Spreading Based Multi-Branch Non-Orthogonal Multiple Access Transmission Scheme for 5G

Abstract

In this paper, a spreading based multi-branch non-orthogonal multiple access (NOMA) scheme is proposed where the information bits are split into several branches with independent channel encoding. A legacy quadrature phase shift keying (QPSK) modulation with different power allocation is applied for bit to symbol mapping of each branch. After superposition of constellations from different branches, user-specific spreading sequence is applied which is used for multi-user interference suppression. At receiver side minimum mean square error (MMSE) elementary signal estimator (ESE) is used for multi-user detection. Due to independent channel decoding and QPSK as constellation where two bits have the same reliability, the quality of the log likelihood ratio for the branch with high power is high whose signals will be successfully decoded first. This will facilitate the decoding of the signals of the branch with low power. Our simulation results show NOMA using multi-branch strategy is superior to its counterpart and thus it is a strong candidate as 5G transmission scheme.