Teledyne LeCroy QPHY-UWB - Manual (Page 16)

16
QPHY-UWB-OM-E Rev C
POWER SPECTRAL DENSITY (PSD) ANALYSIS
The power spectral density analysis does the following:
1. Performs a packet detect to identify and isolate the individual packets
2. For each packet:
o Performs a correlation on the sync preamble of the packet with the expected preamble symbols to
determine a first order timing reference and frequency offset.
o Use timing information to determine exact locations of symbols.
o For each symbol in each band perform an FFT and smooth FFT results to a resolution Bandwidth of
5 MHz.
3. For each band, sum the FFT spectra from all the symbols in that band to get the spectrum averaged over all
the symbols.
4. For each band in the band group, plot the spectrum (power spectral density). The spectrum is normalized by
setting the highest value to 0 dB.
Two tests are available on the calculated power spectra. The first is the mask test, which looks for violations of the
power spectral density with respect to masks that are defined in the “WiMedia PHY Compliance and
Interoperability Test Specification” (C&I specification). The mask test roughly tests that any out-of-band frequency
bin in the band group must be at least 20 dB below the highest active in-band bin. Things are a bit more
complicated in the transition zones. As said before, the details are found in the WiMedia C&I specification. The
second test is the Adjacent Channel Power Ratio (ACPR) test which calculates the ratio of the total in-band power
to the total out-of-band power for each of the 2 inactive bands in the band group. This yields 2 numbers for each
active band. So for a TFI (Time Frequency Interleave) mode like TFC 1 there will be 6 ACPR results, and for an
FFI (Fixed Frequency Interleave) mode like TFC 5, there will only be 2 ACPR results. The ACPR lower limits are
20 dB.