variance shenanigans

mlat/server/clocknorm.py

@@ -22,6 +22,7 @@
 
 import pygraph.classes.graph
 import pygraph.algorithms.minmax
+import time
 
 from mlat import profile
 
@@ -37,7 +38,7 @@ def _identity_predict(x):
  return x
 
 
-def _make_predictors(clocktracker, station0, station1):
+def _make_predictors(clocktracker, station0, station1, now):
  """Return a tuple of predictors (p_01, p_10) where:
 
  p_01 will predict a station1 timestamp given a station0 timestamp
@@ -46,7 +47,6 @@ def _make_predictors(clocktracker, station0, station1):
  Returns None if no suitable clock sync model is available for
  this pair of stations.
  """
-
  if station0 is station1:
  return None
 
@@ -58,18 +58,32 @@ def _make_predictors(clocktracker, station0, station1):
  predictor = _Predictor(_identity_predict, station0.clock.jitter ** 2 + station1.clock.jitter ** 2)
  return (predictor, predictor)
 
+ pairing = None
+
  if station0 < station1:
  pairing = clocktracker.clock_pairs.get((station0, station1))
- if pairing is None or not pairing.valid:
- return None
- return (_Predictor(pairing.predict_peer, pairing.variance),
- _Predictor(pairing.predict_base, pairing.variance))
  else:
  pairing = clocktracker.clock_pairs.get((station1, station0))
- if pairing is None or not pairing.valid:
- return None
- return (_Predictor(pairing.predict_base, pairing.variance),
- _Predictor(pairing.predict_peer, pairing.variance))
+
+ if pairing is None or not pairing.valid:
+ return None
+
+ variance = pairing.variance
+ stale = now - pairing.updated
+
+ # increase variance for stale pairings
+ variance *= 1 + stale / 12
+
+ # increase variance for pairing with fewer sync points
+ if pairing.n < 10:
+ variance *= 1 + (10 - pairing.n) / 10
+
+ if station0 < station1:
+ return (_Predictor(pairing.predict_peer, variance),
+ _Predictor(pairing.predict_base, variance))
+ else:
+ return (_Predictor(pairing.predict_base, variance),
+ _Predictor(pairing.predict_peer, variance))
 
 
 def _label_heights(g, node, heights):
@@ -175,11 +189,13 @@ def normalize(clocktracker, timestamp_map):
  # also build a map of predictor objects corresponding to the
  # edges for later use
 
+ now = time.monotonic()
+
  predictor_map = {}
  for si in timestamp_map.keys():
  for sj in timestamp_map.keys():
  if si < sj:
- predictors = _make_predictors(clocktracker, si, sj)
+ predictors = _make_predictors(clocktracker, si, sj, now)
  if predictors:
  predictor_map[(si, sj)] = predictors[0]
  predictor_map[(sj, si)] = predictors[1]

mlat/server/clocksync.py

@@ -104,17 +104,15 @@ def is_new(self, base_ts):
  return bool(self.n == 0 or self.ts_base[-1] < base_ts)
 
  def updateVars(self):
- """Variance of recent predictions of the sync point versus the actual sync point."""
  if self.n == 0:
  self.variance = None
+ self.error = None
  else:
+ """Variance of recent predictions of the sync point versus the actual sync point."""
  self.variance = self.var_sum / self.n
 
- """Standard error of recent predictions."""
- if self.n == 0:
- self.error = None
- else:
- self.error = math.sqrt(self.var_sum / self.n)
+ """Standard error of recent predictions."""
+ self.error = math.sqrt(self.variance)
 
  def check_valid(self, now):
  """True if this pairing is usable for clock syncronization."""
@@ -142,7 +140,7 @@ def update(self, address, base_ts, peer_ts, base_interval, peer_interval, now):
  prediction = self.predict_peer(base_ts)
  prediction_error = (prediction - peer_ts) / self.peer_clock.freq
 
- if abs(prediction_error) > self.outlier_threshold and abs(prediction_error) > self.error * 2.5 : # 2.5 sigma
+ if abs(prediction_error) > self.outlier_threshold and abs(prediction_error) > self.error * 3 : # 3 sigma
  self.outliers += 1
  if self.outliers < 5:
  # don't accept this one