随着北斗卫星导航系统的逐渐完善，有关北斗系统定位的研究越来越深入，为了对比分析北斗系统和全球定位导航系统（GPS）定位的差异性，充分利用北斗地球静止轨道卫星（GEO）和倾斜地球同步轨道卫星（IGSO）高轨道卫星的特殊性，本文提出一种新的组合选星方法，选取卫星数较少且Position Dilution of Precision（PDOP）最小的北斗/GPS组合，分别对比分析北斗系统、GPS系统及其组合系统在楼顶开放环境和楼间恶劣环境下的定位效果。实验结果表明：北斗比GPS有更加稳定的定位效果，依据本文组合选星方法，利用少量卫星即可获得较好的定位精度。

With the development of the BeiDou system, the features of mixed constellation have become more obvious with GEO and IGSO satellite orbits, the number of high elevation satellites has obviously increased, and the number of visible satellites has increased among high buildings. Therefore, we propose a new method wherein fewer satellites can also have better positioning accuracy with GEO/IGSO satellites. This method is also applicable to urban environment. To prove the effectiveness of this new method, we perform tests under open and urban environments. We also use two modes to verify the new method. The first mode uses combinations from all BeiDou satellites with several GPS satellites, and the second mode uses combinations from several BeiDou and several GPS satellites. We select fewer satellites of BeiDou and GPS whose position dilution of precision is the smallest and then compare the positioning results with the BeiDou, GPS, and BeiDou/GPS systems under the two environments.Experimental results under the two environments show that the BeiDou system has better positioning performance than the GPS system. Under open environment, both modes of the new method can use fewer satellites to perform better positioning performance than the BeiDou/GPS system. The performance with the second mode is better than that with the first mode. Under urban environment, the features of the GEO and IGSO satellites of the BeiDou system can be maximized. Compared with the GPS system, the BeiDou system has more visible satellites because of the particularity of GEO and IGSO satellite orbits, as well as better positioning performance. In the first mode, the positioning error of our method is always less than that of the BeiDou or GPS system and is frequently less than that of the BeiDou/GPS system. In the second mode, the new method has less positioning error and fewer satellites than the BeiDou/GPS system. Therefore, under urban environment, using fewer satellites can also have better positioning performance with the new method.This study proposes a new method to select fewer satellites. Two modes are used to verify the new method under open and urban environments. The BeiDou system displays better performance than the GPS system under both environments. Considering the full use of GEO and IGSO satellites in the two modes, we can conclude from the experiments that fewer satellites can also have better positioning performance. This research is necessary and effective particularly under urban environment.