I've been having trouble implementing 16 and 32-QAM with turbo coding. I've been using the qammod and qamdemod functions as well as the Comm.TurboEncoder and Comm.TurboDecoder functions from the communications toolbox to do this. At low SNR it gives me no issues. However, when the SNR gets high enough (i.e. 15 dB), I notice that the ouptut of the qamdemodulate function contains multiple values that are registered as infinite. Additionally, when this output is fed into the Comm.TurboDecoder functions, I notice that the output is all zeros which is incorrect. I'm thinking that it's related to the noise variance (i.e. 10^(-SNR/10)) I pass into the qamdemod function in order to perform soft demodulation. Can anyone help me understand why this happening as well as why this isn't happening at low SNR?