| In recent years,to satisfy users’ demand for broadband access,the construction of Low Orbit Satellite Internet is very fast,and it is likely to become critical infrastructures to realize global users’ seamless broadband communication.Multibeam satellite can generate multiple adjacent beams within its service range,with higher beam coverage quality and larger communication system capacity,which is an ideal way to serve in low orbit broadband satellite.Therefore,it will be widely used in the future mobile satellite constellation communication system.When full frequency multiplexing is implemented between beams,the interference between all adjacent beams will have a serious cumulative effect.There is still no mature scheme to quantify the interference superposition of many beams.On the other hand,to ensure that users can continuously transmit data,the beam needs to be fixed in a fixed area,which will also lead to time-varying interference between beams.If the channel matrix is obtained,TomlinsonHarashima precoding can be used to eliminate inter-beam interference,but the performance deteriorates when the channels are similar between users.Based on the above problems,this paper quantifies the inter-beam interference matrix,and proposes a beam-gazing algorithm and a Min-max Correlation user Grouping algorithm to optimize the performance of THP algorithm.The main contributions and innovations of this paper include:(1)The communication scenario of low orbit satellite Internet is analyzed,and the user distribution is modeled.Then,the transmission model of the system is analyzed based on different multi-carrier modulation modes,and the expression of user channel vector and system channel matrix is given.Phased array antenna radiation field intensity was deduced expressions,and on the basis of quantitative user channel matrix,the influence of different subarray arrangement and the number of antenna elements on the antenna pattern of phased array antenna is analyzed.The simulation results intuitively reflect the influence of beam sidelobe superposition on the main lobe of adjacent beams.(2)In this paper,a single beam gazing algorithm is proposed to calculate the elevation angle of the phased array antenna when beam is gazed on the ground according to the known ephemeris information.The algorithm can accurately estimate the antenna elevation angle during the whole process of satellite service.The simulation results show that the estimation error of the actual elevation angle of the satellite is controlled within 0.6°.Then the causes of the error are analyzed,and the rationality of the setting of beam staring threshold is explained.(3)The user channel similarity is defined by the channel correlation coefficient.Through calculation and derivation,it shows that the receiver will suffer from the loss of signal-to-noise ratio under the high channel correlation of users.In order to avoid this loss of signal-to-noise ratio,we propose a Min-max Correlation user Grouping algorithm,which can divide a pair of users with high channel correlation of different point beam services into different groups,so as to keep the correlation in each user group at a low level.Simulation results show that the proposed Min-max Correlation user Grouping algorithm has 3dB gain and larger channel capacity compared with sum rate maximization grouping algorithm and power fair grouping algorithm when the bit error rate level is 10-4.Except for the above work,a joint simulation platform for interference cancellation of low orbit satellite broadband satellite phased array antenna is built,and the bit error rate performance and channel capacity in the case of large elevation angle and small elevation angle are selected for simulation.The simulation results first illustrate the feasibility of joint simulation,and also show that the proposed algorithm still has performance advantages under the condition of joint simulation. |
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