Nawaz Farhan, Kumar Hemant, Hassan Syed Ali, Jung Haejoon
School of Electrical Engineering & Computer Science (SEECS), National University of Sciences & Technology (NUST), Islamabad 44000, Pakistan.
Department of Information and Telecommunication Engineering, Incheon National University, Incheon 22012, Korea.
Sensors (Basel). 2021 Jun 19;21(12):4206. doi: 10.3390/s21124206.
Enabled by the fifth-generation (5G) and beyond 5G communications, large-scale deployments of Internet-of-Things (IoT) networks are expected in various application fields to handle massive machine-type communication (mMTC) services. Device-to-device (D2D) communications can be an effective solution in massive IoT networks to overcome the inherent hardware limitations of small devices. In such D2D scenarios, given that a receiver can benefit from the signal-to-noise-ratio (SNR) advantage through diversity and array gains, cooperative transmission (CT) can be employed, so that multiple IoT nodes can create a virtual antenna array. In particular, Opportunistic Large Array (OLA), which is one type of CT technique, is known to provide fast, energy-efficient, and reliable broadcasting and unicasting without prior coordination, which can be exploited in future mMTC applications. However, OLA-based protocol design and operation are subject to network models to characterize the propagation behavior and evaluate the performance. Further, it has been shown through some experimental studies that the most widely-used model in prior studies on OLA is not accurate for networks with networks with low node density. Therefore, stochastic models using quasi-stationary Markov chain are introduced, which are more complex but more exact to estimate the key performance metrics of the OLA transmissions in practice. Considering the fact that such propagation models should be selected carefully depending on system parameters such as network topology and channel environments, we provide a comprehensive survey on the analytical models and framework of the OLA propagation in the literature, which is not available in the existing survey papers on OLA protocols. In addition, we introduce energy-efficient OLA techniques, which are of paramount importance in energy-limited IoT networks. Furthermore, we discuss future research directions to combine OLA with emerging technologies.
在第五代（5G）及以后的5G通信的推动下，预计物联网（IoT）网络将在各个应用领域大规模部署，以处理海量机器类型通信（mMTC）服务。设备到设备（D2D）通信可以成为大规模物联网网络中克服小型设备固有硬件限制的有效解决方案。在这种D2D场景中，鉴于接收器可以通过分集和阵列增益从信噪比（SNR）优势中受益，可以采用协作传输（CT），以便多个物联网节点可以创建一个虚拟天线阵列。特别是，机会主义大阵列（OLA）作为一种CT技术，已知无需事先协调即可提供快速、节能和可靠的广播和单播，这可用于未来的mMTC应用。然而，基于OLA的协议设计和操作取决于网络模型，以表征传播行为并评估性能。此外，一些实验研究表明，先前关于OLA的研究中使用最广泛的模型对于节点密度低的网络并不准确。因此，引入了使用准平稳马尔可夫链的随机模型，这些模型更复杂但在实际中估计OLA传输的关键性能指标更准确。考虑到应根据网络拓扑和信道环境等系统参数仔细选择此类传播模型，我们对文献中OLA传播的分析模型和框架进行了全面综述，这在现有的关于OLA协议的综述论文中是没有的。此外，我们介绍了节能OLA技术，这在能量受限的物联网网络中至关重要。此外，我们讨论了将OLA与新兴技术相结合的未来研究方向。
