Study of SER and BER in NOMA Systems

At present, non-orthogonal multiple access (NOMA) techniques have attracted broad attentions, since they could improve the throughput of cellular networks efficiently. However, the symbol error rate (SER) and bit error rate (BER) have not been studied comprehensively in the NOMA, even they play a key role in communication system control, e.g., power allocation. To address such an issue, this paper studies the SER and BER with consideration of the downlink/uplink transmission, the number of information streams, and the channel coding jointly. For analyzing the impact of channel coding, Gray coding is introduced for the downlink transmission. The derived SER and BER are given by closed-form expressions, by which the transmission performance could be evaluated efficiently. We also show an approximate SER/BER when the transmitter could employ Gray-coding. Additionally, associating with the derived closed-form expressions, we show that there exists no error propagation/error accumulation phenomenon when the successive interference cancellation (SIC) is adopted in signal demodulation, which is treated as a major drawback of SIC demodulation in the NOMA systems. Furthermore, by analyzing the encoding/decoding processes in the current NOMA works, a joint Gray-coding scheme is introduced to reduce the SER and BER in the downlink transmission effectively. Through simulations, we validate the correctness of the derived expressions of SER and BER from different aspects.