[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: a.ortiz@ieee.org >< www.standards.ieee.org
FOSTERING TECHNOLOGICAL INNOVATION
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o.ieee.org Subject: 802 news IEEE 802.16 Backgrounder
05/14/2002 11:41 AM
IEEE-SA News
IEEE 802.16 Backgrounder
Contact: Roger Marks,
303 497 3037, marks@nist.gov
or
Dean Chang,
408 719 9977, dchang@apertonet.com
or
Karen McCabe
732 562 3824, k.mccabe@ieee.org
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
use.
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.
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