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Recycled spectrum to help realize global LTE roaming

Operators look to 1.8GHz for 4G, but more bands are needed for global roaming

As more LTE (Long Term Evolution) networks go live across the globe, operators have started planning to offer data roaming, and reusing existing spectrum is seen as one of the best chances of getting worldwide coverage, according to speakers at the LTE Forum conference this week in Stockholm.

So far, operators have launched about 17 commercial networks in countries including Austria, Germany, Japan, Sweden and the U.S., according to data from industry organization GSA (Global mobile Suppliers Association). Add to that another 140 networks that operators have committed to building, and LTE can be considered the fastest-growing mobile system ever, GSA president Alan Hadden said at the conference.

A year ago, roaming on LTE didn't make much sense, but the growing interest in the technology is changing that, according to Andrés Suazo, head of Tele2's 4G Network Project. Tele2 has launched commercially in Sweden, using a network it shares with Telenor, and is testing LTE in Estonia, Latvia, Lithuania and the Netherlands.

From a roaming perspective, the advantage of LTE compared with previous technologies is that it will eventually have a truly global reach. But just like existing GSM networks, different parts of the world use different frequencies to roll out the technology. That makes developing products able to access the Internet using either LTE -- starting with USB modems -- more complicated, especially for users traveling to different continents.

One band that has the potential to offer LTE roaming across several continents is 1.8GHz, which more than 350 operators have already been allocated and now mainly use for GSM voice, according to Hadden.

The world's first commercial LTE network on 1.8GHz was launched by Mobyland in Poland in September last year. At Mobile World Congress in February, Australia's Telstra announced that it would launch LTE on 1.8GHz by the end of the year. Other operators that have also shown an interest include Elisa in Finland, Deutsche Telekom in Germany and StarHub in Singapore.

"What we are seeing today is a lot of interest [in 1.8GHz] from operators in Europe, Asia-Pacific and also in Brazil," said Frédéric Pujol, head of radio technologies and spectrum practice at IDATE Consulting and Research.

Frequencies below 1GHz provide good indoor coverage, and are also a good fit for expanding LTE coverage to rural areas. But there is no particular band below 1GHz that is widely used globally. And while operators have spectrum available in, for example, 2.6GHz band, which allows them to offer higher speeds, it comes at the cost of diminished indoor performance. Meanwhile, the 1.8GHz band can offer users and operators a good compromise of speed and coverage.

To free up the spectrum, operators would first have to move the voice traffic from GSM to 3G. But how long it will take before LTE on 1.8GHz reaches critical mass depends on regulators and courts, as much as the operators themselves.

For operators to use the 1.8GHZ band for LTE, however, regulators have to give them the go-ahead. This might provoke complaints from competing operators that lack spectrum in that band. In Sweden, the local regulator's decision was appealed, and is now being handled by the Administrative Court of Appeals.

In the end, despite the promise of the 1.8GHz band, no one frequency used for LTE is likely to offer global roaming. Products will have to support multiple frequencies. For example, Huawei is working on a modem that will support a combination of the 800MHz, 900MHz, 1.8GHz, 2.1GHz and 2.6GHz band on a mix of GSM, 3G and LTE networks.

That modem would still leave users without LTE coverage in the U.S. -- for that, 700MHz also has to be added to the list. Suazo compares the current situation for LTE roaming to the GSM phone market before the arrival of "world phones."

Operators are keeping mum on when LTE roaming will become available. Meanwhile, users will have to rely on HSPA (High-Speed Packet Access) for data roaming. But some operators have started tests to ensure that their LTE networks are ready, including TeliaSonera.

"For data roaming to work, there are a number of interfaces that have to be able to talk with each other, and we have tested that on the vendors we use: Ericsson, Huawei and Nokia Siemens ... so technically there are no barriers," said Tommy Ljunggren, vice president of system development at TeliaSonera.

But roaming involves far more than just equipment. Operators also have to sign new roaming agreements, and agree on a business model, according to Ljunggren.

Part of the business model could be sending subscribers' data sessions directly to the Internet via the visited network, using a feature called Local Breakout, instead of sending the traffic back home and then onto the Internet, which is what operators do today. That would be a boon to latency-sensitive applications, Ljunggren said.

So far, data roaming has been very expensive, especially for doing more than just checking emails.

"The industry has to do something about the roaming setup, that's for sure. We can't continue to have the current prices. A few operators are doing something, but I think it is moving a little too slow," said Ljunggren.

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