power_control: implement BS (Downlink) Power Control

We already have MS Power Control, which according to 3GPP 45.008
shall be implemented in the MS to minimize the transmit power in
the Uplink direction.  The BS Power Control may optionally be
implemented by the network side for the same purpose.

Using Downlink signal measurements reported by the MS, the BSS
(either BSC, or BTS) may control Downlink attenuation in a way
that the transmit power remains as low as possible, or remains
in a specific range corresponding to good RxLev values on the
MS side.  This change implements autonomous BS Power Control,
that can optionally be enabled by the BSC.

BS Power Control re-uses parts of the MS Power Control code,
so all parameters can be configured in the same way - via the
VTY interface or a configuration file.  This basically means
that features like hysteresis and EWMA based filtering are
also available for BS Power Control.

The only difference is that RxQual values higher than 0 would
trigger the logic to reduce the current attenuation twice.

Note that one of the unit tests ('TC_rxlev_max_min') fails,
as the power step limitations for raising and lowering look
wrong to me, and the related discussion is still ongoing.

Change-Id: I5b509e71d5f668b6b8b2abf8053c27f2a7c78451
Related: SYS#4918

6 files changed, 145 insertions, 20 deletions

diff --git a/src/common/l1sap.c b/src/common/l1sap.c
index 2038fbad..33d10a5a 100644
--- a/src/common/l1sap.c
+++ b/src/common/l1sap.c
@@ -1546,6 +1546,7 @@ static int l1sap_ph_data_ind(struct gsm_bts_trx *trx,
 		lchan->meas.flags |= LC_UL_M_F_L1_VALID;
 
 		lchan_ms_pwr_ctrl(lchan, data[0] & 0x1f, data_ind->rssi);
+		lchan_bs_pwr_ctrl(lchan, (const struct gsm48_hdr *) &data[5]);
 	} else
 		le = &lchan->lapdm_ch.lapdm_dcch;
 
diff --git a/src/common/power_control.c b/src/common/power_control.c
index 34414392..4c4e2831 100644
--- a/src/common/power_control.c
+++ b/src/common/power_control.c
@@ -209,3 +209,105 @@ int lchan_ms_pwr_ctrl(struct gsm_lchan *lchan,
 
 	return 1;
 }
+
+ /*! compute the new Downlink attenuation value for the given logical channel.
+  *  \param lchan logical channel for which to compute (and in which to store) new power value.
+  *  \param[in] gh pointer to the beginning of (presumably) a Measurement Report.
+  */
+int lchan_bs_pwr_ctrl(struct gsm_lchan *lchan,
+		      const struct gsm48_hdr *gh)
+{
+	struct gsm_bts_trx *trx = lchan->ts->trx;
+	struct gsm_bts *bts = trx->bts;
+	uint8_t rxqual_full, rxqual_sub;
+	uint8_t rxlev_full, rxlev_sub;
+	uint8_t rxqual, rxlev;
+	int delta, new;
+
+	const struct bts_power_ctrl_params *params = &bts->dl_power_ctrl;
+	struct lchan_power_ctrl_state *state = &lchan->bs_power_ctrl;
+
+	/* Check if BS Power Control is enabled */
+	if (state->fixed)
+		return 0;
+	/* Check if this is a Measurement Report */
+	if (gh->proto_discr != GSM48_PDISC_RR)
+		return 0;
+	if (gh->msg_type != GSM48_MT_RR_MEAS_REP)
+		return 0;
+
+	/* Check if the measurement results are valid */
+	if ((gh->data[1] & 0x40) == 0x40) {
+		LOGPLCHAN(lchan, DLOOP, LOGL_DEBUG,
+			  "The measurement results are not valid\n");
+		return 0;
+	}
+
+	/* See 3GPP TS 44.018, section 10.5.2.20 */
+	rxqual_full = (gh->data[2] >> 4) & 0x7;
+	rxqual_sub = (gh->data[2] >> 1) & 0x7;
+
+	rxlev_full = gh->data[0] & 0x3f;
+	rxlev_sub = gh->data[1] & 0x3f;
+
+	LOGPLCHAN(lchan, DLOOP, LOGL_DEBUG, "Rx DL Measurement Report: "
+		  "RXLEV-FULL(%02u), RXQUAL-FULL(%u), "
+		  "RXLEV-SUB(%02u), RXQUAL-SUB(%u), "
+		  "DTx is %s => using %s\n",
+		  rxlev_full, rxqual_full, rxlev_sub, rxqual_sub,
+		  lchan->tch.dtx.dl_active ? "enabled" : "disabled",
+		  lchan->tch.dtx.dl_active ? "SUB" : "FULL");
+
+	/* If DTx is active on Downlink, use the '-SUB' */
+	if (lchan->tch.dtx.dl_active) {
+		rxqual = rxqual_sub;
+		rxlev = rxlev_sub;
+	} else { /* ... otherwise use the '-FULL' */
+		rxqual = rxqual_full;
+		rxlev = rxlev_full;
+	}
+
+	/* Bit Error Rate > 0 => reduce by 2 */
+	if (rxqual > 0) {
+		LOGPLCHAN(lchan, DLOOP, LOGL_INFO, "Reducing Downlink attenuation "
+			  "by half: %u -> %u dB due to RXQUAL %u > 0\n",
+			  state->current, state->current / 2, rxqual);
+		state->current /= 2;
+		return 1;
+	}
+
+	/* Calculate a 'delta' for the current attenuation level */
+	delta = calc_delta(params, state, rxlev2dbm(rxlev));
+
+	/* Basic signal transmission / reception formula:
+	 *
+	 *   RxLev = TxPwr - (PathLoss + TxAtt)
+	 *
+	 * Here we want to change RxLev at the MS side, so:
+	 *
+	 *   RxLev + Delta = TxPwr - (PathLoss + TxAtt) + Delta
+	 *
+	 * The only parameter we can change here is TxAtt, so:
+	 *
+	 *   RxLev + Delta = TxPwr - PathLoss -  TxAtt + Delta
+	 *   RxLev + Delta = TxPwr - PathLoss - (TxAtt - Delta)
+	 */
+	new = state->current - delta;
+	if (new > state->max)
+		new = state->max;
+	if (new < 0)
+		new = 0;
+
+	if (state->current != new) {
+		LOGPLCHAN(lchan, DLOOP, LOGL_INFO, "Changing Downlink attenuation: "
+			  "%u -> %u dB (maximum %u dB, target %d dBm, delta %d dB)\n",
+			  state->current, new, state->max, params->target, delta);
+		state->current = new;
+		return 1;
+	} else {
+		LOGPLCHAN(lchan, DLOOP, LOGL_INFO, "Keeping Downlink attenuation "
+			  "at %u dB (maximum %u dB, target %d dBm, delta %d dB)\n",
+			  state->current, state->max, params->target, delta);
+		return 0;
+	}
+}
diff --git a/src/common/rsl.c b/src/common/rsl.c
index 8760c242..2ebfb323 100644
--- a/src/common/rsl.c
+++ b/src/common/rsl.c
@@ -1036,8 +1036,8 @@ static void clear_lchan_for_pdch_activ(struct gsm_lchan *lchan)
 	lchan->tch_mode = 0;
 	memset(&lchan->encr, 0, sizeof(lchan->encr));
 	memset(&lchan->ho, 0, sizeof(lchan->ho));
-	lchan->bs_power_red = 0;
 	memset(&lchan->ms_power_ctrl, 0, sizeof(lchan->ms_power_ctrl));
+	memset(&lchan->bs_power_ctrl, 0, sizeof(lchan->bs_power_ctrl));
 	lchan->rqd_ta = 0;
 	copy_sacch_si_to_lchan(lchan);
 	memset(&lchan->tch, 0, sizeof(lchan->tch));
@@ -1153,11 +1153,16 @@ static int rsl_rx_chan_activ(struct msgb *msg)
 	LOGPLCHAN(lchan, DRSL, LOGL_DEBUG, "rx Channel Activation in state: %s.\n",
 		  gsm_lchans_name(lchan->state));
 
-	/* Initialize channel defaults */
+	/* Initialize MS Power Control defaults */
 	lchan->ms_power_ctrl.max = ms_pwr_ctl_lvl(lchan->ts->trx->bts->band, 0);
 	lchan->ms_power_ctrl.current = lchan->ms_power_ctrl.max;
 	lchan->ms_power_ctrl.fixed = true;
 
+	/* Initialize BS Power Control defaults */
+	lchan->bs_power_ctrl.max = 2 * 15;
+	lchan->bs_power_ctrl.current = 0;
+	lchan->bs_power_ctrl.fixed = true;
+
 	rsl_tlv_parse(&tp, msgb_l3(msg), msgb_l3len(msg));
 
 	/* 9.3.3 Activation Type */
@@ -1209,9 +1214,11 @@ static int rsl_rx_chan_activ(struct msgb *msg)
 			return rsl_tx_chan_act_nack(lchan, RSL_ERR_SERV_OPT_UNIMPL);
 		}
 
-		lchan->bs_power_red = BS_POWER2DB(*TLVP_VAL(&tp, RSL_IE_BS_POWER));
+		lchan->bs_power_ctrl.max = BS_POWER2DB(*TLVP_VAL(&tp, RSL_IE_BS_POWER));
+		lchan->bs_power_ctrl.current = lchan->bs_power_ctrl.max;
+
 		LOGPLCHAN(lchan, DRSL, LOGL_DEBUG, "BS Power attenuation %u dB\n",
-			  lchan->bs_power_red);
+			  lchan->bs_power_ctrl.current);
 	}
 
 	/* 9.3.13 MS Power */
@@ -1224,7 +1231,6 @@ static int rsl_rx_chan_activ(struct msgb *msg)
 	if (TLVP_PRES_LEN(&tp, RSL_IE_TIMING_ADVANCE, 1))
 		lchan->rqd_ta = *TLVP_VAL(&tp, RSL_IE_TIMING_ADVANCE);
 
-	/* 9.3.32 BS Power Parameters */
 	/* 9.3.31 MS Power Parameters */
 	if (TLVP_PRESENT(&tp, RSL_IE_MS_POWER_PARAM)) {
 		/* Spec explicitly states BTS should only perform
@@ -1232,6 +1238,14 @@ static int rsl_rx_chan_activ(struct msgb *msg)
 		* Parameters' IE is present! */
 		lchan->ms_power_ctrl.fixed = false;
 	}
+
+	/* 9.3.32 BS Power Parameters */
+	if (TLVP_PRESENT(&tp, RSL_IE_BS_POWER_PARAM)) {
+		/* NOTE: it's safer to start from 0 */
+		lchan->bs_power_ctrl.current = 0;
+		lchan->bs_power_ctrl.fixed = false;
+	}
+
 	/* 9.3.16 Physical Context */
 
 	/* 9.3.29 SACCH Information */
@@ -1753,7 +1767,7 @@ static int rsl_rx_bs_pwr_ctrl(struct msgb *msg)
 	struct abis_rsl_dchan_hdr *dch = msgb_l2(msg);
 	struct gsm_lchan *lchan = msg->lchan;
 	struct tlv_parsed tp;
-	uint8_t old_bs_power_red;
+	uint8_t old, new;
 
 	rsl_tlv_parse(&tp, msgb_l3(msg), msgb_l3len(msg));
 
@@ -1766,18 +1780,24 @@ static int rsl_rx_bs_pwr_ctrl(struct msgb *msg)
 		return rsl_tx_error_report(msg->trx, RSL_ERR_SERV_OPT_UNIMPL, &dch->chan_nr, NULL, msg);
 	}
 
-	old_bs_power_red = lchan->bs_power_red;
-	lchan->bs_power_red = BS_POWER2DB(*TLVP_VAL(&tp, RSL_IE_BS_POWER));
-
-	LOGPLCHAN(lchan, DRSL, LOGL_INFO, "BS POWER CONTROL Attenuation %d -> %d dB\n",
-		  old_bs_power_red, lchan->bs_power_red);
+	new = BS_POWER2DB(*TLVP_VAL(&tp, RSL_IE_BS_POWER));
+	old = lchan->bs_power_ctrl.current;
 
 	/* 9.3.31 MS Power Parameters (O) */
 	if (TLVP_PRESENT(&tp, RSL_IE_BS_POWER_PARAM)) {
-		/* Spec explicitly states BTS should perform autonomous
-		 * BS power control loop in BTS if 'BS Power Parameters'
-		 * IE is present!  WE don't support that. */
-		return rsl_tx_error_report(msg->trx, RSL_ERR_OPT_IE_ERROR, &dch->chan_nr, NULL, msg);
+		/* NOTE: it's safer to start from 0 */
+		lchan->bs_power_ctrl.current = 0;
+		lchan->bs_power_ctrl.max = new;
+		lchan->bs_power_ctrl.fixed = false;
+	} else {
+		lchan->bs_power_ctrl.current = new;
+		lchan->bs_power_ctrl.fixed = true;
+	}
+
+	if (lchan->bs_power_ctrl.current != old) {
+		LOGPLCHAN(lchan, DRSL, LOGL_INFO, "BS POWER CONTROL: "
+			  "attenuation change %u -> %u dB\n",
+			  old, lchan->bs_power_ctrl.current);
 	}
 
 	return 0;
@@ -2975,7 +2995,7 @@ int rsl_tx_meas_res(struct gsm_lchan *lchan, uint8_t *l3, int l3_len, const stru
 		msgb_tlv_put(msg, RSL_IE_UPLINK_MEAS, ie_len, meas_res);
 		lchan->meas.flags &= ~LC_UL_M_F_RES_VALID;
 	}
-	msgb_tv_put(msg, RSL_IE_BS_POWER, lchan->bs_power_red / 2);
+	msgb_tv_put(msg, RSL_IE_BS_POWER, lchan->bs_power_ctrl.current / 2);
 	if (lchan->meas.flags & LC_UL_M_F_L1_VALID) {
 		msgb_tv_fixed_put(msg, RSL_IE_L1_INFO, 2, lchan->meas.l1_info);
 		lchan->meas.flags &= ~LC_UL_M_F_L1_VALID;
diff --git a/src/common/scheduler.c b/src/common/scheduler.c
index 84918e31..3d780fdd 100644
--- a/src/common/scheduler.c
+++ b/src/common/scheduler.c
@@ -1237,7 +1237,7 @@ void _sched_dl_burst(struct l1sched_trx *l1t, struct trx_dl_burst_req *br)
 
 	/* BS Power reduction (in dB) per logical channel */
 	if (l1cs->lchan != NULL)
-		br->att = l1cs->lchan->bs_power_red;
+		br->att = l1cs->lchan->bs_power_ctrl.current;
 
 	/* encrypt */
 	if (br->burst_len && l1cs->dl_encr_algo) {
diff --git a/src/common/tx_power.c b/src/common/tx_power.c
index 0741429f..348aba5c 100644
--- a/src/common/tx_power.c
+++ b/src/common/tx_power.c
@@ -68,7 +68,7 @@ int get_p_target_mdBm(const struct gsm_bts_trx *trx, uint8_t bs_power_red)
 }
 int get_p_target_mdBm_lchan(const struct gsm_lchan *lchan)
 {
-	return get_p_target_mdBm(lchan->ts->trx, lchan->bs_power_red);
+	return get_p_target_mdBm(lchan->ts->trx, lchan->bs_power_ctrl.current);
 }
 
 /* calculate the actual total output power required, taking into account the
@@ -134,7 +134,7 @@ int get_p_trxout_target_mdBm(const struct gsm_bts_trx *trx, uint8_t bs_power_red
 }
 int get_p_trxout_target_mdBm_lchan(const struct gsm_lchan *lchan)
 {
-	return get_p_trxout_target_mdBm(lchan->ts->trx, lchan->bs_power_red);
+	return get_p_trxout_target_mdBm(lchan->ts->trx, lchan->bs_power_ctrl.current);
 }
 
 
diff --git a/src/common/vty.c b/src/common/vty.c
index f32f6cdf..5d21e584 100644
--- a/src/common/vty.c
+++ b/src/common/vty.c
@@ -1335,10 +1335,13 @@ static void lchan_dump_full_vty(struct vty *vty, const struct gsm_lchan *lchan)
 		lchan->state == LCHAN_S_BROKEN ? " Error reason: " : "",
 		lchan->state == LCHAN_S_BROKEN ? lchan->broken_reason : "",
 		VTY_NEWLINE);
+#if 0
+	/* TODO: print more info about MS/BS Power Control */
 	vty_out(vty, "  BS Power: %d dBm, MS Power: %u dBm%s",
 		lchan->ts->trx->nominal_power - (lchan->ts->trx->max_power_red + lchan->bs_power_red),
 		ms_pwr_dbm(lchan->ts->trx->bts->band, lchan->ms_power_ctrl.max),
 		VTY_NEWLINE);
+#endif
 	vty_out(vty, "  Channel Mode / Codec: %s%s",
 		gsm48_chan_mode_name(lchan->tch_mode),
 		VTY_NEWLINE);
@@ -1380,7 +1383,6 @@ static void lchan_dump_full_vty(struct vty *vty, const struct gsm_lchan *lchan)
 	if (lchan->loopback)
 		vty_out(vty, "  RTP/PDCH Loopback Enabled%s", VTY_NEWLINE);
 	vty_out(vty, "  Radio Link Failure Counter 'S': %d%s", lchan->s, VTY_NEWLINE);
-	/* TODO: MS Power Control */
 }
 
 static void lchan_dump_short_vty(struct vty *vty, const struct gsm_lchan *lchan)