# HG changeset patch
# User Ali Rostami <a.rostami@rutgers.edu>
# Date 1459599970 25200
#      Sat Apr 02 05:26:10 2016 -0700
# Node ID 36a50be853f9e3f0d5402567085cca1d98f6801b
# Parent  c0943e24cccca0530a36b8f576472e879ba13463
mobility:  (fixes #2363) Avoid accumulated position errors for ns-2 mobility

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
slight discontinuity in the nodes trajectory can occur. Although, we have
not observed any adverse effect on the simulation results.

This patch has been developed jointly at WINLAB, Rutgers University and
West Virginia University as part of the V2V safety communications
scalability activity of the Interoperability Issues of Vehicle-to-Vehicle
Based Safety Systems (V2V-Interoperability) Project headed by the
Crash Avoidance Metrics Partnership (CAMP) Vehicle Safety
Communications 3 (VSC3) Consortium, in partnership with the United States
Department of Transportation (USDOT).

diff -r c0943e24cccc -r 36a50be853f9 src/mobility/helper/ns2-mobility-helper.cc
--- a/src/mobility/helper/ns2-mobility-helper.cc	Thu Mar 31 23:31:50 2016 +0200
+++ b/src/mobility/helper/ns2-mobility-helper.cc	Sat Apr 02 05:26:10 2016 -0700
@@ -755,9 +755,10 @@
         {
           return retval;
         }
-      // now calculate the xSpeed = distance / time
-      double xSpeed = (xFinalPosition - retval.m_finalPosition.x) / time;
-      double ySpeed = (yFinalPosition - retval.m_finalPosition.y) / time; // & same with ySpeed
+      // distance traveled based on input mobility trace file  
+      double total_Dist = std::sqrt (std::pow (xFinalPosition - retval.m_finalPosition.x, 2) + std::pow (yFinalPosition - retval.m_finalPosition.y, 2));
+      double xSpeed = speed * (xFinalPosition - retval.m_finalPosition.x) / total_Dist; // comment out for the scheduled movement
+      double ySpeed = speed * (yFinalPosition - retval.m_finalPosition.y) / total_Dist; // & same with ySpeed comment out for the scheduled movement
       retval.m_speed = Vector (xSpeed, ySpeed, 0);
 
       // quick and dirty set zSpeed = 0
@@ -766,11 +767,11 @@
       NS_LOG_DEBUG ("Calculated Speed: X=" << xSpeed << " Y=" << ySpeed << " Z=" << zSpeed);
 
       // Set the Values
-      Simulator::Schedule (Seconds (at), &ConstantVelocityMobilityModel::SetVelocity, model, Vector (xSpeed, ySpeed, zSpeed));
-      retval.m_stopEvent = Simulator::Schedule (Seconds (at + time), &ConstantVelocityMobilityModel::SetVelocity, model, Vector (0, 0, 0));
-      retval.m_finalPosition.x += xSpeed * time;
-      retval.m_finalPosition.y += ySpeed * time;
-      retval.m_targetArrivalTime += time;
+      Simulator::Schedule (Seconds (at), &ConstantVelocityMobilityModel::SetPosition, model, Vector (xFinalPosition, yFinalPosition, 0));  // update the speed according to the input mobility trace file
+      Simulator::Schedule (Seconds (at), &ConstantVelocityMobilityModel::SetVelocity, model, Vector (xSpeed, ySpeed, zSpeed)); // update the position according to the input mobility trace file
+      retval.m_finalPosition.x = xFinalPosition; //comment out for use scheduled postion
+      retval.m_finalPosition.y = yFinalPosition; //comment out for use scheduled postion 
+      retval.m_targetArrivalTime = at;	//comment out for use scheduled postion       
     }
   return retval;
 }