Traditionally, even though the base station (BS) is equipped with multiple antennas, it has not been able to apply antenna technique such as an uplink multi-user multiple-input multiple-output (MU-MIMO) during the random access (RA) procedure due to the contention feature of the RA. To overcome such limitation, this letter proposes a novel RA framework leveraging both non-orthogonal preambles and multi-antenna technique. In our proposed framework, the non-orthogonal preambles effectively increase the total amount of contention resources, i.e., RA preambles, and thus the occurrence of preamble collisions can be significantly reduced. Accordingly, the BS can take an opportunity to exploit an uplink MU-MIMO even in the contention-based RA procedure under the belief that the contention may be resolved. We mathematically analyze the proposed framework in terms of packet collision probability and resource efficiency. Analysis and simulation results reveal that our proposed framework is able to accommodate more internet-of-things (IoT) devices in a resource-efficient way, compared to the conventional one.

中文翻译：

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用于上行链路蜂窝物联网的新型随机接入框架：非正交前导码和多天线

传统上，即使基站（BS）配备了多个天线，在随机接入（RA）期间也无法应用诸如上行多用户多输入多输出（MU-MIMO）之类的天线技术由于 RA 的争用特性。为了克服这种限制，这封信提出了一种利用非正交前同步码和多天线技术的新型 RA 框架。在我们提出的框架中，非正交前导有效地增加了竞争资源的总量，即RA前导，因此可以显着减少前导冲突的发生。因此，即使在基于竞争的RA过程中，BS也可以利用可以解决竞争的机会来利用上行链路MU-MIMO。我们在数据包冲突概率和资源效率方面对所提出的框架进行了数学分析。分析和模拟结果表明，与传统框架相比，我们提出的框架能够以资源高效的方式容纳更多的物联网 (IoT) 设备。