103 lines
3.3 KiB
C
103 lines
3.3 KiB
C
/* Loop control for Timing Advance */
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/* (C) 2013 by Andreas Eversberg <jolly@eversberg.eu>
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* (C) 2021 by sysmocom - s.f.m.c. GmbH <info@sysmocom.de>
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*
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* All Rights Reserved
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU Affero General Public License as published by
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* the Free Software Foundation; either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Affero General Public License for more details.
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*
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* You should have received a copy of the GNU Affero General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*
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*/
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/* Related specs: 3GPP TS 45.010 sections 5.5, 5.6 */
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#include <osmo-bts/gsm_data.h>
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#include <osmo-bts/bts_trx.h>
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#include <osmo-bts/logging.h>
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/* 3GPP TS 45.010 sec 5.6.3 Delay assessment error:
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* 75% of one bit duration in 1/256 symbols: 256*0.75 */
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#define TOA256_THRESH 192
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/* rqd_ta value range */
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#define TA_MIN 0
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#define TA_MAX 63
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/* TODO: make configurable over osmo-bts VTY? Pass it BSC->BTS? */
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#define TA_MAX_INC_STEP 2
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#define TA_MAX_DEC_STEP 2
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/*! compute the new "Ordered Timing Advance" communicated to the MS and store it in lchan.
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* \param lchan logical channel for which to compute (and in which to store) new power value.
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* \param[in] ms_tx_ta The TA used by the MS and reported in L1SACCH, see struct gsm_sacch_l1_hdr field "ta".
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* \param[in] toa256 Time of Arrival (in 1/256th bits) computed at Rx side
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*/
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void lchan_ms_ta_ctrl(struct gsm_lchan *lchan, uint8_t ms_tx_ta, int16_t toa256)
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{
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int16_t new_ta;
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/* Shall we skip current block based on configured interval? */
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/* TA control interval: how many blocks do we skip? */
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if (lchan->ta_ctrl.skip_block_num-- > 0)
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return;
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/* Reset the number of SACCH blocks to be skipped:
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* ctrl_interval=0 => 0 blocks to skip,
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* ctrl_interval=1 => 1 blocks to skip,
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* ctrl_interval=2 => 3 blocks to skip,
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* so basically ctrl_interval * 2 - 1. */
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lchan->ta_ctrl.skip_block_num = lchan->ts->trx->ta_ctrl_interval * 2 - 1;
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int16_t delta_ta = toa256/256;
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if (toa256 >= 0) {
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if ((toa256 - (256 * delta_ta)) > TOA256_THRESH)
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delta_ta++;
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if (delta_ta > TA_MAX_INC_STEP)
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delta_ta = TA_MAX_INC_STEP;
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} else {
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if ((toa256 - (256 * delta_ta)) < -TOA256_THRESH)
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delta_ta--;
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if (delta_ta < -TA_MAX_DEC_STEP)
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delta_ta = -TA_MAX_DEC_STEP;
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}
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new_ta = ms_tx_ta + delta_ta;
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/* Make sure new_ta is never negative: */
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if (new_ta < TA_MIN)
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new_ta = TA_MIN;
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/* Don't ask for out of range TA: */
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if (new_ta > TA_MAX)
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new_ta = TA_MAX;
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if (lchan->ta_ctrl.current == (uint8_t)new_ta) {
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LOGPLCHAN(lchan, DLOOP, LOGL_DEBUG,
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"Keeping current TA at %u: TOA was %d\n",
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lchan->ta_ctrl.current, toa256);
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return;
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}
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LOGPLCHAN(lchan, DLOOP, LOGL_INFO,
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"%s TA %u => %u: TOA was too %s (%d)\n",
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(uint8_t)new_ta > lchan->ta_ctrl.current ? "Raising" : "Lowering",
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lchan->ta_ctrl.current, (uint8_t)new_ta,
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(uint8_t)new_ta > lchan->ta_ctrl.current ? "late" : "early",
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toa256);
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/* store the resulting new TA in the lchan */
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lchan->ta_ctrl.current = (uint8_t)new_ta;
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}
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