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
diff --git a/src/tbf_dl.cpp b/src/tbf_dl.cpp
index 0aa41a2..0726ef7 100644
--- a/src/tbf_dl.cpp
+++ b/src/tbf_dl.cpp
@@ -412,6 +412,7 @@
/* now we still have untransmitted LLC data, so we fill mac block */
rlc_data = m_rlc.block(bsn);
data = rlc_data->prepare(block_data_len);
+ rlc_data->cs = cs;
rh = (struct rlc_dl_header *)data;
rh->pt = 0; /* Data Block */
@@ -669,6 +670,53 @@
return dl_msg;
}
+static uint16_t bitnum_to_bsn(int bitnum, uint16_t ssn, uint16_t mod_sns)
+{
+ return (ssn - 1 - bitnum) & mod_sns;
+}
+
+int gprs_rlcmac_dl_tbf::analyse_errors(char *show_rbb, uint8_t ssn)
+{
+ gprs_rlc_data *rlc_data;
+ uint16_t lost = 0, received = 0, skipped = 0;
+
+ /* SSN - 1 is in range V(A)..V(S)-1 */
+ for (int bitpos = 0; bitpos < m_window.ws(); bitpos++) {
+ uint16_t bsn = bitnum_to_bsn(bitpos, ssn, m_window.mod_sns());
+
+ if (bsn == ((m_window.v_a() - 1) & m_window.mod_sns()))
+ break;
+
+ rlc_data = m_rlc.block(bsn);
+ if (!rlc_data)
+ continue;
+
+ if (rlc_data->cs != current_cs()) {
+ /* This block has already been encoded with a different
+ * CS, so it doesn't help us to decide, whether the
+ * current CS is ok. Ignore it. */
+ skipped += 1;
+ continue;
+ }
+
+ if (show_rbb[m_window.ws() - 1 - bitpos] == 'R') {
+ if (!m_window.m_v_b.is_acked(bsn))
+ received += 1;
+ } else {
+ lost += 1;
+ }
+ }
+
+ LOGP(DRLCMACDL, LOGL_DEBUG, "%s DL analysis, range=%d:%d, lost=%d, recv=%d, skipped=%d\n",
+ name(), m_window.v_a(), m_window.v_s(), lost, received, skipped);
+
+ if (lost + received == 0)
+ return -1;
+
+ return lost * 100 / (lost + received);
+}
+
+
int gprs_rlcmac_dl_tbf::update_window(const uint8_t ssn, const uint8_t *rbb)
{
int16_t dist; /* must be signed */
@@ -676,6 +724,7 @@
char show_rbb[65];
char show_v_b[RLC_MAX_SNS + 1];
const uint16_t mod_sns = m_window.mod_sns();
+ int error_rate;
Decoding::extract_rbb(rbb, show_rbb);
/* show received array in debug (bit 64..1) */
@@ -698,6 +747,11 @@
return 1; /* indicate to free TBF */
}
+ if (bts_data()->cs_adj_enabled && ms()) {
+ error_rate = analyse_errors(show_rbb, ssn);
+ ms()->update_error_rate(this, error_rate);
+ }
+
m_window.update(bts, show_rbb, ssn,
&lost, &received);