Re: [Discuss-gnuradio] /gnuradio-examples/python/digital/transmit_path.py and bitrate Question?

[w w]

What's confusing for me is that I see the bitrate variable (it seems to have a profound importantance) but it looks to me like it never gets assigned to a block.   The following is line 119 from transmit_path.py.  In my mind the function of lines 119-121,  is to assign/derive values for bitrate, interp and SPS from pick_tx_bitrate.....Is this correct?   Of course it looks like bitrate stays the same unless it goes above 4 mbs.  

I don't see where the bitrate is being assigned  to either the packet transmitter or the modulator (which seems to me the most logical place to use bitrate).   I see where interpolation is being set for the usrp and I also see where sample per symbol is being used in various places.   With my mind looking from all angles, the only thing I come up with is that interpolation is being used to control bitrate...but that don't make sense.  

 

Where I'm going astray?

 

Cheers,

Jody

 

# derive values of bitrate, samples_per_symbol, and interp from desired info

      (self._bitrate, self._samples_per_symbol, self._interp) = \

                                   pick_tx_bitrate(self._bitrate, self._modulator_class.bits_per_symbol(),

                                   self._samples_per_symbol, self._interp, dac_rate)

 

 

      self.u.set_interp_rate(self._interp)

On Thu, Mar 19, 2009 at 1:38 PM, Eric Blossom <address@hidden> wrote:

On Thu, Mar 19, 2009 at 09:27:03AM -0700, Johnathan Corgan wrote:
> 2009/3/19 w w <address@hidden>:
>
> > I've been trying to analyse the transmit_path.py script and stumped with the
> > bitrate value.   I see bitrate being brought in from the options and also
> > derived from pick_bitrate but I don't see where somthing is being done with
> > it.
>
> It is assigned in transmit_path.py, line 119.
>
> It is used in tunnel.py, line 255.
>
> The bitrate is a derived variable, mostly for display to the user,
> though tunnel.py warns if the TX and RX sides don't match.

The possibly confusing part is that if the user specifies the bitrate,
we'll derive the other related values.  It's basically a constraint
satisfaction problem.

Eric


From pick_bitrate.py:


def pick_tx_bitrate(bitrate, bits_per_symbol, samples_per_symbol,
                   interp_rate, converter_rate=128e6):
   """
   Given the 4 input parameters, return at configuration that matches

  address@hidden bitrate: desired bitrate or None
  address@hidden bitrate: number or None
  address@hidden bits_per_symbol: E.g., BPSK -> 1, QPSK -> 2, 8-PSK -> 3
  address@hidden bits_per_symbol: integer >= 1
  address@hidden samples_per_symbol: samples/baud (aka samples/symbol)
  address@hidden samples_per_symbol: number or None
  address@hidden interp_rate: USRP interpolation factor
  address@hidden interp_rate: integer or None
  address@hidden converter_rate: converter sample rate in Hz
  address@hidden converter_rate: number

  address@hidden tuple (bitrate, samples_per_symbol, interp_rate)
   """
   return _pick_bitrate(bitrate, bits_per_symbol, samples_per_symbol,
                        interp_rate, converter_rate, _gen_tx_info)


def pick_rx_bitrate(bitrate, bits_per_symbol, samples_per_symbol,
                   decim_rate, converter_rate=64e6):
   """
   Given the 4 input parameters, return at configuration that matches

  address@hidden bitrate: desired bitrate or None
  address@hidden bitrate: number or None
  address@hidden bits_per_symbol: E.g., BPSK -> 1, QPSK -> 2, 8-PSK -> 3
  address@hidden bits_per_symbol: integer >= 1
  address@hidden samples_per_symbol: samples/baud (aka samples/symbol)
  address@hidden samples_per_symbol: number or None
  address@hidden decim_rate: USRP decimation factor
  address@hidden decim_rate: integer or None
  address@hidden converter_rate: converter sample rate in Hz
  address@hidden converter_rate: number

  address@hidden tuple (bitrate, samples_per_symbol, decim_rate)
   """
   return _pick_bitrate(bitrate, bits_per_symbol, samples_per_symbol,
                        decim_rate, converter_rate, _gen_rx_info)