Study of the Symbol Error Rate/Bit Error Rate in Non-orthogonal Multiple Access (NOMA) Systems

Abstract

Recently, the non-orthogonal multiple access (NOMA) and the related power division multiple access (PDMA) techniques have attracted broad attentions, since they could efficiently improve the throughput of current networks. In NOMA/PDMA, parallel data from different information streams (or services) are encoded and modulated concurrently and then are superposed together for transmission. As a result, it is difficult to analyze the related symbol error rate (SER) and bit error rate (BER) which play a key role in system control, e.g., power allocation. To circumvent such an issue, we derive both SER and BER given by closed-form expressions in conditions of Gray coding and quadrature phase shift keying (QPSK) modulation. According to our outcomes, it is shown that SER and BER could be reduced efficiently, when the information streams are processed with Gray coding jointly. Furthermore, it is also indicated that the jointly Gray coding could improve the independence among the signals which composite a superposition signal. Consequently, our results are helpful to improve the performance of the downlink transmission in NOMA/PDMA.