Service manual

WLAN TX Measurements
R&S
®
FSV-K91/91n/91ac/91p
36Operating Manual 1176.7649.02 ─ 04
3.6 IEEE 802.11n/ac MIMO Measurements
For measurements according to the IEEE 802.11n or ac standard, the R&S FSV can
measure multiple data streams between multiple transmitters and multiple receivers
(MIMO = multiple in, multiple out).
To understand which results come from which part of the data flow it is sensible to
have a look at the fundamental processing in transmitter and receiver. The following
figure shows the basic processing steps needed at the transmitter and the complemen-
tary blocks in reverse order applied at the receiver:
Fig. 3-3: Transmitter-Receiver block diagram
Especially of interest is the representation of specific results, i.e. for which sections of
the processing the results are shown. Usually results are calculated according to par-
ticular signal processing steps in the transmitter (except for the results “Burst Power”
and “Crest Factor” which refer tor the receive antennas):
Fig. 3-4: Possible results and Channel Representation (effective / physical)
For example EVM and Constellation results are calculated according to the spatial or
space time streams in the transmitter, i.e. by using the effective channel which includes
the spatial mapping. Since Space Time Block Encoding is only applied to data carriers
but pilot carriers are inserted without STBC, the EVM analysis is applied to spatial
streams (STBC decoded) for data carriers and to space time streams for pilot streams.
As a consequence we might get results (EVM and Constellation) for a different number
of streams for data and pilot carriers if STBC is applied. For example using 2x2 MIMO
with active STBC we get only pilot carriers in the second stream, because due to
STBC there is only one spatial (data) stream but 2 space time (pilot) streams.
IEEE 802.11n/ac MIMO Measurements