The Small Cell Forum has laid out the details of the architectural framework for so-called "HetNet" deployments in a 5G future while flagging recent impressive rates of growth in the small cells industry.

The association was set up to guide standardization efforts around small cell deployments and to popularize the technology, which -- as the name implies -- is designed to serve hotspots requiring connectivity over a small area.

Small cell rollout has been fueled by capacity demands in specific locations as well as the emergence of new applications in areas such as the Internet of Things (IoT). While most growth so far has come from the enterprise sector, about 85% of all cells in operator networks will be small cells by 2020, according to Alan Law, the current chair of the Small Cell Forum Ltd. and a distinguished engineer at Vodafone Group plc (NYSE: VOD).

The "Release 7" blueprint being published today considers various emerging technologies and trends, including virtualization, self-optimizing networks (SONs) and the concept of the "HetNet" -- a heterogeneous network that can support a variety of technologies and deployment scenarios.

In Release 7 documentation, the Forum is defining a HetNet as a "multi-x environment -- multi-technology, multi-domain, multi-spectrum, multi-operator and multi-vendor." All of that makes interoperability a key focus of the Forum's efforts.

Of critical importance, however, is the expected arrival of 5G technology in the next few years: Much of the current 5G focus is on very high-frequency spectrum bands that fall into the "millimeter wave" category and are able to support bandwidth-hungry services but over very short distances.

"The barriers we've been addressing are more relevant as we transition to 5G," said Mark Grayson, a distinguished consulting engineer with Cisco Systems Inc. (Nasdaq: CSCO) who also sits on the executive board of the Small Cell Forum, during a press briefing in London on the new release and research.

Previously, the Forum has focused on addressing the challenges of integrating small cells into the macro network, but with Release 7 it has also turned its attention to concerns around the underlying transport network, the use of "license-exempt" spectrum and the virtualization of network functions.

"This is the next step in evolution -- not just looking at small cells and macros but the need to consider the transport network and look at WiFi and license exempt as a whole, because all operators will need to embrace that in one way or another," said Grayson.

That virtualization is on the Forum's agenda is also notable: A number of the world's biggest operators are now accelerating their investments in so-called New IP technologies, like SDN and NFV, as they prepare for the introduction of 5G after 2020, when the next-generation mobile standard is expected to appear.

Major operators including Telenor Group (Nasdaq: TELN) and Telia Company (formerly TeliaSonera) have indicated that NFV will allow them to take advantage of network slicing, whereby 5G resources are dynamically allocated to customer groups with very specific service requirements. (See NFV Key to 5G Business Case, Says TeliaSonera, Net Neutrality Rules Threaten 5G, NFV – Telenor and 5G: Hurdles on the Track.)

"The HetNet … release provides a comprehensive, independent guide to building a fully integrated HetNet which is ready for virtualization and, in future, 5G," said Law in a published statement about Release 7.

For all the latest news from the wireless networking and services sector, check out our dedicated mobile content channel here on Light Reading.

The Forum has also unveiled new figures -- commissioned from analyst firm Mobile Experts -- indicating that more than 14 million small cells have now been deployed.

According to Mobile Experts' research, the number of non-residential small cells grew by 78% in the first quarter of 2016, while small cell revenues are forecast to more than double this year from $1 billion in 2015.

In a survey of more than 70 operators carried out by Rethink Research, more than two thirds of respondents said the HetNet would be very important or critical to their commercial success between now and 2020. The Small Cell Forum said that figure rose to nearly three quarters when operators were asked to factor in their requirements for new revenue models.

US operators including Sprint Corp. (NYSE: S) and Verizon Communications Inc. (NYSE: VZ) have been especially vocal about the need for what they call "network densification" incorporating small cells and related technologies. Indeed, only this week, Sprint CEO Marcello Claure shed more light on the operator's plans to use small cells, repeaters and "light pole options" as it prepares for 5G. (See Sprint CEO: Our Spectrum Is for 5G.)

Vodafone's Law, however, says there is huge interest in densification in other parts of the world, including the vast Indian market, where operators are struggling to cope with capacity constraints on their macro networks.

"Mumbai has four times the population density of Shanghai and yet access to spectrum is 20% of that in China, so you have a huge densification problem," he said during the Forum's press briefing. "We are seeing tremendous interest across small cells in India and that is coming down to the unique challenges operators face."

— Iain Morris, , News Editor, Light Reading