Satellite Communications

Propagation delay for range km: Number of carrier cycles at MHz: Since this is an integer number of cycles, the residual phase at reception is Rounded to two decimals: .

(A) True. Tropospheric delay has a dry (hydrostatic) and a wet component; the wet component grows with water vapour content higher relative humidity increases delay.
(B) False. Ionospheric delay is driven mainly by solar radiation and geomagnetic activity (diurnal/solar-cycle dependence), not the Moon’s position.
(C) False. Multipath arises from reflections/scattering from any nearby surface—buildings, metallic structures, ground, and also vegetation (leaves/branches). Vegetation can and does cause multipath (though often weaker).
(D) True. Code-based measured range includes receiver/satellite clock biases and propagation errors, so it is not the true geometric range; hence the term pseudorange.

GNSS satellites (GPS, Galileo, BeiDou and modern GLONASS) transmit on common carrier frequencies but with distinct spreading codes. Receivers separate satellites by correlating with each satellite’s PRN code—i.e., CDMA. (Legacy GLONASS also used FDMA, but CDMA is the widely adopted method across constellations.)

Differential GPS (DGPS) uses a reference receiver at a known location to estimate range errors for each satellite and broadcast corrections to nearby rovers. Because the base and rover are close, several errors are common-mode and hence removable:
Atmospheric delays (ionosphere and troposphere) — largely similar over short baselines.
Satellite clock drift — common to all receivers for a given satellite.
Orbital (ephemeris) error — same broadcast for both receivers.
Errors that are receiver-specific, such as receiver clock and multipath, do not cancel reliably with simple DGPS. Therefore the best match is option (B).

A GNSS constellation that covers the entire globe is a stand-alone satellite navigation system with worldwide service. As of today, the four such constellations are: GPS (USA), GLONASS (Russia), Galileo (EU), and BeiDou (China).
IRNSS/NavIC (India) and QZSS (Japan) are regional systems (coverage over specific regions, not global). GAGAN, WAAS, and EGNOS are SBAS augmentations, not core constellations. Hence only option (D) lists the complete set of globally covering constellations.