The challenges of improving wireless connectivity in buildings

Sept. 18, 2020

By William Wong, Advanced RF Technologies Inc.

As our society moves further toward a completely digital future, building owners are acknowledging the necessity of indoor wireless connectivity to power digital services and deliver better tenant expectations. It is quickly becoming the “fourth utility,” joining gas, electric, and water as an essential resource for any modern site. Although the macro network often gets the most attention, 80% of all connections start and terminate inside buildings.

However, providing cellular reception inside buildings is easier said than done. With a growing reliance on wireless technologies, it’s important for building owners to recognize the negative impact of obstructions in and around their buildings on radio frequency (RF) signals.

Common material interference for LTE frequency bands

A normal cell phone receives signal levels ranging from > -70 decibels relative to a milliwatt (dBm) to -120 dBm, the equivalent of having full bars or no signal, respectively. There are numerous natural and manmade obstructions that inhibit RF signals from entering buildings. Considering so many modern elements of a positive customer experience lean on mobile phone support and digital services, building owners should be more mindful of locations and construction materials that are a detriment to connectivity.

The most common examples of natural elements that disrupt cellular signals include terrain, such as mountains and hills, vegetation (-7 dB to -20 dB loss), including tall trees and shrubbery, and even minor atmospheric conditions (-1 dB to -5 dB), such as thick fog and rainstorms.

Whereas natural obstructions are largely beyond the building owner’s control, they may have a say in construction materials. As designs begin to incorporate double or triple-pane and low-emission (low-E) glass to help reduce heating and cooling costs in buildings, it can cause serious RF obstruction. Single-pane glass only attenuates 4 dB, whereas the multi-paned and low-E glass attenuation can range from 24 to 40 dB.

In terms of building materials beyond glass, following are estimated ranges of dB loss for common building materials.

·       Fiberglass (-2 dB): Fiberglass insulation helps to naturally regulate the temperature inside buildings at certain times of year, but can have a slightly negative impact on signal strength.

·        Drywall (-4 dB): Drywall is popular to build interior walls or ceilings, but it can also disrupt the frequencies from penetrating. The thicker the drywall, the harder it is for the RF signal to penetrate.

·        Concrete 6 inches (-10 to -20 dB): As the most commonly used manmade material, it is also the greatest obstructor of RF signal. This is particularly true in major urban areas, where architects depend on its strength to develop robust high-rise multi-tenant commercial real estate buildings.

·        Brick (-8 to -28 dB): Many older buildings were constructed primarily of brick, and it is one of the most egregious forms of cellular signal disruption. As owners look to modernize their wireless infrastructure, systems integrators will face challenging installations.

·        Metal (-32 to -50 dB): Aluminum, lead, brass, steel, iron, and other metals are the single largest cellular reception disruptor, and it’s also growing as an element of building construction. According to Metal Construction News, the reported use of steel jumped from 1,801.4 tons in 2017 to 2,495.8 in 2018—a 36% year-over-year increase.

The types of materials used in the building, among other factors such as size and architectural design, will alter equipment (and expenses) required to provide ubiquitous wireless connectivity indoors. For LTE, buildings should use distributed antenna systems (DAS) to provide sufficient coverage. Depending on the interference caused by the material obstruction, the number of remotes and antennas required will vary immensely, as will cabling needs.

How will building materials affect 5G deployments?

As building owners think about providing 5G connectivity to their workers, guests or tenants, they should be wary of how object interference impacts the development of indoor networks. On the surface, 5G is simply the next generation wireless technology that will support a new era of technologies for consumers and businesses with faster speeds and ultra-reliable low-latency communication (URLLC). Under the hood, however, 5G is more complicated. The four major mobile carriers are using different frequency bands to power their 5G networks, which means different network characteristics for in-building deployments than LTE. For instance, the new T-Mobile (post-Sprint merger) is predominantly using a mix of low-band and mid-band spectrum, 600 MHz and 2.5 GHz, to develop their national 5G network, with select areas receiving high-band millimeter wave (mmWave) spectrum. Verizon is using 28 GHz and 39 GHz, with AT&T currently using 39 GHz and the mid-band sub-6 GHz beyond 2020.

Low-band spectrum is characterized by lower speeds, the ability to travel further distances and is less susceptible to object interference. High-band spectrum delivers the high speeds and low latency that people envision from 5G networks, but travels much shorter distances and has even more issues penetrating building materials than LTE frequency bands. As a result, building owners that wish to provide true 5G coverage for all four major carriers will likely need more in-building wireless solutions to reach a similar level of coverage compared to in-building LTE networks. The small coverage radius of mmWave is why mobile carriers aim to deploy small cells across the country to increase network capacity. Leveraging a DAS, using small cells as a signal source, will initially be the most cost-effective solution for in-building multi-carrier 5G networks to limit the backhaul considerably.

As in-building connectivity becomes a necessity to remain competitive and keep up with the latest innovations, building owners must understand how their designs will impact cellular reception. It’s important that wireless infrastructure be considered at the onset of development to mitigate ballooning costs and deliver exemplary coverage for guests or tenants.

William Wong is the DAS engineering manager at Advanced RF Technologies Inc., in charge of overseeing customer training and technical support of ADRF’s equipment for DAS projects. He has 10 years of experience in the in-building/DAS sector and related engineering fields, including several years at a DAS integrator where he focused on survey, design, project management, implementation and optimization of carrier and neutral-host DAS.

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