Mobility Models for Next Generation Wireless Networks

Chapter 21

Random Waypoint Model and Wireless Network Simulation

In Chapter 5, we introduced the most popular mobility model for ad hoc networks, the random waypoint (RWP) model, and studied its properties. In particular, two phenomena generated by RWP mobility have been illustrated: the border effect and speed decay. The border effect is present whenever RWP mobile nodes move in a bounded region: due to the presence of the border, and since waypoints are uniformly selected in the movement region, we know that the node spatial density generated by RWP mobility is not uniform, but it is relatively higher in the center than at the border of the movement region. The speed decay phenomenon is due to the fact that, when RWP mobile nodes choose trip velocity in a bounded interval [v_min, v_max] with v_min < v_max, the average nodal speed observed at the beginning of the simulation is different (higher) from that observed when stationary conditions are reached.

As we will see, the border effect and speed decay, if not adequately accounted for when performing simulations, can cause significant inaccuracies in the simulation results obtained when estimating the performance of, say, a routing protocol for ad hoc networks.

In this case study, after discussing why the border effect and speed decay can impair the accuracy of simulation results, we will present recently developed methodologies aimed at completely removing the border effect and speed decay in RWP mobile networks. At the end of the ...