Polar Coded Power Domain Non-Orthogonal Multiple Access System: Construction and Optimization

The generalized polarization phenomenon exists in non-orthogonal multiple access (NOMA) systems. This letter specifically focuses on two-user coding-NOMA systems, which provide a practical joint optimization solution for next-generation mobile communication. In this letter, we employ the finite code length normal approximation bound to establish the connection among error probabilities, power allocation, and code rate allocation in coding-NOMA systems. First, we formulate an optimization problem to minimize error probability, and another one to maximize energy efficiency under a given system error performance for practical scenarios. Then, we derive the relationship between optimal code rates and powers, and then compute suitable power scheme using an iterative algorithm. Finally, we optimize polar coded NOMA systems using polarization subchannels. The proposed optimization scheme exhibits only a 0.5dB deviation from the normal approximation bound at a block error rate of 10−3. Furthermore, the polar coded NOMA scheme outperforms low-density parity-check code (LDPC) coding.