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-rw-r--r--src/libbsc/handover_decision.c297
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diff --git a/src/libbsc/handover_decision.c b/src/libbsc/handover_decision.c
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+/* Handover Decision making for Inter-BTS (Intra-BSC) Handover. This
+ * only implements the handover algorithm/decision, but not execution
+ * of it */
+
+/* (C) 2009 by Harald Welte <laforge@gnumonks.org>
+ *
+ * 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 <stdlib.h>
+#include <errno.h>
+
+#include <osmocore/msgb.h>
+#include <openbsc/debug.h>
+#include <openbsc/gsm_data.h>
+#include <openbsc/meas_rep.h>
+#include <openbsc/signal.h>
+#include <osmocore/talloc.h>
+#include <openbsc/handover.h>
+#include <osmocore/gsm_utils.h>
+
+/* issue handover to a cell identified by ARFCN and BSIC */
+static int handover_to_arfcn_bsic(struct gsm_lchan *lchan,
+ u_int16_t arfcn, u_int8_t bsic)
+{
+ struct gsm_bts *new_bts;
+
+ /* resolve the gsm_bts structure for the best neighbor */
+ new_bts = gsm_bts_neighbor(lchan->ts->trx->bts, arfcn, bsic);
+ if (!new_bts) {
+ LOGP(DHO, LOGL_NOTICE, "unable to determine neighbor BTS "
+ "for ARFCN %u BSIC %u ?!?\n", arfcn, bsic);
+ return -EINVAL;
+ }
+
+ /* and actually try to handover to that cell */
+ return bsc_handover_start(lchan, new_bts);
+}
+
+/* did we get a RXLEV for a given cell in the given report? */
+static int rxlev_for_cell_in_rep(struct gsm_meas_rep *mr,
+ u_int16_t arfcn, u_int8_t bsic)
+{
+ int i;
+
+ for (i = 0; i < mr->num_cell; i++) {
+ struct gsm_meas_rep_cell *mrc = &mr->cell[i];
+
+ /* search for matching report */
+ if (!(mrc->arfcn == arfcn && mrc->bsic == bsic))
+ continue;
+
+ mrc->flags |= MRC_F_PROCESSED;
+ return mrc->rxlev;
+ }
+ return -ENODEV;
+}
+
+/* obtain averaged rxlev for given neighbor */
+static int neigh_meas_avg(struct neigh_meas_proc *nmp, int window)
+{
+ unsigned int i, idx;
+ int avg = 0;
+
+ idx = calc_initial_idx(ARRAY_SIZE(nmp->rxlev),
+ nmp->rxlev_cnt % ARRAY_SIZE(nmp->rxlev),
+ window);
+
+ for (i = 0; i < window; i++) {
+ int j = (idx+i) % ARRAY_SIZE(nmp->rxlev);
+
+ avg += nmp->rxlev[j];
+ }
+
+ return avg / window;
+}
+
+/* find empty or evict bad neighbor */
+static struct neigh_meas_proc *find_evict_neigh(struct gsm_lchan *lchan)
+{
+ int j, worst = 999999;
+ struct neigh_meas_proc *nmp_worst;
+
+ /* first try to find an empty/unused slot */
+ for (j = 0; j < ARRAY_SIZE(lchan->neigh_meas); j++) {
+ struct neigh_meas_proc *nmp = &lchan->neigh_meas[j];
+ if (!nmp->arfcn)
+ return nmp;
+ }
+
+ /* no empty slot found. evict worst neighbor from list */
+ for (j = 0; j < ARRAY_SIZE(lchan->neigh_meas); j++) {
+ struct neigh_meas_proc *nmp = &lchan->neigh_meas[j];
+ int avg = neigh_meas_avg(nmp, MAX_WIN_NEIGH_AVG);
+ if (avg < worst) {
+ worst = avg;
+ nmp_worst = nmp;
+ }
+ }
+
+ return nmp_worst;
+}
+
+/* process neighbor cell measurement reports */
+static void process_meas_neigh(struct gsm_meas_rep *mr)
+{
+ int i, j, idx;
+
+ /* for each reported cell, try to update global state */
+ for (j = 0; j < ARRAY_SIZE(mr->lchan->neigh_meas); j++) {
+ struct neigh_meas_proc *nmp = &mr->lchan->neigh_meas[j];
+ unsigned int idx;
+ int rxlev;
+
+ /* skip unused entries */
+ if (!nmp->arfcn)
+ continue;
+
+ rxlev = rxlev_for_cell_in_rep(mr, nmp->arfcn, nmp->bsic);
+ idx = nmp->rxlev_cnt % ARRAY_SIZE(nmp->rxlev);
+ if (rxlev >= 0) {
+ nmp->rxlev[idx] = rxlev;
+ nmp->last_seen_nr = mr->nr;
+ } else
+ nmp->rxlev[idx] = 0;
+ nmp->rxlev_cnt++;
+ }
+
+ /* iterate over list of reported cells, check if we did not
+ * process all of them */
+ for (i = 0; i < mr->num_cell; i++) {
+ struct gsm_meas_rep_cell *mrc = &mr->cell[i];
+ struct neigh_meas_proc *nmp;
+
+ if (mrc->flags & MRC_F_PROCESSED)
+ continue;
+
+ nmp = find_evict_neigh(mr->lchan);
+
+ nmp->arfcn = mrc->arfcn;
+ nmp->bsic = mrc->bsic;
+
+ idx = nmp->rxlev_cnt % ARRAY_SIZE(nmp->rxlev);
+ nmp->rxlev[idx] = mrc->rxlev;
+ nmp->rxlev_cnt++;
+ nmp->last_seen_nr = mr->nr;
+
+ mrc->flags |= MRC_F_PROCESSED;
+ }
+}
+
+/* attempt to do a handover */
+static int attempt_handover(struct gsm_meas_rep *mr)
+{
+ struct gsm_network *net = mr->lchan->ts->trx->bts->network;
+ struct neigh_meas_proc *best_cell = NULL;
+ unsigned int best_better_db = 0;
+ int i, rc;
+
+ /* find the best cell in this report that is at least RXLEV_HYST
+ * better than the current serving cell */
+
+ for (i = 0; i < ARRAY_SIZE(mr->lchan->neigh_meas); i++) {
+ struct neigh_meas_proc *nmp = &mr->lchan->neigh_meas[i];
+ int avg, better;
+
+ /* skip empty slots */
+ if (nmp->arfcn == 0)
+ continue;
+
+ /* caculate average rxlev for this cell over the window */
+ avg = neigh_meas_avg(nmp, net->handover.win_rxlev_avg_neigh);
+
+ /* check if hysteresis is fulfilled */
+ if (avg < mr->dl.full.rx_lev + net->handover.pwr_hysteresis)
+ continue;
+
+ better = avg - mr->dl.full.rx_lev;
+ if (better > best_better_db) {
+ best_cell = nmp;
+ best_better_db = better;
+ }
+ }
+
+ if (!best_cell)
+ return 0;
+
+ LOGP(DHO, LOGL_INFO, "%s: Cell on ARFCN %u is better: ",
+ gsm_ts_name(mr->lchan->ts), best_cell->arfcn);
+ if (!net->handover.active) {
+ LOGPC(DHO, LOGL_INFO, "Skipping, Handover disabled\n");
+ return 0;
+ }
+
+ rc = handover_to_arfcn_bsic(mr->lchan, best_cell->arfcn, best_cell->bsic);
+ switch (rc) {
+ case 0:
+ LOGPC(DHO, LOGL_INFO, "Starting handover\n");
+ break;
+ case -ENOSPC:
+ LOGPC(DHO, LOGL_INFO, "No channel available\n");
+ break;
+ case -EBUSY:
+ LOGPC(DHO, LOGL_INFO, "Handover already active\n");
+ break;
+ default:
+ LOGPC(DHO, LOGL_ERROR, "Unknown error\n");
+ }
+ return rc;
+}
+
+/* process an already parsed measurement report and decide if we want to
+ * attempt a handover */
+static int process_meas_rep(struct gsm_meas_rep *mr)
+{
+ struct gsm_network *net = mr->lchan->ts->trx->bts->network;
+ int av_rxlev;
+
+ /* we currently only do handover for TCH channels */
+ switch (mr->lchan->type) {
+ case GSM_LCHAN_TCH_F:
+ case GSM_LCHAN_TCH_H:
+ break;
+ default:
+ return 0;
+ }
+
+ /* parse actual neighbor cell info */
+ if (mr->num_cell > 0 && mr->num_cell < 7)
+ process_meas_neigh(mr);
+
+ av_rxlev = get_meas_rep_avg(mr->lchan, MEAS_REP_DL_RXLEV_FULL,
+ net->handover.win_rxlev_avg);
+
+ /* Interference HO */
+ if (rxlev2dbm(av_rxlev) > -85 &&
+ meas_rep_n_out_of_m_be(mr->lchan, MEAS_REP_DL_RXQUAL_FULL,
+ 3, 4, 5))
+ return attempt_handover(mr);
+
+ /* Bad Quality */
+ if (meas_rep_n_out_of_m_be(mr->lchan, MEAS_REP_DL_RXQUAL_FULL,
+ 3, 4, 5))
+ return attempt_handover(mr);
+
+ /* Low Level */
+ if (rxlev2dbm(av_rxlev) <= -110)
+ return attempt_handover(mr);
+
+ /* Distance */
+ if (mr->ms_l1.ta > net->handover.max_distance)
+ return attempt_handover(mr);
+
+ /* Power Budget AKA Better Cell */
+ if ((mr->nr % net->handover.pwr_interval) == 0)
+ return attempt_handover(mr);
+
+ return 0;
+
+}
+
+static int ho_dec_sig_cb(unsigned int subsys, unsigned int signal,
+ void *handler_data, void *signal_data)
+{
+ struct lchan_signal_data *lchan_data;
+
+ if (subsys != SS_LCHAN)
+ return 0;
+
+ lchan_data = signal_data;
+ switch (signal) {
+ case S_LCHAN_MEAS_REP:
+ process_meas_rep(lchan_data->mr);
+ break;
+ }
+
+ return 0;
+}
+
+void on_dso_load_ho_dec(void)
+{
+ register_signal_handler(SS_LCHAN, ho_dec_sig_cb, NULL);
+}