Hi Moe,
You have a really good point about multipath and synchronization.
Regarding the Yaesu paper, I've seen this paper as pure marketing and
not particularly technically adept until now. In my presentations I've
said as much and nobody has corrected me so far. Please point out what
the valid arguments in there are.
Thanks
Bruce
On 12/21/2014 06:49 AM, ae4jy wrote:
> Hi David,
> From a practical standpoint I wonder how much of an advantage a
> theoretical limit synchronous GMSK demodulator would be in the VHF/UHF
> mobile environment where signals rarely hover around the Shannon limit.
> They are either well above or well below due to multipath/Doppler etc.
> My gut feeling is an interleaver and FEC would do much more in that
> environment. I know folks are paranoid about turn around delays but in
> reality hundreds of mSecs is not that big a deal and not having to
> listen to squawks from a bit starved vocoder might be worth it.
>
> For whatever reason, the commercial world seems to have moved to C4FM
> instead of GMSK so might be worth a look as to why. Here is a(of course
> biased) report but I think the arguments at the low level modulation
> level are valid, the system level arguments not so much.
>
> http://www.yaesu.com/downloadFile.cfm?FileID=7146&FileCatID=151&FileName=DigitalCommunicationsGuide%5FE%5B1%5D.pdf&FileContentType=application%2Fpdf
>
> One could also leverage some of the existing signalling technology
> instead or re-inventing the wheel.
> Google for ts_102658v010201p.pdf will find an ETSI TS 102 658 spec for
> dPMR which has a section on the physical layer that might be of use.
>
> As a side note it looks like the STM32F7 series will be pin for pin
> compatible with the stm32f4 and give us a little more of everything
> especially ram which is what I seem to run out of first when doing DSP.
>
> 73,
> Moe ae4jy
>
>
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