SK Telecom bolsters coverage with LTE/Wi-Fi femtocells

The South Korean carrier will deploy the cells indoors and let users choose Wi-Fi if they have reached their monthly data cap

South Korean mobile operator SK Telecom has already begun installing the type of gear that is the talk of the show at Mobile World Congress this week: a dual-mode femtocell with LTE and Wi-Fi.

Small cells and Wi-Fi access points are twin touchstones for vendors and mobile operators trying to address booming data traffic. Technology advances centered around the Hotspot 2.0 standard make it easier for carriers to shift their subscribers to Wi-Fi, which offloads data traffic from their cellular infrastructure, and small cells allow service providers to both improve the subscriber experience and reuse scarce spectrum.

The cells that SK Telecom is showing off at the conference point toward the future in several ways. According to the Small Cell Forum, they are the first LTE femtocells on a commercial network and use APIs (application programming interfaces) published by the Forum. The cells combine Wi-Fi and LTE in a single unit, an approach that both new and established infrastructure makers are pursuing to give carriers more options to handle growing data demands. And the carrier says its femtocells use specialized algorithms to adjust their transmit power, eliminating interference with nearby macro cells operating on the same spectrum.

SK Telecom began to deploy a few of the small cells in December. They are intended to extend the performance of the carrier's national South Korean LTE network, which was launched last July and has more than 1 million subscribers. Full-scale deployment of the femtocells is set to start in April, at which point the network of conventional LTE macro cells is expected to have achieved 95 percent coverage.

The carrier will deploy the femtocells proactively, based on studies of the macro network's reach, said Jeong Yeonjune, a manager in SK Telecom's Access Network Development Team. It will install the units free of charge in homes, offices and other indoor spaces. The femtocells operate Wi-Fi and LTE radios simultaneously, so users can choose to switch their LTE devices to Wi-Fi if they are near their monthly data cap, Jeong said. SK Telecom caps its least expensive LTE plan at about 2GB per month, he said.

The largest femtocell that SK Telecom is showing off, which is designed for enterprises, has two external antennas and can serve as many as 32 users at a time. It can deliver as much as 75Mbps (bits per second) per cell. The carrier also showed off prototypes of smaller versions of the femtocell for other locations, which will have the same capacity. The products were made by a South Korean manufacturer that SK Telecom did not identify.

LTE data calls can be handed off seamlessly between a macro cell and a femtocell as the user moves in and out of a building, Jeong said. The femtocells can be administered through the same network management system used for SK Telecom's macro cells, he said. However, there is no seamless handoff yet from a macro cell to the femtocell's Wi-Fi radio. Though the carrier doesn't yet offer voice over LTE, voice calls can be forwarded to the 3G network from the femtocell, Jeong said.

SK Telecom has taken a multi-technology approach to handling mobile data demand and has Wi-Fi hotspots and 3G femtocells already in place to boost coverage and capacity. The carrier is also exploring multimode 3G/4G/Wi-Fi femtocells for the future, Jeong said. SK Telecom has about 26 million total subscribers.

Stephen Lawson covers mobile, storage and networking technologies for The IDG News Service. Follow Stephen on Twitter at @sdlawsonmedia. Stephen's e-mail address is

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