It is really a bit simpler than all that thwere is a drive in mobile comms to increase density. For an FM modulation, having four states per symbol instead of two does just this, reduces bandwidth.
At a cost of CNR requirement... At least 3dB, up to 6dB depending on how it is done. Amateur radio is not about density and spectral efficiency (well depends on what you want) Amateur Radio is (I think) about pushing the limits, not convenience. and we all know from experience that 90 % of the radio comms is in the last 10 % of the receiver sensitivity. and this is why low CNR requirements are important (i THINK) Therefore I think we'll get enjoyable results from a 2 state per axis FM system, or QPSK (2 sates on each axis I and Q). OFDM over a existign radio system has a the advantage that it makes OPTIMAL use of the available bandwidth, and is OPTIMAL when it comes to making the most of the SNR v frequency and the fairly rough channel (IE the rather nasty amplitude and phase response) . I think the OFDM over a FM audio system (with the preemphasis and de emp( IE the mic input) would outperform the direct mod systems like GMSK, MSK, FSK) . g On 23/12/2014 12:39 AM, ae4jy wrote: > Hi Bruce, David > I agree that paper is just a glossy marketing promo but I think the > comment that the commercial markets have moved away from GMSK is valid. > I can't address technically why but I would think that companies > spending millions of R&D dollars are not going to change to a new > modulation scheme just to be different. Perhaps the shift is more due > to something other than raw sensitivity such as higher data rates for a > given channel BW or maybe it is easier to implement convolution coding > using the dibits, better multipath performance, etc. > In the end it probably doesn't matter what the low level modulation > scheme is as system/network features are what the users will ultimately > care about. Why Dstar has been mildly popular is its ability to use the > internet to connect repeaters/reflectors certainly not its weak signal > or voice quality performance. > > Just my 2c. > 73's > Moe > > On 12/21/2014 12:24 PM, Bruce Perens wrote: >> 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 >> >> > > ------------------------------------------------------------------------------ > 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 > -- - Glen English RF Communications and Electronics Engineer CORTEX RF & Pacific Media Technologies Pty Ltd ABN 40 075 532 008 PO Box 5231 Lyneham ACT 2602, Australia. au mobile : +61 (0)418 975077 ------------------------------------------------------------------------------ Dive into the World of Parallel Programming! The Go Parallel Website, sponsored by Intel and developed in partnership with Slashdot Media, is your hub for all things parallel software development, from weekly thought leadership blogs to news, videos, case studies, tutorials and more. Take a look and join the conversation now. http://goparallel.sourceforge.net _______________________________________________ Freetel-codec2 mailing list Freetel-codec2@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freetel-codec2
