Rohde & Schwarz R&S FSL3 - WLAN TX Measurements (Option K91;K91 N); Signal Processing of the IEEE 802.11 A Application; Abbreviations

R&S FSL WLAN TX Measurements (Option K91)
1300.2519.12 2.129 E-11
WLAN TX Measurements (Option K91/K91n)
This section describes measurement examples for the WLAN TX Measurements option (K91) and gives
details to signal processing. For further information on measurement examples refer also to the Quick
Start Guide, chapter 5 "Basic Measurement Examples".
This option is available from firmware version 1.20. The option R&S FSL-K91n is available from firmware
Signal Processing of the IEEE 802.11a application
Abbreviations
kl
a
,
symbol at symbol l of sub carrier k
k
EVM
error vector magnitude of sub carrier
k
EVM
error vector magnitude of current packet
g
signal gain
f
frequency deviation between Tx and Rx
l
symbol index
]_,1[ Symbolsnofl
=
symbolsnof _
number of symbols of payload
k
H
channel transfer function of sub carrier k
k
channel index ]32,31[=k
mod
K
modulation dependant normalization factor

relative clock error of reference oscillator
kl
r
,
sub carrier k of symbol l
This description gives a rough view of the IEEE 802.11a application signal processing. Details are
disregarded in order to get a concept overview.
A diagram of the interesting blocks is shown in Fig. 2-87 First the RF signal is down converted to the IF
frequency
=
IF
f 20.4 MHz. The resulting IF signal )(tr
IF
is shown on the left–hand side of the figure. After
bandpass filtering, the signal is sampled by an Analog to Digital Converter (ADC) at a sampling rate of
=
1s
f 81.6 MHz. This digital sequence is resampled to the new sampling frequency of =
2s
f 80 MHz which is
a multiple of the Nyquist rate (20 MHz). The subsequent digital down converter shifts the IF signal to the
complex base band. In the next step the base band signal is filtered by a FIR filter. To get an idea, the rough
transfer function is plotted in the figure. This filter fulfills two tasks: first it suppresses the IF image frequency,
secondly it attenuates the aliasing frequency bands caused by the subsequent down sampling. After filtering,
the sequence is sampled down by the factor of 4. Thus the sampling rate of the down sampled sequence
)(ir is the Nyquist rate of =
3s
f 20 MHz. Up to this point the digital part is implemented in an ASIC.
version 1.90.