Design of Large Doppler Shift Mitigation in NTN Scenarios Through a Paired Index Based PRACH Transmission Scheme

This paper proposes a design of paired indexed sequence to enhance the resilience of the physical random access channel (PRACH) against significant Doppler shifts, which are inevitable in high-speed scenarios such as satellite communications. The proposed scheme links two Zadoff-Chu (ZC) sequences via a paired index, ensuring PRACH transmission compatibility with existing terrestrial communication systems while concurrently mitigating the challenges posed by large frequency offsets to achieve accurate timing estimation. Furthermore, a novel maximum likelihood (ML) based joint time-frequency refinement algorithm (JTFR) is introduced to further minimize the estimated frequency error, thereby improving timing estimation accuracy. Simulation results demonstrate that the proposed PRACH transmission scheme with the dedicated JTFR algorithm effectively mitigates Doppler shifts up to 29.64 KHz, with 87% of the remaining error within ±200 Hz, hence reducing the average timing estimation error to 72.68 ns. Compared to existing work, our design meets the requirements of the 3rd Generation Partnership Project (3GPP) standard while leveraging the existing PRACH format deployed in terrestrial networks.