Hi Bruce, On Thu, 2012-05-10 at 18:51 -0700, Bruce Perens wrote: > On 05/10/2012 06:36 PM, David Rowe wrote: > > At VHF it's probably OK to use a single tone (single carrier) PSK modem. > OK. Currently I compare our FDMDV to FM, D-STAR, and DMR/TRBO in > marketing literature, but that's not really valid if we plan to use some > other modulation on VHF. > > So, potentially 1 GMSK carrier?
Well I am not sure how GMSK or the various FSK flavours in use relate to PSK In terms of SNR v BER. Probably a few dB worse. However on a AWGN channel (VHF is much closer to this than HF), we can use one QPSK carrier with the same SNR v BER performance to our multi-carrier FDMDV. So we would get good PAPR, and for a SNR of 4dB (measured in 3kHz) a 1% BER where the codec is usable, and use 1100 Hz or so of spectrum. If we use coherent (non-differential) QPSK (possible on a AWGN channel) we would get the same BER at 1dB SNR. However I think any form of PSK would still require a SSB tcvr, so no HT. Not sure how that compares to other digital modes. Re FM a friend of mine said: "NBFM 5k dev needs about 6dB CN in a 15kHz BW to be listenable ... so the VHFDV should be about 12dB better." But I haven't run the maths myself on FM. Maybe we should ask a modem guy to work it all out in a table for presentation? Cheers, David > > Thanks > > Bruce ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Freetel-codec2 mailing list Freetel-codec2@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freetel-codec2
