说明：  究了适用于低轨卫星的Doppler-Range联合定位法及TDOA-TDOF联合定位法。分析了联合定位的误差计算公式，并提出了一种衡量联合定位性能的参数。
(Study of low-orbit satellites for the Doppler-Range joint positioning method and TDOA-TDOF joint positioning method. Analysis of the joint positioning error formula, and proposes a measure of joint positioning performance parameters.)