Abstract: To meet the access demands of massive terminal users, the space-based Internet of Things (IoT) requires sufficient frequency resources for allocation. However, the frequency resources that are currently available have already been allocated to a great extent. Furthermore, the utilization rate of the allocated frequency resources is low. To support massive user access under restricted frequency resources, this work proposes a scheme based on Doppler frequency offset (DFO) pre-compensation to enhance spectrum utilization efficiency. By calculating the relative motion between the satellite and the transmitting terminal, combined with the length and transmission rate of the message, the optimal compensation value of the Doppler frequency deviation is determined. The frequency-protection interval is reduced. Simulation results show that the pre-compensation method can expand the user access volume by 90–400 times. Properly selecting the number of message splits and transmission rate to perform DFO pre-compensation calculations can increase user access by an additional 45% or more. This method improves the spectrum utilization efficiency and provides a solution to the challenge of access by a large number of users.

Key words: Protection interval; Spectrum utilization; Doppler frequency offset pre-compensation; Massive user access

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