Re: [Discuss-gnuradio] Simple digital data transmitter

[Tom Rondeau]

On Thu, May 13, 2010 at 1:18 AM, marcin_w <address@hidden> wrote:
>
>
> Eric Blossom wrote:
>>
>> Your baseband sample rate is 100M/32 -> 3.125MS/s
>>
>> You're using 2 samples/symbol, thus your symbol rate is
>>   3.125MS/s / 2 -> 1.5625Msymbols/s
>> And since you're using DBPSK, you're getting 1 bit/symbol, thus your
>> raw over-the-air bit rate is 1.5625Mbit/s
>>
>
> Hi Eric, a quick question about this.
>
> According to:
>  _pick_bitrate(bitrate, bits_per_symbol, samples_per_symbol, xrate,
> converter_rate, xrates, gen_info) in pick_bitrate.py
>
> when the samples per symbol and interpolation are given, then our bitrate
> can be determined straight away.
> i.e Bitrate = converter_rate / xrate / samples_per_symbol
>
> Is this correct though, in determining the bitrate for both dbpsk & dqpsk?
> For instance if we passed the_pick_bitrate() function an interpolation of
> 128 and Samples/symbol of 2, then according to the code, our bit rate for
> both dqpsk and dbpsk will be 500kbs.
>
> But according to what your saying:
> 1) for dbpsk
>
> if DAC rate = 128e6  Interpolation = 128  Samples/symbol = 2
> Bitrate = 128e6 / 128 / 2 = 500k
>
> 2) for dqpsk
>
> Using the same parameters
> Bitrate = 128e6 / 128 / 2 / 2bits per symbol = 256K
>
> Have i missed something here, or in the code?
>
> Regards,
>
> Marcin


This does appear to be a bug. That calculation in pick_bitrate.py
should also be divided by bits_per_symbol.

Tom