TD-LTE: The most powerful weapon in the LTE arsenal against WiMAX

Monica Paolini, Senza Fili ConsultingI have always considered LTE to be somewhat boring. As a technology, LTE is almost indistinguishable from WiMAX. The standards evolution steps are not in sync, which means that at any time the latest version of one of the two technologies may be a bit ahead, but the endless comparisons have failed to conclusively show that one technology is better than the other. As for the market opportunity, LTE was developed by mobile operators--along with their vendors--and there has never been any doubt that the great majority would adopt LTE, not WiMAX.

For a long time I thought the market split between the two technologies was decided. WiMAX was for greenfield players or operators with TDD spectrum that did not need the backwards compatibility with legacy cellular technologies supported by LTE. Vertical markets--transportation, healthcare, utilities, public safety--would also naturally gravitate towards WiMAX. Mobile operators with FDD spectrum would instead pick LTE. Because of mobile operators' large subscriber base, deep pockets and ability to secure spectrum, LTE was slated to get a much larger slice of the wireless broadband market.

The disruptive side of LTE

TD-LTE throws a wrench into this picture. LTE becomes much more intriguing--almost disruptive. There are two versions of LTE. FDD-LTE uses the FDD paired spectrum with two separated channels, one for the uplink and one for the downlink, which is the type of spectrum most mobile operators have. TD-LTE uses TDD unpaired spectrum channels that combine uplink and downlink, and split resources on the basis of real-time demand. Voice is inherently symmetric in the uplink and downlink so it is well suited for FDD spectrum allocations. Data traffic benefits from TDD spectrum, as it is typically asymmetric but the degree of uplink/downlink asymmetry is not fixed. The development of TD-LTE was initially pushed by China Mobile and regarded as a mainly Chinese standard, similarly to TD-SCDMA.

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.

WiMAX: losing the battle, but winning the war

There is no hurry to choose which way to go. WiMAX operators are increasingly keen on requiring vendors to be able to support both a transition to WiMAX 16m and to TD-LTE as smooth as possible. But the support for multiple air interfaces is an industry ongoing trend dictated by the rapid evolutions wireless technologies which does not affect only--or primarily--WiMAX vendors and operators.

Even if some or most WiMAX operators migrate to TD-LTE, WiMAX may after all succeed in changing some of the entrenched ways in which the wireless industry operates.

To a large extent, WiMAX emerged as a reaction to mobile operators and their control over the ecosystem--which explains why mobile operators never really warmed to WiMAX in the first place. The WiMAX industry has successfully pushed for a more open and competitive offering of mobile data services and devices that is now being adopted by cellular operators.

Google's Nexus One is an incarnation of WiMAX's retail model. Even in the United States, no-contract data plans have started to appear. With the examples of Yota, Clear and Packet One, mobile operators are getting ready for the massive data traffic that subscribers are likely to generate when a truly broadband connection is available. Possibly this could have happened even without WiMAX, but the pressure of a new technology and new business models has definitely accelerated the pace of change among mobile operators, unused to competition and comfortable with the status quo.

More importantly, however, WiMAX has been successfully in making regulators more comfortable with TDD spectrum allocations and, as a result, with increases in the availability of spectrum that can be used for TDD interfaces and that is technology neutral. Mobile operators have traditionally shown little interest in TDD spectrum and tried to stop additional TDD allocations to prevent WiMAX players to enter in their markets. With TD-LTE, however, they may finally have a way to use TDD spectrum and benefit from it. As the list of potential bidders in the upcoming Indian auction shows, mobile operators seem to have developed a taste for TDD after all.

Monica Paolini is the founder and president of Senza Fili Consulting and can be contacted at mailto:[email protected]. Senza Fili Consulting provides expert advisory services on wireless data technologies and services.