Hi David,
On 13-03-13 00:00, David Rowe wrote: > Hi Kristoff, > > I had a look at the mod and demod demo programs and the design looks > fine. Well, I still need to finish some documentation but I happy you like it sofar. > Unlike the current HF protocol you have three states (e.g. > pre/post amble and voice data), so you need a way to handle start > up/shut down of the stream. Well, that's how it seams to be done in most specification of digital communication for VHF/UHF I've come across. I don't know if it is stricktly necessairy but it looked like the most easy thing to do. The advantage of the pre-amble is that -in addition to giving the radio some time to sync- you can do some things with it: insert a c2gmsk version-number (allowing a more flexible path for upgrading the protocol) or a complete header (something I still need to add). I think having a fixed well-known and well-defined pattern in the beginning of the stream will probably also help to implement auto-bitrate detection once we have both a 2400 and a 4800 bps modem. > We can work this into FreeDV OK. I have some ideas where the > START/VOICE/STOP code would go. We would need to change the FreeDV > design a little to handle protocols with state, one example is to ensure > the "MOD END" data gets transmitted before PTT is de-asserted. > Has the modem been performance tested. e.g. BER versus Eb/No, sync time > at a given Eb/No (SNR) or other channel artefacts like timing offsets? > I am not sure how to do this on a GMSK modem without simulating the FM > part. Well, this is one of the reasons I am interested in a GNUradio port of it. This would probably help to run simulations of it and get a better "objective" view of what needs to be done first to make it better. > Cheers, > David 73 Kristoff - ON1ARF ------------------------------------------------------------------------------ Everyone hates slow websites. So do we. Make your web apps faster with AppDynamics Download AppDynamics Lite for free today: http://p.sf.net/sfu/appdyn_d2d_mar _______________________________________________ Freetel-codec2 mailing list Freetel-codec2@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freetel-codec2
