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International Journal of Computer Applications (0975 – 8887)
Volume78– No.1, September 2013s
14
2.4GHz 5GHz 4.9GHz 3.65GHz 5.9GHz 60GHz
Figure 1: The 802.11 PHY Layer Amendments and Their Dependencies
2. PHY RELATED AMENDMENTS
Even though not interoperable, the DSSS and FHSS PHY
initially appeared to have same possibilities in the market.
Alike the FHSS PHY had a duplicate in the Home RF group
that proposed at integrated data and voice services. This
needed plain 802.11 with FHSS for transmission of data,
accomplished with a protocol for voice that was very similar
to the Digital Enhanced Cordless Telecommunications
standard. Neither 802.11 nor Home RF saw FHSS extensions,
despite ideas for a second generation Home RF occurred that
directed at 10 Mbps. In contradict, the high data-rate scheme
802.11b was originated in December 1997 and sustained the
data rates of the DSSS PHY to 11 Mbps. This induced
802.11b to eventually override FHSS, containing Home RF,
in the market. Figure 1 specifies a sketch of the 802.11 PHY
amendments and their dependencies [8].
2.1 IEEE 802.11a
The first extension scheme, IEEE 802.11a was introduced in
September 1997. It included an OFDM (Orthogonal
Frequency Division Multiplexing) PHY that supports speeds
up to 54 Mbps. Communication with plain 802.11 devices is
impossible, as 802.11a conducted in the 5 GHz band . This
deficiency of interoperability forced to the formation of
802.11g, which carried the advantages of OFDM to the 2.4
GHz band.
Table 2 shows the physical layer parameters of the IEEE
802.11a.
Table 2: The IEEE 802.11a Physical Layer Parameters
Data
Rate
(Mb/s)
Modul-
ation
Coding
rate
( R)
Coding Bits
Per
Subcarrier
(N
BPSC
)
Coded
Bits per
OFDM
symbol
(N
CBPS
)
Data
Bits Per
OFDM
Symbol
(N
DBPS
)
6
BPSK
1/2
1
48
24
9
BPSK
3/4
1
48
36
12
QPSK
1/2
2
96
48
18
QPSK
3/4
2
96
72
24
16-
QAM
1/2
4
192
96
36
16-
QAM
3/4
4
192
144
48
64-
QAM
2/3
6
288
192
54
64-
QAM
3/4
6
288
216
FHSS
DSSS
OFDM
OFDM (To be
defined)
802.11
802.11a
HR/DSSS
802.11b
802.11g
802.11i
802.11-2007
MIMO
802.11n
802.11v
802.11p
802.11-2011
802.11ac
802.11ad