Questions regarding USRP N200 streaming

Hi,
I am working on a USRP project. I am using a USRP N200 with a BasicRX
daughter board to perform data streaming. I am using GRC 3.6.4.1 on a
Ubuntu 12.04 machine. The USRP N200 is set to have a decimation factor
of 8
to achieve a streaming rate of 12.5 MSPS, the daughter board is set to
A:A
to perform single channel real sampling. The I Q data wire format is set
to
be 16 integer each, and the host data format is set to be complex float
32.
The settings above are also in the attachments. For analyzing data, I am
using Matlab R2013b on Windows 7. My question is: when I am streaming
data
for about 10 seconds, I am getting a file around 500,000,000 bytes which
is
reasonable ((16 bits/sample I+16 bits/sample Q)*(10 seconds)12.5
MSPS
(1/8
bytes/bits)=500 Mbytes), but when I use read_complex_binary.m provided
by
GNUradio to read the file in Matlab, I am only getting half of the
expected
samples (~62,500,000 samples) instead of 125,000,000 samples. Could
anyone
please explain why this is happening? Doesn’t 16 bits I and 16 bits Q
wire
format give me 32 bits per sample? Any help would be appreciated.

Hi Marcus,

Thank you for your explanation. It is clear to me now.

Nicholas

On 09/16/2014 04:57 PM, Nicholas Hu wrote:

getting a file around 500,000,000 bytes which is reasonable ((16
Discuss-gnuradio mailing list
[email protected]
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Nick, I think I answered this at [email protected] last night.

But, you’re flowing complex-floats into your file-sink. That’s 64-bits
per sample (32-I 32-Q). The wire-format and CPU format a different
things.

A UHD source will translate to complex-float, because that’s the
“natural” format within Gnu Radio flow-graphs, but you can also ask it
to use
complex-int16 on the “host format” side, if you’re just saving to a
file.

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