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Re: [Discuss-gnuradio] Data Rate is doubled after receiving data from US

From: Muhammad Munir
Subject: Re: [Discuss-gnuradio] Data Rate is doubled after receiving data from USRP
Date: Wed, 3 Jan 2018 18:42:46 +0500

Thank Kyeong Su Shin.
Is there any chance of loosing information if I convert complex data back to 16bit as you suggested? I think it would loose information?


On Wed, Jan 3, 2018 at 12:16 PM, Kyeong Su Shin <address@hidden> wrote:
Hello M.Munir,

By default, USRP gives you data in 16bit integer format (x2, for I and Q). GNU Radio's complex data type uses IEEE754 single precision (x2, for I and Q). The data type is converted by UHD (the USRP driver). Each IEEE754 data point requires 32bit of storage (or memory, bandwidth, etc). This is why the data size is doubled.

You can set the UHD block to output the raw int16 (interleaved) data, or you can convert back the GNU Radio's complex data type to a int16 based format and then send them over TCP (*make sure that you re-scale the I-Q data, as the complex data is normalized to [0,1] by UHD). 

Kyeong Su Shin

On Wed, Jan 3, 2018 at 2:25 PM, Muhammad Munir <address@hidden> wrote:
Dear All,
I am confused to understand a behavior of GNURADIO USRP Source block. The problem is,
1. I connected USRP N200 with my PC.
2. I set both the cahnnels of USRP
3. I set the sampling rate of both as 5MHz
4. I connected one channel directly to the Frequency Sink Block
5. I connected the 2nd channel with TCP sink to transfer data of channel 2 to the other PC.
6. When I started the flow graph and checked for data rate on system monitor,
 I was receiving data at 40MBps and sending data was at 80 MBps.
Can anyone explain this behaviour? 
Is it the issue with Gnuradio USRP source block? 
I read a long before that UHD block gets samples from USRP and combine two samples into single for comples output. If it is, then It should not affect the data rate?

Kind Regards,
M. Munir

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