Satellite Orbit and Ephemeris Determination using Inter Satellite Links

Inter Satellite LinksSoftware DescriptionThe relationship between code noise and range is approximately, but not exactly linear, as canbe seen in the figure above. The integration time of 20 ms has been chose as a typical valuefor a GPS user receiver. Using only ten times higher integration time for example would leadto an even more linear relationship between code noise and distance. The integration time of aDORIS receiver, for example is around 10 seconds. Presuming a sufficiently long integrationtime T i , the receiver noise of a code range measurement, a phase measurement or a Dopplermeasurement is indirect proportional to the range. The same could be done by decreasing chiplength, which would also directly enhance measurement precision.The next figure shows the dependence of carrier noise and range. This can be regarded as anearly linear function of the geometric distance.0.0100.008Ti = 2 msTi = 20 msTi = 200 msCarrier Noise [m]0.0060.0040.0020.0000 10000 20000 30000 40000Distance [km]Figure 5-4 Carrier Noise vs. RangeFor system level studies, it is therefore accurate enough to model the range measurementaccuracy using linear relationship between distance and measurement precision due tothermal noise given bywithdσ ≈ ⋅ dEq. 5.3-14RK RDistance, RangeR. Wolf Page 79