862 karma · joined April 3, 2016
https://web.archive.org/web/20040622004325/http://www.monkey...
It started with piFM [1] where the possibility was explored to modulate the internal PLL Raspberry Pi with FM and output it on pin GPIO4. This was then further refined and a PWM phase and amplitude modulation technique was applied which made it possible to generate SSB signals [2]. Based on this rpitx [3] was then created which made it possible to basically modulate any type of signal, enabling to use a raspberry pi for analog and digital broadcasts, and to replace key fobs for RF smart plugs and other wireless devices. So yes, it is possible..
[1] GPIO4 piFM transmitter, by Oliver Mattos and Oskar Weigl http://www.icrobotics.co.uk/wiki/index.php/Turning_the_Raspb...
[2] Direct SSB generation by frequency modulating a PLL, by Guido http://pe1nnz.nl.eu.org/2013/05/direct-ssb-generation-on-pll...
[3] Universal I/Q TX for rpi, Evariste Courjaud, https://github.com/F5OEO/rpitx
The nodes here in the Netherlands used the multicast to distribute link information and IP autorouting. It was very well possible to join a multicast group somehwere in the network by multiple parties, and then stream UDP frames accross the network.
A very fun experiment at the time was to send CELP-compressed (1-2kb/s) audio packets through the multicast network, and hence it was possible to have conversation with multiple people spanning a distance larger then the radio horizon. The latency and packet loss were disrupting good operation, but it more or less worked.
I think this exponential decay or growth is the major difference compared to an IFFT, and hence the algorithm can work more efficient over a larger time/frequency domain.
Think of improvements anywhere FFT is used today, but where there is a need to work over a non-linear time/frequency domain.
Program received signal SIGSEGV, Segmentation fault. 0x00007ffff7de88b8 in __GI__IO_fread (buf=buf@entry=0x7fffffffd4f0, size=size@entry=1, count=count@entry=1024, fp=0x0) at iofread.c:35