Internet-of-Things (IoT) is emerging, while the spectrum is at a premium. To enhance spectrum efficiency, a promising solution is Non-Orthogonal Multiple Access (NOMA) that enables users to communicate with the same resource at the same time, while decoding the superimposed signal at the receiver. Existing NOMA technologies, however, rely on strict power control to decode the superimposed signal, infeasible for heterogeneous and low-cost IoT devices. In contrast, we propose I-Talk, a new NOMA scheme that is designed for IoT and can decode the superimposed signals from two transmitters without power control. Importantly, considering the IoT systems in the wild, both the hardware imperfections and mobility are unavoidable, which can cause severe signal variations, resulting in an unreliable decoding performance. To solve this problem, we design a synthesis channel coefficient to track all signal offsets caused by the hardware imperfection. Meanwhile, we propose a diversity transmission and smart combining scheme to achieve high reliable decoding performance. To demonstrate the feasibility of this new NOMA approach in practical systems, we implement I-Talk with USRP devices and the experimental results illustrate that I-Talk achieves a one-order lower bit-error-rate and a $1.47\times $ higher throughput gain than the state-of-the-art superimposed signal decoding scheme.

中文翻译：

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I-Talk：无需功率控制的可靠且实用的叠加信号解码

物联网 (IoT) 正在兴起，而频谱却非常宝贵。为了提高频谱效率，一个很有前途的解决方案是非正交多址 (NOMA)，它使用户能够同时使用相同的资源进行通信，同时在接收器处对叠加信号进行解码。然而，现有的 NOMA 技术依赖于严格的功率控制来解码叠加信号，这对于异构和低成本的物联网设备是不可行的。相比之下，我们提出了 I-Talk，这是一种新的 NOMA 方案，专为物联网而设计，可以在没有功率控制的情况下解码来自两个发射器的叠加信号。重要的是，考虑到野外的物联网系统，硬件缺陷和移动性都是不可避免的，这会导致严重的信号变化，导致解码性能不可靠。为了解决这个问题，我们设计了一个合成通道系数来跟踪由硬件缺陷引起的所有信号偏移。同时，我们提出了一种分集传输和智能合并方案，以实现高可靠的解码性能。为了证明这种新的 NOMA 方法在实际系统中的可行性，我们使用 USRP 设备实现了 I-Talk，实验结果表明 I-Talk 实现了低一阶的误码率和 $1.47\times $ 比最先进的叠加信号解码方案更高的吞吐量增益。