Highly Robust Multiple Frequency Shift Chirp Modulation for Time-Frequency Dual-Selected Channels

Aiming at the problem of signal demodulation performance degradation caused by time delay and Doppler shift in ionospheric time-frequency dual-selected channels, a highly robust multiple frequency shift chirp modulation (RO-M-FSCM) method based on linear frequency modulation was proposed. Through address code design, identical time-frequency resources were mapped into multiple parallel transmission channels exhibiting fractional orthogonality. Real-time correction of the information-branch demodulation window alignment with the main path was achieved by the synchronization branch. An equivalent offset was introduced to reveal the coupling effect of delay and Doppler shift on the signal's spectral peak in the fractional domain. Consequently, the asymptotic closed-form expression for the symbol error rate of RO-M-FSCM signals was derived, and the length of robust code was optimized. The received SNR for non-coherent demodulation of RO-M-FSCM signals was enhanced based on a robust-domain multipath energy aggregation method. Simulation results demonstrated that under typical ionospheric broadband channel environment, the RO-M-FSCM scheme achieved co-optimization of transmission reliability and transmission rate. This approach provides an effective solution for ultra-long-distance communication in complex time-frequency dual-selected channels.