Praise for Fundamentals of WiMAX

12.2 Methodology for System-Level Simulation 405System-level simulations usually model the wireless channel based on median propagation lossand shadow fading—channel variation over large scales—to the fullest extent. However, in orderto increase the accuracy of the results by capturing small-scale variations in the channel, systemlevelsimulations can also model the multipath fading—channel variation over small scales. Inthe case of a WiMAX, it is imperative to model the behavior of the channel in the frequencydomain over both short and long time scales to the multicarrier nature and its MIMO features.12.2.1Simulator for WiMAX NetworksSimulating a wireless network that consists of a very large number of cell sites is often computationalyprohibitive and inefficient. Therefore, the system simulator used to generate the resultspresented in this chapter consists of only two tiers of cell sites that are present in a hexagonalgrid, as shown in Figure 12.1.Owing to the finite size of the simulated network, cell sites that lie toward the edge of thesimulated network (outer tier) have missing neighbor cell sites, which causes the other-cellcochannel interference to be modeled inaccurately in these cells. This edge effect mandates thatstatistics related to network performance indicators, such as data rate and throughput, should besampled only in the center cell, where the modeling of the other-cell interference is accurateenough. One solution to edge effect is the wraparound approach, which allows the simulator tomodel the interference and collect statistics even in the cells at the edge of the network. The systemsimulator used to generate the results presented in this chapter implements such a wraparoundto mitigate the edge effect.Missing Neighbor CellsFigure 12.1 Two-tier layout of cells for the system simulator