How do i add SNR to BPSK modulating signal?

I want to add SNR = -20:2:30 in following code

function y = bpskModulator(x,sps)

persistent filterCoeffs

if isempty(filterCoeffs)

filterCoeffs = rcosdesign(0.35, 4, sps);

end

syms = pskmod(x,2); %% syms = 256x1

y = filter(filterCoeffs, 1, upsample(syms,sps)); %% upsampling like (sps-1) e.g 1 0 0 1 if sps = 3

end