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authorJacob Erlbeck <jerlbeck@sysmocom.de>2015-06-04 12:12:32 +0200
committerJacob Erlbeck <jerlbeck@sysmocom.de>2015-06-08 09:40:09 +0200
commit1751c62c980f8d6ed965e08fcb9ad1af485d8854 (patch)
tree80b46ca4327c0902778eb3fd62e4c751af866f98
parentf47f68a9d8e4421398e2369e4b18de8c52a9d396 (diff)
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
-rw-r--r--src/bts.h3
-rw-r--r--src/gprs_ms.cpp36
-rw-r--r--src/gprs_ms.h2
-rw-r--r--src/pcu_main.cpp3
-rw-r--r--src/rlc.h2
-rw-r--r--src/tbf.h1
-rw-r--r--src/tbf_dl.cpp54
7 files changed, 101 insertions, 0 deletions
diff --git a/src/bts.h b/src/bts.h
index af66dfc..b31db5f 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 */
diff --git a/src/gprs_ms.cpp b/src/gprs_ms.cpp
index dc8783c..f5924fd 100644
--- a/src/gprs_ms.cpp
+++ b/src/gprs_ms.cpp
@@ -351,3 +351,39 @@ void GprsMs::set_ms_class(uint8_t ms_class_)
m_ms_class = ms_class_;
}
+void GprsMs::update_error_rate(gprs_rlcmac_tbf *tbf, int error_rate)
+{
+ struct gprs_rlcmac_bts *bts_data;
+
+ OSMO_ASSERT(m_bts != NULL);
+ bts_data = m_bts->bts_data();
+
+ if (error_rate < 0)
+ return;
+
+ /* TODO: Support different CS values for UL and DL */
+
+ if (error_rate > bts_data->cs_adj_upper_limit) {
+ if (m_current_cs_dl > 1) {
+ m_current_cs_dl -= 1;
+ m_current_cs_ul = m_current_cs_dl;
+ LOGP(DRLCMACDL, LOGL_INFO,
+ "MS (IMSI %s): High error rate %d%%, "
+ "reducing CS level to %d\n",
+ imsi(), error_rate, m_current_cs_dl);
+ }
+ } else if (error_rate < bts_data->cs_adj_lower_limit) {
+ if (m_current_cs_dl < 4) {
+ m_current_cs_dl += 1;
+ m_current_cs_ul = m_current_cs_dl;
+ LOGP(DRLCMACDL, LOGL_INFO,
+ "MS (IMSI %s): Low error rate %d%%, "
+ "increasing CS level to %d\n",
+ imsi(), error_rate, m_current_cs_dl);
+ }
+ } else {
+ LOGP(DRLCMACDL, LOGL_DEBUG,
+ "MS (IMSI %s): Medium error rate %d%%, ignored\n",
+ imsi(), error_rate);
+ }
+}
diff --git a/src/gprs_ms.h b/src/gprs_ms.h
index 0185836..27c4be4 100644
--- a/src/gprs_ms.h
+++ b/src/gprs_ms.h
@@ -86,6 +86,8 @@ public:
void detach_tbf(gprs_rlcmac_tbf *tbf);
+ void update_error_rate(gprs_rlcmac_tbf *tbf, int percent);
+
bool is_idle() const {return !m_ul_tbf && !m_dl_tbf && !m_ref;}
void* operator new(size_t num);
diff --git a/src/pcu_main.cpp b/src/pcu_main.cpp
index 9e96af0..2e4a970 100644
--- a/src/pcu_main.cpp
+++ b/src/pcu_main.cpp
@@ -173,6 +173,9 @@ int main(int argc, char *argv[])
bts->n3105 = 8;
bts->alpha = 0; /* a = 0.0 */
bts->ms_idle_sec = 60; /* slightly above T3314 (default 44s, 24.008, 11.2.2) */
+ bts->cs_adj_enabled = 1;
+ bts->cs_adj_upper_limit = 33; /* Decrease CS if the error rate is above */
+ bts->cs_adj_lower_limit = 10; /* Increase CS if the error rate is below */
msgb_set_talloc_ctx(tall_pcu_ctx);
diff --git a/src/rlc.h b/src/rlc.h
index 55cae3f..313f3c7 100644
--- a/src/rlc.h
+++ b/src/rlc.h
@@ -59,6 +59,8 @@ struct gprs_rlc_data {
uint8_t block[RLC_MAX_LEN];
/* block len of history */
uint8_t len;
+
+ uint8_t cs;
};
/*
diff --git a/src/tbf.h b/src/tbf.h
index f50c489..8e4c3b9 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;
};
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 @@ struct msgb *gprs_rlcmac_dl_tbf::create_new_bsn(const uint32_t fn, const uint8_t
/* 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 @@ struct msgb *gprs_rlcmac_dl_tbf::create_dl_acked_block(
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 @@ int gprs_rlcmac_dl_tbf::update_window(const uint8_t ssn, const uint8_t *rbb)
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 @@ int gprs_rlcmac_dl_tbf::update_window(const uint8_t ssn, const uint8_t *rbb)
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);