mobile telephony and health

how does mobile telephony work?

Whether it’s the GSM system of the newer UMTS technology, mobile telephony uses radio connections to ensure users’ mobility. This is achieved using base stations installed at various locations. Without them, the network couldn’t exist.

When a call is made, the mobile connects to the nearest base station. From there, the call is directed to a switchboard which then contacts the switchboard in the area where the mobile called is located. This switch looks for the mobile called. If the mobile called is turned on, localisation takes place almost instantly, and the nearest base station will make the connection required for the call, with the mobile called starting to ring.

Each base station allows mobiles to function in the area nearby, called a cell (thus the name, cellular phone). This area’s characteristics depend on a number of factors, but generally it’s smaller in urban environments and larger in rural areas.

Base stations are located on various structures, depending on the environment. If the majority of base stations are installed on top of tall buildings in towns and cities, in rural areas, where the average height of buildings is low, they are placed on metal masts 30-40 metres tall.

A base station is made up of several distinct parts. The most visible parts are the aerials. They achieve the transformation of the electrical signal into electromagnetic waves and the other way around. There are two types of aerials in a base station: radio aerials, which ensure the connection with mobiles, and microwave aerials, which connect with the network. Radio aerials are shaped like small panels, and microwave aerials usually look like cylinders.

components of a base station

A frequent misconception is that aerials emit in all directions, in the way a light bulb emits light. In reality, they are directional, in other words the power received is radiated like a beam, similar to the light beam from a headlight. This beam is almost flat vertically and has an opening of between 65 and 90 degrees horizontally. These aerials are the main generators of electromagnetic fields in the base station.

The microwave aerials emit a narrow beam of a few degrees, both vertically and horizontally, as they connect two fixed points. This is why the field generated by them outside of this beam is regarded as negligible.

Aerials are connected by means of cables to a metal cabinet which houses the electronic equipment used for control and transmission, power, cooling etc. Although less visible, this equipment represents the actual base station.

Mobile telephony systems don’t use a lot of transmission power, because this varies according to the size of the cell. The smaller the surface area covered by the cell, the lower its power use, because of the need to eliminate interference. Even the power used to cover large territories is quite low, never exceeding 20-40 W. However, these are maximum values which are seldom reached. The base station always checks the power it emits in order to ensure the connection with mobiles using a minimum of resources. By comparison, an FM radio station uses relatively constant power emissions of between 100 and 30000 W, while AM and long wave radio transmitters exceed 250000 W.

In turn, the mobile phone controls the power level it emits, so that it uses the minimum possible amount of energy. This is why having more base stations means lower power emissions from the mobile phone.