Regarding to the design of GPS signals, why 154f and 120f are selected in L1 and L2 frequencies, respectively?
I know this information since I studied GPS signal processing, however I never really the reason or motivation to select 154f and 120f. I will very appreciate if I can learn this history of GPS signal.
Good Question Hsu,
I was on one of the original design teams for NAVSTAR GPS in the 1970s. The frequencies were chosen to make the frequency synthesizer design in the receiver as simple as possible and maintain strict frequency coherence of the L1, L2, and data clocks (or reference frequencies). In the 1970, frequency synthesizers had to be designed with lots of discrete logic and using frequency multipliers and frequency dividers. The frequency synthesizer also had to be compatible with the precision quartz crystal oscillator used for the clock.
Good Luck,
Steve
The response you need it is in this book
DARDARI, Davide, FALLETTI, Emanuela, et LUISE, Marco. Satellite and terrestrial radio positioning techniques: a signal processing perspective. Academic Press, 2012.
The frequency of GNSS signals is a compromise.
On the one hand, because of the rather high bandwidth, it is hard to fit them in the VHF spectrum. Also the influence of the ionosphere on the measurements is lower at higher frequencies. This is a reason to go up in frequency.
On the other hand, the atmospheric absorption increases at higher frequencies, this is a reason for not going too high in frequency.
Therefore, the frequencies were chose to be in the L-band, which houses more satellite communications, like Inmarsat downlink (around 1550 MHz), Irridium uplink (around 1620 MHz), radio astronomy observations etc.
Good Question Hsu,
I was on one of the original design teams for NAVSTAR GPS in the 1970s. The frequencies were chosen to make the frequency synthesizer design in the receiver as simple as possible and maintain strict frequency coherence of the L1, L2, and data clocks (or reference frequencies). In the 1970, frequency synthesizers had to be designed with lots of discrete logic and using frequency multipliers and frequency dividers. The frequency synthesizer also had to be compatible with the precision quartz crystal oscillator used for the clock.
Good Luck,
Steve
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