Re: [Discuss-gnuradio] Modulation question

[Marcus Müller]

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Ah yes you're right; I've just taken a look myself, and gr-air-modes
uses a moving average as a matched filter, which implies a rectangular
shape. So your pulse bandwidth is the same as system bandwidth.

On 30.01.2014 11:11, Andrew Rich wrote:
> When you demodulate ads-b it becomes just square waves
> 
> Sent from my iPhone
> 
>> On 30 Jan 2014, at 8:01 pm, Marcus Müller <address@hidden>
>> wrote:
>> 
> Basically, yes, but that's communication theory. I'd refer you to 
> Kammeyer -- Nachrichtenübertragung, but that's a German book. I
> guess Proakis would be a fine source, too, but I don't have his
> book at hand right now.
> 
> Anyway, ADB-S should *define* the pulse shape. Best look into
> Nick's gr-airmodes code for matched filtering; the matched filter
> directly gives you the transmission filter. (But that's even more
> signal theory)
> 
> Greetings, Marcus
> 
>>>> On 30.01.2014 10:44, Andrew Rich wrote: Thanks Marcus
>>>> 
>>>> Pulse shape and repetition frequency determine bandwidth then
>>>> ?
>>>> 
>>>> Square is the worst - gausian is better ?
>>>> 
>>>> - Andrew -
>>>> 
>>>> 
>>>> ----- Original Message ----- From: "Marcus Müller" 
>>>> <address@hidden> To: "Andrew Rich"
>>>> <address@hidden> Cc: <address@hidden>
>>>> Sent: Thursday, January 30, 2014 5:27 PM Subject: Re:
>>>> Modulation question
>>>> 
>>>> 
>>>> Hi Andrew,
>>>> 
>>>> just a quick heads-up: I nearly missed your message because
>>>> it was hidden in another thread, since you seem to have hit
>>>> reply and changed subject and text; however, my mail client
>>>> recognized the In-Reply-To header, and sorted you in - please
>>>> directly write mails unless you actually mean to reply.
>>>> 
>>>> So now for your question
>>>>>>> Ads-b uses a 1 MHz pulse position modulation scheme
>>>> On 30.01.2014 01:22, Andrew Rich wrote:
>>>>>>> Ads-b uses a 1 MHz pulse position modulation scheme
>>>>>>> 
>>>>>>> Is this possible to create on gnu ?
>>>> GNU Radio is only a software radio framework. Basically you
>>>> can do anything with it that can be done in baseband signal
>>>> of a sample rate that your ADC/DAC and mixers (and analog
>>>> filters, amps and so on) support. With gr-air-modes there is
>>>> a comfortable receiver implemented in GNU Radio, and as a
>>>> not-to-rough simplification you can transmit everything with
>>>> a software radio that you can receive with one.
>>>> 
>>>>>>> 
>>>>>>> Is it the data rate that makes the spectrum wide ? 7
>>>>>>> MHz ?
>>>> Ok, I don't really understand your question, could you
>>>> please elaborate? Reception of ADB-S works quite well with a
>>>> 4MHz sampling bandwidth, but I'm not quite sure on the
>>>> technical requirements of ADB-S transmission.
>>>> 
>>>> The actual bandwidth of PPM systems of course depends on
>>>> pulse shape and pulse frequency.
>>>> 
>>>> Hope I was able to help a little, Marcus
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