12.6 NETWORK LAYOUT FOR SYSTEM-LEVEL SIMULATIONS In rural or high-speed, macro- and micro-cellular environments, no specific topographical details are taken into consideration. Base stations are placed in regular grids conforming to a hexagonal layout. A basic hexagonal layout with three cells/sectors per site is shown in Figure 12-6 where antenna bore- sight, cell range, and inter-site distance are also illustrated. The system-level simulations use a wrap- around model with 19 sites each comprising 3 cells. The users are dropped uniformly over the entire coverage area (Monte Carlo method in order to model the inter-cell interference. Depending on the "Monte Carlo methods are a class of computational algorithms that rely on repeated random sampling to compute their results. Monte Carlo methods are often used in simulating physical and mathematical systems. Because of their reliance on repeated computation of random or pseudo-random quantities, these methods are most suited to calculation by a computer and tend to be used when it is infeasible or impossible to find a closed-form result with a deterministic algorithm. 12.6 Network layout for system-level simulations FIGURE 12-6 An illustration of a hexagonal cellular layout and basic antenna terms [6] configuration being simulated and the required output, the effect of the surrounding outer-cells may be disregarded. In such cases, only 19 cells of the center cluster may be modeled. For the cases where modeling of the interfering outer-cells is necessary for accuracy of the results, the wrap-around structure with the 7-cluster network can be used. A cluster is defined as six displacements of the center hexagon. In the wrap-around inter-cell interference model, the network is extended to a cluster of networks consisting of seven replicas of the original hexagonal network, with the original hexagonal network in the middle while the other six copies are attached to it symmetrically on six sides. The number of mobile stations is predetermined for each sector/cell, where