Impacts of Imperfect CSI, Residual Hardware Impairments, and Imperfect SIC on Alamouti-Coded Short-Packet NOMA Systems With Hybrid Multicast–Unicast Transmission

This paper analyzes the performance of Alamouti coded short-packet non-orthogonal multiple access (NOMA) systems with hybrid multicast-unicast transmission over Nakagami-<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> fading, where only the statistical channel state information is available at the transmitter, and the multicast and unicast signals are intended for all users and a particular user, respectively. Due to practical limitations, channel estimation errors (CEEs), residual hardware impairments (RHIs), and imperfect successive interference cancellation (SIC) are considered. We first derive approximate closed-form expressions for the average block error rate (BLER) and the corresponding asymptotic expressions at all users. Using such expressions, we analyze the diversity performance including conventional diversity order and finite signal-to-noise ratio (SNR) diversity order. After this, we quantify the relationship among the blocklength of information transmission, power allocation, and pilot sequence length under users’ reliability constraints. Finally, numerical and simulation results show that CEEs, RHIs, and imperfect SIC greatly affect the transmission blocklength. Moreover, RHIs lead to the error floor at high SNRs and finite-SNR diversity order is an effective performance metric at low or medium SNRs. They also show that there exist optimal values for the power allocation coefficients, blocklength of information transmission, and pilot sequence length that minimize the transmission blocklength in the considered hybrid multicast-unicast system. They further show that the NOMA scheme is superior to the orthogonal multiple access counterpart by achieving low-latency transmission.