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Today’s wireless networks are under serious strain from the data deluge, driven by the growth in mobile video and the pervasiveness of tablets and smartphones around the world. Consequently, spectrum is at a premium, and operators must consider their spectrum strategy moving forward. The deployment of LTE, and its high spectral efficiency, is one part of the strategy. However, the deployment of LTE-TDD (time division duplex) is starting to gain momentum. LTE-TDD is a complimentary approach to FDD (frequency division duplex), bringing additional capacity to congested areas.
LTE-FDD and TDD were both defined and introduced as part of the 3GPP specification in 2009 to make efficient use of paired and unpaired spectrum allocations over a common, core network architecture. How does this impact an operator’s spectrum strategy? Traditional LTE-FDD deployments use paired spectrum, leveraging one frequency band for upload and one for download. However, most consumers are downloading video content – think Netflix and YouTube – rather than uploading new content that they’ve created. This is where LTE-TDD gets interesting because it leverages the unpaired spectrum. What this means is that the downlink and uplink traffic travel in both directions on the same frequency band. By offering asymmetrical allocation in UL and DL directions, TDD makes the most efficient use of paired and unpaired spectrum allocations, while fitting consumer usage models for downloading or uploading premium content.
LTE-TDD spectrum is already allocated in several countries. While most FDD spectrum has already been auctioned, TDD spectrum is still available and not as expensive as its FDD counterpart. Several UMTS mobile operators in Europe and Asia have also received small chunks of TDD spectrum in the 2.1 GHz band. The spectrum was allocated at the same time as larger channels of UMTS FDD spectrum, and in most cases the TDD spectrum went unused. However, most operators are opting to roll out TDD on 2.3 GHz and 2.6 GHz. These bands offer the largest contiguous blocks of spectrum, thereby enabling the best possible performance.
It’s also going to be easier – and faster – for operators to deploy LTE-TDD than it was to make the transition from 3G to LTE. For starters, TDD uses the same LTE network architecture as FDD, so operators that have rolled out LTE on FDD spectrum can leverage that same infrastructure for their TDD deployment, resulting in significant capital expenditure and operating expense savings. In addition, operators will be able to support downlink heavy traffic modes for their subscriber base without affecting existing deployments.
Traction for LTE-TDD deployments in China, Japan and India is already underway, with trials beginning in 2014 and full-scale deployments in the latter half of the year. Mobile operators in China and Japan are leveraging their TDD spectrum for their small cell deployments to add capacity and bandwidth to dense urban areas. These small cells will leverage the higher range of the spectrum, resulting in less fragmentation. In addition, in the enterprise/public domain, LTE-TDD small cells will serve as the basis for hotspots. We’re also seeing initial LTE-TDD deployments in the United States, with Sprint beginning to roll-out its LTE-TDD networks following its merger with Japan-based SoftBank. LTE-TDD devices are already in the market, just ready to take advantage of this technology.
Another trend we’re seeing is mobile operators around the world beginning to look at how they can make use of the LTE-TDD spectrum in non-traditional ways as well. This could include the delivery of broadcast services on the TDD spectrum in certain regions or leveraging it for machine-to-machine communications between devices. The addition of TDD into the LTE network enables operators to introduce LTE to new markets such as public safety, health care and more.
LTE-TDD will not disappoint. It provides a solid path forward for mobile operators to overcome the challenges their wireless networks face today, while allowing the reuse of existing LTE infrastructure. The time for LTE-TDD is now.
