Research On Key Technologies Of Nonlinear Interference Cancelation In Inter Satellite Links

Inter-Satellite Link is a vital part in satellite communication and next generation threedimensional space network. It is referred to as one of the most efficent way for satellitecommunication space network connection, and has received worldwide attention and focus.Inter-satellite link communication presents a number of challenges relative to traditionalwireless communication, such as long communication distance and large time latency.Furthermore, limited by the satellite size and transmission power, satellite-carrier-amplifieralways works in saturation region, which leads to great non-linear interference of the satellitetransmit signal. Also, long run of the satellite-carrier-amplifier may result in momerialinterference. Current inter-satellite link works in Ka/Ku band, which will lead to longermemory length and higher non-linear interference as well.Stresses on the impact of the non-linear interference in the inter-sattellite links, the maincontent of this paper are as follows:1、Focus on the non-linear distortion caused by the spaceborne power amplifier which alwaysworks in the saturation zone, pre-distortion algorithm is proposed, which samples the outputof the power amplifier and realizes the linear output of the transmit signal by updating thepre-distorter coeffients. Theoretic analysis has shown that the proposed method could abatemost of non-linear interference as long as the order of the pre-distorter is high enough.2、In order to decrease the great computation burden of current pre-distortion algorithm,dual-loop feedback pre-distortion algorithm is proposed, in which a cascaded one-orderVolterra filter is adopted to subsistute the three-order Volterra model. Construct the dual-looppre-distortion updating model with the input signal and the attenuated output of the poweramplifier as the expected signal. Then mix these two pre-distortion models together to updatethe coeffients. This method could speeds up the convergency of the pre-distorter andconstruction of the inter-sattellite link.3、Aim at the large non-linear interference existed in amplifier with high-order modulation, aneural network pre-distortion algorithm is proposed. Through parallel processing of theamplitude and phase of the transmitted signal, the neural network factor input signal on realbasis is obtained, combined with feedback factor in neural network input layer, the number of hidden layer is reduced, and the high precise non-linear cancellation for high order signalmodulation is achieved.4、According to the non-linear and memory characteristics of the inter-satellite link, a blindequalization available to high carrier frequency and fast transmission is proposed. Itconstructs a sparse filter matrix through several cascaded Volterra filter to cancel interferencein received signal. Simulation results show that it could realize the linear processing andsuppress background noise efficiently.5、To improve utility of the spectrum resource and anti-interference capability of inter-satellitelink, a relay and forward anti-interference technology available for inter-satellite link isproposed, which could be adopted in inter-satellite link communication without requirementof satellite carrier processing capability. Under the basis of no code divison multiple accessand frequency division multiple access, the received signal at the terminal would be the mixsignal with self transmit signal. Two demodulation algorithms to recover the required signalwithout the help of pre-distortion and blind equalization are proposed. The lookup table (LUT)algorithm stores self signal and theory signal of the other node and chooses the requiredsignal through likelihood comparison. The self signal cancellation algorithm gets the decisionthrough cancelling self signal from register. Simulation results show that both methods couldrealize same band satellite transmission, but the self signal cancellation algorithm is superioron computation efficiency, so it’s more suitable for practical satellite communication system.The work in this paper would serve as a theoretic base for inter-satellite non-linearinterference cancellation, and provide evidence for optimazation design of inter-satellite linkcommunication system.