NOMA - How superposition coding works?
Non Orthogonal Multiple Access (NOMA) is a candidate multiple access scheme for 5G. The fact that NOMA allows multiple users to transmit and receive simultaneously using the same frequency may appear intriguing. The two key operations that make NOMA possible are superposition coding which must be done at the transmitter side and successive interference cancellation (also known as SIC) at the receiver side. In this post we will see about superposition coding. Let us say two users User 1 and User 2 are going to communicate simultaneously using the same frequency. Let x 1 denote User 1's data and x 2 denote User 2's data. For simplicity, let us assume that each user has just 4 bits of data to send. This assumption is far from reality, but is sufficient to understand the basic working of NOMA. Let x 1 = 1010 and x 2 = 0110. A graphical view of x 1 and x 2 is shown below. x 1 and x 2 must undergo digital modulation before transmission. Let's use BPSK fo