This paper studies the performance of a transmission and reception scheme for massive access under some practical challenges. One challenge is the near-far problem, i.e., an access point often receives signals from different transmitting devices at vastly different signal strengths. Another challenge is that the signals from different devices may be subject to arbitrary, analog, and heterogeneous delays. This paper considers a fully asynchronous model which is more realistic than the frame or symbol level synchrony needed in most existing work. A main theorem characterizes the asymptotic scaling of the codelength with the number of devices, a device delay upper bound, and the dynamic range of received signal strengths across devices. The scaling result suggests potential advantages of grouping devices with similar received signal strengths and letting the groups use time sharing. The performance of the proposed scheme is evaluated using simulations with and without grouping.

翻译：本文研究了在实际挑战下用于大规模接入的发送与接收方案的性能。其中一个挑战是远近效应，即接入点接收来自不同发送设备的信号时，信号强度往往差异巨大。另一个挑战是不同设备的信号可能遭受任意、模拟及异质的时延。本文考虑了一种完全异步模型，该模型比现有大多数工作所需的帧级或符号级同步更为现实。一个主要定理刻画了码长随设备数量、设备时延上界以及各设备接收信号强度动态范围的渐近缩放关系。该缩放结果表明，将接收信号强度相近的设备分组并采用时分复用方式具有潜在优势。通过有无分组情况的仿真，评估了所提方案的性能。