Hi Maya,
SNR values are something that you have to determine to get for example BER for a MMSE receiver.
If you want to get the curve SNR vs BER for a MMSE receiver then you must do a simulation according to your chosen modulation (BPSK, QPSK, etc) and system (GSM, CDMA, OFDM, etc).
If you just want to get the curve without having to do the simulation yourselft, then please refer to signal processing or communication textbooks, or just search in the Internet.
best