Operators and vendors are seeking to mitigate the effects, with Qualcomm developing a chipset which supports no fewer than seven bands. Meanwhile NTT DoCoMo, always an influential carrier on standards developments, believes the best way is to rely heavily on existing frequencies.
Qualcomm's plan was revealed in a filing it made to the US regulator, the FCC, opposing proposals that operators should be mandated to support roaming between LTE services located in different parts of the US 700-MHz band plan. This issue highlights the interoperability and roaming challenges which LTE's host of frequencies create, since there are four band classes within 700-MHz. Small operators run their 4G services in Band Class 12 of the spectrum, while AT&T is in Band Class 17 and Verizon mainly in Band Class 13.
Devices for these different sections are not interoperable and the smaller cellcos claim that, if the big names are not forced to roam, their business models will be weakened because they will have limited power to acquire high impact devices, or offer their subscribers national roaming coverage. AT&T retorts that a mandate would increase its device development costs and slow time to market, as well as risking interference to its users' signals.
Qualcomm says the market is moving quickly and it would be premature for the FCC to issue mandates at this stage. It said it has accelerated development of its next generation RF chip, the WTR1605L, which will support a total of seven bands, three below 1-GHz, three higher bands, and one very high band (presumably 2.5-GHz/2.6-GHz). The chip giant, which tends to set the bar for the whole industry in terms of modem frequency support, said it was just starting to transition towards a chipset based on the new RF offering, the MSM8960. This will be made in the new 28nm process and despite issues with securing sufficient capacity in its foundries, Qualcomm expects the first MSM8960s to ship to OEMs this July, in time for holiday season devices.
These will not support all the bands from day one, but they will enable Band 12, and the chip supplier told carriers that it will also provide software to OEMs to enable them to add filters and perform integration and testing, to support LTE roaming on Bands 13 or 17, as well as Sprint's PCS G spectrum (Band 25).
“Because the transition to the WTR1605L and 28 nanometer chips is in its infancy, it would be inappropriate for the FCC to mandate their use,” Qualcomm wrote, adding. “Furthermore, as shown above, carriers holding Lower A Block or other 700-MHz spectrum have many different band combinations to choose from to meet their customers' interoperability needs, both within the 700-MHz band and between any of the long list of other 4G bands. A Band 12/17 combination is merely one such combination, and it would be inappropriate for the FCC to mandate that carriers must make this one combination available on every consumer device.”
Verizon promises roaming
Verizon Wireless is at the heart of the 700-MHz roaming debate. Its CTO, Tony Melone, told a media conference that the carrier aims to offer global roaming for its LTE devices, and even fallback to HSPA, a network it has never supported at home. But he gave no firm dates for offering these global devices, nor any commitment to support roaming with other LTE networks in different US bands.
“There will absolutely be roaming for 4G LTE devices,” he said. "And where 4G LTE isn't available or it's not economical to support those LTE frequencies, we'll allow customers to fall back on 3G HSPA networks.”
But he made it clear that global, rather than domestic, roaming would be Verizon's priority, especially as it aims to achieve universal coverage very quickly. He pointed out that LTE runs in a huge number of bands, but there is a limit to how many radios a handset can accommodate effectively – about eight today, spanning 2G, 3G and 4G; perhaps rising to 12 in future. Verizon currently needs to support 850-MHz and 1.9-GHz CDMA radios, 700-MHz LTE and, in future, the AWS bands, also for 4G. And for world phones it will need to include international GSM frequencies.
This pushes other US carriers' bands into a secondary position. “The number of radios that you have to use adds up quickly," Melone said. “So we need to look at what band plans countries around the world are planning for with their 4G LTE deployments. And then we have to make some bets. There's so much uncertainty now, we are limited in saying which ones we'll support and when.”
He added: “We will drive our OEMs to build for our network specifications. We are not going to ask them to invest in and increase our cost to do something we don't need. AT&T will do the same thing.” However, if operators are using the same 700-MHz band plan as Verizon, he said the firm would be happy to offer roaming deals, pointing to its alliance program with rural cellcos for LTE.
DoCoMo goes its own way
Meanwhile, while they wait for advanced multiband chips to emerge, other operators are making progress in their own way. The head of DoCoMo's R&D strategy division says the immediate solution is to refarm existing 3G bands to reduce fragmentation.
Seizo Onoe told this week's Computex trade fair in Taiwan: "We don't need to cry over LTE spectrum fragmentation.” He pointed out that DoCoMo, which launched its LTE service in December 2010, now has nearly three million subscribers and aims for coverage of 98% of Japan's population by March 2015, plus upgrades to LTE-Advanced in 2013.
Other Asian operators are taking the lead in LTE roaming. Hong Kong's CSL and South Korea's SK Telecom claim the world's first international LTE roaming service, which will go live next month with the same prices as their 3G roaming offerings. CSL's CTO, Christian Daigenault, said the partnership with SKT was “a significant milestone for the telecoms industry, which continues to debate the feasibility of 4G LTE international roaming.”
During the pilot stage this month, only SKT users with the Pantech Vega Racer 2 handset will be able to roam without borrowing 4G handsets at the airport (with their own SIM cards). But the capability will be extended to more smartphones soon. The two carriers were the first cellcos to achieve interconnection between LTE networks during a pilot in March.