Hello Prisca, usually additive white gaussian noise (AWGN) channel is considered, you may have control of the impairments through the noise power by controlling the signal to noise ratio (SNR).

https://es.mathworks.com/help/comm/ref/awgnchannel.html

https://es.mathworks.com/help/comm/ref/awgn.html

https://es.mathworks.com/help/comm/gs/compute-ber-for-a-qam-system-with-awgn-using-matlab.html?searchHighlight=16-qam&s_tid=doc_srchtitle

With these pages from Matlab I think you can start, you can make variations on SNR and obtain the curves log10(BER) vs. SNR (dB) for differente modulation schemes.

Regards

Eduardo