antenna is too high and directed incorrectly, then the signal will be heard well beyond the boundaries of the cell. This may result in interference with another cell using the same frequencies. Figure 10.4 A typical cellular telecommunications base station along the roadside 260 Newnes Guide to Radio and Communications Technology The performance of the equipment in the base station must make up for many of the deficiencies in the mobile set. The base station will often have an output power of around 10 watts. The receiver must be sensitive, the site must be free from high levels of noise which might mask out the wanted signals, and the antennas must have gain to enable the cell signal to be heard throughout the cell, and to enable it to receive signals in the antenna will be small and not offer a good performance, cell. and the location The mobile or portable set on the other hand has a limited power, the may be very poor as mobile phones are often used inside buildings or in other poor radio locations. Infrastructure Although the phones and base stations are the obvious elements of a mobile telecommunications system, there is a considerable amount of infrastructure behind the base stations that are equally as important. Its operation enables the whole system to come together and operate seamlessly giving the user a high quality of performance. While the To public telephone system To public To public telephone telephone system system Figure 10.5 A simplified version of a cellular phone system Cellular telecommunications 261 different phone standards employ different types of infrastructure many of the same basic concepts are applicable to all types of network. For the cellular system to operate satisfactorily the base stations must be able to route calls through to the ordinary telephone network as well as contacting other mobile phones. Additionally they must be able to control the phones within the cell and pass them on to the next cell when the phone moves out of their service area into the next. All this requ