344 lines
9.1 KiB
C
344 lines
9.1 KiB
C
/* Handover Decision making for Inter-BTS (Intra-BSC) Handover. This
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* only implements the handover algorithm/decision, but not execution
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* of it */
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/* (C) 2009 by Harald Welte <laforge@gnumonks.org>
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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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#include <stdlib.h>
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#include <errno.h>
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#include <osmocom/core/msgb.h>
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#include <osmocom/bsc/debug.h>
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#include <osmocom/bsc/gsm_data.h>
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#include <osmocom/bsc/meas_rep.h>
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#include <osmocom/bsc/signal.h>
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#include <osmocom/core/talloc.h>
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#include <osmocom/gsm/gsm_utils.h>
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#include <osmocom/bsc/handover.h>
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#include <osmocom/bsc/handover_cfg.h>
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/* Find BTS by ARFCN and BSIC */
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struct gsm_bts *bts_by_arfcn_bsic(const struct gsm_network *net,
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uint16_t arfcn, uint8_t bsic)
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{
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struct gsm_bts *bts;
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llist_for_each_entry(bts, &net->bts_list, list) {
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if (bts->c0->arfcn == arfcn &&
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bts->bsic == bsic)
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return bts;
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}
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return NULL;
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}
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/* issue handover to a cell identified by ARFCN and BSIC */
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static int handover_to_arfcn_bsic(struct gsm_lchan *lchan,
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uint16_t arfcn, uint8_t bsic)
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{
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struct gsm_bts *new_bts;
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/* resolve the gsm_bts structure for the best neighbor */
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/* FIXME: use some better heuristics here to determine which cell
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* using this ARFCN really is closest to the target cell. For
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* now we simply assume that each ARFCN will only be used by one
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* cell */
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new_bts = bts_by_arfcn_bsic(lchan->ts->trx->bts->network, arfcn, bsic);
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if (!new_bts) {
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LOGP(DHODEC, LOGL_NOTICE, "unable to determine neighbor BTS "
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"for ARFCN %u BSIC %u ?!?\n", arfcn, bsic);
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return -EINVAL;
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}
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/* and actually try to handover to that cell */
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return bsc_handover_start(HODEC1, lchan, new_bts, lchan->type);
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}
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/* did we get a RXLEV for a given cell in the given report? */
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static int rxlev_for_cell_in_rep(struct gsm_meas_rep *mr,
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uint16_t arfcn, uint8_t bsic)
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{
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int i;
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for (i = 0; i < mr->num_cell; i++) {
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struct gsm_meas_rep_cell *mrc = &mr->cell[i];
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/* search for matching report */
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if (!(mrc->arfcn == arfcn && mrc->bsic == bsic))
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continue;
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mrc->flags |= MRC_F_PROCESSED;
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return mrc->rxlev;
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}
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return -ENODEV;
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}
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/* obtain averaged rxlev for given neighbor */
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static int neigh_meas_avg(struct neigh_meas_proc *nmp, int window)
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{
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unsigned int i, idx;
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int avg = 0;
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/* reduce window to the actual number of existing measurements */
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if (window > nmp->rxlev_cnt)
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window = nmp->rxlev_cnt;
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/* this should never happen */
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if (window <= 0) {
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LOGP(DHODEC, LOGL_ERROR, "Requested Neighbor RxLev for invalid window size of %d\n", window);
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return 0;
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}
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idx = calc_initial_idx(ARRAY_SIZE(nmp->rxlev),
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nmp->rxlev_cnt % ARRAY_SIZE(nmp->rxlev),
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window);
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for (i = 0; i < window; i++) {
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int j = (idx+i) % ARRAY_SIZE(nmp->rxlev);
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avg += nmp->rxlev[j];
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}
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return avg / window;
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}
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/* find empty or evict bad neighbor */
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static struct neigh_meas_proc *find_evict_neigh(struct gsm_lchan *lchan)
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{
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int j, worst = 999999;
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struct neigh_meas_proc *nmp_worst = NULL;
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/* first try to find an empty/unused slot */
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for (j = 0; j < ARRAY_SIZE(lchan->neigh_meas); j++) {
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struct neigh_meas_proc *nmp = &lchan->neigh_meas[j];
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if (!nmp->arfcn)
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return nmp;
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}
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/* no empty slot found. evict worst neighbor from list */
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for (j = 0; j < ARRAY_SIZE(lchan->neigh_meas); j++) {
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struct neigh_meas_proc *nmp = &lchan->neigh_meas[j];
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int avg = neigh_meas_avg(nmp, MAX_WIN_NEIGH_AVG);
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if (!nmp_worst || avg < worst) {
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worst = avg;
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nmp_worst = nmp;
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}
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}
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return nmp_worst;
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}
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/* process neighbor cell measurement reports */
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static void process_meas_neigh(struct gsm_meas_rep *mr)
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{
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int i, j, idx;
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/* for each reported cell, try to update global state */
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for (j = 0; j < ARRAY_SIZE(mr->lchan->neigh_meas); j++) {
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struct neigh_meas_proc *nmp = &mr->lchan->neigh_meas[j];
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unsigned int idx;
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int rxlev;
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/* skip unused entries */
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if (!nmp->arfcn)
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continue;
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rxlev = rxlev_for_cell_in_rep(mr, nmp->arfcn, nmp->bsic);
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idx = nmp->rxlev_cnt % ARRAY_SIZE(nmp->rxlev);
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if (rxlev >= 0) {
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nmp->rxlev[idx] = rxlev;
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nmp->last_seen_nr = mr->nr;
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} else
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nmp->rxlev[idx] = 0;
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nmp->rxlev_cnt++;
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}
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/* iterate over list of reported cells, check if we did not
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* process all of them */
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for (i = 0; i < mr->num_cell; i++) {
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struct gsm_meas_rep_cell *mrc = &mr->cell[i];
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struct neigh_meas_proc *nmp;
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if (mrc->flags & MRC_F_PROCESSED)
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continue;
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nmp = find_evict_neigh(mr->lchan);
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nmp->arfcn = mrc->arfcn;
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nmp->bsic = mrc->bsic;
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nmp->rxlev_cnt = 0;
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idx = nmp->rxlev_cnt % ARRAY_SIZE(nmp->rxlev);
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nmp->rxlev[idx] = mrc->rxlev;
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nmp->rxlev_cnt++;
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nmp->last_seen_nr = mr->nr;
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mrc->flags |= MRC_F_PROCESSED;
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}
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}
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/* attempt to do a handover */
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static int attempt_handover(struct gsm_meas_rep *mr)
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{
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struct gsm_bts *bts = mr->lchan->ts->trx->bts;
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struct neigh_meas_proc *best_cell = NULL;
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unsigned int best_better_db = 0;
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int i, rc;
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/* find the best cell in this report that is at least RXLEV_HYST
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* better than the current serving cell */
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for (i = 0; i < ARRAY_SIZE(mr->lchan->neigh_meas); i++) {
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struct neigh_meas_proc *nmp = &mr->lchan->neigh_meas[i];
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int avg, better;
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/* skip empty slots */
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if (nmp->arfcn == 0)
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continue;
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/* caculate average rxlev for this cell over the window */
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avg = neigh_meas_avg(nmp, ho_get_hodec1_rxlev_neigh_avg_win(bts->ho));
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/* check if hysteresis is fulfilled */
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if (avg < mr->dl.full.rx_lev + ho_get_hodec1_pwr_hysteresis(bts->ho))
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continue;
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better = avg - mr->dl.full.rx_lev;
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if (better > best_better_db) {
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best_cell = nmp;
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best_better_db = better;
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}
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}
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if (!best_cell)
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return 0;
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LOGP(DHODEC, LOGL_INFO, "%s: Cell on ARFCN %u is better: ",
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gsm_ts_name(mr->lchan->ts), best_cell->arfcn);
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if (!ho_get_ho_active(bts->ho)) {
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LOGPC(DHODEC, LOGL_INFO, "Skipping, Handover disabled\n");
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return 0;
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}
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rc = handover_to_arfcn_bsic(mr->lchan, best_cell->arfcn, best_cell->bsic);
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switch (rc) {
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case 0:
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LOGPC(DHODEC, LOGL_INFO, "Starting handover: meas report number %d \n", mr->nr);
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break;
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case -ENOSPC:
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LOGPC(DHODEC, LOGL_INFO, "No channel available\n");
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break;
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case -EBUSY:
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LOGPC(DHODEC, LOGL_INFO, "Handover already active\n");
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break;
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default:
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LOGPC(DHODEC, LOGL_ERROR, "Unknown error\n");
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}
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return rc;
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}
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/* process an already parsed measurement report and decide if we want to
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* attempt a handover */
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static void on_measurement_report(struct gsm_meas_rep *mr)
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{
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struct gsm_bts *bts = mr->lchan->ts->trx->bts;
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enum meas_rep_field dlev, dqual;
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int av_rxlev;
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unsigned int pwr_interval;
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/* If this cell does not use handover algorithm 1, then we're not responsible. */
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if (ho_get_algorithm(bts->ho) != 1)
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return;
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/* we currently only do handover for TCH channels */
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switch (mr->lchan->type) {
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case GSM_LCHAN_TCH_F:
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case GSM_LCHAN_TCH_H:
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break;
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default:
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return;
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}
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if (mr->flags & MEAS_REP_F_DL_DTX) {
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dlev = MEAS_REP_DL_RXLEV_SUB;
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dqual = MEAS_REP_DL_RXQUAL_SUB;
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} else {
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dlev = MEAS_REP_DL_RXLEV_FULL;
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dqual = MEAS_REP_DL_RXQUAL_FULL;
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}
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/* parse actual neighbor cell info */
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if (mr->num_cell > 0 && mr->num_cell < 7)
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process_meas_neigh(mr);
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av_rxlev = get_meas_rep_avg(mr->lchan, dlev,
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ho_get_hodec1_rxlev_avg_win(bts->ho));
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/* Interference HO */
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if (rxlev2dbm(av_rxlev) > -85 &&
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meas_rep_n_out_of_m_be(mr->lchan, dqual, 3, 4, 5)) {
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LOGPC(DHO, LOGL_INFO, "HO cause: Interference HO av_rxlev=%d dBm\n",
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rxlev2dbm(av_rxlev));
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attempt_handover(mr);
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return;
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}
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/* Bad Quality */
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if (meas_rep_n_out_of_m_be(mr->lchan, dqual, 3, 4, 5)) {
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LOGPC(DHO, LOGL_INFO, "HO cause: Bad Quality av_rxlev=%d dBm\n", rxlev2dbm(av_rxlev));
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attempt_handover(mr);
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return;
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}
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/* Low Level */
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if (rxlev2dbm(av_rxlev) <= -110) {
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LOGPC(DHO, LOGL_INFO, "HO cause: Low Level av_rxlev=%d dBm\n", rxlev2dbm(av_rxlev));
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attempt_handover(mr);
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return;
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}
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/* Distance */
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if (mr->ms_l1.ta > ho_get_hodec1_max_distance(bts->ho)) {
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LOGPC(DHO, LOGL_INFO, "HO cause: Distance av_rxlev=%d dBm ta=%d \n",
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rxlev2dbm(av_rxlev), mr->ms_l1.ta);
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attempt_handover(mr);
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return;
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}
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/* Power Budget AKA Better Cell */
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pwr_interval = ho_get_hodec1_pwr_interval(bts->ho);
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/* handover_cfg.h defines pwr_interval as [1..99], but since we're using it in a modulo below,
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* assert non-zero to clarify. */
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OSMO_ASSERT(pwr_interval);
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if ((mr->nr % pwr_interval) == pwr_interval - 1)
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attempt_handover(mr);
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}
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struct handover_decision_callbacks hodec1_callbacks = {
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.hodec_id = HODEC1,
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.on_measurement_report = on_measurement_report,
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};
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void handover_decision_1_init(void)
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{
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handover_decision_callbacks_register(&hodec1_callbacks);
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}
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