Abstract: With the development of new broadband multimedia services, the demand for broadband wireless spectrum has been growing rapidly, which makes spectrum resources scarcer. Meanwhile, low Earth orbit (LEO) satellites deployed on a large scale have the advantages of low transmission loss and small propagation delay. To improve the spectrum utilization rate, a coexistence scheme of geostationary Earth orbit (GEO) satellites and LEO satellites was adopted. In order to avoid the interferences of LEO satellites to GEO satellites during spectrum coexistence, an algorithm combining spectrum sensing and beam hopping was proposed. First, the signaltonoise ratio (SNR) of LEO satellite communication was estimated. Then the optimal threshold was selected according to the estimated SNR. An energy detection algorithm based on dynamic threshold was used to discriminate between the GEO satellite signals, and the beam adjustment was carried out according to the judgment results. Simulation results show that the error of the energy detection algorithm based on the dynamic threshold proposed is significantly lower than that of the traditional energy detection algorithm based on fixed threshold and spectrum sensing method based on secondorder cyclic statistics. When the signal to noise ratio is lower than -10dB the detection error is lower than 0。2, and when the signaltonoise ratio is higher than -5dB the detection error approaches zero.

Key words: satellite communication； cognitive radio, energy detection, dynamic threshold, beam hopping