Grant-free access is an attractive approach to enable spectrum-efficient low-latency access for systems with massive number of users. Pilot design plays a crucial role for grant-free access as it needs to provide a large number of access codes with fast collision detection capability and good channel estimation performance. Recently, pilot designs with fast collision detection capability have been proposed for compressed sensing (CS) based channel estimation. But the existing designs are not optimized for the estimation of highly sparse and block-sparse channels. In this paper, we present several propositions related to the performances of the CS based sparse and block-sparse channel estimation. Utilizing these propositions, we develop a novel non-orthogonal pilot design with fast collision detection capability for grant-free access in block-sparse channels. We also propose two methods to optimize the Peak-to-Average Power Ratio (PAPR) of the proposed non-orthogonal pilot codes. The simulation results illustrate that the proposed design provides similar or better channel estimation and collision detection performances with much better pilot resource efficiency when compared to the existing designs. Finally, we investigate the trade-offs among different design parameters and the channel estimation performances to facilitate better design choices.

中文翻译：

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基于压缩感知的非正交多天线免授权接入系统的非正交设计

免授权访问是一种吸引人的方法，可为拥有大量用户的系统实现频谱有效的低延迟访问。飞行员设计对于无授权访问起着至关重要的作用，因为它需要提供大量具有快速冲突检测功能和良好信道估计性能的访问代码。最近，已经提出了具有快速冲突检测能力的飞行员设计用于基于压缩感测（CS）的信道估计。但是，现有设计并未针对估计高度稀疏和块稀疏信道进行优化。在本文中，我们提出了一些与基于CS的稀疏和块稀疏信道估计性能有关的命题。利用这些命题，我们开发了一种具有快速冲突检测功能的新颖的非正交导频设计，可用于块稀疏通道中的无授权访问。我们还提出了两种方法来优化建议的非正交导频码的峰均功率比（PAPR）。仿真结果表明，与现有设计相比，所提出的设计提供了相似或更好的信道估计和冲突检测性能，并具有更好的导频资源效率。最后，我们研究了不同设计参数和信道估计性能之间的权衡，以促进更好的设计选择。仿真结果表明，与现有设计相比，所提出的设计提供了相似或更好的信道估计和冲突检测性能，并具有更好的导频资源效率。最后，我们研究了不同设计参数和信道估计性能之间的权衡，以促进更好的设计选择。仿真结果表明，与现有设计相比，所提出的设计提供了相似或更好的信道估计和冲突检测性能，并具有更好的导频资源效率。最后，我们研究了不同设计参数和信道估计性能之间的权衡，以促进更好的设计选择。