aboutsummaryrefslogtreecommitdiffstats
path: root/src/osmo-bsc/handover_decision.c
blob: 25c297f7120a32b2753706478b328532b4b32b7b (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
/* 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 gsm_bts *bts = mr->lchan->ts->trx->bts;
	struct neigh_meas_proc *best_cell = NULL;
	unsigned int best_better_db = 0;
	int i;

	/* 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;

	LOGP(DHODEC, LOGL_INFO, "%s: Cell on ARFCN %u is better: ",
		gsm_ts_name(mr->lchan->ts), best_cell->arfcn);
	if (!ho_get_ho_active(bts->ho)) {
		LOGPC(DHODEC, LOGL_INFO, "Skipping, Handover disabled\n");
		return;
	}

	{
		struct handover_mo_req req = {
			.from_hodec_id = HODEC1,
			.old_lchan = mr->lchan,
			.target_nik = {
				.from_bts = bts->nr,
				.arfcn = best_cell->arfcn,
				.bsic_kind = BSIC_6BIT,
				.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);
}