# To implement successive interference cancellation (SIC) process, should the receiver know the power allocated to each symbol?

My question is as follows:

• To implement successive interference cancellation (SIC) process in downlink non-orthogonal multiple access (NOMA), should receivers know all power allocated to each symbol?

Consider a single-cell network consisting of one base station (BS) and $$N$$ users. Let $$x_i$$ be the symbol for user $$i$$, $$h_i$$ be the complex-valued channel gain between user $$i$$ and the BS, $$p_i$$ be the power allocated to symbol $$x_i$$. Then, the transmitted signal is given by $$x = \sum_{i=1}^N \sqrt{p_i} x_i.$$ The corresponding received signal at user $$k$$ is given by $$y = h_k \sum_{i=1}^N \sqrt{p_i} x_i + n_k,$$ where $$n_k\sim\mathcal{CN}(0,\sigma^2)$$ is the additive white Gaussian noise of user $$k$$.

Assuming that $$\lvert h_1 \rvert^2 \le \lvert h_2 \rvert^2 \le \cdots \le \lvert h_N \rvert^2$$, user $$k$$ decodes its own symbol $$x_k$$ according to the following process:

1. Decode $$x_1$$ by treating $$\sum_{i=2}^N h_k\sqrt{p_i}x_i + n_k$$ as noise.
2. Subtract $$\hat{x}_1 \triangleq h_k\sqrt{p_1}x_1$$ from $$y$$.
3. Decode $$x_2$$ by treating $$\sum_{i=3}^N h_k\sqrt{p_i}x_i + n_k$$ as noise.
4. Subtract $$\hat{x}_2 \triangleq h_k\sqrt{p_2}x_2$$ from $$y-\hat{x}_1$$.
5. Repeat to (i) decode $$x_l$$ by treating $$\sum_{i=l+1}^N h_k\sqrt{p_i}x_i+n_k$$ as noise, and (ii) subtract $$\hat{x_l} \triangleq h_k\sqrt{p_l}x_l$$ from $$y-\sum_{i=1}^{l-1}\hat{x}_i$$ until $$x_k$$ is decoded.

In my opinion, to decode its own symbol $$x_k$$, user $$k$$ should know $$p_l$$ for any other user $$l$$ such that $$\lvert h_l \rvert^2 < \lvert h_k \rvert^2$$. Is this opinion true? If this is true, the BS should inform the user about the power allocated to each symbol. Nevertheless, is NOMA useful?