Digital telecommunications: planning guidance

Annex B

A basic technical summary of how digital communications and fixed line networks operate.

1. This annex provides a basic technical summary of how digital communications infrastructure operate and the physical components required to allow this. Digital communications infrastructure is generally defined as a set of fixed and mobile communications networks. This annex mainly focuses on mobile networks familiar to most as how they receive information on their mobile devices.

2. As technology has evolved, individuals have been able to do more and more with their personal mobile equipment. Second Generation (2G) technology gave us voice calls and text messages. Third Generation (3G) gave us access to the Internet and other data on the move. Fourth Generation (4G) created superfast mobile broadband at speeds roughly equivalent to those you would expect from a fixed broadband connection. 5G provides ultrafast mobile broadband and the capability to support a range of new technologies, such as connected automated vehicles, smart city applications and other internet of things (IOT) uses including industrial and real time monitoring. The future of connectivity will continue to accelerate through enhancements, advancements and innovations in next generation technologies.

What base stations are and their purpose

3. A base station is a fixed communication location which is part of a network’s mobile device system. It relays information to and from a transmitting/receiving unit, such as a mobile phone or tablet, by radio waves which carry data, text, picture, video or voice. These signals are connected into the wider network through either fibre or microwave dish links.

4. A base station can be made up of several components including radio antennas; masts; equipment cabinets; underground cables; power supply; fencing; landscaping and access tracks. In order for mobile networks to function, they need a substantial network of “base stations” to provide sufficient radio coverage in any geographical area. Operators often need to upgrade existing base stations in their mobile network due to network consolidation, the introduction of new technologies or changes in the surrounding environment.

5. As telecommunications systems have evolved, there has been a need for more base stations to keep pace with customer demand (e.g., by accessing data on the internet puts more pressure on network capacity).

How base stations operate

6. Mobile networks operate by using and re-using the same radio frequencies and allocating them to geographical cells. Mobile Network Operators (MNO) divide the country into thousands of individual cells and at the centre of each is a base station. Base stations are connected to one another by central switching centres, which track calls and transfer them as the caller moves from one cell to the next. The area covered by each cell is governed by the anticipated capacity (i.e., volume of calls); the height of the antenna above the ground; the local terrain; the power output and the radio frequency. In general, the higher the frequency, the shorter the distance that the signal can travel.

7. Generally, the largest cells are in sparsely populated rural areas and the smallest cells are in town and city centres. The capacity of existing sites can, in some cases, be increased, but there is a limit to this and once this is reached it becomes necessary to split each cell into smaller areas, each served by its own base station. This is an effective solution in areas where many mobile users congregate, such as shopping centres and railway stations.

8. Mobile networks are a mixture of large macrocell base stations (paragraph 17 refers), smaller street side base stations and microcell base stations (paragraph 18 refers), in dense urban areas. All are comprised of a mix of antennas installed on supporting structures or mounted on buildings and connected by feeder cables to radio equipment housing located either in its own cabinets or within a building. The various types of base station are discussed below.

9. The management and licensing of the radio spectrum lies with the Office of Communications (OFCOM^[8]). The operators own and use different frequencies and wavelengths depending on their ownership of spectrum. Different wavelengths bring with them different coverage characteristics and can determine design options for new infrastructure.

10. 5G and further generations use a broad range of frequencies, including higher radio frequencies (such as 3.4 gigahertz and millimetre wave bands – 28 gigahertz and above) to transmit data. Propagation both in terms of distance and through materials reduces as frequency increases. This dictates the siting of infrastructure including height requirements to ensure radio frequency is not blocked.

11. This can, therefore, create technical constraints in the delivery of effective infrastructure. Base stations may need to be situated higher in order for antennas to effectively transmit data over buildings, trees etc. In addition, more, and possibly robust, antennas will be needed to meet service demands and, particularly, in relation to operators sharing sites. Equipment, therefore, need to be carefully designed in order to meet such requirements in terms of providing effective coverage and to ensure ICNIRP compliance is met on public safety.

The role of base stations antennas

12. Mobile base stations generally use two forms of antenna systems, which are the most common on 4G and 5G technologies.

• Sector Antennas - these are vertically orientated to transmit and receive signals to and from mobile devices in the target area. These antennas are typically split into three 120-degree sectors that combine to provide 360-degree coverage – they are normally placed on masts or buildings. Any physical obstruction in front of the antennas inhibits the radio signal from the antennas and the closer the obstruction the greater the inhibition. This is why new masts tend to need to be taller than the surrounding buildings and trees etc. Such technical matters dictate the design of rooftop sites and, therefore, will need to address antenna ‘clipping’ and ensure ICNIRP compliance.
• Dish Antennas – these operate on a direct line of sight (LOS) basis to other dish antennas in the operator’s surrounding network. These antennas are often not required if there is fibre available. The dish antennas link an individual base station to the wider network, which in turn is linked to other national and international networks. These are located close to the sector antennas on masts or buildings. Transmission dish links can be critical to network integrity, but their LOS requirements mean that they are also susceptible to interference by tall developments, such as wind turbines and tall buildings. Any physical interference to the transmission link could compromise an entire cell and impact on the wider network as transmission dishes can operate over significant distance (particularly those for the television and radio broadcasting networks).

13. Interference can require separation distance between antennas both horizontally and vertically influencing the final design of base stations. For instance, on cross water tidal path LOS may mean additional dishes are required.

14. As well as operating licence obligations, the demand for a new base station is driven by public demand for geographic coverage and ever-increasing amounts of data. Base stations are therefore sited to maximise the quantity and quality of coverage to any particular locality where there is such demand. However, a base station is only physically able to cover a limited geographic area and can only handle a finite amount of traffic at any one time. Therefore, base stations need to be sited in specific locations where they can be operationally effective. This specific locational constraint is unlike most other forms of development.

15. Each base station has a finite capacity to handle the traffic generated by users of mobile devices. The greatest level of growth in mobile traffic has been in data, and this trend is projected to continue. In some cases, new installations may be required to split existing coverage areas in order to provide more capacity, known as ‘cell splitting’. This is likely to be more common in urban areas where customer usage is the greatest although may be required in rural areas where topography may prevent coverage of transport routes and areas of population.

16. All electronic communications base stations are often referred to as ‘masts’. However, mobile networks are made up of a mix of different types of infrastructure: roadside masts, rooftop equipment and small cell technologies – many being largely unnoticed by passers-by. The large, free-standing mast structures, such as those often found on hilltops or the side of motorways for example, represent only one element of the mobile network infrastructure, and small cells are an increasingly large proportion of networks, particularly in urban environments. All operators of radio transmitters are under a legal obligation to operate transmitters in accordance with the conditions of their licence. Operation of transmitters in accordance with the conditions of their licence fulfils the legal obligations in respect of interference to other radio systems, and as such will not cause significant and irremediable interference with other electrical equipment, air traffic services or other instrumentation operated in the national interest.

The role of base station cells

17. Macrocells provide radio coverage to a large area within a mobile network. Antennas for macrocells are usually mounted on either ground-based masts, rooftops or other existing structures. Antennas must be positioned at a height that is not obstructed by terrain or buildings and they provide radio coverage over varying distances depending on the frequency used, the number of users in the area and the physical terrain; and to afford the necessary LOS for the dish links that provide backhaul to the operator’s network

18. Microcells, which include small cell systems, provide additional coverage and capacity where there are high numbers of users within urban and suburban macrocells. They are usually deployed later in network roll-out where macrocells are unable to meet the coverage and capacity demands. The microcell antennas are small boxes about the size of burglar alarms which are mounted at street level typically on the external walls of existing structures, lampposts and other street furniture however, they only have a range of around 100 metres. Microcell base stations are suitable for transmitting signals to pedestrians but are less suited to fast moving traffic. Microcells should not be seen as a replacement for macrocells.

Small Cell antennas

19. Small cells are a form of microcell but cover a smaller area – these are also known as femtocells or picocells – these can be used through campuses or in shopping centres and can help radio waves penetrate buildings.

Street poles

20. These are macro base stations however they offer a more limited solution for MNOs. This is because the amount of ground-based apparatus is usually limited due to space and constraints around complexed underground services on the public road. Importantly, the antennas tend to be of fixed orientation and, as they are tightly packed within a glass reinforced plastic shroud, cannot be tilted. These constraints have a direct impact on the efficiency of the radio coverage provided. The height of a street pole may require antenna ‘clipping’ to be addressed and ensure ICNIRP compliance (paragraphs 4.6 and 4.7 refer).

Fibre

21. Fibre optic communication is a method of transmitting information from one place to another. 5G will require more instances of fixed line fibre optic cable for reliable and high capacity backhaul. However, this can be constrained by the availability of fibre which in some rural areas may be several kilometres away. There are severe economic constraints of getting fibre to all base stations.

Microwave

22. The radio access network requires a ‘backhaul’ connection to the core network in order for the mobile base station or cell site to be operational. This is provided by fibre optic cables or, if fibre is not available, a microwave link. A microwave link requires a clear LOS between the two ends of the link. Microwave transmission dishes themselves generally vary from 0.3 metres to 1.2 metres in diameter, depending on the site location and terrain involved. Obtaining LOS may require a taller mast than would otherwise be necessary to provide coverage to the surrounding area. Where it is not possible to gain direct LOS between two locations, an interim (sometimes known as ‘a hop’) site can be installed at a suitable position to bounce the signal between the two end points via more than one base station.

Satellite

23. Where LOS cannot be achieved to provide transmission links between 2 locations, satellite communications may be required to provide the link, depending on the system and other operational factors. This would typically involve the installation of a satellite dish with a diameter of approximately 0.6 metres to 2 metres on a ground-based support pole within the site compound. There may be instances where the satellite dish needs to be located remotely from the main site compound to achieve the necessary satellite connection. This may occur where trees, buildings or the terrain block visibility of the satellite. Growing networks in remote rural areas of Scotland will result in an increase in the number of satellite communications links required. This is however a sub-optimal solution as it has a far lower capacity for data than fibre or microwave link.

Fixed-Line Broadband

24. Fibre line broadband is generally delivered by Fibre to the Cabinet (FTTC) technology. A typical approach to fixed-line broadband deployment involves street cabinets hosting electronics near to underground cables. Alternative deployments comprise a street cabinet connected to the local telephone exchange by underground cables. In some locations, fibre services are delivered using Fibre to the Premises (FTTP) technology, which consists of underground fibre connecting premises to a central location, typically a building where access equipment is hosted. This architecture, assuming underground fibre, offers the least impact in terms of visible equipment in the streetscene.

Fixed Wireless Broadband

25. Wireless technologies, particularly Fixed Wireless Access (FWA), are often adopted to deliver broadband connectivity in rural and remote areas where traditional fixed-line broadband can be challenging or economically unviable to deploy. FWA is also commonly found in city and other urban landscapes to deploy public access to Wi-Fi networks. This technology requires antennas to be positioned at height in strategic locations to offer the required extent of coverage/capacity to premises and for point to point backhaul connections to other network nodes.

Smart metering/ Internet of Things (IoT)

26. The Smart Network supports smart meters which enables them to communicate directly with energy suppliers thereby negating the need for meter reading. Smart meters give real time information thereby allowing people to better manage their energy use; save money and reduce emissions. The network supports the wider objectives for our society to be resource efficient, lowering carbon footprint and tackling climate change.

27. The Smart network allows for some everyday objects to have network connectivity, allowing them to send and receive data. The economic, environmental and social impact of the IoT will positively impact business in all industries, from manufacturing and energy to retail and healthcare.

Radio and Terrestrial Television Broadcast Networks

28. Radio and terrestrial television broadcast networks are largely mature networks, but still require changes from time to time to reflect technological advances. The broadcast networks form part of the UK Critical National Infrastructure and have a vital societal role to play in our security, entertainment and education. Installations within these networks range from main stations with the largest masts in Scotland that broadcast television services to hundreds of thousands, to smaller television relay stations, similar in appearance to telegraph poles that serve small local populations.