War Walking vs. War
Driving
Trying to find the reasons why war
walking radio map performs better
War Walking Radio-map Performs
Better
Major Possible Origin of Error
 Bias
on war-driving ground truths
 Quality of collected WiFi signal patterns


Signal strength and variance
Amount of data
GPS as War Driving Ground Truth


GPS itself suppose to have a 15m error
GPS and WiFi reading does not synchronized in our
experiment
GPS
Lags
Uniformly Shift GPS Readings
Driving Testing Trace

Intuition: same manner for training and testing
leads better result

Not in our tests
 If
“resemblance” does not account for
difference in war walking and war
driving, what does?
 Signal
strength
 Variance of signals
 …?
Signal Strength

Intuition: Lower strength in radio map  larger errors

somewhat
Variance of signals

Intuition: Higher variance in signals is better for
differentiation, so lowering the variance  larger errors

somewhat
Number of Access Points in Radiomap

Intuition: war walking tend to receive more APs
and those may be critical
War walking:
War driving:
Signal as recv’d
by walking
Signal as recv’d
by driving
Walking
reduced:
Signal as recv’d
by walking
Driving plus:
Signal as recv’d
by driving
Only in war walking
In both
Only in war driving
Only in war walking
War driving only
War walking only
Number of Access Points in Radiomap

Intuition: war walking tend to receive more APs
and those may be critical

 The additional APs seems to be redundant
Number of Samples

Intuition: war walking tends to receive more samples and
it’s critical

it’s not critical
Recap
 Signal
quality (strength, variance)
 Amount
of data