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 ------------------------------------------------------------------------------ Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server from Actuate! Instantly Supercharge Your Business Reports and Dashboards with Interactivity, Sharing, Native Excel Exports, App Integration & more Get technology previously reserved for billion-dollar corporations, FREE http://pubads.g.doubleclick.net/gampad/clk?id=164703151&iu=/4140/ostg.clktrk _______________________________________________ Freetel-codec2 mailing list Freetel-codec2@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freetel-codec2
