Adding simple highway mobility model
diff --git a/utils/highway-position-allocator.cc b/utils/highway-position-allocator.cc
new file mode 100644
index 0000000..9ad52ba
--- /dev/null
+++ b/utils/highway-position-allocator.cc
@@ -0,0 +1,103 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/*
+ * Copyright (c) 2007 INRIA
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation;
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ * Author: Lucas Wang <lucas@cs.ucla.edu>
+ */
+
+
+#include "highway-position-allocator.h"
+#include "ns3/random-variable.h"
+#include "ns3/log.h"
+#include "ns3/double.h"
+#include <math.h>
+
+NS_LOG_COMPONENT_DEFINE ("HighwayPositionAllocator");
+
+namespace ns3 {
+
+NS_OBJECT_ENSURE_REGISTERED (HighwayPositionAllocator);
+
+TypeId HighwayPositionAllocator::GetTypeId (void){
+  static TypeId tid = TypeId("ns3::HighwayPositionAllocator").
+    SetParent<PositionAllocator> ().
+    SetGroupName("Mobility").
+    AddConstructor<HighwayPositionAllocator>().
+    AddAttribute("Start", "the start position of the highway",
+		 VectorValue (Vector(0.0, 0.0, 0.0)),
+		 MakeVectorAccessor(&HighwayPositionAllocator::SetStartPosition,
+				    &HighwayPositionAllocator::GetStartPosition),
+                 MakeVectorChecker ()).
+    AddAttribute("Direction", "the direction of the highway",
+		 DoubleValue (0.0),
+		 MakeDoubleAccessor(&HighwayPositionAllocator::SetDirection,
+				    &HighwayPositionAllocator::GetDirection),
+                 MakeDoubleChecker<double> ()).
+    AddAttribute("Length", "the length of the highway",
+		 DoubleValue (0.0),
+		 MakeDoubleAccessor(&HighwayPositionAllocator::SetLength,
+				    &HighwayPositionAllocator::GetLength),
+                 MakeDoubleChecker<double> ());
+
+  return tid;
+}
+
+HighwayPositionAllocator::HighwayPositionAllocator (){
+  m_previous_position = Vector(0.0, 0.0, 0.0);
+}
+
+Vector HighwayPositionAllocator::GetNext (void) const{
+  UniformVariable random_gap_var (1.0, 10.0);
+  double random_gap = random_gap_var.GetValue();
+  
+  double delta_x = random_gap * cos(m_direction);
+  double delta_y = random_gap * sin(m_direction);
+  
+  
+  Vector new_position(m_previous_position.x - delta_x, m_previous_position.y - delta_y, m_previous_position.z);
+  m_previous_position.x = new_position.x;
+  m_previous_position.y = new_position.y;
+  m_previous_position.z = new_position.z;
+
+  return new_position;
+}
+
+void HighwayPositionAllocator::SetStartPosition(Vector start){
+  m_start = start;
+  m_previous_position = m_start; // initialize the m_previous_position to be start of the highway
+}
+
+Vector HighwayPositionAllocator::GetStartPosition(void) const {
+  return m_start;
+}
+
+void HighwayPositionAllocator::SetDirection(double direction){
+  m_direction = direction;
+}
+
+double HighwayPositionAllocator::GetDirection(void) const {
+  return m_direction;
+}
+
+void HighwayPositionAllocator::SetLength(double length){
+  m_length = length;
+}
+
+double HighwayPositionAllocator::GetLength(void) const {
+  return m_length;
+}
+
+}
diff --git a/utils/highway-position-allocator.h b/utils/highway-position-allocator.h
new file mode 100644
index 0000000..4028b4a
--- /dev/null
+++ b/utils/highway-position-allocator.h
@@ -0,0 +1,53 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/*
+ * Copyright (c) 2007 INRIA
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation;
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ * Author: Lucas Wang <lucas@cs.ucla.edu>
+ */
+#ifndef HIGHWAY_POSITION_ALLOCATOR_H
+#define HIGHWAY_POSITION_ALLOCATOR_H
+
+#include "ns3/position-allocator.h"
+
+namespace ns3 {
+  
+/**
+ * This position allocator is used to generate positions for cars 
+ * on a highway.
+ */
+
+class HighwayPositionAllocator : public PositionAllocator
+{
+public:
+  static TypeId GetTypeId (void);
+  HighwayPositionAllocator ();
+  virtual Vector GetNext (void) const;
+  void SetStartPosition(Vector start);
+  Vector GetStartPosition(void) const;
+  void SetDirection(double direction); // the angle in terms of radian degrees
+  double GetDirection(void) const ;
+  void SetLength(double length);
+  double GetLength(void) const ;
+
+private:
+  mutable Vector m_previous_position; // previously generated vehicle position
+  Vector m_start; // highway starting point
+  double m_direction; //highway direction
+  double m_length; // highway length
+};
+}
+
+#endif