Research On The Technologies Of User Detection In Spaceborn Multi-beam Receivers

LEO Satellite communication system has potentials to launch inexpensively.And it usually plays an important role in many applications since its low time delay and low user transmission power.To establish the satellite-ground communication,eligible user detection is the first key problem which needs to be resolved.However,the Near-far Effect and Doppler Effect,under the low orbit situation,cause severe difficulties to user detection.The traditional single-antenna receiver is congenitable deficient to give consideration to the referred problems.By contrast,the multi-beam receiver based on antenna array is more powerfull,since it is favourable to form a sharp beam and point at a specific direction with high gain,which would guarentee the realization of low-power communication between the satellite and ground users.Nevertheless,the narrow beam lobe of array antenna also brings problems while detecting the eligible ground users,esspecially,for the applications of burst satellite-ground communication.To be more specific,the problem can be concluded as whether the eligible user exsit and where it is.It just is the starting point of the research work presented in this paper,which gives attention on how to detcet the eligible user in a spaceborn multi-beam receiver.Around this issue,this paper focuses on the following key problems:1.Eligible user detection on a specific direction.User detection would be expressed as a problem of determination the eligible user’s existance,if we assume there exists an eligible user on a specific direction and the spceborn multibeam receiver has pointed at the direction correctly by presetting the parameters of the beamformers.Because of the relative motion between the satellite and ground users,there is a big cause of the received signal doppler frequency,especially for the low orbit communication system.Also limited by the situation of burst commnucation and computing capability in the satellite receiver,it is difficult to detect eligible users exactly,which makes it to be a key problem.2.Beam configuration in a given area.We need to divide the visible scope of the satellite to multi-subareas,to reduce the cost of user detection,and configure one beam to each area.And if a user is located at a given area but the direction is unkown,then the signal-to-noise(SNR)of the satellite received signals would be changed with the beam pointing and beam shape,and degradate the fiducial probability of user detection.To ensure the fiducial probability high enough for any user in the given area,beam configuration is the key problem.3.Area division in the visible scope of satellite.This problem deals with the case that the user located at a random position in the visible scope of satellite.In this situation,eligible user detection would be accomplished by cooperation of multiple beams and multiple subareas.In reality,considering the detection cosr,we expect the number of the beams or areas as little as better.But on the other hans,we need the received signal with high SNR to ensure the fiducial probability for user detection.The two apeals are conflicted obviously.The solution would be fall into dividing the visible scope of satellite reasonablly,which makes area division to be the key problem.To solve the above key technical problems,the paper proposed a scheme for user detection based on fiducial probability,a new method for optimal beam configuration,and a novel technique for area division based on the character of doppler frequency distribution.These technical methods corresponding to the three key technical problems to solve,and they are verified by theoretical analysis and simulations,which show the technical feasibility and effectiveness and would provides a reference to the other satellite-ground communication systems.