OverviewThe latest technology
buzz is WiMAX wireless networks. We have heard many
things about this wonderful new long haul wireless
technology that it almost seems as though you are just
a phone call away from having yours' designed and
installed. Well before you start assuming things like
we all do, we thought as engineers and network
architects we would share personal experiences and the
experiences of colleagues from around the world, in a
manner that is direct, helpful, educational, and
certainly reality based. This is a back-pocket Primer
for anyone now dealing with the implementation of a
WiMAX network.
First, there are several
misconceptions surrounding WiMAX that need to be
cleared up so that the business aspects and
engineering basis have a common understanding.
Secondly, the people who make the
various decisions within your organizations need to
understand that there are differences between a
private network and an interoperable network strategy.
This subtle difference does exist and requires a plan
which considers the final transition aspects, if
considered now, to easily provide a lower cost upgrade
to a true interoperable network, now incorporating
diverse vendor equipment.
Finally, while WiMAX has been out
internationally for several years, it is very new to
the United States, only a few years old, with very
little training and education available to those who
have the responsibility to build these systems or
those who will make the financial and technical
decisions to have these systems built for them as part
of their long haul wireless strategy.
Our experiences and the experiences
of our colleagues are offered here as contributions as
well as tying these in to the standards and
certification authorities all meant to provide a
reality based quick reference education for anyone in
the throws of How to Build a WiMAX network.
Primer
WiMAX is a standard designed for
fixed broadband wireless access featuring a
controlling base station, that connects subscriber
stations not to each other but to various public
networks, such as the Internet, linked to that base
station. The acronym means “ worldwide
interoperability for microwave access” or (WiMAX).
WiMAX, as a standards initiative, is
based on a "set of profiles" supporting a wide range
of frequencies (up to 66GHz)with channel sizes
(1.25MHz to 20MHz) and applications (LOS and NLOS),
and finally PTP and PTMP. The WiMAX profiles narrow
the scope of 802.16 to focus on first service specific
configurations. The IEEE titled the specification
802.16 and released it December 2002. The profiles
addressed in that “profiles release” are 802.16-2004
(old d) and 802.16e as presented further down.
The WIMAX forum was formed eight
months earlier in April 2002 to support, promote and
certify compatibility and interoperability of devices
based on the 802.16 specification, and to develop such
devices for the marketplace. Founding Members of the
organization include Airspan, Alvarion, Analog
Devices, Aperto Networks, Ensemble Communications,
Fujitsu, Intel, Nokia, OFDM Forum, Proxim, and Wi-LAN.
WiMAX is the IEEE 802.16
Point-to-Multipoint broadband wireless access standard
for systems in the stated frequency ranges. WiMAX will
initially provide fixed nomadic, portable and
eventually, mobile wireless broadband connectivity. To
that end there are two standards (802.16d (new -2004)
and 802.16e respectively) although they will both
perform similar functions because they must be
interoperable. One clearly is a fixed solution and the
other a mobile solution that must still communicate
with a fixed solution. So one of the first
considerations is whether you want to build out a
mobile or fixed network. In many cases you would have
already considered your target market segments,
spectrum availability, regulatory constraints and your
deployment need.
Which One do I Need?
Generally speaking, the current
802.16-2004 (originally 802.16d) fixed network
products are less complex than 802.16e mobile network
systems because; they can be used in a wider range of
unlicensed bands, they offer a faster time-to-market,
and in many cases a higher throughput than 802.16e
equipment. On the other hand, there is better support
for mobility and a wider range of terminal form
factors advantages of 802.16e equipment.
It’s certainly a consideration but
no matter what you chose the migration paths to move
in either direction are easily achieved through
overlay networks, software upgradeable base stations,
dual mode devices and dual mode base stations. This
consideration assures you are not stuck in one mode or
the wrong mode and that your initial investment is
protected. Makes the CTO and CEO happy.
WiMAX base stations transmit up to
30 miles, but because it is a cell-based topology,
would yield a more typical range of 3 to 5 miles.
WiMAX systems can deliver a capacity of up to 75 Mbps
per channel, for fixed and portable access
applications. This is enough bandwidth to
simultaneously support hundreds of businesses with T-1
speed connectivity and thousands of residences with
DSL speed connectivity as we have seen.
WiMAX technology will be
incorporated in portable computers and PDAs expected
in late 2006 and early 2007, allowing for urban areas
and cities to become “MetroZones”, the new buzz word,
for portable outdoor broadband wireless access. In
addition, Wireless service providers and
telecommunication equipment industries are embracing
WiMAX technology because of its tremendous cost
advantages to provide that last-mile connectivity to
large parts of the world that are too expensive to
serve with wired technologies requiring all that
trenching.
Security
Due to the security issues with WEP
in the 802.11 Wi-Fi arenas, the standards bodies took
no chances with WiMAX, and wisely prioritized security
from the onset. Base station designers went to work to
assure a dedicated high performance security
processor. The WiMAX security standard requires that
all traffic be encrypted with CCMP (which is Counter
Mode with Cipher Block Chaining Message Authentication
Code Protocol).
According to the WiMAX forum, the
group's aim is for end-to-end authentication. WiMAX
uses PKM-EAP (Extensible Authentication Protocol),
which relies on the TLS standard following public key
cryptography. Having addressed this level of security
from the start provides an excellent reference point
to add multi-level security options as well, if your
implementation requires an MLS approach. Secure
(blacker) implementations would require such an
approach.
What is Released?
The first certification release for
802.16-2004 fixed is out there already and includes
products from certified vendors with two profiles in
the 3.5GHz and the 5.8GHz bands supporting fixed and
nomadic access. The profiles for 802.16e mobile are
not available nor released as of this writing but are
expected to be in the ranges of 2.3GHz to 2.5GHz when
officially released. WiMAX profiles based on
802.16-2004 are better suited to fixed applications
that use directional antennas because OFDM is
inherently less complex than SOFDMA used in the mobile
application. As a results, 802.16-2004 networks will
be deployed much faster and at a lower cost. Our
experiences are with these released systems in the US
and around the world in ground applications, mobile
military, public safety and maritime applications.
Planning for WIMAX
Companies, cities or projects in
maritime or ground systems in the US that have decided
to or are considering building and operating a WiMAX
network will have a few important issues to consider.
The initial spectrum for WiMAX in the USA is
unlicensed spectrum in the 5GHz range. Given this
spectrum is open it will have inherent interference
issues and risks which will require attention. There
are many ways of overcoming interference issues. The
answers come from a proper site selection, following
your RF survey training and from the actual selected
equipment. So, the planning and site survey results
remain the key to your confident success.
Summary
WiMAX provides optimized solutions
for fixed, nomadic, portable and mobile broadband
wireless access. There are two flavors in various
release and implementation modes. The first is
802.16-2004 WiMAX with two initial frequency profiles
– the 3.5GHz and the 5.8GHz bands supporting fixed and
nomadic access in LOS and NLOS environments now. The
other flavor is 802.16e WiMAX with expected profiles
in the 2.3GHz and 2.5GHz ranges optimized for dynamic
mobile radio channels supporting hands-off and roaming
--arriving by 2007. Another exciting technology for
all of us.
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