This paper proposes a unified semi-blind detection framework for sourced and unsourced random access (RA), which enables next-generation ultra-reliable low-latency communications (URLLC) with massive devices. Specifically, the active devices transmit their uplink access signals in a grant-free manner to realize ultra-low access latency. Meanwhile, the base station aims to achieve ultra-reliable data detection under severe inter-device interference without exploiting explicit channel state information (CSI). We first propose an efficient transmitter design, where a small amount of reference information (RI) is embedded in the access signal to resolve the inherent ambiguities incurred by the unknown CSI. At the receiver, we further develop a successive interference cancellation-based semi-blind detection scheme, where a bilinear generalized approximate message passing algorithm is utilized for joint channel and signal estimation (JCSE), while the embedded RI is exploited for ambiguity elimination. Particularly, a rank selection approach and a RI-aided initialization strategy are incorporated to reduce the algorithmic computational complexity and to enhance the JCSE reliability, respectively. Besides, four enabling techniques are integrated to satisfy the stringent latency and reliability requirements of massive URLLC. Numerical results demonstrate that the proposed semi-blind detection framework offers a better scalability-latency-reliability tradeoff than the state-of-the-art detection schemes dedicated to sourced or unsourced RA.

翻译：本文提出了一种面向有源与无源随机接入（RA）的统一半盲检测框架，该框架可支持大规模设备的下一代超可靠低时延通信（URLLC）。具体而言，活跃设备以免授权方式发送上行接入信号以实现超低接入时延。同时，基站在不依赖显式信道状态信息（CSI）的情况下，旨在克服严重的设备间干扰实现超可靠数据检测。我们首先提出了一种高效的发射机设计方案，通过在接入信号中嵌入少量参考信息（RI）来消除由未知CSI引起的固有模糊性。在接收端，我们进一步开发了一种基于串行干扰消除的半盲检测方案，其中利用双线性广义近似消息传递算法进行联合信道与信号估计（JCSE），并通过嵌入的RI实现模糊消除。特别地，我们引入了一种秩选择方法和一种RI辅助初始化策略，分别用于降低算法计算复杂度和提升JCSE可靠性。此外，为满足大规模URLLC的严苛时延与可靠性要求，本方案集成了四项使能技术。数值结果表明，相较于专用子有源或无源RA的最先进检测方案，所提出的半盲检测框架在可扩展性-时延-可靠性权衡方面更具优势。