Synchronization Under Hardware Impairments in Over-6-GHz Wireless Industrial IoT Systems

Mobile devices perform cell search for initial access in cellular-based industrial Internet of Things (IoT) systems. Existing fifth-generation (5G) new radio (NR) cell-search scheme provides timing synchronization and cell identification. Usage scenarios emerging with the growth of the IoT market require unprecedented precision, reliability, and scalability in the future network, and a shift toward high-frequency bands can be one of the key enablers to achieve these stringent requirements. However, in high-frequency bands, hardware (HW) impairments, including carrier frequency offset and phase noise are exacerbated, and a sharp beam causes the problem of cell identity (ID) ambiguity that can reach further than a reduced cell coverage. In this article, a cell-search scheme is proposed for time-critical industrial IoT over mobile networks operating in high-frequency bands. To achieve high timing accuracy under the increased HW impairments, primary synchronization signals (SSs) are designed based on the distributed concatenations of a Zadoff-Chu sequence and its modification. Next, a secondary SS is designed based on the distributed concatenation of a Kasami sequence and its modification, which provides a larger set of cell IDs and is robust to the impairments. Compared to 5G NR under the increased HW impairments, our analysis and evaluation show that the proposed cell-search scheme has advantages, such as 25% lower timing detection complexity, 150% larger set of cell IDs, up to 15 and 6-dB signal-to-noise ratio gain in terms of timing and cell ID detection performance, respectively, and 60% shorter cell-search time, thereby realizing 80% lower battery consumption.