Grant-free (GF) access has been one of the enablers for the various use cases in 5th generation (5G) mobile system, especially for time-critical massive machine-type communication (mMTC). However, these use cases have diverse quality of service (QoS) requirements, which can be measured in terms of an access success rate from a GF random access perspective. Consequently, a GF scheme that enables supporting of diverse QoS is highly sought. This article proposes a GF access scheme in which high-QoS users superpose multiple preambles to improve their access success rate as a result of the diversity in access collision and multiple access interference seen by multiple preambles. We further show that in the presence of multiple antennas in the base station (BS), a low-complexity receiver can correctly detect active preambles with a significantly high probability, even under severe multiple access interference caused by non-orthogonal preamble transmission. A theoritical performance analysis is conducted by modeling the preamble reception as a multiple measurement vector-based compressive sensing problem. The preamble misdetection probability is shown to decrease exponentially as the number antennas at BS increases. Numerical results demonstrate multiple-order improvement in terms of the access success rate for critical-QoS users, even under severe noise and multiple access contamination.

中文翻译：

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基于MIMO的5G及更高质量的QoS区分可靠无授权大规模访问

无授权（GF）访问已成为第五代（5G）移动系统中各种用例的促成因素之一，尤其是对于时间紧迫的大型机器类型通信（mMTC）。但是，这些用例具有多种服务质量（QoS）要求，可以从GF随机访问的角度根据访问成功率来衡量。因此，高度寻求能够支持各种QoS的GF方案。本文提出了一种GF接入方案，其中由于访问冲突的多样性和多个前导码所引起的多路访问干扰，高QoS用户叠加多个前导码以提高其访问成功率。我们进一步表明，在基站（BS）中存在多个天线的情况下，即使在非正交前导码传输引起的严重多址干扰下，低复杂度的接收机也可以以很高的概率正确检测活动前导码。通过将前同步码接收建模为基于多重测量矢量的压缩感测问题，可以进行理论上的性能分析。前同步码误检测概率显示为随着BS处天线数量的增加而呈指数下降。数值结果表明，即使在严重的噪声和多路访问污染的情况下，关键QoS用户的访问成功率也得到了多级改善。通过将前同步码接收建模为基于多次测量矢量的压缩感测问题，可以进行理论上的性能分析。前同步码误检测概率显示为随着BS处天线数量的增加而呈指数下降。数值结果表明，即使在严重的噪声和多路访问污染的情况下，关键QoS用户的访问成功率也得到了多级改善。通过将前同步码接收建模为基于多重测量矢量的压缩感测问题，可以进行理论上的性能分析。前同步码误检测概率显示为随着BS处天线数量的增加而呈指数下降。数值结果表明，即使在严重的噪声和多路访问污染的情况下，关键QoS用户的访问成功率也得到了多级改善。