Building factors to consider

The design and layout of hospitals, and the materials used to construct them, generally hinder or block the propagation of radio frequencies (RF).

Walls and partitions are commonly constructed from brick, concrete, plasterboard, wood and glass. Radiology rooms require walls that are lead-lined. Each material has a particular effect on the RF signal strength and quality which is called the clutter profile effect.

The clutter profile effect is determined by the transmission, diffraction, reflection and refraction losses caused by the wall material.

Transmission loss is the signal degradation caused by the RF penetrating wall and is measured in decibels (dB).

The following table summarises the transmission loss of different frequencies/technologies caused by different building materials. As one might expect, a partition wall causes a lower transmission loss than a heavy concrete wall.

A technology such as 4G may be able to penetrate one heavy wall, but after penetrating two or more walls the signal may become so degraded as to be unusable for voice or data. Other factors such as the proximity of the macro cell to the building will also have an effect here.

The clutter profile effect is also determined by diffraction, reflection and refraction losses caused by the wall material. These additional effects are described below. 

Diffraction

The effect caused by a change in direction of radio waves as they pass through an opening or around a barrier in their path.

Reflection

The effect caused by a radio wave bouncing in another direction when hitting a smooth object larger than the wave itself.

Refraction 

The change in the direction of radio waves as they pass from one medium to another which causes a change in speed and wavelength.

The implications of clutter profiles for the design, layout and construction of hospitals are considered further in the following sections.

Structural isolation may or may not be a requirement. This refers to the separation of external network coverage (such as outdoor commercial 4G and 5G networks provided by MNOs) from internal network coverage (such as in-building Wi-Fi and private 5G networks owned and managed by a hospital).

In some cases, it may be desirable to allow commercial mobile network coverage to penetrate a health and care building. For example, when medical equipment or clinical and administrative devices need a commercial 4G or 5G signal to send and receive data, or when patients need to use their personal devices to contact relatives or for entertainment.

In some cases, preventing outdoor signals from penetrating a building is a requirement. Furthermore, structural isolation can even be required within the same building, to prevent the coverage of one wireless network reaching or interfering with that of another. It may also be necessary to use structural isolation design techniques to prevent a wireless network from leaking into a particular room.

Achieving effective structural isolation is cited as the most challenging aspect of 90% of indoor wireless network installations. Choosing a heavy construction material for exterior walls will almost guarantee the dominance of an in-building signal over that of an outdoor network. Aluminium‑coated facades offer an alternative method for achieving high levels of structural isolation.

Structural isolation requires the dominance of the in-building network to be maintained throughout the building including areas close to windows. Many of today’s energy‑efficient windows are coated with a thin metallic layer which reduces the ability of outdoor networks such as commercial 4G and 5G networks from entering a building (signal attenuation is typically 20–40 dB).

The reflection of RF from the metallic coating on the glass also has the effect of improving coverage of in building networks, further supporting dominance of the in-building networks over outdoor networks.

Windows are increasingly being fitted with new forms of glass that are described by the manufacturers as being ‘Wi-Fi Proof’ and able to prevent hackers from accessing wireless local area networks (WLANS) from outside a building. Transparent films that have the same effect can be applied to existing glass. This new glass and film attenuate radio signals by up to 50–70 dB further supporting structural isolation.

Aluminium facades and treated glass windows typical of many modern buildings can provide 40–70 dB of isolation and are efficiently shielded, even when situated close to a commercial macro site.

As stated above, structural isolation may not always be desirable. Here, it would be appropriate to choose construction materials that allow outdoor signals to penetrate the building, such as brick; in order to provide employees, patients and other stakeholders with access to commercial mobile networks and long range IOT.

In all cases, the services of an appropriately skilled and experienced radio frequency (RF) expert should be utilised to provide advice and guidance and to ensure that structural isolation requirements are met – whether that is to prevent leakage or to encourage it.

In-building Wi-Fi access points and small cells are typically installed in corridors rather than in each of the individual rooms that are accessed from the corridor. This is for two reasons.

Firstly, ease of access for installation and maintenance of radios and cables. Cable trays and conduits can be installed along corridors more easily than they can within every room along the corridor. This makes the initial installation simpler, faster and less costly. Furthermore, corridors are often left ‘static’ when buildings are being refurbished. This means that antennas can be left in situ and can continue to provide the same level of coverage whilst the internal structure of a building is changed.

Secondly, because of the ‘corridor effect which results in an effective signal distribution from a smaller number of antennas. The following figure illustrates how 2 antennas provide coverage for 14 separate rooms because of the line of sight along the corridor and into the rooms and because of the reflection of RF signals from corridor walls into the rooms. This is a more cost-effective solution than installing an antenna in each of the 14 rooms and provides efficient coverage. Additional antennas can be installed to increase coverage by exception rather than as a matter of course.

Figure 1 The ‘Corridor Effect’: The Corridor In The Building Will Distribute The RF signal

The corridor effect is particularly relevant to the health and care sector as the internal layout of clinical environments typically feature corridors and multiple adjoining treatment rooms.

The use of heavy wall types (such as heavy concrete or double brick) should be avoided as this causes the RF signal to suffer high transmission, diffraction, and reflection losses. This will prevent the RF signal from penetrating the corridor and reaching the internal rooms smoothly.

The main corridors are intended to help distribute the RF signal. Therefore, it is desirable to have a line of sight throughout the corridor with as few obstacles in the way as possible.

Doors should not be constructed from heavy wood. One of the many types of light wood doors should be used instead. Light door materials allow the RF signal to leak into the rooms and offices along the corridor through the door itself.

The use of light wall types and light door types will reduce the number of antennas and access points needed to provide wireless network coverage when compared to the use of heavy wall and door types.

Double ceilings (false ceilings) should also be constructed from a light material. This enables antennas and access points to be located above the ceiling and out of view whilst still being able to provide adequate coverage. This is an aesthetic consideration rather than an engineering one. If the double ceiling material causes a high penetration loss, then additional antennas and access points will be required, at an additional cost.

Hospitals and larger health and care buildings are usually divided into several ‘fire-zones’. The fire zones within the building are separated both vertically and horizontally using heavy walls and metal doors. This is to contain any potential fire inside the building, thus minimising the damage to property and people.

The heavy materials used to construct firewalls or cells will typically also attenuate the RF signal by 30–40 dB and sometimes more. This significantly limits the ability of the signal to pass from one ‘fire-zone’ to another and has a major impact on the antenna layout required in the building.

To mitigate the impact of the attenuation of firewalls, it is necessary to install a minimum of one antenna inside each of the cells.

Figure 2 shows a typical building layout including the heavy firewalls and proposed antenna locations. Note that two antennas are placed near the lift to provide coverage inside the lift. Another two antennas are placed on the edge between two fire zones and will provide service on both sides of the firewall, thus saving one antenna placement.

Figure 2 Fire Cells Separated By Heavy Walls To Contain Any Potential Fire

Fire zones cause major signal degradation. The pattern, number, and location of fire zones should be considered from a wireless coverage perspective as well as a health and safety perspective.

The services of an appropriately skilled and experienced RF expert should be utilised to provide advice and guidance, and to help design the wireless network solution to align with the requirements for fire zones.

Today’s mobile devices cause relatively little interference with other devices and modern medical equipment is far better shielded from interferences than ever before.

However, there have been cases of interference found between digital phones and their antennas, and dialysis machines, defibrillators, ventilators and monitors. 

Medical devices usually suffer from electromagnetic interference from digital mobile phones at a distance of 1 metre.They are also affected by interference caused by handsets used by emergency services staff and porters. This interference can reduce the accuracy and effectiveness of electrocardiographs and other sensitive medical devices.

Since then, as a precautionary measure, antennas are generally prohibited from being installed inside Emergency Departments, Operating Theatres and Intensive Care Units. Furthermore, antennas that are located within close range of these rooms are prohibited from transmitting at high power.

The reason for such precautions is that even if the interference with the medical equipment was minimal, the risk to a patient’s life arising from a malfunction would be too great.

There are other less critical health and safety considerations and medical regulations that affect the design and installation of wireless infrastructure. For example, an infection control specialist might forbid the placement of wireless infrastructure in sterile environments.

Though the placing of antennas inside Emergency Departments, Operating Theatres and Intensive Care Units may be prohibited, it may be possible to review the configuration of those located outside of these rooms but within close range. It may be possible to allow them to transmit at a higher power and provide a greater coverage, provided the walls of the Emergency Departments, Operating Theatres and Intensive Care Units are constructed from heavy materials and the signal does not penetrate the room.

Hospitals typically contain medical devices that emit radiation, for example radiology equipment, and cause interference with radio frequencies used by wireless communication networks.

Example of medical devices and rooms that cause interference inside hospitals include X-Ray devices, CT (Computed Tomography) equipment and angiogram rooms.

Wireless network designs and installations should therefore consider a specific inter-spacing distance between the proposed antenna locations and the existing radiation devices/rooms.

Antennas should be installed at least 2m away from the source of the radiation.

Furthermore, a greater number of antennas will be required in these locations and will need to be spaced at shorter distances than would otherwise be the case, in order to overcome the interference caused and to maintain effective isolation of the RF signal.

The interior of most buildings have wireless ‘not-spots’ – areas where wireless networks either do not reach or do not provide adequate service. These areas can include lifts, stairwells, basements, bathrooms and toilets.

However, for health and care buildings such as hospitals, not-spots are simply not an option. Mobile medical equipment requires a constant network connection between floors of a hospital and patient monitors must issue an alert when a patient collapses in a bathroom or toilet, so health and care professionals must be contactable in almost every part of a hospital.

The services of an appropriately skilled and experienced RF expert should be utilised to provide advice and guidance, and to help ensure that there is ubiquitous coverage and that not-spots are eliminated.

Hospitals and other larger health and care settings must eliminate coverage not-spots. Wireless networks must provide an adequate service throughout the building including lifts, stairwells, basements, bathrooms and toilets.