trxcon/scheduler: refactor Downlink measurement processing

So far we used to store the sums of ToA and RSSI measurements in the
logical channel state, and after decoding of a block, we did calculate
the average. This approach works fine for xCCH and PDTCH, but when it
comes to block-diagonal interleaving (which is used on TCH/F and TCH/H
channels), the results are incorrect. The problem is that a burst on
TCH may carry 57 bits of one encoded frame and 57 bits of another.

Instead of calculating the sum of measurements on the fly, let's push
them into a circular buffer (the measurement history), and keep them
there even after decoding of a block. This would allow us to calculate
the average of N last measurements depending on the interleaving type.

A single circular buffer can hold up to 8 unique measurements, so the
recent measurements would basically override the oldest ones.

Change-Id: I211ee3314f0a284112a4deddc0e93028f4a27cef

1 files changed, 4 insertions, 11 deletions

diff --git a/src/host/trxcon/sched_lchan_common.c b/src/host/trxcon/sched_lchan_common.c
index 813f3157..55ec7e95 100644
--- a/src/host/trxcon/sched_lchan_common.c
+++ b/src/host/trxcon/sched_lchan_common.c
@@ -126,9 +126,9 @@ int sched_send_dt_ind(struct trx_instance *trx, struct trx_ts *ts,
 	struct trx_lchan_state *lchan, uint8_t *l2, size_t l2_len,
 	int bit_error_count, bool dec_failed, bool traffic)
 {
+	const struct trx_meas_set *meas = &lchan->meas_avg;
 	const struct trx_lchan_desc *lchan_desc;
 	struct l1ctl_info_dl dl_hdr;
-	int dbm_avg = 0;
 
 	/* Set up pointers */
 	lchan_desc = &trx_lchan_desc[lchan->type];
@@ -140,15 +140,8 @@ int sched_send_dt_ind(struct trx_instance *trx, struct trx_ts *ts,
 	dl_hdr.frame_nr = htonl(lchan->rx_first_fn);
 	dl_hdr.num_biterr = bit_error_count;
 
-	/* Convert average RSSI to RX level */
-	if (lchan->meas.num) {
-		/* RX level: 0 .. 63 in typical GSM notation (dBm + 110) */
-		dbm_avg = lchan->meas.rssi_sum / lchan->meas.num;
-		dl_hdr.rx_level = dbm2rxlev(dbm_avg);
-	} else {
-		/* No measurements, assuming the worst */
-		dl_hdr.rx_level = 0;
-	}
+	/* RX level: 0 .. 63 in typical GSM notation (dBm + 110) */
+	dl_hdr.rx_level = dbm2rxlev(meas->rssi);
 
 	/* FIXME: set proper values */
 	dl_hdr.snr = 0;
@@ -162,7 +155,7 @@ int sched_send_dt_ind(struct trx_instance *trx, struct trx_ts *ts,
 	/* Optional GSMTAP logging */
 	if (l2_len > 0 && (!traffic || lchan_desc->chan_nr == RSL_CHAN_OSMO_PDCH)) {
 		sched_gsmtap_send(lchan->type, lchan->rx_first_fn, ts->index,
-				  trx->band_arfcn, dbm_avg, 0, l2, l2_len);
+				  trx->band_arfcn, meas->rssi, 0, l2, l2_len);
 	}
 
 	return 0;