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
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@ -142,6 +142,9 @@ struct gprs_rlcmac_bts {
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uint8_t alpha, gamma;
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uint32_t dl_tbf_idle_msec; /* hold time for idle DL TBFs */
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uint32_t ms_idle_sec;
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uint8_t cs_adj_enabled;
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uint8_t cs_adj_upper_limit;
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uint8_t cs_adj_lower_limit;
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/* TBF handling, make private or move into TBFController */
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/* list of uplink TBFs */
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@ -351,3 +351,39 @@ void GprsMs::set_ms_class(uint8_t ms_class_)
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m_ms_class = ms_class_;
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}
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void GprsMs::update_error_rate(gprs_rlcmac_tbf *tbf, int error_rate)
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{
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struct gprs_rlcmac_bts *bts_data;
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OSMO_ASSERT(m_bts != NULL);
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bts_data = m_bts->bts_data();
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if (error_rate < 0)
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return;
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/* TODO: Support different CS values for UL and DL */
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if (error_rate > bts_data->cs_adj_upper_limit) {
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if (m_current_cs_dl > 1) {
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m_current_cs_dl -= 1;
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m_current_cs_ul = m_current_cs_dl;
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LOGP(DRLCMACDL, LOGL_INFO,
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"MS (IMSI %s): High error rate %d%%, "
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"reducing CS level to %d\n",
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imsi(), error_rate, m_current_cs_dl);
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}
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} else if (error_rate < bts_data->cs_adj_lower_limit) {
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if (m_current_cs_dl < 4) {
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m_current_cs_dl += 1;
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m_current_cs_ul = m_current_cs_dl;
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LOGP(DRLCMACDL, LOGL_INFO,
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"MS (IMSI %s): Low error rate %d%%, "
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"increasing CS level to %d\n",
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imsi(), error_rate, m_current_cs_dl);
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}
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} else {
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LOGP(DRLCMACDL, LOGL_DEBUG,
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"MS (IMSI %s): Medium error rate %d%%, ignored\n",
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imsi(), error_rate);
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}
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}
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@ -86,6 +86,8 @@ public:
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void detach_tbf(gprs_rlcmac_tbf *tbf);
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void update_error_rate(gprs_rlcmac_tbf *tbf, int percent);
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bool is_idle() const {return !m_ul_tbf && !m_dl_tbf && !m_ref;}
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void* operator new(size_t num);
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@ -173,6 +173,9 @@ int main(int argc, char *argv[])
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bts->n3105 = 8;
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bts->alpha = 0; /* a = 0.0 */
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bts->ms_idle_sec = 60; /* slightly above T3314 (default 44s, 24.008, 11.2.2) */
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bts->cs_adj_enabled = 1;
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bts->cs_adj_upper_limit = 33; /* Decrease CS if the error rate is above */
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bts->cs_adj_lower_limit = 10; /* Increase CS if the error rate is below */
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msgb_set_talloc_ctx(tall_pcu_ctx);
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@ -59,6 +59,8 @@ struct gprs_rlc_data {
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uint8_t block[RLC_MAX_LEN];
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/* block len of history */
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uint8_t len;
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uint8_t cs;
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};
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/*
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@ -363,6 +363,7 @@ protected:
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bool dl_window_stalled() const;
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void reuse_tbf(const uint8_t *data, const uint16_t len);
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void start_llc_timer();
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int analyse_errors(char *show_rbb, uint8_t ssn);
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struct osmo_timer_list m_llc_timer;
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};
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@ -412,6 +412,7 @@ struct msgb *gprs_rlcmac_dl_tbf::create_new_bsn(const uint32_t fn, const uint8_t
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/* now we still have untransmitted LLC data, so we fill mac block */
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rlc_data = m_rlc.block(bsn);
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data = rlc_data->prepare(block_data_len);
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rlc_data->cs = cs;
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rh = (struct rlc_dl_header *)data;
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rh->pt = 0; /* Data Block */
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@ -669,6 +670,53 @@ struct msgb *gprs_rlcmac_dl_tbf::create_dl_acked_block(
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return dl_msg;
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}
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static uint16_t bitnum_to_bsn(int bitnum, uint16_t ssn, uint16_t mod_sns)
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{
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return (ssn - 1 - bitnum) & mod_sns;
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}
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int gprs_rlcmac_dl_tbf::analyse_errors(char *show_rbb, uint8_t ssn)
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{
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gprs_rlc_data *rlc_data;
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uint16_t lost = 0, received = 0, skipped = 0;
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/* SSN - 1 is in range V(A)..V(S)-1 */
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for (int bitpos = 0; bitpos < m_window.ws(); bitpos++) {
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uint16_t bsn = bitnum_to_bsn(bitpos, ssn, m_window.mod_sns());
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if (bsn == ((m_window.v_a() - 1) & m_window.mod_sns()))
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break;
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rlc_data = m_rlc.block(bsn);
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if (!rlc_data)
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continue;
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if (rlc_data->cs != current_cs()) {
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/* This block has already been encoded with a different
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* CS, so it doesn't help us to decide, whether the
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* current CS is ok. Ignore it. */
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skipped += 1;
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continue;
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}
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if (show_rbb[m_window.ws() - 1 - bitpos] == 'R') {
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if (!m_window.m_v_b.is_acked(bsn))
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received += 1;
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} else {
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lost += 1;
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}
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}
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LOGP(DRLCMACDL, LOGL_DEBUG, "%s DL analysis, range=%d:%d, lost=%d, recv=%d, skipped=%d\n",
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name(), m_window.v_a(), m_window.v_s(), lost, received, skipped);
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if (lost + received == 0)
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return -1;
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return lost * 100 / (lost + received);
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}
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int gprs_rlcmac_dl_tbf::update_window(const uint8_t ssn, const uint8_t *rbb)
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{
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int16_t dist; /* must be signed */
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@ -676,6 +724,7 @@ int gprs_rlcmac_dl_tbf::update_window(const uint8_t ssn, const uint8_t *rbb)
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char show_rbb[65];
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char show_v_b[RLC_MAX_SNS + 1];
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const uint16_t mod_sns = m_window.mod_sns();
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int error_rate;
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Decoding::extract_rbb(rbb, show_rbb);
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/* show received array in debug (bit 64..1) */
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@ -698,6 +747,11 @@ int gprs_rlcmac_dl_tbf::update_window(const uint8_t ssn, const uint8_t *rbb)
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return 1; /* indicate to free TBF */
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}
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if (bts_data()->cs_adj_enabled && ms()) {
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error_rate = analyse_errors(show_rbb, ssn);
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ms()->update_error_rate(this, error_rate);
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}
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m_window.update(bts, show_rbb, ssn,
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&lost, &received);
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