(posted on behalf of Ali Rostami)

The default Ns2MobilityHelper class extrapolates the new positions of the nodes using their current
velocity vectors and previous extrapolated positions. Relying only on GPS speed and heading
information for the duration of the simulation causes an increasing cumulative position error
between positions of nodes in the simulation and the actual positions (The actual positions could
be obtained from real experiment logs). By modifying the Ns2MobilityHelper class, both speed and
position of mobile nodes are updated in the simulation. Specifically, we set the position of nodes
to the GPS-reported position at the time of every location update and extrapolate the position at
the time of network events based on the GPS-reported speed vector. Therefore, the simulated node
positions are reset to the GPS-reported position at every GPS location update and a slightdiscontinuity in the nodes trajectory can occur. Although, we have not observed any adverse effect
on the simulation results.