tbf: Add adaptive DL CS adjustment

To cope with transmission failures due to bad radio conditions, a
different coding scheme with more redundance can be used.

This commit adds an implemenation that is based on the Ack/Nack
ratio per PACKET DOWNLINK ACK/NACK message received from the MS.

Basically the CS level is decreased, if the block error rate goes
above cs_adj_upper_limit (default 33%), and it is increased, if the
rate drops below cs_adj_lower_limit (default 10%). Only blocks that
have been encoded with the current CS are taken into account.

Note that this approach doesn't measure the MS->BTS conditions and
that the measurement values reported by the MS are not taken into
account.

Ticket: #1739
Sponsored-by: On-Waves ehf

1 files changed, 3 insertions, 0 deletions

diff --git a/src/bts.h b/src/bts.h
index af66dfc8..b31db5fc 100644
--- a/src/bts.h
+++ b/src/bts.h
@@ -142,6 +142,9 @@ struct gprs_rlcmac_bts {
 	uint8_t alpha, gamma;
 	uint32_t dl_tbf_idle_msec; /* hold time for idle DL TBFs */
 	uint32_t ms_idle_sec;
+	uint8_t cs_adj_enabled;
+	uint8_t cs_adj_upper_limit;
+	uint8_t cs_adj_lower_limit;
 
 	/* TBF handling, make private or move into TBFController */
 	/* list of uplink TBFs */