Cellular Network Infrastructure » Radio Access Network » OsmoBTS

/* Loop control for OsmoBTS-TRX */

/* (C) 2013 by Andreas Eversberg <jolly@eversberg.eu>

 *

 * 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 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 <stdlib.h>

#include <errno.h>

#include <osmo-bts/gsm_data.h>

#include <osmo-bts/logging.h>

#include <osmo-bts/l1sap.h>

#include <osmocom/core/bits.h>

#include "trx_if.h"

#include "l1_if.h"

#include "loops.h"

/*

 * MS Power loop

 */

/*! Input a new RSSI value into the MS power control loop for the given logical channel.

 *  \param lchan logical channel

 *  \param chan_state L1 channel state of the logical channel.

 *  \param rssi Received Signal Strength Indication (in dBm) */

static void ms_power_val(struct gsm_lchan *lchan, struct l1sched_chan_state *chan_state, int8_t rssi)

{

int8_t ms_send;

int8_t my_target;

int8_t target_hi;

my_target = trx_phy_instance(lchan->ts->trx)->phy_link->u.osmotrx.trx_target_rssi;

target_hi = my_target - 15;

//LOGPLCHAN(lchan, DLOOP, LOGL_DEBUG, "Target check: %d\n", target_hi);

ms_send = lchan->ms_power_ctrl.current;

if (rssi > my_target)

{

ms_send = ms_send + 1;

LOGPLCHAN(lchan, DLOOP, LOGL_INFO, "RSSI value: %d, Set ms_power_ctrl.current +1 (DOWN power) value: %d\n", rssi, ms_send);

}

if (rssi < target_hi)

{

ms_send = ms_send - 1;

LOGPLCHAN(lchan, DLOOP, LOGL_INFO, "RSSI value: %d, Set ms_power_ctrl.current -1 (UP power) value: %d\n", rssi, ms_send);

}

//Protect 30..5:

if (ms_send > 30)

   ms_send = 30;

if (ms_send < 5)

   ms_send = 5;

//Write

lchan->ms_power_ctrl.current = ms_send;

}

/* 90% of one bit duration in 1/256 symbols: 256*0.9 */

#define TOA256_9OPERCENT	230

/*

 * Timing Advance loop

 */

void ta_val(struct gsm_lchan *lchan, struct l1sched_chan_state *chan_state, int16_t toa256)

{

	/* check if the current L1 header acks to the current ordered TA */

	if (lchan->meas.l1_info[1] != lchan->rqd_ta)

		return;

	/* sum measurement */

	chan_state->meas.toa256_sum += toa256;

	if (++(chan_state->meas.toa_num) < 16)

		return;

	/* complete set */

	toa256 = chan_state->meas.toa256_sum / chan_state->meas.toa_num;

	/* check for change of TOA */

	if (toa256 < -TOA256_9OPERCENT && lchan->rqd_ta > 0) {

		LOGPLCHAN(lchan, DLOOP, LOGL_DEBUG, "TOA is too early (%d), now lowering TA from %d to %d\n",

			toa256, lchan->rqd_ta, lchan->rqd_ta - 1);

		lchan->rqd_ta--;

	} else if (toa256 > TOA256_9OPERCENT && lchan->rqd_ta < 63) {

		LOGPLCHAN(lchan, DLOOP, LOGL_DEBUG, "TOA is too late (%d), now raising TA from %d to %d\n",

			toa256, lchan->rqd_ta, lchan->rqd_ta + 1);

		lchan->rqd_ta++;

	} else

		LOGPLCHAN(lchan, DLOOP, LOGL_DEBUG, "TOA is correct (%d), keeping current TA of %d\n",

			toa256, lchan->rqd_ta);

	chan_state->meas.toa_num = 0;

	chan_state->meas.toa256_sum = 0;

}

/*! Process a SACCH event as input to the MS power control and TA loop.  Function

 *  is called once every uplink SACCH block is received.

 * \param l1t L1 TRX instance on which we operate

 * \param chan_nr RSL channel number on which we operate

 * \param chan_state L1 scheduler channel state of the channel on which we operate

 * \param[in] rssi Receive Signal Strength Indication

 * \param[in] toa256 Time of Arrival in 1/256 symbol periods */

void trx_loop_sacch_input(struct l1sched_trx *l1t, uint8_t chan_nr,

	struct l1sched_chan_state *chan_state, int8_t rssi, int16_t toa256)

{

	struct gsm_lchan *lchan = &l1t->trx->ts[L1SAP_CHAN2TS(chan_nr)]

					.lchan[l1sap_chan2ss(chan_nr)];

	struct phy_instance *pinst = trx_phy_instance(l1t->trx);

	/* if MS power control loop is enabled, handle it */

	if (pinst->phy_link->u.osmotrx.trx_ms_power_loop)

		ms_power_val(lchan, chan_state, rssi);

	/* if TA loop is enabled, handle it */

	if (pinst->phy_link->u.osmotrx.trx_ta_loop)

		ta_val(lchan, chan_state, toa256);

}

/*! Called once every downlink SACCH block needs to be sent. */

void trx_loop_sacch_clock(struct l1sched_trx *l1t, uint8_t chan_nr,

	struct l1sched_chan_state *chan_state)

{

	struct gsm_lchan *lchan = &l1t->trx->ts[L1SAP_CHAN2TS(chan_nr)]

					.lchan[l1sap_chan2ss(chan_nr)];

//	struct phy_instance *pinst = trx_phy_instance(l1t->trx);

	if (lchan->ms_power_ctrl.fixed)

	        return;

//	if (pinst->phy_link->u.osmotrx.trx_ms_power_loop)

//		ms_power_clock(lchan, chan_state);

	/* count the number of SACCH clocks */

	chan_state->meas.clock++;

}

void trx_loop_amr_input(struct l1sched_trx *l1t, uint8_t chan_nr,

	struct l1sched_chan_state *chan_state, float ber)

{

	struct gsm_bts_trx *trx = l1t->trx;

	struct gsm_lchan *lchan = &trx->ts[L1SAP_CHAN2TS(chan_nr)]

					.lchan[l1sap_chan2ss(chan_nr)];

	/* check if loop is enabled */

	if (!chan_state->amr_loop)

		return;

	/* wait for MS to use the requested codec */

	if (chan_state->ul_ft != chan_state->dl_cmr)

		return;

	/* count bit errors */

	if (L1SAP_IS_CHAN_TCHH(chan_nr)) {

		chan_state->ber_num += 2;

		chan_state->ber_sum += (ber + ber);

	} else {

		chan_state->ber_num++;

		chan_state->ber_sum += ber;

	}

	/* count frames */

	if (chan_state->ber_num < 48)

		return;

	/* calculate average (reuse ber variable) */

	ber = chan_state->ber_sum / chan_state->ber_num;

	/* reset bit errors */

	chan_state->ber_num = 0;

	chan_state->ber_sum = 0;

	LOGPLCHAN(lchan, DLOOP, LOGL_DEBUG, "Current bit error rate (BER) %.6f "

		"codec id %d\n", ber, chan_state->ul_ft);

	/* degrade */

	if (chan_state->dl_cmr > 0) {

		/* degrade, if ber is above threshold FIXME: C/I */

		if (ber >

		   lchan->tch.amr_mr.bts_mode[chan_state->dl_cmr-1].threshold) {

			LOGPLCHAN(lchan, DLOOP, LOGL_DEBUG, "Degrading due to BER %.6f "

				"from codec id %d to %d\n", ber, chan_state->dl_cmr,

				chan_state->dl_cmr - 1);

			chan_state->dl_cmr--;

		}

	} else if (chan_state->dl_cmr < chan_state->codecs - 1) {

		/* degrade, if ber is above threshold  FIXME: C/I*/

		if (ber <

		    lchan->tch.amr_mr.bts_mode[chan_state->dl_cmr].threshold

		  - lchan->tch.amr_mr.bts_mode[chan_state->dl_cmr].hysteresis) {

			LOGPLCHAN(lchan, DLOOP, LOGL_DEBUG, "Upgrading due to BER %.6f "

				"from codec id %d to %d\n", ber, chan_state->dl_cmr,

				chan_state->dl_cmr + 1);

			chan_state->dl_cmr++;

		}

	}

}

void trx_loop_amr_set(struct l1sched_chan_state *chan_state, int loop)

{

	if (chan_state->amr_loop && !loop) {

		chan_state->amr_loop = 0;

		return;

	}

	if (!chan_state->amr_loop && loop) {

		chan_state->amr_loop = 1;

		/* reset bit errors */

		chan_state->ber_num = 0;

		chan_state->ber_sum = 0;

		return;

	}

}