[aprssig] 9600 Baud Packet Network?

Andrew rich vk4tec at tech-software.net
Mon Jun 13 15:51:31 EDT 2016



Add AMP and your are laughing


Mr Andrew Rich

vk4tec at tech-software.net

vk4tec at internode.on.net


0419 738 223


From: aprssig [mailto:aprssig-bounces at tapr.org] On Behalf Of Andrew Rich via
Sent: Monday, 13 June 2016 8:55 PM
To: Ross Whenmouth; TAPR APRS Mailing List
Subject: Re: [aprssig] 9600 Baud Packet Network?




Sent from my iPhone

Andrew Rich

vk4tec at tech-software.net


0419 738 223

On 13 Jun 2016, at 19:20, Ross Whenmouth via aprssig <aprssig at tapr.org>


Robert Bruninga wrote;

19k2 is there - the modules are $40

Bob, could you please post a link to these modules?

Re: faster than 9k6 without modifying radios
At the penalty of increased sensitivity to noise, modulations more complex
than K9NG/G3RUH can be fed through the linear audio channel of a pair of
9k6-ready ham transceivers. A 9k6 audio channel provides 5 kHz bandwidth,
more than that of a standard telephone land-line - a quick back of the
envelope with Shanon's Law indicates that we should be able to push bits
much faster than 9k6
Think DSP "TNC" software running in your PC, smartphone, Raspberry pi, or in
a processor like a PIC32 or STM32, with automatic channel equalisation,
GMSK/QPSK/n-QAM and Forward Error Correction. Note that about twenty years
ago you could just go to the computer store and buy a consumer modem that
would push 33k6 in 3.4 kHz BW down a (then) 40 year old telephone line...

Re: Utilising smartphones, tablets, laptops, etc as user interfaces;
Why not use Bluetooth to link your device to the TNC? - it is pretty much
well universally supported by mobile devices and doesn't chew through as
much battery power as WiFi
eg http://www.mobilinkd.com/tnc2/

Re: Transferring (larger) files;
Send larger packets so there is less time consumed per unit payload on
TXdelay, ACK, etc. eg a 1500 byte/12kbit packet takes less than 1.5 seconds
to send at 9k6, and only incurs one TXdelay, where as, if you limit yourself
to 256 byte AX.25 packets, you need to send 6 of them to move 1500 bytes... 
Forward Error Correction seems like a good way to reduce packet
re-transmissions (corruption of a single bit in standard AX.25 results in
rejection of the packet, requiring a resend)
New data transfer protocols eg using a "Fountain Code" would allow most of
the ACK/REJ packets to be eliminated and would be very efficient for
simultaneously distributing a file to multiple recipients

Ross Whenmouth

aprssig mailing list
aprssig at tapr.org

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