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 <e...@comsec.com> wrote:
> On Thu, Mar 19, 2009 at 09:27:03AM -0700, Johnathan Corgan wrote:
> > 2009/3/19 w w <biscuitk...@gmail.com>:
> >
> > > 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
>
> @param bitrate: desired bitrate or None
> @type bitrate: number or None
> @param bits_per_symbol: E.g., BPSK -> 1, QPSK -> 2, 8-PSK -> 3
> @type bits_per_symbol: integer >= 1
> @param samples_per_symbol: samples/baud (aka samples/symbol)
> @type samples_per_symbol: number or None
> @param interp_rate: USRP interpolation factor
> @type interp_rate: integer or None
> @param converter_rate: converter sample rate in Hz
> @type converter_rate: number
>
> @returns 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
>
> @param bitrate: desired bitrate or None
> @type bitrate: number or None
> @param bits_per_symbol: E.g., BPSK -> 1, QPSK -> 2, 8-PSK -> 3
> @type bits_per_symbol: integer >= 1
> @param samples_per_symbol: samples/baud (aka samples/symbol)
> @type samples_per_symbol: number or None
> @param decim_rate: USRP decimation factor
> @type decim_rate: integer or None
> @param converter_rate: converter sample rate in Hz
> @type converter_rate: number
>
> @returns tuple (bitrate, samples_per_symbol, decim_rate)
> """
> return _pick_bitrate(bitrate, bits_per_symbol, samples_per_symbol,
> decim_rate, converter_rate, _gen_rx_info)
>
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