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, 1 insertions, 0 deletions

diff --git a/src/tbf.h b/src/tbf.h
index f50c489a..8e4c3b98 100644
--- a/src/tbf.h
+++ b/src/tbf.h
@@ -363,6 +363,7 @@ protected:
 	bool dl_window_stalled() const;
 	void reuse_tbf(const uint8_t *data, const uint16_t len);
 	void start_llc_timer();
+	int analyse_errors(char *show_rbb, uint8_t ssn);
 
 	struct osmo_timer_list m_llc_timer;
 };