Flex power on GPS Block IIR-M and IIF

GPS Block IIR-M and Block IIF satellites have the capability to redistribute transmit power between individual signal components. This so-called flex power can be used for increased protection against jamming and was already demonstrated in September 2010. Since January 2017, a geographically driven flex power mode has been enabled on ten Block IIF satellites. It is visible in carrier-to-noise density ratio observations of ground-based GPS receivers as well as differential code bias estimates between the L1 C/A- and P(Y)-code signals. Measurements with a 30 m high-gain antenna revealed a 2.5 dB increase of the L1 C/A and P(Y) power when the L1 M-code is regularly disabled. During four days in April 2018, a different flex power mode was put in place for all healthy Block IIR-M and IIF satellites. Carrier-to-noise density observations of geodetic GPS receivers show an increase of about 11 dB for combined L1 + L2 P(Y)-code power. The high-gain antenna measurements consistently show an increase of P(Y)-code power by 5 and 6 dB for L1 and L2, respectively, due to deactivation of the military M-code on both frequencies. Finally, during three days in April/May 2018, another type of flex power was observed: for 11 h of each of the three days, another geographically driven flex power mode was enabled but over a different area than the flex power mode mentioned above. Next to measurements of signal spectra, in-phase/quadrature components, and signal power with a high-gain antenna, the impact of flex power on the tracking and measurements of geodetic receivers is investigated.

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