In this chapter, we will study power and bandwidth allocation in a multi-cell scenario where inter-cell interference dominates. As in Chapter 5, we assume that the channel gain does not vary over time or frequency.
Recall from Section 1.1 that spectrum reuse among cells is the key to increasing overall spectrum utilization and that spectrum reuse leads inter-cell interference to be managed. In a conventional cellular deployment, there are two basic tools to manage inter-cell interference. One is cell planning, including carefully choosing base station locations and fine tuning antenna patterns to maximize service quality. In an ideal world with homogeneous wireless channel propagation, base stations are placed in the hexagonal grids as shown in Figure 6.1. Practical considerations such as local terrain characteristics affect cell planning choices. The second tool is handoff. A user switches to a new base station as it moves across the boundary between two cells. Under so-called unrestricted association where the user is allowed to connect to any base station, handoff ensures that the user is always connected to the “best” base station, which is usually the closest one. As a result, the interference from an adjacent base station does not exceed the desired signal from a serving base station.