$P_{ICD}=-128.5 dBm$	is the guaranteed minimum signal level for the GPS L1 C/A signals on the Earth according to [21].
$O_G=+3 dB$	is the global offset, chosen to obtain in simulation the performance obtained when real signals are received. Typically, the transmitted signal power levels are from 1 to 5 dB higher than the minimum received ones [23], for this reason an intermediate value of 3 dB has been chosen.
$R_0$	is the reference range used for inverse-square variation calculation and equal to the range from a receiver to the GNSS satellite at zero elevation.
$R$	is the range from GNSS satellite to the receiver.
$L_{tx}$	is the loss from the GNSS satellite transmit antenna in the direction of the receiver. 3D GPS antenna patterns have been modelled, as described in our previous study [24,25].
$L_{rx}$	is the loss from the receiver antenna in the direction of the GNSS satellite.