I have been doing some channel sounding measurements with the USRP,
and there is something that I am not sure about.
- The gr-sounder default transmit amplitude is 4096, is there a
particular reason why this number is chosen? My guess is because a 12-
bit DAC is used.
- All my measurements were conducted with RFX 2400 d’board, and the
d’board is connected directly to a spectrum analyzer, the measured
output power levels are listed below:
128: -28 dBm
256: -23 dBm
512: -17 dBm
1024: -11 dBm
2048: -6 dBm
4096: 1 dBm
so far so good(roughly 6dB step when I double the tx amplitude), and
all signals cover 32MHz bandwidth, but when I change --tx-amplitude
to 8192, it gave me a spike at the center frequency with very narrow
bandwidth, the power measured is about 11 dBm, any tx amplitude value
greater than 8192 yields a small power (-61dBm) with 32MHz bandwidth.
I am sure this has something to do with the DAC and PA, but not sure
exactly how to explain it.
- I did a indoor measurement with TX-RX separation of 50 meters (w/
LOS), the received channel impulse response has 5 chunks of CIRs
instead of one, and the number of samples between each chunk is
always 800 chips, I am sure those CIRs are not multipath delays since
in an indoor environment the corresponding delays can’t be 800-chips
apart from each other(way too long). Am I missing something here?
Thanks in advance for any help.