Base Stations and Masts

What is a mast?

Radio base stations are commonly called masts. The terms are used interchangeably, but they are in fact two different things.

A mast is a freestanding structure (the same as a telegraph pole) which supports antennas at a height where they can transmit and receive radio waves. A mast is typically 15m high and plays no part in the transmission of radio waves. To minimise the environmental impact, more slim line versions with smaller head frames are now in place. These can be painted to blend in with their surroundings, disguised as trees or used in conjunction with street lighting.

Radio base stations are sites that enable mobile phones to work. They can be big or small and have transmitters and receivers in a cabin or cabinet connected to antennas. They can be mounted on a large mast or tower, an existing building, rooftops or street furniture such as street lamps. Without base stations, mobiles will not work. At the start of 2008 there were around 50,300 base station sites in the UK - two thirds of which are located on existing buildings, roof tops, street furniture etc.

How it all works

A mobile phone is a low-powered two-way radio - converting human voice and data messages into radio waves. When making a call, these radio signals are transmitted from the mobile phone to the nearest base station. Once a signal reaches a base station it is then transmitted to the main telephone network where it is transferred to the network of the person receiving the call.

What is a cell?

In order to enable millions of people across the country to make calls, each of the five mobile phone operators divides the UK into thousands of individual geographic areas known as 'cells'. At the heart of each cell is a base station. The cells overlap at the edges to prevent holes in coverage. If the radio base stations are too far apart, calls cannot be handed over from one area to another and are interrupted or 'dropped' when mobile users are on the move.

There are three types of cells: macrocells, microcells and picocells.

A macrocell provides the main coverage in a mobile network. The antennas for macrocells are mounted on ground-based masts, rooftops and other existing structures. They must be positioned at a height that is not obstructed by surrounding buildings and terrain. Macrocell base stations have a typical power output of tens of watts.

Microcells provide infill radio coverage and additional capacity where there are high numbers of users within macrocells. The antennas for microcells are mounted at street level, typically on the external walls of existing structures, lamp posts and other street furniture. The antennas are smaller than macro cell antennas and, when mounted on existing structures, often blend in with building features to minimise visual impact. Typically, microcells provide radio coverage across smaller distances and are placed 300m-1000m apart. They have lower outputs than macrocells, usually a few watts.

A picocell provides more localised coverage than a microcell. They are normally found inside buildings where coverage is poor or where there are a high number of users, such as airport terminals, train stations or shopping centres.

The size of a cell depends on:

• current and future customer call use because each base station can only support a limited number of calls simultaneously
• the physical terrain of an area as radio signals are blocked by man-made and natural obstacles such as buildings, trees and hills
• the frequency band in which the network operates can affect cell size - normally the higher the radio frequency (as in advanced 3G technology) the smaller the cell

The cells in a new third generation (3G) network will be smaller because 3G uses a higher radio frequency. These cells also expand and contract in size depending on the number of simultaneous calls being made. For this reason, 3G cells will have to overlap more than the current 2G cells.

Expanding the Mobile Network

More base stations will be in place shortly as part of a programme to enhance the infrastructure for the existing mobile generation (2G) and create a new network for 3G.

New base stations are required as each cell can only support a finite number of mobile phone calls at any one time. If there is a high customer demand in a cell, greater capacity is needed to enable more calls to be made. This can be done by placing another mast in between the existing cells and creating additional smaller cells.

3G networks will use smaller cells because they have to support the transmission of large amounts of information and operate at a higher frequency. 3G cells also expand and contract in size depending on the number of simultaneous calls being made. For this reason, 3G cells will need to overlap more than the current 2G cells.

Site Sharing

Site sharing is when two or more mobile phone operators agree to put their base station antennas on the same structure, such as water tower or roof-top. Mast sharing is when the antennas are put on the same mast.

Operators try to share sites whenever possible. However, it is not always a viable option. Shared masts are normally taller and have more impact on the environment because they have to accommodate two or more sets of antennas. The more antennas that are clustered together, the higher the overall radio frequency emissions are likely to be. Further, the radio frequencies that different mobile network operators use are not always compatible and could interfere with existing antennas.

Future technological developments

With the burgeoning of the information society, users of data and multimedia communications services have come to expect and demand that these services be mobile. Third generation radio services, which started to become available in 2003, will deliver voice, graphics, video and other sophisticated information direct to the user, regardless of location or terminal, using base station networks similar to those supporting existing mobile services.

However, these services will be accessible across multiple mobile and fixed line networks, as technology converges. The key benefits of third generation include improvements in quality and security, incorporating broadband (i.e. capable of transmitting high volumes of data) and networked multimedia services, flexibility in service and service availability.

With growing demand for computer-based communications, so has there been growing demand for information and entertainment services while mobile – as evidenced by the growth in the mobile telecommunications market and, separately, the Internet. Third generation mobile's increased capacity, data capability and greater range of services will thus provide a step-change in the way in which individuals communicate and access information. The technology will also facilitate and drive convergence in the computing, broadcasting and communications sectors.

Whilst voice communication over conventional handsets is still the dominant service used, the explosion of growth in, for example, the use of the Internet has already led to the appearance on the market of first generation Internet phones. Text messaging services in some locations generate as much traffic as voice calls.

Other changes aniticipated over the next few years are:

Changes in mobile phone design

Because of the move towards multimedia type applications in third generation systems, the design of handsets will change significantly and the use, ability and size of the screen becomes key. There is already a move towards this type of product in phones being brought to the market with Internet connectivity.

Bluetooth technology

Bluetooth is a technology specification designed to eliminate the cables and infrared links used to connect disparate devices. Its aim is to provide small design, low-cost, short range wireless interconnectivity between, for example, laptop computers, mobile phones, headsets, watches, digital cameras and cars. It also enables close-range applications in public areas like e-cash transactions.

Based on low power radio frequency technology using 2.4 GHz spectrum and a power level of 10mW, the data rate is almost 1Mbit per second and the range is approximately 10 metres. The technology will enable users to connect a wide range of computing and telecommunications devices easily and simply, without the need to buy, carry, or connect cables.

It also delivers opportunities for rapid ad hoc connections, and the possibility of automatic, unconscious, connections between devices. It will virtually eliminate the need to purchase additional or proprietary cabling to connect individual devices. Because Bluetooth can be used for a variety of purposes, it will potentially replace multiple cable connections via a single radio link.