12.6 CELLULAR NETWORK OPERATION
In the previous discussion, we introduced the simplified network architecture of a UMTS or GPRS cellular network, as shown in Figure 12.22. We are concerned in this section with the basic network architecture, particularly how we interface the IP network with the RF network, so that we can begin to see how we shall connect our J2EE content world with the device network.
Elaborating upon the architecture (see Figure 12.22), we already discussed that in cellular systems the cells are supported by base stations, which are the sources of RF connectivity in each cell (or sector). In a GSM/GPRS network, the name given to the base station is Base Transceiver Station, or BTS. In UMTS, the equivalent unit is a Node-B. These units actually contain the RF transmission systems and the required RF antennae to enable the RF waves to propagate in the required sector pattern. Some antennae disguise themselves as trees, or other objects, to avoid unpleasant eyesores on the landscape, such as the ‘Scots Pine’ shown in Figure 12.25.
Base stations are housed in equipment cabinets that can accommodate several radios, one per cell (sector). The number of radios depends on the nature of the site, which come in a variety of sizes, but are loosely categorised into macro-cells (up to 20 km radius for GSM), micro-cells (a little as a few hundred metres) and pico-cells (usually limited to indoor coverage, such as the floor of a large building). Installing smaller and smaller ...