Re: [Discuss-gnuradio] 8-channel receiver

[Anisha Gorur]

Thank you very much again!

On Sun, Sep 30, 2012 at 6:22 PM, Josh Blum <address@hidden> wrote:

On 09/29/2012 09:46 AM, Anisha Gorur wrote:
> 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
>

The reason that shrinking the receive frame size reduces latency is that
the RX DSP chain produces samples at a fixed rate. Therefore, the device
cannot release a packet until samples_per_packet / sample_rate. The
first sample is a packet is delayed by the time it takes to produce the
last sample.

However, in the case of transmission/send there is no such issue.
Essentially your application is the pacer and producer of samples. So
you have total control.

-Josh

> 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