| Recently,with the social and economic development,there are increasing activities in the sea.Therefore,many researches for sea have been widely carried out.In order to ensure safety of people who do some research in this area,it is important for gathering information or monitoring targets in these areas.Therefore,it is necessary for us to establish data collecting system(DCS)based on satellite.Nowadays,some countries make use of communication satellite equipped with DCS load to do experiment or for commercial applications.However,there is no working standard for DCS.Constellation systems are also mostly for mobile communications,which have better performance on densely populated area compared to remote ones.Moreover,the function of load on satellite is simple,and it cannot achieve all-round perform information collection.Thus,it is significant to research key technology aimed for DCS based on satellite.For the monitoring sea-sky targets and data collection,this passage does some research in DCS communication system,DCS constellation for area coverage,DCS load and ground station.(1)Satellite-based DCS communication system is developed.It can be mainly divided into four parts,which are physical layer,link layer,network layer and transport layer.In physical layer,it mainly considers parameters of choosing frequency,signal modulation and encoding.According to current status of maritime communication and radio spectrum management,six frequency of UHF are chosen.And then the way of modulation are GMSK,DQPSK and DS-GMSK.The encoding is NRZI which is used for designing channel bandwidth,channel spacing and related physical layer parameters.Link layer mainly analyzes two access systems including FDMA+TDMA and CDMA+TDMA,and multi-frequency message transmission mechanism is proposed for different users.Network layer designs multi-channel mode of working.Target area is divided into some subnets based on different frequency.Transport layer designs packet format.Based on a variety of signal transmission and reception,time slot limiting mechanism is also proposed to avoid data blocking.(2)DCS constellation aiming for area coverage is designed and optimized.Traditional regional coverage performance has been analyzed.The target area is divided into sub-network by the point digital simulation method.Optimization parameters and their value are obtained based on different satellite orbits? characteristics.Comb ined with DCS communication system,high/low-frequency packet service response time of DCS constellation system is considered as optimization objective.Based on multi-objective multi-step genetic algorithm,the low frequency response time is 287.5s and high frequency response time is 80 s,which are close to optimal value.(3)Based on the theory of DCS commun ication system and constellation design,this section designs an integrated load which has function of receiving AIS,ADS-B,DCP signals and sending remote control signals.In order to improve detection performance,the function of multiple antennas? independently receiving message information is designed.Moreover,based on different signals? characteristics and software radio ideas,this load deals with these four signals from RF front end to baseband.At last,multi-sub-channel processing mechanism is proposed for Doppler shift.(4)Ground station software based on Labview is designed.This software contains continuous decoding and displaying of telemetry data or scientific data.Steady monitoring of DCP is mainly accomplished by the remote control of DCS load,and the function of ?Beidou? short message is regarded as an assisted way.Finally,ground demonstration experiment has been operated,which indicates that DCS load and ground station software can perform sending,receiving signals and analytic data. |
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