[Ground-station] Baseband => decimation - questions

Ron Economos w6rz at comcast.net
Fri Jan 25 19:27:21 EST 2019


Okay. De-multiplexing is a much better and less confusing terminology. 
As you stated, decimation is a DSP thing and channelizing the downlink 
payload has nothing to do with DSP (all the DSP has already been down in 
order to deliver payload packets).

Ron W6RZ

On 1/25/19 16:17, Michelle Thompson wrote:
> To me, decimation is what we do in order to channelize in the payload.
>
> I don't think that's exactly what I'm being asked about in the ground 
> station receiver, though.
>
> -Michelle W5NYV
>
>
>
>
> On Fri, Jan 25, 2019 at 4:14 PM Ron Economos <w6rz at comcast.net 
> <mailto:w6rz at comcast.net>> wrote:
>
>     I'm not sure we are talking about the same thing yet. So what
>     exactly do you expect to decimate and why?
>
>     Ron W6RZ
>
>     On 1/25/19 16:07, Michelle Thompson wrote:
>>     The beginning of wisdom being the definition of terms and all, it
>>     would be good to make sure we're all talking about the same thing.
>>
>>     So far, I've used LNBs and USRPs for receive, with the LNB doing
>>     an IF at 618MHz (LNB-on-a-Stick) and giving reasonable performance.
>>
>>     Decimation to me is a DSP thing, or used to reduce power
>>     consumption when you don't need to sample as high as you can.
>>
>>     -Michelle W5NYV
>>
>>
>>
>>
>>     On Fri, Jan 25, 2019 at 3:52 PM Ron Economos via Ground-Station
>>     <ground-station at lists.openresearch.institute>
>>     <mailto:ground-station at lists.openresearch.institute> wrote:
>>
>>         The standard IF for DVB-S2 receivers is 950 to 2150 MHz.
>>
>>         DB6NT was selling a down-converter from 10489-10500 MHz to
>>         1129-1140 MHz for P4A.
>>
>>         https://shop.kuhne-electronic.com/kuhne/en/shop/new/MKU+LNC+10+OSCAR+P4A/?card=1832
>>
>>         I'm not sure what decimation has to do with receiving DVB-S2.
>>         The entire 10 MHz signal needs to be demodulated. Individual
>>         baseband frames will be selected for processing, but I call
>>         that de-multiplexing.
>>
>>         Ron W6RZ
>>
>>         On 1/25/19 15:32, David Vieira via Ground-Station wrote:
>>>         Michelle - Thanks for posting.  I'll frame some of the
>>>         questions.
>>>
>>>         Typical 10 GHz terrestrial contesting rigs are Heterodyne;
>>>         that is a Mixer works with a Local Oscillator (LO) to take
>>>         the RF down to an IF (Intermediate Frequency).
>>>         For an SDR, that IF can be digitized by an Analog-Digital
>>>         Converter.
>>>
>>>         The most popular IF for contesting/SSB rigs is 144 MHz.
>>>         For a data BW of 10 MHz that may or may not be a fast enough
>>>         IF carrier.  If we can digitize and recover the data, it
>>>         would allow a lot of re-use of existing equipment.
>>>
>>>         I've heard suggestions/proposals up to the 1.2 GHz Ham band.
>>>         In some sense, the IF carrier could be 144/220/440/915/1200
>>>         MHz, or even any Non-Ham frequency in between.
>>>
>>>         There are a lot of proof of existence designs for a 10 GHz
>>>         Mixed down to an IF; and lots of off the shelf ADC
>>>         dev-boards.  (catch me off thread for details).
>>>
>>>         Some questions I have are:
>>>         ---from an FPGA side of the SDR, what data rate(s) can the
>>>         FPGA absorb in to a decimator?
>>>
>>>         Must we decide upfront on a single frequency; or
>>>         preferably allow flexibility in the RF front end design (ie,
>>>         Mixer, PLL and Local Oscl hardware choices) by allowing a
>>>         wide and programmable variety of ADC and decimation rates?
>>>
>>>         {This is where RF and Digital folks must communicate across
>>>         walls.}  ;-)
>>>
>>>         Comments welcome.
>>>
>>>         regards,
>>>         David
>>>         KI6CLA
>>>
>>>
>>>         On Friday, January 25, 2019, 2:41:54 PM PST, Michelle
>>>         Thompson via Ground-Station
>>>         <ground-station at lists.openresearch.institute>
>>>         <mailto:ground-station at lists.openresearch.institute> wrote:
>>>
>>>
>>>         While we are striving to enable all sorts of wonderful
>>>         designs by putting prototypes into GNU Radio, a central goal
>>>         is to design our own hardware.
>>>
>>>         We've had a lot of progress on the protocol and algorithm
>>>         front (GSE, LDPC, some of the polyphase).
>>>
>>>         Some fundamental decisions about our own hardware need to be
>>>         made.
>>>
>>>         When we receive, we expect to have to decimate. This is
>>>         because we are receiving at a relatively high frequency (10GHz).
>>>
>>>         Our bandwidth is (up to) 10MHz. For DVB-S2/X, we fix our
>>>         sampling rate, depending on what bandwidth we want to
>>>         support. We have a lot of freedom here.
>>>
>>>         Picking the right frequencies for the receive chain is
>>>         therefore important.
>>>
>>>         What are our options?
>>>
>>>         What options make the best sense?
>>>
>>>         I'd like to build and test as soon as possible, so let's get
>>>         some discussion going.
>>>
>>>         -Michelle W5NYV
>>>
>>>
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