Recently, grant-free random access (GFRA) schemes have received significant attention by the research community as a solution for extremely low-latency and short packet transmissions in new industrial Internet-of-Things and digital twins applications. However, implementing such schemes in the mmWave and THz frequency bands is challenging due to the need for multiple-input multiple-output (MIMO) links to counteract the high path loss and provide sufficient spatial filtering. This results in unacceptable signaling overhead for channel estimation, slow beam alignment procedures between the access point (AP) and the sensors, as well as high sensor complexity and energy consumption. In this paper, we propose the adoption of a self-conjugating metasurface (SCM) at the sensor side, where the signal sent by the AP is backscattered after being conjugated and phase-modulated according to the data to be transmitted by the sensor. We introduce a novel SCM-based GFRA protocol enabling the detection of new sensors and the establishment of parallel MIMO uplink communications with extremely low latency. This is achieved in a blind manner, eliminating the need for radiofrequency chains and digital processing at the sensor side, as well as explicit channel estimation and time-consuming beam alignment schemes.

中文翻译：

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具有反向散射自共轭超表面的无资助随机访问


最近，无授权随机接入（GFRA）方案作为新型工业物联网和数字孪生应用中极低延迟和短数据包传输的解决方案受到了研究界的极大关注。然而，由于需要多输入多输出（MIMO）链路来抵消高路径损耗并提供足够的空间滤波，因此在毫米波和太赫兹频段实施此类方案具有挑战性。这会导致信道估计的信令开销不可接受、接入点 (AP) 和传感器之间的波束对准过程缓慢，以及传感器复杂性和能耗较高。在本文中，我们建议在传感器侧采用自共轭超表面（SCM），其中AP发送的信号根据传感器要传输的数据进行共轭和相位调制后进行反向散射。我们引入了一种新颖的基于 SCM 的 GFRA 协议，能够检测新传感器并以极低的延迟建立并行 MIMO 上行链路通信。这是以盲方式实现的，消除了传感器端对射频链和数字处理的需要，以及显式的信道估计和耗时的波束对准方案。