Characterization analysis and processing of low earth orbit broadband OFDM signals

In LEO broadband internet systems, the satellite gNB is the core equipment to achieve seamless global coverage and ubiquitous access. The 5G NR physical layer adopts OFDM waveform, and the high-dynamic LEO environment introduces time and frequency domain deformations to OFDM signals, which cause wrong decoding for the satellite gNB. These deformations are more severe for OFDM signals with a 400 MHz bandwidth, which prevents the NTN system from supporting high-speed data services. To solve this problem, this paper first analyzes the OFDM deformations in the LEO environment, and then proposes a hardware-in-the-loop simulation platform that verifies the analysis results. The verification shows that when the equivalent sampling frequency offset caused by the LEO environment is greater than ±70 ppm, the traditional terrestrial base station receiving algorithm does not work. Finally, a resampling method is proposed to compensate for the ±70 ppm deformation. Data analysis show that with the proposed method, the sampling frequency offset reduces from ±70 ppm to ±16 ppm, and the EVM performance is improved from 21.5% to 3.2% for 16 QAM~400 MHz OFDM signal, such that satellite can decode the signal correctly.