#126 Error for high SNR for Modulator_2d::demodulate_soft_bits

[Anonymous]

Modulator_2d::demodulate_soft_bits does not work well
for high SNR. For high SNR value, it produces inf and
-inf, which generates error when channel decoding is
operate on the demodulated bits. I have change to
demodulate_soft_bits_approx and it works well then.

Regards,
Arthur.

[Erik G. Larsson]

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Arthur, Could you send us an example of code where you
reproduce this error? On my system, I was able to set N0 to
well below 1e-300 before the demodulator output was inifite
(this infinity output seems to be caused by the 1/N0
calculation) - note that such a low noise level is zero for
all practical purposes. Possibly system dependent.

Updated documentation to suggest Modulator_ND class be used
instead -- faster and better numerical stability.

Erik

[Adam Piątyszek]

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Finally, we managed to solve the problem in Modulator_2d
demodulate_soft_bits() function. The fix is already in the
repository (rev. 599). See ChangeLog for more information.
Closing this bug report.

/ediap