1 files changed, 297 insertions, 0 deletions
diff --git a/src/osmo-bsc/handover_decision.c b/src/osmo-bsc/handover_decision.c
new file mode 100644
index 000000000..0bfbce20d
--- /dev/null
+++ b/src/osmo-bsc/handover_decision.c
@@ -0,0 +1,297 @@
+/* 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 <osmocom/core/msgb.h>
+#include <osmocom/bsc/debug.h>
+#include <osmocom/bsc/gsm_data.h>
+#include <osmocom/bsc/meas_rep.h>
+#include <osmocom/bsc/signal.h>
+#include <osmocom/core/talloc.h>
+#include <osmocom/gsm/gsm_utils.h>
+
+#include <osmocom/bsc/handover_fsm.h>
+#include <osmocom/bsc/handover_cfg.h>
+
+/* 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,
+				 uint16_t arfcn, uint8_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;
+
+	/* reduce window to the actual number of existing measurements */
+	if (window > nmp->rxlev_cnt)
+		window = nmp->rxlev_cnt;
+	/* this should never happen */
+	if (window <= 0) {
+		LOGP(DHODEC, LOGL_ERROR, "Requested Neighbor RxLev for invalid window size of %d\n", window);
+		return 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 = NULL;
+
+	/* 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 (!nmp_worst || 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;
+
+		nmp->rxlev_cnt = 0;
+		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 void attempt_handover(struct gsm_meas_rep *mr)
+{
+	struct handover_out_req req;
+	struct gsm_bts *bts = mr->lchan->ts->trx->bts;
+	struct neigh_meas_proc *best_cell = NULL;
+	unsigned int best_better_db = 0;
+	int i;
+
+	if (!ho_get_ho_active(bts->ho))
+		return;
+
+	/* 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, ho_get_hodec1_rxlev_neigh_avg_win(bts->ho));
+
+		/* check if hysteresis is fulfilled */
+		if (avg < mr->dl.full.rx_lev + ho_get_hodec1_pwr_hysteresis(bts->ho))
+			continue;
+
+		better = avg - mr->dl.full.rx_lev;
+		if (better > best_better_db) {
+			best_cell = nmp;
+			best_better_db = better;
+		}
+	}
+
+	if (!best_cell)
+		return;
+
+	req = (struct handover_out_req){
+		.from_hodec_id = HODEC1,
+		.old_lchan = mr->lchan,
+		.target_nik = {
+			.from_bts = bts->nr,
+			.arfcn = best_cell->arfcn,
+			.bsic = best_cell->bsic,
+		},
+	};
+	handover_request(&req);
+}
+
+/* process an already parsed measurement report and decide if we want to
+ * attempt a handover */
+static void on_measurement_report(struct gsm_meas_rep *mr)
+{
+	struct gsm_bts *bts = mr->lchan->ts->trx->bts;
+	enum meas_rep_field dlev, dqual;
+	int av_rxlev;
+	unsigned int pwr_interval;
+
+	/* If this cell does not use handover algorithm 1, then we're not responsible. */
+	if (ho_get_algorithm(bts->ho) != 1)
+		return;
+
+	/* 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;
+	}
+
+	if (mr->flags & MEAS_REP_F_DL_DTX) {
+		dlev = MEAS_REP_DL_RXLEV_SUB;
+		dqual = MEAS_REP_DL_RXQUAL_SUB;
+	} else {
+		dlev = MEAS_REP_DL_RXLEV_FULL;
+		dqual = MEAS_REP_DL_RXQUAL_FULL;
+	}
+
+	/* 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, dlev,
+				    ho_get_hodec1_rxlev_avg_win(bts->ho));
+
+	/* Interference HO */
+	if (rxlev2dbm(av_rxlev) > -85 &&
+	    meas_rep_n_out_of_m_be(mr->lchan, dqual, 3, 4, 5)) {
+		LOGPC(DHO, LOGL_INFO, "HO cause: Interference HO av_rxlev=%d dBm\n",
+		      rxlev2dbm(av_rxlev));
+		attempt_handover(mr);
+		return;
+	}
+
+	/* Bad Quality */
+	if (meas_rep_n_out_of_m_be(mr->lchan, dqual, 3, 4, 5)) {
+		LOGPC(DHO, LOGL_INFO, "HO cause: Bad Quality av_rxlev=%d dBm\n", rxlev2dbm(av_rxlev));
+		attempt_handover(mr);
+		return;
+	}
+
+	/* Low Level */
+	if (rxlev2dbm(av_rxlev) <= -110) {
+		LOGPC(DHO, LOGL_INFO, "HO cause: Low Level av_rxlev=%d dBm\n", rxlev2dbm(av_rxlev));
+		attempt_handover(mr);
+		return;
+	}
+
+	/* Distance */
+	if (mr->ms_l1.ta > ho_get_hodec1_max_distance(bts->ho)) {
+		LOGPC(DHO, LOGL_INFO, "HO cause: Distance av_rxlev=%d dBm ta=%d \n",
+					rxlev2dbm(av_rxlev), mr->ms_l1.ta);
+		attempt_handover(mr);
+		return;
+	}
+
+	/* Power Budget AKA Better Cell */
+	pwr_interval = ho_get_hodec1_pwr_interval(bts->ho);
+	/* handover_cfg.h defines pwr_interval as [1..99], but since we're using it in a modulo below,
+	 * assert non-zero to clarify. */
+	OSMO_ASSERT(pwr_interval);
+	if ((mr->nr % pwr_interval) == pwr_interval - 1)
+		attempt_handover(mr);
+}
+
+struct handover_decision_callbacks hodec1_callbacks = {
+	.hodec_id = HODEC1,
+	.on_measurement_report = on_measurement_report,
+};
+
+void handover_decision_1_init(void)
+{
+	handover_decision_callbacks_register(&hodec1_callbacks);
+}