Compensation System Design and Comparison of Very High Doppler Frequency Effect

One of the serious problems in the low earth orbit (LEO) satellite communication system is the very high Doppler frequency effect since the LEO satellite system runs very fast to keep the orbit altitude. Especially, this problem produces the critical performance degradation when the broad bandwidth is necessary for the very high speed satellite transmission of the very high resolution image data. As the data speed is increased, the higher efficient communication technology will be required to transmit the high-capacity of data to the ground station. In the LEO satellite communication systems, very large Doppler influence is generated because of the very fast movement of satellite. This Doppler spectrum shift effect, similar to the carrier frequency offset effect, can cause performance degradation in the satellite communication system. Therefore, it is very important to effectively compensate for this Doppler frequency shift. So, in this paper, we analyze this Doppler effect of LEO satellite receiver and propose an efficient compensation system design against the Doppler frequency. Two compensation methods are proposed: pilot method and phase locked loop (PLL) method. As simulation results show, when the SNR is approximately 5 dB or less, the pilot method provides better performance, compared with the PLL method. When the SNR is approximately 6 dB or more, it can be confirmed that the PLL method outperforms than the pilot method, which is almost same to the theoretical performances. Furthermore, it can be said that the PLL method is very spectrum-efficient than the pilot method since it does not require any pilots. However, it is very difficult and expensive to design the accurate, agile, broadband operating PLL system to compensate the very wide range of Doppler frequency shift.