JNTU B.Tech IV SATELLITE COMMUNICATIONS Previous Question Paper (September - 2022 - R18)

Satellite frequency allocations are governed by the International Telecommunication Union (ITU) to prevent interference between services. The spectrum is divided into specific bands, primarily in the microwave region:

• L-band (1-2 GHz): Primarily used for mobile satellite services (MSS) and GPS, offering high penetration but limited bandwidth.
• S-band (2-4 GHz): Utilized for mobile services and some weather radar applications.
• C-band (4-8 GHz): Widely used for satellite TV and VSAT networks; it is highly reliable in adverse weather conditions but requires larger antennas.
• X-band (8-12 GHz): Reserved mainly for military and government satellite communications.
• Ku-band (12-18 GHz): Commonly used for Direct-to-Home (DTH) television and broadband services, allowing for smaller dish sizes.
• Ka-band (26-40 GHz): Provides high-capacity broadband and high-speed data links, though it is more susceptible to rain fade.

Orbital effects significantly influence the performance and design of satellite communication systems, primarily through the following factors:

1. Doppler Shift: Due to the relative motion between a non-geostationary satellite and an earth station, the received frequency shifts. This necessitates frequency tracking and compensation mechanisms in the receiver to maintain signal lock.
2. Propagation Delay: In Geostationary (GEO) orbits, the large distance (approx. 35,786 km) introduces a round-trip delay of about 250-280 ms. This latency impacts real-time applications like voice calls and requires specific protocols for data transmission to manage acknowledgments.
3. Eclipse Effects: During equinoxes, satellites enter the Earth's shadow, cutting off solar power. The system must rely on onboard batteries, which may limit transponder capacity or require power management strategies.
4. Sun Transit Outage: When the sun aligns directly behind the satellite as viewed from an earth station, solar electromagnetic radiation causes significant noise interference, potentially leading to temporary service degradation or total signal loss for a few minutes daily.
5. Orbital Perturbations: Gravitational forces from the sun, moon, and the Earth's oblateness cause orbital drift. Station-keeping maneuvers are required to maintain the satellite within its designated orbital slot, which consumes onboard fuel and defines the satellite's operational lifespan.