[aprssig] NextGen

[Ray Wells]

Jon,

The packet experience showed us how reluctant users were to modifying 
(suitable) radios for higher data rates. The experience in other 
countries might be different but here in Oz there was a severe lack of 
economical, suitable radios for 9k6 and as a result it failed to take 
off. Even HAPN 4k8, which would work (sort of) with a 2m voice radio, 
never took off. My attempt to get a 2k4 network going with MFJ1270BT 
TNC's also failed, even though every club member had the TNC and only 
had to select the data rate. I set up a port on the node/bbs and 
eventually removed it through lack of use.

I suspect that many "casual" users of aprs will react similarly, 
certainly the case in Oz, to moves away from 1k2 AFSK, as unfortunate as 
that may be in the eyes of the serious (ARES, WICEN, etc) users.

As for allocating timeslots in AIS, would European contributors like to 
comment on the success of DAMA in the packet service? It never took off 
in Oz.

Ray vk2tv

Jon K Hellan wrote:
> Andrew Rich (Home) wrote:
>> Do you think 1200 baud will do us ?
>>  
>> I have been playing with 19k2 manchester encoding I can send my 
>> position in ms
>>  
>> I have been looking at PPM Pulse Position Modulation you can send you 
>> posisition in us
>>  
>> Do we have congestion on packet freq ?
>
> There is a bit rate / required SNR tradeoff. Higher bit rates require 
> higher SNR. But AFSK, which APRS
> is now using, is far from the state of the art. It is used because it 
> is compatible with voice FM
> equipment.
>
> There are also tradeoff involving range, burst lengths and congestion. 
> In a metropolitan area, if you
> somehow were able to install as many digis as you like, shorter ranges 
> would help avoid congestion.
> In areas with a low ham population, 2m digis are appropriate. Whatever 
> the range, shorter burts lengths
> would help, if required SNR were the same.
>
> The maritime Automatic Identification System (AIS) is a commercial 
> system with similar requirements
> to APRS. They use 9600 bps GMSK (Gaussian minimum shift keying) on 
> frequencies around 160 MHz. AIS also
> has a patented algorithm to assign time slots to vessels. It is called 
> "Self-Organized Time-Division
> Multiple Access" (STDMA).
>
> D-STAR is also GMSK modulated, and sends a 4800 bps bitstream in a 
> 6.125 kHz channel.
>
> A more advanced coding / modulation scheme for APRS could either stick 
> to 1200 bps, but work with
> a lower SNR. Or it could increase the bitrate and keep SNR 
> requirements unchanged. There's a lot
> of room for experimentation here, but don't expect wide deployment 
> anytime soon.
>
> 73
> Jon LA4RT
>
> _______________________________________________
> aprssig mailing list
> aprssig at tapr.org
> https://www.tapr.org/cgi-bin/mailman/listinfo/aprssig
>