuals/chapters/power_control.adoc b/doc/manuals/chapters/power_control.adoc
index fe2bf26..b146e2a 100644
--- a/doc/manuals/chapters/power_control.adoc
+++ b/doc/manuals/chapters/power_control.adoc
@@ -357,6 +357,30 @@
power reduction mode" in the feature vector. This can be checked by issuing
`show bts` command in the VTY interface.
+==== Interworking with static and dynamic power control
+
+The key difference between BCCH carrier power reduction and the BS power control
+is that the former affects *inactive* timeslots (or sub-channels), so only dummy
+bursts are affected. The later depends on the Downlink measurement reports sent
+by the MS, and thus applies to *active* channels only. However, both features
+are interconnected: the maximum BCCH carrier power reduction value constrains
+the BS Power value that can be used for dynamic or static BS power control.
+
+BS power control on the BCCH carrier will not be enabled unless the BTS is in BCCH
+carrier power reduction mode of operation. Once it is, the BS power reduction
+value in either of `dyn-bts` or `static` modes would be constrained by currently
+applied BCCH power reduction value, and thus would never exceed the maximum of 6 dB.
+
+For example, consider a BTS with BS power control configured to use _dynamic_ mode
+and the maximum power reduction of 16 dB. Once this BTS is switched into the BCCH
+carrier power reduction mode with the maximum attenuation of 4 dB, the maximum
+power reduction value for the BS power loop on the C0 carrier would be 4 dB.
+
+Moreover, according to 3GPP TS 45.008, between a timeslot used for BCCH/CCCH and
+the timeslot preceding it, the difference in output power actually transmitted by
+the BTS shall not exceed 3 dB. This means that on some timeslots the power
+reduction value can be constrained even further.
+
==== Managing BCCH carrier power reduction
The BCCH carrier power reduction can be controlled via the CTRL and VTY interfaces.
diff --git a/include/osmocom/bsc/gsm_data.h b/include/osmocom/bsc/gsm_data.h
index 569e288..19a168e 100644
--- a/include/osmocom/bsc/gsm_data.h
+++ b/include/osmocom/bsc/gsm_data.h
@@ -841,6 +841,9 @@
} rbs2000;
};
+ /* Maximum BCCH carrier power reduction */
+ uint8_t bcch_max_power_red_db;
+
/* Maximum number of lchans that could become usable, for example by switching a dynamic timeslot's type or by
* enabling VAMOS secondary lchans. This does include the maximum count of possible VAMOS secondary lchans. */
uint8_t max_lchans_possible;
diff --git a/src/osmo-bsc/bts.c b/src/osmo-bsc/bts.c
index e055981..05d52a7 100644
--- a/src/osmo-bsc/bts.c
+++ b/src/osmo-bsc/bts.c
@@ -749,6 +749,8 @@
int gsm_bts_set_bcch_power_red(struct gsm_bts *bts, const uint8_t red)
{
+ struct gsm_bts_trx *c0 = bts->c0;
+ unsigned int tn;
int rc;
if (!osmo_bts_has_feature(&bts->features, BTS_FEAT_BCCH_POWER_RED))
@@ -762,6 +764,32 @@
bts->bcch_max_power_red_db = red;
+ /* Timeslot 0 is always transmitting BCCH/CCCH */
+ c0->ts[0].bcch_max_power_red_db = 0;
+
+ for (tn = 1; tn < ARRAY_SIZE(c0->ts); tn++) {
+ struct gsm_bts_trx_ts *ts = &c0->ts[tn];
+ const struct gsm_bts_trx_ts *next;
+
+ if (ts->pchan_is == GSM_PCHAN_CCCH)
+ ts->bcch_max_power_red_db = 0;
+ else
+ ts->bcch_max_power_red_db = red;
+
+ if (ts->bcch_max_power_red_db > 0) {
+ /* Next timeslot following this one */
+ next = &c0->ts[(tn + 1) % 8];
+
+ /* If BCCH/CCCH follows, limit to 2 dB */
+ if (next->pchan_is == GSM_PCHAN_CCCH)
+ ts->bcch_max_power_red_db = 2;
+ }
+ }
+
+ /* Timeslot 7 is always preceding BCCH/CCCH */
+ if (c0->ts[7].bcch_max_power_red_db > 0)
+ c0->ts[7].bcch_max_power_red_db = 2;
+
return 0;
}
diff --git a/src/osmo-bsc/lchan_fsm.c b/src/osmo-bsc/lchan_fsm.c
index 03ccec0..8ae83da 100644
--- a/src/osmo-bsc/lchan_fsm.c
+++ b/src/osmo-bsc/lchan_fsm.c
@@ -675,6 +675,13 @@
lchan->bs_power_db = bts->bs_power_ctrl.bs_power_val_db;
}
+ /* BS Power Control is generally not allowed on the BCCH/CCCH carrier.
+ * However, we allow it in the BCCH carrier power reduction mode of operation. */
+ if (lchan->ts->trx == bts->c0) {
+ lchan->bs_power_db = OSMO_MIN(lchan->ts->bcch_max_power_red_db,
+ lchan->bs_power_db);
+ }
+
if (lchan_activate_set_ch_mode_rate_and_mr_config(lchan))
return;
--
To view, visit https://gerrit.osmocom.org/c/osmo-bsc/+/24804
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Gerrit-Project: osmo-bsc
Gerrit-Branch: master
Gerrit-Change-Id: I2cc6a86731984f586ef35b43a8d3de631f7d8a2f
Gerrit-Change-Number: 24804
Gerrit-PatchSet: 1
Gerrit-Owner: fixeria <vyanitskiy at sysmocom.de>
Gerrit-MessageType: newchange
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