introduction to WiMAX networking which is based on IEEE 802.16.
What is WiMAX?
WiMAX is defined as Worldwide Interoperability for
Microwave Access by the WiMAX Forum, formed in June 2001 to
promote conformance and interoperability of the IEEE 802.16 standard,
officially known as WirelessMAN. The Forum describes WiMAX as "a
standards-based technology enabling the delivery of last mile wireless
broadband access as an alternative to cable and DSL".
- "WiMAX is not a technology, but rather a certification mark,
or 'stamp of approval' given to equipment that meets certain
conformity and interoperability tests for the IEEE 802.16 family of
standards. A similar confusion surrounds the term Wi-Fi, which like
WiMAX, is a certification mark for equipment based on a different set
of IEEE standards from the 802.11 working group for wireless local
area networks (WLAN). Neither WiMAX, nor Wi-Fi is a technology but
their names have been adopted in popular usage to denote the
technologies behind them. This is likely due to the difficulty of
using terms like 'IEEE 802.16' in common speech and writing."
The bandwidth and reach of WiMAX make it suitable for the following
- Connecting Wi-Fi
hotspots with each other and to other parts of the Internet.
- Providing a wireless alternative to cable and DSL for last mile
(last km) broadband access.
- Providing high-speed mobile data and telecommunications services
- Providing a diverse source of Internet connectivity as part of a
business continuity plan. That is, if a business has a fixed and a
wireless internet connection they are unlikely to be affected by the
same service outage.
- Providing Nomadic connectivity.
Many companies are closely examining WiMAX for "last mile"
connectivity at high data rates. This could result in lower pricing for
both home and business customers as competition lowers prices.
In areas without pre-existing physical cable or telephone networks,
WiMAX will, it appears, be a viable alternative for broadband access that
has been economically unavailable. Prior to WiMax, many operators have
been using proprietary fixed wireless technologies for broadband services.
WiMAX subscriber units are available in both indoor and outdoor
versions from several manufacturers. Self install indoor units are
convenient, but the subscriber must be significantly closer to the WiMAX
base station than with professionally installed units. As such, indoor
installed units require a much higher infrastructure investment as well as
operational cost (site lease, backhaul, maintenance) due to the high
number of base stations required to cover a given area. Indoor units are
comparable in size to a cable modem or DSL modem. Outdoor units allow for
the subscriber to be much further away from the WiMAX base station, but
usually require professional installation. Outdoor units are roughly the
size of a textbook, and their installation is comparable to a residential
A commonly held misconception is that WiMAX will deliver 70 Mbit/s,
over 70 miles (112.6 kilometers). Each of these is true individually,
given ideal circumstances, but they are not simultaneously true. In
practice this means that in Line of sight environments you could deliver
symmetrical speeds of 10Mbps at 10Km but in Urban Environments it is more
likely that 30% of installtions may be Non Line of sight and therefore
Users may only receive 10Mbps over 2Km. WiMAX has some similarities to DSL
in this respect, where one can either have high bandwidth or long reach,
but not both simultaneously. The other feature to consider with WiMAX is
that available bandwidth is shared between users in a given radio sector,
so if there are many active users in a single sector, each will get
reduced bandwidth. However, unlike SDSL where contention is very
noticeable at a 5:1 ratio if you are sharing your connection with a large
media firm for example WiMax does not have this problem. Typically each
cell has a 100Mbps backhaul so there is is no contention here. On the
radio side in practice many users will have a range of 2,4,6,8 or 10Mbps
services and the bandwidth can be shared. If the network becomes busy the
business model is more like GSM or UMTS than DSL in that it is easy to
predict the capacity requirements as you sign more customers and
additional radio cards can be added on the same sector to increase the
Some cellular companies are evaluating WiMAX as a means of increasing
bandwidth for a variety of data-intensive applications; indeed, Sprint
Nextel has announced in mid-2006 that it will be investing about US$ 3
billion in a WiMAX technology buildout over the next few years.
In line with these possible applications is the technology's ability to
serve as a high bandwidth "backhaul" for Internet or cellular
phone traffic from remote areas back to an internet backbone. Although the
cost-effectiveness of WiMAX in a remote application will be higher, it is
not limited to such applications, and may be an answer to reducing the
cost of T1/E1 backhaul as well. Given the limited wired infrastructure in
some developing countries, the costs to install a WiMAX station in
conjunction with an existing cellular tower or even as a solitary hub are
likely to be small in comparison to developing a wired solution. Areas of
low population density and flat terrain are particularly suited to WiMAX
and its range. For countries that have skipped wired infrastructure as a
result of inhibitive costs and unsympathetic geography, WiMAX can enhance
wireless infrastructure in an inexpensive, decentralized,
deployment-friendly and effective manner.
WiMAX is a term coined to describe standard, interoperable
implementations of IEEE 802.16 wireless networks, in a rather similar way
to Wi-Fi being interoperable
implementations of the IEEE 802.11 Wireless LAN standard. However, WiMAX
is very different from Wi-Fi in the way it works.
In Wi-Fi the media access controller (MAC) uses contention access —
all subscriber stations that wish to pass data through a wireless
access point (AP) are competing for the AP's attention on a random
interrupt basis. This can cause subscriber stations distant from the AP to
be repeatedly interrupted by closer stations, greatly reducing their
throughput. This makes services such as Voice over IP (VoIP) or IPTV,
which depend on an essentially constant Quality of Service (QoS) depending
on data rate and interruptibility, difficult to maintain for more than a
few simultaneous users.
In contrast, the 802.16 MAC uses a scheduling algorithm for which the
subscriber station need compete once (for initial entry into the network).
After that it is allocated an access slot by the base station. The time
slot can enlarge and contract, but remains assigned to the subscriber
station which means that other subscribers cannot use it. The 802.16
scheduling algorithm is stable under overload and over-subscription
(unlike 802.11). It can also be more bandwidth efficient. The scheduling
algorithm also allows the base station to control QoS parameters by
balancing the time-slot assignments among the application needs of the
The original WiMAX standard (IEEE 802.16) specified WiMAX for the 10 to
66 GHz range. 802.16a, updated in 2004 to 802.16-2004 (also known as
802.16d), added specification for the 2 to 11 GHz range. 802.16d (also
known as "fixed WiMAX") was updated to 802.16e in 2005 (known as
"mobile WiMAX"). and uses scalable orthogonal
frequency-division multiplexing (OFDM) as opposed to the OFDM version
with 256 sub-carriers used in 802.16d. This brings potential benefits in
terms of coverage, self installation, power consumption, frequency re-use
and bandwidth efficiency. 802.16e also adds a capability for full mobility
support. The WiMAX certification allows vendors with 802.16d products to
sell their equipment as WiMAX certified, thus ensuring a level of
interoperability with other certified products, as long as they fit the
Most interest will probably be in the 802.16d and .16e standards, since
the lower frequencies suffer less from inherent signal attenuation and
therefore give improved range and in-building penetration. Already today,
a number of networks throughout the World are in commercial operation
using certified WiMAX equipment compliant with the 802.16d standard.
Advantages over Wi-Fi
- The WiMAX specification provides symmetrical bandwidth over many
kilometers and range with stronger encryption (TDES or AES) and
typically less interference. Wi-Fi is short range (approximately 10's
of metres) has WEP or WPP encryption and suffers from interference as
in metropolitan areas where there are many users.
- Wi-Fi Hotspots are typically backhauled over ADSL in most coffee
shops therefore Wi-Fi access is typically highly contended and has
poor upload speeds between the router and the internet.
- It provides connectivity between network endpoints without the need
for direct line of sight in favourable circumstances. The
non-line-of-sight propagation (NLOS) performance requires the .16d or
.16e revisions, since the lower frequencies are needed. It relies upon
multi-path signals, somewhat in the manner of 802.11n.
Spectrum Allocations issues
The 802.16 specification applies across a wide swath of the RF
spectrum. However, specification is not the same as permission to use.
There is no uniform global licensed spectrum for WiMAX. In the US, the
biggest segment available is around 2.5 GHz, and is already assigned,
primarily to Sprint Nextel and Clearwire. Elsewhere in the world, the most
likely bands used will be around 3.5 GHz, 2.3/2.5 GHz, or 5 GHz, with
2.3/2.5 GHz probably being most important in Asia. In addition, several
companies have announced plans to utilize the WiMAX standard in the
1.7/2.1 GHz spectrum band recently auctioned by the FCC, for deployment of
"Advanced Wireless Services" (AWS).
There is some prospect in the U. S. that some of a 700 MHz band might
be made available for WiMAX use, but it is currently assigned to analog TV
and awaits the complete rollout of digital TV before it can become
available, likely by 2009. In any case, there will be other uses suggested
for that spectrum if and when it actually becomes open.
It seems likely that there will be several variants of 802.16,
depending on local regulatory conditions and thus on which spectrum is
used, even if everything but the underlying radio frequencies is the same.
WiMAX equipment will not, therefore, be as portable as it might have been
- perhaps even less so than WiFi, whose assigned channels in unlicensed
spectrum vary little from jurisdiction to jurisdiction.
The actual radio bandwidth of spectrum allocations is also likely to
vary. Typical allocations are likely to provide channels of 5 MHz or 7
MHz. In principle the larger the bandwidth allocation of the spectrum, the
higher the bandwidth that WiMAX can support for user traffic.
The 802.16 standard IEEE Std 802.16e-2005, approved in December
2005 follows on from IEEE Std 802.16-2004, which replaced IEEE Standards
802.16-2001, 802.16c-2002, and 802.16a-2003.
IEEE Std 802.16-2004 (802.16d) addresses only fixed systems. 802.16e
adds mobility components to the standard.
IEEE 802.16e-2005 (formerly named, but still best known as, 802.16e or
Mobile WiMAX) provides an improvement on the modulation schemes stipulated
in the original (fixed) WiMAX standard. It allows for fixed wireless and
mobile Non Line of Sight (NLOS) applications primarily by enhancing the
OFDMA (Orthogonal Frequency Division Multiple Access).
SOFDMA (Scalable OFDMA) improves upon OFDM256 for NLOS applications by
- Improving NLOS coverage by utilizing advanced antenna
diversity schemes, and hybrid-Automatic Retransmission Request (hARQ)
- Increasing system gain by use of denser sub-channelization, thereby
improving indoor penetration
- Introducing high-performance coding techniques such as Turbo Coding
and Low-Density Parity Check (LDPC), enhancing security and NLOS
- Introducing downlink sub-channelization, allowing administrators to
trade coverage for capacity or vice versa
- Improving coverage by introducing Adaptive Antenna Systems (AAS) and
Multiple Input Multiple Output (MIMO) technology
- Eliminating channel bandwidth dependencies on sub-carrier spacing,
allowing for equal performance under any RF channel spacing (1.25-14
- Enhanced Fast Fourier transform (FFT) algorithm can tolerate larger
delay spreads, increasing resistance to multipath interference
On the other hand, 802.16-2004 (fixed WiMAX) offers the benefit of
available commercial products and implementations optimized for fixed
access. Fixed WiMAX is a popular standard among alternative service
providers and operators in developing areas due to its low cost of
deployment and advanced performance in a fixed environment. Fixed WiMax is
also seen as a potential standard for backhaul of wireless base stations
such as cellular, WiFi or even mobile WiMAX.
SOFDMA and OFDMA256 are not compatible so most equipment will have to
be replaced. However, some manufacturers are planning to provide a
migration path for older equipment to SOFDMA compatibility which would
ease the transition for those networks which have already made the
OFDMA256 investment. This effects a relatively small number users and
The equivalent of 802.16 in Europe is HIPERMAN. The WiMAX Forum is
working to ensure that 802.16 and HIPERMAN inter-operate seamlessly.
Korea's electronics and telecommunication industry spearheaded by
Samsung Electronics and ETRI has developed its own standard, WiBro. In
late 2004, Intel and LG Electronics have agreed on interoperability
between WiBro and WiMAX.
WiBro has South Korean government support with the requirement for each
carrier to spend over US$1 billion for deployments. The Koreans sought to
develop WiBro as a regional and potentially international alternative to
3.5G or 4G cellular systems. But given the lack of momentum as a standard,
WiBro has joined WiMAX and agreed to harmonize with the similar OFDMA
802.16e version of the standard. What makes WiBro roll-outs a good 'test
case' for the overall WiMAX effort is that it is mobile, well thought out
for delivery of wireless broadband services, and the fact that the
deployment is taking place in a highly sophisticated, broadband-saturated
market. WiBro will go up against 3G and very high bandwidth wire-line
services rather than as gap-filler or rural under-served market
deployments as is often exampled as the 'best fit' markets for WiMAX.
The WiMAX Forum is "the exclusive organization dedicated to
certifying the interoperability of BWA products, the WiMAX Forum defines
and conducts conformance and interoperability testing to ensure that
different vendor systems work seamlessly with one another." Those
that pass conformance and interoperability testing achieve the "WiMAX
Forum Certified" designation and display this mark on their products
and marketing materials. Vendors claiming their equipment is
"WiMAX-ready", "WiMAX-compliant", or
"pre-WiMAX" are not WiMAX Forum Certified, according to the
WiMAX Spectrum Owners Alliance - WiSOA
WiSOA is the first global organisation composed exclusively of owners
of WiMAX spectrum. WiSOA is focussed on the regulation, commercialisation,
and deployment of WiMAX spectrum in the 2.3–2.5 GHz and the 3.4–3.5
GHz ranges. WiSOA are dedicated to educating and informing its members,
industry representatives and government regulators of the importance of
WiMAX spectrum, its use, and the potential for WiMAX to revolutionise
WiMAX is a framework for wireless development based on a
forward-looking core set of technologies. More recently 3GPP cellular's
4G, 802.22 Cognitive Radio RAN (Rural Area Network), and 802.20, the High
Speed Mobile Broadband Wireless Access (MBWA) Working Group, have shifted
toward use of similar constructs of multi-channel scalable OFDM, HARQ, FEC,
MIMO-AAS and other complementary technologies as are part of WiMAX.
Within the marketplace, WiMAX's main competition comes from widely
deployed wireless systems with overlapping functionality such as UMTS
and CDMA2000, as well as a
number of Internet oriented systems such as HIPERMAN and WiBro.
Cellular Phone Systems 3G and 4G
Both of the two major 3G systems,
CDMA2000 and UMTS, compete with WiMAX. Both offer DSL-class Internet
access in addition to phone service. UMTS has also been enhanced to
compete directly with WiMAX in the form of UMTS-TDD, which can use WiMAX
oriented spectrum and provides a more consistent, if lower bandwidth at
peak, user experience than WiMAX. Moving forward, similar air interface
technologies to those used by WiMAX are being considered for the 4G
evolution of UMTS.
3G cellular phone systems usually benefit from already having
entrenched infrastructure, being upgrades from earlier systems. Users can
usually fall back to older systems when they move out of range of upgraded
equipment, often relatively seamlessly.
In addition to obvious competition, in some areas of the world the wide
availability of UMTS and a general desire for standardization has meant
spectrum has not been allocated for WiMAX: in July 2005, the EU-wide
frequency allocation for WiMAX was blocked by France and Finland, where
manufacturers have invested heavily in UMTS technology. In September 2006,
frequency bidding in Malaysia was stopped and any allocation of WiMAX has
been suspended indefinitely. The ITU has, however, advised agnostic use of
spectrum for IMT-2000 and is considering WiMAX as an alternative specified
use for IMT-2000 and IMT-Advanced. Growing interest among operators is
building for 'technology agnostic' allocation of spectrum in which
operators are free to make best use of their large investments and insure
against regulated obsolescence.
Internet Oriented Systems
Early WMAN standards, the European standard HIPERMAN and Korean
standard WiBro have been harmonized as part of WiMAX and are no longer
seen as competition but as complimentary. All networks now being deployed
in Korea, the home of the Wibro standard, are now WiMAX.
As a short-range mobile internet solution, such as in cafes and at
transportation hubs like airports, the popular WiFi 802.11g system is
widely deployed, and provides enough coverage for some users to feel
subscription to a WiMAX service is unnecessary.
Comparison of Mobile Internet Access methods
||Quoted speeds only achievable at short range more practically
10Mbps at 10Km.
||Short range (<5km)
|HSDPA downlink widely deployed. Roadmap shows HSDPA up to
28.8Mbps from the basestation . Users can expect downloads of 400
to 600Kbps but around 100Kbps uplink speeds.
||Reported speeds according to IPWireless
||Still in development
||Obsoleted by EV-DO
|EV-DO 1x Rev. 0
|Proposed Rev. B improves downlink to nearly 5Mbps.
Notes: All speeds are theoretical maximums and will vary by a number of
factors, including the distance from the tower and the ground speed (ie
communications on a train may be slower than when standing still.) Usually
the bandwidth is shared between several terminals.