Definition

A memoryless fading channel is given by $$Y_{i}=A_{i}X_{i}+Z_{i}$$where $Z_{i}$ is the additive noise, $X_{i},Y_{i}$ are the input and output, and $A_{i}$ which is the fading at time $i$. Note that $A_{i}\perp\!\!\!\perp X_{i} \perp\!\!\!\perp Z_{i}, \ \forall i,j,k$.