A technology that will be a part of the next generation of LTE not only promises to bolster mobile broadband capacity for commercial mobile operators, but could also play a crucial role in helping public-safety LTE networks gain the additional spectrum they need as the demand for mobile broadband services continues to grow.

A new technology called “carrier aggregation” will be a key element in the next iteration of LTE, known as LTE Advanced (aka 3GPP Release 10). The technology will allow operators to marry non-contiguous spectrum into a single broad channel, enabling LTE operators to handle huge downlink flows of data, such as video, more efficiently.

Chris Pearson, president of 4G Americas, which represents the interests of GSM, HSPA and LTE operators in the Americas, said that carrier aggregation will enable operators to mix and match disparate frequency division duplex (FDD) spectrum, and that should help regulators find paired spectrum to issue for the next generation of mobile broadband systems.

Through carrier aggregation operators can take the current 20 MHz spectrum ceiling (the maximum amount of spectrum LTE can operate in today) and push it all the way to 100 MHz, achieving downlink speeds as high as 1 Gbps.

Some mobile operators already have deployed iterations of carrier aggregation technology. Last week T-Mobile USA announced that it is deploying dual-carrier HSPA+ technology, which effectively doubles the speed of its 3G network from theoretical speeds of 21 Mbps to 42 Mbps. T-Mobile is taking two 5-MHz HSPA+ downlink carriers — each supporting theoretical speeds of 21 Mbps — and bonding them together.
Nokia Siemens Networks demonstrated carrier aggregation technology earlier this year by bonding LTE channels in non-contiguous spectrum. Specifically, it combined spectrum at 800 MHz and 2.6 GHz—two bands that Europe is auctioning for 4G technologies—by using the same base station but with two radios tuned to the two different spectrum bands.

AT&T and Verizon Wireless, which are planning nationwide LTE networks, eventually could move 3G users off existing spectrum and bond that spectrum to the 700 MHz band. Public safety already holds 10 MHz of spectrum at 700 MHz for LTE services and may see a direct allocation of another 10 MHz in the D Block, giving it the 20 MHz maximum for LTE. As broadband services grow and voice becomes a reliable service on the LTE network, carrier aggregation technology could prove to play a vital role down the line in giving public safety networks the ability to add disparate spectrum, either from new sources or existing spectrum that can be refarmed for LTE use.

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