Downlink Sampling Frequency Offset Estimation and Compensation Method for LEO Satellite Multi-Carrier Communication System
A multi-carrier communication and sampling frequency offset technology, which is applied in the modulation carrier system, multi-frequency code system, transmission system, etc., can solve the problem of low estimation accuracy, limited frequency offset estimation range, and inability to meet the Doppler sampling of low-orbit satellites. Frequency offset compensation range requirements and other issues, to achieve the effect of reducing the range and reducing the complexity of the implementation
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[0048] refer to figure 2 , the specific example of the downlink sampling frequency offset estimation and compensation method is as follows:
[0049] Step 1: The gateway station estimates the frequency offset of the downlink common Doppler sampling based on the ephemeris, and uses the estimated value of the downlink common Doppler sampling frequency offset to precompensate the downlink transmitted signal. Specifically, the gateway station calculates the Doppler sampling frequency offset of the downlink feeder link according to the ephemeris information, the location of the gateway station, and the carrier frequency of the downlink feeder link. refer to Figure 4 , the downlink feeder link Doppler sampling frequency offset f s,feeder is calculated as:
[0050]
[0051] in, is the connection direction between the satellite and the gateway station, is the velocity vector of the satellite, c is the speed of light, f s is the sampling frequency of the multi-carrier syste...
Embodiment 1
[0071] The altitude of the satellite is 1175km, and the speed of the satellite is 7.2km / s. The elevation angle of the gateway station to the satellite is 5°, the maximum elevation angle between the common reference point of the user link and the satellite is 30°, and the sampling frequency f s is 491.52MHz. Calculate the frequency offset by Doppler sampling formula The gateway station can calculate from the ephemeris that the Doppler sampling frequency offset of the common part of the downlink user link is 4.7kHz; the downlink Doppler sampling frequency offset of the feeder link is 9.8kHz.
[0072] The width of the satellite beam is 3°, and the Doppler frequency deviation of the user link of the cell edge user is calculated as 13.6 kHz by the above Doppler frequency deviation calculation formula. Therefore, the user's residual Doppler frequency offset is 14.5kHz-13.6kHz=900Hz. The sampling frequency deviation caused by the user and the satellite crystal oscillator is 50Hz....
Embodiment 2
[0074] Gateway station-satellite-ground channel Gaussian white noise channel, using 8PSK modulation, the code rate is 0.891, and the receiving signal-to-noise ratio is 10dB. Assuming that the initial sampling frequency offset is 5000 Hz, without pre-compensation in step 1, the sampling frequency offset is estimated only by segment correlation in step 2. Simulation results such as Figure 6 As shown, the estimated root mean square error obtained through simulation is 32.4 Hz. It can be seen that this method has high accuracy in estimating the residual sampling frequency offset. As shown in the simulation results, in this simulation scenario, the sampling frequency offset will cause a performance loss of about 2.6dB to the system, but after being estimated and compensated by the algorithm of the present invention, the link performance is compared with the ideal link without sampling frequency offset The performance loss is within 0.02dB, and the performance has been improved by...
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