Efficient Detection and Synchronization of Superimposed NB-IoT NPRACH Preambles

In the third-generation partnership project narrowband Internet-of-Things specifications, a new narrowband physical random-access channel (NPRACH) is specified as a single-tone frequency-hopping preamble. When multiple uplink users attempt to attach simultaneously, the base station receives superimposed NPRACH preambles and must detect all users and acquire their synchronization parameters: time-of-arrival (ToA) and residual carrier frequency offset (RCFO). In this paper, we first solve the detection problem and derive the optimal Neyman-Pearson detection threshold. Then, we analyze the theoretical detection performance and find the maximum coupling loss under both additive white Gaussian noise and Rayleigh fading channels. Next, the FFT phase trace of each detected user is exploited to estimate the user's ToA and RCFO parameters. Simulations reveal that the algorithm has both favorable detection and estimation performances with very low complexity.