低成本单频伪卫星基带/中频设计与实现

Design and Implementation of Base Band and IF of Low-Cost GPS L1 Pseudolite

GPS伪卫星是一种用来生成并发射类似GPS信号的地面装置;在卫星信号微弱的情况下,伪卫星可以作为GPS辅助增强,也可以在没有任何卫星信号的情况下用来建立室内独立定位系统;虽然伪卫星技术的研究已经开展了数十年,但由于其昂贵的成本和复杂的硬件结构使它的应用远远落后了;为了使伪卫星技术能得到广泛应用,提出并讨论了一种低成本伪卫星的基带/中频模块的设计与实现;硬件结构上采用二次变频技术,先利用直接数字合成器生成一个调制过的中频信号,再上变频至L1波段;这种DDS技术有着非常好的频率调制能力,并且相位噪声很低;文中最后给出了基带/中频模块的实验结果,得到了预期的基带和中频信号;同时在实验过程中调校了参考时钟。

GPS pseudolite is a kind of ground equipment that generates and transmits signal in space similar to GPS satellites. Pseudolites can he used as the augment of the GPS constellation, where signal seems to be too weak or in-comprehensive. They can also be used to build an independent in-door positioning system without any satellite signals. Although pseudolite technology has been researched for decades, the application is dropping behind owing to its high cost and complex hardware architecture. In this paper, design and implementation of base band and IF of a low- cost pseudolite is discussed. A preferred dual frequency conversion structure is selected. The pseudolite utilizes a direct digital synthesizer （DDS） chip to generate a modulated IF, and then up-converted to L1 band. This DDS technology provides fine frequency tuning capability, and very low phase noise. Test results of base band ＆ IF are demonstrated. Expected base hand ＆ IF signals are obtained. Reference clock is tuned in the test.