Mobile Wireless
Overview of mobile wireless systems

The original analog AMPS consisted of three major components, which remain the basic components of a cellular system today:

  • Mobile telephone switching office (MTSO)
  • Base stations
  • Cellular phones or other devices

In some cellular systems, functions may reside in the base station rather than the MTSO. The terminology may differ slightly, but most cellular systems include these three components, as shown in Figure . The new 3G technologies have additional components to interface with the Internet or an intranet, using IP.

The basic idea behind cellular communications divides a serving area into geographic zones, called cells. The bandwidth within a cell is shared among the users according to a media access control method. Each cell has a base station in the center. All cellular devices communicate through this base station. This is similar to a WLAN cell with an AP. There will be at least one MTSO per cellular system. The MTSO communicates with the base stations and with the PSTN.

Cells are normally roughly circular. In general, a smaller cell size means less power is needed, which leads to smaller and cheaper devices. However, it also means that more cell sites are required for the complete coverage of an area. When a cell becomes too crowded, the overloaded cell is split into smaller cells by sectoring the coverage of the cell into pie shaped segments using directional antennas on the cell site. Cell sites are many times initially designed to have mutiple sectors due to projected traffic loading and coverage. This allows more frequency reuse and therefore, more capacity.