Signal Estimation in Underlay Cognitive Networks for Industrial Internet of Things

Underlay cognitive radio (CR) holds the promise to address spectrum scarcity and let industrial wireless sensor networks obtain spectrum extension from shared frequency band resources. However, underlay CR devices should be capable of properly adjusting wireless transmission parameters according to the sensing of wireless environments. To realize the goal, in this article, two different signal-to-noise ratio (SNR) estimation methods are proposed for time-frequency overlapped signal estimations in the underlay CR-based industrial Internet of Things (IoT). In the first method, normalized higher order cumulant equations and the theoretical value of normalized higher order cumulants are adopted to estimate the SNR of component signals and the SNR of received signals. In the second one, the power of each component signals and the received signals is estimated based on the second-order time-varying moments. For the performance analysis, the Cramer-Rao lower bound of the SNR estimation for the time-frequency overlapped signals is derived. Simulation results show that the proposed method based on normalized higher order cumulants not only can effectively estimate the SNR of the time-frequency overlapped signals, but also has the strong robustness to the spectrum overlapped rate and the hybrid power ratio. The proposed method with second-order time-varying moments is able to accurately estimate the SNR of the time-frequency overlapped signals effectively, especially in the low-SNR region. These features are extremely useful in the industrial IoT, which usually operate in low-SNR regimes.

I. Introduction

Wireless communications in industrial and factory scenarios are very challenging with high reliability requirements and unfriendly wireless environments [1]. In an industrial wireless sensor network (IWSN), coexistence and interference issues should be addressed for effective wireless transmissions, which is becoming increasingly serious because of the prevalence of the wireless connectivity and the explosive growth of wireless devices, like Internet of Things (IoT) [2]. As a result, the radio spectrum resource radio spectrum has been becoming very scarce, and different wireless communication systems have to coexist on the shared spectrum for the spectrum extension and capacity enhancement. Furthermore, viable approaches to cope with interference and realize the effective use of temporarily available frequency bands are very crucial to guarantee the communication quality in a preferable level [3].