4G World: Verizon exploring small cells for adding future capacity

For the first time, a Verizon Wireless executive dropped the term ‘small cells’ in a speech, putting the mammoth U.S. operator’s stamp of approval on the emerging network concept. Speaking at 4G World, Verizon Wireless Executive Vice President of Network Planning Bill Stone said Verizon’s network evolution roadmaps included the use of heterogeneous network architectures and the deployment of small micro and pico cells under the macro umbrella, targeted at adding network capacity rather than mere coverage.

Stone said given the spectrum constraints Verizon faces, it needs to utilize its existing airwaves in the most efficient way possible, even as Verizon goes to the markets to buy more licenses. That means re-using the same frequencies in the same places, allowing it to squeeze more capacity into the same square-footage.

“Small cells is one of the ways we’re going to keep up growth,” Stone said. “The other is more spectrum.” Even if Verizon were to stumble onto a spectrum bonanza, the increasing pressure to address growing mobile data demands and to effectively offer cheap capacity would drive Verizon to implement small cell architectures in those new bands as well, he said. “The bottom line is we need more spectrum and we need small cells to utilize it,” Stone said.

Verizon has dabbled in different network topologies before. It has deployed distributed antenna systems (DAS) in big public buildings and even some outdoor areas (CP: LTE driving new DAS deployments), though those deployments have been aimed at distributing capacity more efficiently rather than increasing it. It has also begun the limited deployment of carrier Wi-Fi services in public hotspot areas like stadiums where sporting events and concerts can drive huge spikes in data traffic at intervals (CP: Verizon to offload 3G/4G data through free Wi-Fi hotspots).

But the approach Verizon now appears to be advocating goes far beyond supplemental coverage or spot capacity deployments. Small cells when combined with heterogeneous network (or hetnet) topology would allow Verizon to deploy two networks over the same spectrum—one on top of the other. The macro LTE and CDMA EV-DO networks would still function as the primary coverage network and handle most of the everyday capacity demands of Verizon’s mobile data customer base. But underneath that macro umbrella would be a much larger network of cheaper short-range micro or pico cells clustered in dense urban areas and other high traffic data zones. Those small cells would become the mobile data workhorses of their network, servicing fewer customers but providing those customers much greater average capacity.

Stone didn’t lay out any specific rollout plans for small cells or discuss to what extent Verizon would use them in the network. In fact, he addressed small cells as one of a number of technologies Verizon hopes to implement to get more bang out of its LTE network. Also on Sprint’s wish list is 4x4 multiple input/multiple output (MIMO) smart antenna configurations and LTE carrier aggregation, which would allow Verizon to stack carriers at contiguous frequencies as well as on different bands to create extremely fat mobile broadband pipes.

Theoretically small cell deployments could scale into the hundreds of thousands of devices, with multiple cells transmitting under the umbrella of a single cell, adding an order of magnitude of more capacity to the network. In reality, small cells might be more difficult to implement. If deployed on a different band than the macro network, there would be no interference, but the carrier gets no benefit of spectrum re-use. If deployed as heterogeneous network, the small cells would share the same spectrum as the macro network, an overlap which would normally produce such interference problems as to render either or both networks useless. Vendors, however, are working on interference management and self-organizing network (SON) techniques that would allow the two cells to coexist in the same place. Stone said that was one of Verizon’s key concerns about HetNet architectures. To work, he said, small cells need “to play well with our macro network.

Verizon certainly has plenty of vendors willing to address the concerns. Its primary LTE radio vendors both have been pursuing various small cell/heterogeneous network strategies. Ericsson calls its architecture HetNet, which utilizes discreet network elements like micro-and picocells already in its portfolio (CP: Shrinking cells and narrowing beams). Meanwhile, Alcatel-Lucent has done away with the concept of macrocells and microcells and has launched a new modular radio architecture called lightRadio, which uses small lower power radio ‘cubes’ as the building blocks for any radio configuration, scaling from the smallest femto to the biggest macro (CP: ALU’s new building block architecture does away with the base station). Femtocell makers have also been trying to stake a claim in small cells claiming their home base stations can evolve into small cell architectures that can be deployed in millions, at a fraction of the installation cost of the big vendors microcell solutions (CP: Will femtocells evolve into the small cells of the future?).

Sprint Senior Vice President of Network Bob Azzi also broached the topic of small cells during his later keynote address at 4G World, though he primarily discussed the different micro-, pico-, and femtocell configurations Sprint is deploying in its new Network Vision deployment (CP: Sprint strikes out on its own with LTE). While those different configurations give Sprint flexibility on sizing its cells for the bandwidth demands in different parts of its network, they aren’t necessarily the overlapping cells using the same spectrum of a heterogeneous network. However, Azzi did say hetnets were on Sprint's future roadmap.