power_control: generalize measurement pre-processing state

This way EWMA based filtering can also be applied to RxQual.

Change-Id: I439c00b394da670e314f217b3246cc85ce8213c6
Related: SYS#4918, SYS#4917

3 files changed, 35 insertions, 22 deletions

diff --git a/include/osmo-bts/gsm_data.h b/include/osmo-bts/gsm_data.h
index 6efc7176..253b115d 100644
--- a/include/osmo-bts/gsm_data.h
+++ b/include/osmo-bts/gsm_data.h
@@ -213,18 +213,28 @@ struct gsm_power_ctrl_params {
 /* Default MS/BS Power Control parameters */
 extern const struct gsm_power_ctrl_params power_ctrl_params_def;
 
+/* Measurement pre-processing state */
+struct gsm_power_ctrl_meas_proc_state {
+	/* Algorithm specific data */
+	union {
+		struct {
+			/* Scaled up 100 times average value */
+			int Avg100;
+		} ewma;
+	};
+};
+
 struct lchan_power_ctrl_state {
 	/* Dynamic Power Control parameters (NULL in static mode) */
 	const struct gsm_power_ctrl_params *dpc_params;
+	/* Measurement pre-processing state (for dynamic mode) */
+	struct gsm_power_ctrl_meas_proc_state rxlev_meas_proc;
 
 	/* Depending on the context (MS or BS power control), fields 'current' and 'max'
 	 * reflect either the MS power level (magic numbers), or BS Power reduction level
 	 * (attenuation, in dB). */
 	uint8_t current;
 	uint8_t max;
-
-	/* Scaled up (100 times) average UL/DL RxLev (in dBm) */
-	int avg100_rxlev_dbm;
 };
 
 struct gsm_lchan {
diff --git a/src/common/power_control.c b/src/common/power_control.c
index e159740e..06296308 100644
--- a/src/common/power_control.c
+++ b/src/common/power_control.c
@@ -38,29 +38,29 @@
 
 /* Base Low-Pass Single-Pole IIR Filter (EWMA) formula:
  *
- *   Avg[n] = a * Pwr[n] + (1 - a) * Avg[n - 1]
+ *   Avg[n] = a * Val[n] + (1 - a) * Avg[n - 1]
  *
- * where parameter 'a' determines how much weight of the latest UL RSSI measurement
- * result 'Pwr[n]' carries vs the weight of the average 'Avg[n - 1]'.  The value of
- * 'a' is usually a float in range 0 .. 1, so:
+ * where parameter 'a' determines how much weight of the latest measurement value
+ * 'Val[n]' carries vs the weight of the accumulated average 'Avg[n - 1]'.  The
+ * value of 'a' is usually a float in range 0 .. 1, so:
  *
- *  - value 0.5 gives equal weight to both 'Pwr[n]' and 'Avg[n - 1]';
+ *  - value 0.5 gives equal weight to both 'Val[n]' and 'Avg[n - 1]';
  *  - value 1.0 means no filtering at all (pass through);
  *  - value 0.0 makes no sense.
  *
  * Further optimization:
  *
- *   Avg[n] = a * Pwr[n] + Avg[n - 1] - a * Avg[n - 1]
+ *   Avg[n] = a * Val[n] + Avg[n - 1] - a * Avg[n - 1]
  *   ^^^^^^                ^^^^^^^^^^
  *
  * a) this can be implemented in C using '+=' operator:
  *
- *   Avg += a * Pwr - a * Avg
- *   Avg += a * (Pwr - Avg)
+ *   Avg += a * Val - a * Avg
+ *   Avg += a * (Val - Avg)
  *
  * b) everything is scaled up by 100 to avoid floating point stuff:
  *
- *   Avg100 += A * (Pwr - Avg)
+ *   Avg100 += A * (Val - Avg)
  *
  * where 'Avg100' is 'Avg * 100' and 'A' is 'a * 100'.
  *
@@ -70,20 +70,20 @@
  *   https://en.wikipedia.org/wiki/Low-pass_filter#Simple_infinite_impulse_response_filter
  *   https://tomroelandts.com/articles/low-pass-single-pole-iir-filter
  */
-static int8_t do_pf_ewma(const struct gsm_power_ctrl_meas_params *mp,
-			 struct lchan_power_ctrl_state *state,
-			 const int8_t Pwr)
+static int do_pf_ewma(const struct gsm_power_ctrl_meas_params *mp,
+		      struct gsm_power_ctrl_meas_proc_state *mps,
+		      const int Val)
 {
 	const uint8_t A = mp->ewma.alpha;
-	int *Avg100 = &state->avg100_rxlev_dbm;
+	int *Avg100 = &mps->ewma.Avg100;
 
 	/* We don't have 'Avg[n - 1]' if this is the first run */
 	if (*Avg100 == 0) {
-		*Avg100 = Pwr * EWMA_SCALE_FACTOR;
-		return Pwr;
+		*Avg100 = Val * EWMA_SCALE_FACTOR;
+		return Val;
 	}
 
-	*Avg100 += A * (Pwr - *Avg100 / EWMA_SCALE_FACTOR);
+	*Avg100 += A * (Val - *Avg100 / EWMA_SCALE_FACTOR);
 	return *Avg100 / EWMA_SCALE_FACTOR;
 }
 
@@ -104,7 +104,9 @@ static int calc_delta(const struct gsm_power_ctrl_params *params,
 	/* Filter RxLev value to reduce unnecessary Tx power oscillations */
 	switch (params->rxlev_meas.algo) {
 	case GSM_PWR_CTRL_MEAS_AVG_ALGO_OSMO_EWMA:
-		rxlev_dbm_avg = do_pf_ewma(&params->rxlev_meas, state, rxlev_dbm);
+		rxlev_dbm_avg = do_pf_ewma(&params->rxlev_meas,
+					   &state->rxlev_meas_proc,
+					   rxlev_dbm);
 		break;
 	/* TODO: implement other pre-processing methods */
 	case GSM_PWR_CTRL_MEAS_AVG_ALGO_NONE:
diff --git a/tests/power/ms_power_loop_test.c b/tests/power/ms_power_loop_test.c
index e93a2efe..eb0e3e9b 100644
--- a/tests/power/ms_power_loop_test.c
+++ b/tests/power/ms_power_loop_test.c
@@ -164,7 +164,7 @@ static void test_pf_algo_ewma(void)
 
 	init_test(__func__);
 	lchan = &g_trx->ts[0].lchan[0];
-	avg100 = &lchan->ms_power_ctrl.avg100_rxlev_dbm;
+	avg100 = &lchan->ms_power_ctrl.rxlev_meas_proc.ewma.Avg100;
 
 	struct gsm_power_ctrl_meas_params *mp = &lchan->ms_dpc_params.rxlev_meas;
 	mp->algo = GSM_PWR_CTRL_MEAS_AVG_ALGO_OSMO_EWMA;
@@ -204,7 +204,8 @@ static void test_pf_algo_ewma(void)
 
 	mp->ewma.alpha = 70; /* 30% smoothing */
 	lchan->ms_power_ctrl.current = 15;
-	lchan->ms_power_ctrl.avg100_rxlev_dbm = 0;
+	lchan->ms_power_ctrl.rxlev_meas_proc = \
+		(struct gsm_power_ctrl_meas_proc_state) { 0 };
 
 	/* This is the first sample, the filter outputs it as-is */
 	apply_power_test(lchan, -50, 0, 15);