All you need to know about cell towers

Network operators are converting existing mobile communications sites – masts, for example – for 5G, as well as building new ones. Without this, citizens will be unable to avail themselves of this fast network. But what are transmission masts? What are mobile base stations and how do they work?

Base stations supply the entire country with mobile communications. They are what ensures that a phone call made on a hiking tour doesn’t simply evaporate into the void. They allow us to send photographs to the people we love whilst on the move. The different kinds of base stations are the backbone of our mobile life. 

Mobile base stations are stationary installations. Their basic components are 

• one or more antennas, for transmitting and receiving radio signals, 
• a supply unit housing switching and control elements for the antennas. 

Base stations are built on a carrier (such as a mast or a rooftop). The quality of the connection between the base station and the end device – a smartphone, for example – does not just depend on the transmitting power of the antennas. The supply unit that is used is also a major factor – which is precisely where 5G mobile technology offers new effective possibilities.  

Small cells vs large cells 

Every base station supplies a specific area – a radio cell – with mobile reception. But a radio cell can only accommodate a limited number of users. In urban areas, where there are many users, many base stations that generate small radio cells are installed – in other words, sites with low transmitting power. 

The ability to supply as many users as possible does not come from building base stations with very high transmitting power. Instead, many small cells with relatively low transmitting power are built up. This is the only way to make sure transmissions from neighbouring radio cells do not disrupt each other. Experts speak in terms of picocells, microcells or macrocells. In areas where users are relatively thin on the ground, these supply cells can cover a range of 20 to 70 kilometres. 

The end device itself is a further significant factor influencing the emitted power of the mobile communications installation with which it is connected. The closer together the end device and base station are, the lower the transmitting power required on either side. Conversely, as the distance between the two increases, both units increase their transmitting power – right up to the point at which the connection is taken over on a technical level by the next nearest cell. So provided the reception is good, neither the base station nor the mobile phone requires high transmitting power. Therefore, a high density of mobile communications sites makes sense on several levels, ensuring that users receive good network coverage along with a good supply. 

Transmission mast, base station – what does it all mean? 

Our smartphones are constantly connected to antennas in the vicinity as we move around. But what is a transmission mast? What does “radio installation site” mean and when do we speak of a “base station”? Let’s try to clarify and classify these terms. 

Radio installations or mobile communications installations are devices capable of emitting and/or receiving radio waves for communication purposes. They may have one or more antennas. This generally means one antenna per mobile communications standard, but there will sometimes also be antennas for more than one, for instance one antenna handling both LTE and 5G. Radio installation sites or mobile communications installation sites are terms used for all locations where a radio or mobile communications installation is or can be installed. Mobile communications installation sites are also referred to as mobile communications sites. In urban areas, mobile communications sites are often found on top of tall buildings. These are known as “rooftop sites”. In rural areas, mobile phone masts are more usual, and these are referred to as cell towers. 

To operate a stationary radio installation at or above a specified transmission power level, in Germany there must be a valid site certificate in respect of that site. A site certificate is issued by the Federal Network Agency as part of the site certification procedure. This procedure helps ensure compliance with the permitted thresholds for electromagnetic fields and is designed to protect the population. 

Base stations, or mobile communications base stations, are stationary radio or mobile communications installations essentially consisting of two elements: (1) one or more antennas for transmitting and receiving radio signals, and (2) a supply unit housing switching and control elements for the antennas. These base stations generate the radio signals that ultimately constitute the cell. This is the only way to make sure transmissions from neighbouring network cells do not disrupt each other. 

Wireless communication – how it works 

Wireless data transmission between mobiles and base stations uses radio frequency electromagnetic fields (EMFs). These are generated when the current flowing in an electrical conductor continuously changes its direction. 

The frequency is measured in hertz. All other wireless technologies, such as radio broadcasting (radio or television), Wi-Fi or baby monitors, also use frequencies. Second- to fourth-generation mobile communications (GSM, UMTS and LTE) use frequency bands between 800 megahertz and 2.6 gigahertz (abbreviated as GHz). These will also be used by 5G in the future. As it expands, the 5G network will also use the frequency range from 3.4 to 3.7 GHz. 

So-called 5G campus networks can already be assigned frequencies within the range of 3.7 to 3.8 GHz by the Federal Network Agency. Campus networks are highly localised and limited 5G networks. They are used, for example, to supply research institutes, medical facilities or factory premises, allowing devices and machines to interact. Depending on the requirements and utilisation, these networks too aim for real-time communications and high data transmission rates. In the near future, it will also be possible for campus networks to be assigned frequencies in the 26 GHz range by the Federal Network Agency. 

The authorities are keeping a watchful eye on these strict thresholds 

To protect the population, base stations are also subject to thresholds, imposing clear limits on electromagnetic fields. These thresholds are defined in the Ordinance on Electromagnetic Fields, taking the Federal Immission Control Act as their basis. They can be requested here, on the website of the Federal Office for Radiation Protection (BfS). 

More on this topic, along with further information about thresholds, can be found in this article. 

The basis for the consistent implementation of these thresholds is the Ordinance on the Verification Procedure for the Limitation of Electromagnetic Fields (BEMFV). The Federal Network Agency checks each individual case and issues a site certificate for each stationary radio installation at or above a specified transmitting power, provided it satisfies the conditions. To find out how this works in practice, please see our article on the site certification procedure. 

When we’re on a phone call and both phones involved are mobiles, our mobile connects wirelessly to the closest base station. The other person’s mobile is likewise connected to a base station. These base stations are in turn connected to central computers that process the data transmitted and link the two mobile communications installations with each other. You can learn more about how data transmission functions in this article. 

Transmission masts make safe neighbours 

Many people are concerned about where companies erect transmission masts. In principle, it is important to note that in Germany, no totally new mobile infrastructure is being built for 5G. In many locations, 5G technology can be retrofitted on to existing sites to produce, so to speak, multigenerational radio installation sites. 

New radio installation sites become necessary when there is no other way to meet the demand in a given area effectively. Or if the Federal Network Agency, for safety reasons, does not issue a site certificate for the upgrading of existing sites. This applies if an additional radio installation is envisaged but cannot maintain the requisite safety distances. It follows that new sites for mobile communications will only be added if this is necessary from a structural standpoint. We are currently in the early stages of the 5G network expansion, and network operators are for the most part upgrading existing installations.

article.sources

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