QoS-Based NOMA in Hybrid Short and Long-Packet Communications

Considering diverse quality of service (QoS) requirements in the Internet of Things, non-orthogonal multiple access (NOMA) is adopted in this paper to serve a delay-sensitive user (DU) and a broadband user (BU) simultaneously. Short-packet communication is employed by the DU to ensure the low-delay requirement, while the BU conveys long-packet to achieve high data rate transmission. As the reliability of DU is guaranteed by resource allocation schemes, we focus on the transmission efficiency of the BU. General and deep fading scenarios are considered in the communications and the corresponding resource allocation schemes are designed. The closed-form expressions for effective throughput of the BU for the NOMA and orthogonal multiple access (OMA) schemes are derived in the two fading scenarios with the corresponding resource allocation schemes. Numerical results are presented to verify our analysis and give more insights into system performance. The results show that the proposed resource allocation schemes are effective in their corresponding fading scenarios. Moreover, the results also show that NOMA can outperform OMA in both two fading scenarios in terms of effective throughput. Especially when the packet length is short and the reliability constraint is strict, the performance gains of NOMA over OMA become more remarkable.