This means error free operation at -2dB SNR for AWGN, and 2dB SNR over a challenging fast fading HF channel (two paths, 1Hz Doppler, 1ms delay). It looks like FreeDV 700D has a gain of 4dB over 700C. I have wrapped my head around such arcane mysteries as coding gain and now have LDPC codes playing nicely over that nasty old HF channel. As an aside – Bill is part if the communications payload team for the QB50 SUSat Cubesat – currently parked at the ISS awaiting launch! Very Kerbal.Īnyhoo – I’ve developed a new OFDM modem that has less syncronisation overhead, works better, and occupies less RF bandwidth (1000 Hz) than the cohpsk modem used for 700C. This work was inspired by Bill, VK5DSP, who kindly developed some short LDPC codes for me and suggested I could improve on the synchronisation overhead of the cohpsk modem.
AMBE+2 and MELPe 600 Compared to Codec 2.