Short-Packet Downlink Transmission with Non-Orthogonal Multiple Access

Abstract: This work introduces downlink non-orthogonal multiple access (NOMA) into short-packet communications. NOMA has great potential to improve fairness and spectral efficiency with respect to orthogonal multiple access (OMA) for low-latency downlink transmission, thus making it attractive for the emerging Internet of Things. We consider a two-user downlink NOMA system with finite blocklength constraints, in which the transmission rates and power allocation are optimized. To this end, we investigate the trade-off among the transmission rate, decoding error probability, and the transmission latency measured in blocklength. Then, a one-dimensional search algorithm is proposed to resolve the challenges mainly due to the achievable rate affected by the finite blocklength and the unguaranteed successive interference cancellation. We also analyze the performance of OMA as a benchmark to fully demonstrate the benefit of NOMA. Our simulation results show that NOMA significantly outperforms OMA in terms of achieving a higher effective throughput subject to the same finite blocklength constraint, or incurring a lower latency to achieve the same effective throughput target. Interestingly, we further find that with the finite blocklength, the advantage of NOMA relative to OMA is more prominent when the effective throughput targets at the two users become more comparable.

• The paper demonstrates that NOMA significantly outperforms OMA by enhancing spectral efficiency and fairness in short-packet IoT communications.
• It introduces a one-dimensional search algorithm to optimize transmission rate, power allocation, and error probability under finite blocklength conditions.
• Findings indicate that NOMA reduces latency and maximizes throughput, offering a superior solution for low-latency, high-device-density scenarios.

An Analytical Study on Short-Packet Downlink Transmission with NOMA

The paper "Short-Packet Downlink Transmission with Non-Orthogonal Multiple Access" provides an in-depth analysis of incorporating downlink non-orthogonal multiple access (NOMA) in short-packet communication systems, with a particular focus on low-latency downlink transmissions pertinent to the Internet of Things (IoT). This study examines the potential of NOMA to enhance spectral efficiency and fairness compared to the more traditional orthogonal multiple access (OMA) schemes.

System Model and Problem Formulation

The authors consider a two-user downlink NOMA system constrained by finite blocklength, where both transmission rates and power allocations need to be optimized. A critical aspect of the study is the examination of trade-offs between the transmission rate, decoding error probability, and latency, measured in terms of blocklength. Such considerations differ significantly from Shannon's capacity theorem, which assumes infinite blocklength leading to negligible error probability; in contrast, a finite blocklength introduces a non-zero error probability, impacting successful transmission.

Algorithm and Performance Evaluation

To address the computational challenges arising from finite blocklength and unguaranteed successive interference cancellation (SIC), a one-dimensional search algorithm was developed. This algorithm explores the effect of finite blocklength on NOMA's achievable rate and demonstrates how the performance of OMA can serve as a benchmark to further highlight NOMA's advantages.

The simulation results are promising. NOMA consistently outperforms OMA in various scenarios, particularly in terms of effective throughput under the same blocklength constraints or when aiming to meet a target throughput at lower latency. The study discovers that NOMA's advantage is more pronounced as user throughput requirements become comparable, aligning with fairness objectives among users.

Theoretical and Practical Implications

Theoretically, this research advances our understanding of short-packet communication under finite blocklength conditions. It highlights the potential of NOMA to serve as a superior alternative to OMA by improving network capability in scenarios with strict latency requirements, such as in industrial IoT applications.

Practically, this paper implies that adopting NOMA in low-latency short-packet transmission can lead to more efficient utilization of the frequency spectrum, particularly in environments where a high number of devices are expected to communicate concurrently, as in IoT.

Future Directions

Several future research directions naturally emerge from this study. For instance, extending the analysis to multi-user scenarios or systems with more complex channel conditions would be beneficial. Additionally, integrating machine learning techniques to optimize resource allocation dynamically in real-time could further enhance the potential benefits of using NOMA in constrained environments.

In conclusion, this research offers valuable insights into the capabilities and advantages of NOMA in short-packet communications, laying a foundation for future explorations in efficiently managing communications in increasingly connected environments such as the IoT. The study's findings are crucial as they could guide the deployment strategies of future wireless communication systems, ensuring they meet the stringent requirements of emerging applications.