Use of ADC and DAC for communication systems Tx/Rx in Simulink? If and how?

Hello All,

This may sound a trivial question, but I would like someone to share his thoughts on this. Normally when we are modelling a transmitter for a digital communication system we use the following blocks in cascade:

Data source --> M-Psk Modulator (for example) --> Pulse shaping (e.g. RRC) --> Up-convertor (e.g. simple multiply block with LO) --> AWGN -->>

Now, my question is do we need an DAC block before the AWGN block while modeling the transmitter side in Simulink? I ask this because everywhere I see the architecture of digital communication system's transmitter side in literature, I see an DAC block.

The same goes at the receiver end, where usually the first block is the ADC block, before prefiltering or downconversion.

Anyone who could shed some light on that? Thanks!