Dual-mode Wi-Fi services and femtocells, also known as home base stations, are expected to proliferate in a big way in the coming years as nearly all mobile operators plan to push one or the other at consumers as a cost-effective way to boost coverage and offload peak traffic. With potentially thousands of mobile customers buying these little boxes to boost their coverage and with a large share of 911 calls coming from mobile devices, the ability to identify the location of a mobile call when it is routed through a femtocell has the potential to be both problematic and advantageous to the public-safety community.

A femtocell is a type of cellular base station shrunk down to the size of a Wi-Fi router and connected to the broadband Internet connection, such as DSL or cable, to handle several mobile devices. Within the femtocell coverage area, voice and data calls approved to use the femtocell are carried through the femtocell itself and not through the main mobile network. These calls are connected via a licensed interface, such as GSM, CDMA or WiMAX. Dual-mode Wi-Fi services operate in a similar manner, with calls placed over a Wi-Fi network when within range of an access point and handed over to a licensed interface when out of range.

According to ABI Research, the femtocell market is primed to grow from just under $72 million in 2008 to more than $1.8 billion in 2013, with a compound annual growth rate of more than 300%. As these types of services proliferate and customers begin to view them as primary communications tools, operators will have to ensure 911 services are delivered at the same level of today's wireless 911 capabilities or even better — which could prove to be challenging given their technical architectures and the uncertain regulatory framework that surrounds them when it comes to 911.

“Simply put, if you dial 911, you expect someone to take care of you,” said Todd Young, vice president of marketing for location-technology vendor Rosum. “The last thing the femtocell industry needs is newspaper articles like we saw with early VoIP 911, where the ambulance was sent to the wrong place.”

While femtocells are designed to be kept in a fixed location such as the home — theoretically making it easier for first responders to pinpoint a location — many of the femtocells in the market today include an antenna. As the range of these antennas increases, callers could be far from the actual base station, making it difficult to accurately pinpoint them, said Roger Hixson, director of technical issues for the National Emergency Number Association (NENA), which has established a working group to tackle the 911 issues associated with both femtocells and dual-mode Wi-Fi services.

“The primary issue from a 911 standpoint is identifying the location of the caller because of the way the femtocell is connected into the cellular network,” Hixson said. “Mobile calls are usually identified with a specific address associated with where the antenna is placed. But the antennas have enough range that the caller could be at a different physical address.”

In short, the services usually meet the requirements the FCC established for wireless 911 calls but can't necessarily give an exact location of a caller dialing 911 two blocks away, Hixson said.

This potentially is a big problem, given that many believe the accuracy of wireless 911 in general needs improvement. Public-safety officials often express frustration with the location information from cellular calls because inaccuracies can result in losing valuable time trying to search for an incident.

But meeting the wireless 911 mandate is exactly what femtocells will be designed to do, said Simon Saunders, chair of the Femto Forum, which was established to promote the adoption of femtocells worldwide.

“One of the areas seen as mandatory is to make sure that the support for emergency calls is no less than what is provided for the wireless network,” Saunders said. He added that finding a caller blocks away should not prove to be difficult, as the range of the femtocell antennas is relatively short because the devices operate using low power. As such, operators should be able to use triangulation techniques to find callers away from home.

How the FCC views femtocells and dual-mode services is unclear at this point, as it has yet to make any rulings on the issue. Is a mobile device connected to a femtocell wireless router or Wi-Fi box classified as a VoIP call or a wireless call? And how should the user's location be identified — via VoIP 911 processes or by using existing methods for wireless networks?

Services that already exist in the market, such as T-Mobile's dual-mode Wi-Fi service called HotSpot@Home and Sprint's femtocell service, known as Airwave — which was rolled out nationwide this past summer — rely on the 911 location capabilities that are already built into their wireless networks, whether that's network triangulation for GSM networks or assisted GPS for CDMA networks.

When a T-Mobile subscriber dials 911 using a Wi-Fi connection in the home, the handset automatically defaults to the operator's GSM network or a roaming partner's GSM network. If a GSM connection isn't found, then the call is routed over Wi-Fi to the nearest public-safety answering point (PSAP), said a company spokesperson.

“If you are at a base station and the phone moves to Wi-Fi mode, that makes it a VoIP-type of service,” said Hixson. “The connectivity is the cellular switch, and it travels to the 911 center from the cellular switch even though it's a wireless VoIP call. That causes issues because Wi-Fi and cellular have different characteristics.”

However, Kathleen O'Brien Ham, T-Mobile's vice president of regulatory affairs, said that the operator's dual-mode service is beneficial because it enables customers to place emergency calls where they otherwise could not. Moreover, the operator, in a letter sent to the FCC in August, argued that the way it routes 911 calls via its HotSpot@Home service is appropriate and that the service should not be regulated as a VoIP service.

It should be noted that T-Mobile conceded that location becomes more problematic when an emergency call has to be routed over Wi-Fi. But in that instance, T-Mobile uses a combination of user-supplied location information and other information such as the HotSpot location address, the last GSM cell site on which the user's handset is detected and the IP addresses used to route emergency calls. The operator noted in a recent FCC filing that very few 911 calls are routed over a Wi-Fi connection. For instance, out of the 86,640 emergency calls that were placed from dual-mode handsets in July 2008, T-Mobile said just 119 calls — or 0.1% — were routed over its Wi-Fi network.

At any rate, it's clear mobile operators will be required to stress that femtocells aren't a reasonable substitution for their fixed landline services and to educate users on the limitations of 911 services. One fear is that users may move their femtocells from one location to another — as VoIP users often do — causing calls to be routed according to the original location because that is the location registered with the operator.

But Saunders said most operators will include in their products some type of locking mechanism to ensure their customers can't take the femtocells from place to place. In addition, if the power is knocked out at the femtocell user's location, the service won't work.

“We wouldn't want people to incorrectly imagine that a femtocell was going to work when the power is off,” Saunders said. “It's important that vendors and operators make this product more akin to a cordless phone. It's up to the user to keep it operating.”

While 911 location may be problematic for users wandering away from their home base stations, femtocells are expected to enhance 911 location for those who have them in their homes — especially in apartment buildings.

Saunders said femtocells will be designed with the ability to continually report their locations — most likely using global positioning system (GPS) technology. While GPS typically doesn't penetrate indoors very easily, its signals can be detected indoors because enabled devices continually transmit location information.

“Generally, the GPS receiver measures the moment it receives signals from multiple satellites and uses the time it receives them to measure a location,” Saunders said. “This code is transmitted repetitively. The first time it's received it is very weak, but the more the code is transmitted, the clearer it becomes.”

That means femtocells will enable emergency personnel to better pinpoint 911 callers in multidwelling units. Moreover, Rosum, after several years of testing its TV+GPS hybrid positioning system, already has integrated the solution into femtocells. Rosum's technology integrates signals from existing commercial TV towers with signals from GPS satellites to support greater accuracy in all environments, including indoors. That means the system can indicate the exact floor of a building where the caller is located, which will be especially useful in apartment buildings. The company notes that several vendors want to offer more enhanced location capabilities.

“The way we help is to provide automatic location for femtocells and VoIP terminal adapters that live indoors where GPS doesn't,” Rosum's Young said. “If a femtocell is deployed in a person's home where there might not be good cell coverage due to urban density of buildings and bad RF characteristics, we have a way to locate those devices.”


Out of the 86,640 emergency calls that were placed from dual-mode handsets in July 2008, T-Mobile said just 119 calls — or 0.1% — were routed over its Wi-Fi network.