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[802SEC] 802 news IEEE 802.16 Backgrounder ++FYI++

Angela Ortiz
Program Manager - Technical Program Development
IEEE Standards, 445 Hoes Lane,
Piscataway, NJ  08855-1331 USA
Telephone: 1732-562-3809  ><  Fax: 1732-562-1571
E-m:   ><


--- Forwarded by Angela Ortiz/STDS/STAFF/US/IEEE on 05/14/2002 12:13 PM
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                             Subject:     802 news IEEE 802.16 Backgrounder                            
                    05/14/2002 11:41 AM                                                                                    

IEEE 802.16 Backgrounder

Contact:  Roger Marks,
          303 497 3037,
          Dean Chang,
          408 719 9977,
          Karen McCabe
          732 562 3824,

Broadband Wireless Access:  An Introduction to the Technology
Behind the IEEE 802.16 WirelessMAN? Standard

     Broadband wireless access (BWA) has become the best way to meet

escalating business demand for rapid Internet connection and integrated

data, voice and video services.  BWA can extend fiber optic networks and

provide more capacity than cable networks or digital subscriber lines

(DSL).  One of the most compelling aspects of BWA technology is that

networks can be created in just weeks by deploying a small number of base

stations on buildings or poles to create high-capacity, point-to-multipoint

(PMP) systems.

     BWA has had limited reach so far, in part because of the unmet need

for a universal standard.  While providing such a standard is important for

developed countries, it is even more important for the undeveloped world

where wired infrastructures are minimal.

The IEEE 802.16 WirelessMAN? Standard

     The Institute of Electrical and Electronics Engineers Standards

Association (IEEE-SA) sought to make BWA more widely available by

developing IEEE Standard 802.16, which specifies the WirelessMAN? Air

Interface for wireless metropolitan area networks.  The standard, which

received final IEEE approval on Dec. 6, 2001 was published on 8 April 2002,

was created in a two-year, open-consensus process by hundreds of engineers

from the world's leading operators and vendors.

     IEEE 802.16 addresses the "first-mile/last-mile" connection in

wireless metropolitan area networks.  It focuses on the efficient use of

bandwidth between 10 and 66 GHz (the 2 to 11 GHz region will be added in

mid 2002) and defines a medium access control (MAC) layer that supports

multiple physical layer specifications customized for the frequency band of


     The 10 to 66 GHz standard supports continuously varying traffic levels

at many licensed frequencies (e.g., 10.5, 25, 26, 31, 38 and 39 GHz) for

two-way communications.  It enables interoperability among devices, so

carriers can use products from multiple vendors.  The draft amendment for

the 2 to 11 GHz region will support both unlicensed and licensed bands.

Telecommunications Choices

     Business-based telecommunications encompasses many options.  Major

businesses often access large-capacity, high-speed fiber optic networks for

broadband, converged services.  Less than five percent of commercial

structures worldwide are served by fiber networks, however, and extending

these networks with cable is costly and time consuming.

     Small businesses and home offices typically use lower-bandwidth wired

networks such as cable modem networks and DSL.  Cable systems are based on

residential cable TV infrastructure, so they are often not competitive in

serving business subscribers.  DSL is a copper-based method that typically

offers 128 kbps to 2 Mbps data services.  It faces many technical hurdles

and is limited in both bandwidth and range.

      DSL, cable and older wireless systems tend to have low upstream

bandwidth.  The same is true of another option, two-way satellite

transmission, which is still early in its life cycle.  While invaluable in

some rural areas, it has limited application in more populous locales due

to limited spectrum availability and high latency (i.e., a short time

between transmitted packets).

     Early BWA networks were costly and problematical and had limited

information capacity per channel. They were also inefficient in the use of

spectrum.  Current BWA systems offer true differentiated broadband services

at minimal cost.  They let thousands of users share capacity for data,

voice and video.  They also are scalable: carriers can expand them as

subscriber demand for bandwidth grows by adding channels or cells.

Quality of Service (QoS) in Broadband Wireless

     BWA networks use air as the transmission medium and so are affected by

temperature, humidity and obstructions such as vegetation or buildings.

This makes them less predictable than networks based on copper or glass.

IEEE Standard 802.16 recognizes this and includes mechanisms to make robust

links for PMP BWA systems with line-of-sight, obstructed line-of-sight, and

non line-of-sight transmission.

     Mechanisms in the WirelessMAN MAC provide for differentiated QoS to

support the different needs of different applications.  For instance, voice

and video require low latency but tolerate some error rate.  By contrast,

generic data applications cannot tolerate error, but latency is not

critical.  The standard accommodates voice, video, and other data

transmissions by using appropriate features in the MAC layer, which is more

efficient than doing so in layers of control overlaid on the MAC.

     Many systems in the past decade have involved fixed modulation.

Higher-order modulation in such systems offers higher data rates but

requires optimal links, while lower orders of modulation are more robust

but support lower data rates.  The new standard supports adaptive

modulation, effectively balancing different data rates and linkage quality.

The modulation method may be adjusted almost instantaneously for optimum

data transfer. Adaptive modulation allows efficient use of bandwidth and a

broader customer base.

     The standard also supports both frequency and time division duplexing

(FDD and TDD).  Frequency division duplexing (FDD), the legacy duplexing

method, has been widely deployed in cellular telephony.  It requires two

channel pairs, one for transmission and one for reception, with some

frequency separation between them to mitigate self-interference.

     TDD is a more efficient method in which data is sent and received in a

single channel.  It is especially valuable for data transmission and

Internet traffic in which the asymmetry can vary greatly over time.  TDD

allows efficient use of spectral resources by continuously adapting the

fractions of time dedicated to uplink and downlink traffic in order to meet

current traffic requirements.