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

[Eric Blossom]

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

    @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)