Service manual

WLAN TX Measurements
R&S
®
FSV-K91/91n/91ac/91p
23Operating Manual 1176.7649.02 ─ 04
First the FFT of the LS is calculated. After the FFT calculation the known symbol infor-
mation of the LS sub-carriers is removed by dividing by the symbols. The result is a
coarse estimate Ĥ
k
of the channel transfer function.
In the next step the complex channel impulse response is computed by an IFFT. Next
the energy of the windowed impulse response (the window size is equal to the guard
period) is calculated for every trial time. Afterwards the trail time of the maximum
energy is detected. This trial time is used to adjust the timing.
Now the position of the LS is known and the starting point of the useful part of the first
payload symbol can be derived. In the next block this calculated time instant is used to
position the payload window. Only the payload part is windowed. This is sufficient
because the payload is the only subject of the subsequent measurements.
In the next block the windowed sequence is compensated by the coarse frequency
estimate Δ
course
. This is necessary because otherwise inter channel interference (ICI)
would occur in the frequency domain.
Signal Processing of the IEEE 802.11a Application