Hetnet has become the most commonly used word in mobile infrastructure world. It was created from a rarely used term in the computer world: heterogeneous networks. That was coined to describe connecting different computers using different protocols on different diverse networks. Heterogeneous networks was applied first in 2009 to describe the integration of various mobile RAN network assets including macrocells, microcells, picocells, femtocells, distributed antenna system, and Wi-Fi access points. Because heterogeneous was such a mouthful, it was shortened in 2010 to hetnet. IEEE made a call for papers on hetnet in 2010 and held the first IEEE HetNet workshop in 2011.
Hetnet is a good descriptor of the problem and the solution. From 2006 to 2010, several very different mobile RAN technologies developed. In parallel to the development of the new RAN alternatives, the demand on the mobile networks, caused by the proliferation of smartphones accessing data, called for a seamless, integrated solution for the new RAN technologies. Three mobile RAN solutions developed during this period: Wi-Fi mesh access radios; mobile network small cells, known to industry insiders during the period as femtocells and picocells; and DAS. Wi-Fi mesh radios were designed to cover cities and towns with integrated Wi-Fi mesh with each radio delivering backhaul through the other Wi-Fi access points in the network. Femtocells and picocells were designed to take RAN antenna and base station from the macro tower into a micro form factor that could be placed into homes (femtocell) and businesses (picocell). Rather than having your mobile phone access the mobile RAN through an outdoor macro cell tower locations, your phone could connect to a femtocell in your home and then transmit voice and data through your broadband connection. Both Wi-Fi mesh and femtocells seemed like great solutions for the mobile data crunch, but both floundered for different reasons. DAS deployments, on the other hand, flourished.
Municipal Wi-Fi mesh, known as muni-Wi-Fi, failed because the business model generally did not work. Cities building muni-Wi-Fi networks did not want to pay for them. Companies that built muni-Wi-Fi could not generate profits because users did not want to pay for Wi-Fi service. Femtocells and picocells floundered because the major mobile RAN engineers worried about these smaller mobile cells interfering with the larger macro cell tower network. It was similar to the way the mobile RAN engineers were bothered by cell phone power boosters, which became popular during Hurricane Sandy. Also, some would say that femtocells and picocells were words that required a lot of explaining, not understood by regulators, sales teams, customers, or investors.
But industry lexicon evolution stepped up to fill the communication gap for users, marketing teams, and engineers. In 2012 the term small cell networks started being used to describe femtocells, picocells, and microcells. Everyone seemed to understand what a small cell network was: anything smaller than a cell tower.
From 2008 to 2013, rather than seeing massive small cell deployments in homes and businesses as mobile RAN industry leaders had projected, carriers and DAS providers constructed DAS networks alongside macro cell tower construction. DAS uses multiple antennas connected by long fiber runs on utility poles or in buildings to a single, central base station radio. Small cells, unlike DAS, are each very small standalone BTS radios and antennas much like Wi-Fi access points. DAS was initially designed for inside large buildings or stadiums. However, because municipalities had become so adverse to allowing new tower construction, DAS providers like NextG (acquired by Crown Castle for $1 billion in April 2012) and Extenet began deploying neutral host DAS networks outside of buildings on street utility poles as a supplement for cell towers. Neutral hosted DAS can serve multiple mobile providers using one DAS system. DAS placed on utility poles enabled the carriers to fill in gaps not covered well by macro towers urban and suburban areas, significantly helping mobile carriers to lower customer churn through increased coverage.
By 2012, the problem was clear, and hetnets were the solution. Rather than have many uncoordinated, separate RAN networks like DAS, small cells, macro towers, and Wi-Fi access points, why not use a hetnet incorporating them all. Hetnets leveraged the Self Organizing Network, or SON, software to coordinate the use of the various RAN radios. SK Telecom (News - Alert) discussed the use of SON for hetnets as early as 2010. If there was heavy demand on a macro cell tower, for example, during an event like a marathon or parade in a downtown area, the SON could push connections to Wi-Fi access points or to available small cells.
In the past, carriers have avoided the solution of driving users to Wi-Fi, but users have become comfortable with the delivery of voice and data on Wi-Fi. In home environments, smartphone subscribers principally access Wi-Fi for both data needs, like YouTube (News - Alert) watching, and voice needs, accessing Google voice or Skype. There are industry rumblings that major carriers are going to being using SON to push subscribers onto carrier controlled Wi-Fi access points. Users’ iPhones and Samsung Galaxy S4s will automatically access the Wi-Fi networks, preferentially, driven or pushed by the SON knowing the location of the device and identifying the phone passing by a Wi-Fi access point.
As small cells start to populate homes, businesses, and buildings, it is expected that mobile RAN SON will also push mobile smartphone users onto these small cell radios.
Hetnets and small cells have entered the regulatory arena. On Dec. 12, 2012, the FCC (News - Alert) opened the 3.5gHz Notice of Proposed Rule Making. One of the principal purposes of the FCC docket is to examine the proposal to allocate dedicated or shared spectrum for use by mobile carriers’ small cells and hetnets. Mobile carriers are generally supporting the position to use part of the 3.5gHz band as dedicated, exclusive backhaul spectrum for the massive deployment of hetnet infrastructure coming in the next few years. Other commenters, such as Google, however, are urging the FCC to take advantage of the opportunity in the 3.5gHz NPRM to create a spectrum sharing strategy for 3.5gHz that could be applied across all spectrum in the future.
Spectrum (News - Alert) sharing, building on the database model applied in the 700mHz White Spaces FCC rule making, would enable a more efficient use of the scarce spectrum resources. If one carrier was not using the spectrum, another carrier could use it. Everyone would benefit, the carriers, their competitors, the subscribers, and the public.
Edited by Stefania Viscusi