Digital Suppression Technique Of Passive Intermodulation Interference For Satellite Systems

The threat of passive intermodulation?PIM?interference has been exposed with the satellite communication systems featuring high power,multiple channels,and wide bandwidth.PIM can be received by sensitive receivers as a type of interference when it falls into the receiving band.PIM has become a major obstacle for satellite communication.PIM problem may become increasing severe due to the variational temperature and contaminated surfaces or contacts and loose mechanical junctions.The burst PIM interference cannot be suppressed by traditional suppression methods.PIM is a nonstationary self-interference with a wide bandwidth.In this paper,a digital cancellation technique is proposed to suppress the time-varying PIM interference.Firstly,the risk assessment of PIM interference for satellite systems is analyzed with high precision.Secondly,due to the non-stationary property of PIM,a PIM suppression algorithm based on sparse fractional Fourier transform is proposed.Thirdly,a PIM suppression algorithm based on the decorrelated normalized adaptive filter is proposed for the memory effect and time-variation.In consideration of the time delay and frequency offset,a joint estimation and compensation algorithm is proposed.Finally,the PIM suppression technique is verified in the wideband satellite system.The main novelties and contributions are summarized as follows:1.In order to improve the precision of current PIM risk assessment,the statistical model of PIM-modified Cauchy distribution model is proposed due to the experimental measurement data.The bit error rate and acquisition probability for satellite systems under PIM interference are calculated based on the modified Cauchy PIM distribution model.The calculated BER performance outperforms the existing analysis methods,and approximates the experimental results within 2 dB.2.In order to improve the estimated accuracy of PIM interference,a PIM suppression algorithm based on linear frequency modulation?LFM?pilot signal is proposed.According to the properties of time-frequency concentration of PIM caused by LFM signal,a PIM suppression algorithm based on the fractional Fourier transform is proposed.Due to the sparsity caused by the concentration of PIM,a PIM suppression algorithm based on sparse fractional Fourier transform is proposed to reduce the computation complexity.Numerical simulation results show that the bit error rate in uncoded communication systems adapting this algorithm is lower than 10^-2,when the signal-to-interference ratio is 10dB.3.In consideration of the memory effect of passive devices with wire mesh structure,a blind PIM suppression algorithm based on Hammerstein model is proposed.A suppression algorithm based on a bilinear polynomial adaptive filter is proposed for multiple PIM products.In order to achieve a faster convergence rate and a stronger stationarity,the bilinear polynomial decorrelated normalized least mean square algorithm is proposed.Numerical simulation results show that the algorithm can effectively compensate the passive intermodulation interference,and achieve a 20 dB signal-to-interference ratio gain in a 10^-2 bit error rate.4.A general scheme for the adaptive feedforward PIM cancellation is presented for wideband satellite systems.A joint synchronization of the time delay and frequency offset is presented through cross-correlation between received signals and the corresponding reconstructed PIM signal.The experimental results of cancelling 9th-order PIM show that an interference suppression gain over 10dB is achieved.