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Alright lets get started with NaviC then. You are by now already aware on how basic ranging works and position is solved for from a GNSS constellation. We will look at a basic structure of the constellation, how the signal is generated, rcv'd and solved for.
First lets look at the basic maths behind the positioning and our general sources of error. The basic term you need to know is called pseudorange. we will come to it later
Now lets start with the satellites of NaviC. GPS orbits 31 MEO satellites at ~20,200 km in 6 orbital planes inclined at 55°. Any ground observer sees satellites sweeping across the entire sky dome over a ~12hr orbital period. Navic takes a diff approach
Navic has 3 GEOs that sit at fixed longitude slots and 4 IGSOs orbit in two planes crossing the equator at 55°E and 111.75°E. Because their orbital period exactly matches Earth's rotation, IGSOs trace a fig8 ground track straddling the equator, over India for the majority of day
This arrangement means from anywhere in India, GEO satellites appear as immovable high elv points the full constellation covers the primary service area with 100% availability of ≥4 satellites with just 7 sv. All satellites reside at the same ~35,786 km altitude.
One minor tradeoff is there are no low-elevation satellites to triangulate vertical position. This yields NavIC-standalone PDOP values of 3.3 to 6.2 versus GPS's ~1.5-2.5. All you need to know about PDOP is, its a measure of quality and depends on satellite geometry.
Onboard each satellite is a clock, and it is this clock that is the heart of the entire positioning. This clock's measurements will cascade down to earth. This clock simultaneously creates both the chip sequence (code) and the carrier wave on which chips are encoded
Here comes one of the pri differences in GPS and Navic. Navic instead of using a single frequency uses two bands to encode messages in L5 and S from each satellite. Technically even GPS now uses multiple bands L1 L2 L5 -L5 is shared with GPS L5 and GAL E5a -S unique to NaviC
There are two services onboard NaviC, the SPS or Standard Positioning Service for civilian app and RS or Restricted Service for mil app. RS shifts spectral energy to ±5.115 MHz lobes around the carrier separating them spectrally and allow simul broadcast w/o mutual degradation
The NVS-01/02 satellites add L1 (1575.42 MHz) using SBOC modulation (a composite BOC variant), interoperable with GPS L1C and Galileo E1-OS. Both NavIC freq travel ~35,786 km to the ground through the same atmosphere. 3layers matter: vacuum path, ionosphere, troposphere.
Look back at the pseudorange equation, you can see them as the sources of error. Now, you can either use a model to estimate ionospheric and tropo electron activity or you can use a smart trick that NaviC does from its dual freq.
S-band sees ~4.5× less ionospheric delay than L5. Over India's equatorial ionosphere, daytime TEC can spike to 60-100 TECU during solar max, causing >1.7 m of L5 delay. India is also near equatorial ionospheric anomaly, where post-sunset plasma bubbles cause rapid signal fading.
The freq separation of NavIC ( ≈ 2.12) is much larger than GPS L1/L2 (≈ 1.28), making NavIC's iono-free combination ~1.79× less noise-amplifying than GPS L1/L2's (~2.98× amplification). And S-band's lower scintillation directly reduces cycle slips in PLL tracking
If you measure pseudoranges on two frequencies f₁ and f₂, the iono delay scales differently on each, and you can use them to calculate that a IonoFree pseudorange which is independent of TEC. No model needed
Free-space path loss scales as f², so S-band (2492 MHz) arrives at the receiver~6.5 dB weaker than L5 (1176 MHz) for equal transmit power. So the satellites transmits S-band at ~3.5 dB higher power (~29.5 dBW vs ~26 dBW for L5), to compensate
Both the bands have their own characteristics and the NavIC receivers are made to receive both together and solve, but due to diff atmospheric events (and other things) you can have band specific degradation as well
Both bands tracked -> iono-free combination, ~3-5 m accuracy L5 only -> ~10-20 m S-band only -> model fallback, raw S delay 4.5x smaller than L5 Neither -> satellite excluded from PVT for that epoch
There is a integrity flag in the navigation message signals whether dual-band correction is healthy for a given satellite, so the receiver always knows which operating mode it is in.
So know we know, how the satellites transmit it, how about the receivers which receive it. Firstly the antennas themselves have to be made to be able to detect not only Navic's spread out frequencies but other constellations (usually GPS) as well
Btw you need to be aware of level of signal strength once these signals reach earth (and that will give you an idea about jamming them as well)
