FDD/TDD: WiMAX and LTE Crossing Paths?

The timing is still uncertain, but inclusion in IMT-advanced seems to be
uncontroversial for both technologies. What is interesting, however, is that the
issue around duplexing is somewhat breaking down – with WiMAX using TDD (time
division duplex) and LTE using FDD (frequency division duplex).

The WiMAX camp is pushing to have an FDD version of WiMAX as an IMT-2000 and as
an IMT-Advanced technology (WiMAX TDD is already an IMT-2000 technology).
Support for FDD is included in the IEEE standard-so nothing new from a standards
perspective. Is there a market for FDD WiMAX though? Not much to date and this
is mostly because TDD is almost universally accepted by WiMAX operators as the
best option for the inherently asymmetric data traffic they have to transport.

Besides, there is currently no beamforming solution available for FDD wireless
interfaces (either WiMAX or LTE-and this constitutes an advantage for WiMAX,
although one that is seldom acknowledged). So the only reason to use FDD WiMAX
is linked to regulatory requirements. Some WiMAX operators may have to use FDD
in their allocated spectrum, but to date it does not seem that there are enough
of them to justify FDD WiMAX 16e product development.

On the LTE side, there is a growing interest for a TDD version of LTE, mostly
driven by China Mobile, but relevant to other mobile operators too, which often
have TDD spectrum and do not know what to do with it. TD-LTE is currently being
trialed in China by multiple vendors. Chipsets are being developed by Qualcomm,
Ericsson, Huawei, Sequans, Altair. TD-LTE will support MIMO, but beamforming as
well and will, like FDD LTE, use channel sizes up to 20 MHz.

A femtocell prototype from Nokia was also on display in Geneva in the China
Mobile’s booth. Combined (TDD and FDD) chipsets in subscriber devices will make
it easier to roam across TDD and FDD networks. With China Mobile’s commitment,
TD-LTE has gained the needed momentum, but it still uncertain where and how TD-LTE
will be deployed in other countries.

At this stage, TD-LTE appears to have better prospects than FDD WiMAX, but it is
interesting to see that while it is not possible at this stage for WiMAX and LTE
to converge into a single standard, they seem to increasingly cross paths and
move in the same direction.

Monica Paolini is the founder and president of Senza Fili Consulting and can
be contacted at
monica.paolini@senzafiliconsulting.com.   Senza Fili Consulting (
www.senzafiliconsulting.com)
provides advisory support on wireless data technologies and services financial
modeling, market research, business plan support, business development, RFPs,
due diligence, and white paper preparation.   Independent advice, a strong
quantitative approach, and an international perspective are the hallmarks of our
work.