# What is SIC? And why should we decode some signal first when we know that we will decode it again in the future?

First ,$$x_s=x_1+x_2$$,and the transmitter transmit the $$x_s$$ to $$U_1$$,and the received signal in the $$U_1$$ is $$y_1=h_i x_s+n_i$$,and there is a power splitter in the $$U_1$$,and $$y_1^{ip}=\sqrt{1-\rho}y_1$$
$$U_1$$ decodes $$x_2$$ based on $$y^{ip}_1$$, then applies successive interference cancellation (SIC) before decoding $$x_1$$.I don't really understand about here
My question is that what does "then applies successive interference cancellation (SIC)" mean ?and what does it do? I know that $$U_1$$ decode $$x_2$$ first then decode $$x_1$$,so is this called "SIC"?
Another question is that the paper also said the $$U_1$$ deocode the $$x_2$$ then decode $$x_1$$,and harvest the power of $$x_s$$,then use this energy to send the $$x_2$$ to another receiver $$U_2$$,then $$U_2$$ will decode the $$x_2$$.Why should we decode the $$x_2$$ in the $$U_1$$ when we know we will decode $$x_2$$ again in the $$U_2$$ in the future?Is there any application about this in the real world?