Added timing advance support for up and downlink TBFs

The timing advance of any TBF is stored when it ends. Whenever a new TBF
with the same TLLI is created (downlink TBF), the stored TA is recalled.

This algorithm assumes that the mobile does not move too fast during
transfer. Also the mobile must start a connection in order to get correct
initial timing advance.

This algorithm does not implement the timing advance procedure as defined
in TS 04.60. To implement the standard timing advance procedure, the BTS
must decode RACH on certain bursts, the mobile is expected to send them.
This requires much more complexity to a transceiver like USRP/UmTRX or
Calypso BTS.

The algorithm was tested at TA >= 8 and works quite well.

1 files changed, 42 insertions, 2 deletions

diff --git a/src/gprs_rlcmac_data.cpp b/src/gprs_rlcmac_data.cpp
index 1109451e..4f2b649a 100644
--- a/src/gprs_rlcmac_data.cpp
+++ b/src/gprs_rlcmac_data.cpp
@@ -206,6 +206,15 @@ int gprs_rlcmac_poll_timeout(struct gprs_rlcmac_tbf *tbf)
 	return 0;
 }
 
+int gprs_rlcmac_sba_timeout(struct gprs_rlcmac_sba *sba)
+{
+	LOGP(DRLCMAC, LOGL_NOTICE, "Poll timeout for SBA\n");
+	llist_del(&sba->list);
+	talloc_free(sba);
+
+	return 0;
+}
+
 static uint8_t get_ms_class_by_capability(MS_Radio_Access_capability_t *cap)
 {
 	int i;
@@ -263,6 +272,7 @@ int gprs_rlcmac_rcv_control_block(bitvec *rlc_block, uint8_t trx, uint8_t ts,
 	int8_t tfi = 0; /* must be signed */
 	uint32_t tlli = 0;
 	struct gprs_rlcmac_tbf *tbf;
+	struct gprs_rlcmac_sba *sba;
 	int rc;
 
 	RlcMacUplink_t * ul_control_block = (RlcMacUplink_t *)talloc_zero(tall_pcu_ctx, RlcMacUplink_t);
@@ -420,6 +430,7 @@ int gprs_rlcmac_rcv_control_block(bitvec *rlc_block, uint8_t trx, uint8_t ts,
 			if (!tbf) {
 				uint8_t ms_class = 0;
 				struct gprs_rlcmac_tbf *dl_tbf;
+				uint8_t ta;
 
 				if ((dl_tbf = tbf_by_tlli(tlli, GPRS_RLCMAC_DL_TBF))) {
 					LOGP(DRLCMACUL, LOGL_NOTICE, "Got RACH from "
@@ -431,12 +442,28 @@ int gprs_rlcmac_rcv_control_block(bitvec *rlc_block, uint8_t trx, uint8_t ts,
 				LOGP(DRLCMAC, LOGL_DEBUG, "MS requests UL TBF "
 					"in packet ressource request of single "
 					"block, so we provide one:\n");
+				sba = sba_find(trx, ts, fn);
+				if (!sba) {
+					LOGP(DRLCMAC, LOGL_NOTICE, "MS requests UL TBF "
+						"in packet ressource request of single "
+						"block, but there is no resource request "
+						"scheduled!\n");
+					rc = recall_timing_advance(tlli);
+					if (rc >= 0)
+						ta = rc;
+					else
+						ta = 0;
+				} else {
+					ta = sba->ta;
+					remember_timing_advance(tlli, ta);
+					llist_del(&sba->list);
+					talloc_free(sba);
+				}
 				if (ul_control_block->u.Packet_Resource_Request.Exist_MS_Radio_Access_capability)
 					ms_class = get_ms_class_by_capability(&ul_control_block->u.Packet_Resource_Request.MS_Radio_Access_capability);
 				if (!ms_class)
 					LOGP(DRLCMAC, LOGL_NOTICE, "MS does not give us a class.\n");
-				tbf = alloc_ul_tbf(trx, ms_class, tlli, 0, NULL);
-#warning FIXME TA!!!
+				tbf = alloc_ul_tbf(trx, ms_class, tlli, ta, NULL);
 				if (!tbf)
 					break;
 				/* set control ts to current MS's TS, until assignment complete */
@@ -469,6 +496,17 @@ int gprs_rlcmac_rcv_control_block(bitvec *rlc_block, uint8_t trx, uint8_t ts,
 		LOGP(DRLCMAC, LOGL_ERROR, "RX: [PCU <- BTS] %s TFI: %u TLLI: 0x%08x FIXME: Packet ressource request\n", (tbf->direction == GPRS_RLCMAC_UL_TBF) ? "UL" : "DL", tbf->tfi, tbf->tlli);
 		break;
 	case MT_PACKET_MEASUREMENT_REPORT:
+		sba = sba_find(trx, ts, fn);
+		if (!sba) {
+			LOGP(DRLCMAC, LOGL_NOTICE, "MS send measurement "
+				"in packet ressource request of single "
+				"block, but there is no resource request "
+				"scheduled!\n");
+		} else {
+			remember_timing_advance(ul_control_block->u.Packet_Measurement_Report.TLLI, sba->ta);
+			llist_del(&sba->list);
+			talloc_free(sba);
+		}
 		gprs_rlcmac_meas_rep(&ul_control_block->u.Packet_Measurement_Report);
 		break;
 	default:
@@ -888,6 +926,8 @@ int gprs_rlcmac_rcv_data_block_acknowledged(uint8_t trx, uint8_t ts,
 		}
 		/* mark TLLI valid now */
 		tbf->tlli_valid = 1;
+		/* store current timing advance */
+		remember_timing_advance(tbf->tlli, tbf->ta);
 	/* already have TLLI, but we stille get another one */
 	} else if (rh->ti) {
 		uint32_t tlli;