I assume that the signal is at a known frequency and that the modulation rate is a small fraction of the signal frequency.
If you know that the transmitter has an oscillator in it that is at a constant frequency, you can reconstruct the transmitter's clocking rate with a PLL at the receiver.
You can use the output of the PLL as the carrier in the detection stage. This will give you a significant advantage against the random noise. The sync detection method reduces noise power by a factor of
- The filtering you can do after detection further reduces the noise.
A cheap method is to rectify, band pass filter the rectified output, AGC the AC amplitude, DC baseline restore and then use a comparitor. This puts the noise near zero volts and the signal at some positive voltage. It assumes that the SNR is large enough that the signal jumps up out of the background.