[Top][All Lists]

 From: Lee Patton Subject: Re: [Discuss-gnuradio] Bandwidth Across USB Date: Wed, 05 Apr 2006 20:54:43 -0400

```John -

I must have been drunk when I wrote those equations. I wrote 64e10 when
I meant 64e6, and put the D in a weird place. Sorry for any confusion.
This makes more sense:

(16 bit/sample)*(64e6/D sample/sec)*(1/2^23 MB/bit) <= 32 MB/sec

therefore, for real

D >=   16*64e6/(32*2^23) = 3.81 --> D = 4

and for complex

D >= 2*16*64e6/(32*2^23) = 7.63 --> D = 8

On Wed, 2006-04-05 at 17:46 -0400, Lee Patton wrote:
> Hi John -
>
> 16/D bits/sample x 64e10 samples/sec x 1 B/8 bits x 1 MB / 2^20 B <= 32
> MB/sec
>
> Therefore,
>
> D >= 16*64e10 /(32*8*2^20) = 3.814 -> 4
>
> So, if you want to transmit twice as many sample across the bus...
>
> D > = 2*16*64e10 /(32*8*2^20) = 7.63 -> 8
>
> ...you have to halve your sampling frequency.
>
> Are you aware that there is a -8 option in some of the scripts that
> allows you to send 8 bits instead of 16.
>
> Hope that helps,
>  - Lee
>
>
>
> ----- Original Message -----
> Date: Wednesday, April 5, 2006 5:31 pm
> Subject: [Discuss-gnuradio] Bandwidth Across USB
>
> >
> > I know this is probably an extremely stupid question, but I wanted
> > to get
> > some verification.  I've noticed that the minimum decimation rate
> > you can
> > use in all of the sample programs is 4 (giving you an effective
> > samplingrate of 16 MHz).  If you are transmitting 1 real channel of
> > data (16 bits)
> > at this rate, that seems to be maxing out the USB transfer rate of
> > 32 MB/s.
> > Am I correct in my deduction that you need to use a decimation rate
> > of at
> > least 8 in order to transmit complex data (such as for FM
> > demodulation)successfully across the USB?  Thanks.
> >
> > Thanks,
> > John
> > --
> > View this message in context: http://www.nabble.com/Bandwidth-
> > Across-USB-t1402318.html#a3773742
> > Sent from the GnuRadio forum at Nabble.com.
> >
> >
> >
> > _______________________________________________
> >
>
>
> _______________________________________________