Re: [Discuss-gnuradio] 8-channel receiver

[Anisha Gorur]

Thanks Josh, that helps quite a bit! Our sampling frequency is not particularly fast, it will only be around 5 MS/S. Right now the send and receive frame size are still the defaults, 1472 for receive and 1444 for send. In the notes, it says "to improve receive latency, configure the transport for a smaller frame size", will this work for send latency as well? Also is there an equation I can use to determine what the best frame sizes would be, or should I just go with trial and error and use latency_test.cpp to determine if it has shifted? If you change the frame size, how much improvement in latency do you usually see?

Again, thank you so much.

-Anisha

On Fri, Sep 28, 2012 at 6:57 PM, Josh Blum <address@hidden> wrote:

On 09/28/2012 02:46 PM, Anisha Gorur wrote:
> Thanks Matt!
> Do you have any idea for what kind of latency we would expect? Also would

The dominating factor in latency here is the gigabit ethernet, this
tends to be around 100us. Here are a few notes about that:

http://files.ettus.com/uhd_docs/manual/html/transport.html#latency-optimization

> the data be routed through the host? My Radio, We only have a couple months

Normally the samples would all go to the host computer that configured
the USRP. It is possible to configure the USRP with one machine but send
the samples to an arbitrary network location:

http://files.ettus.com/uhd_docs/manual/html/usrp2.html#alternative-stream-destination

For that matter, there is nothing wrong with splitting up the USRP
configuration among several computers. It all depends how you plan on
using the data.

> to do this, but we have tried to synchronize USRPs before, so we are aware
> of some of the problems.

Anything in particular that I could help to clarify?

-josh

> Thanks,
> Anisha
>
> On Wed, Sep 26, 2012 at 3:51 PM, My Radio <address@hidden> wrote:
>
>> One should remember the extremes involved in syncing all USRP'S which will
>> lead to developing a new driver for USRP2.
>>
>> What about the your APP development time?. Are you interested in
>> developing new driver or app ?
>>
>>
>> On Thu, Sep 27, 2012 at 12:04 AM, Matt Ettus <address@hidden> wrote:
>>
>>> You can use a gigabit ethernet switch and put all the USRPs on there.
>>> You should be able to make USRPs send data to each other.  You will of
>>> course need to do work to get your algorithms into the FPGA.
>>>
>>> Matt
>>>
>>> On Wed, Sep 26, 2012 at 12:38 PM, Anisha Gorur <address@hidden>
>>> wrote:
>>>> I have a quick theoretical question. Is there any way to construct an
>>>> 8-channel receiver using 4 USRPS without data going through the host
>>>> computer? Basically some kind of way to daisy chain mimo cables (though
>>> I
>>>> know this is not possible), or at least get the same benefits you would
>>>> receive from daisy chaining mimo cables, without using a switch or
>>> network
>>>> connections.
>>>>
>>>> Thank you,
>>>> Anisha
>>>>
>>>>
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--
Anisha Gorur
Class of 2012
Electrical Engineering