One of the main challenges in Internet of Things (IoT) is providing communication support to an increasing number of connected devices. In recent years, the narrowband radio technology has emerged to address this situation: narrowband IoT (NB-IoT), which is now part of 5G. Supporting massive connectivity becomes particularly demanding in extreme coverage scenarios, such as underground or deep inside building sites. We propose a novel strategy for these situations focused on optimizing NB-IoT shared channels through the selection of link parameters: modulation and coding scheme, as well as the number of repetitions. These parameters are established by the base station (BS) for each block transmitted until reaching a target block error rate (BLERt). A wrong selection of these magnitudes leads to radio resource waste and a decrease in the number of possible concurrent connections. Specifically, our strategy is based on a lookup table (LUT) scheme which is used for rapidly delivering the optimal link parameters given a target QoS. To validate our proposal, we compare with alternative strategies using an open-source NB-IoT uplink simulator. The experiments are based on transmitting blocks of 256 bits using an AWGN channel over the NPUSCH. Results show that, especially under extreme conditions, only a few options for link parameters are available, favoring robustness against measurement uncertainties. Our strategy minimizes resource usage in all scenarios of the acknowledged mode and remarkably reduces losses in the unacknowledged mode, presenting also substantial gains in performance. We expect to influence the future BS software design and implementation, favoring connection support under extreme environments.

中文翻译：

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5G 窄带物联网的极致覆盖：基于 LUT 的共享通道优化策略


物联网 (IoT) 的主要挑战之一是为越来越多的联网设备提供通信支持。近年来，窄带无线电技术的出现就是为了解决这种情况：窄带物联网（NB-IoT），现已成为5G的一部分。在极端覆盖场景（例如地下或建筑工地深处）中，支持大规模连接变得尤为困难。针对这些情况，我们提出了一种新颖的策略，重点是通过选择链路参数来优化 NB-IoT 共享信道：调制和编码方案以及重复次数。这些参数由基站 (BS) 为每个传输的块建立，直到达到目标块错误率 (BLERt)。这些幅度的错误选择会导致无线资源浪费并减少可能的并发连接数量。具体来说，我们的策略基于查找表 (LUT) 方案，该方案用于在给定目标 QoS 的情况下快速提供最佳链路参数。为了验证我们的建议，我们使用开源 NB-IoT 上行链路模拟器与替代策略进行比较。实验基于使用 AWGN 信道通过 NPUSCH 传输 256 位块。结果表明，特别是在极端条件下，链路参数只有少数选项可用，有利于针对测量不确定性的鲁棒性。我们的策略最大限度地减少了已确认模式所有场景中的资源使用，并显着减少了未确认模式下的损失，同时也带来了性能的显着提升。我们期望影响未来的BS软件设计和实现，有利于极端环境下的连接支持。