MWC: NSN mixing and maxing LTE frequencies

Last year at Mobile World Congress, Nokia Siemens Networks (NYSE:NOK, NYSE:SI) demoed its new multi-carrier wireless technology, bonding together several high-speed packet access plus (HSPA+) carriers to create the mother of all 3G pipes. At this year’s Congress, NSN is doing the same bonding trick with long-term evolution (LTE), but with a twist. Rather than using contiguous spectrum—which few operators have in abundance—NSN is taking stacking carriers from frequencies all over the electromagnetic spectrum, showing that operators can build massive wireless pipes with the spectrum they already own rather than search fruitlessly for outsized license blocks in the same band.

Specifically NSN is combining spectrum at 800 MHz and 2.6 GHz, the two bands that European regulators are reserving for so-called 4G technologies. By using the same base station but two radio heads tuned to the differing frequencies, NSN is able to create a ‘virtual’ carrier, that allows the network to combine both band’s capacity while still taking advantage of the lower frequency’s propagation characteristics. It’s the best of both worlds, explained Phil Twist, NSN head of marketing and communications for network systems.

“2600 MHz is good for high-density deployments, while 800 MHz is good for [coverage] and in-building penetration,” Twist said. “You get the benefits of both bands in the same carrier.”

NSN is demoing the carrier aggregation technology on commercial equipment, namely its Flexi Multiradio platform to show that the baseband and software capabilities of its current radio access install base can support it (though Twist said that the enormous bandwidth requirements would make its forthcoming Single RAN Advanced architecture more sensible for such a deployment). But LTE carrier aggregation technically won’t be a commercial viability until the LTE-Advanced standard (3GPP release 10) is passed later this year. LTE-Advanced takes the current carrier size ceiling from 20 MHz all the way up to 100 MHz, promising downlink capacities as high as 1 Gb/s. And as NSN is demonstrating, those LTE-Advanced networks won’t be confined to single frequency.

Such flexibility could prove enormously useful to U.S. operators, which have frequency holdings all over the map. AT&T (NYSE:T) for instance is deploying LTE over 700 MHz and the Advanced Wireless Service (AWS) band, which goes all the way up to 2.1 GHz. With LTE Advanced AT&T could combine those frequencies into a single carrier. In later LTE-Advanced releases, AT&T could even start splicing together non-contiguous spectrum in the same band. AT&T recently acquired more 700 MHz spectrum from Qualcomm (NASDAQ:QCOM) after the latter shuttered FLO TV, but those frequencies sit at rather inconvenient place in the band plan, leaving AT&T with few options for merging those 6 MHz into the LTE network it’s currently deploying. But a working item in the 3GPP release 11 standard, if implemented, would allow AT&T to use carrier aggregation to slot those frequencies into its downlink carrier even though they sit 24 MHz further down the spectrum chart.

Though we haven’t heard too much about this kind of technology yet, Twist said the technique will become critical to future networks. Without it, LTE-Advanced would just be wishful thinking. To achieve the massive speeds LTE-Advanced promises, operators will need to dedicate an enormous quantity of spectrum to LTE. “It’s going to be impossible for an operator to get those high bandwidths, to get 100 MHz of spectrum, unless they can use multiple bands,” Twist said.

A quick survey of the U.S. wireless operators’ spectrum holding bears out that truth. Verizon Wireless (NYSE:VZ, NYSE:VOD) only has enough 700 MHz spectrum nationwide to launch 10 MHz carriers, though it has loaded up on more in key markets. Even with Clearwire’s (NYSE:CLWR) enormous spectrum holdings of 100-plus MHz of unpaired spectrum, an LTE implementation could support an aggregated carrier of 50 to 60 MHz. And Clearwire is supposedly negotiating with T-Mobile and other operators to sell off some of its spectrum hoard. Getting to LTE-Advanced will require operators to either start piecing together licenses in different bands or for regulators to start releasing enormous blocks of contiguous spectrum, Twist said. The former is much more likely.

While NSN’s demo centers on LTE, the same principle’s can be applied to earlier generation technologies. In fact, NSN is working with T-Mobile USA (NYSE: DT) and other operators to create dual-band carrier aggregation for HSPA+, which is already supported in the standards. T-Mobile is deploying dual-carrier HSPA+ next year, allowing it to combine its two AWS carriers into a 10 MHz downlink supporting a theoretical 42 Mb/s, but after that it will have run out of room in the AWS band. But using newer aggregation technologies it could splice together PCS and AWS spectrum, allowing it to get 15 MHz, even 20 MHz channels.