depends on the applied data/modulator filter prior to modulation.
the trellis coding doesnt actually remove the isi it's all about pre
filtering and post equalisation, directed rather than static. Though the
DMR modem is super simple.
Be aware, some modulation types are designed to have
The ISI interpretation really only makes sense if you are using an
analog FM demodulator for both waveforms. This is not the best way to
demodulate FSK - it's a rough method - a kludge - that has somehow found
it's way into a standard!
BTW it's not really "David's modem" - Brady and I just
Hi Adrian,
Nice to see some one else working in this area.
I imagine another reason is that the people setting the DMR standard
were constrained by having a black box, closed source speech codec which
constrained the bit rate they had to deal with.
Have you performed any BER tests to
Hi Phil,
Of course, you are right, but Trellis is computationally more
expensive than a straight change of the modem parameters. The DMR
software stack is huge, compared to what a small community of largely
open source enthusiasts can come up with. (my problem with DMR as a
radio equipment
Wouldn't the ISI largely (theoretically, completely) be ameliorated by
trellis decoding? And I'm not talking about FEC, but rather incorporating
the ISI into the expected Cartesian coordinates for each symbol.
I did some experimentation with this technique on BPSK31, and I was able to
get a
Hi,
In this post: http://www.rowetel.com/?p=4650 David was asking the question
why the 4FSK modem used by the DMR standard seemed to be performing so
poorly, especially as compared to his ideal 4FSK modem.
I was curious myself, so I implemented both and analysed them using my
modified version of
