The Institute of Electrical and Electronics Engineers (IEEE) this week passed a key amendment to a standard which may open the floodgates for the
creation of wireless metropolitan area networks (MANs).
On Wednesday, the IEEE approved 802.16a, an amendment to the IEEE Standard
802.16-2001, which the standards body approved in April 2002.
The original standard specifies the WirelessMAN-SC air interface, a
single-carrier (SC) modulation scheme designed to operate in the 10-66 GHz
spectrum. That spectrum supports continuously varying traffic levels at
many licensed frequencies (including 10.5, 25, 26, 31, 38 and 39 GHz) for
two-way communications. This opens the door for the creation of fixed
Broadband Wireless Access (BWA), which could provide network access support
to buildings with speeds that approach those offered by high-speed fiber
optic networks.
While fiber is plentiful on the backbone, it is much more rarified at the
network access level. The IEEE said less than 5 percent of commercial
structures worldwide are served by fiber networks, largely due to the
expense and time involved in extending fiber networks. With 802.16, the
IEEE hopes to open the doors for thousands of users to share capacity for
data, voice and video, while giving carriers a scalable solution that they
can easily grow as subscribers demand more bandwidth.
In the 802.16 vision, carriers would set up base stations connected to a
public network. Each base station would support hundreds of fixed
subscriber stations, probably mounted on rooftops. The base stations would
then use the standard’s medium access control layer (MAC) — a common
interface that makes the networks interoperable — to nearly
instantaneously allocate uplink and downlink bandwidth to subscribers
according to their needs.
Conceivably, 802.16 MANs could anchor 802.11
which serve as wireless local area networks (LANs), as well as servicing
end-users directly.
However, the 10-66 GHz spectrum is strictly line-of-sight. That’s where the
802.16a amendment comes in. The amendment addresses the low-frequency 2-11
GHz spectrum, some of which is unlicensed, and which allows for
non-line-of-sight operation.
The new 802.16a standard defines three physical layer modes. It retains the
single-carrier access method for special-purpose networks, but adds a
256-carrier orthogonal frequency division multiplexed
OFDM, layer which splits the radio signal into multiple smaller sub-signals
that are then transmitted simultaneously at different frequencies to the
receiver, allowing for the transmission of large amounts of digital data
and reducing multipath (reflections of a signal — caused when the signal bounces off metal obstructions — which can create interference). The standard also defines a
2,048-carrier OFDMA, or orthogonal frequency division multiple access, layer, which offers advanced multiplexing in tiered
MANs and supports selective multicast applications.