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TD-LTE explained

Posted: 11 Oct 2011 ?? ?Print Version ?Bookmark and Share

Keywords:LTE? TD-LTE? frequency division duplexing?

What is TD-LTE and how will it affect the mobile world? What will the implications be for test engineers working in device development? This technology may seem confusing as LTE networks have just been rolled out and a growing number of new LTE devices have been introduced to market.

To date, most of the high profile news around LTE has concerned its frequency division duplexing (FDD) variant. This technology has been deployed by operators including Verizon and Europe's TeliaSonera.

In FDD, a carrier frequency is used for data uplink and downlink respectively. By contrast, TD-LTE uses a single carrier frequency for both uplink and downlink, dividing the radio frame into subframes that can be allocated to either uplink or downlink as per the immediate user need. This dynamic approach is well suited to the changeable data profile of today's users C who for the most part download more than they upload, but will occasionally upload data like photos or videos.

Originally, TD-LTE had been championed principally by China Mobile, which saw TD-LTE as an evolutionary path from the TD SCDMA technology deployed as a Chinese 3G standard. As such, TD-LTE was initially perceived as a China-specific standard. However, spectrum for mobile communications is a valuable commodity and TD-LTE's use of single frequency rather than paired spectrum is advantageous to any operator in countries where spectrum is limited or where an operator only has access to a single unpaired frequency.

In meeting a worldwide need, TD-LTE has all the potential to be much more than a Chinese solution. This is exactly what happened at the start of 2011 with the launch of the Global TD-LTE Initiative (GTI), through which many of the leading global operators, including Vodafone, Bharti Airtel and Softbank joined with China Mobile to declare their interest in the technology. Indeed, many operators see TD-LTE as being a complementary technology to be deployed alongside FDD: According to research group Informa's 2011 LTE Study, 33% of 250 global operators surveyed are considering deploying TD-LTE as well as FDD networks. With a further 19% considering TD-LTE alone, over half of operators are looking at rolling out TD-LTE. However, despite this level of support, TD-LTE is still a little way behind FDD. A key reason for this is the limited availability of mobile devices but this is set to change now that the technology can rely on a global market.

 test cases

Figure: This table shows that the number of test cases validated by the Global Certification Forum�for�TDD bands�is reaching parity with the number for FDD bands. This table shows test cases provided by Anite.

In test and measurement, TD-LTE's move into the mainstream has seen intense activity over the past year to make available the test infrastructure necessary to bring new devices to the market. Test solution providers such as Anite having recognised the potential of TD-LTE back in 2009 have been able to quickly respond and accelerate the availability of test cases based on the 3GPP standard for protocol conformance testing.

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