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A Design of NB-IOT Random Access Preamble Receiver for Large Frequency Offset

In the fifth generation (5G) and beyond, the satellite communication system is expected to support Narrowband Internet of Things (NB-IoT). However, the residual frequency offset in a channel may be large because of the large velocity of the satellites. In a legacy narrowband internet of things system, the users are assumed to have low velocity, and the random access preamble consists of single-subcarrier orthogonal frequency-division multiplexing symbols. With a large frequency offset, the power of the preamble leaks into adjacent subcarriers, which will cause severe performance degradation. In this paper, the influence of the leaked power is theoretically investigated, based on which a novel random access receiver is proposed to alleviate the performance degradation. The adjacent subcarriers are actually coherently combined to take advantages of the leaked power. The weights in combination are designed to suppress the interference of other users when the frequency offset is large. Numerical results show that the proposed receiver has good performance in preamble detection.