Frequency offset estimation algorithm of spread spectrum coherent heterodyne based on ISFT

Satellite to ground laser uplink is seriously affected by atmospheric environment, resulting in greater power attenuation than downlink. Uplink is used to transmit low speed instructions and control signals. In order to improve the sensitivity of satellite to ground uplink, and reduce the influence of large frequency offset on receiver, coherent heterodyne detection and spread spectrum technique are applied to uplink. To cut down the consumption of resources on the satellite, the inverse sparse Fourier transform (ISFT) is used to reduce the computational complexity of the frequency offset estimation algorithm. The frequency offset estimation algorithm based on ISFT is theoretically analyzed and validated by simulation. The simulation results reveal that compared with the direct detection of 16PPM, the sensitivity of spread spectrum coherent heterodyne detection is improved by 16dB when the error rate is 10−8. In the high signal-to-noise ratio environment at satellite to ground uplink, ISFT can estimate the frequency offset as accurate as IFFT while saving computational complexity.