Massive machine-type communications (mMTC) or massive access is a critical scenario in the fifth generation (5G) and the future cellular network. With the surging density of devices from millions to billions, unique pilot allocation becomes inapplicable in the user ID-incorporated grant-free random access protocol. Unsourced random access (URA) manifests itself by focusing only on unwrapping the received signals via a common codebook. In this paper, we propose a URA protocol for a massive access cellular system equipped with multiple antennas at the base station. The proposed scheme encompasses a codebook enabling construction of sparse transmission frame, a receiver equipped with dictionary learning and error-correcting codes and a collision resolution strategy for the collided codeword. Discrepant to the existing schemes with necessary overhead for preamble signals, no overhead or pre-defined pilot sequences are needed in the proposed scheme, which is favorable for energy-efficient transmission and latency reduction. Numerical results verify the viability of the proposed scheme in practical massive access scenario.

翻译：大规模机器类通信（mMTC）或海量接入是第五代（5G）及未来蜂窝网络的关键场景。随着设备密度从数百万激增至数十亿，传统基于用户标识的免授权随机接入协议中，唯一导频分配已不可行。非协调随机接入（URA）通过仅依赖公共码本解译接收信号而独具优势。本文针对配备多天线的基站海量接入蜂窝系统，提出一种URA协议。该方案包含：用于构建稀疏传输帧的码本、配备字典学习与纠错码的接收机，以及针对碰撞码字的冲突解决策略。与现有需前导信号开销的方案不同，本方案完全无需前导开销或预定义导频序列，有利于实现高能效传输与低时延。数值结果验证了该方案在实际海量接入场景中的可行性。