Re: [Discuss-gnuradio] Benchmark_tx/rx does not work below 500k bitrate

[Srinivas]

I faced the same issues and my findings on this was:

•Empirically:
 for Reliable transmission 120 Kbps <= Br (data rate) <= 2 Mbps (For
GMSK, Pkt. Size = 1500)

•Theoretically:

- Maximum Bit rate corresponds to Minimum Decimation Rate and min.
samples/symbol value
- ADC Sampling Rate = 100 MSamples/Sec
- Min. Decimation Factor (D) =4,  Min. Samples/Symbol (S) = 2
- Maximum bitrate = ADC rate / (D * S) = 12.5 Mbps

However the host computer is not fast enough to generate samples at
this rate and therefore the practical max. is limited to 2 - 5 Mbps

•Minimum Bit rate corresponds to Max. Interpolation and Max Samples/Sym
- DAC Sampling Rate = 400 Msamples/Sec
- Max. Interpolation Factor (I) = 512, Max Samples/Symbol (S) = 7
- Minimum bit rate = DAC rate /(I * S) = 111.6 Kbps

which more or less confirms with the empirical minimum

Srinivas
Graduate Student
WINLAB, Rutgers University

On Sat, Aug 22, 2009 at 2:12 AM, udadidd<address@hidden> wrote:
>
> hi
> I tried setting the bit rate of benchmark_tx/rx below 500k and the receiver
> senses no messages below this rate. Is there any specific reason why is it
> so? I use xcvr2450 boards. and i transmit at 5.1G.
>
> Thanks
> Udaya
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