TD-LTE: The Next Frontier

Lately, a new dimension has been added to the fight between WiMax and LTE, which is TD-LTE. Developed largely in China, TD-LTE has started to make inroads into other markets as well. Huawei recently launched TD-LTE network for China Mobilewhile Qualcomm has put in a bid for BWA spectrum in 2300 MHz in India and plans to roll out TD-LTE network. It is reported that TD-LTE networks may also come up in Indonesia. In the US there have been statements by Clearwire that they want to migrate from their current Wimax to TD-LTE deployment. Reports state Russian operator Svyazinvest has also picked TD-LTE for mobile broadband deployment. GSM association has also thrown its weight behind TD-LTE. All in all, TD-LTE has crept out of its Chinese comfort zone and been unexpectedly linked to some of the world’s most influential mobile markets. These developments are a major blow to the WiMAX camp, the technology normally associated with TD spectrum bands.

What is TD-LTE?

There are two versions of LTE. FDD-LTE uses the FDD (Frequency Division Duplex) 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 (Time Division Duplex) 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.

TD-LTE provides backward compatibility with 2G and 3G networks and hence would work even outside the LTE coverage area.

Why sudden interest in TD-LTE?

All vendors are trying to increase the installations of the network in which they hold the maximum number of patents and not necessarily moving towards development of a standard platform with a clear migration plan. In a statement, Qualcomm made it clear that it intended to act only as a facilitator: If it wins the spectrum auction, Qualcomm plans to partner with an India-based operator to build a TD-LTE network and then exit the business. The bulk of Qualcomm’s sales come from technology licensing agreements. Qualcomm has a veritable monopoly on CDMA patents and is seeking to expand the market for its other intellectual property holdings as the global wireless market moves toward 4G technology. The CDMA evolutionary path is coming to end after EVDO and hence Qualcomm would not like to risk the revenues by allowing the operators to move to a technology (read WiMax) where it has fewer patents. NSN, Motorola, Sequans and other companies are also reported to be active in the TD-LTE space so that they do not miss the bus in China.

In many countries, there are upcoming spectrum auctions for 2.3 GHz and 2.5 GHz spectrum bands that is better suited for TDD. Operators so far found little interest in the TDD band and WiMax had positioned itself very well for the TDD band. Operators are in general opposed to the WiMax roll out as it encourages open ecosystem and moreover was an entirely different technology with no evolutionary path from either GSM or CDMA. WiMAX  is controlled by IEEE, the consumer electronics industry, which is far more open than telecom/3GGP. However, now operators see a clear synergy in rolling out TD-LTE networks if the TDD spectrum comes up for auction. In India, the operators may actually be bidding for BWA to roll-out TD-LTE rather than WiMax.

There is another belief that is gaining traction is the fact that TD-LTE provides a migration path for WiMax players. Bruce Brda, Motorola’s senior vice president and general manager of home and networks mobility, said in an interview with a leading technology magazine that

Carriers can choose to deploy LTE networks either in FDD (frequency division duplex) or TDD (time division duplex) versions. Since WiMax is a TD technology and shares more assets with the latter, TD-LTE presents a more efficient migration option for WiMax operators. Those with broad spectrum rights such as Clearwire in the US have the option of dividing up that spectrum between WiMax and TD-LTE so that they can enter the LTE market without cutting off their existing subscriber base. But a small carrier with limited spectrum will not be able to maintain both business lines, and will have to decide between the two platform.

On the handset side, there is a flurry of activity with HTC announcing TD-LTE handset pilot and RIM’s announcement on TD-LTE Blackberry for China Mobile. Efforts are on to produce a converged LTE device, capable of supporting both TDD and FDD versions of the next-generation technology.

TD-LTE seems to be a technology which is seeing the ecosystem building around it and has a potential to co-exist with FDD LTE. It would be interesting to see if it indeed leaves behind WiMax in terms of roll-outs.

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