Noise reduction caused by band limited white noise

the signal strength at receiver is 200uV and noise is added to signal before amplifying .

The noise floor is 0.7nV/rtHz .

To add this noise I've used band limited white noise block in simulink.

And after adding this noise to signal, the amplitude of signal becomes too high and the signal is no longer a pulse . It is converted to noise.

Any methods to recover the signal ?

Please suggest me any techniques to recover the signal back..

I have tried LPF. It's not working

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Please help me to sort out noisy thing.