Service manual

WLAN TX Measurements
R&S
®
FSV-K91/91n/91ac/91p
30Operating Manual 1176.7649.02 ─ 04
ŝ
n
(v) estimate of the power normalized and undisturbed reference signal
REAL{...} calculation of the real part of a complex value
IMAG{...} calculation of the imaginary part of a complex value
3.4.1 Understanding Signal Processing of the IEEE 802.11b Application
A block diagram of the measurement application is shown below in figure 3-2. The
baseband signal of an IEEE 802.11b wireless LAN system transmitter is sampled with
a sampling rate of 44 MHz.
The first task of the measurement application is to detect the position of the bursts
within the measurement signal r
1
(v). The detection algorithm is able to find the posi-
tions of the beginning of short and long bursts and can distinguish between them. The
algorithm also detects the initial state of the scrambler. This is required if IEEE 802.11
signals should be analyzed, because this standard does not specify the initial state of
the scrambler.
With the knowledge of the start position of the burst, the header of the burst can be
demodulated. The bits transmitted in the header provide information about the length
of the burst and the modulation type used in the PSDU.
After the start position and the burst length is fully known, better estimates of timing off-
set, timing drift, frequency offset and phase offset can be calculated using the entire
data of the burst.
At this point of the signal processing a demodulation can be performed without deci-
sion error. After demodulation the normalized and undisturbed reference signal s(v) is
available.
If the frequency offset is not constant and varies with time, the frequency- and phase
offset in several partitions of the burst must be estimated and corrected. Additionally,
timing offset, timing drift and gain factor can be estimated and corrected in several par-
titions of the burst. These corrections can be separately switched off in the "Demod
Settings" menu.
Signal Processing of the IEEE 802.11b Application