Research on Receiving and Demodulating Technology of GMSK Signal Under Complex Channel Conditions

GMSK modulation is widely used for signal transmission in complex electromagnetic environments with dense and variable interference signals, low signal-to-noise ratio, noise, and fading over time due to its excellent performance. However, the traditional reception processing structure based on the principle of correlation reception and Viterbi phase path search is susceptible to time-varying noise and interference, which cannot meet the requirements of signal reception and demodulation processing under actual complex channel conditions. To address this issue, this paper proposes a new optimal receiving structure that considers the actual channel background and the characteristics of GMSK signals. The structure includes four functions: pre-filtering, parameter estimation, synchronization, and judgment based on eye diagram features. Simulation experiments were conducted to test the processing effect of GMSK signals under multiple channels. The results show that the demodulation error performance of the new optimal receiving structure is comparable to that of the traditional receiving processing structure for GMSK signals in a Gaussian white noise environment. Moreover, the best receiving structure outperforms the traditional receiving processing structure in situations where in-band aliasing has strong adjacent band interference. Additionally, the new optimal receiving structure can stably realize synchronous recovery even when strong interference with a high aliasing ratio makes the traditional receiving processing structure unable to synchronize normally. Engineering implementation and actual tests demonstrate that the new optimal receiving structure greatly improves the bit error performance and robustness under complex interference and noise channel conditions compared to the traditional receiving processing structure.