Re: [Discuss-gnuradio] Re: Further explain about receiving packets using 2 daughter

[Matt Ettus]

William Sherman wrote:
> William Sherman wrote:
> > Ok the problem was I set my decimation too high (256), even though on 
> > the faq it says I can go [8, 256]. I tried it with 128 and it worked.
>
>
> Yet I am able to receive packets generated by my own usrp (usrp 
> transmits and receives its own packet) correctly. Does performance of 
> dbpsk modulation decrease with increased decimation so that a packet 
> generated from another usrp some distance away has really bad 
> performance?


Under ideal conditions, the lower the bit rate, the better the 
performance should be.  However, real radios have a frequency offset. 
When you lower the data rate (i.e. increase the decimation rate), the 
same absolute frequency offset in Hz will look like a bigger and bigger 
fraction of the signal bandwidth.  If you lower the signal bandwidth 
enough, the frequency error might put the signal completely out of the 
receiver bandwidth.

The normal way to solve this is to add an algorithm that will scan the 
receiver frequency in order to find signals.  The gnuradio examples do 
not do this.  Thus, you will sometimes find that you get better 
performance at higher data rates than you get with lower data rates.

Matt