Grant-free multiple-input multiple-output (MIMO) usually employs non-orthogonal pilots for joint user detection and channel estimation. However, existing methods are too complex for massive grant-free access in massive MIMO. This letter proposes pilot detection reference signal (PDRS) to greatly reduce the complexity. In PDRS scheme, no iteration is required. Direct weight estimation is also proposed to calculate combining weights without channel estimation. After combining, PDRS recovery errors are used to decide the pilot activity. The simulation results show that the proposed grant-free scheme performs good with a complexity reduced by orders of magnitude.

中文翻译：

---

PDRS：大规模 MIMO 中大规模免授权接入的快速非迭代方案

免授权多输入多输出 (MIMO) 通常采用非正交导频进行联合用户检测和信道估计。然而，现有方法对于大规模 MIMO 中的大规模免授权访问来说过于复杂。这封信提出导频检测参考信号（PDRS）来大大降低复杂度。在PDRS方案中，不需要迭代。还提出了直接权重估计来计算没有信道估计的组合权重。合并后，PDRS 恢复错误用于决定试播活动。仿真结果表明，所提出的免授权方案性能良好，复杂度降低了几个数量级。