Adding small cells to mobile networks made up of full-sized base stations should help to fuel more voice and data calls, but outdoors, linking those dispersed cells to wired networks presents its own problems.
Connecting a high-capacity data line to a cell mounted on a lamp post or a telephone pole isn't as easy as wiring up a cell tower. Power, security and wiring are all harder to arrange, vendors and analysts say. The problems are unique to outdoor small cells, versus indoor ones that tend to have easy access to wiring.
[ BACKGROUND: Small Cell Forum pushes progress beyond femtocells ]
Several vendors will try to help carriers meet those challenges at Mobile World Congress later this month. Their product announcements may help to speed a small-cell boom that has been promoted as the next generation of mobile networks since before last year's show.
"How quickly you will see massive deployment of the small cells is, I still think, an open issue," Ovum analyst Ron Kline said. The difficulty of providing backhaul from those cells is a big part of the uncertainty, he said.
It's just one of several challenges facing carriers that would follow the small-cell star to a future of mobile abundance, analysts said. Others are finding room to mount the cells, getting local approval for the new street clutter, and preventing interference with the larger "macro" cells on towers and rooftops. But backhaul is such a serious problem that it's forcing mobile operators to change how they plan networks, according to Ed Gubbins of Current Analysis. They used to find backhaul after putting up cells where they were most needed, but now they have to plan both together. Some carriers are even looking for backhaul sites first, he said.
Much of what the vendors will be pitching at MWC is wireless backhaul, which is available in several forms over different frequency bands. All these technologies can deliver enough speed to carry traffic to and from a small cell, and they can be deployed at cell sites where wired connections can't be set up or would be too expensive. Most small cells are indoors today, but as carriers deploy them outdoors, 75 percent of those cells will use wireless backhaul, according to Infonetics Research.
To deploy wireless backhaul, service providers still need space and power for the equipment and approval from the local planning authorities. But when it comes to the connections themselves, no fiber or copper needs to be strung out to the site. All that's required is a clear line of sight to another radio that is plugged into a wired network, or a non-line-of-sight wireless path that can find its way around whatever obstacles may be in the way.
In Barcelona, wireless backhaul vendor DragonWave plans to show off a set of products that it will introduce on Tuesday ahead of the show. The company has long experience in the field and is now introducing smaller devices for operation in both high and low frequencies.
DragonWave's Avenue Link Lite is a new design for a radio that uses bands under 6GHz. The company already has gear for those bands that's designed for specialized networks such as public safety, said Alan Solheim, vice president of corporate development.
The Avenue Link Lite radios can use either licensed or unlicensed frequencies. Sub-6GHz backhaul in some bands can suffer interference from other networks, including some Wi-Fi systems, but it's well suited to dense urban areas, Solheim said. That's because sub-6GHz radios are good at bouncing around buildings and other obstacles to reach a wired-up destination radio that may be around a corner, he said.
DragonWave has also repackaged a higher-frequency backhaul unit, the Avenue Link, to better fit with small-cell installations. It shrank the high-frequency radio by half, to less than nine eight inches square and six inches deep, Solheim said. Also at MWC, DragonWave will introduce the Avenue Site, a small cabinet that can accommodate a base station, backhaul radio, antennas and other components in a unit that's small enough to be mounted on a light pole.
Tarana, also a wireless backhaul specialist, will demonstrate a line of products it announced last week. The AbsoluteAir series can provide a full 75M bps (bit-per-second) backhaul capacity to each small cell in a metropolitan area, the company said. That means carriers can expand their networks to keep up with subscriber demand and enjoy the same backhaul speed each time they add a cell, according to Tarana. The AbsoluteAir products can be deployed in just 15 minutes, the company said. They are in trials at multiple carriers in the U.S. and Europe.
Mobile infrastructure giant Ericsson is updating its Mini-Link small-cell backhaul offerings as part of a broad set of new products coming at MWC. Among the products the company plans to roll out are a microwave backhaul system using the unlicensed 60GHz band and another unit that uses an even higher band at 70-80GHz for 1G bps throughput. China's ZTE also announced small-cell wireless backhaul gear earlier this month, including products that use microwave, Wi-Fi and time-division LTE links.
Look for small cells to start easing mobile bottlenecks first in dense urban areas, where demand is usually highest. The first of those will probably feed off wireless links to the nearest large cell, taking advantage of its fast fiber connection, according to Infonetics. Those wireless links to small cells are likely to use a mix of high-frequency and low-frequency systems depending on the site, Infonetics analyst Michael Howard said. Where macrocells on building roofs don't have line of sight to small cells that are closer to the street, carriers may have to use sub-6GHz non-line-of-sight technology to get around corners.
The obstacles are more than just buildings, but also include trees, rain and wind that blows lampposts around and changes the direction of point-to-point links, said Gubbins of Current Analysis.
"As they deploy small cells in urban canyons ... a toolkit approach is important," Gubbins said.