The Two Faces of LTE

Carl Weinschenk

The big news of the past year or so in the cellular world has been the successful rollout of LTE. Indeed, announcements of carrier expansions to long lists of new towns and cities hardly qualify as news any longer.

It is important to note, however, that there are two kinds of LTE: Frequency-Division Duplex LTE and Time-Division Duplex LTE (FDD-LTE and TDD-LTE). This sounds arcane, but that doesn’t mean it isn’t important to folks who travel internationally and the IT departments who serve them. Phones that operate on one version of LTE don’t automatically function on the other.

The sky, or the advanced cellular service flying through it, is not falling, however. Before looking at the emerging solutions, it makes sense to understand the differences between the two technologies. This post by Light Reading Mobile’s Dan Jones does the trick:

The key difference between LTE TDD, sometimes also known as TD-LTE, and the frequency division duplex (FDD) version more common today is in what spectrum the technology is deployed in and how the signal is transmitted. TDD technology uses a single channel and a timed signal to separate uploads and downloads. FDD systems have two channels of paired spectrum separated with a guard band for uploads and downloads.


The problems that this could cause are so obvious that fixes are being readied before subscribers are inconvenienced. Sprint now supports both types of networks, according to Extreme Tech. Samsung said this week that it will release versions of the Galaxy S4 and S4 Mini that also run on both. The CNET story on the Samsung announcement says that FDD-LTE now predominates worldwide, but that TDD-LTE is expected to grow in many areas. The site quotes Strategy Analytics as predicting that TDD-LTE will represent 18 percent of the market in 2015.

Samsung isn’t the first device vendor to offer dual-service devices. Late last year, for instance, ZTE introduced the Grand Era LTE, a dual-mode smartphone. The phone is specially aimed at China Mobile Hong Kong’s dual-mode network. Creation of such networks could, over time, alleviate or lessen the need for devices that support both standards. Putting the onus on tablet and smartphone makers to accommodate both seems to be an inefficient and wasteful approach.

Test and measurement vendors also are adjusting to the bifurcated world.  FierceBroadbandWireless reported this week that Spirent has updated its CS8 mobile device tester and the DatumLab solution to support TDD-LTE as well as FDD-LTE. The story notes that Aritsu, another test and measurement vendor, made an announcement concerning the number of TDD-LTE test points that its ME7834 mobile test platform supports. The device also supports FDD-LTE.

The threat of incompatible networks is great, and the entire ecosystem knows it. The good news is that it is proactively reacting, and the threat is unlikely to evolve into an actual problem.



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