The challenges to good indoor cellular coverage are structural. Newer, more environmentally friendly window glass is hard for wireless signals to penetrate. But, the most important reasons are more financial than technological.

In big venues like sports stadiums and airports, mobile operators have commonly deployed distributed antenna systems (DAS), which contain radio equipment from multiple operators. But, DAS are expensive to install and maintain. In big venues with big crowds, it is worth the expense for mobile operators. But for medium-sized venues such as an average office building with less than 20 floors, DAS is typically cost-prohibitive.

Ed Gubbins, Technology Analyst at GlobalData says: “Mobile network equipment vendors have, in the past five years, introduced low-power radio network solutions similar to DAS that they say are cost-effective for medium-sized venues. But these solutions (distributed small cells) have not been as good as DAS at providing support for multiple operators. That fact has impeded their adoption, since the people in any given office building usually get their mobile service from a mix of different providers.”

When 5G comes along, it will bring its own complications to the indoor coverage challenge. It will make greater use of high-frequency spectrum than 4G did. High-frequency spectrum does not penetrate walls as well as low- or mid-frequency spectrum, which could increase the need for indoor networks like DAS. However, some DAS cannot transmit over 5G’s high frequencies, and many DAS lack the ability to add antenna arrays needed for 5G.

Gubbins concludes: “DAS’ 5G hurdles put more pressure on distributed small-cell solutions to provide 5G. Yet, distributed small-cell solutions may not be cost-effective in very large venues, and they may not be as effective as DAS at supporting multiple operators. One of the primary drivers for enterprise networks will be machine-to-machine connections, adoption of which is likely to take time. What’s more, even when they’re adopted, they’re likely to be offered by a single provider – not helping multi-operator con-sumer service coverage much.”