Zohdy Maha, Tajer Ali, Shamai Shitz Shlomo
Department of Electrical, Computer, and Systems Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180, USA.
Faculty of Electrical Engineering, Technion-Israel Institute of Technology, Haifa 3200003, Israel.
Entropy (Basel). 2022 Nov 30;24(12):1757. doi: 10.3390/e24121757.
Emerging wireless technologies are envisioned to support a variety of applications that require simultaneously maintaining low latency and high reliability. Non-orthogonal multiple access techniques constitute one candidate for grant-free transmission alleviating the signaling requirements for uplink transmissions. In open-loop transmissions over fading channels, in which the transmitters do not have access to the channel state information, the existing approaches are prone to facing frequent outage events. Such outage events lead to repeated re-transmissions of the duplicate information packets, penalizing the latency. This paper proposes a multi-access broadcast approach in which each user splits its information stream into several information layers, each adapted to one possible channel state. This approach facilitates preventing outage events and improves the overall transmission latency. Based on the proposed approach, the average queuing delay of each user is analyzed for different arrival processes at each transmitter. First, for deterministic arrivals, closed-form lower and upper bounds on the average delay are characterized analytically. Secondly, for Poisson arrivals, a closed-form expression for the average delay is delineated using the Pollaczek-Khinchin formula. Based on the established bounds, the proposed approach achieves less average delay than single-layer outage approaches. Under optimal power allocation among the encoded layers, numerical evaluations demonstrate that the proposed approach significantly minimizes average sum delays compared to traditional outage approaches, especially under high arrival rates.
新兴无线技术有望支持各种需要同时保持低延迟和高可靠性的应用。非正交多址技术是一种免授权传输的候选技术，可减轻上行传输的信令要求。在衰落信道上的开环传输中，发射机无法获取信道状态信息，现有方法容易频繁出现中断事件。此类中断事件会导致重复重传重复的信息包，从而影响延迟。本文提出了一种多址广播方法，其中每个用户将其信息流拆分为几个信息层，每个信息层适应一种可能的信道状态。这种方法有助于防止中断事件并改善整体传输延迟。基于所提出的方法，针对每个发射机处不同的到达过程，分析了每个用户的平均排队延迟。首先，对于确定性到达，通过解析方法确定了平均延迟的闭式上下界。其次，对于泊松到达，使用Pollaczek-Khinchin公式给出了平均延迟的闭式表达式。基于已建立的界限，所提出的方法比单层中断方法实现了更低的平均延迟。在编码层之间进行最优功率分配的情况下，数值评估表明，与传统中断方法相比，所提出的方法显著最小化了平均总延迟，尤其是在高到达率情况下。
