Re: [Discuss-gnuradio] RFX2400+USRP buffers

[Eric Blossom]

On Thu, Sep 11, 2008 at 01:59:39AM -0700, kaleem ahmad wrote:
> 
> Any ideas or comments will be helpful for me and I am anxiously waiting!!!.
> 
> Kaleem Ahmad
> 
> kaleem ahmad wrote:
> > 
> > Hello everyone,
> > 
> > I am trying to implement a simple FSK system to measure bit error rate
> > (BER), and packet loss rate (PLR) using:
> > 
> > 1-Linux
> > 2-USRP motherboard
> > 3-RFX2400 daughter card
> > 
> > I want to implement an echo back system where one Transceiver (say Master)
> > will transmit a small frame (let say 48 byte, and important thing is that
> > I neccessarily need small payload) to other transceiver (say Slave). The
> > Salve returns the frame immediatelly without any processing to Master  and
> > Master measures BER and PLR.
> > 
> > The problem which I am facing is that I am unable to transmitt such small
> > packets. I have noticed that if I have a large file with let say few
> > Kbytes contents then it is transmitted (partially, the end of file is
> > always missing...I guess it is stuck somewhere in buffer????) but if I
> > have such small packets as I metioned earlier then most of the time the
> > packets are lost. If the packet is received then it is totally corrupt
> > (say almost 100% BER) unlike large files which are received in very good
> > quality (But important and notable point is that even the large files are
> > 100% courrupt at the end). This makes me wonder why last few hundered
> > bytes are always courrupt??? (for small file the whole file lies in that
> > category of last few hundered bytes)

Kaleem, until the inband code is completely sorted out, you'll need to
ensure that the number of samples generated for your burst always ends
up as a multiple of 512 bytes on the USB.  We use 16-bit I & Q on the
USB, so if you're using complex baseband, you need to make sure that
you're sending a multiple of 128 samples.  This includes any frame
synchronization header, the payload, crc, etc.

Eric