###### Abstract  
The multi-satellites cooperative transmission can effectively increase the data rate that can be achieved by internet of things (IoT) terminals. However, the dynamic characteristics brought by low Earth orbit (LEO) satellites will seriously decrease the data rate and make the data rate fluctuate. In this paper, dual-stream transmission and downlink power control for multiple LEO satellites-assisted IoT networks are investigated. To mitigate the effects of the frequency offset caused by different LEO satellites, a multi-satellites synchronization scheme is proposed. Then, different power control schemes are given to resist the data rate fluctuation during the transmission. The simulation results show that the proposed schemes can effectively compensate for the varied frequency offset and keep the data rate stable. dual-satellite system  
increased the spectral efficiency compared to the conventional techniques. In [8], the cooperative transmission strategy of the GEO satellite colocation (GEOSC) system was studied. The multipath component and the line-of-sight (LOS) component in the Rician channel were comprehensively considered to improve the transmission rate of the system through the user selection strategy and opportunistic beamforming. In [9], the cooperative transmission strategy for the multi-satellite colocation (MSC) system was proposed, which adopted the cooperative beamforming and constructed an orthogonal channel by geometric criterion. The communication rate was better than the two-satellite GEOSC system. A full frequency reuse-based dual-satellite system was studied in [10] to achieve a high data transmission rate by designing a relay-aided decision support system. In recent years, with the development of LEO satellite techniques, the cooperative techniques between GEO and LEO satellites have attracted attention. The multi-satellites relay systems based on time division multiple access (TDMA) and non-orthogonal multiple access (NOMA) were introduced in [11]. In [12; 13], spectrum sharing and cooperative technology were considered in the LEO-GEO co-existing systems, which can solve the interference issue between different satellites. In addition, a cooperative LEO satellites system was studied in [14; 15]. In [14], the effect of different antenna distributions with multiple antenna terminals in a dual-LEO-satellite system was analyzed. In [15], the ultra-dense LEO satellite constellation networks were considered, and the algorithm based on the max-min fairness criterion and analog beamforming was proposed to improve the system capacity. Due to large path loss, power control is especially important in satellite systems. In [16], the application of Q-learning for power control was investigated in the satellite communication system, and the proposed method effectively extended the service life of the satellite battery. Considering the distributed power control problem in downlink cognitive satellite-terrestrial networks, a static non-cooperative game model was proposed in [17] to improve the resource utilization efficiency and reduce interference. The authors in [18] studied the LEO satellite constellation model under the dynamic characteristics of an LEO satellite. Aiming to limit the maximum delay and minimize the outage probability, two optimal power control schemes were proposed. In order to improve the performance of the uplink random access, a power control scheme based on spatial grouping was proposed in [19], which effectively reduced the energy consumption of satellite IoT terminals. In [20], the pilot-based channel estimation and back-off interference power constraint were employed for the satellite link and the terrestrial interference link, respectively, and the proposed method can alleviate the impact of imperfect channel station information. However, the above research works related to cooperative satellite systems did not consider the large frequency offset caused by LEO satellites.