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osmo-bsc/src/osmo-bsc/power_control.c

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/* MS Power Control Loop L1 */
/* (C) 2014 by Holger Hans Peter Freyther
* (C) 2020-2021 by sysmocom - s.f.m.c. GmbH <info@sysmocom.de>
* Author: Vadim Yanitskiy <vyanitskiy@sysmocom.de>
*
* All Rights Reserved
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as published by
* the Free Software Foundation; either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
*/
#include <stdint.h>
#include <unistd.h>
#include <errno.h>
#include <inttypes.h>
#include <osmocom/bsc/debug.h>
#include <osmocom/bsc/bts.h>
#include <osmocom/bsc/gsm_data.h>
#include <osmocom/bsc/bsc_subscriber.h>
#include <osmocom/bsc/abis_rsl.h>
#include <osmocom/bsc/meas_rep.h>
#include <osmocom/bsc/power_control.h>
/* We don't want to deal with floating point, so we scale up */
#define EWMA_SCALE_FACTOR 100
/* EWMA_SCALE_FACTOR/2 = +50: Round to nearest value when downscaling, otherwise floor() is applied. */
#define EWMA_ROUND_FACTOR (EWMA_SCALE_FACTOR / 2)
/* Base Low-Pass Single-Pole IIR Filter (EWMA) formula:
*
* Avg[n] = a * Val[n] + (1 - a) * Avg[n - 1]
*
* where parameter 'a' determines how much weight of the latest measurement value
* 'Val[n]' carries vs the weight of the accumulated average 'Avg[n - 1]'. The
* value of 'a' is usually a float in range 0 .. 1, so:
*
* - value 0.5 gives equal weight to both 'Val[n]' and 'Avg[n - 1]';
* - value 1.0 means no filtering at all (pass through);
* - value 0.0 makes no sense.
*
* Further optimization:
*
* Avg[n] = a * Val[n] + Avg[n - 1] - a * Avg[n - 1]
* ^^^^^^ ^^^^^^^^^^
*
* a) this can be implemented in C using '+=' operator:
*
* Avg += a * Val - a * Avg
* Avg += a * (Val - Avg)
*
* b) everything is scaled up by 100 to avoid floating point stuff:
*
* Avg100 += A * (Val - Avg)
*
* where 'Avg100' is 'Avg * 100' and 'A' is 'a * 100'.
*
* For more details, see:
*
* https://en.wikipedia.org/wiki/Moving_average
* https://en.wikipedia.org/wiki/Low-pass_filter#Simple_infinite_impulse_response_filter
* https://tomroelandts.com/articles/low-pass-single-pole-iir-filter
*/
static int do_pf_ewma(const struct gsm_power_ctrl_meas_params *mp,
struct gsm_power_ctrl_meas_proc_state *mps,
const int Val)
{
const uint8_t A = mp->ewma.alpha;
int *Avg100 = &mps->ewma.Avg100;
/* We don't have 'Avg[n - 1]' if this is the first run */
if (mps->meas_num++ == 0) {
*Avg100 = Val * EWMA_SCALE_FACTOR;
return Val;
}
*Avg100 += A * (Val - (*Avg100 + EWMA_ROUND_FACTOR) / EWMA_SCALE_FACTOR);
return (*Avg100 + EWMA_ROUND_FACTOR) / EWMA_SCALE_FACTOR;
}
/* Calculate target RxLev value from lower/upper thresholds */
#define CALC_TARGET(mp) \
((mp).lower_thresh + (mp).upper_thresh) / 2
static int do_avg_algo(const struct gsm_power_ctrl_meas_params *mp,
struct gsm_power_ctrl_meas_proc_state *mps,
const int val)
{
int val_avg;
switch (mp->algo) {
case GSM_PWR_CTRL_MEAS_AVG_ALGO_OSMO_EWMA:
val_avg = do_pf_ewma(mp, mps, val);
break;
/* TODO: implement other pre-processing methods */
case GSM_PWR_CTRL_MEAS_AVG_ALGO_NONE:
default:
/* No filtering (pass through) */
val_avg = val;
}
return val_avg;
}
/* Calculate a 'delta' value (for the given MS/BS power control parameters)
* to be applied to the current Tx power level to approach the target level. */
static int calc_delta_rxlev(const struct gsm_power_ctrl_params *params, const uint8_t rxlev)
{
int delta;
/* Check if RxLev is within the threshold window */
if (rxlev >= params->rxlev_meas.lower_thresh &&
rxlev <= params->rxlev_meas.upper_thresh)
return 0;
/* How many dBs measured power should be increased (+) or decreased (-)
* to reach expected power. */
delta = CALC_TARGET(params->rxlev_meas) - rxlev;
/* Don't ever change more than PWR_{LOWER,RAISE}_MAX_DBM during one loop
* iteration, i.e. reduce the speed at which the MS transmit power can
* change. A higher value means a lower level (and vice versa) */
if (delta > params->inc_step_size_db)
delta = params->inc_step_size_db;
else if (delta < -params->red_step_size_db)
delta = -params->red_step_size_db;
return delta;
}
/* Shall we skip current block based on configured interval? */
static bool ctrl_interval_skip_block(const struct gsm_power_ctrl_params *params,
struct lchan_power_ctrl_state *state)
{
/* Power control interval: how many blocks do we skip? */
if (state->skip_block_num-- > 0)
return true;
/* Can we be sure if ONE Report is always going to correspond
* to ONE SACCH block at the BTS? - If not this is as approximation
* but it should not hurt. */
/* Reset the number of SACCH blocks to be skipped:
* ctrl_interval=0 => 0 blocks to skip,
* ctrl_interval=1 => 1 blocks to skip,
* ctrl_interval=2 => 3 blocks to skip,
* so basically ctrl_interval * 2 - 1. */
state->skip_block_num = params->ctrl_interval * 2 - 1;
return false;
}
int lchan_ms_pwr_ctrl(struct gsm_lchan *lchan, const struct gsm_meas_rep *mr)
{
struct lchan_power_ctrl_state *state = &lchan->ms_power_ctrl;
struct gsm_bts_trx *trx = lchan->ts->trx;
struct gsm_bts *bts = trx->bts;
enum gsm_band band = bts->band;
const struct gsm_power_ctrl_params *params = &bts->ms_power_ctrl;
int8_t new_power_lvl; /* TS 05.05 power level */
int8_t ms_dbm, new_dbm, current_dbm, bsc_max_dbm;
uint8_t rxlev_avg;
uint8_t ms_power_lvl = ms_pwr_ctl_lvl(band, mr->ms_l1.pwr);
int8_t ul_rssi_dbm;
bool ignore;
if (params == NULL)
return 0;
/* Not doing the power loop here if we are not handling it */
if (params->mode != GSM_PWR_CTRL_MODE_DYN_BSC)
return 0;
/* Shall we skip current block based on configured interval? */
if (ctrl_interval_skip_block(params, state))
return 0;
/* If DTx is active on Uplink,
* use the '-SUB', otherwise '-FULL': */
if (mr->flags & MEAS_REP_F_UL_DTX)
ul_rssi_dbm = rxlev2dbm(mr->ul.sub.rx_lev);
else
ul_rssi_dbm = rxlev2dbm(mr->ul.full.rx_lev);
ms_dbm = ms_pwr_dbm(band, ms_power_lvl);
if (ms_dbm < 0) {
LOGPLCHAN(lchan, DLOOP, LOGL_NOTICE,
"Failed to calculate dBm for power ctl level %" PRIu8 " on band %s\n",
ms_power_lvl, gsm_band_name(band));
return 0;
}
bsc_max_dbm = bts->ms_max_power;
rxlev_avg = do_avg_algo(&params->rxlev_meas, &state->rxlev_meas_proc, dbm2rxlev(ul_rssi_dbm));
new_dbm = ms_dbm + calc_delta_rxlev(params, rxlev_avg);
/* Make sure new_dbm is never negative. ms_pwr_ctl_lvl() can later on
cope with any unsigned dbm value, regardless of band minimal value. */
if (new_dbm < 0)
new_dbm = 0;
/* Don't ask for smaller ms power level than the one set by ms max power for this BTS */
if (new_dbm > bsc_max_dbm)
new_dbm = bsc_max_dbm;
new_power_lvl = ms_pwr_ctl_lvl(band, new_dbm);
if (new_power_lvl < 0) {
LOGPLCHAN(lchan, DLOOP, LOGL_NOTICE,
"Failed to retrieve power level for %" PRId8 " dBm on band %d\n",
new_dbm, band);
return 0;
}
current_dbm = ms_pwr_dbm(band, lchan->ms_power);
/* In this Power Control Loop, we infer a new good MS Power Level based
* on the previous MS Power Level announced by the MS (not the previous
* one we requested!) together with the related computed measurements.
* Hence, and since we allow for several good MS Power Levels falling into our
* thresholds, we could finally converge into an oscillation loop where
* the MS bounces between 2 different correct MS Power levels all the
* time, due to the fact that we "accept" and "request back" whatever
* good MS Power Level we received from the MS, but at that time the MS
* will be transmitting using the previous MS Power Level we
* requested, which we will later "accept" and "request back" on next loop
* iteration. As a result MS effectively bounces between those 2 MS
* Power Levels.
* In order to fix this permanent oscillation, if current MS_PWR used/announced
* by MS is good ("ms_dbm == new_dbm", hence within thresholds and no change
* required) but has higher Tx power than the one we last requested, we ignore
* it and keep requesting for one with lower Tx power. This way we converge to
* the lowest good Tx power avoiding oscillating over values within thresholds.
*/
ignore = (ms_dbm == new_dbm && ms_dbm > current_dbm);
if (lchan->ms_power == new_power_lvl || ignore) {
LOGPLCHAN(lchan, DLOOP, LOGL_INFO, "Keeping MS power at control level %d (%d dBm): "
"ms-pwr-lvl[curr %" PRIu8 ", max %" PRIu8 "], RSSI[curr %d, avg %d, thresh %d..%d] dBm\n",
new_power_lvl, ms_dbm, ms_power_lvl, bsc_max_dbm, ul_rssi_dbm, rxlev2dbm(rxlev_avg),
rxlev2dbm(params->rxlev_meas.lower_thresh), rxlev2dbm(params->rxlev_meas.upper_thresh));
return 0;
}
LOGPLCHAN(lchan, DLOOP, LOGL_INFO, "%s MS power control level %d (%d dBm) => %d (%d dBm): "
"ms-pwr-lvl[curr %" PRIu8 ", max %" PRIu8 "], RSSI[curr %d, avg %d, thresh %d..%d] dBm\n",
(new_dbm > current_dbm) ? "Raising" : "Lowering",
lchan->ms_power, current_dbm, new_power_lvl, new_dbm, ms_power_lvl,
bsc_max_dbm, ul_rssi_dbm, rxlev2dbm(rxlev_avg),
rxlev2dbm(params->rxlev_meas.lower_thresh), rxlev2dbm(params->rxlev_meas.upper_thresh));
lchan_update_ms_power_ctrl_level(lchan, new_dbm);
return 1;
}
/* Default MS/BS Power Control parameters (see 3GPP TS 45.008, table A.1) */
const struct gsm_power_ctrl_params power_ctrl_params_def = {
/* Static Power Control is the safe default */
.mode = GSM_PWR_CTRL_MODE_STATIC,
/* BS Power reduction value / maximum (in dB) */
.bs_power_val_db = 0, /* no attenuation in static mode */
.bs_power_max_db = 12, /* up to 12 dB in dynamic mode */
/* Power increasing/reducing step size */
.inc_step_size_db = 4, /* 2, 4, or 6 dB */
.red_step_size_db = 2, /* 2 or 4 dB */
/* RxLev measurement parameters */
.rxlev_meas = {
.enabled = true,
/* Thresholds for RxLev (see 3GPP TS 45.008, A.3.2.1) */
.lower_thresh = 32, /* L_RXLEV_XX_P (-78 dBm) */
.upper_thresh = 38, /* U_RXLEV_XX_P (-72 dBm) */
/* Increase {UL,DL}_TXPWR if at least LOWER_CMP_P averages
* out of LOWER_CMP_N averages are lower than L_RXLEV_XX_P */
.lower_cmp_p = 10, /* P1 as in 3GPP TS 45.008, A.3.2.1 (case a) */
.lower_cmp_n = 12, /* N1 as in 3GPP TS 45.008, A.3.2.1 (case a) */
/* Decrease {UL,DL}_TXPWR if at least UPPER_CMP_P averages
* out of UPPER_CMP_N averages are greater than L_RXLEV_XX_P */
.upper_cmp_p = 19, /* P2 as in 3GPP TS 45.008, A.3.2.1 (case b) */
.upper_cmp_n = 20, /* N2 as in 3GPP TS 45.008, A.3.2.1 (case b) */
/* No averaging (filtering) by default */
.algo = GSM_PWR_CTRL_MEAS_AVG_ALGO_NONE,
/* Hreqave: the period over which an average is produced */
.h_reqave = 4, /* TODO: investigate a reasonable default value */
/* Hreqt: the number of averaged results maintained */
.h_reqt = 6, /* TODO: investigate a reasonable default value */
},
/* RxQual measurement parameters */
.rxqual_meas = {
.enabled = true,
/* Thresholds for RxQual (see 3GPP TS 45.008, A.3.2.1) */
.lower_thresh = 3, /* L_RXQUAL_XX_P (0.8% <= BER < 1.6%) */
.upper_thresh = 0, /* U_RXQUAL_XX_P (BER < 0.2%) */
/* Increase {UL,DL}_TXPWR if at least LOWER_CMP_P averages
* out of LOWER_CMP_N averages are lower than L_RXQUAL_XX_P */
.lower_cmp_p = 5, /* P3 as in 3GPP TS 45.008, A.3.2.1 (case c) */
.lower_cmp_n = 7, /* N3 as in 3GPP TS 45.008, A.3.2.1 (case c) */
/* Decrease {UL,DL}_TXPWR if at least UPPER_CMP_P averages
* out of UPPER_CMP_N averages are greater than L_RXQUAL_XX_P */
.upper_cmp_p = 15, /* P4 as in 3GPP TS 45.008, A.3.2.1 (case d) */
.upper_cmp_n = 18, /* N4 as in 3GPP TS 45.008, A.3.2.1 (case d) */
/* No averaging (filtering) by default */
.algo = GSM_PWR_CTRL_MEAS_AVG_ALGO_NONE,
/* Hreqave: the period over which an average is produced */
.h_reqave = 4, /* TODO: investigate a reasonable default value */
/* Hreqt: the number of averaged results maintained */
.h_reqt = 6, /* TODO: investigate a reasonable default value */
},
/* C/I measurement parameters.
* Target C/I retrieved from "GSM/EDGE: Evolution and Performance" Table 10.3.
* Set lower and upper so that (lower + upper) / 2 is equal or slightly
* above the target.
*/
.ci_fr_meas = { /* FR: Target C/I = 15 dB, Soft blocking threshold = 10 dB */
.enabled = false,
.lower_thresh = 13,
.upper_thresh = 17,
/* Increase {UL,DL}_TXPWR if at least LOWER_CMP_P averages
* out of LOWER_CMP_N averages are lower than L_CI_FR_XX_P */
.lower_cmp_p = 5, /* P3 as in 3GPP TS 45.008, A.3.2.1 (case c) */
.lower_cmp_n = 7, /* N3 as in 3GPP TS 45.008, A.3.2.1 (case c) */
/* Decrease {UL,DL}_TXPWR if at least UPPER_CMP_P averages
* out of UPPER_CMP_N averages are greater than L_CI_FR_XX_P */
.upper_cmp_p = 15, /* P4 as in 3GPP TS 45.008, A.3.2.1 (case d) */
.upper_cmp_n = 18, /* N4 as in 3GPP TS 45.008, A.3.2.1 (case d) */
/* No averaging (filtering) by default */
.algo = GSM_PWR_CTRL_MEAS_AVG_ALGO_NONE,
/* Hreqave: the period over which an average is produced */
.h_reqave = 4, /* TODO: investigate a reasonable default value */
/* Hreqt: the number of averaged results maintained */
.h_reqt = 6, /* TODO: investigate a reasonable default value */
},
.ci_hr_meas = { /* HR: Target C/I = 18 dB, Soft blocking threshold = 13 dB */
.enabled = false,
.lower_thresh = 16,
.upper_thresh = 21,
/* Increase {UL,DL}_TXPWR if at least LOWER_CMP_P averages
* out of LOWER_CMP_N averages are lower than L_CI_HR_XX_P */
.lower_cmp_p = 5, /* P3 as in 3GPP TS 45.008, A.3.2.1 (case c) */
.lower_cmp_n = 7, /* N3 as in 3GPP TS 45.008, A.3.2.1 (case c) */
/* Decrease {UL,DL}_TXPWR if at least UPPER_CMP_P averages
* out of UPPER_CMP_N averages are greater than L_CI_HR_XX_P */
.upper_cmp_p = 15, /* P4 as in 3GPP TS 45.008, A.3.2.1 (case d) */
.upper_cmp_n = 18, /* N4 as in 3GPP TS 45.008, A.3.2.1 (case d) */
/* No averaging (filtering) by default */
.algo = GSM_PWR_CTRL_MEAS_AVG_ALGO_NONE,
/* Hreqave: the period over which an average is produced */
.h_reqave = 4, /* TODO: investigate a reasonable default value */
/* Hreqt: the number of averaged results maintained */
.h_reqt = 6, /* TODO: investigate a reasonable default value */
},
.ci_amr_fr_meas = { /* AMR-FR: Target C/I = 9 dB, Soft blocking threshold = 4 dB */
.enabled = false,
.lower_thresh = 7,
.upper_thresh = 11,
/* Increase {UL,DL}_TXPWR if at least LOWER_CMP_P averages
* out of LOWER_CMP_N averages are lower than L_CI_AMR_FR_XX_P */
.lower_cmp_p = 5, /* P3 as in 3GPP TS 45.008, A.3.2.1 (case c) */
.lower_cmp_n = 7, /* N3 as in 3GPP TS 45.008, A.3.2.1 (case c) */
/* Decrease {UL,DL}_TXPWR if at least UPPER_CMP_P averages
* out of UPPER_CMP_N averages are greater than L_CI_AMR_FR_XX_P */
.upper_cmp_p = 15, /* P4 as in 3GPP TS 45.008, A.3.2.1 (case d) */
.upper_cmp_n = 18, /* N4 as in 3GPP TS 45.008, A.3.2.1 (case d) */
/* No averaging (filtering) by default */
.algo = GSM_PWR_CTRL_MEAS_AVG_ALGO_NONE,
/* Hreqave: the period over which an average is produced */
.h_reqave = 4, /* TODO: investigate a reasonable default value */
/* Hreqt: the number of averaged results maintained */
.h_reqt = 6, /* TODO: investigate a reasonable default value */
},
.ci_amr_hr_meas = { /* AMR-HR: Target C/I = 15 dB, Soft blocking threshold = 10 dB */
.enabled = false,
.lower_thresh = 13,
.upper_thresh = 17,
/* Increase {UL,DL}_TXPWR if at least LOWER_CMP_P averages
* out of LOWER_CMP_N averages are lower than L_CI_AMR_HR_XX_P */
.lower_cmp_p = 5, /* P3 as in 3GPP TS 45.008, A.3.2.1 (case c) */
.lower_cmp_n = 7, /* N3 as in 3GPP TS 45.008, A.3.2.1 (case c) */
/* Decrease {UL,DL}_TXPWR if at least UPPER_CMP_P averages
* out of UPPER_CMP_N averages are greater than L_CI_AMR_HR_XX_P */
.upper_cmp_p = 15, /* P4 as in 3GPP TS 45.008, A.3.2.1 (case d) */
.upper_cmp_n = 18, /* N4 as in 3GPP TS 45.008, A.3.2.1 (case d) */
/* No averaging (filtering) by default */
.algo = GSM_PWR_CTRL_MEAS_AVG_ALGO_NONE,
/* Hreqave: the period over which an average is produced */
.h_reqave = 4, /* TODO: investigate a reasonable default value */
/* Hreqt: the number of averaged results maintained */
.h_reqt = 6, /* TODO: investigate a reasonable default value */
},
.ci_sdcch_meas = { /* SDCCH: Target C/I = 14 dB, Soft blocking threshold = 9 dB */
.enabled = false,
.lower_thresh = 12,
.upper_thresh = 16,
/* Increase {UL,DL}_TXPWR if at least LOWER_CMP_P averages
* out of LOWER_CMP_N averages are lower than L_CI_SDCCH_XX_P */
.lower_cmp_p = 5, /* P3 as in 3GPP TS 45.008, A.3.2.1 (case c) */
.lower_cmp_n = 7, /* N3 as in 3GPP TS 45.008, A.3.2.1 (case c) */
/* Decrease {UL,DL}_TXPWR if at least UPPER_CMP_P averages
* out of UPPER_CMP_N averages are greater than L_CI_SDCCH_XX_P */
.upper_cmp_p = 15, /* P4 as in 3GPP TS 45.008, A.3.2.1 (case d) */
.upper_cmp_n = 18, /* N4 as in 3GPP TS 45.008, A.3.2.1 (case d) */
/* No averaging (filtering) by default */
.algo = GSM_PWR_CTRL_MEAS_AVG_ALGO_NONE,
/* Hreqave: the period over which an average is produced */
.h_reqave = 4, /* TODO: investigate a reasonable default value */
/* Hreqt: the number of averaged results maintained */
.h_reqt = 6, /* TODO: investigate a reasonable default value */
},
.ci_gprs_meas = { /* GPRS: Target C/I = 20 dB, Soft blocking threshold = 15 dB */
.enabled = false,
.lower_thresh = 18,
.upper_thresh = 24,
/* Increase {UL,DL}_TXPWR if at least LOWER_CMP_P averages
* out of LOWER_CMP_N averages are lower than L_CI_GPRS_XX_P */
.lower_cmp_p = 5, /* P3 as in 3GPP TS 45.008, A.3.2.1 (case c) */
.lower_cmp_n = 7, /* N3 as in 3GPP TS 45.008, A.3.2.1 (case c) */
/* Decrease {UL,DL}_TXPWR if at least UPPER_CMP_P averages
* out of UPPER_CMP_N averages are greater than L_CI_GPRS_XX_P */
.upper_cmp_p = 15, /* P4 as in 3GPP TS 45.008, A.3.2.1 (case d) */
.upper_cmp_n = 18, /* N4 as in 3GPP TS 45.008, A.3.2.1 (case d) */
/* No averaging (filtering) by default */
.algo = GSM_PWR_CTRL_MEAS_AVG_ALGO_NONE,
/* Hreqave: the period over which an average is produced */
.h_reqave = 4, /* TODO: investigate a reasonable default value */
/* Hreqt: the number of averaged results maintained */
.h_reqt = 6, /* TODO: investigate a reasonable default value */
},
};
void power_ctrl_params_def_reset(struct gsm_power_ctrl_params *params,
enum gsm_power_ctrl_dir dir)
{
*params = power_ctrl_params_def;
params->dir = dir;
/* Trigger loop every N-th SACCH block. See 3GPP TS 45.008 section 4.7.1. */
if (dir == GSM_PWR_CTRL_DIR_UL)
params->ctrl_interval = 2; /* N=4 (1.92s) */
else
params->ctrl_interval = 1; /* N=2 (0.960) */
}
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