| With the development of satellite application technology,some space missions are hard to be realized by only one satellite.Meanwhile,single satellite system is inherently weak in reliability and adaptability.Thereby,an idea happened in design of small satellite emerges at the right moment.Relative to large satellite,satellite formation is featured by its physically unlimited long “base line”,low cost in space mission,strong flexibility and high survivability and so on.The determination of the relative distance of the formation satellites is a necessary condition for the normal operation of formation satellites.Using the ground equipment to locate the formation small satellites has the disadvantages of short measurement arcs and more measurement targets.Realizing the distance measurement between formation satellites and maintaining the formation of formations,establishment of information links has become an urgent need for the development of small-satellite technology.This paper explicitly proposes a communication distance measuring compound system based on visible light LED,designed a 60-meter ground prototype,realized the verification of the LED communication ranging compounding function,and analyzed the feasibility of using 10 kilometers working space;And introduced the extended function of the composite system: using LED antenna for active illumination,with the visible light detection camera can achieve active detection of space debris at a certain distance and determine the orientation among the formation satellites.The specific research work includes the following aspects:(1)The visible light communication ranging system and channel are modeled.First,the electrical,optical,and modulation characteristics of the transmit antenna LED of the composite system are analyzed.The I-V characteristic of the PN junction of the LED is rendered non-linear due to the influence of parasitic resistance.A linear model for compensating the LED I-V is proposed to make the selected XT-E-EAQ4.The linearity of it is compensated from 0.5665 to 0.0838,which is nearly 7 times higher.Second,a discrete component is used to establish the simulation model of the receiving antenna PIN of the composite system,and the amplification circuit is used to determine the bandwidth analysis model of the PIN.Third,the attenuation characteristics of visible light channels are studied,and the related factors that affect the visible light channels are analyzed.The gain model of the channel is proposed,the optical design of the channel gain is performed based on this.Fourth,in order to carry out the ground test to complete the principle verification of the composite system,the spatial transmission characteristics of the ground simulation experiment were analyzed,and the attenuation model of the light intensity in the atmosphere was established.(2)The technical scheme of the visible light composite communication system with both ranging and communication functions was analyzed.In order to ensure the requirements of formation satellite network and relative navigation,a composite scheme of OOK communication and pseudo code ranging both considering the communication bandwidth and ranging accuracy was designed.In the same hardware link,both communication and ranging can be performed.When using OOK to perform pseudo-code sequence ranging,single-code ranging can be performed at the same time,which improves the utilization of system resources and reduces system power consumption.A variety of methods for measuring single-code phase difference in pseudo code ranging are compared and analyzed.It is concluded that spectral analysis method can effectively suppress Gaussian white noise.It is further proposed that all-phase spectrum analysis is used to suppress spectral leakage,so that the system can obtain accurate phase difference measurements and improve the system's ability to resist noise.(3)Design and integrate the prototypes for visible light composite communication systems.First,a compensating circuit for an op amp driving a large capacitor is proposed.The Bias-Tee circuit with a smooth ripple and the design of processing for reducing the ripple of the bias power supply of the LED are designed.Second,design a signal detection circuit with low noise gain and high system sensitivity.The secondary signal amplification circuit uses a monolithic microwave integrated amplifier to reduce signal distortion.The three-stage circuit adopts AGC amplifying circuit to ensure the dynamic range of the system ranging.Third,a ?-type equalizer is proposed to compensate for the frequency response of the transmitter and receiver signals,and two frequency signals with the same degree of amplitude are provided for the difference algorithm of amplitude and phase consistency in the following text.Fourth,the system's accuracy,dynamic range and other characteristics are analyzed.The scheme of realizing the 10 km range dynamic range of the communication system in space is given and its feasibility is analyzed.(4)In-depth study of the role of information processing technology on the performance of the entire system.First,aiming at the phase shift caused by the amplitude variation of the received signal in the optical receiver,it is proposed to introduce two types of frequency signals for differential measurement and to compensate the consistency of amplitude and phase.Second,when sampling the signal,a method of increasing the phase quantization step is proposed to reduce the quantization error and improve the phase measurement accuracy.This increases the phase accuracy by nearly 3 times,and this method reduces measurement inaccuracies when the phase difference is around 0° or 360°.Third,use the filtering algorithm to correct the obtained ranging data,reduce system colored noise and white noise,thereby reducing the system error of phase measurement.(5)Design the phase meter stability measurement experiment to perform a loopback test on the phase meter and perform multiple measurements on the cable of the same length.The distance measurement error is within ±1.21 cm.The stability of the phase meter measurement was verified.(6)The system's visual field capability was analyzed and verified.The experimental results showed that the transmitter was in the ±2.5° field of view,and the average percentage error of phase measurement was 8.73%.After phase drift compensation,the average percentage error was 5.41%,increased accuracy by 37%.Experiments show that visible light ranging has better visual field capability than laser ranging,and the phase shift compensation algorithm has been verified.Compared with the traditional laser ranging method,the large divergence angle of the visible LED does not require an auxiliary aiming system,and the large visual field capability is favorable for real-time ranging of the formation satellites in team formation.(7)Ground test experiments were carried out on the prototype of the visible light composite communication system,and the accuracy measurement of ±45cm within the dynamic range of 5.4m to 60 m within 17.4us was realized.Based on the principle of long-baseline binocular ranging,the relative navigation experiment of the small satellite formation was designed to actively identify space debris and avoid collision within 2 km. |
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