Performance Analysis and Solutions for Interference Leakage in FFH/DS Systems

Fast Frequency Hopping/Direct Sequence (FFH/DS) hybrid spread spectrum is an effective technology for satellite communications in complex electromagnetic environments, and higher hopping rates ensure the system's anti-interference and anti-interception capabilities. This study finds that in FFH/DS systems, strong interference in the channel can cause leakage due to the convolution tailing of filters and frequency switching rectangular pulses, leading to signal distortion and deterioration in symbol error rate (SER) performance. However, this phenomenon becomes more severe as the hopping rate increases. This paper proposes a parallel two-path ping-pong dehopping method to avoid the interference leakage. Compared with the conventional dehopping structure of the single local oscillator, it allows FFH/DS systems to maintain SER performance at higher hopping rates by doubling the resource complexity for dehopping and filtering. Base on this, this paper reveals the trade-off relationship between the hopping rate, SER performance, and resource complexity. Simulations show that in an environment with strong Multi-Tone Interference (MTI), the SER performance deteriorates with increasing hopping rate, even after removing frequency bins affected by interference. Moreover, using the parallel two-path ping-pong mixing for dehopping can restore the ideal SER performance at high hopping rates, thus verifying the findings of this study.