With IEEE 802.16e WiMAX, license-exempt operators have access to the most
advanced wireless broadband technology on the market today and can take
advantage of the same performance, ecosystem, and volume of scale that
incumbent, nationwide wireless operators with licensed-spectrum can. 

While often positioned as a mobile broadband technology that operates in
licensed bands, 802.16e WiMAX can also support fixed and nomadic services, and
vertical applications in a range of frequencies up to 6 GHz, including
license-exempt bands such as the 5.x GHz band and, in the US, the lightly
licensed 3.65 GHz band.

As 802.16e WiMAX products for license-exempt bands are introduced in the market,
operators need to know what the value proposition of using 802.16e WiMAX
compared to alternative solutions is.  How do they stand to gain from a
technology that was developed to support mobility? Do they need the extra
features that 802.16e WiMAX offers?

Why choose 802.16e WiMAX-based equipment?

The appeal of 802.16e WiMAX-based equipment to wireless operators either serving
residential and business subscribers or hosting vertical applications is driven
by the ability of the technology to meet operators’ requirements, both from a
business model perspective and from a performance one. 

The strongest pull towards 802.16e WiMAX is that it is a technology with a well
established evolution roadmap, with strong industry backing and a rapidly
expanding ecosystem.  The 802.16e WiMAX has a path toward the next WiMAX
version, 802.16m, which 802.16d TDD WiMAX lacks.  Operators with 802.16e
WiMAX-based networks will be able to upgrade their infrastructure to 802.16m
WiMAX when the equipment becomes available.  Operators with 802.16d TDD
WiMAX do not have this opportunity, unless they are ready to build an overlay
network or entirely replace the old equipment with the new 802.16e one. 

With the introduction of 802.16e WiMAX-based equipment for use in license-exempt
bands, 802.16d TDD WiMAX is rapidly becoming a legacy technology, as it already
is in licensed bands.  Wireless operators that do not have a clear
migration path to 802.16e WiMAX are concerned that their vendors might cease
their development of new 802.16d TDD WiMAX-based products in favor of the newer
standard. 

The availability, selection, and cost of subscriber devices present even bigger
constraints as they depend on overall market size.  Operators using 802.16e
WiMAX-based equipment in license-exempt bands can take advantage of the
economies of scale achieved in licensed bands because vendors can modify the
existing network equipment and devices to operate in license-exempt bands. 
Furthermore, having launched commercial products in the licensed WiMAX bands
(i.e., 2.3 GHz, 2.5 GHz, and 3.5 GHz), some vendors are expected to extend their
produce line to license-exempt bands rapidly. 

Support for mobility is another major appeal of 802.16e WiMAX, even though most
operators do not yet have specific plans on how to leverage it within the fixed
services they currently offer.  The prevailing attitude among operators is
that mobility is a nice-to-have feature that gives them additional flexibility
in how they market their services.  From a business model perspective,
operators in license-exempt bands have so far been focused on fixed services and
applications.  From a technology perspective, full mobility in
high-frequency license-exempt bands is very challenging. 

The interest from wireless operators and vertical market players is mostly tied
to the potential to offer nomadic access or limited mobility, which can be
easily tied to the service currently available as an add-on service.  The
ability to support mobile devices, for instance, may be valuable to subscribers
who just want to access the network from different locations, but not
necessarily within a fully mobile scenario.  A student with a laptop
needing to access a college WiMAX network will prefer a data card or built-in
module over a desktop modem.  As these types of applications do not require
blanket coverage of an entire region or country, they can be supported within
license-exempt bands within carefully chosen hot zones. 

Mobility will also enable operators to expand the range of services they offer
their vertical customers within their coverage area, and to include applications
that require, for instance, support for the mobile workforce or in-vehicle
connectivity (e.g., for safety and security, government, utilities, and
transportation applications).

Finally, 802.16e WiMAX-based equipment supports advanced functionality that is
conducive to improved performance compared to 802.16d WiMAX and other wireless
broadband technologies.  The spectral efficiency of the air interface in
the two versions of WiMAX in their basic configurations is comparable, but
several features that are available or required in 802.16e WiMAX are not
implemented in 802.16d TDD WiMAX equipment.  For instance, QoS is available
in both versions of WiMAX, but 802.16e WiMAX can provide better support for
voice services though an additional QoS level that makes it possible to
dynamically allocate capacity to voice traffic only when needed. 
Furthermore, 802.16m WiMAX is expected to provide enhanced voice support. 

Similarly, 802.16d WiMAX supports only multiple input multiple output (MIMO
Matrix) A as an option.  In 802.16e WiMAX, support for MIMO A-to provide
more robust coverage-and for MIMO B-to increase capacity-are part of the
standard.  MIMO A is especially attractive to rural operators because it
allows them to deploy fewer base stations to cover the same area.  MIMO A
also uses a diversity transmission scheme that helps operators to manage
interference.  MIMO B is better suited to operators in metropolitan areas,
where multipath environments, including indoor locations, dominate.

The use of subchannelization with orthogonal frequency division multiple access
(OFDMA) in 802.16e WiMAX also enhances coverage as terminal devices can receive
and transmit more efficiently than with other wireless interfaces.  Hybrid
automatic repeat request (ARQ) and convolutional turbo code (CTC) also provide
improved coverage, but they are not supported in 802.16d WiMAX. 

Finally, 802.16d WiMAX equipment today only supports channel widths up to 7 MHz,
while 802.16e WiMAX supports up to 10 MHz, and it is expected to reach 20 MHz
with 802.16m WiMAX.  The increase in channel size effectively lowers the
cost per bit to the operator, because each base station can transport more
traffic. 

Conclusions

802.16e WiMAX is rapidly becoming the technology of choice for wireless
operators, and not only for operating in licensed bands and with a strong focus
on mobility.  As they plan to expand their residential or business service,
or to grow their vertical market applications, wireless operators looking for a
future-proof technology find 802.16e WiMAX equally compelling for license-exempt
bands.  Equipment based on 802.16e WiMAX supports full mobile access, but
it also supports high-performance fixed networks. 

Thanks to the wide industry support for the 802.16e version of the standard,
operators using 802.16e WiMAX-based equipment will be able to rely on a stronger
ecosystem than available to 802.16d TDD WiMAX operators, which in turn will
translate into more robust interoperability and the availability of a wider
range of affordable subscriber devices. 

To download a full copy of the whitepaper including operator case studies

click here.

Monica Paolini is President of Senza Fili Consulting, a consulting and
analyst firm that focuses on wireless data technologies and services.  She
can be contacted at
monica.paolini@senzafiliconsulting.com.