Wireless carriers are always looking to improve and extend their coverage for their consumers. But these days, traditional antennas and outdoor cell towers aren’t enough. Carriers are depending on new technology—Distributed Antenna Systems (DAS), picocells and femtocells, for example—to help solve sticky problems, such as how to strengthen indoor coverage. This is important, especially as users increasingly demand data and other services from their wireless phones.

As subscriber demand continues to grow, how can wireless carriers deploy the infrastructure to support these new services and, at the same time, improve their coverage? The good news is that “the technology is here now,” according to Manish Singh, Vice-President of Product Line Management for Continuous Computing in San Diego, Calif.

The tricky part is getting the technology rolled out in an efficient and affordable way and resolving the usual issues of security and establishing universal standards.

Evaluating options

Have you ever seen a neighbor talking outside on a cell phone? Is he just more comfortable in the yard? Perhaps. But he also might have trouble getting a good cell signal inside his house. Office workers face the same issues. Proximity to a cell site and other factors dictate whether we get full-bar service— or something less than that—when inside.

It’s highly improbable that people will give up on wireless communication because of these occasional glitches. Still, if consumers have bad experiences with their wireless—or at least fear the prospect of trouble—they will use their landlines when inside. According to some, this is still a factor in consumers’ mindsets, despite federal statistics showing about 16 percent of American households are “cord-free,” and another 13 percent are classified as nearly wireless-exclusive. The result, some say, is that wireless carriers essentially are leaving money on the table.

“Simply put, (wireless) carriers lose revenue as mobile minutes are lost to landline minutes when consumers experience dropped calls, poor quality of voice, and lower data rates when indoors,” Singh wrote in a recent article for Wireless Design & Development magazine. He expanded on those thoughts during a telephone interview with Wireless Wave.

Erecting more traditional cell sites (whether antennas on pre-existing buildings, or on monopoles or new towers) will only get you so far in terms of system enhancement. Although more sites are deployed every day, just building more traditional cell sites might not solve the issues involved in providing better in-building coverage. Plus, the infrastructure realities—cost and otherwise—are prohibitive. “People don’t want those antennas in their backyards,” said Dave Kaun, Chief Technology Officer for Elert & Associates, a Minnesota-based technology consulting firm.

So, what are the alternatives for improving in-building coverage? Going from small to big:

Femtocells: These are free-standing base stations that link with a home or office high speed Internet connection. The voice traffic is routed through the Internet, thus improving connection quality and saving money (you don’t use as many cell phone minutes). An apartment complex or office campus could use one; then again, femtocells also can be used at the single-user level. A call can be “handed off” from the macro-cellular network to the femtocell whenever the user steps inside.

“The very walls which are a radio signal’s adversary actually become their friend as they attenuate RF signal propagation out of the home from the femtocell, thereby minimizing radio interference with an existing macrocellular network or another nearby femtocell,” Singh wrote in his article. (See the full text at www.wirelessdesignmag.com.)

In addition to providing good indoor coverage, femtocells also free up capacity in the macro-cellular network, Singh wrote. When a call is “handed off,” it results in one fewer user on the bigger network. That’s a big benefit, especially during peak usage hours.

Singh noted that the environment for significant use of femtocells is good now because:

  • The wide proliferation of IP broadband connections provides the necessary “backhaul infrastructure.”
  • Integrated custom silicon parts for femtocells are widely available.
  • There are more than 2.5 billion wireless subscribers worldwide, so “the economy of scale to justify femtocell deployment is finally in place.”

AT&T Mobility says it is evaluating femtocell technology. Verizon Wireless says it plans a rollout later this year. Sprint Nextel Corp. has gone further, introducing its Airave femtocell product last year in select markets. Experts say 2009 will be the year femtocell technology really hits the consumer market.

Picocells: Like femtocells, picocells function like small cellular base stations and use an IP connection for “backhaul.” Also like femtocells, they operate with very low output power.

But picocells have a bit more range: They can cover buildings up to 30,000 square feet, according to an article from Stefan Scheinert of LGC Wireless. Some airports have used picocells.

The biggest distinction: “Picocells are normally installed and maintained directly by the network operator, who would pay for site rental, power and fixed network connections back their switching center,” according to ThinkFemtocell.com, a leading authority on the technology. “Femtocells differ from picocells because they are intended to be much more autonomous. They are self-installed by the end user in the home or offi ce, primarily for the user’s benefit.

“Femtocells automatically determine at which frequency and power levels to operate, rather than being directed from a centrally determined master plan. This allows the network to adapt automatically as new femtocells are added or moved without the need for a complete frequency replan.”
Ip.access, based in the United Kingdom, is one of the main picocell players.

Like femtocells, picocells have the potential to interfere with the larger, outdoor network and with other picocells. But they also can partner well with the following technology: Distributed Antenna Systems.

DAS: Distributed Antenna Systems are bigger solutions for bigger spatial areas, such as college campuses, large hospitals and casinos. A DAS connects to one or several wireless services and rebroadcasts the signals. An onsite cellular carrier base station or repeater is put in place, and the signal is ”boosted” to improve reception. Multiple remote antennas are placed throughout the site, allowing the signal to be extended.

The University of Notre Dame set up a carrier-neutral distributed antenna system throughout the campus using 16 small “stealth” antenna sites.

San Jose, Calif.-based NextG Networks, Inc. is one of the leaders in the distributed antenna system (DAS) world. It uses fiber-optic architecture and low-impact, low-emission equipment. Other leaders include ADC, Andrew, Cellvine, InnerWireless, Powerwave, and Spotwave Wireless, plus integrators such as LComm Global Solutions, InSite Wireless Group, and Nsoro, according to Wendy Chretien, a senior network systems consultant with Elert & Associates.

Finally, there is another solution that T-Mobile USA has adopted, which the company is marketing as “Hotspot@Home.” Consumers may purchase wireless routers and enhance their in-home coverage utilizing a technology called Unlicensed Mobile Access, which also has traction among overseas carriers as well.

The challenges

The drawback of UMA: It requires mobile phones equipped with Wi-Fi (although more Wi-Fi equipped handsets and devices are becoming available to consumers).

In his article, Continuous Computing’s Singh pointed out several challenges to the widespread usage of femtocells:

  • Integrating millions of femtocells with an existing 3G wireless core infrastructure.
  • Managing RF interference
  • Security. “Since the traffic from femtocells can be carried over a public IP network, the traffic needs to be encrypted to avoid eavesdropping,” he wrote.
  • Ensuring quality of service.
  • Too much of a good thing. If many tenants in an office or apartment building use femtocells, it could lead to interference. (The same could be said for picocells.)

As for DAS: One of the biggest challenges is getting the system in place. Femtocells and picocells aren’t very obtrusive, and their remote antennas can be moved with ease. DAS has more infrastructure worries, and the cost can be high. Also, the industry has not yet established uniform standards, so there are competing technologies at play. And remember that carriers are responsible to the FCC to ensure that the higher output generated by a DAS does not interfere with other wireless services, so they must pre-approve any privately installed systems.

Wireless carriers often will help with the cost, since it’s to their financial advantages, said Dave Kaun of Elert & Associates. But you want the infrastructure to be as unobtrusive as possible. One college put the antennas in the light poles of the football stadium. Casinos, government buildings and other large campuses also employ “hiding” techniques.

Of course, it’s always easier to build in the system when the client is constructing a new building. But clients who do that must be sure the system also supports radio traffic for emergency responders. “Always make that a priority,” Kaun said. And be aware that some cities now require that police and fire fighters’ handheld radios have good coverage in new commercial buildings.