Re: [Discuss-gnuradio] Problem with underruns

[Andy Walls]

> Hi Sverre,
> 
> hm, I've taken the time to look at pulse_shaper_bs.py[1], but I didn't
> fully understand what it does, mathematically/technically. 
> 
> 
> 
> It does in fact look like a very complicated way to do something that
> I'm not 100% sure wouldn't be covered by a simple FIR filter, but
> lacking a bit of documentation, and not finding the time to go into
> all the if()-cases right now, can you explain what it does? 

Hi Marcus:

The pulse shaper bs block looks like an MSK I or Q bit to half-sine
pulse convertor, which one would use when generating MSK as an Offset
QPSK with half-sine shaped pulses.
Definitely the hard way to generate MSK, when using FSK with square
pulses is much easier.

The pulse shape block seems fairly inflexible WRT sample rate, and is
using integers - as if it were a prototype for an FPGA implementation.

Sverre,
The whole block would be much faster in C++ instead of python.
If it is just straight MSK that you need to generate, just use a repeat
block followed by a frequency modulator block and then a filter block to
limit the occupied bandwidth.

I'm not that familiar with DSRC, but that's an odd pulse shaping for ASK
(ASK usually has no pulse shaping).  Also ASK is usually horrible for
anything but the simplest remote functions.  Is another aspect of the
system that uses PSK or FSK?

-Andy

> You told me the bit rate, but not the sampling rate of the USRP sink,
> but that would be very relevant here!
> 
> Best regards,
> Marcus 
> 
> [1]
> https://github.com/sverrets/dsrc/blob/master/gr-dsrcmod/python/pulse_shaper_bs.py
> On 03/17/2017 01:04 PM, Sverre Turter Sandvold wrote:
> 
> > Hi, thank you for answering!
> > 
> > 
> > I'm using a USRP N200 with a CBX daughterboard. 
> > 
> > 
> > 
> > I think the problem is that the block "pulse_shaper_bs" is not
> > processing fast enough, and then the USRP Sink don't receive data
> > fast enough and this causes the underrun. 
> > 
> > 
> > 
> > I want to send a packet with bits to a DSRC-unit. The main specs
> > are:
> > 
> >       * Carrier Frequency: 5,8025 GHz
> >       * Modulation: Two level amplitude modulation
> >       * Data Coding: FM0
> >       * Bit rate: 500 kbit/s
> > 
> > SverreTS
> > 
> > 
> > 
> > 
> > 
> > ____________________________________________________________________
> > Fra: Discuss-gnuradio <address@hidden> på vegne av Marcus Müller
> > <address@hidden>
> > Sendt: 16. mars 2017 19:38
> > Til: address@hidden
> > Emne: Re: [Discuss-gnuradio] Problem with underruns 
> >  
> > Hi SverreTS,
> > 
> > 
> > can you be more specific? Why do you think it's the problem? Can you
> > give us a rough idea of what your program does? At which rates are
> > you working, with which hardware, and so on.
> > 
> > 
> > 
> > Best regards,
> > 
> > Marcus
> > 
> > 
> > 
> > On 03/16/2017 01:52 PM, Sverre Turter Sandvold wrote:
> > 
> > > Hi!
> > > 
> > > 
> > > Need some help with this gnuradio-block called "pulse_shaper_bs":
> > > https://github.com/sverrets/dsrc/blob/master/gr-dsrcmod/python/pulse_shaper_bs.py
> > >  used in this program:  https://github.com/sverrets/dsrc . I got alot of 
> > > underruns and think the "pulse_shaper_bs" is causing the problem. 
> > > 
> > > 
> > > 
> > > Anyone want to help?
> > > 
> > > 
> > > SverreTS
> > > 
> > > 
> > >