Industry momentum behind Time Division LTE continues to grow with news that a number of major operators and vendors are working with the 3GPP to allow the standard to be deployed in the USA, using the 2.6GHz spectrum band. Clearwire and its partners own the majority of that spectrum. Most of Clear’s 2.6 GHz spectrum goes unused.
Light Reading Mobile notes that China Mobile, Clearwire, Sprint Nextel, Motorola, Huawei, Nokia Siemens Networks, Alcatel-Lucent and Cisco Systems are asking for the 2.6GHz spectrum (2496MHz to 2690MHz) to be defined as a TDD band for LTE.
Outside the United States, part of the band (2570MHz to 2620MHz) is already specified for TDD. The new work will extend this compliance. The report adds that specifications for the US 2.6GHz band for TD-LTE is scheduled to be completed by March 2011.
LTE pioneers TeliaSonera, NTT DoCoMo and Verizon Wireless, will all use different frequency bands for their respective LTE networks, explains TechWorld. So for roaming in the U.S, Japan and Europe to work, modems will have to support 700MHz, 2100MHz and 2600MHz, with more bands to be used in the future. That will be a challenge for roaming, says Light Reading.
The appeal of TD-LTE has widened well beyond China. The recent announcement of Qualcomm to bid for TDD spectrum in India to support a TD-LTE deployment confirms--although it was not required to validate--the emergence of TD-LTE as global technology, likely to command a substantial market share.
Why the sudden interest in TD-LTE?
There are four main factors driving a growth in support for TD-LTE:
- The FDD LTE and TD-LTE versions of the 3GPP standard are very similar. As a result, devices can support both the FDD and TDD interfaces through a single chipset--i.e., without any additional cost. This is a hugely important new development: TD-LTE will benefit from the wide availability of FDD LTE devices that will be able to support TD-LTE as well. Unlike WiMAX, TD-LTE does not need to prove to have a substantial market share to convince vendors to develop devices. Vendors do not need to develop new devices, they simply need to add TD-LTE support to the existing ones.
- There is a lot of TDD spectrum available, and in most cases it is cheaper and under-utilized. 3G licenses frequently have TDD allocations and upcoming 2.5 GHz auction in most cases contemplate TDD bands.
- The increasing availability of base stations that can be cost-effectively upgraded will make it possible and relatively inexpensive for WiMAX operators to transition to TD‑LTE using the same spectrum allocation. The transition will still require substantial efforts and be justified only in some cases, but it will make it easier for WiMAX operators to have roaming deals and to have access to the same devices that LTE operators have.
- Industry commitment to WiMAX 16m, the ITU-Advanced version of WiMAX and successor to the current WiMAX 16e, is still limited.
What's next?
In the near term very little will change. TD-LTE is still being developed and it will take time before it gets deployed beyond core markets like China and possibly a few others like China. In Europe, for instance, mobile operators will deploy LTE in the FDD spectrum and only when they will need additional capacity they are likely to move to TDD. Unlike FDD LTE, TD-LTE will move from initial deployments in developing countries, with a later introduction as a mature technology in developed countries--a quite interesting trend reversal.
WiMAX operators will also be barely affected by TD-LTE in the short term. WiMAX is years ahead in terms of technological maturity, devices and ecosystem. This gives them a strong advantage in comparison to TD-LTE operators: They know the technology already, they have a network, and they have customers. They also have the choice whether to switch to TD-LTE or not--and, more importantly, they have no pressure to do so before TD-LTE has reached the maturity they feel comfortable with or until the WiMAX 16m prospects become clearer.
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