jolly has uploaded this change for review.
Transmit invalid AMR speech blocks instead of dummy FACCH
Every BTS needs to have some graceful handling for the scenario
where it is time to send out a speech frame on TCH DL, but there is
no frame to be sent. One possible solution is to transmit dummy
FACCH, but this option is unattractive for TCH/HS where FACCH
displaces two speech frames rather than one. A more elegant solution
is to emit a speech frame that is bad, causing the MS receiver to
declare a BFI condition to trigger substitution and muting procedure.
A bad frame is generated by gsm0503_tch_{afs,ahs}_encode() by setting
the playload length to 0.
Depends: libosmocore.git I82ce2adf995a4b42d1f378c5819f88d773b9104a
Related: OS#6049
Change-Id: I056f379715c91ad968f198e112d363a9009dc1c3
---
M src/osmo-bts-trx/sched_lchan_tchf.c
M src/osmo-bts-trx/sched_lchan_tchh.c
2 files changed, 49 insertions(+), 1 deletion(-)
git pull ssh://gerrit.osmocom.org:29418/osmo-bts refs/changes/32/35132/1
diff --git a/src/osmo-bts-trx/sched_lchan_tchf.c b/src/osmo-bts-trx/sched_lchan_tchf.c
index 0138a2a..8f5a2db 100644
--- a/src/osmo-bts-trx/sched_lchan_tchf.c
+++ b/src/osmo-bts-trx/sched_lchan_tchf.c
@@ -538,6 +538,9 @@
/* - If the channel mode is TCH/FS or TCH/EFS, transmit a dummy
* speech block with inverted CRC3, designed to induce a BFI
* condition in the MS receiver.
+ * - If the channel mode is AMR, transmit a dummy with speech
+ * block with inverted CRC6, designed to induce a BFI
+ * condition in the MS receiver.
* - If the channel mode is one of the CSD modes, transmit an
* idle frame as described in 3GPP TS 44.021, sections 8.1.6
* and 10.2.3 (all data, status and E-bits set to binary '1').
@@ -554,6 +557,18 @@
case GSM48_CMODE_DATA_3k6:
case GSM48_CMODE_DATA_14k5:
break; /* see below */
+ case GSM48_CMODE_SPEECH_AMR:
+ /* the first FN 4,13,21 defines that CMI is included in frame,
+ * the first FN 0,8,17 defines that CMR is included in frame.
+ */
+ gsm0503_tch_afs_encode(BUFPOS(bursts_p, 0),
+ NULL, 0,
+ !sched_tchf_dl_amr_cmi_map[br->fn % 26],
+ chan_state->codec,
+ chan_state->codecs,
+ chan_state->dl_ft,
+ chan_state->dl_cmr);
+ goto send_burst;
case GSM48_CMODE_SPEECH_V1:
case GSM48_CMODE_SPEECH_EFR:
rc = gsm0503_tch_fr_encode(BUFPOS(bursts_p, 0), NULL, 0, 1);
diff --git a/src/osmo-bts-trx/sched_lchan_tchh.c b/src/osmo-bts-trx/sched_lchan_tchh.c
index e0d7aca..afd4eb8 100644
--- a/src/osmo-bts-trx/sched_lchan_tchh.c
+++ b/src/osmo-bts-trx/sched_lchan_tchh.c
@@ -451,7 +451,7 @@
LOGL1SB(DL1P, LOGL_INFO, l1ts, br, "No TCH or FACCH prim for transmit.\n");
/* - If the channel mode is TCH/HS, transmit a dummy speech block
- * with inverted CRC3, designed to induce a BFI condition in
+ * with inverted CRC3 or CRC6, designed to induce a BFI condition in
* the MS receiver.
* - If the channel mode is one of the CSD modes, transmit an
* idle frame as described in 3GPP TS 44.021, sections 8.1.6
@@ -467,6 +467,18 @@
case GSM48_CMODE_DATA_6k0:
case GSM48_CMODE_DATA_3k6:
break; /* see below */
+ case GSM48_CMODE_SPEECH_AMR:
+ /* the first FN 4,13,21 or 5,14,22 defines that CMI is included
+ * in frame, the first FN 0,8,17 or 1,9,18 defines that CMR is
+ * included in frame. */
+ gsm0503_tch_ahs_encode(BUFPOS(bursts_p, 0),
+ NULL, 0,
+ !sched_tchh_dl_amr_cmi_map[br->fn % 26],
+ chan_state->codec,
+ chan_state->codecs,
+ chan_state->dl_ft,
+ chan_state->dl_cmr);
+ goto send_burst;
case GSM48_CMODE_SPEECH_V1:
rc = gsm0503_tch_hr_encode(BUFPOS(bursts_p, 0), NULL, 0);
if (rc == 0)
To view, visit change 35132. To unsubscribe, or for help writing mail filters, visit settings.