Satellite Orbit and Ephemeris Determination using Inter Satellite Links

Software DescriptionInter Satellite LinksPRPR 0PRDRange measurementReal rangeRange rate measurementPR D 0 Real range rateand RANDOM is a function generating a normally distributed random number with zeromean and variance 1.5.3.1 Thermal NoiseAn important number in a link budget calculation is the signal to noise ratio expressed bywithC( ) dB−Hz = PT+ G T + AT+ A D + G R + A R + AS− TsysdB − kN0k Boltzmann's constant k=1.38 × 10 -23 [Ws / 0 K]T SYSA DG TG RA SA TEquivalent noise temperature of the systemFree space attenuationdBEq. 5.3-6Transmit antenna gain in main direction; f(frequency, beamwidth)Receiver antenna gain in main direction; f(frequency, beamwidth)System losses (including cable losses, the A/D converter, signal processinglosses)Pointing loss of the transmit antennaA R Pointing loss of the receive antennaP T Antenna transmitted powerThe equation above, as well as the following equation concerning link budget can be foundfor instance in the "Blue Books" [BLU-96] by Parkinson / Spilker. Most of the parameters inthe equation above are a function of the link technology used, e.g. power, antenna pattern,frequency etc, and therefore not directly dependent of the link geometry, i.e. distance. Theonly directly geometry dependent component is the free space attenuation given byλ( A D ) dB = 20⋅log10( )4πdEq. 5.3-7The carrier to noise ratio can therefore coarsely be regarded as a function of the inversesquare of the geometric distance.C ⎛ 1 ⎞≈ f ⎜ ⎟Eq. 5.3-8N2⎝ ⎠0 dCode range, phase and doppler measurements are strongly dependent of the carrier to noiseratio, as indicated in equation 5.3-9, 5.3-10 and 5.3-11.Page 76R. Wolf