Digital Signal Processing Reference
In-Depth Information
Output power [dBW]
RF p
o
wer a
m
plifie
r
Third-order interception point
OIP
3
1dB compression point
~8dB
P
out, avg
noise floor TX DAC
power back-of
f
9.6dB
P
in, avg
P
in, 1dBc
IIP
3
Input power [dBW]
Probability density P
in
(simulation 1Mbit)
PAPR~8dB
0.15
0.10
0.05
0
P
in, avg
P
in
+10dB
P
in
-20dB
P
in
-10dB
Input power [dBW]
Figure 1.6.
The
bottom
graph shows the power PDF of an wlan transmission with
52 active subbands. The peak power of the rf amplifier (
top
)is8dB
higher than the average output power.
This is also why, although the 802
.
11a standard was ratified in 1999, difficulties
in the implementation of the 5 GHz analog front-end have delayed the avail-
ability of compatible products until 2003. In the mean time, the 802
.
11g stan-
dard was brought to life, as a transitional solution between the older 802
.
11b
devices and the new 802
.
11a system.
Basically, 802
.
11g uses the same digital baseband subsystem as 802
.
11a, but
the latter one is deployed in the 2
.
4 GHz band.
10
The conclusion is that the changeover to a more intelligent baseband modula-
tion algorithm (ofdm) has solved the issue of the non-ideal characteristics of
10
Unfortunately, apart from offering much less available frequency space than the 5 GHz band, the 2
.
4 GHz
band is also crowded with other users such as the older 802
.
11b wlan network, Bluetooth devices and
interference from microwave ovens [Kam97].
