We all know the problem: mobile phone service is working fine … until you move indoors. Then, sometimes it works (you don't notice), sometimes it sort of works (meh) and sometimes it clings on by one tiny bar or drops out entirely (argh).

Diagnosing the problem is relatively simple. The loss of mobile service indoors is fundamentally a result of outside-in coverage strategies and building entry loss (BEL) — i.e., the attenuation of radio signals due to walls and windows. This is particularly an issue for 5G mid-band frequencies (the main 5G band in most markets). At these frequencies, BEL is typically 20–30 dB* (depending on building type). For users already toward the outdoor cell edge, this amount of loss is enough to seriously degrade service quality or block service entirely as the user moves indoors.

Addressing the problem is harder. There are myriad physical, commercial and technical factors that combine to make indoor 5G service a knotty problem to solve on a countrywide basis. It is certainly a fixable problem technically — there are several great solutions — but who pays and how to deal with the sheer variety of buildings and venues, and their owners and tenants, remain big challenges.

The case for indoor 5G

Indoor coverage matters because we spend so much time indoors (Americans apparently spend an average of 87% of their time in enclosed buildings**). A better experience for customers, with less frustration, is surely worthwhile. And in a business context, there is a direct line from good/poor mobile service to productivity.

There are also opportunities that build on better indoor 5G service:

The good news is there are several ways to deliver brilliant indoor 5G networks to industrial venues, campus networks and all manner of commercial buildings.

Why we shouldn't fret too much

Indoor service has always been a problem, and we live with it. Gradually, operators and building owners get around to fixing the locations where there is the most demand, and life goes on. It is not great, but it's OK. Incremental progress over a decade adds up to make a difference.

And there are other reasons why there is no rush to address indoor 5G:

If the objective is to offer fantastic 5G services, it is clear the industry should do more to improve indoor performance. The challenge is that the diversity of venues makes for a fragmented market, and this is mirrored by the diverse technical and commercial solutions available. I'll dig into the key issues in later blogs and upcoming research. Get in touch if you want to become involved.

The starting point is to make the case for why brilliant indoor 5G service matters and establish an intent to address it. The commercial models and technical solutions will then present themselves.

* BEL of 20–30 dB for mid-band spectrum is a rule of thumb based on numerous studies presented in ITU-Report P.2346-4, "Compilation of measurement data relating to building entry loss," last updated in July 2021. Click here for more information.

** According to the oft-cited National Human Activity Pattern Survey by Neil E. Klepeis et al. (2001, page 239).