[aprssig] NextGen

[Pierre Thibaudeau]

Today, 09:47 +0200, Jon K Hellan wrote:

>    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).

Let me add to this,

In the AIS system, timeslots are 256 bits, so there are 2250 timeslots per 
minute. Data is transmitted in a very compact binary format. The most 
frequent messages (like position reports) occupy a single timeslot. As a 
result, this system can carry a lot of payload without congestion.

ITU Recommendation M.1371-3 is a highly recommended reading for 
inspiration.

'73 - Pierre
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Pierre Thibaudeau
VA2RKA/VA2RKB/VE2RIO/VE2RVR/VE2RQF/VE2RTO/VE2LKL/VE2TXD sysadmin