It’s a statement of the obvious perhaps, but operators planning to offer 5G need new ways to offer service indoors. This matters because this is mostly where we use our phones, and also because some of the major new opportunities for 5G in industrial verticals will need dedicated, high-performance indoor networks -- think factories, warehouses, airports, hospitals, etc.

The basic logic runs like this:

The classic mobile business model is built on “outside-in” network coverage using radio basestations deployed hundreds of meters, or even kilometres, apart. Each basestation can connect 1,000 or so users (approximately speaking), making it a very efficient way to connect large numbers of customers to a valuable service. This network architecture underpins one of the greatest business models in history.

The issue is that a lot of the growth in demand is indoor. The penetration loss from buildings turns these indoor users into, effectively, cell edge users, reducing cell capacity/efficiency and limiting end-user performance. Energy efficient windows, now often fitted as standard in new buildings or renovations, only add to the problem.

This is further exacerbated because 5G is expected to be deployed in higher frequency bands such as at 3.5GHz or even in mmWave. These frequencies penetrate buildings poorly relative to the bands used in LTE today. This can be offset to an extent by using massive MIMO antenna systems and beamforming, but this is expensive in terms of tower-top electronics and only gets you so far. Operators can also deploy 5G in the low-band by refarming 3G/4G spectrum. But again, this has it limits. Fundamentally, operators need novel solutions for indoor 5G.

The good news is there are lots of interesting propositions. Most obvious is to deploy new or upgraded small cell systems in the new frequency bands. In the enterprise, there are some interesting new approaches to small cells that can loosely be described as vRAN architectures. Similarly, the classic distributed antenna (DAS) systems, which are not designed to support high frequencies, will need to be over-hauled and “digitized” to support 5G.

There are also opportunities in mmWave, which is a technology well-suited to indoor environments with lots of multipath. And given the large amount of spectrum in these bands, there are some very interesting opportunities for mesh systems using relaying and multi-hopping techniques.

Finally, in both sub 6GHz and mmWave bands, shared spectrum has a potentially very important role indoors, especially for many of industrial verticals targeted by 5G.

— Gabriel Brown, Principal Analyst, Heavy Reading