Design and Implementation of Time-Sensitive Wireless IoT Networks on Software-Defined Radio
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Time-sensitive wireless networks are important enabling building blocks for many emerging industrial Internet of Things (IoT) applications. Quick prototyping and evaluation of time-sensitive wireless technologies are becoming increasingly important. Software-defined radio (SDR), which enables wireless signal processing on a personal computer (PC), has been widely used for such quick prototyping efforts. However, because of the uncontrollable latency between the PC and the radio board, SDR is generally deemed not suitable for time-sensitive wireless applications that demand communication with low and deterministic latency. For a rigorous evaluation of its suitability for industrial IoT applications, this paper conducts a quantitative investigation of the synchronization accuracy and end-to-end latency achievable by an SDR wireless system. To this end, we designed and implemented a time-slotted wireless system on the Universal Software Radio Peripheral (USRP) SDR platform. To address the latency challenge, we developed a time synchronization mechanism to maintain synchrony among nodes in the system. To reduce the latency and to handle the delay jitter between the USRP board and its PC, we devised a Wake-ahead-a-bit algorithm to ensure that packets sent by the PC to the USRP can reach the USRP just before the time slots they are to be transmitted. Our experiments demonstrate that 90% (100%) of the time slots of different nodes can be synchronized and aligned to within ± 0.5 samples or ± 0.05μ s (± 1.5 samples or ± 0.15μ s), and that the end-to-end packet delivery latency can be down to 3.75ms. This means that SDR-based solutions can be applied in a range of IIoT applications that require tight synchrony and moderately low latency, e.g., sensor data collection, automated guided vehicle (AGV) control, and Human-Machine-Interaction (HMI).
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