Improved GNSS Ambiguity Resolution with a C-Band Signal

Both S-band and C-band signals have been suggested as possible additions to the transmission of GNSS satellite signals. In particular a C-band signal in the 5.01 to 5.03 GHz band has been suggested as a possible additional signal to be broadcast by the GPS satellites. In a prior paper the author looked at the benefits of three-frequency ambiguity resolution by comparing the L1, L2 and L5 signals available from the future GPS satellites with that of the L1, E5a, and E6 signals which will be broadcast by Europe's Galileo satellites. While the three Galileo signals were judged to be significantly better than the three GPS signals, the addition of a fourth GPS signal in the vicinity of 5 GHz could dramatically ease the ambiguity resolution problem. While the increased signal path loss at the higher frequencies has been used as an argument against their transmission, the much smaller ionospheric refraction is a significant argument in their favor. In addition, the shorter wavelength and consequent smaller antenna size could allow a small phased array antenna to overcome some of the signal loss via a substantially increased antenna gain in the direction of the satellites. This could recover much of the signal strength needed while simultaneously reducing the interfering multipath. A low cost MEMS inertial unit could be used to keep the antenna pattern pointing in the direction of the satellites. In conclusion, the addition of a C-band signal to the GPS satellites could be of substantial benefit.