According to the status that COMPASS system′s PNT(Position,Navigation,and Timing) is asymmetry in the worldwide,the polar constellation and rose constellation are proposed to enhance the COMPASS,and then their coverage performances are simulated and analysed.Furthermore,the structure and principle of enhanced COMPASS system are discussed.By using the index of position dilution of precision and the number of visible satellites,the performance of enhanced system is comparatively analysed.

本文首先介绍了Wi-Fi定位系统的组成,分析了Wi-Fi定位的原理,还讨论了Wi-Fi定位技术的应用领域及发展状况,最后分析了Wi-Fi定位技术存在的瓶颈及改善措施。

由低轨（LEO）和中轨（MEO）卫星构成的卫星通信系统可以充分利用LEO和MEO的各自轨道优势．具有较好的组网通信性能。在LEO与MEO卫星之间建立星间链路，使卫星之间存在直接的通信路径．可以提高网络的自治性．减少传输时延．降低对地面站的依赖。本文首先分析建立MEO星座与低轨LEO星座星间链路的可行性，然后通过STK软件仿真影响LEO／MEO星间链路特征参数的变化情况．进一步分析LEO／MEO星间链路预算。

With the development of COMPASS in civilian and military domain,the request of anti-jamming performance is becoming more and more demanding.Adopting LEO communication satellite system to enhance COMPASS positioning and timing performance is an effective way,especially under jamming.In the angle of signal enhanced,the anti-jamming performance of enhanced signal broadcasted by LEO satellites was researched.Firstly,the system model and the work principle of LEO enhanced system was introduced.Secondly,the effects of the interfering link were analyzed.Then via the calculations of the enhanced signals from LEO satellites,the antijamming performance of the enhanced signal was analyzed.Finally,some measures were proposed to improve the anti-jamming performance of the enhanced signal.The results show that the enhanced signal can tolerate about 50 dB jamming to signal ratio,and the ability of anti-jamming is equal to GPS M-code.