What is 802.11a?
802.11a is a high speed wireless LAN physical layer standard in the
5 GHz Unlicensed
National Information Infrastructure (U-NII) band. 802.11a was
almost simultaneously launched with 802.11b, in late 1999. It also
provides higher data rates than 802.11b, upto 54 Mbps.
About the technology
standard uses Orthogonal Frequency Division Modulation (OFDM) at the
PHY layer to provide higher data rates. OFDM has excellent resistance
to multipath fading, while also providing high data speeds.
Each channel has the same bandwidth as in the 802.11b standard, 20
MHz. The overall system bandwidth is 300 MHz, which is divided into
three 100 MHz bands, each with its own permissible power levels. Each
20 MHz channel contains 52 subcarriers of 300 kHz each. The standard
specifies variable data rates of 6, 9, 12, 18, 24, 36, 48 and 54 Mbps,
of which 6, 12, and 24 Mbps are mandatory. To allow variable data
modulation technique can also be varied among
BPSK, QPSK, 16-QAM and 64-QAM, coupled with
variable coding rates of 1/2, 2/3 and 3/4.
layer in this standard, however, is the same employed by 802.11b,
Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) with RTS
and CTS signals.
802.11a in the market
GHz U-NII band is relatively clear of other interfering sources, which
is not the case in the 2.4 GHz band. The 2.4 GHz band has BluetoothTM,
personal cordless phones and a host of other interfering
sources which greatly reduce the environments and the range of
operation of 802.11b networks. This however is not the case in
802.11a. Currently all those places which have not implemented
wireless LAN (or 802.11b) can look to 802.11a as their solution as it
provides higher speeds with less interference.