北斗系统GEO-3卫星临退役期B1信号质量研究

北斗2号系统于2012年正式向亚太地区提供服务,其中GEO-3卫星已退役,由GEO-7卫星替代。研究卫星临退役期间的信号质量特性不仅能够分析北斗2号系统卫星载荷状态,而且为其它临退役星的信号特性估计提供重要的参考价值,同时对北斗3号系统GEO卫星载荷信号质量控制与优化具有重要的借鉴意义。该文利用昊平观测站40 m大口径天线的多源多手段数据,分析了GEO-3卫星B1民用信号的功率谱、地面接收功率、S曲线过零点偏差(SCB)的长期变化趋势,给出了相应的统计结果,提出了针对卫星载荷信号质量优化的相关建议,也对超期服役卫星的决策提供了参考。     

基于三层卫星网络的星间链路性能分析

星间链路性能分析是建立星间通信的基础。以包含GEO卫星、IGSO卫星和MEO卫星的三层卫星网络为例,仿真了三层卫星网络层间卫星星间距离的变化范围。在设定星间传输体制、链路参数、传输损耗等条件下,分别分析了该三层卫星网络的GEO-IGSO、GEO-MEO和IGSO-MEO三种链路在Ka频段和激光频段的性能。结果表明,在Ka频段,0.5m天线仅需5W的发射功率,可以满足2Mb/s以上的星间数据传输率;激光频段仅需0.5W的发射功率,直径0.25m的天线,可以达到2Gb/s以上的星间数据传输率,激光链路更有利于星间链路性能的提高。研究结果在未来三层卫星网络建立星间链路时,为卫星的发射功率、天线直径和星间链路数据传输速率等方面的选择提供了参考。     

Influence of the second-order ionospheric delay on GPS PPP time transfer

In view of the practical problem that the second-order ionospheric delay error (Ion2) is not corrected in Precise Point Positioning (PPP) time transfer,the PPP observation equation with the Ion2 is derived.The PPP clocks and time transfer with and without the Ion2 correction are compared and analyzed using two test periods.Based on the measured data,analysis shows that the influence of the Ion2 on the PPP clocks at a low-latitude are more significant than that of mid-latitude and polar regions.The difference series of PPP clock solutions shows fixed deviation plus some diurnal variations,and the sign of fixed deviation is opposite in the northern and southern hemispheres.The maximum influence of the Ion2 on the long time-links transfer can be up to more than 26ps,but for the short time-links,it can be ignored.Therefore the Ion2 correction is necessary for sub-nanosecond PPP time transfer over long time-links,especially when the time-links are made by the stations located in low-latitude regions.     

Influence of nominal distortion of Beidou-3 B1C signal on ranging performance

The B1C signal is selected as a civil navigation signal for the BDS-3 system,which adopts a complex constant envelope modulation in the B1 frequency band.Therefore,it is easy to generate nominal distortion during signal generation.Such nominal distortion of each satellite produces inconsistent ranging deviation and directly degrades the system positioning performance.A complete ranging deviation estimation method was proposed for B1C signals in this paper.Firstly,the S-Curve Bias (SCB) was used to quantitatively analyze the B1C signal ranging deviation,and the standard correlation curve estimation method was proposed to realize the accurate estimation of the code phase deviation at the peak of the correlation curve.Secondly,a algorithm was designed to solve the problem of QMBOC signal mislocking at the platform during receiver tracking.Finally,the actual ranging bias and nature ranging bias of each satellite of Beidou-3 under different correlation intervals and front-end bandwidth of the user receiver were analyzed based on the satellite downlink signals collected from the 40-meter high-gain antenna at the National Time Service Center,and the recommended user receiver parameter range was given.The strategy proposed in this paper can be extended to other MBOC signal ranging error estimation,and the test results can be thought of as a reference to the development of BeiDou-3 receiver.     

GPS III首星空间信号质量监测评估

GPS （Global Positioning System）在新一代卫星载荷中采用了大量新技术,首颗卫星成功发射后,官方尚未系统公布各导航信号的调制方式、复用方法等关键信息,因而其在轨测试阶段的空间信号质量评估具有重要的意义.该文选择地面接收功率、功率分配、相位关系、调制特性和测距性能等评估参数,深入分析了GPS III卫星L1频点空间信号质量,剖析了该卫星上多种新技术的信号特征.论文成果对其它GNSS（Global Navigation Satellite System）卫星载荷设计及信号体制设计等方面具有重要的参考意义.